Nickel on Mars: Constraints on meteoritic material at the surface
A. S. Yen,1 D. W. Mittlefehldt,2 S. M. McLennan,3 R. Gellert,4 J. F. Bell III,5
H. Y. McSween Jr.,6 D. W. Ming,2 T. J. McCoy,7 R. V. Morris,2 M. Golombek,1
T. Economou,8 M. B. Madsen,9 T. Wdowiak,10 B. C. Clark,11 B. L. Jolliff,12 C. Schro?der,13
J. Bru?ckner,14 J. Zipfel,15 and S. W. Squyres5
Received 20 July 2006; revised 28 September 2006; accepted 6 November 2006; published 15 December 2006.
[1] Impact craters and the discovery of meteorites on Mars indicate clearly that there is
meteoritic material at the Martian surface. The Alpha Particle X-ray Spectrometers
(APXS) on board the Mars Exploration Rovers measure the elemental chemistry of
Martian samples, enabling an assessment of the magnitude of the meteoritic contribution.
Nickel, an element that is greatly enhanced in meteoritic material relative to samples of the
Martian crust, is directly detected by the APXS and is observed to be geochemically
mobile at the Martian surface. Correlations between nickel and other measured elements
are used to constrain the quantity of meteoritic material present in Martian soil and
sedimentary rock samples. Results indicate that analyzed soils samples and certain
sedimentary rocks contain an average of 1% to 3% contamination from meteoritic debris.
Citation: Yen, A. S., et al. (2006), Nickel on Mars: Constraints on meteoritic material at the surface, J. Geophys. Res., 111, E12S11,
doi:10.1029/2006JE002797.
1. Introduction
[2] In the ongoing study of the composition, origin, and
weathering of rocks and soils at the surface of Mars, it is
essential to understand the magnitude of meteoritic contri-
butions. Analyses of minor and trace elements establish the
geochemical history of surface materials, and neglecting to
account for signatures of material non-native to Mars may
result in erroneous interpretations. Quantifying the meteor-
itic influx of organic material is vital for constraining carbon
oxidation rates in support of Martian habitability assess-
ments, and establishing the likelihood that future sample
return missions will collect meteoritic rather than Martian
material is essential in developing mission strategies. In
addition, the quantity of meteoritic material in the soils
establishes age constraints, with potentially important impli-
cations for the geological and climatic history of the surface.
[3] In lunar soils, the meteoritic component is established
to be 1.5?2% with a composition consistent with the CI
class of carbonaceous chondrites [Taylor, 1982]. Given its
size, its location, and presence of an atmosphere, the
preservation of meteoritic material at the surface of Mars
could be substantially higher [Boslough, 1988, 1991].
Estimates of the fine-grained meteoritic contribution to the
Martian surface in previous studies, however, vary widely.
Extrapolating from accumulation rates measured at Earth,
Flynn and McKay [1990] estimate that the Martian soil
contains between 2% and 29% meteoritic matter by mass.
Morris et al. [2000] tested a variety of mixing models to
explain Pathfinder soils and found that the compositions
were consistent with 0%?22% meteoritic material. Com-
paring Martian meteorite analyses with Viking Lander data,
Newsom and Hagerty [1997] suggested that up to 10% of
the iron in Martian soils could be meteoritic, corresponding
to an overall meteoritic concentration of up to 7%. Yen and
Murray [1998] describe a model predicting a total accumu-
lated nickel abundance in excess of 1000 ppm, equivalent to
approximately 7.5% meteoritic material at the Martian
surface. On the basis of Viking analyses, Clark and Baird
[1979] showed that up to 40% meteoritic material could be
consistent with the elemental chemistry of the analyzed soil
samples. It is clear that there have been significant uncer-
JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 111, E12S11, doi:10.1029/2006JE002797, 2006
1Jet Propulsion Laboratory, California Institute of Technology,
Pasadena, California, USA.
2NASA Johnson Space Center, Houston, Texas, USA.
3Department of Geosciences, State University of New York at Stony
Brook, Stony Brook, New York, USA.
4Department of Physics, University of Guelph, Guelph, Ontario,
Canada.
5Department of Astronomy, Cornell University, Ithaca, New York,
USA.
6Department of Earth and Planetary Sciences, University of Tennessee,
Knoxville, Tennessee, USA.
7National Museum of Natural History, Smithsonian Institution,
Washington, D.C., USA.
8Enrico Fermi Institute, University of Chicago, Chicago, Illinois, USA.
9Niels Bohr Institute, University of Copenhagen, Copenhagen,
Denmark.
10Department of Physics, University of Alabama at Birmingham,
Birmingham, Alabama, USA.
11Lockheed Martin Corporation, Littleton, Colorado, USA.
12Department of Earth and Planetary Sciences, Washington University,
St. Louis, Missouri, USA.
13Johannes Gutenberg University, Mainz, Germany.
14Max Planck Institut fu?r Chemie, Mainz, Germany.
15Forschungsinstitut und Naturmuseum Senckenberg, Frankfurt,
Germany.
Copyright 2006 by the American Geophysical Union.
0148-0227/06/2006JE002797
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tainties in the accumulations of meteoritic material in the
Martian surface layer.
[4] The Mars Exploration Rovers (MER) provide a new
and unique capability for addressing the magnitude of the
meteoritic contributions to the Martian surface. The
instrument suite on board each rover consists of a 0.27
mrad/pixel, multiple filter Panoramic camera [Bell et al.,
2003], a miniature Thermal Emission Spectrometer cov-
ering the 5 to 29 mm wavelength region [Christensen et
al., 2003], a 30 mm/pixel Microscopic Imager [Herkenhoff
et al., 2003], an Alpha Particle X-ray Spectrometer (APXS)
for elemental composition [Rieder et al., 2003], a Mo?ssba-
uer Spectrometer for mineralogy of iron-bearing phases
[Klingelho?fer et al., 2003], a set of magnets for attracting
dust particles [Madsen et al., 2003], a Rock Abrasion Tool
(RAT) to remove surface contamination and weathering
rinds from rock surfaces [Gorevan et al., 2003], and
engineering cameras to support mobility, navigation, sci-
ence, and placement of the instrument arm [Maki et al.,
2003].
[5] In this paper, we show how the MER instruments in
combination with the mobility of the rovers have been used
to evaluate the quantity of fine-grained meteoritic materials
dispersed in the surficial deposits and ancient sedimentary
rocks encountered at Gusev crater by Spirit and by Oppor-
tunity on the Meridiani plains. The initial form of this
material may have been interplanetary dust particles, micro-
meteorites, or comminuted, vaporized and/or recondensed
portions of larger objects.
[6] In section 2 we examine evidence for meteors and
meteorites from MER imaging data sets to illustrate a clear
exogenic contribution to the Martian surface. In section 3
we show that MER APXS measurements of nickel content
provide the primary constraints on the magnitude of a
possible meteoritic contribution to the samples analyzed at
both rover sites. We then examine the observed concen-
trations of nickel in section 4, and assess possible mixing
relationships between a meteoritic component and Martian
materials in section 5. Quantitative constraints on the
meteoritic infall are presented in section 6. Relationships
to the magnetic properties investigations of Martian soil and
dust are described in section 7. In section 8, meteoritic infall
estimates derived from nickel measurements are compared
to models of likely meteoritic contribution based on ob-
served impact craters and the influx of interplanetary dust
particles. In section 9, we synthesize these different measure-
ments and approaches to arrive at an estimate of the
minimum and maximum likely magnitude of the meteoritic
component of the Martian surface. Finally, in section 10,
implications for the meteoritic carbon abundance at the
Martian surface are presented.
2. Meteors and Meteorites
[7] MER observations and measurements provide clear
macroscopic evidence for a meteoritic contribution to the
Martian surface. Abundant impact craters, hollows, shallow
depressions, and small pits (Figure 1) are all evidence of
material falling from above. Many of the smaller craters
observed directly by MER may be the result of secondary
impacts but nevertheless provide unambiguous evidence
that the surface of Mars has been profoundly influenced
by meteorite impact.
[8] One serendipitous observation provides remarkable
evidence for ongoing influx of meteoritic material to the
Martian surface. A Pancam image collected by Spirit on
sol 63 shows a streak with an orientation, apparent
velocity, and light curve consistent with a meteor origi-
nating from dust shed along a cometary orbit [Selsis et al.,
2005]. A number of other studies have also pointed out the
likelihood of Martian meteor detection and the probability
of the resulting delivery of meteoritic fragments to the
surface [e.g., Davis, 1993; Adolfsson et al., 1996; Christou
and Beurle, 1999].
[9] Over a traverse of 8.5 kilometers, Opportunity has
analyzed two meteorites, and has perhaps driven past many
more, on the surface of Meridiani Planum. A 
30 cm
diameter rock in the plains south of Endurance crater known
informally as ??Heatshield Rock?? (Figure 2) was determined
by the Mo?ssbauer spectrometer to have 
94% of its iron in
the iron-nickel alloy kamacite [Morris et al., 2006b] and by
the APXS to have a total of 7 wt% Ni (R. Gellert et al., In
situ chemistry along the traverse of Opportunity at Mer-
idiani Planum: Sulfate rich outcrops, iron rich spherules,
global soils and various erratics, manuscript in preparation,
2006; hereinafter referred to as Gellert et al., manuscript in
preparation, 2006). This rock is a meteorite on the surface of
Mars and has been classified as a IAB iron formally
designated ??Meridiani Planum?? by the Meteoritical Society
nomenclature committee.
[10] A small (
3 cm diameter) rock fragment (informally
referred to as ??Barberton??, Figure 3) analyzed by the
Opportunity APXS and Mo?ssbauer spectrometers at the
rim of Endurance crater was originally thought to be an
olivine-rich basaltic pebble ejected from some other locality
on Mars. Upon closer examination of the data, this pebble
was found to exhibit a weak magnetic sextet in the Mo?ss-
bauer data consistent with iron in the form of kamacite,
which does not occur in Martian basalts [Morris et al.,
2006b]. This observation in combination with one of the
highest Ni concentrations measured on Mars (
1700 ppm)
indicates that this pebble is not a piece of Mars. The
elemental composition of this sample, but perhaps not the
mineralogy, is most consistent with a mesosiderite
[Schro?der et al., 2006]. Barberton could be a fragment of
a larger impactor or a member of the population 20 to
50 gram objects predicted to survive intact to the Martian
surface [Bland, 2001].
[11] Given the abundance of rocks at the Gusev landing
site relative to the Meridiani plains, meteorites are more
difficult to find. Nonetheless, the Spirit Mini-TES has
identified two 
25 to 30 cm rocks with thermal infrared
characteristics similar to those of Heatshield Rock (S. Ruff,
personal communications, 2006).
[12] There is clearly direct evidence for a rare but
??macroscopic?? meteoritic population at the surface of Mars.
A more challenging issue is determining the magnitude of
the ??microscopic?? meteoritic component of the Martian
surface. That is, what is the fraction of the soil or of
sedimentary rocks that is meteoritic? Answering this ques-
tion requires a more detailed assessment of the chemistry
of fine-grained materials on the surface, with a specific
E12S11 YEN ET AL.: NICKEL ON MARS
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Figure 1. Indications of meteoritic input to the Martian surface: (a) Mars Orbiter Camera image showing
the cratered surface of the Gusev plains [Malin et al., 2005]. The Spirit rover track traverse extends
from the lander to Bonneville crater (upper left) to the West Spur of the Columbia Hills (lower right).
(b) A rock-deficient ??hollow?? is apparent after an impact crater is filled with aeolian sediments (a portion
of the Spirit ??Mission Success?? Pan). (c) Navcam image of small impact craters (possibly secondaries) at
Meridiani Planum (sol 387). The diameter of the crater in the foreground is approximately 8 meters.
(d) False color Pancam image of an impact depression (center of image), possibly due to ejecta, with
associated debris which postdates aeolian bedforms (Opportunity sol 373, sequence p2375). (e) False
color Pancam image of a 
20 cm diameter pit in the Meridiani sand sheet (sol 436, sequence p2592),
consistent with models of centimeter-scale objects impacting the surface [Ho?rz et al., 1999].
E12S11 YEN ET AL.: NICKEL ON MARS
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focus on key elements that can be tracers of a meteoritic
contribution.
3. Elemental Tracers
[13] The Alpha Particle X-ray Spectrometers (APXS)
utilizes a combination of Particle Induced X-ray Emission
(PIXE) and X-ray Fluorescence (XRF) spectroscopic tech-
niques to determine the elemental composition of analyzed
samples [Rieder et al., 2003]. Through sol 720, over 200
distinct targets have been analyzed at Gusev crater and
Meridiani Planum. The following elements are typically
measured in soil and rock samples at the two landings sites:
Na, Mg, Al, Si, P, S, Cl, K, Ca, Ti, Cr, Mn, Fe, Ni, Zn, and
Br [e.g., Gellert et al., 2004]. Definitive detections of Co,
Cu, Ga, Ge, Rb, Sr, Y, Ba, and Pb have also been made in
certain specific samples [Gellert et al., 2006; B. C. Clark et
al., Evidence for montmorillonite or its compositional
precursors in Columbia Hills, Mars, submitted to Journal
of Geophysical Research, 2006 (hereinafter referred to as
Clark et al., submitted manuscript, 2006)]. The APXS data
which support the analyses in this paper are listed in
Tables 1a and 1b.
3.1. Chondritic Nickel
[14] Of the 16 elements that are detected on a regular basis,
nickel is the most effective for constraining the extent of
meteoritic contributions to the Martian samples (Figure 4).
Other elements, such as Fe, Mg, S, and Cr, even though
they are typically enhanced in meteoritic material, are less
useful in studying the exogenic contribution, as the range of
Martian sample compositions encompasses the meteoritic
abundances of these elements. That is, some samples
analyzed by MER have greater concentrations of these
elements, while others have less. This produces inherent
difficulties in attempting to discern small admixtures of
meteoritic elements other than nickel in the midst of
significant diversity in rock and soil compositions.
[15] Ni is present in CI chondrites, representative of
average solar system composition, at a level of 10.6 mg/g
(13.1 mg/g on a volatile free basis) [Lodders, 2003]. This is
roughly a factor of 20 larger than rocks analyzed by
Opportunity, a factor of 90 times the concentration in
Adirondack class basalts analyzed by Spirit, and between
30 and 410 times the Ni concentration typical of Martian
meteorites [Lodders, 1998]. Other classes of chondrites that
could potentially dominate the meteoritic material arriving
at Mars all have high nickel. The H, L, and LL groups
of ordinary chondrites, which dominate the observed falls
on Earth, have average Ni concentrations of 17.1 mg/g,
12.4 mg/g, and 10.6 mg/g, respectively [Lodders and
Fegley, 1998].
3.2. Other Elements
[16] The viability of using other potentially detectable
trace elements in constraining the magnitude of meteoritic
input to surface materials was assessed. Of the elements
detectable by the MER APXS (X-ray energies between 1
and 16 keV) and not including the 16 elements that are
typically quantifiable, cobalt is the most abundant in CI
averages: 500 mg/g [Lodders, 2003]. Unfortunately, the
separation between the Ka peak of Co at 6.93 keV and
the Kb peak of Fe at 7.06 keV is only 130 eV. Using a
sensor with an inherent energy resolution of 170 eV under
the best conditions means that these peaks are essentially
superimposed. As a result, the quantity of Co required in a
MER analysis to produce a confident detection is approx-
imately 100 mg/g. This is 20% of the chondritic value and is
Figure 2. Approximate true color Pancam image of an
iron-nickel meteorite found near the Opportunity heat shield
designated ??Meridiani Planum?? by the Meteoritical Society
nomenclature committee (sol 346, sequence p2591).
Figure 3. False color Pancam image from the rim of
Endurance crater (sol 123, sequence p2535) of a likely
meteorite fragment informally referred to as ??Barberton.??
The backward ??C?? to the right of the rock fragment is an
indentation made by the contact plate of the Mo?ssbauer
spectrometer.
