Bounce Rock?A shergottite-like basalt encountered at Meridiani Planum, Mars
Jutta ZIPFEL1*, Christian SCHRO?DER2, Bradley L. JOLLIFF3, Ralf GELLERT4,
Kenneth E. HERKENHOFF5, Rudolf RIEDER6, Robert ANDERSON7, James F. BELL III8,
Johannes BRU?CKNER6, Joy A. CRISP7, Philip R. CHRISTENSEN9, Benton C. CLARK10,
Paulo A. de SOUZA Jr.11, Gerlind DREIBUS6, Claude d?USTON12, Thanasis ECONOMOU13,
Steven P. GOREVAN14, Brian C. HAHN15, Go?star KLINGELHO?FER2, Timothy J. McCOY16,
Harry Y. McSWEEN Jr.17, Douglas W. MING18, Richard V. MORRIS18, Daniel S. RODIONOV2,
Steven W. SQUYRES8, Heinrich WA?NKE6, Shawn P. WRIGHT19, Michael B. WYATT20, and
Albert S. YEN7
1Sektion Meteoritenforschung, Senckenberg Forschungsinstitut und Naturmuseum Frankfurt, Senckenberganlage 25,
60325 Frankfurt a. M., Germany
2Institut fu?r Anorganische Chemie und Analytische Chemie, Johannes Gutenberg-Universita?t Mainz, Staudinger Weg 9,
55128 Mainz, Germany
Present address: Universita?t Bayreuth und Eberhard Karls Universita?t Tu?bingen, Sigwartstr. 10, 72076 Tu?bingen, Germany
3Department of Earth and Planetary Sciences, Washington University, St. Louis, Missouri 63130, USA
4Department of Physics, University of Guelph, Guelph, Ontario, Canada N1G 2W1
5Astrogeology Science Center, U.S. Geological Survey, Flagstaff, Arizona 86001, USA
6Abteilung Geochemie, Max-Planck-Institut fu?r Chemie, Postfach 3060, 55020 Mainz, Germany
7Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California 91109, USA
8Department of Astronomy, Cornell University, Ithaca, New York 14853, USA
9School of Earth and Space Exploration, Arizona State University, Tempe, Arizona 85287?6305, USA
10Lockheed Martin Corporation, Littleton, Colorado 80127, USA
11Tasmanian ICT Centre, CSIRO, GPO Box 1538, Hobart, Tasmania 7001, Australia
12Centre d?Etude Spatiale des Rayonements, F-31028 Toulouse, France
13Laboratory for Atmospheric and Space Research, Enrico Fermi Institute, Chicago, Illinois 60637, USA
14Honeybee Robotics, New York, New York 10012, USA
15Department of Geosciences, State University of New York, Stony Brook, New York 11794, USA
16Department of Mineral Sciences, National Museum of Natural History, Smithsonian Institution, Washington,
District of Columbia 20560?0119, USA
17Department of Earth and Planetary Sciences, University of Tennessee, Knoxville, Tennessee 37996, USA
18Astromaterials Research and Exploration Science, NASA Johnson Space Center, Houston, Texas 77058, USA
19Institute of Meteoritics, University of New Mexico, 1 University of New Mexico, MSC03-2050, Albuquerque,
New Mexico 87131, USA
20Department of Geological Sciences, Brown University, Box 1846, Providence, Rhode Island 02912, USA
*Corresponding author. E-mail: jzipfel@senckenberg.de
(Received 29 January 2010; revision accepted 09 September 2010)
Abstract?The Opportunity rover of the Mars Exploration Rover mission encountered an
isolated rock fragment with textural, mineralogical, and chemical properties similar to
basaltic shergottites. This ?nding was con?rmed by all rover instruments, and a
comprehensive study of these results is reported here. Spectra from the miniature thermal
emission spectrometer and the Panoramic Camera reveal a pyroxene-rich mineralogy, which
is also evident in Mo?ssbauer spectra and in normative mineralogy derived from bulk
chemistry measured by the alpha particle X-ray spectrometer. The correspondence of
Bounce Rock?s chemical composition with the composition of certain basaltic shergottites,
especially Elephant Moraine (EET) 79001 lithology B and Queen Alexandra Range (QUE)
94201, is very close, with only Cl, Fe, and Ti exhibiting deviations. Chemical analyses
further demonstrate characteristics typical of Mars such as the Fe ?Mn ratio and P
 The Meteoritical Society, 2011.1
Meteoritics & Planetary Science 46, Nr 1, 1?20 (2011)
doi: 10.1111/j.1945-5100.2010.01127.x
concentrations. Possible shock features support the idea that Bounce Rock was ejected from
an impact crater, most likely in the Meridiani Planum region. Bopolu crater, 19.3 km in
diameter, located 75 km to the southwest could be the source crater. To date, no other
rocks of this composition have been encountered by any of the rovers on Mars. The ?nding
of Bounce Rock by the Opportunity rover provides further direct evidence for an origin of
basaltic shergottite meteorites from Mars.
INTRODUCTION
The chemical composition and physical properties
of the Martian surface studied by the Viking landers
from 1976 to 1982, Mars Path?nder in 1997, and the
Mars Exploration Rovers (MER) since 2004 have had a
great impact on our understanding of the evolution of
Mars. These data provide ground-truth for orbital
experiments and allow a certain group of meteorites
found on Earth to be linked to Mars. This group of
meteorites was named ??SNCs?? after three of its
members and divided into three classes: shergottites
(igneous rocks subdivided into basaltic shergottites and
lherzolitic shergottites), nakhlites (clinopyroxenites), and
Chassigny (a dunite). Later, the classi?cation was
expanded to include the unique orthopyroxenite, Allan
Hills (ALH) 84001. Relative elemental abundances and
isotopic compositions of trapped atmospheric gases
extracted from shock-melt pockets, namely in the
basaltic shergottite Elephant Moraine (EET) 79001,
provide the only direct evidence that Martian meteorites,
formerly ??SNCs,?? originated from Mars (Bogard and
Johnson 1983). Relatively young crystallization ages
must be considered as indirect evidence. With the
exception of ALH 84001, crystallization ages range from
1300 to 200 Myr or less (Borg et al. 1997; Nyquist et al.