E12S11 YEN ET AL.: NICKEL ON MARS
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Table 1a. APXS Data Used in This Papera
Sample Na2O MgO Al2O3 SiO2 P2O5 SO3 Cl K2O CaO TiO2 Cr2O3 MnO FeO Ni Zn Br
Gusev Basaltic Soilsb
A014 2.76 8.34 9.89 46.3 0.87 6.61 0.78 0.48 6.36 0.86 0.31 0.33 16.0 556 293 31
A041 2.80 8.67 10.02 46.0 0.80 5.26 0.69 0.43 6.98 0.72 0.49 0.36 16.6 341 329 112
A043 2.88 8.45 10.30 46.8 0.81 5.00 0.60 0.45 6.52 0.91 0.41 0.36 16.5 364 257 56
A044 2.54 8.69 10.23 46.3 0.87 6.06 0.71 0.43 6.58 0.77 0.26 0.29 16.2 287 246 38
A045 3.09 8.59 9.96 45.5 0.78 6.19 0.78 0.48 6.69 0.68 0.38 0.30 16.5 551 211 69
A047 3.13 8.41 10.05 46.0 0.86 6.33 0.73 0.44 6.32 0.89 0.33 0.34 16.1 318 288 19
A049 2.44 8.90 9.83 46.2 0.68 6.11 0.69 0.38 6.14 1.00 0.43 0.34 16.8 443 318 61
A050 2.65 8.77 9.96 46.1 0.73 5.69 0.77 0.37 6.24 1.02 0.40 0.35 16.8 592 255 65
A052 3.18 8.47 9.67 45.6 0.83 6.10 0.80 0.41 6.60 0.81 0.37 0.34 16.7 429 229 63
A065 3.20 8.57 9.86 45.9 0.81 6.76 0.84 0.47 6.04 0.83 0.31 0.31 15.9 620 435 0
A071 2.91 8.25 9.56 45.0 0.91 7.61 0.88 0.49 6.17 0.89 0.31 0.31 16.5 641 409 30
A074A 2.89 8.86 10.12 46.7 0.66 4.39 0.54 0.40 6.57 0.94 0.46 0.36 17.0 475 210 53
A074B 2.23 9.06 9.54 46.0 0.15 6.56 0.85 0.40 6.57 0.88 0.44 0.31 16.9 450 391 108
A105 3.01 8.43 9.68 46.3 0.79 6.67 0.72 0.44 6.45 0.89 0.32 0.34 15.8 237 308 11
A113 3.10 8.39 9.92 46.1 0.88 6.37 0.79 0.47 6.07 1.00 0.37 0.31 16.1 467 192 32
A122 3.07 8.41 10.65 47.0 0.95 5.45 0.63 0.47 6.38 0.88 0.33 0.28 15.4 391 239 31
A126 3.06 8.15 10.02 46.3 0.83 6.40 0.77 0.45 6.50 0.96 0.29 0.32 15.9 641 402 0
A135 3.04 8.73 10.71 47.0 0.77 4.67 0.54 0.42 6.27 0.89 0.42 0.34 16.1 483 291 19
A158 3.25 8.73 11.29 47.8 0.75 4.10 0.52 0.45 6.31 0.67 0.36 0.33 15.3 536 200 36
A227 2.77 8.42 9.59 45.7 0.87 7.50 0.94 0.49 5.88 0.84 0.28 0.31 16.3 533 264 263
A259 3.21 8.42 10.13 46.4 0.90 6.65 0.76 0.46 6.22 0.84 0.29 0.30 15.3 467 293 24
A280 3.17 8.94 9.80 45.0 1.02 6.48 0.87 0.42 6.36 0.88 0.34 0.34 16.2 469 252 101
A315 3.37 8.68 10.31 46.9 0.88 5.82 0.68 0.43 6.24 0.84 0.31 0.32 15.1 412 237 13
A342 3.45 9.42 10.63 46.7 0.84 4.80 0.57 0.40 6.20 0.70 0.33 0.31 15.5 679 162 37
A477 3.09 8.58 10.78 47.7 0.83 4.75 0.55 0.43 6.37 0.83 0.34 0.33 15.3 427 228 32
A587 3.18 8.61 9.79 45.4 0.93 7.42 0.83 0.45 6.08 0.86 0.26 0.31 15.7 433 411 31
A588 3.17 8.84 9.86 45.6 0.93 6.95 0.76 0.43 6.10 0.87 0.28 0.31 15.8 460 367 48
A607 3.48 8.13 11.38 47.0 1.11 5.28 0.60 0.46 6.33 1.17 0.28 0.28 14.4 313 248 60
Gusev Plains Basaltsc
A034 2.41 10.83 10.87 45.7 0.52 1.23 0.20 0.07 7.75 0.48 0.61 0.41 18.8 165 81 14
A060 2.54 10.41 10.68 45.9 0.56 1.28 0.26 0.10 7.84 0.55 0.60 0.41 18.8 164 112 52
A086 2.78 9.72 10.70 45.8 0.65 1.48 0.23 0.16 8.02 0.59 0.54 0.42 18.9 132 75 161
Gusev Clovis Class Rocks
A195 3.41 8.54 9.68 44.8 0.96 7.33 1.08 0.40 5.62 0.89 0.24 0.20 16.7 516 193 185
A197 3.33 10.92 12.60 46.8 1.24 2.87 0.78 0.07 3.64 0.94 0.27 0.10 16.3 607 89 318
A199 2.92 11.62 10.34 46.4 1.20 2.41 1.03 0.04 3.44 0.91 0.18 0.13 19.2 553 54 493
A214 3.46 8.80 9.66 44.9 1.02 7.77 1.23 0.42 6.15 0.85 0.19 0.27 15.0 562 175 908
A216 3.55 10.79 9.34 43.4 1.13 7.98 1.88 0.35 5.86 0.75 0.18 0.27 14.3 538 107 901
A218 3.64 11.52 8.95 42.2 1.05 7.53 1.63 0.35 6.04 0.84 0.17 0.30 15.6 735 118 239
A225 3.02 11.46 8.85 42.6 0.81 9.29 1.74 0.45 5.39 0.84 0.18 0.23 14.9 670 99 993
A228 2.87 11.16 10.71 47.4 0.94 4.67 1.33 0.36 4.24 0.79 0.14 0.21 15.1 453 146 193
A229 3.20 10.89 10.40 46.8 1.00 5.18 1.32 0.35 4.31 0.78 0.17 0.17 15.3 478 92 267
A231 2.59 13.57 9.93 47.5 0.97 3.81 1.54 0.32 3.63 0.76 0.16 0.15 15.0 497 72 293
A232 2.32 14.82 9.28 47.4 0.97 3.20 1.46 0.33 3.44 0.79 0.16 0.16 15.6 523 99 222
A235 3.01 13.49 10.18 45.3 0.94 3.01 1.38 0.30 3.93 0.90 0.18 0.18 17.1 731 56 352
A266 3.27 9.06 9.47 45.3 0.98 7.37 1.33 0.41 5.75 0.85 0.19 0.35 15.4 568 175 1543
A274 3.31 9.49 10.10 46.4 0.91 6.52 1.42 0.43 5.18 0.86 0.20 0.28 14.7 558 204 694
A284 3.21 9.14 9.74 45.1 0.98 7.38 1.32 0.43 5.90 0.86 0.19 0.30 15.2 564 206 735
A287 2.44 14.28 9.52 45.6 0.94 5.26 1.85 0.35 4.48 0.80 0.15 0.25 13.9 593 118 674
A291 2.82 12.14 9.96 45.4 1.04 5.92 2.62 0.40 4.39 0.80 0.16 0.23 13.9 547 158 903
A300 2.56 14.34 10.29 46.0 0.95 3.44 2.02 0.29 4.59 0.80 0.16 0.17 14.2 629 103 581
A304 2.45 15.12 10.17 45.5 1.04 3.05 2.47 0.24 4.62 0.78 0.16 0.18 14.1 605 112 339
Gusev Wishstone and Watchtower Class Rocks
A334 5.12 4.94 15.64 46.3 2.63 3.47 0.59 0.54 6.86 2.16 0.01 0.22 11.5 99 96 14
A335 4.98 4.50 15.03 43.8 5.19 2.20 0.35 0.57 8.89 2.59 0.00 0.22 11.6 67 64 22
A349 4.48 5.64 14.68 47.0 1.74 4.10 0.71 0.56 6.62 1.86 0.03 0.25 12.2 57 122 58
A353 4.20 6.15 13.48 46.4 1.79 4.40 0.72 0.53 6.67 1.97 0.04 0.25 13.3 86 105 54
A355 5.30 4.56 15.75 45.8 2.64 2.50 0.62 0.51 6.59 2.84 0.00 0.22 12.6 41 71 38
A356 5.04 3.94 14.86 43.4 5.07 1.94 0.60 0.53 8.78 2.99 0.00 0.24 12.5 24 81 72
A357 5.02 3.98 14.83 43.5 5.05 1.96 0.60 0.53 8.75 2.96 0.00 0.25 12.5 45 58 68
A416 2.78 10.10 12.22 44.1 2.72 4.70 1.14 0.76 6.06 1.89 0.00 0.22 13.3 58 132 262
A417 2.67 10.00 12.33 42.4 4.50 3.43 0.80 0.74 7.44 2.21 0.00 0.22 13.2 67 140 251
A469 3.32 8.38 12.44 47.0 1.23 4.95 0.92 0.51 5.75 2.21 0.11 0.31 12.8 155 117 232
A470 3.44 8.48 13.61 46.9 2.41 4.15 1.23 0.56 6.36 1.96 0.05 0.27 10.5 92 81 204
A475 3.32 8.30 12.49 44.6 3.17 4.73 1.36 0.45 7.40 1.90 0.05 0.21 12.0 147 100 460
A481 3.48 8.16 12.52 46.3 2.62 4.92 1.06 0.40 7.02 1.52 0.13 0.24 11.5 184 97 208
A484 3.60 8.64 12.07 45.2 2.51 6.43 1.28 0.37 6.71 1.94 0.04 0.22 10.9 83 89 302
A491 3.42 7.91 13.73 46.8 2.31 4.97 1.05 0.37 6.45 1.37 0.02 0.17 11.4 74 76 151
A495 3.42 7.82 13.37 46.4 2.68 4.33 0.96 0.39 7.15 1.99 0.06 0.19 11.1 114 88 243
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Table 1a. (continued)
Sample Na2O MgO Al2O3 SiO2 P2O5 SO3 Cl K2O CaO TiO2 Cr2O3 MnO FeO Ni Zn Br
A496 3.48 8.42 13.10 46.0 2.83 4.29 0.98 0.38 7.13 1.92 0.05 0.20 11.1 94 80 250
A499 3.45 7.98 12.62 45.8 2.56 4.81 1.02 0.43 7.03 1.83 0.08 0.21 12.1 137 96 197
A630 4.00 7.90 13.37 46.8 2.35 4.55 1.17 0.54 5.93 1.91 0.02 0.21 11.2 51 121 262
A633 4.06 6.98 13.69 46.5 2.79 4.22 1.18 0.52 6.19 2.24 0.01 0.19 11.4 53 113 342
Gusev Mafic/Ultramafic Rock Sequence
A630 4.00 7.90 13.37 46.8 2.35 4.55 1.17 0.54 5.93 1.91 0.02 0.21 11.2 51 121 262
A633 4.06 6.98 13.69 46.5 2.79 4.22 1.18 0.52 6.19 2.24 0.01 0.19 11.4 53 113 342
A646 3.41 8.58 9.35 44.0 2.24 7.81 2.08 0.41 6.17 2.12 0.08 0.29 13.4 220 270 235
A660 2.78 11.18 8.49 39.7 2.89 4.80 0.93 0.54 6.40 1.19 0.19 0.37 20.5 229 196 64
A672 2.78 13.80 7.05 43.0 0.90 4.59 1.45 0.94 4.00 0.65 0.42 0.36 20.0 538 235 171
A675 2.98 12.38 7.72 44.1 0.91 4.65 1.24 0.66 4.66 0.61 0.39 0.36 19.3 545 204 126
A687 2.49 13.57 7.29 42.6 0.78 5.62 0.79 0.26 4.12 0.53 0.73 0.39 20.7 858 169 69
A688 1.59 22.30 4.00 40.6 0.63 4.32 0.87 0.12 2.61 0.35 0.87 0.38 21.2 891 131 72
A699 2.43 14.22 6.98 41.9 0.73 5.14 0.70 0.24 4.02 0.51 0.66 0.44 21.9 867 166 153
A700 1.12 24.75 2.93 41.3 0.45 2.69 0.61 0.04 1.93 0.25 0.71 0.43 22.6 1000 132 156
Meridiani Basaltic Soilsd
B011 1.83 7.58 9.26 46.3 0.83 4.99 0.63 0.47 7.31 1.04 0.45 0.37 18.8 423 241 32
B025 2.03 7.49 9.21 45.9 0.80 6.96 0.70 0.49 6.69 1.13 0.40 0.35 17.7 634 428 159
B026 1.92 7.42 9.05 45.3 0.75 5.69 0.59 0.45 6.72 1.24 0.46 0.36 19.9 631 348 130
B060 2.24 7.63 9.22 45.3 0.94 7.34 0.79 0.48 6.59 1.02 0.33 0.34 17.6 470 404 26
B081 2.34 7.59 9.88 47.1 0.74 4.57 0.49 0.41 6.73 1.23 0.48 0.36 17.9 592 256 40
B090 2.35 7.78 9.25 45.6 0.86 5.81 0.60 0.44 6.70 1.09 0.46 0.38 18.5 456 320 232
B123 2.38 7.61 9.21 45.3 0.87 7.12 0.84 0.51 6.73 0.97 0.36 0.37 17.6 503 376 35
B166 2.40 7.14 10.04 47.7 0.81 5.19 0.64 0.55 7.32 0.85 0.34 0.39 16.6 339 226 25
B237 2.39 6.90 10.41 48.8 0.84 4.56 0.58 0.59 7.38 0.85 0.28 0.35 15.9 323 178 21
B249 2.39 7.65 9.59 46.7 0.85 4.62 0.59 0.48 7.30 0.91 0.45 0.40 18.0 344 184 24
B499 2.32 7.05 8.74 44.8 0.91 6.59 0.72 0.47 7.06 1.02 0.41 0.39 19.4 445 298 130
B507 2.13 7.02 8.70 44.1 0.94 7.36 0.76 0.50 6.75 1.05 0.35 0.37 19.8 463 452 121
Meridiani Hematitic Soils
B023 2.12 7.50 8.59 42.7 0.81 4.77 0.68 0.43 6.13 0.78 0.30 0.31 24.8 633 312 37
B046 2.29 6.82 8.02 39.5 0.76 5.60 0.72 0.38 5.24 0.70 0.27 0.27 29.3 801 331 41
B080 2.21 6.81 7.66 38.6 0.77 4.90 0.68 0.37 5.10 0.68 0.30 0.27 31.5 882 304 35
B091 2.34 7.27 7.67 38.8 0.82 4.83 0.70 0.34 4.93 0.70 0.28 0.28 30.9 1089 361 53
B100 2.44 6.89 7.82 39.2 0.82 5.95 0.77 0.38 5.14 0.72 0.25 0.28 29.2 773 331 46
B369 2.13 6.39 7.36 37.4 0.87 4.64 0.71 0.33 4.88 0.67 0.27 0.29 33.8 1292 357 101
B370 2.17 6.61 7.83 39.8 0.82 5.05 0.68 0.40 5.67 0.78 0.32 0.29 29.4 750 300 47
B416 2.21 6.75 8.19 41.5 0.86 5.21 0.67 0.42 6.17 0.85 0.33 0.33 26.3 608 282 39
B420A 2.11 6.67 7.72 39.5 0.88 5.90 0.72 0.39 5.30 0.80 0.28 0.29 29.3 850 371 73
B420B 2.19 6.61 7.76 39.0 0.84 5.15 0.70 0.36 5.27 0.78 0.27 0.29 30.6 965 348 96
B443 2.01 6.43 7.78 40.0 0.83 5.54 0.72 0.43 5.69 0.79 0.32 0.32 29.0 729 354 48
B505 2.15 6.54 7.80 39.3 0.82 5.24 0.65 0.39 5.39 0.75 0.32 0.28 30.2 743 331 48
B509 2.18 6.37 7.94 39.9 0.80 5.07 0.66 0.42 5.54 0.73 0.29 0.26 29.7 865 328 45
Meridiani outcrop: RATted Interior Measurementse
B031 1.67 8.00 6.20 38.3 0.99 21.31 0.60 0.56 4.42 0.81 0.19 0.30 16.5 735 279 342
B036 1.66 8.45 5.85 36.2 0.97 24.91 0.50 0.53 4.91 0.65 0.17 0.30 14.8 589 324 30
B045 1.64 8.38 6.18 36.3 1.01 23.61 0.54 0.59 5.19 0.74 0.20 0.26 15.3 656 427 105
B087 1.50 8.63 5.82 34.7 0.97 25.21 0.66 0.50 4.82 0.76 0.19 0.36 15.7 634 526 33
B108 1.72 8.80 6.22 37.2 1.01 22.84 0.91 0.58 5.03 0.77 0.18 0.29 14.3 572 415 268
B139 1.36 8.38 5.87 35.0 1.03 24.94 0.65 0.58 5.03 0.79 0.20 0.32 15.7 679 533 35
B145 1.54 9.20 5.90 35.9 1.05 24.38 0.65 0.57 4.72 0.71 0.18 0.33 14.7 618 371 54
B147 1.83 9.00 6.32 36.9 1.07 22.09 0.60 0.60 4.43 0.84 0.21 0.39 15.5 664 381 74
B149 1.64 9.14 5.99 36.4 1.11 23.71 0.72 0.57 4.85 0.74 0.20 0.31 14.5 638 357 27
B153 1.70 8.38 6.36 38.0 1.07 21.50 1.45 0.58 4.64 0.83 0.19 0.33 14.8 604 319 39
B155 1.45 8.63 5.85 36.2 1.03 23.03 1.75 0.55 4.85 0.80 0.20 0.33 15.2 644 346 19
B162 1.58 7.41 6.20 37.6 1.17 21.11 1.98 0.59 5.11 0.75 0.21 0.31 15.8 616 437 11
B178 1.72 6.47 6.71 40.6 1.05 19.62 1.37 0.63 5.09 0.79 0.17 0.33 15.4 531 444 23
B180 1.71 6.49 6.70 40.1 1.06 19.64 1.64 0.63 5.03 0.81 0.22 0.31 15.5 611 486 14
B184 1.93 5.43 7.27 43.0 1.15 17.01 1.90 0.69 4.60 0.86 0.20 0.32 15.6 546 447 9
B187 1.79 5.45 7.17 39.9 1.11 18.17 1.67 0.67 5.48 0.86 0.22 0.36 17.1 606 489 13
B195 1.86 6.81 6.52 37.9 1.01 19.33 1.69 0.60 5.01 0.77 0.23 0.37 17.7 933 499 10
B220 1.63 8.37 6.06 36.5 1.01 23.03 0.78 0.57 5.00 0.75 0.18 0.24 15.7 564 314 425
B307 1.84 7.86 6.36 37.7 1.13 21.35 1.42 0.57 4.59 0.77 0.16 0.33 15.7 571 628 10
B312 1.83 9.11 6.43 37.5 1.08 21.33 1.49 0.56 4.10 0.81 0.20 0.32 15.1 605 259 38
B403 1.35 7.33 4.90 32.6 1.07 28.62 0.61 0.51 5.78 0.68 0.17 0.35 15.9 585 436 54
B548 1.74 7.31 5.91 36.2 1.04 23.81 0.64 0.58 5.49 0.78 0.21 0.31 15.8 449 480 109
B558 1.57 8.09 5.72 32.8 0.99 27.39 0.57 0.50 5.13 0.72 0.19 0.39 15.8 504 563 84
B560 2.02 7.83 6.17 35.1 1.05 23.12 1.54 0.54 5.20 0.75 0.19 0.38 16.0 508 457 67
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therefore not useful in providing constraints on the extent
of meteoritic material at the Martian surface. In addition,
Martian meteorites typically contain between 30?70 mg/g
Co. CI chondrites thus contain only 7 to 17 times more
Co than Martian meteorites. As a result, cobalt is a much
less sensitive indicator of meteoritic contamination than
nickel.
[17] Attempts to use other elements to help determine the
magnitude of meteoritic contributions to the Martian surface
were unsuccessful because of either inadequate detection
limits or lack of sensitivity to mixtures with small quantities
of meteoritic material. The concentrations of iridium, gold,
and germanium, which can be diagnostic of a meteoritic
input, are far below detection limits. The most useful
element for establishing the potential level of exogenic flux
is clearly nickel.
3.3. Nickel in the Rock Abrasion Tool (RAT)
[18] The viability of using nickel as a meteoritic tracer
is dependent upon the absence of analysis artifacts. The
abrasive pads on the MER RAT utilize 120 mesh syn-
thetic diamonds impregnated in a phenolic resin with
silicon carbide and cryolite (Na3AlF6) fibers [Myrick et
al., 2004]. To increase the adhesion characteristics with
the resin, the diamond grit is coated with nickel [Myrick
et al., 2004]. The abrading capability of the RAT is
maintained by exposing fresh diamond as the worn grains
fall out. Thus there is a possibility of Ni contamination in
APXS measurements of abraded surfaces. However, the
decrease in Ni levels from brushed to abraded analyses
for the Ni-poor, Wishstone rock sample [Gellert et al.,
2006] is an indication that Ni contamination in abraded
surfaces is generally negligible. On the basis of specific
grind energies calculated from the RAT telemetry [Bartlett
et al., 2005], Wishstone is among the harder rocks
abraded by the rovers. Even in the hardest rocks encoun-
tered by the rovers (Gusev plains basalts, ??Adirondack??
Class), the differences between the determined Ni con-
centrations before and after abrading are within the
precision of the measurements. Thus, given that brushing
operations do not deposit nickel-coated diamonds, and
that subsequent abrading of the target, even in the hardest
Table 1a. (continued)
Sample Na2O MgO Al2O3 SiO2 P2O5 SO3 Cl K2O CaO TiO2 Cr2O3 MnO FeO Ni Zn Br
B634 1.78 7.39 6.52 37.5 0.98 20.72 0.56 0.55 5.84 0.79 0.25 0.33 16.6 496 394 67
B696 1.51 7.08 5.40 34.6 1.01 26.52 0.46 0.55 5.74 0.71 0.18 0.32 15.8 537 554 182
Meridiani Outcrop: Brushed and Undisturbed Surfacesf
B015 1.56 8.29 7.46 39.6 0.97 19.42 0.81 0.57 5.03 0.74 0.19 0.28 15.0 597 569 7
B029 2.28 8.14 8.39 43.1 0.97 12.73 0.87 0.53 5.72 0.87 0.26 0.30 15.7 588 295 211
B030 1.88 7.95 7.26 40.3 1.01 18.75 0.87 0.58 4.92 0.84 0.17 0.30 15.1 657 373 43
B040 2.09 7.65 7.06 38.4 1.00 18.91 0.90 0.56 4.84 0.70 0.16 0.30 17.4 686 397 32
B041 2.40 8.10 8.75 43.9 0.97 11.42 0.84 0.55 5.70 0.94 0.29 0.33 15.6 625 292 346
B043 2.26 7.82 8.39 43.0 0.98 12.97 0.86 0.56 5.98 0.88 0.23 0.29 15.6 633 414 90
B048 2.11 7.86 8.12 42.7 0.97 14.08 0.99 0.56 5.51 0.84 0.20 0.34 15.6 607 426 103
B049 2.29 8.41 8.34 41.4 1.01 15.19 0.93 0.61 5.29 0.84 0.16 0.27 15.1 553 460 177
B051 2.16 8.16 6.99 38.3 0.99 18.70 0.85 0.52 4.37 0.67 0.17 0.24 17.7 653 388 100
B106 1.98 8.03 7.21 39.7 0.98 18.80 1.00 0.57 5.11 0.78 0.19 0.29 15.3 573 389 76
B142 0.88 8.04 7.89 43.2 0.80 13.41 0.83 0.53 6.34 0.92 0.24 0.24 16.5 652 439 139
B283 1.95 7.43 8.47 43.5 0.95 11.93 0.96 0.59 6.79 0.89 0.29 0.33 15.8 417 391 18
B306 1.74 8.08 6.45 38.7 1.09 21.47 1.10 0.54 4.49 0.76 0.18 0.27 14.9 564 624 147
B308 1.68 9.38 6.28 37.0 1.02 21.55 1.07 0.54 4.27 0.76 0.21 0.29 15.8 804 301 103
B311 2.55 7.86 8.63 42.6 0.91 11.14 0.84 0.50 6.33 0.77 0.24 0.28 17.3 466 273 44
B381 1.84 7.15 6.81 38.5 1.05 20.82 0.94 0.57 5.47 0.80 0.20 0.30 15.4 628 585 60
B393 2.00 7.39 7.10 39.4 1.01 19.81 0.89 0.56 5.16 0.83 0.20 0.30 15.3 634 441 53
B400 2.00 7.19 7.54 41.0 1.04 16.51 0.98 0.56 5.46 0.89 0.20 0.34 16.2 543 450 73
B401 1.79 7.25 6.71 38.3 1.03 21.46 0.92 0.57 5.36 0.78 0.17 0.31 15.2 574 405 67
B556 2.22 7.07 7.49 40.2 1.07 15.30 1.49 0.55 6.07 0.89 0.24 0.37 17.0 525 474 67
B593 1.84 7.37 6.84 38.8 1.08 19.53 0.90 0.61 5.49 0.79 0.22 0.28 16.1 576 450 294
B594 1.79 7.45 6.63 38.5 1.05 19.83 0.74 0.58 5.06 0.80 0.19 0.23 17.0 515 423 103
B638 1.73 7.36 6.26 36.9 1.02 23.00 0.84 0.55 5.12 0.76 0.18 0.31 15.8 544 559 74
B675 1.88 7.50 6.93 39.1 1.01 19.62 0.75 0.57 5.45 0.83 0.19 0.25 15.8 549 470 65
B679 2.04 7.27 7.29 40.1 1.03 17.51 0.90 0.57 5.61 0.85 0.21 0.32 16.2 571 541 161
B680 1.93 7.23 6.69 38.2 1.03 20.62 0.80 0.58 5.45 0.78 0.19 0.31 16.0 548 536 177
B686 2.00 7.48 7.00 39.2 1.01 19.06 0.76 0.55 5.23 0.80 0.20 0.29 16.3 561 634 157
Meridiani ??Bounce?? Rockg
B068 1.66 6.84 10.48 51.6 0.92 0.56 0.10 0.11 12.09 0.74 0.11 0.40 14.4 81 38 39
aData reduction follows techniques described by Gellert et al. [2006]. Concentrations are normalized to 100% with all iron as FeO. Accuracies of
elemental concentrations are tabulated by Gellert et al. [2004]; precisions are listed in Table 1b. Ni, Zn, and Br values are presented in mg/g; all other values
are weight percentages.
bNot including ferric sulfates, altered trench deposits, short integrations with poor statistics, or samples with significant rock fragments.
cAdirondack class rocks, RATted interior measurements only.
dNot including short integrations with poor statistics or subsurface deposits with evidence of chemical mobility.
eIncludes samples with embedded high-Ni spherules.
fNot including samples with known rinds/coatings or obvious soil mantle.
gRATted data only.
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Table 1b. Two Sigma Statistical Uncertainties Associated With the APXS Data Listed in Table 1aa
Sample Na2O MgO Al2O3 SiO2 P2O5 SO3 Cl K2O CaO TiO2 Cr2O3 MnO FeO Ni Zn Br
Gusev Basaltic Soils
A014 0.23 0.12 0.14 0.44 0.08 0.08 0.02 0.06 0.05 0.07 0.03 0.01 0.11 51 18 17
A041 0.93 0.27 0.29 0.71 0.26 0.17 0.04 0.15 0.12 0.20 0.06 0.06 0.21 100 51 30
A043 0.27 0.15 0.17 0.53 0.09 0.10 0.02 0.06 0.07 0.08 0.04 0.02 0.15 65 27 21
A044 1.25 0.37 0.38 0.92 0.32 0.26 0.06 0.17 0.16 0.23 0.07 0.09 0.29 138 74 39
A045 1.79 0.47 0.36 0.64 0.28 0.21 0.05 0.16 0.14 0.15 0.07 0.07 0.18 135 63 37
A047 0.21 0.11 0.11 0.33 0.08 0.09 0.02 0.06 0.05 0.07 0.03 0.01 0.08 51 20 17
A049 0.25 0.13 0.14 0.47 0.08 0.09 0.02 0.06 0.06 0.08 0.04 0.01 0.12 61 26 21
A050 0.24 0.13 0.16 0.47 0.08 0.08 0.02 0.06 0.05 0.07 0.04 0.01 0.12 56 20 18
A052 0.96 0.28 0.29 0.77 0.26 0.21 0.05 0.15 0.13 0.18 0.06 0.07 0.24 112 53 34
A065 1.03 0.30 0.28 0.75 0.26 0.23 0.05 0.16 0.13 0.16 0.06 0.07 0.24 131 67 10
A071 0.29 0.15 0.16 0.52 0.09 0.13 0.03 0.07 0.07 0.08 0.04 0.02 0.15 73 32 22
A074A 0.25 0.14 0.15 0.48 0.08 0.08 0.02 0.06 0.06 0.07 0.04 0.01 0.13 60 22 19
A074B 1.07 0.24 0.31 0.47 0.34 0.17 0.05 0.15 0.11 0.14 0.06 0.07 0.15 113 53 30
A105 1.19 0.34 0.31 0.82 0.29 0.25 0.05 0.17 0.15 0.18 0.07 0.08 0.25 129 74 35
A113 1.23 0.33 0.26 0.64 0.24 0.18 0.04 0.15 0.11 0.16 0.06 0.06 0.19 108 50 31
A122 1.00 0.29 0.27 0.71 0.26 0.19 0.04 0.15 0.12 0.16 0.06 0.07 0.21 100 48 31
A126 1.65 0.46 0.40 0.83 0.30 0.24 0.05 0.17 0.14 0.19 0.07 0.08 0.25 141 73 10
A135 1.67 0.46 0.37 0.69 0.27 0.16 0.03 0.15 0.11 0.20 0.06 0.06 0.20 95 45 26
A158 0.85 0.26 0.26 0.70 0.23 0.15 0.03 0.15 0.12 0.16 0.06 0.06 0.21 102 45 29
A227 0.90 0.26 0.26 0.68 0.25 0.20 0.04 0.15 0.10 0.14 0.05 0.06 0.20 100 44 37
A259 0.23 0.12 0.14 0.45 0.08 0.09 0.02 0.06 0.05 0.07 0.03 0.01 0.11 48 17 16
A280 0.21 0.12 0.12 0.43 0.08 0.08 0.02 0.06 0.05 0.07 0.03 0.01 0.11 47 15 17
A315 0.31 0.16 0.16 0.50 0.08 0.09 0.02 0.06 0.06 0.07 0.04 0.01 0.12 51 18 17
A342 0.23 0.13 0.14 0.46 0.08 0.08 0.01 0.06 0.06 0.07 0.03 0.01 0.12 52 15 17
A477 0.31 0.15 0.15 0.49 0.08 0.08 0.01 0.06 0.06 0.07 0.03 0.01 0.11 47 16 16
A587 0.28 0.13 0.12 0.42 0.07 0.08 0.01 0.06 0.04 0.06 0.03 0.01 0.10 40 14 15
A588 0.20 0.10 0.11 0.40 0.07 0.08 0.01 0.06 0.04 0.06 0.03 0.01 0.10 39 12 15
A607 0.20 0.10 0.12 0.40 0.07 0.06 0.01 0.06 0.04 0.07 0.03 0.01 0.09 36 10 14
Gusev Plains Basalts
A034 0.20 0.12 0.12 0.41 0.07 0.03 0.01 0.05 0.05 0.06 0.03 0.01 0.12 39 11 15
A060 0.28 0.14 0.13 0.43 0.07 0.03 0.01 0.05 0.05 0.06 0.03 0.01 0.12 39 11 16
A086 0.20 0.11 0.12 0.41 0.07 0.03 0.01 0.05 0.06 0.06 0.03 0.01 0.12 39 11 17
Gusev Clovis Class Rocks
A195 0.20 0.11 0.12 0.41 0.07 0.09 0.02 0.06 0.04 0.07 0.03 0.01 0.11 44 13 17
A197 0.22 0.14 0.17 0.44 0.08 0.05 0.02 0.05 0.04 0.07 0.03 0.01 0.11 47 12 20
A199 0.20 0.13 0.12 0.43 0.08 0.04 0.02 0.05 0.03 0.07 0.03 0.01 0.12 46 11 21
A214 0.21 0.11 0.12 0.42 0.08 0.09 0.02 0.06 0.05 0.07 0.03 0.01 0.10 44 12 24
A216 0.23 0.14 0.13 0.42 0.08 0.10 0.03 0.06 0.05 0.07 0.03 0.01 0.10 47 13 26
A218 0.23 0.13 0.10 0.38 0.08 0.10 0.03 0.06 0.05 0.07 0.03 0.01 0.08 55 16 20
A225 1.11 0.30 0.27 0.52 0.36 0.25 0.06 0.15 0.09 0.14 0.05 0.06 0.15 94 33 45
A228 0.75 0.25 0.24 0.67 0.21 0.14 0.05 0.14 0.08 0.13 0.04 0.04 0.18 80 32 29
A229 0.20 0.13 0.12 0.42 0.07 0.07 0.02 0.06 0.04 0.06 0.03 0.01 0.10 41 9 17
A231 0.21 0.15 0.12 0.43 0.07 0.06 0.02 0.06 0.03 0.06 0.03 0.01 0.10 43 10 18
A232 0.22 0.17 0.13 0.45 0.08 0.06 0.02 0.06 0.04 0.07 0.03 0.01 0.11 47 13 19
A235 0.81 0.28 0.24 0.64 0.22 0.12 0.05 0.13 0.08 0.14 0.05 0.04 0.20 93 29 36
A266 0.20 0.11 0.11 0.40 0.07 0.08 0.02 0.06 0.04 0.06 0.03 0.01 0.10 42 11 28
A274 0.22 0.11 0.11 0.40 0.08 0.08 0.02 0.06 0.04 0.07 0.03 0.01 0.08 48 15 23
A284 0.22 0.12 0.12 0.43 0.08 0.09 0.02 0.06 0.05 0.07 0.03 0.01 0.11 47 14 24
A287 0.20 0.13 0.10 0.35 0.07 0.06 0.02 0.06 0.03 0.06 0.03 0.01 0.06 41 9 20
A291 0.22 0.14 0.12 0.42 0.08 0.08 0.03 0.06 0.04 0.07 0.03 0.01 0.10 44 12 24
A300 0.20 0.15 0.12 0.41 0.07 0.05 0.02 0.06 0.04 0.06 0.03 0.01 0.09 42 10 20
A304 0.22 0.17 0.13 0.43 0.08 0.05 0.03 0.06 0.04 0.07 0.03 0.01 0.10 46 12 19
Gusev Wishstone and Watchtower Class Rocks
A334 0.28 0.14 0.24 0.49 0.11 0.07 0.02 0.06 0.07 0.09 0.03 0.01 0.10 41 14 17
A335 0.25 0.10 0.17 0.44 0.13 0.05 0.01 0.06 0.07 0.10 0.02 0.01 0.10 40 13 16
A349 0.29 0.13 0.21 0.52 0.10 0.09 0.02 0.06 0.07 0.10 0.03 0.01 0.11 48 19 19
A353 0.23 0.10 0.15 0.36 0.09 0.08 0.02 0.06 0.06 0.09 0.03 0.01 0.08 44 15 18
A355 0.21 0.07 0.15 0.38 0.08 0.04 0.01 0.06 0.04 0.08 0.02 0.01 0.08 30 7 13
A356 0.25 0.09 0.17 0.42 0.12 0.04 0.01 0.06 0.07 0.10 0.02 0.01 0.09 40 13 18
A357 0.23 0.08 0.14 0.32 0.11 0.04 0.01 0.06 0.06 0.09 0.02 0.01 0.08 41 13 16
A416 0.27 0.16 0.19 0.48 0.11 0.08 0.03 0.07 0.06 0.09 0.03 0.01 0.11 45 17 21
A417 0.23 0.13 0.15 0.41 0.11 0.06 0.02 0.06 0.06 0.08 0.02 0.01 0.10 37 12 19
A469 0.23 0.11 0.13 0.37 0.08 0.07 0.02 0.06 0.05 0.08 0.03 0.01 0.07 40 13 18
A470 0.21 0.09 0.12 0.34 0.09 0.05 0.02 0.06 0.04 0.07 0.03 0.01 0.05 34 9 16
A475 0.28 0.13 0.15 0.38 0.11 0.09 0.03 0.06 0.07 0.09 0.03 0.01 0.08 47 17 24
A481 0.23 0.11 0.14 0.42 0.09 0.07 0.02 0.06 0.05 0.08 0.03 0.01 0.08 37 10 17
A484 0.22 0.11 0.13 0.40 0.09 0.07 0.02 0.06 0.05 0.08 0.03 0.01 0.07 32 8 17
A491 0.23 0.11 0.15 0.43 0.09 0.07 0.02 0.06 0.05 0.07 0.03 0.01 0.08 35 9 17
A495 0.22 0.11 0.15 0.41 0.09 0.06 0.02 0.06 0.05 0.08 0.03 0.01 0.08 34 9 17