2001).
Martian meteorites are important because they can
be analyzed in detail and at much higher precision in
terrestrial laboratories than any surface material on
Mars that is studied by remotely operated instruments.
Most models of the geochemical evolution of Mars?
mantle and crust are based on studies of the
mineralogical, geochemical, and isotopic composition of
such meteorites. Isotopic analyses have been used to
infer early differentiation with the formation of a crust,
mantle, and small core (e.g., Lee and Halliday 1997;
Lugmair and Shukolyukov 1998). In comparison to
Earth, the inferred bulk composition of Mars has higher
abundances of moderately volatile elements (Mn, Na,
etc.) and higher FeO in the source region of basalts
(e.g., Dreibus and Wa?nke 1985).
The two MER landed in January 2004 on opposite
sides of Mars, more than 10,000 km apart. Mission
overviews are given by Squyres et al. (2004a, 2004b,
2006a, 2006b, 2009) and Arvidson et al. (2006, 2008).
Surface analyses have revealed primarily igneous
bedrock, altered to variable degrees through weathering
processes at Gusev crater, and sedimentary bedrock at
Meridiani Planum (Squyres et al. 2004a, 2004b). None
of these materials have compositions similar to those of
Martian meteorites. At Meridiani, individual small
cobbles and rock fragments can be recognized easily
because the vast plains are predominantly covered with
?ne-grained material, i.e., Martian soil. Detailed studies
of some such rocks showed them to be either locally
derived fragments of bedrock, potential fragments of
igneous rocks or impact-breccias, or meteorites (Jolliff
et al. 2006; Schro?der et al. 2008). The most prominent
meteorites are iron meteorites and a potential
mesosiderite (Schro?der et al. 2008; Fleischer et al. 2010).
In March 2004, after leaving Eagle crater,
Opportunity approached an isolated rock on the plains
of Meridiani Planum. Because it was close to a bounce
mark from the lander?s airbag and may have been
struck by an airbag during the landing, the rock was
dubbed ??Bounce Rock.?? With the exception of Bopulo
crater, Gusev crater, and Meridiani Planum, all other
names used in this report to identify geographic features
on Mars are informal and are not approved by the
International Astronomical Union. Because of its large
size compared to anything else that could be seen on
the plains and its unusual appearance (Fig. 1), the
science team decided to study Bounce Rock between
sols 63 and 70 of Opportunity?s surface mission. A sol
is a day on Mars, 24 h and 40 min long.
Bounce Rock has properties very similar to those of
Martian meteorites. Data from the entire MER
instrument suite demonstrate that Bounce Rock is
closely related to basaltic shergottites. Initially published
results from individual instruments were scattered
across a collection of MER papers (Arvidson et al.
2004; Bell et al. 2004; Christensen et al. 2004;
Herkenhoff et al. 2004; Klingelho?fer et al. 2004; Rieder
et al. 2004; Squyres et al. 2004b). This article is
exclusively devoted to Bounce Rock and integrates all
?ndings, adding further details and discussion.
METHODS
Here, we present methods applied to study a rock
on Mars and related samples in laboratories on Earth.
2 J. Zipfel et al.
For comparison to the analyses of Bounce Rock on
Mars, a powdered aliquot of the Zagami meteorite was
analyzed with the Alpha Particle X-ray Spectrometer
(APXS) ?ight spare instrument, BB10, at the Max-
Planck-Institut in Mainz. An unpolished sample (butt)
of EETA79001 lithology B was provided by the
Meteorite Working Group and inspected in re?ected
light with an optical microscope. It was also analyzed
with a ?ight spare of the Mo?ssbauer Spectrometer (MB)
at the University of Mainz. For details about the APXS
and MB instruments, see below.
Bounce Rock was studied on Mars with
instruments onboard the Opportunity rover, which is
equipped with a movable instrument deployment device,
a set of engineering cameras, and the Athena scienti?c
instrument payload. The Athena payload comprises the
Panoramic Camera (Pancam), the Miniature Thermal
Emission Spectrometer (Mini-TES), the Rock Abrasion
Tool (RAT), the Microscopic Imager (MI), the MB,
and the APXS.
Pancam is a stereo camera that obtains high-
resolution images to assess morphology, topography,
and geologic context. Thirteen narrowband ?lters that
span a spectral range from 432 to 1009 nm provide
information on mineralogical, photometric, and physical
properties of surface materials. Details of the
instrument calibration and performance are given by
Bell et al. (2003, 2004, 2006).
Mini-TES is a Fourier Transform spectrometer that
obtains infrared spectra from 5 to 29 lm (339?
1997 cm)1) with a spectral sampling of 10.0 cm)1.
Mini-TES provides remote measurements of mineralogy
and thermophysical properties of the surrounding
scenery and guides the rovers to key targets for detailed
in situ measurements. A detailed description of the
instrument is given by Christensen et al. (2003, 2004).
The RAT is a brushing and grinding tool that
cleans surfaces of Martian rocks of dust and debris, and
exposes their fresh interior. The amount of energy
needed to grind into a rock, expressed as speci?c grind
energy (SGE), is the ratio of energy expended to the
volume of material removed. The SGE is related to
rock strength, primarily compressive yield strength
(Gorevan et al. 2003; Arvidson et al. 2004).
The MI acquires images at a spatial resolution of
31 lm per pixel over a broad, visible spectral range
(400?700 nm). MI images, 3.2 cm ? 3.2 cm across, place
other MER data in context and provide textural details
to aid petrologic and geologic interpretations. Details of
the instrument calibration and performance are given by
Herkenhoff et al. (2003, 2004, 2008).
The MB observes a sample area approximately
1.4 cm in diameter in backscatter geometry. From MB
spectra, one can determine Fe oxidation states, identify
Fe-bearing phases, and determine relative abundances
of Fe among those phases. Spectra are stored separately
according to temperature. Klingelho?fer et al. (2003) and
Morris et al. (2006a, 2003b) describe the instrument and
data reduction procedures.
The APXS emits alpha particles and X-rays that
interact with an approximately 2.5 cm sample area.
Concentrations of major, minor and some trace
elements, with Z ranging from 3 (Na) to 35 (Br), are
determined from X-ray spectra. Details of the
instrument calibration, and data reduction procedures
are reported by Rieder et al. (2003) and Gellert et al.
(2006).
In addition to the Athena payload, the rover has six
engineering cameras that assist navigation and mobility.
Two sets of stereo pairs of hazard avoidance cameras
(Hazcam) facing front and rear are located under the
rover deck. A stereo pair of navigation cameras
(Navcam) is mounted on the Pancam mast. Details of
these cameras are given by Maki et al. (2003).
RESULTS
Textures and Physical Properties
Bounce Rock is an isolated rock, approximately
40 cm ? 20 cm across, sitting on the plains of Meridiani
Planum. Pancam images show that its surface is covered
Bounce Rock
Two views
Air bag 
bounce 
mark
Fig. 1. ??Bounce Rock predrive???Pancam false-color image
(L256) from sol 63, P2570. Effective wavelengths of the
Pancam ?lters, L2, L5, and L6 are 753, 535, and 482 nm,
respectively. Grayscale inset is from the sol 63 Hazcam image
after the approach drive. White lines connect the same
features in the two views. Blue line indicates approximate
scale.
Bounce Rock 3
with dust and soil. Images also show that the surface
displays lustrous, subparallel striations (Figs. 1?3) (Bell
et al. 2004). These striations are also apparent in
individual MI images and a mosaic composed of MI
images of surface target ??Case?? (before RAT grinding;
Fig. 3) (Herkenhoff et al. 2004). Nine positions on the
rock surface and the RAT hole were documented with
the MI (Figs. 3?5).
When the RAT was used to grind into Bounce
Rock, the measured SGE was 3.7 joules per cubic mm,
which is signi?cantly less energy than required for
typical basalts at Gusev crater (51?83 J mm)3; see
Arvidson et al. 2004). The RAT was set to a typical
preload force of 60 N and it took 2 h and 17 min to
grind a 4.5 cm diameter and 6.4 mm deep hole (target
??Case??; see Figs. 6 and 7).
(a)
(b)
(c)
Fig. 2. Bounce Rock Pancam image from sol 65, P2574. a)
Approximate true color (Savransky and Bell 2004; Bell et al.
2006). b) L257 false color. c) L7 ?lter, contrast stretched to
enhance re?ections from rock surface. Parts (b) and (c), with
glinting, emphasize the striations that are reminiscent of
shatter-cone textures. Image source for (a) is http://
marswatch.astro.cornell.edu/pancam_instrument/images/True/
Sol065B_P2574_1_True_RAD.jpg.
(a)
(b)
Fig. 3. Same Pancam image as in Fig. 2c. a) Position of target
Case as documented by the MI on the pre-RAT surface. b)
Details of the pre-RAT MI mosaic of Case. Fractures are
partly ?lled with loose material.
4 J. Zipfel et al.
The RAT-abraded surface shows bright features
and reveals the interior texture of target Case to be ?ne-
grained and crosscut by mm- to cm-sized fractures. For
comparison, inspection of the unpolished sample of
basaltic shergottite EETA79001 lithology B with the
optical microscope reveals the ?ne-grained, subophitic
texture typical for this meteorite (Steele and Smith
1982) (Fig. 7).
Bulk Chemistry
The APXS analyzed the chemical composition of
two natural surface targets, Maggie and Glanz2, and
the abraded target, Case (Figs. 4 and 5). The X-ray
spectrum of Case is shown in Fig. 8. Re?nements in
instrument calibration lead to slightly different results
from those published earlier (Rieder et al. 2004; Zipfel
et al. 2004) and are listed in Table 1.
A comparison of published data with results from
APXS analyses of a powdered aliquot of the Martian
meteorite Zagami are presented in Table 1 and Fig. 9.
The APXS results are, for most elements, in excellent
agreement with published data (Banin et al. 1992;
Lodders 1998), within calibration accuracy. Larger
deviations for Cl and K (only upper limits are given), and
Na, P, S, and Ni probably re?ect sample heterogeneity
because no systematic deviations in the abundance of
these particular elements are observed if results for other
rock standards are compared (Gellert et al. 2006).
Alpha Particle X-ray Spectrometer surface analyses
of Maggie and Glanz2 show that Bounce Rock is
covered by soil ?dust. Elements typically enriched in soil
(e.g., S, Cl, and Zn; Rieder et al. 2004; Gellert et al.
Sol 63 Front Hazcam
Bounce Rock
Glanz2
MI,MB,APXS
Eifel
MB
Loreley
MB
Case
Achsel
MI
E
L
Fips2
MI,MB
Traube
MI
Post-RAT view
Case
Fips2
Traube
Achsel
Glanz2
Fig. 4. Sol 63 Front Hazcam image showing locations of pre-
RAT targets and rover arm instrument(s), MI, MB, and
APXS used to study the rock at these targets. MI single
frames (3.2 ? 3.2 cm) show details of Bounce Rock?s surface
texture.
GraceMaggie
Wrigley2 Ginnie2
Fig. 5. Sol 68 Front Hazcam image of post-RAT targets.
Target locations and approximate orientations to the right of
the dashed line (limit of RAT ??tailings??) are shown. MI single
frames (3.2 ? 3.2 cm) show details of Bounce Rock?s surface
texture.
Bounce Rock 5
2006) are signi?cantly higher than for the abraded
target Case. Surface concentrations of S, for example,
are 1.47 and 1.85 wt%, but only 0.22 wt% in the
interior of the rock. Depletions of S, Cl, and Zn in the
analysis of Case are compensated mostly by an increase
in SiO2 and CaO. Other major and minor element
concentrations show only small differences between
rock surfaces and interiors, indicating that the surface
alteration is minor. Because of large uncertainties,
concentrations of K, Ni, and Br do not warrant further
characterization of the surface alteration.
The bulk composition of Case has SiO2 of
51.6 wt% and Na2O of 1.7 wt%, and plots in the
compositional ?eld of basalts from Earth, on the basis
of the alkali versus SiO2 contents, as de?ned by Le Bas
et al. (1986). Concentrations of Al2O3 and CaO are
relatively high, at 10.5 and 12.1 wt%, respectively.