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Table 1b. (continued)
Sample Na2O MgO Al2O3 SiO2 P2O5 SO3 Cl K2O CaO TiO2 Cr2O3 MnO FeO Ni Zn Br
A496 0.22 0.11 0.14 0.41 0.09 0.06 0.02 0.06 0.05 0.07 0.03 0.01 0.08 34 9 17
A499 0.22 0.11 0.14 0.41 0.09 0.06 0.02 0.06 0.05 0.08 0.03 0.01 0.08 35 9 17
A630 0.25 0.11 0.15 0.44 0.09 0.07 0.02 0.06 0.05 0.08 0.03 0.01 0.08 37 12 18
A633 0.20 0.08 0.12 0.30 0.09 0.05 0.02 0.06 0.04 0.08 0.03 0.01 0.05 33 9 17
Gusev Mafic/Ultramafic Rock Sequence
A630 0.25 0.11 0.15 0.44 0.09 0.07 0.02 0.06 0.05 0.08 0.03 0.01 0.08 37 12 18
A633 0.20 0.08 0.12 0.30 0.09 0.05 0.02 0.06 0.04 0.08 0.03 0.01 0.05 33 9 17
A646 0.21 0.10 0.11 0.39 0.09 0.09 0.02 0.06 0.04 0.08 0.03 0.01 0.09 35 11 17
A660 0.29 0.15 0.13 0.39 0.09 0.07 0.02 0.06 0.05 0.07 0.03 0.01 0.13 40 13 16
A672 0.38 0.19 0.11 0.43 0.07 0.06 0.02 0.06 0.03 0.06 0.03 0.01 0.12 43 12 17
A675 0.21 0.12 0.08 0.30 0.07 0.05 0.02 0.06 0.03 0.06 0.03 0.01 0.09 42 11 15
A687 0.19 0.14 0.09 0.37 0.07 0.07 0.01 0.05 0.03 0.06 0.03 0.01 0.12 44 10 15
A688 0.19 0.20 0.06 0.34 0.07 0.05 0.01 0.05 0.02 0.06 0.03 0.01 0.12 43 9 15
A699 0.19 0.13 0.08 0.30 0.07 0.06 0.01 0.05 0.03 0.06 0.03 0.01 0.10 46 11 16
A700 0.25 0.23 0.08 0.36 0.07 0.04 0.01 0.05 0.02 0.06 0.03 0.01 0.13 49 11 17
Meridiani Basaltic Soils
B011 0.28 0.12 0.13 0.47 0.08 0.08 0.02 0.06 0.06 0.07 0.04 0.01 0.13 57 20 17
B025 0.24 0.11 0.12 0.38 0.08 0.09 0.02 0.06 0.06 0.08 0.04 0.01 0.11 61 24 21
B026 0.30 0.13 0.14 0.48 0.08 0.09 0.02 0.06 0.06 0.08 0.04 0.02 0.15 69 28 21
B060 0.19 0.08 0.09 0.29 0.07 0.07 0.01 0.06 0.04 0.07 0.03 0.01 0.07 42 14 14
B081 0.29 0.14 0.15 0.50 0.08 0.08 0.02 0.06 0.07 0.08 0.04 0.02 0.14 66 25 21
B090 0.23 0.11 0.14 0.41 0.07 0.07 0.01 0.06 0.05 0.07 0.03 0.01 0.11 43 14 17
B123 0.30 0.15 0.16 0.50 0.09 0.12 0.02 0.06 0.07 0.08 0.04 0.02 0.14 62 26 19
B166 0.28 0.13 0.15 0.49 0.08 0.09 0.02 0.06 0.06 0.08 0.04 0.01 0.13 52 19 17
B237 0.24 0.11 0.13 0.47 0.07 0.07 0.01 0.06 0.06 0.07 0.03 0.01 0.11 46 14 16
B249 0.22 0.10 0.11 0.35 0.08 0.07 0.01 0.06 0.06 0.07 0.04 0.01 0.10 48 15 16
B499 0.28 0.17 0.20 0.60 0.11 0.16 0.03 0.07 0.10 0.09 0.05 0.03 0.21 87 40 27
B507 0.22 0.12 0.17 0.44 0.08 0.11 0.02 0.06 0.06 0.07 0.04 0.01 0.15 55 23 21
Meridiani Hematitic Soils
B023 0.26 0.12 0.13 0.45 0.08 0.08 0.02 0.06 0.06 0.07 0.04 0.01 0.17 64 24 19
B046 0.21 0.09 0.12 0.34 0.07 0.06 0.01 0.06 0.04 0.06 0.03 0.01 0.15 45 13 15
B080 0.27 0.13 0.13 0.47 0.08 0.10 0.02 0.06 0.06 0.07 0.04 0.02 0.24 84 31 23
B091 0.23 0.11 0.11 0.39 0.08 0.08 0.02 0.06 0.05 0.07 0.03 0.01 0.20 66 22 19
B100 0.23 0.11 0.11 0.39 0.08 0.08 0.02 0.06 0.05 0.07 0.03 0.01 0.18 60 20 19
B369 0.20 0.10 0.13 0.37 0.08 0.08 0.02 0.06 0.05 0.07 0.04 0.01 0.22 73 23 21
B370 0.22 0.10 0.10 0.40 0.07 0.07 0.01 0.06 0.05 0.07 0.03 0.01 0.18 56 18 17
B416 0.26 0.13 0.13 0.36 0.08 0.08 0.02 0.06 0.06 0.07 0.04 0.01 0.15 63 22 17
B420A 0.30 0.14 0.12 0.41 0.08 0.09 0.02 0.06 0.05 0.07 0.04 0.01 0.19 63 22 19
B420B 0.20 0.10 0.11 0.41 0.08 0.09 0.02 0.06 0.05 0.07 0.04 0.01 0.21 71 25 21
B443 0.20 0.09 0.11 0.42 0.08 0.09 0.02 0.06 0.06 0.07 0.04 0.02 0.20 75 28 20
B505 0.18 0.09 0.10 0.38 0.07 0.07 0.02 0.06 0.05 0.07 0.03 0.01 0.19 61 20 17
B509 0.18 0.08 0.09 0.29 0.07 0.07 0.02 0.06 0.05 0.07 0.03 0.01 0.13 64 21 17
Meridiani Outcrop: RATted Interior Measurements
B031 0.27 0.13 0.12 0.40 0.09 0.22 0.02 0.06 0.05 0.08 0.03 0.01 0.12 56 19 21
B036 0.26 0.12 0.10 0.37 0.09 0.25 0.01 0.06 0.05 0.07 0.03 0.01 0.11 50 17 16
B045 0.27 0.13 0.10 0.38 0.09 0.24 0.02 0.06 0.05 0.07 0.03 0.01 0.12 54 21 19
B087 0.22 0.11 0.08 0.33 0.08 0.22 0.01 0.06 0.04 0.06 0.03 0.01 0.10 45 16 15
B108 0.32 0.15 0.11 0.39 0.09 0.24 0.02 0.06 0.05 0.08 0.03 0.01 0.11 52 19 20
B139 0.24 0.11 0.11 0.33 0.08 0.22 0.01 0.06 0.04 0.07 0.03 0.01 0.10 47 17 15
B145 0.39 0.17 0.12 0.39 0.09 0.26 0.02 0.06 0.05 0.07 0.03 0.01 0.12 55 20 17
B147 0.29 0.14 0.11 0.40 0.09 0.24 0.02 0.06 0.05 0.07 0.03 0.01 0.12 58 22 18
B149 0.28 0.15 0.11 0.40 0.09 0.26 0.02 0.06 0.05 0.07 0.03 0.01 0.12 57 21 18
B153 0.28 0.13 0.11 0.39 0.09 0.23 0.03 0.06 0.05 0.07 0.03 0.01 0.11 53 18 17
B155 0.31 0.15 0.11 0.39 0.09 0.26 0.03 0.06 0.05 0.08 0.04 0.01 0.12 59 22 17
B162 0.29 0.13 0.11 0.41 0.09 0.24 0.04 0.06 0.05 0.08 0.04 0.01 0.13 59 24 19
B178 0.23 0.10 0.10 0.34 0.08 0.19 0.03 0.06 0.05 0.07 0.03 0.01 0.09 52 20 16
B180 0.31 0.14 0.13 0.44 0.09 0.23 0.03 0.06 0.06 0.07 0.04 0.01 0.13 61 26 19
B184 0.31 0.13 0.13 0.46 0.09 0.21 0.03 0.06 0.05 0.08 0.04 0.01 0.12 58 24 17
B187 0.25 0.11 0.11 0.37 0.09 0.20 0.03 0.07 0.06 0.08 0.04 0.01 0.12 64 27 18
B195 0.29 0.13 0.12 0.42 0.09 0.23 0.03 0.06 0.05 0.07 0.04 0.02 0.14 67 26 19
B220 0.28 0.13 0.11 0.39 0.09 0.25 0.02 0.06 0.05 0.07 0.03 0.01 0.12 55 19 24
B307 0.31 0.15 0.12 0.44 0.09 0.26 0.03 0.06 0.06 0.07 0.04 0.02 0.14 62 29 17
B312 0.27 0.14 0.11 0.40 0.09 0.23 0.03 0.06 0.05 0.07 0.03 0.01 0.12 55 18 18
B403 0.20 0.10 0.08 0.32 0.09 0.28 0.02 0.06 0.06 0.08 0.03 0.01 0.11 56 22 17
B548 0.18 0.08 0.07 0.25 0.07 0.17 0.01 0.06 0.04 0.06 0.03 0.01 0.07 41 14 15
B558 0.17 0.09 0.07 0.29 0.07 0.22 0.01 0.06 0.04 0.06 0.03 0.01 0.10 39 14 15
B560 0.22 0.10 0.08 0.32 0.08 0.20 0.02 0.06 0.04 0.06 0.03 0.01 0.10 41 14 15
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rocks, did not increase the Ni-concentration relative to the
brushed surface, the addition of Ni to the sample by the
RAT abrasion must be insignificant.
4. Abundance of Nickel
[19] In constraining the extent of meteoritic contributions
to the Martian surface, it is not appropriate to simply assume
that materials with low nickel concentrations are indigenous
to Mars while higher Ni levels represent exogenic contam-
ination. A number of factors, including the possible pres-
ence of high-Ni magmas and redistribution in aqueous
solutions affect the observed Ni levels. Table 2 presents
an approximate ordering of Ni content of various groupings
of Martian rocks and soils.
4.1. Fe-Ni and Stony Meteorites
[20] The upper end of Ni concentrations in Table 2
represents samples that are entirely meteoritic. As discussed
above, the Meridiani Planum ??Heatshield Rock?? is a IAB
iron meteorite, and the Barberton pebble is likely a mete-
orite as well.
4.2. Younger Basalts
[21] Interpretation of the low end of Ni concentrations in
Table 2 is also straightforward. These are clearly volcanic
rocks, and there is no reason to suspect contamination from
meteoritic debris in the measurements. The Adirondack
Class rocks are ubiquitous on the Gusev plains and are
classified as picritic basalts similar to olivine-phyric sher-
gottites [McSween et al., 2006a]. Backstay (trachybasalt),
Irvine (basalt), and Wishstone (trachyte) are relatively
unaltered and may have formed during fractional crystalli-
zation of Adirondack-class magmas [McSween et al.,
2006b]. Bounce rock at Meridiani is a pyroxene-rich vol-
canic rock similar to basaltic shergottites EETA 79001
lithology B and QUE 94201 [Zipfel et al., 2004]. These
rocks all have Ni concentrations less than 300 ppm, which is
inadequate to directly account for the Ni levels in the soils
and in sedimentary rocks such as the Meridiani outcrop
rocks.
[22] These Ni concentrations are consistent with predic-
tions of the bulk composition of the Martian primitive
mantle (present mantle plus core), which may differ signif-
icantly from that of the Earth [Halliday et al., 2001]. Mars is
widely viewed to be an iron- and moderately volatile
element-enriched planet. The Martian primitive mantle also
may be depleted in S, which was extracted into the early-
formed core. This history has led to depletion of the
moderately volatile siderophile elements, including nickel
and to a lesser degree cobalt. Accordingly, Wa?nke [1991]
proposed a primitive mantle Ni content of 400 ppm, about a
factor of five less than that of the Earth.
4.3. Ancient Mafic/Ultramafic Sequence
[23] In contrast to the younger basalts, high-Ni magmas
are suggested in a series of rock outcrops analyzed by
Spirit in the descent from Husband Hill. As introduced in
Table 1b. (continued)
Sample Na2O MgO Al2O3 SiO2 P2O5 SO3 Cl K2O CaO TiO2 Cr2O3 MnO FeO Ni Zn Br
B634 0.22 0.10 0.09 0.35 0.08 0.18 0.01 0.06 0.04 0.07 0.03 0.01 0.10 42 14 15
B696 0.22 0.11 0.09 0.36 0.09 0.27 0.02 0.06 0.05 0.07 0.03 0.01 0.12 55 23 20
Meridiani Outcrop: Brushed and Undisturbed Surfaces
B015 0.88 0.21 0.18 0.49 0.19 0.28 0.03 0.07 0.07 0.12 0.04 0.04 0.14 72 34 21
B029 0.25 0.12 0.12 0.41 0.08 0.14 0.02 0.06 0.05 0.07 0.03 0.01 0.11 49 16 18
B030 0.30 0.14 0.12 0.44 0.09 0.22 0.02 0.06 0.05 0.08 0.04 0.01 0.12 60 23 19
B040 0.23 0.10 0.09 0.36 0.08 0.18 0.02 0.06 0.04 0.06 0.03 0.01 0.11 48 16 15
B041 1.36 0.35 0.35 0.76 0.30 0.31 0.05 0.08 0.11 0.24 0.06 0.08 0.21 109 49 39
B043 0.25 0.12 0.12 0.43 0.08 0.15 0.02 0.06 0.05 0.07 0.03 0.01 0.11 52 19 17
B048 0.27 0.13 0.12 0.44 0.08 0.16 0.02 0.06 0.05 0.07 0.03 0.01 0.12 53 21 19
B049 1.06 0.31 0.27 0.65 0.25 0.37 0.06 0.08 0.12 0.22 0.06 0.07 0.21 119 63 36
B051 0.25 0.13 0.11 0.40 0.08 0.20 0.02 0.06 0.05 0.07 0.03 0.01 0.13 55 21 18
B106 0.25 0.12 0.11 0.39 0.08 0.19 0.02 0.06 0.04 0.07 0.03 0.01 0.11 48 17 16
B142 2.77 0.49 0.48 0.95 0.49 0.36 0.07 0.09 0.14 0.24 0.07 0.11 0.23 127 62 35
B283 0.35 0.17 0.17 0.53 0.10 0.19 0.03 0.07 0.08 0.08 0.04 0.02 0.15 74 33 22
B306 0.27 0.13 0.14 0.41 0.09 0.23 0.02 0.06 0.05 0.08 0.03 0.01 0.11 51 22 18
B308 0.27 0.14 0.11 0.40 0.09 0.24 0.02 0.06 0.05 0.07 0.03 0.01 0.12 58 19 18
B311 0.28 0.14 0.17 0.45 0.09 0.15 0.02 0.06 0.06 0.07 0.03 0.01 0.13 55 20 18
B381 0.20 0.10 0.10 0.36 0.08 0.21 0.02 0.06 0.05 0.07 0.03 0.01 0.11 51 21 16
B393 0.22 0.12 0.14 0.42 0.09 0.23 0.02 0.06 0.06 0.07 0.03 0.01 0.13 58 23 18
B400 0.28 0.13 0.12 0.43 0.09 0.19 0.02 0.06 0.06 0.08 0.03 0.01 0.13 56 23 19
B401 0.28 0.13 0.12 0.40 0.09 0.23 0.02 0.06 0.05 0.07 0.03 0.01 0.12 55 21 18
B556 0.16 0.07 0.07 0.25 0.07 0.12 0.02 0.06 0.04 0.06 0.03 0.01 0.06 41 14 14
B593 0.24 0.13 0.13 0.44 0.10 0.25 0.03 0.07 0.07 0.09 0.04 0.02 0.14 66 29 24
B594 0.17 0.09 0.08 0.30 0.07 0.16 0.01 0.06 0.04 0.07 0.03 0.01 0.09 46 16 16
B638 0.16 0.07 0.06 0.23 0.07 0.16 0.01 0.06 0.03 0.06 0.03 0.01 0.06 39 13 14
B675 0.18 0.09 0.09 0.35 0.08 0.18 0.01 0.06 0.04 0.07 0.03 0.01 0.10 44 15 15
B679 0.31 0.15 0.14 0.44 0.09 0.21 0.02 0.06 0.06 0.07 0.04 0.02 0.14 59 26 21
B680 0.16 0.07 0.07 0.24 0.07 0.15 0.01 0.06 0.04 0.06 0.03 0.01 0.06 40 13 15
B686 0.22 0.10 0.09 0.35 0.07 0.16 0.01 0.06 0.04 0.06 0.03 0.01 0.10 40 15 16
Meridiani ??Bounce?? Rock
B068 0.25 0.11 0.14 0.51 0.08 0.03 0.01 0.05 0.09 0.07 0.03 0.01 0.11 42 12 17
aThese values are representative of the precision of the analyses. Ni, Zn, and Br values are presented in mg/g; all other values are weight percentages.