Mineralogy
Pancam observations of Case reveal spectral
characteristics from 750 to 1000 nm that are consistent
with the presence of pyroxene or olivine (Bell et al.
2004). The Mini-TES obtained spectra from the rock,
itself, and some adjacent soil. Christensen et al. (2004)
evaluated ??dust-removed?? spectra, subtracting TES
spectra of surface ?nes from high-albedo regions. The
resulting spectrum is consistent with a rock that has a
pyroxene-rich mineral assemblage. Deconvolution of
this spectrum yields modal mineralogy as follows:
clinopyroxene (55%), orthopyroxene (5%),
plagioclase (20%), olivine (5%), and oxides (10%)
(Christensen et al. 2004).
Mo?ssbauer spectra from Case, and seven additional
targets on the natural surface of the rock were acquired
(Glanz2, Eifel, Loreley, Fips2, Grace, Wrigley2, and
Maggie; see Figs. 4 and 5). All Fe2+ is hosted in high-
and low-Ca pyroxenes (Klingelho?fer et al. 2004; Morris
et al. 2006b). Table 2 shows results from MB spectra
obtained at two different energies, 6 and 14 keV. The
higher-energy spectra penetrate deeper into the rock
Fig. 6. Pancam ??true color?? (Savransky and Bell 2004; Bell
et al. 2006) image of Bounce Rock, Sol 068 P2581, after the
target ??Case?? was ground with the rock abrasion tool.
Unlike the Meridiani outcrop rocks, the grinding dust from
Bounce Rock appears white, not red, consistent with an
unoxidized, primary silicate interior. Image source is http://
marswatch.astro.cornell.edu/pancam_instrument/images/True/
Sol068B_P2581_1_True_RAD.jpg.
Fig. 7. MI mosaic of post-RAT target Case. The RAT hole
(4.5 cm across) shows that the rock interior is crosscut by a
number of open fractures. Bright features indicate a very weak
preferred orientation running ??NNE to SSW?? relative to the
image frame. An enlarged area is shown in direct comparison
to the texture of EETA79001 (both areas are 1 ? 1 cm).
Fig. 8. APXS spectrum of post-RAT target Case measured on
Mars by the ?ight instrument on Opportunity. Peaks from Cu
and Zr are background peaks from the instrument doors and
casing. The apparently high Ni peak is a background artifact.
6 J. Zipfel et al.
(Klingelho?fer et al. 2003; Fleischer et al. 2008) and
differences in Fe3+ abundances may be attributed to
surface alteration. The highest amounts of a ferric phase
de?ne the upper limit for iron oxides to be 10% of total
Fe (Table 2). Features characteristic of olivine were not
observed in any of the Bounce Rock spectra. In the MB
spectrum of EETA79001 lithology B, all Fe2+ is hosted
in pyroxenes. No other Fe-bearing phases were detected
(Table 4). As support for the pyroxene-rich spectral
observations, mineral norm calculations from the APXS
data for Case give a pyroxene-normative composition
(Table 3).
DISCUSSION
Texture
Herkenhoff et al. (2004) originally interpreted
striations observed on the surface of Bounce Rock to be
similar in appearance to slickensides formed by
differential motion under pressure in terrestrial rocks.
However, when inspecting detailed MI images, these
striations are also reminiscent of those of shatter cones
(Fig. 10). Gibson and Spray (1998) and Nicolaysen and
Reimold (1999) describe similar features in shatter cones
from Sudbury and Vredefort impact structures,
respectively. Striations on shatter-cone surfaces are
fractures that may be divergent or subparallel, to almost
parallel. They are generally thought to be caused by
shock waves during the compression stage of impact.
However, it has also been proposed that shatter cones
are tensile fractures forming immediately after the
passage of the shock wave through the target rock and
during shock unloading (Wieland et al. 2006). The
relative weakness of Bounce Rock in comparison to
weathered basaltic rocks studied in the Gusev plains is
possibly also the result of impact-produced fracturing.
Alternatively, wind erosion could have sculpted Bounce
Rock?s surface with striation-like features.
The exposed interior of Bounce Rock, as seen in a
mosaic of MI images of Case, shows a ?ne-grained,
fractured texture unlike that of a sedimentary rock,
Table 1. Composition of Bounce Rock and selected basaltic shergottites (wt%).
SD
%a
Bounce Rock EETA79001b
QUE
94201b Zagamic Zagamib Shergottyb
Maggie
(surface)
Glanz2
(surface)
Case
(interior) Lithology B
(wt%)
SiO2 3.5 47.5 48.5 51.6 49.4 47.9 50.8 50.5 51.3
TiO2 20 0.69 0.83 0.74 1.18 1.84 0.96 0.79 0.82
Al2O3 7 10.7 9.7 10.5 11.2 11 5.7 6.05 6.88
Cr2O3 20 0.12 0.10 0.11 0.17 0.14 0.33 0.33 0.20
FeO 6 14.2 15.5 14.4 17.4 18.5 17.7 18.1 19.4
MnO 8 0.37 0.42 0.40 0.43 0.45 0.52 0.5 0.52
CaO 8 9.8 10.9 12.1 10.8 11.4 11.2 10.5 9.6
MgO 17 7.7 6.6 6.8 6.57 6.25 10.2 11.3 9.3
Na2O 8.5 2.2 2.0 1.7 1.74 1.58 1.3 1.23 1.39
K2O 15 0.3 (1) 0.3 (1) 0.1 (1) 0.075 0.045 <0.10 0.14 0.17
P2O5 17 0.88 0.99 0.92 1.28 0.82 0.5 0.67
Sumd 100.0 99.9 100.0 100.2 99.1 100.0 99.9 100.3
S 15 1.85 1.47 0.22 0.193 0.15 0.19 0.323
Cl 12 0.94 0.57 0.10 0.0048 0.0091 <0.03 0.0137 0.0108
(ppm)
Nie 20 160 (40) 150 (60) 80 (40) 28 <20 110 (10) 48 79
Zn 12 145 (15) 110 (30) 40 (20) 91 110 60 (10) 60 69
Br <40 <40 <40 0.025 0.35 <10 0.83 0.88
Molar
(MgO ? [MgO+FeO])
0.49 0.43 0.46 0.40 0.38 0.51 0.53 0.46
Ca ?Al wt% 1.24 1.52 1.56 1.30 1.40 2.63 2.34 1.88
Fe ?Mn wt% 38.5 37.0 36.1 40.6 41.3 34.3 36.3 37.4
Note: < = Upper limit.
aAverage deviation from certi?ed value in percent during calibration (Gellert et al. 2006). If statistical error is larger than this standard
deviation, the absolute statistical error is shown in brackets.
bData from Lodders (1998).
cResult of APXS analyses with ?ight spare instrument (BB10).
dTotals of APXS analyses include sulfur as SO3 in wt%.
eNi in Bounce Rock corrected for background in the Opportunity ?ight instrument.
Bounce Rock 7
although brighter features indicate a weak preferred
orientation. Herkenhoff et al. (2004) noted a hint of a
brecciated texture. Results from our study indicate a
texture similar to that of igneous rocks that may be
comparable to Martian meteorites. An enlarged area
1 cm across allows direct comparison to an unpolished
sample of EETA79001 of lithology B (Fig. 7).
EETA79001 is the only Martian meteorite recovered so
far that contains two igneous lithologies separated along
a gradational, unbrecciated contact (e.g., Steele and
Smith 1982). The mineralogy of lithology A and B is
similar, but lithology A is slightly ?ner grained
(<0.3 mm) and contains megacrysts of olivine (e.g.,
McSween and Treiman 1998 and references therein).
Like other basaltic shergottites both lithologies have a
subophitic texture consisting of laths of pyroxenes,
augite, and pigeonite, and interstitial maskelynite, a
diapletic glass formed from plagioclase under high
shock pressures (e.g., Milton and De Carli 1963).
Although there are discernable lath-shaped crystals, a
similar texture in Bounce Rock is dif?cult to resolve but
cannot be excluded. Bounce Rock may be ?ner grained
or it has obscured grain boundaries from either shock
fracturing or adhering dust from the RAT abrasion.
Bulk Composition
Concentrations of most elements in the abraded
rock target (Case) agree within the limits of calibration
accuracy of 12.5?20 rel% or better with the
compositions of two basaltic shergottites, lithology B of
EETA79001 and Queen Alexandra Range (QUE) 94201
(Fig. 11 and Table 1). A high Cl concentration in
Bounce Rock could imply that minor alteration
products are present even in the rock?s interior, possibly
concentrated along fractures. Lower TiO2, FeO, and
Cr2O3 concentrations than typical for basaltic
shergottites indicate a relatively low content of minor
opaque phases, such as ilmenite and ulvo?spinel (see also
mineralogy discussion of MB results).
Basaltic shergottites span a wide range in
composition, with MgO ranging from 4 to 11.5 wt%.
Compositional trends of decreasing Al2O3, CaO, and
P2O5 and increasing Cr2O3 with increasing MgO exist
for these meteorites and are indicated by the linear
regression lines in Fig. 11. All three Bounce Rock
analyses fall on?or plot close to?these trend lines at
MgO concentrations varying from 6.6 to 7.7 wt%.
Other rocks analyzed on Mars deviate signi?cantly
from these trends. Path?nder soil-free rock, which has a
basaltic-andesite-like composition (Bru?ckner et al. 2003;
Foley et al. 2003), falls considerably off these trends,
with very low MgO. It should be noted that this
Path?nder rock composition was derived from surface
analyses after subtracting contributions from adhering
soil. Gusev basalts, especially the Adirondack-class
basalts, which are close to picritic basalts in
composition and are olivine-rich (Gellert et al. 2004;
McSween et al. 2004, 2006), plot on the high-MgO side.
In the Gusev basalts, concentrations of P2O5 fall on the
trend line, those of Al2O3 and Cr2O3 plot signi?cantly
above the trend, and those of CaO plot signi?cantly
below the trend. Rocks of other basaltic classes
analyzed in Gusev Crater, such as Irvine or Backstay,
also deviate from the compositional trends de?ned by
Martian meteorites (e.g., McSween et al. 2009). The
sulfur-rich sedimentary rocks from Meridiani Planum
(Rieder et al. 2004) have signi?cantly lower CaO
concentrations than basaltic shergottites and even
Gusev basalts (Gellert et al. 2004). None of these rocks
have chemical similarities to other subgroups of
Martian meteorites (e.g., olivine-phyric and lherzolitic
shergottites, nakhlites, chassignites, and the
orthopyroxenite ALH 84001). Therefore, Bounce Rock
is exceptional; compared to all other rocks analyzed on
Mars to date, it is the only rock with a chemical
composition that is similar enough to those of two
Martian meteorites to permit unambiguous classi?cation
as one of them.
Mineral Composition
Studies with the Pancam, Mini-TES, MB, and APXS
consistently show that Bounce Rock has a mineralogy
Si Al Fe Ca Mn Na Cl Mg K P S Ni Zn Cr Ti
0.0
0.5
1.0
1.5
2.0
2.5
3.0
decreasing calibration accuracy
-20%
+20%
-12.5%
+12.5%
Co
nc
en
tra
tio
n 
ra
tio
s
 Zagami (BB10) vs Zagami (Lodders 1998) 
 Zagami (BB10) vs Zagami (Banin et al. 1992) 
Fig. 9. Comparison of APXS results and published data. A
powder aliquot of Zagami was analyzed in the laboratory with
an APXS ?ight spare instrument (BB10). The agreement for
major and some minor elements is excellent and well within
the calibration uncertainties. Larger discrepancies as observed
for P, S, and Ni probably re?ect sample heterogeneity. Arrows
at Cl and K indicate upper limits for these elements in the
Zagami (BB10) analyses.
8 J. Zipfel et al.
dominated by pyroxene. The mineralogy derived from
deconvolution of a Mini-TES spectrum shows that
Bounce Rock contains about three times more pyroxene,
mostly clinopyroxene, than plagioclase (Christensen et al.
2004). This composition is unlike that of any other
igneous rock analyzed by Mini-TES on Mars, but similar
to Martian meteorites.