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Figure 4. CI chondrite composition normalized to selected Martian rocks. CI chondrites have large
excesses in Ni compared to all samples analyzed by the MER rovers. Mg, S, K, Cr, Mn, Fe, and Zn are
enriched in CIs compared to certain samples, but the enrichment factor is generally substantially less than
that for Ni. CI data [Lodders, 2003] are recomputed to an oxide sum of 100% to be consistent with MER
APXS data.
Table 2. Samples Grouped by Increasing Nickel Contenta
Group/Sample Rover Approximate Range, ppm Comments
Low Ni
Wishstone Class A 30?70 Volcanic rocks indigenous to
Mars which are unlikely
to contain meteoritic
material.
Bounce rock B 80
Watchtower Class A 50?150
Adirondack Class A 150
Backstay A 200
Kansas/Larry?sBench A 200
Irvine A 290
Mars meteorites (exc. Chassigny) - 30?330
Chassigny (dunite) - 460
Intermediate Ni
Home Plate A 300?400 Could contain meteoritic
nickel. Elevated Ni
concentrations due to
formation from a Ni-rich
magma and/or enhanced
Ni concentrations through
aqueous transport are
also possible.
Basaltic soils A/B 300?650
Seminole A 550
Meridiani outcrop B 500?650
Clovis Class A 500?700
Peace Class A 600?750
PasoRobles ??class?? A 100?900
Pot of Gold region A 700?900
Algonquin/Comanche A 850?1000
Hematite-rich soils B 600?1300
Assemblee/Independence A 450?2100
High Ni
Barberton B 1700 Meteoritic samples.
CI Chondrites (volatile free) - 13100
Heatshield rock B 70000
aRovers ??A?? and ??B?? represent data from Spirit and Opportunity, respectively. Refer to text and Squyres et al. [2006] for
descriptions of the sample groups.
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Mittlefehldt et al. [2006], the set of targets from Larry?s
Bench, to Seminole, to Algonquin, to Comanche represents
a possible mafic-ultramafic magmatic sequence. Analyses
from samples progressively further downhill exhibit a
systematic increase in compatible elements Mg, Cr, and
Ni, while Al, P, Ca, and Ti decrease [Mittlefehldt et al.,
2006]. These geochemical trends are unlikely to occur as a
product of impact mixing or aqueous weathering. The
likelihood that this is an igneous sequence is important in
this discussion because the Comanche sample exhibits a
relatively high Ni concentration (1000 ppm). That is, if
Mars is inherently high in Ni, a meteoritic component might
not be necessary to account for the Ni in soils and
sedimentary rocks.
[24] To further explore this possibility, the data points
considered by Mittlefehldt et al. [2006] are extended uphill
to include the targets Kansas and the summit of Husband
Hill (Hillary). Figure 5 plots the behavior of the compatible
and incompatible elements versus vertical elevation. The
trends do in fact continue uphill beyond the Larry?s Bench
target. The leveling off of the P and Ca trend lines for the
uphill samples might be a result of the removal of apatite at
Figure 5. Molar element trends along the downhill traverse from the summit of Husband Hill. The
elevation is indicated in meters above the lander. Samples from highest elevation to lowest: Hillary
(summit), Kansas, Larry?s Bench, Seminole, Algonquin, and Comanche. In cases where multiple
analyses of a sample were acquired, the data point with the lower sulfur content (less dust) is plotted here.
Elements are scaled as indicated in the legend for clarity. Error bars representing the precision of the
APXS analyses are within the marker for each data point. (a) Compatible elements generally increase
downhill. (b) Incompatible elements generally decrease downhill.
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the surfaces of the Hillary and Kansas targets, a weathering
process which has been described by Gellert et al. [2006]
and Hurowitz et al. [2006]. Kansas also has a residual of
almost 8 wt% SO3 after brushing by the RAT. This is an
indication of surface dust contamination and/or an altered
coating, which will also affect the fidelity of the measure-
ments. Nonetheless, a definite trend in compatible and
incompatible elements extends across 6 data points covering

60 meters of vertical relief. Such a pattern should not exist
at random and provides strong evidence for a fractional
crystallization process. This trend indicates that there may
be examples of indigenous Martian rocks that are rich in Ni,
making it more difficult to constrain the extent of meteoritic
influx based solely on the Ni abundance.
4.4. Mobility in Solution
[25] Further complicating this story is the issue of aque-
ous weathering. Ni is soluble in chloride brines [Rose and
Bianchimosquera, 1993] and could therefore be redistrib-
uted and concentrated in certain samples. On the other hand,
relatively little research has been carried out on the aqueous
geochemistry of Ni, especially under conditions relevant to
Mars where acid-sulfate weathering may be dominant.
[26] The Independence, Assemblee, and Ben?s Clod tar-
gets analyzed by Spirit exhibit low Fe, high Al/Si, and
highly irregular concentrations of trace elements (including
more than 2000 ppm Ni in one measurement). These
characteristics are consistent with the initial development
of smectite-like clay minerals or their compositional equiv-
alents through aqueous processing of primary volcanic
rocks (Clark et al., submitted manuscript, 2006).
[27] Additional evidence for the mobility of Ni in aque-
ous solution is evident in analyses of the hematitic spherules
at Meridiani. Figure 6 shows a Ni-Fe plot with points
representing basaltic soils, hematite-rich soils, and Meri-
diani outcrop. The soils dominated by hematite spherules
and fragments show a clear Ni-Fe correlation with Ni
concentrations up to 700 ppm greater than average abraded
outcrop analyses. Ni mobilized in solution readily adsorbs
onto pre-existing hematite [Beukes et al., 2000] and could
be responsible for the elevated Ni in the spherules. Alter-
natively, during the groundwater recharge events responsi-
ble for the development of the hematitic concretions in the
model described by McLennan et al. [2005], Ni may have
been coprecipitated with the iron.
[28] Where did this Ni originate? As shown in Figure 6,
the outcrop rocks generally have higher levels of Ni
compared to the non-hematitic portion of the overlying
sand sheet, but there is no a priori reason to believe that
the younger sand unit has any compositional relationship to
the basaltic material in the sedimentary rocks. The situation
is poorly constrained: The outcrop matrix could have
initially had a higher concentration of Ni that diffused into
the spherules, or the Ni could have originated from greater
depths and precipitated in both the outcrop matrix and the
analyzed spherules. The latter option is supported by the
observation of lower Ni concentrations in outcrop measure-
ments (Figure 7) where the hematite concretions are smaller
and less defined (Figure 8), further suggesting a relationship
between Ni content and spherule production. This is con-
sistent with the scenario where the material that formed the
outcrop was initially compositionally similar over extensive
Figure 6. Molar Ni versus Fe showing positive correlation for hematitic spherules at Meridiani. Error
bars represent 2-sigma precision of the APXS analyses.
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lateral scales [Clark et al., 2005], and where Fe and Ni-rich
fluids interacted more extensively with sediments in certain
regions, perhaps those that were at greater depths.
5. Mixtures
[29] The majority of primary volcanic rocks analyzed on
Mars and Martian meteorites studied in terrestrial labs
(except the Chassigny dunite), have Ni concentrations less
than 330 ppm. Physical mixtures of these rocks cannot
achieve the higher levels of Ni observed in targets such as
average Mars soil, the outcrops at Meridiani, or the Clovis
Class rocks. The possible mafic/ultramafic sequence intro-
duced by Mittlefehldt et al. [2006] does indicate that there
may be materials in the Martian crust that have inherently
high Ni concentrations, but the associated high concentra-
tions of Mg restrict the extent to which physical mixtures of
a target such as Comanche can be accommodated in other
samples. Table 3 lists a number of mixing constraints for the
high Ni Comanche material and generalizes to include other
samples. Shown in the table are the maximum quantities of
a given component that could be mixed into soils and
sedimentary rocks, the element that limits the contribution
of that component, and the difference in nickel at the
maximum contribution of that component. For example,
the abundance of Mg limits the amount of Comanche-like
material in average basaltic soil to 
30%. With a compo-
sition of 30% Comanche, an additional 200 ppm Ni needs to
be added to obtain the level measured in average basaltic
soils.
[30] The numbers in Table 3 represent physical mixtures
of bulk rock compositions only and do not account for
chemical (other than isochemical) weathering that might
have occurred after the hypothetical mixing. Given the
likelihood of S and Cl condensates from volcanic outgas-
sing, the mobility of Cl and Br [Yen et al., 2005], and their
overall volatility, these elements are excluded from this
exercise of calculating mixing constraints. Also assumed
is a maximum of only two components in the mixture.
5.1. Components of Basaltic Soils
[31] The bright surface dust found at the Martian surface
is a globally homogenized unit, and the darker basaltic
sands at the two landing sites could also be a global unit
or simply a reflection of the similarity in the rocks from
which they are derived [Yen et al., 2005; Morris et al.,
2006b]. Basaltic compositions clearly dominate the Mar-
tian soils and crustal rocks, but the soils cannot be derived
from known rock compositions without the addition of
nickel.
[32] Table 3 lists the classes of material analyzed thus far
that could contribute to the chemical makeup of the soils at
Meridiani Planum and in Gusev crater. Of the various
groups of rocks that could comprise the soil unit, the Irvine
composition allows the greatest percentage contribution to
the soils (70%). This value is somewhat suspect, as Irvine
was a small target (
10 cm) and was not brushed or
abraded prior to analysis. A dust coating indicated by

2.4 weight percent SO3 could have artificially skewed
this measurement toward the elemental composition of the
Figure 7. Molar Ni versus S for basaltic soils and Meridiani outcrop. The brushed and undisturbed
surfaces of outcrop rocks exhibit lower sulfur levels consistent with soil contamination. Lower Ni
concentrations are found in the recent abraded measurements (sols 450?720). Error bars represent
2-sigma precision of the APXS analyses.
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soils. Nonetheless, approximately 300 ppm of additional Ni
is still required to produce the Ni levels in the soils. In fact,
not even Comanche with 1000 ppm Ni can, by itself, add
enough Ni to account for the concentration in the soils,
because the addition of Comanche to the soils is limited to
30% by the abundance of Mg.
[33] An excess of Ni in the soils is also apparent from a
plot of this element versus the percentage of olivine from
candidate source rocks for the soil (Figure 9). During
crystallization from a magma, Ni2+ partitions strongly into
olivine, as indicated by the roughly linear relationship for
the Martian meteorites. Adirondack and Wishstone class
rocks plot within the field of Martian meteorites, while soil
samples have much more Ni than indicated by the plotted
Ni-Ol trend line.
[34] It is therefore reasonable to hypothesize that a few
percent meteoritic material is necessary to account for the
Ni in the soils, with the caveat that the origin of the global
soil unit is not yet fully understood. There could be a high-
Ni source with a soil-like composition (different from all the
primary rocks analyzed, including the Martian meteorites
available here on Earth) or a process for weathering and
concentrating Ni in surface fines, such as preferential
alteration of olivine [Newsom et al., 2005]. Perhaps there
was a process whereby a Ni-rich target like Comanche
could be responsible for the Ni content of the soils but
chemical weathering removed the excess Mg, Fe, and Cr
(see section 6.1). While these ad hoc alteration processes
cannot be ruled out with the available data, they do seem
unlikely given the relatively unweathered nature of the
Martian soils, especially the dark sands where the Fe-
mineralogy is dominated by olivine.
[35] An interesting exercise is to consider the composi-
tion of other material in the solar system that could
potentially contribute to Martian soils. The average solar
abundance is useful for providing certain constraints; how-
ever, given Mars? proximity to the asteroid belt and the
likelihood that dust and sand grains generated there spiral
inward toward the sun [Rietmeijer, 1998] to be swept up by
the Martian gravity well, it makes sense to consider an
influx with the composition of average interplanetary dust
particles (IDP). Many IDPs are chondritic in composition,
but they are very heterogeneous. To first order they have
compositions that cluster around that of CI chondrites
[Rietmeijer, 1998]. Thus the discussion above regarding
chondritic mixing in Mars soils applies to IDPs as well.
[36] The enhanced abundances of siderophile elements in
lunar soils and breccias, and in howardites, polymict brec-
cias likely from 4 Vesta, are best matched as being derived
from CM chondrite debris [Chou et al., 1976; Wasson et al.,
1975]. This led to the conclusion that CM chondrites have
been the most common type of debris in the inner solar
system for the last 
4 Gyr [e.g., Chou et al., 1976]. Clasts
of CM chondrites are the most commonly observed mete-
oritic debris in vestan breccias [Zolensky et al., 1996] in
accord with the siderophile element evidence [Chou et al.,
1976]. In addition, a CM fragment was found in an Apollo
Figure 8. Opportunity MI images of abraded targets, each
approximately 4.5 cm by 3 cm. (a) ??Guadalupe?? (sol 35)
showing partially abraded spherules. (b) ??Ted?? (sol 691;
mosaic of 4 images) with no clear evidence of hematitic
spherules, one of several indicators of distinct changes in
outcrop rocks along the traverse.
Table 3. Mixing Constraintsa
Component
Maximum Contribution ? Limiting Element ? Ni Deficiency
Basaltic Soils Meridiani Outcrop Clovis Class Home Plate
Adirondack Class 60% ? Cr ? 400 ppm 30% ? Cr ? 600 ppm 30% ? Cr ? 550 ppm 80% ? Ca ? 200 ppm
Wishstone/Watchtower 15% ? P ? 500 ppm 20% ? P ? 600 ppm 20% ? P ? 600 ppm 20% ? P ? 300 ppm
Backstay 45% ? K ? 400 ppm 45% ? Al ? 550 ppm 35% ? K ? 550 ppm 30% ? K ? 250 ppm
Irvine 70% ? Mg ? 300 ppm 75% ? Na,Al ? 400 ppm 50% ? K ? 450 ppm 45% ? K ? 200 ppm
Bounce rock 55% ? Ca ? 450 ppm 40% ? Ca ? 600 ppm 40% ? Ca ? 550 ppm 50% ? Ca ? 300 ppm
Comanche 30% ? Mg ? 200 ppm 30% ? Mg ? 350 ppm 20% ? Cr ? 400 ppm 35% ? Ni ? 0
Basaltic soil ? 60% ? Na, Al ? 350 ppm 35% ? Zn ? 400 ppm 65% ? Ni ? 0
CI 4.7% ? Ni ? 0 5.9% ? Ni ? 0 5.6% ? Ni ? 0 3.1% ? Ni ? 0
Barberton 30% ? Ni ? 0 35% ? Ni ? 0 35% ? Ni ? 0 20% ? Ni ? 0
aThe maximum amount of the component in the left column, the limiting element, and the amount of additional Ni necessary to make up the difference is
calculated for 4 groups of samples.
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12 regolith sample [Zolensky et al., 1996]. However, com-
pared to the differences between Mars surface rocks and CI
chondrites, CM chondrites are insignificantly different from
the latter. CM chondrites show slight depletions in volatile
and moderately volatile elements, thus Na, S, Cl, K, Zn and
Br are depleted in CM chondrites compared to CI, but by
factors of <2. As is the case for CI chondrites, enhanced Ni
is the most significant result of small amounts of CM
chondrite debris in Mars soil.
5.2. Components of Meridiani Outcrop
[37] The Late Noachian to Early Hesperian layered out-
crop at Meridiani consists of a mixture of sulfate and silicate
sediments [Squyres and Knoll, 2005] that experienced
multiple stages of diagenesis resulting from episodes of
groundwater exposure [McLennan et al., 2005; Grotzinger
et al., 2005]. The Ni levels in the outcrop average approx-
imately 630 ppm, which is significantly higher than can be
reproduced by mixtures with known materials from Mars
(Table 3). The collection of known Martian meteorites also
has insufficient quantities of Ni to account for the compo-
sition of the Meridiani rocks.
[38] Options for accounting for the Ni content of the
outcrop include the following: (1) The silicate portion of the
rocks are derived from yet-unidentified Ni-rich materials,
(2) the groundwater which infiltrated the sediments carried
Ni ions in solution which deposited in the outcrop matrix,
possibly as an adsorbate on, or coprecipitate with, the fine
grained hematite and/or were incorporated directly into
sulfate minerals, or (3) influx of meteoritic Ni occurred
when the sand sheet and dunes lithified in the outcrop were
active. If the excess Ni in Meridiani outcrop relative to
average Martian meteorites resulted entirely from meteoritic
influx, as much as 6% of a CI composition would need to be
added [McLennan et al., 2005].