The iron-bearing mineralogy of Bounce Rock is
determined by MB spectroscopy. Spectra are dominated
by features consistent with pyroxenes; olivine was not
identi?ed in any of the MB spectra. Given the presence
of Fe-bearing pyroxene, we argue that coexisting
forsterite (the Fe-free olivine endmember), which would
not be detected by MB, can be excluded. Therefore,
Table 3. Calculated normative mineralogy and plagioclase composition (wt%)a.
Bounce Rock EETA79001b
QUE 94201b Zagamib ShergottybCase Lithology B
Ilmenite 1.4 2.2 3.5 1.5 1.6
Chromite 0.2 0.3 0.2 0.5 0.3
Apatite 2.2 3.0 n.d. 1.2 1.6
Orthoclase 0.4 0.3 0.8 1.0
Albite 14.6 15.3 14.0 10.7 12.1
Anorthite 20.9 22.0 22.3 10.3 11.7
Diopside 27.8 19.1 28.9 31.9 26.2
Hypersthene 29.2 32.6 23.5 38.7 45.1
Olivine 0 0 7.0 4.8 0
Quartz 3.9 0.6 0 0 0.8
PlagioclaseAn 58.8 59.0 61.6 49.0 49.1
Note: n.d. = not detected.
aFor calculation of the norm it was assumed that bulk compositions are S- and Cl-free and that all Fe is Fe2+.
bCalculated from compositions given by Lodders (1998).
Table 2. Mo?ssbauer parameters from 6.4 and 14.4 keV spectra of Bounce Rock summed over all temperature
windows.
T
(K) (kEV)
PxM1 PxM2 npOx
da
(mm s)1)
DEQ
b
(mm s)1)
Ac
(%)
d
(mm s)1)
DEQ
(mm s)1)
A
(%)
d
(mm s)1)
DEQ
(mm s)1)
A
(%)
Glanz2 200?260 14.4 1.16 2.75 69 1.13 2.04 29 [0.47] [0.67] 2
6.4 1.17 2.75 68 1.14 2.04 28 [0.47] [0.67] 3
Case 200?260 14.4 1.17 2.76 73 1.14 2.05 27 [0.47] [0.67] 1
6.4 1.18 2.77 75 1.15 2.07 24 [0.47] [0.67] 1
Eifel 250?260 14.4 1.20 2.74 65 1.16 2.01 31 [0.47] [0.67] 3
6.4 [1.20] [2.74] 77 [1.16] [2.01] 21 [0.47] [0.67] 2
Loreley 250?260 14.4 1.18 2.76 71 1.15 2.03 29 [0.47] [0.67] 0
6.4 [1.18] [2.76] 69 [1.15] [2.03] 28 [0.47] [0.67] 3
Fips2 200?250 14.4 1.16 2.76 66 1.14 2.05 31 [0.47] [0.67] 3
6.4 1.16 2.85 75 1.15 2.11 20 [0.47] [0.67] 5
Grace 240?260 14.4 1.17 2.72 74 1.15 2.08 23 [0.47] [0.67] 3
6.4 [1.17] [2.72] 75 [1.15] [2.08] 20 [0.47] [0.67] 5
Wrigley2 250?260 14.4 1.17 2.70 63 1.15 2.01 32 [0.47] [0.67] 5
6.4 [1.17] [2.70] 64 [1.15] [2.01] 35 [0.47] [0.67] 2
Maggie
(red.)d
200?250 14.4 1.17 2.78 70 1.14 2.07 25 0.47 0.67 4
6.4 1.17 2.78 67 1.15 2.08 24 [0.47] [0.67] 8
Maggie
(full)e
200?210 14.4 1.16 2.82 73 1.13 2.07 24 [0.47] [0.67] 3
6.4 1.19 2.75 66 1.16 2.11 24 [0.47] [0.67] 10
Note: Values in square brackets were ?xed during ?tting procedure.
aCenter shift, relative to a-Fe. Uncertainty is ?0.02 mm s)1.
bQuadrupole splitting. Uncertainty is ?0.02 mm s)1.
cRelative subspectral area, f-factor corrected with f(Fe3+) ? f(Fe2+) = 1.21 (cf. Morris et al. 2006b). Uncertainty is ?2%.
dMaggie (red.) spectrum obtained with reduced maximum drive velocity, approximately 4 mm s)1.
eMaggie (full) spectrum obtained at full standard maximum drive velocity, approximately 12 mm s)1.
Bounce Rock 9
?tted olivine in the Mini-TES spectrum may be an
artifact of missing endmembers in the spectral library
used for deconvolution.
There is no evidence in the various spectra of
Bounce Rock for detectable quantities of minor
Fe-bearing phases, such as ilmenite, chromite,
ulvo?spinel, or pyrrhotite, which are typically present in
Martian meteorites. Small amounts of Fe3+ in Bounce
Rock MB spectra have been noted by Morris et al.
(2006b) who interpreted the Fe3+ component as
nanophase ferric oxide, which is also identi?ed in
surrounding soil and dust. This species is a valid choice
because all analyzed natural surfaces, i.e., dust-covered,
have higher amounts of Fe3+ than the abraded target
Case. However, if the Fe3+ was exclusively from surface
dust, it should also show an enhanced abundance in the
6 keV spectra of all natural targets (Table 2). A
signi?cant difference was only observed for target
Maggie. Therefore, one additional spectrum, Maggie
(Maggie [red] in Table 2 and Fig. 12) was obtained at
increased resolution (reduced velocity) over the energy
range of the pyroxene feature. The MB parameters of
the Fe3+ doublet derived from this spectrum differ from
those of nanophase ferric oxide reported by Morris
et al. (2006b), but are similar to those reported for
Fe3+ in whole rock samples and pyroxene separates of
Martian meteorites, and basaltic shergottites in
particular (Dyar 2003). Therefore, it is also possible that
the Fe3+ is inherent to the pyroxene.
Normative mineralogy calculations from APXS
bulk chemical data from Case (Table 3) show that
Bounce Rock has a pyroxene-normative composition,
with 57 wt% pyroxene distributed in about equal
amounts to high-Ca pyroxene (diopside) and low-Ca
pyroxene (hypersthene). Plagioclase, calculated as albite
and anorthite, sums to about 35.5%. Minor phases
include ilmenite, chromite and apatite. Excess SiO2
leads to calculation of free quartz.
Bounce Rock has a mineral norm that agrees well
with those of lithology B of EETA79001 and QUE
94201, re?ecting its close chemical relationship to these
meteorites. Albite and anorthite normative values agree
well with these two meteorites and are unlike those
calculated for Zagami and Shergotty, two basaltic
shergottites with cumulus pyroxene. A major difference,
however, is the low abundance of ilmenite (not detected
by MB), which re?ects low TiO2 and FeO bulk-rock
concentrations in Bounce Rock. The higher diopside
component, if compared to EETA79001, re?ects the
high CaO concentration in Bounce Rock. No normative
olivine was calculated, which is also the case for
EETA79001 and Shergotty but not for QUE 94201 and
Zagami. The reason for the olivine-normative
composition of QUE 94201 is the lack of P2O5
concentrations in published data sets (Lodders 1998). If
we assume a P2O5 concentration of 2 wt% in QUE
94201 (Mittlefehldt, unpublished data) the mineral norm
would be olivine-free (and slightly quartz-normative)
because normally P combines with Ca in apatite.
Without P, the Ca that would normally be assigned to
apatite is assigned to high-Ca pyroxene, which in turn
has the effect of reducing the amount of normative
hypersthene and increasing the amount of normative
olivine.
We emphasize that normative mineralogy
calculations mainly are intended to characterize and
compare the bulk chemical composition of rocks in
terms of a standard set of minerals. The resulting
normative mineralogy and mineral proportions do not
necessarily re?ect the true modal mineralogy of a rock,
although they may be similar if the rock is composed of
the same mineral assemblage as the standard set of
normative minerals.
Pyroxene Mineralogy
Basaltic shergottites EETA79001 lithology B and
QUE 94201 have pyroxene grains with Mg-rich
pigeonite cores (En64Fs26Wo10 and En62Fs30Wo8,
respectively) mantled by minor Mg-rich augite
(En46Fs22Wo32 and En44Fs20Wo36, respectively), and
commonly extremely Fe-rich pigeonite rims
(En9Fs76Wo15 and En5Fs81Wo14, respectively)
(Mikouchi et al. 1999). In Shergotty and Zagami,
Piece of shatter cone, Kentland, Indiana
Bounce Rock, 
Meridiani Planum
a
b
c
Fig. 10. Bounce Rock surface textures compared to texture of
a rock from a terrestrial impact structure exhibiting shatter-
cone texture. The surface of Bounce Rock appears fragile as it
shows loose material and many fractures. a) Shatter cone from
Kentland impact structure, Indiana (rock is dolomite). Scale
bar is 3 cm. Photo of Kentland specimen courtesy of Amir
Sagy. b) Bounce Rock (target ??Fips??) MI image, sol 67,
P2956. c) Bounce Rock (target ??Achsel??) MI image, sol 65,
P2956. All three images are shown at approximately the same
scale.
10 J. Zipfel et al.
pigeonite and augite occur as separate grains in about
equal proportions and are zoned from Mg-rich cores to
Fe-rich rims.
Christensen et al. (2004) compared the Mini-TES
spectrum of Bounce Rock to a laboratory spectrum of
EETA79001 lithology B (Bishop and Hamilton 2001).
They also showed spectra and proportions of mineral
endmembers selected from a spectral library that were
used in deconvolution to model the measured data.
The two measured spectra exhibit opposite slopes in
the wavenumber range from 1150 to 800 cm)1. Overall
the spectrum of Bounce Rock has a negative slope and
that of EETA79001 lithology B has a positive slope.
In comparison, the spectrum derived from a synthetic
pigeonite used in the deconvolution of the spectrum of
EETA79001 lithology B shows a positive slope and
four characteristic minima. In the Bounce Rock
spectrum, these minima are present; however, because
of the overall negative slope no pigeonite endmember
was selected in the deconvolution of this spectrum
(Christensen et al. 2004). Perhaps, the synthetic
pigeonite spectral endmember in the mineral spectral
library did not have the appropriate composition. This
possibility was also considered when Mini-TES results
were compared to results of in situ instruments on
rover Spirit in Gusev crater (Ruff et al. 2006;
Fig. 11. Element variation diagrams versus MgO wt% of all Bounce Rock analyses and selected basaltic shergottites; LA = Los
Angeles (G. Dreibus, unpublished data), QUE = QUE 94201 (Lodders 1998), EETA79001, lithology B = EET_B1 (Lodders
1998) and EET_B2 (Banin et al. 1992), Sh = Shergotty (Lodders 1998), N856 = NWA 856 (Jambon et al. 2002),
N480 = NWA 480 (Barrat et al. 2002), Z = Zagami (Lodders 1998). Trend lines are best-?t lines through basaltic shergottites.
For comparison, Path?nder soil-free rock (Bru?ckner et al. 2003), Gusev basalts (Gellert et al. 2006), and one S-rich rock at
Meridiani Planum (Rieder et al. 2004) are shown.
-4 -3 -2 -1 0 1 2 3 4
0,98
1,00
1,02
1,04
1,06
1,08
1,10
1,12
In
te
ns
ity
 (c
ou
nt
s/
ba
se
lin
e)
Velocity (mm/s)
 Pyroxene, M2
 Pyroxene, M1
 Fe3+
 least squares fit
 MB data
Fig. 12. Fitted Mo?ssbauer spectrum of sol 070 Bounce Rock
target Maggie (14 keV; see Table 2). The spectrum is a sum of
?ve temperature bins over a temperature range from 200 to
250 K.
Bounce Rock 11
McSween et al. 2008). Additionally, a negative slope in
the Bounce Rock spectrum may be caused by
plagioclase ?pyroxene ratios and ?or pigeonite ?augite
ratios different from those of EETA79001 lithology B
(Wright 2007).