[39] Thus far, there is no clear evidence for an appropriate
high-Ni source region for the silicate sediments. As pointed
out above, the Ni content of the Martian meteorites, apart
from the Chassigny dunite are low, as are the basaltic rocks
analyzed by both MER rovers. On the other hand, by the
broader standards of basaltic volcanism throughout the solar
system, basaltic Ni contents in excess of 500 ppm are by no
means unusual [Basaltic Volcanism Study Project, 1981].
The Comanche deposits on the other side of the planet
exhibit sufficient levels of Ni, but are limited in the extent of
mixing because of high levels of Mg (Table 3). Addition of
Comanche-like material followed by redistribution of ele-
ments through aqueous processing is possible, though there
are few constraints to test this hypothesis. The data showing
the increase in Ni in the hematite spherules establish the
idea that this element moved with the groundwater
(section 4.4). The down-section trend in Endurance crater
exhibits a gradual decrease in Ni levels in abraded rocks,
suggesting a possible correlation with the water-related
Mg-sulfates [Clark et al., 2005]. Thus there may be mech-
anisms for Ni enhancements in these rocks that do not
necessarily involve the addition of chondritic material.
Figure 9. Ni versus percent olivine. Martian meteorite data from Meyer [2003]; ??small?? olivine
abundances are plotted as 1%. Olivine abundances for MER samples obtained from the Mo?ssbauer
spectrometer [Morris et al., 2006a; 2006b] adjusted for iron content and assuming Fo 50 composition
[McSween et al., 2006a]. Error bars represent 2-sigma precision of the APXS analyses.
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5.3. Other Classes of Material at Gusev Crater
[40] Clovis class rocks in the Columbia Hills are massive
to layered clastic and poorly sorted rocks with a bulk
basaltic composition [Squyres et al., 2006]. Mo?ssbauer
observations showing that up to 40% of the iron is in the
form of goethite (a-FeOOH) indicate that this class of rocks
has been aqueously altered [Morris et al., 2006a]. The
elevated Ni concentrations in these rocks, averaging ap-
proximately 600 ppm, is not a product of simple mixing
with any of the other known groups of Martian samples
(Table 3) including the Martian meteorites. An external
contribution of Ni is likely. However, given the role of
water in the development of goethite in these rocks, the
possibility of aqueous redistribution of the elemental con-
stituents, including concentration of Ni in these rocks,
cannot be ruled out.
[41] Home Plate is a light-toned, approximately circular
feature 
80 meters in diameter which is visible from orbit.
Analyses by Spirit instruments indicate that it consists of
partially weathered layered rocks of basaltic composition. In
contrast to the deposits at Clovis, the Ni concentration at
Home Plate is substantially lower, approximately 330 ppm.
Ni concentrations at these levels are consistent with primary
volcanic material analyzed on Mars (Adirondack-class
basalts) and the higher-Ni Martian meteorites, without the
need for a chondritic addition.
[42] The Peace Class materials are magnetite-rich sand-
stones of dominantly olivine and pyroxene grains cemented
by sulfates [Squyres et al., 2006]. When the sulfate com-
ponent is removed from the Peace composition, the chem-
istry is similar to the high-Ni Comanche rocks of the mafic-
ultramafic sequence described in section 4.3. Given this
apparent genetic relationship, it is unlikely that the elevated
Ni concentrations in Peace class rocks are result from
addition of a meteoritic component.
[43] The Paso Robles Class deposits dominated by hy-
drated ferric sulfates have highly variable minor and trace
element signatures. Ni concentrations in these samples
range from 
100 to 
900 ppm and likely result from
aqueous processes at low water to rock ratios. The details
of the Paso Robles Class of materials are discussed by Ming
et al. [2006] and Morris et al. [2006a].
6. Elemental Relationships
[44] Plotting elemental trends through related samples can
help illustrate the overall chemical variability in the ana-
lyzed samples and provide insight into possible mixing
relationships with chondritic material. Ni-Cr, Ni-Mg, and
Ni-Ti relationships, for example, are useful in establishing
families of volcanic rocks, and identifying classes of mate-
rials that likely had different evolutionary histories. In
addition, plots of S-Cl can help establish limits on the
amount of meteoritic sulfur.
6.1. Nickel Versus Chromium
[45] Ni and Cr are compatible elements in most mafic-
ultramafic liquids and tend to behave similarly during
Figure 10. Molar plot of nickel versus chromium for various classes of material. Two families of
volcanic rocks, each with a characteristic Ni:Cr ratio, are evident. Meridiani outcrop and Clovis class
rocks plot above the blue and magenta trend lines, suggesting either fundamentally different source
materials or the addition of meteoritic nickel. Error bars represent 2-sigma precision of the APXS
analyses.
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crystallization. Figure 10 shows that the Ni:Cr of Gusev
plains basalts (Adirondack class) fit well within the field of
Martian meteorites, consistent with the relationship de-
scribed by McSween et al. [2006a]. The data points from
the mafic-ultramafic sequence described in section 4.3
define a different line that may represent an older family
of volcanics with several samples highly enriched in Ni.
The slope of the Ni-Cr trend in these ancient rocks is much
shallower than the chondritic ratio, indicating that the
elevated Ni and Cr do not likely result from meteoritic
contamination. Thus there are two families of Martian rocks
that can contribute material with fixed Ni-Cr ratios to
Martian soils and sedimentary rocks.
[46] The groupings for Clovis class [Squyres et al., 2006]
and the abraded Meridiani outcrop rocks, however, are
offset from these two sets of volcanic rocks. Several options
for explaining these discrepancies are possible: (1) The
components of these fine-grained sedimentary rock classes
are unrelated to the two identified families of volcanic rocks
and have inherently different Ni-Cr ratios, and/or (2) aque-
ous processes redistributed Ni and Cr to the observed levels
in Clovis and Meridiani outcrop rocks, and/or (3) meteoritic
infall enhanced the Ni concentration in the sedimentary
rocks. The first possibility cannot reasonably be assessed, as
it is difficult to include or exclude components of unknown
materials. The second option is possible, especially given
that both of these rock classes have experienced aqueous
processing. However, the scatter in the majority of the data
(yellow and green points in Figure 10) appears to parallel
the Ni-Cr trend line for a mixture with chondritic material.
If the offset of Ni:Cr in Clovis and Meridiani outcrop rocks
above the magenta (Martian meteorites) and blue (mafic/
ultramafic sequence) lines resulted from a meteoritic addi-
tion of Ni, the addition of 5.0 to 3.3% chondritic material,
respectively, would be indicated.
[47] Section 5.1 addresses the likely contribution of
meteoritic material to Martian soils, which is further high-
lighted in the Ni:Cr plot shown in Figure 10. The Gusev soil
data points exhibit Ni enhancements relative to the family
of volcanics indicated by the Martian meteorites and strad-
dles the trend line established by the mafic/ultramafic
sequence of rocks. From Microscopic Imager images, it is
evident that the soil analyses with lower Ni concentrations
tend to have a greater abundance of rock fragments,
consistent with mixing with Adirondack class basalts. Many
soil data points exhibit statistically significant excesses of
Ni above even the high-Ni mafic/ultramafic sequence of
rocks. On the basis of Ni-Cr ratios, the meteoritic compo-
nent of the soils is up to 2.3% if the ??base?? Ni-Cr value is
defined by the mafic/ultramafic sequence of rocks or an
average of approximately 3.3% if the ??base?? Ni-Cr value
stems from the Martian meteorites and Adirondack class
basalts.
[48] Counterparts to the Ni-Cr plot are Ni-Mg (Figure 11)
and Ni-Ti (Figure 12). If igneous processes dominate,
Ni-Mg should mimic Ni-Cr, and Ni-Ti should show a trend
opposite to that of Ni-Cr. This is, in fact, generally the case
for the fits defined by the Martian meteorites and the mafic/
Figure 11. Molar plot of nickel versus magnesium for various classes of material. Trends of the mafic/
ultramafic sequence and the Martian meteorites are similar to those shown in the Ni:Cr plot (Figure 10),
suggesting that igneous processes dominate. Error bars represent 2-sigma precision of the APXS
analyses.
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ultramafic sequence of rocks. In the Ni-Mg plot, the points
for Clovis class and Meridiani outcrop rocks are shifted to
the right relative to their positions on the Ni-Cr plot
suggesting that Mg has been redistributed by weathering
processes. This inference is consistent with the likelihood of
Mg-sulfates in Meridiani rocks [Clark et al., 2005] and
aqueous alteration of Clovis rocks [Ming et al., 2006; Morris
et al., 2006a]. Figure 11 also shows that the Ni concentration
in Gusev soils is independent of the Mg abundance and
roughly parallels the Ni-Mg ratio of chondritic material.
6.2. Sulfur
[49] Sulfur is another element that is abundant in mete-
oritic material. Unfortunately, it is also a major element in
Martian samples with clear evidence that it is geochemically
mobile. The decrease in Mg-sulfate with depth in Endurance
crater [Clark et al., 2005], the concentration of Mg- and
Ca-sulfate cements in Peace class rocks [Squyres et al.,
2006; Ming et al., 2006], and the significant enhancements
in sulfur in certain subsurface soil samples [Haskin et al.,
2005] all indicate secondary redistribution of S. This trans-
port complicates attempts to estimate the magnitude of
meteoritic input on the basis of sulfur.
[50] There is, however, one perspective on S that provides
a possible constraint. Figure 13 presents a molar plot of S
versus Cl for basaltic soils at Gusev and Meridiani. The
linear relationship is a global attribute that may represent the
addition of condensates of volcanic exhalations [Clark and
van Hart, 1981]. The fit through these points should go
through the origin if the soil simply contained variable
amounts of the volcanic emissions and if neither chemical
reprocessing of the deposits nor addition of S or Cl has
occurred. The least squares fit in Figure 13 intercepts the
y-axis slightly above the origin, indicating a possible
addition of up to 4.5% meteoritic sulfur to the Martian
surface soil unit.
[51] Another approach to looking at S relationships with
meteoritic material is based on the Ni versus S plot shown
in Figure 7. Higher concentrations of sulfur in this set of
Meridiani data are generally found in the abraded and
??clean?? interiors of analyzed outcrop. Undisturbed and
lightly brushed outcrop rocks have lower sulfur contents,
consistent with contamination from dust and basaltic sand,
which have even lower sulfur levels. The interesting aspect
of Figure 7 is in the locations of data points (plotted as stars)
for outcrop samples that were analyzed outside of Eagle and
Endurance craters. These data points still display a similar
behavior in the S content of undisturbed/brushed versus
abraded targets, but the nickel content of these measure-
ments is systematically lower.
[52] One potential explanation for the higher Ni contents
of rocks within craters is that they are more contaminated by
projectile material. Depth-to-diameter ratios suggest that
both Eagle and Endurance craters are primary impacts
[Grant et al., 2006]. Impact simulation models indicate that
a major portion of the projectile coats the floor and walls of
the crater after the impact for near-vertical impacts, but
projectile material is increasingly dispersed outside the
crater as impact angle decreases [Pierazzo and Melosh,
2000]. The most probable impact angle, however, is 45

and thus systematic difference in Ni inside versus outside
craters at Meridiani is not likely. Terrestrial experience is
Figure 12. Molar plot of nickel versus titanium for various classes of material. Trends in the blue and
magenta lines are opposite of those in Figures 10 and 11. The chondritic Ni:Ti ratio lies essentially along
the y-axis of this plot. Error bars represent 2-sigma precision of the APXS analyses.
E12S11 YEN ET AL.: NICKEL ON MARS
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severely limited because most craters are old and degraded;
compositional evidence from the crater walls has been
eliminated. At Meteor Crater, analyses of target rock from
a systematic stratigraphic section collected from within the
crater [Mittlefehldt et al., 2005] did not find evidence for
projectile contamination. The highest Ni content is equiva-
lent to 0.05% projectile material, but this plausibly repre-
sents the natural fluctuation in Ni in the target rock. An
alternate explanation for the lower nickel content of Mer-
idiani outcrop analyses outside craters is that it is unrelated
to meteoritic contributions, but is associated with changes in
the aqueous conditions under which the concretions formed
(section 4.4).
7. Magnetic Properties of the Dust
[53] An additional perspective on possible meteoritic
material in Martian samples is provided by the magnetic
properties investigation. Each rover has of a suite of
Sm2Co17 magnets to collect airborne dust (sweep, capture,
and filter magnets) and magnetic particles in tailings gen-
erated by the rock abrader (RAT magnets) [Madsen et al.,
2003]. The sweep magnet is a small ring magnet designed
with a field strength sufficiently large that only particles
with a specific susceptibility less than 30  10-8 m3/kg can
enter the 4 mm diameter central region [Madsen et al.,
2003]. Pancam imaging of this magnet (Figure 14) has
shown that the central portion has remained essentially free
of dust, indicating that nearly all Martian dust has an
appreciable magnetic susceptibility [Bertelsen et al., 2004].
[54] The capture magnet is a 45 mm diameter magnet
designed to capture airborne dust for analyses by the in-situ
instruments. Mo?ssbauer analyses of the collected dust
indicate the presence of the basaltic components seen by
this instrument in typical soils: Olivine, pyroxene, nano-
phase ferric oxide(s), and magnetite, but at different relative
concentrations [Goetz et al., 2005]. APXS analyses of the
collected dust show that a major portion of the iron-
containing material on the capture magnet is associated
with Ti and Cr (Gellert et al., manuscript in preparation,
2006), consistent with titanomagnetite and possibly chro-
Figure 13. Molar S versus Cl and least squares fit for basaltic soils. Error bars represent 2-sigma
precision of the APXS analyses.
Figure 14. False color image of Spirit sweep magnet
imaged by Pancam (sol 837). Central portion (above the
strong ring magnet) remains mostly clear of atmospheric
dust, indicating a significant level of magnetic susceptibility
for nearly all airborne dust grains.
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mite. The association with Ti suggests that physical weath-
ering of basaltic materials, rather then chemical processes
that would tend to produce a more pure magnetite precip-
itate, may play a significant role in generating the magnetic
fines [Coey et al., 1990; Morris et al., 1990, 2001a; Madsen
et al., 1995].
[55] How is it possible, however, that all of the dust has
some level of magnetic susceptibility and yet they are
physical weathering products of basaltic rocks? If an arbi-
trary Martian rock is crushed by impact into micron-sized
dust grains [e.g., Pollack et al., 1979; Lemmon et al., 2004],
how does each individual grain retain characteristics of a
magnetic phase? The olivine in typical basaltic soils is Fo40
to Fo60 in composition [McSween et al., 2006a], but
chemical zoning is likely. A portion of the olivine will be
Mg-rich with a low magnetic susceptibility, and should
penetrate to the center of the sweep magnet (magnetic
susceptibility of pure forsterite is -0.39  10-8 m3/kg)
[Hunt et al., 1995]. Furthermore, the typical grain sizes in
the Martian meteorites is a few hundred microns, so a
random sampling of micron sized regions should yield low-
susceptibility minerals such as plagioclase and quartz. The
reason the center of the sweep magnet stays clean is likely
because the dust grains are composite particles [Hargraves
et al., 1977; Hviid et al., 1997], each with a (titano)magnetite
component [Goetz et al., 2005].
[56] The generation of such composite particles may
involve secondary alteration processes including dissolu-
tion, oxidation, and precipitation of ferrimagnetic phases
[Arlauckas et al., 2006] and/or the development of coat-
ings of high-susceptibility nanophase ferric oxide (npOx)
particles [e.g., Morris et al., 1989]. Another possible
mechanism for producing composite grains with magne-
tite is related to meteoritic contributions to the surface.
Micrometeorites analyzed in terrestrial laboratories exhibit
magnetite rinds formed as a result of heating during
atmospheric entry [Genge and Grady, 1998]. Similar
examples of surficial magnetite are present on interplan-
etary dust particles [Bradley et al., 1996]. Entry vapori-
zation and recondensation of metallic vapors produce
metal oxides in Earth?s atmosphere [Rietmeijer, 2000],
and similar processes are expected for Mars [Pesnell and
Grebowsky, 2000]. Experimental evidence suggests that
the impact of larger objects under a CO2 atmosphere may
also produce magnetite during crystallization of the im-
pact melts [Morris et al., 2001b]. Taken collectively,
these results suggest that at least a portion of the Martian
dust could be a product of meteoritic material processed
by entry heating, or possibly a product of impact vapor-
ization/melting and recondensation resulting from larger
impacts [e.g., Wdowiak et al., 2001].
8. Cratering Record
[57] In addition to the constraints based on Ni abundan-
ces, an estimate of the lower limit on the quantity of
meteoritic material at the Martian surface can be calculated
using the impact cratering record. Such a calculation also
provides a consistency check of the concentrations deter-
mined from MER APXS data. Studies of the landing sites
indicate that the Gusev plains are Late Hesperian in age
while the layered outcrop at Meridiani are Late Noachian
with an overlying Late Amazonian sand sheet (see discus-
sion and references of Golombek et al. [2006a]). Working
backward from these ages, the crater population in (2)1/2
intervals is calculated using equations of Hartmann [2005]
and summarized in Table 4. We can then calculate the
amount of meteoritic material that corresponds to the
observed crater population.
[58] The projectile size for a given crater diameter is
estimated using scaling relationships from Melosh [1989]:
The apparent diameter (Dat) of the transient crater can be
represented in terms of the projectile density (rp), the target
density (rt), gravity (g), the projectile diameter (L), and the
impact kinetic energy (W) as follows:
Dat ? 1:8 r0:11p r
1=3
t g
0:22 L0:13 W0:22
where all values are in MKS units. For this first-order
approximation, it is reasonable to assume that r 
 rp 
 rt.
Using a transient crater diameter equal to 84% of the
diameter of the final simple crater [Melosh, 1989], repre-
senting W in terms of r, L, and V (impact velocity), and
Table 4. Meteoritic Contribution From the Impact Crater Record
Bin 1 Bin 2 Bin 3 Bin 4 Bin 5 Bin 6 Bin 7 Bin 8 Sum, mm
Crater diameter, km 1.0 1.4 2.0 2.8 4.0 5.7 8.0 11.3
Projectile diameter, m 31 48 74 115 179 277 430 667
Number per square km
Late/Mid Amazonian 1.1E  04 5.6E  05 2.8E  05 1.4E  05 - - - -
Mid/Early Amazonian 4.2E  04 2.1E  04 1.1E  04 5.3E  05 - - - -
Amazonian/Hesperian 1.1E  03 5.6E  04 2.8E  04 1.4E  04 - - - -
Late/Early Hesperian 2.3E  03 1.1E  03 5.6E  04 2.8E  04 1.4E  04 7.0E  05 3.5E  05 1.8E  05
Hesperian/Noachian 3.4E  03 1.7E  03 8.5E  04 4.2E  04 2.1E  04 1.1E  04 5.3E  05 2.6E  05
Late/Mid Noachian - - - - 1.1E  03 5.7E  04 2.8E  04 1.4E  04
Mid/Early Noachian - - - - 2.3E  03 1.1E  03 5.7E  04 2.8E  04
Thickness, mm
Late/Mid Amazonian 1.7E  03 3.1E  03 5.8E  03 1.1E  02 - - - - 0.02
Mid/Early Amazonian 6.3E  03 1.2E  02 2.2E  02 4.1E  02 - - - - 0.08
Amazonian/Hesperian 1.7E  02 3.1E  02 5.8E  02 1.1E  01 - - - - 0.2
Late/Early Hesperian 3.3E  02 6.2E  02 1.2E  01 2.2E  01 4.0E  01 7.5E  01 1.4E + 00 2.6E + 00 5.6
Hesperian/Noachian 5.0E  02 9.3E  02 1.7E  01 3.2E  01 6.1E  01 1.1E + 00 2.1E + 00 3.9E + 00 8.4
Late/Mid Noachian - - - - 3.2E + 00 6.0E + 00 1.1E + 01 2.1E + 01 42
Mid/Early Noachian - - - - 6.5E + 00 1.2E + 01 2.3E + 01 4.2E + 01 83
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rearranging produces the following relationship between
the observed crater diameter (D) and the projectile
diameter:
L ? 0:58 D1:27 g0:28 V0:56
Impact velocities will vary depending upon the orbital
parameters of the object and will range from 
5.6 km/s for
material in nearby orbits to 
31 km/s for long period
comets [Carr, 1984]. The projectile diameters listed in
Table 4 assume an intermediate impact velocity of 10 km/s,
representative of asteroids and short period comets [Carr,
1984].
[59] Using the projectile diameters and the numbers of
impacts for each crater size range, the thickness of meteor-
itic material, if evenly spread over the surface of Mars, is
calculated and summarized in Table 4. These results indi-
cate that the impacts associated with the Late Hesperian
surface age at Gusev Crater contributed meteoritic material
equivalent to a global layer approximately 5.6 mm thick.
The corresponding calculation at Meridiani Planum sug-
gests 42 mm of accumulated meteoritic material after
emplacement of the layered sediments in the Late Noachian.
This value could be an overestimate as Hesperian aged
materials are apparently absent from the geologic record at
Meridiani [Golombek et al., 2006a]. On the other hand, in
the older eras, larger diameter craters (not included in the
calculation) become more important and could add signif-
icantly to the accumulation of meteoritic material. None-
theless, this calculation provides a rough estimate of
meteoritic accumulations since the Late Noachian.
[60] Hydrodynamic modeling shows that tracer particles
representing the projectile end up primarily along the walls
of the crater for near-vertical (60
 to 90
) impacts, while
most of the projectile is ejected from the crater for impact
angles less than 30
 [Pierazzo and Melosh, 2000]. Thus,
even though the impact gardening depth is on the scale of
the crater (
kilometers), the majority of the projectile ends
up at or near the immediate surface after distribution by the
impact plume. If the 
tens of millimeters of meteoritic
material calculated above were spread through a depth of a
few meters through aeolian transport or further impact
gardening, the average quantity of meteoritic material in
this layer would be approximately 1%.
9. Synthesis
[61] Assuming a chondritic composition for the meteoritic
flux to the Martian surface, the nickel content of basaltic
soils, the Meridiani outcrop rocks, and the Clovis class
material establishes an absolute upper limit of 6.5% mete-
oritic debris in these units. This value assumes that all of
the Ni in these fine-grained sediments is exogenic, which
is certainly not correct. Tighter constraints on the upper
limit are derived from relationships between Ni and Cr
(section 6.1) and between S and Cl (section 6.2). These
trends indicate an upper limit of 4.5% meteoritic material in
basaltic soils on the basis of sulfur and upper limits in the
3.3% to 5.0% range based on nickel for Meridiani outcrop
and Clovis class material, depending upon assumptions on
the source rocks. These values also represent fairly conser-
vative upper limits. Given the mobility of Ni in solution,
which may have enhanced the Ni concentrations in Mer-
idiani outcrop rocks and possibly Clovis class rocks as well,
and given indications that ancient volcanics may have been
more Ni-rich, we believe that an upper limit of 3% fine-
grained meteoritic debris in basaltic soils, Meridiani outcrop
rocks, and Clovis class materials is reasonable.
[62] On the other end of the scale, it is clear that the Ni
levels in basaltic soils, Meridiani outcrop rocks, and Clovis
class materials cannot be achieved by simple addition of
other Martian materials of known compositions. In such
mixtures, elemental constraints are violated. Aqueous pro-
cesses may have acted to remove and concentrate various
elements to achieve the Ni-levels in these units from the
addition of Ni-rich Martian rocks, but the addition of a
small meteoritic component provides a simpler explanation.
[63] As established in section 8, the presence of impact
craters can set an approximate lower limit of 
1% on the
incorporation of meteoritic material. The meteoritic contri-
bution from the ongoing influx of interplanetary dust
particles is comparable in magnitude to material delivered
by objects large enough to form craters. Using an interme-
diate value of 107 kg/yr in the estimate of IDP flux
calculated by Flynn and McKay [1990], a 
30 mm thick
global layer is produced every 109 years, which also
corresponds to a 
1% concentration of meteoritic material.
[64] In each of these estimates, it is assumed that the
vertical mixing depth is on the order of several meters. This
is consistent with the 
1 meter thickness of the Meridiani
sand sheet [Soderblom et al., 2004] and the 
10 meters of
impact regolith on the Gusev plains [Golombek et al.,
2006b]. Attempts to establish soil production rates or to
provide higher fidelity estimates in these calculations are
complicated by the apparent loss of the Hesperian aged
surfaces at Meridiani and the removal of soil from the
Gusev site under the current wind regime [Greeley et al.,
2006]. Nonetheless, it is clear that percent-level meteoritic
contributions from IDPs and larger impactors are reasonable
lower limits.
[65] Thus a number of lines of evidence suggest that a
range of 1% to 3% chondritic influx, corresponding to
roughly 100 to 300 ppm Ni, is consistent with the elemental
chemistry of Martian surface materials. Although meteoritic
accumulation processes differ between the moon and Mars,
with aeolian distribution likely dominant for fine grained
meteoritic debris on Mars, this range for the estimate of the
meteoritic contribution to the Martian surface is consistent
with the measured value of 1.5% to 2% CI material on the
lunar surface [Taylor, 1982].
[66] An additional exercise to consider is the accumulation
time required to produce the Ni levels observed in the APXS
data. Using the full range of IDP fluxes calculated by Flynn
and McKay [1990], it takes between 50 Ma and 1 Ga to
produce each 100 ppm of meteoritic Ni. An intermediate
value of 
100 Ma per 100 ppm of Ni is roughly consistent
with the cratering age of the Meridiani sand sheet (
400 Ma)
and the several hundred ppm of Ni in this unit that is
likely to be meteoritic. Interestingly, this Late Amazonian
deposit has Ni levels comparable to the Late Noachian
(
3.7 Ga) rocks at Meridiani and the Clovis class rocks
exposed at the Late Hesperian surface (
3.5 Ga) within
Gusev Crater (Table 2). Given that the absolute ages of
these rocks should be independent of the time it took to
E12S11 YEN ET AL.: NICKEL ON MARS
22 of 25
E12S11
accumulate the sediments that produced them, it is reason-
able that the Ni concentrations measured in these rocks do
not correspond to their ages. The amount of meteoritic
material that should have accumulated above these rocks,
however, should be related to their ages. Unfortunately, the
apparent loss of the Hesperian surface at Meridiani
[Golombek et al., 2006a] and the deflationary environment
at Gusev Crater [Greeley et al., 2006] may have removed
meteoritic accumulations from areas accessed by the rovers.
10. Meteoritic Carbon
[67] Assuming an influx of meteoritic material with an
average composition equivalent to CI chondrites, the addi-
tion to the Martian environment of other important ele-
ments, such as carbon, can be estimated. The solar
abundance of carbon is approximately 3.3 times greater
than the quantity of nickel [Lodders, 2003]. The upper
range of Ni detected in typical MER samples is 
700 ppm,
and if all of this were meteoritic, 
2300 ppm C would
be associated with this influx. However, it is unrealistic
to expect that all the Ni measured by the rovers is
exogenic. As discussed above, a reasonable range for
meteoritic Ni is 100 to 300 ppm, suggesting an associated
330 to 990 ppm C delivered to Mars through meteoritic
influx.
[68] Using measurements of interplanetary dust particle
(IDP) flux at Earth applied to Mars, Flynn [1996] estimates
a current accretion rate of 2.4  105 kg/yr of unaltered
carbon at the Martian surface. Applied over the 
3.5 and
>3.7 Ga cratering ages of the Gusev plains and the Mer-
idiani outcrop [Golombek et al., 2006a], respectively, a
global layer of organic carbon 
2 mm thick is predicted.
This should be a conservative lower limit given that ancient
flux rates were substantially higher than those at present
[Flynn, 1996]. Mixing through an active aeolian regime
several meters in thickness would result in dilution to the

400 ppm level. This value is entirely consistent with the
amount of meteoritic carbon implied by the measured Ni
concentrations. It is expected to be on the lower end of the
330 to 990 ppm range because Ni that enters the Martian
atmosphere, even if vaporized, eventually settles to the
surface, whereas organic molecules can volatilize into
CO2 and other gases during entry heating and remain in
the atmosphere.
[69] The absence of detectable organic compounds
[Biemann et al., 1977] at levels three or four orders of
magnitude lower than what is predicted to be there from
meteoritic input alone is a clear indicator of surface or
atmospheric processes that have destroyed organic com-
pounds [e.g., Yen et al., 2000]. Future missions [Mahaffy
and the SAM Science Team, 2005; Bada et al., 2005] may
achieve lower organic detection limits than the 1976 Viking
Lander instrumentation, access organics in rock interiors
which are protected from oxidizing species, or be able to
attain temperatures capable of pyrolyzing and detecting
photodegraded organics [Benner et al., 2000].
11. Conclusions
[70] 1. Measurements of nickel in Martian samples pro-
vides an excellent tracer for meteoritic contributions to the
surface materials. APXS data from the Mars Exploration
Rovers are consistent with a 1% to 3% chondritic input to
basaltic soils, Meridiani outcrop rocks, and Clovis class
materials.
[71] 2. Nickel is a geochemically mobile element at the
Martian surface, concentrating in hematite-rich spherules at
Meridiani through aqueous processes. Nickel mobility in
solution may also be partially responsible for the enhanced
concentrations in Clovis class rocks of the Columbia Hills.
[72] 3. Nearly all Martian dust is attracted to magnets,
possibly resulting from the presence of high-susceptibility
np-Ox and small quantities of titanomagnetite in each grain.
A portion of the titanomagnetite may have formed through
meteoritic processes, involving the recondensation of mate-
rial vaporized or melted during impact or atmospheric entry.
[73] 4. On the basis of the inferred quantity of meteoritic
Ni and assuming a chondritic composition for the influx,
a quantity of carbon equivalent to an average of 300 to
1000 ppm should have been delivered to the upper fewmeters
of the Martian regolith. Some of the carbon-containing
compounds could have pyrolyzed to carbon dioxide during
entry. The remainder may have oxidized due to exposure
to the Martian surface environment, or might still be
present but not yet detected in the surface or subsurface.
[74] Acknowledgments. We thank the members of the MER project
who enable daily science observations at the Spirit and Opportunity landing
sites, K. Herkenhoff and M. Rosiek for the processed Microscopic Imager
images, T. Myrick for discussions on the RAT, and H. Newsom and
Y. Langevin for thoughtful and constructive reviews. R.V.M., D.W.M.,
and D.W.M. acknowledge support of the NASA Mars Exploration Rover
Project and the NASA Johnson Space Center. The APXS was funded by the
Max Planck Society and by the German Space Agency (DLR). R.G.
acknowledges support from the University of Guelph and the Canadian
Space Agency. A portion of the work described in this paper was conducted
at the Jet Propulsion Laboratory, California Institute of Technology, under a
contract with the National Aeronautics and Space Administration.
References
Adolfsson, L. G., B. A. S. Gustafson, and C. D. Murray (1996), The
Martian atmosphere as a meteoroid detector, Icarus, 119, 144?152.
Arlauckas, S. A., S. M. McLennan, and D. H. Lindsley (2006), The effect
of low-temperature acidic weathering on the magnetic signature of pri-
mary Fe-Ti oxides on Mars, Lunar Planet. Sci., XXXVII, 1609.
Bada, J. L., et al. (2005), New strategies to detect life on Mars, Astron.
Geophys., 46, 6.26?6.27, doi:10.1111/j.1468-4004.2005.46626.x.
Bartlett, P. W., B. Basso, A. Kusack, J. Wilson, and K. Zacny (2005), New
rock physical properties assessments from the Mars Exploration Rover
Rock Abrasion Tool (RAT), Eos Trans. AGU, 86(52), Fall Meet. Suppl.,
P21A-0135.
Basaltic Volcanism Study Project (1981), Basaltic Volcanism on the
Terrestrial Planets, 1286 pp., Elsevier, New York.
Bell, J. F., III, et al. (2003), Mars Exploration Rover Athena Panoramic
Camera (Pancam) investigation, J. Geophys. Res., 108(E12), 8063,
doi:10.1029/2003JE002070.
Benner, S. A., K. G. Devine, L. N. Matveeva, and D. H. Powell (2000), The
missing organic molecules on Mars, Proc. Natl. Acad. Sci. U. S. A., 97,
2425?2430.
Bertelsen, P., et al. (2004), Magnetic Properties Experiments on the Mars
exploration Rover Spirit at Gusev crater, Science, 305, 827?829.
Beukes, J. P., E. W. Giesekke, and W. Elliott (2000), Nickel retention by
goethite and hematite, Miner. Eng., 13, 1573?1579.
Biemann, K., et al. (1977), The search for organic substances and inor-
ganic volatile compounds in the surface of Mars, J. Geophys. Res., 82,
4641?4658.
Bland, P. A. (2001), Quantification of meteorite infall rates from accumula-
tions in deserts, and meteorite accumulations on Mars, in Accretion of
Extraterrestrial Matter Throughout Earth?s History, edited by B. Peucker-
Ehrenbrink and B. Schmitz, pp. 267?303, Springer, New York.
Boslough, M. B. (1988), Evidence for meteoritic enrichment of the Martian
regolith, Lunar Planet. Sci., XIX, 120?121.
E12S11 YEN ET AL.: NICKEL ON MARS
23 of 25
E12S11
Boslough, M. B. (1991), Shock modification and chemistry of planetary
geologic processes, Annu. Rev. Earth Planet. Sci., 19, 101?130.
Bradley, J. P., L. P. Keller, D. E. Brownlee, and K. L. Thomas (1996),
Reflectance spectroscopy of interplanetary dust particles, Meteorit.
Planet. Sci., 31, 394?402.
Carr, M. H. (1984), The Surface of Mars, 232 pp., Yale Univ. Press, New
Haven, Conn.
Chou, C.-L., W. V. Boynton, R. W. Bild, J. Kimberlin, and J. T. Wasson
(1976), Trace element evidence regarding a chondritic component in
howardite meteorites, Proc. Lunar Sci. Conf. 7th, 3501?3518.
Christensen, P. R., et al. (2003), Miniature Thermal Emission Spectrometer
for the Mars Exploration Rovers, J. Geophys. Res., 108(E12), 8064,
doi:10.1029/2003JE002117.
Christou, A. A., and K. Beurle (1999), Meteoroid streams at Mars: Possi-
bilities and implications, Planet. Space Sci., 47, 1475?1485.
Clark, B. C., and A. K. Baird (1979), Is the Martian lithosphere sulfur rich?,
J. Geophys. Res., 84, 8395?8403.
Clark, B. C., and D. C. van Hart (1981), The salts of Mars, Icarus, 45,
370?378.
Clark, B. C., et al. (2005), Chemistry and mineralogy of outcrops at Mer-
idiani Planum, Earth Planet. Sci. Lett., 240, 73?94.
Coey, J. M. D., S. Morup, M. B. Madsen, and J. M. Knudsen (1990),
Titanomaghemite in magnetic soils on Earth and Mars, J. Geophys.
Res., 95, 14,423?14,425.
Davis, P. (1993), Meteoroid impacts as seismic sources on Mars, Icarus,
105, 469?478.
Flynn, G. J. (1996), The delivery of organic matter from asteroids and
comets to the early surface of Mars, Earth Moon Planets, 72, 469?474.
Flynn, G. J., and D. S. McKay (1990), An assessment of the meteoritic
contribution to the Martian soil, J. Geophys. Res., 95(B9), 14,497?
14,509.
Gellert, R., et al. (2004), Chemistry of rocks and soils in Gusev crater from
the alpha particle X-ray spectrometer, Science, 305, 829?832.
Gellert, R., et al. (2006), Alpha Particle X-Ray Spectrometer (APXS):
Results from Gusev crater and calibration report, J. Geophys. Res., 111,
E02S05, doi:10.1029/2005JE002555.
Genge, M. J., and M. M. Grady (1998), Melted micrometeorites from
Antarctic ice with evidence for the separation of immiscible Fe-Ni-S
liquids during entry heating, Meteorit. Planet. Sci., 33, 425?434.
Goetz, W., et al. (2005), Indication of drier periods on Mars from the
chemistry and mineralogy of atmospheric dust, Nature, 436, 62?65.
Golombek, M. P., et al. (2006a), Erosion rates at the Mars Exploration
Rover landing sites and long-term climate change on Mars, J. Geophys.
Res., 111, E12S10, doi:10.1029/2006JE002754.
Golombek, M. P., et al. (2006b), Geology of the Gusev cratered plains from
the Spirit rover transverse, J. Geophys. Res., 111, E02S07, doi:10.1029/
2005JE002503.
Gorevan, S. P., et al. (2003), Rock Abrasion Tool: Mars Exploration Rover
mission, J. Geophys. Res., 108(E12), 8068, doi:10.1029/2003JE002061.
Grant, J. A., et al. (2006), Crater gradation in Gusev crater and Meridiani
Planum, Mars, J. Geophys. Res., 111, E02S08, doi:10.1029/
2005JE002465.
Greeley, R., et al. (2006), Gusev crater: Wind-related features and processes
observed by the Mars Exploration Rover Spirit, J. Geophys. Res., 111,
E02S09, doi:10.1029/2005JE002491.
Grotzinger, J. P., et al. (2005), Stratigraphy and sedimentology of a dry to
wet eolian depositional system, Burns formation, Meridiani Planum,
Mars, Earth Planet. Sci. Lett., 240, 11?72.
Halliday, A. N., H. Wa?nke, J. L. Birck, and R. N. Clayton (2001), The
accretion, composition and early differentiation of Mars, Space Sci. Rev.,
96, 197?230.
Hargraves, R. B., D. W. Collinson, R. E. Arvidson, and C. R. Spitzer
(1977), The Viking magnetic properties experiment: Primary mission
results, J. Geophys. Res., 82, 4547?4558.
Hartmann, W. K. (2005), Martian cratering 8: Isochron refinement and the
chronology of Mars, Icarus, 174, 294?320.
Haskin, L. A., et al. (2005), Water alteration of rocks and soils on Mars at
the Spirit rover site in Gusev crater, Nature, 436, 66?69.
Herkenhoff, K. E., et al. (2003), Athena Microscopic Imager investigation,
J. Geophys. Res., 108(E12), 8065, doi:10.1029/2003JE002076.
Ho?rz, F., M. J. Cintala, W. C. Rochelle, and B. Kirk (1999), Collisionally
processed rocks on Mars, Science, 285, 2105?2107.
Hunt, C. P., B. M. Moskowitz, and S. K. Banerjee (1995), Magnetic proper-
ties of rocks and minerals, in Rock Physics and Phase Relations: A
Handbook of Physical Constants, AGU Ref. Shelf, vol. 3, edited by
T. J. Ahrens, pp. 189?204, AGU, Washington, D. C.
Hurowitz, J. A., S. M. McLennan, N. J. Tosca, R. E. Arvidson, J. R.
Michalski, D. W. Ming, C. Schro?der, and S. W. Squyres (2006), In situ
and experimental evidence for acidic weathering of rocks and soils on
Mars, J. Geophys. Res., 111, E02S19, doi:10.1029/2005JE002515.
Hviid, S. F., et al. (1997), Magnetic properties experiments on the Mars
Pathfinder lander: Preliminary results, Science, 278, 1768?1770.
Klingelho?fer, G., et al. (2003), Athena MIMOS II Mo?ssbauer spectrometer
investigation, J. Geophys. Res., 108(E12), 8067, doi:10.1029/
2003JE002138.
Lemmon, M. T., et al. (2004), Atmospheric imaging results from the Mars
exploration rovers: Spirit and Opportunity, Science, 306, 1753?1756.
Lodders, K. (1998), A survey of shergottite, nakhlite, and chassigny
meteorities whole-rock compositions, Meteorit. Planet. Sci., 33,
A183?A190.
Lodders, K. (2003), Solar system abundances and condensation tempera-
tures of the elements, Astrophys. J., 591(2), 1220?1247.
Lodders, K., and B. Fegley (1998), Presolar silicon carbide grains and their
parent stars, Meteorit. Planet. Sci., 33(4), 871?880.
Madsen, M. B., D. P. Agerkvist, H. P. Gunnlaugsson, S. F. Hviid, J. M.
Knudsen, and L. Vistisen (1995), Titanium and the magnetic phase on
Mars, Hyperfine Interactions, 95, 291?394.
Madsen, M. B., et al. (2003), Magnetic Properties Experiments on the Mars
Exploration Rover mission, J. Geophys. Res., 108(E12), 8069,
doi:10.1029/2002JE002029.
Mahaffy, P. R., and the SAM Science Team (2005), Organics and isotopes
analysis on the 2009 Mars Science Laboratory, paper presented at 37th
DPS Meeting, Div. for Planet. Sci., Am. Astron. Soc., Cambridge, U. K.
Maki, J. N., et al. (2003), Mars Exploration Rover Engineering Cameras,
J. Geophys. Res., 108(E12), 8071, doi:10.1029/2003JE002077.
Malin, M. C., et al. (2005), MOC View of Spirit?s Trek to the Columbia
Hills, NASA?s Planetary Photojournal, PIA07192, NASA, Washington,
D. C., 3 Jan. (Available at http://photojournal.jpl.nasa.gov/catalog/
PIA07192)
McLennan, S. M., et al. (2005), Provenance and diagenesis of the evapor-
ite-bearing Burns formation, Meridiani Planum, Mars, Earth Planet. Sci.
Lett., 240, 95?121.
McSween, H. Y., et al. (2006a), Characterization and petrologic interpreta-
tion of olivine-rich basalts at Gusev Crater, Mars, J. Geophys. Res., 111,
E02S10, doi:10.1029/2005JE002477.
McSween, H. Y., S. W. Ruff, R. V. Morris, J. F. Bell, K. E. Herkenhoff,
R. Gellert, and the Athena Science Team (2006b), Backstay and Irvine:
Alkaline volcanic rocks from Gusev Crater, Mars, Lunar Planet. Sci.,
XXXVII, 1120.
Melosh, H. J. (1989), Impact Cratering: A Geologic Process, 245 pp.,
Oxford Univ. Press, New York.
Meyer, C. (2003), Mars Meteorite Compendium?2003, NASA JSC #27672
Rev. B, NASA, Washington, D. C.
Ming, D. W., et al. (2006), Geochemical and mineralogical indicators
for aqueous processes in the Columbia Hills of Gusev crater, Mars,
J. Geophys. Res., 111, E02S12, doi:10.1029/2005JE002560.
Mittlefehldt, D. W., F. Ho?rz, T. H. See, E. R. D. Scott, and S. A. Mertzman
(2005), Geochemistry of target rocks, impact_melt particles and metallic
spherules from Meteor Crater, Arizona: Empirical evidence on the impact
process, in Large Meteorite Impacts III, edited by T. Kenkmann, F. Ho?rz,
and A. Deutsch, Spec. Pap. Geol. Soc. Am., 384, 367?390.
Mittlefehldt, D. W., R. Gellert, T. McCoy, H. Y. McSween Jr., R. Li, and the
Athena Science Team (2006), Possible Ni-rich mafic-ultramafic mag-
matic sequence in the Columbia Hills: Evidence from the Spirit rover,
Lunar Planet. Sci., XXXVII, 1505.
Morris, R. V., D. G. Agresti, H. V. Lauer Jr., J. A. Newcomb, T. D. Shelfer,
and A. V. Murali (1989), Evidence for pigmentary hematite on Mars
based on optical magnetic and Mossbauer studies of superparamagnetic
(nanocrystalline) hematite, J. Geophys. Res., 94, 2760?2778.
Morris, R. V., J. J. Gooding, H. V. Lauer Jr., and R. B. Singer (1990),
Origins of Marslike spectral and magnetic properties of a Hawaiian
palagonitic soil, J. Geophys. Res., 95, 14,427?14,434.
Morris, R. V., et al. (2000), Mineralogy, composition, and alteration of Mars
Pathfinder rocks and soils: Evidence from multispectral, elemental, and
magnetic data on terrestrial analogue, SNC meteorite, and Pathfinder
samples, J. Geophys. Res., 105, 1757?1817.
Morris, R. V., D. C. Golden, D. W. Ming, T. D. Shelfer, L. C. Jorgensen,
J. F. Bell III, T. G. Graff, and S. A. Mertzman (2001a), Phyllosilicate-
poor palagonitic dust form Mauna Kea Volcano (Hawaii): A mineralo-
gical analogue for magnetic Martian dust?, J. Geophys. Res., 106,
5057?5083.
Morris, R. V., G. E. Lofgren, L. Le, and T. D. Shelfer (2001b),
Crystallization of oxide and silicate phases from impact melts with
average Martian soil composition, Lunar Planet. Sci., XXXII, Abstract
2012.
Morris, R. V., et al. (2006a), Mo?ssbauer mineralogy of rock, soil, and dust
at Gusev crater, Mars: Spirit?s journey through weakly altered olivine
basalt on the plains and pervasively altered basalt in the Columbia Hills,
J. Geophys. Res., 111, E02S13, doi:10.1029/2005JE002584.
E12S11 YEN ET AL.: NICKEL ON MARS
24 of 25
E12S11
Morris, R. V., et al. (2006b), Mo?ssbauer mineralogy of rock, soil, and dust
at Meridiani Planum, Mars: Opportunity?s journey across sulfate-rich
outcrop, basaltic sand and dust, and hematite lag deposits, J. Geophys.
Res., doi:10.1029/2005JE002791, in press.
Myrick, T. M., K. Davis, and J. Wilson (2004), Rock Abrasion Tool, paper
presented at 37th Aerospace Mechanisms Symposium, NASA Johnson
Space Center, Houston, Tex.
Newsom, H. E., and J. J. Hagerty (1997), Chemical components of the
Martian soil: Melt degassing, hydrothermal alteration, and chondritic
debris, J. Geophys. Res., 102(E8), 19,345?19,355.
Newsom, H. E., M. J. Nelson, C. K. Shearer, and D. S. Draper (2005), The
Martian soil as a geochemical sink for hydrothermally altered crustal
rocks and mobile elements: Implications of early MER results, Lunar
Planet Sci. [CD-ROM], XXXVI, Abstract 1142.
Pesnell, W. D., and J. Grebowsky (2000), Meteoric magnesium ions in the
Martian atmosphere, J. Geophys. Res., 105, 1695?1707.
Pierazzo, E., and H. J. Melosh (2000), Hydrocode modeling of oblique
impacts: The fate of the projectile, Meteorit. Planet. Sci., 35, 117?130.
Pollack, J. B., D. S. Colburn, F. M. Flaser, R. Kahn, C. E. Carlston, and
D. Pidek (1979), Properties and effects of dust particles suspended in the
Martian atmosphere, J. Geophys. Res., 84, 2929?2945.
Rieder, R., R. Gellert, J. Bru?ckner, G. Klingelho?fer, G. Dreibus, A. Yen, and
S. W. Squyres (2003), The new Athena alpha particle X-ray spectrometer
for the Mars Exploration Rovers, J. Geophys. Res., 108(E12), 8066,
doi:10.1029/2003JE002150.
Rietmeijer, F. J. M. (1998), Interplanetary dust particles, in Planetary
Materials, Rev. Mineral., vol. 36, edited by J. J. Papike, p. 2-1?2-95,
chap. 2, Mineral. Soc. of Am., Washington, D. C.
Rietmeijer, F. J. M. (2000), Interrelationships among meteoric metals, me-
teors, interplanetary dust, micrometeorites, and meteorites, Meteorit.
Plan. Sci., 35, 1025?1041.
Rose, A. W., and G. C. Bianchimosquera (1993), Adsorption of Cu, Pb, Zn,
Co, Ni, and Ag on goethite and hematite?A control on metal mobiliza-
tion from red beds onto stratiform copper deposits, Econ. Geol. Bull. Soc.
Econ. Geol., 99, 1226?1236.
Schro?der, C., et al., (2006), A stony meteorite discovered by the Mars
Exploration Rover Opportunity on Meridiani Planum, Mars, paper
presented at 69th Annual Meeting of the Meteoritical Society, Zurich,
Switzerland.
Selsis, F., M. T. Lemmon, J. Vaubaillon, and J. F. Bell III (2005), Extra-
terrestrial meteors: A Martian meteor and its parent comet, Nature, 435,
581.
Soderblom, L. A., et al. (2004), Soils of Eagle Crater and Meridiani Planum
at the Opportunity Rover Landing Site, Science, 306, 1723?1726.
Squyres, S. W., and A. H. Knoll (2005), Sedimentary rocks at Meridiani
Planum: Origin, diagenesis, and implications for life on Mars, Earth
Planet. Sci. Lett., 240, 1?10.
Squyres, S. W., et al. (2006), Rocks of the Columbia Hills, J. Geophys.
Res., 111, E02S11, doi:10.1029/2005JE002562.
Taylor, S. R. (1982), Planetary Science: A Lunar Perspective, 481 pp.,
Lunar and Planet. Inst., Houston, Tex.
Wa?nke, H. (1991), Chemistry, accretion, and evolution of Mars, Space Sci.
Rev., 56, 1?8.
Wasson, J. T., W. V. Boynton, C. L. Chou, and P. A. Baedecker (1975),
Compositional evidence regarding the influx of interplanetary materials
onto the lunar surface, Moon, 13, 121?141.
Wdowiak, T. J., L. P. Armendarez, D. G. Agresti, M. L. Wade, S. Y.
Wdowiak, P. Claeys, and G. Izett (2001), Presence of an iron-rich nano-
phase material in the upper layer of the Cretaceous-Tertiary boundary
clay, Meteorit. Planet. Sci., 36, 123?133.
Yen, A. S., and B. Murray (1998), The color of Mars: Oxidation of exo-
genic metallic iron, Bull. Am. Astron. Soc., 30(3), Abstract 22.02.
Yen, A. S., S. S. Kim, M. H. Hecht, M. S. Frant, and B. Murray (2000),
Evidence that the reactivity of the Martian soil is due to superoxide ions,
Science, 289, 1909?1912.
Yen, A. S., et al. (2005), An integrated view of the chemistry and miner-
alogy of Martian soils, Nature, 436, 49?54.
Zipfel, J., et al. (2004), APXS analyses of bounce rock?The first shergot-
tite on Mars, Meteorit. Planet. Sci., 39, A118.
Zolensky, M. E., M. K. Weisberg, P. C. Buchanan, and D. W. Mittlefehldt
(1996), Mineralogy of carbonaceous chondrite clasts in HED achondrites
and the Moon, Meteorit. Planet. Sci., 31, 518?537.

J. F. Bell III and S. W. Squyres, Department of Astronomy, Cornell
University, 428 Space Sciences Building, Ithaca, NY 14853, USA.
J. Bru?ckner, Max Planck Institut fu?r Chemie, Kosmochemie, D-55020
Mainz, Germany.
B. C. Clark, Lockheed Martin Corporation, Littleton, CO 80127, USA.
T. Economou, Enrico Fermi Institute, University of Chicago, Chicago, IL
60637, USA.
R. Gellert, Department of Physics, University of Guelph, Guelph, ON,
Canada N1G 2W1.
M. Golombek and A. S. Yen, Jet Propulsion Laboratory, California
Institute of Technology, Mail Code 183-501, 4800 Oak Grove Drive,
Pasadena, CA 91109, USA. (albert.yen@jpl.nasa.gov)
B. L. Jolliff, Department of Earth and Planetary Sciences, Washington
University, Campus Box 1169, One Brookings Drive, St. Louis, MO 63130,
USA.
M. B. Madsen, Niels Bohr Institute, University of Copenhagen, DK-2100
Copenhagen, Denmark.
T. J. McCoy, National Museum of Natural History, Smithsonian
Institution, MRC 119, Washington, DC 20560, USA.
S. M. McLennan, Department of Geosciences, State University of New
York at Stony Brook, Stony Brook, NY 11794, USA.
H. Y. McSween Jr., Department of Earth and Planetary Sciences,
University of Tennessee, Knoxville, TN 37996, USA.
D. W. Ming, D. W. Mittlefehldt, and R. V. Morris, NASA Johnson Space
Center, Houston, TX 77058, USA.
C. Schro?der, Johannes Gutenberg University, Mainz, Germany.
T. Wdowiak, Department of Physics, University of Alabama at
Birmingham, Birmingham, AL 35294, USA.
J. Zipfel, Forschungsinstitut und Naturmuseum Senckenberg, Frankfurt,
Germany.
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