Mo?ssbauer data permit us to constrain the
pyroxene mineralogy in more detail. Spectra of Bounce
Rock are dominated by two pyroxene doublets. Major
cations in pyroxenes Ca, Mg, and Fe2+ occupy the
centers of two nonequivalent oxygen octahedra,
designated M1 and M2, with Fe2+ having a preference
for M2. The distribution of Fe2+ between M1 and M2
can be derived by the distinct temperature dependence
of a MB parameter, DEQ, which is the quadrupole
splitting de?ned as the distance between peak centers of
a doublet. In the temperature range between 200 and
300 K, DEQ for M1 decreases much faster with
increasing temperature than DEQ for M2 (e.g., Regnard
et al. 1987; Eeckhout et al. 2000; De Grave and
Eeckhout 2003; Eeckhout and De Grave 2003). On
Bounce Rock, MB spectra of four targets (Glanz2,
Case, Fips2, and Maggie) were collected over diurnal
Table 4. Mo?ssbauer parameters of Bounce Rock compared to other basaltic shergottites.
Bounce
Rock
Glanz2
Bounce
Rock
Case
Bounce
Rock
Fips2
Bounce
Rock
Maggie
EETA79001
Lith. B
QUE
94201a Shergottya Zagamia
Los
Angelesa
Fe2+ pyroxene M1
db
(mm s)1)
1.16c 1.17c 1.16c 1.16c 1.17 1.16 1.18 1.18 1.17
DEQ
d
(mm s)1)
2.67 2.59 2.63 2.63 2.52 2.64 2.61 2.58 2.54
Ae
(%)
29c 25c 26c 26c 27 24.1 16.6 13 43.3
Fe2+ pyroxene M2
d
(mm s)1)
1.14c 1.14c 1.14c 1.14c 1.14 1.14 1.15 1.15 1.14
DEQ
(mm s)1)
2.04 2.02 2.07 2.06 2.03 2.01 2.11 1.96 1.96
A
(%)
69c 74c 72c 69c 73 52.0 27.8 23.1 42.7
Fe2+
d
(mm s)1)
? ? ? ? ? 1.13 ? 1.15 1.12
DEQ
(mm s)1)
? ? ? ? ? 1.77 ? 2.05 1.40
A
(%)
? ? ? ? ? 16.3 ? 62.0 4.4
Oxide
d
(mm s)1)
? ? ? ? ? 0.94 1.07 ? 0.96
DEQ
(mm s)1)
? ? ? ? ? 1.03 0.76 ? 0.79
A
(%)
? ? ? ? ? 3.3 2.4 ? 6.6
Fe3+
d
(mm s)1)
[0.47] [0.47] [0.47] [0.47] ? 0.47 0.55 0.46 0.48
DEQ
(mm s)1)
[0.67] [0.67] [0.67] [0.67] ? 0.65 0.82 0.66 0.69
A
(%)
2c 1c 2c 4c ? 4.3 3.4 1.9 3.0
Note: Values in square brackets were ?xed during ?tting procedure.
aValues from Dyar (2003), whole rock samples.
bCenter shift, relative to a-Fe. Uncertainty is ?0.02 mm s)1.
cAverage value from individual temperature window ?ts.
dQuadrupole splitting. Uncertainty is ?0.02 mm s)1.
eRelative subspectral area, f-factor corrected with f(Fe3+) ? f(Fe2+) = 1.21 (cf. Morris et al. 2006b). Uncertainty is ?2%.
12 J. Zipfel et al.
temperature ranges from 200 to 260 K. All spectra were
split into individual temperature bins 10 K wide and
analyzed separately. Although theoretically the
temperature behavior of DEQ is not strictly linear (cf.
Eeckhout et al. 2000; Eeckhout and De Grave 2003; De
Grave and Eeckhout 2003 for details), we applied linear
regression and extrapolated to 295 K to obtain
approximate values of DEQ. This allows us to compare
our data to MB parameters reported for pyroxenes in
Martian meteorites, which are generally obtained at
room temperature, and we ?nd good agreement
(Table 4). The dominant doublet in spectra from
Bounce Rock arises from Fe2+ sited in M2, which is
preferentially occupied by Ca in high-Ca pyroxenes.
This result indicates therefore the predominance of
pyroxene with intermediate to low Ca. By analogy with
the Martian meteorites this is most likely pigeonite. The
minor doublet results from Fe sited in M1 in a high-Ca
pyroxene (most likely augite) and ?or pigeonite (Fig. 13;
Tables 4 and 5). Proportions of relative subspectral
areas derived for pyroxenes in target Case, as well as
for other surface targets, are in excellent agreement with
those of EETA79001 lithology B and are consistent
with those of QUE 94201. Pyroxenes in the Shergotty,
Zagami, and Los Angeles meteorites have clearly
different MB parameters (Table 4).
Relationship to Martian Meteorites and Mars
Martian meteorites are igneous basaltic and
ultrama?c rocks that indicate formation by partial
melting of evolved source regions with broadly similar
compositions (McSween and Treiman 1998). They are
linked together by an oxygen isotopic composition
fractionated in a common reservoir (Clayton and
Mayeda 1996) and by other geochemical characteristics.
The subgroup of basaltic shergottites comprises basalts
with clinopyroxenes, both pigeonite and augite, as
major minerals.
Bounce Rock?s texture is compatible with that of an
igneous rock. It has a pyroxene mineralogy comparable
to that of some basaltic shergottites. Its chemical
composition is compatible with that of an igneous
basalt on the basis of total alkalis versus SiO2 (Le Bas
et al. 1986). As pointed out above, Bounce Rock is very
similar in bulk composition to two basaltic shergottites,
lithology B of EETA79001 and QUE 94201.
Certain geochemical properties deduced from the
composition of basaltic rocks among meteorites, lunar,
and terrestrial samples are widely used to characterize
material from distinct planetary bodies (e.g., Dreibus
and Wa?nke 1985; Drake et al. 1989). One of the
distinguishing geochemical properties is that the
compatible elements remain mostly unfractionated
during igneous processes and therefore constrain the
chemical composition of the mantle source.
Phosphorous and Fe concentrations, and Ca ?Al and
Fe ?Mn weight ratios in basaltic shergottites (Table 1)
were compared to basalts from Earth, Moon, and the
presumed parent body for HEDs (howardites, eucrites,
and diogenites), Vesta, and were used to de?ne Mars-
typical properties (see also McSween et al. 2009).
Bounce Rock and olivine-rich basalts analyzed at Gusev
crater and Path?nder soil-free rock have such Mars-
typical properties (Figs. 14 and 15). This consistency is
a direct indicator that Bounce Rock and Martian
meteorites are indeed derived from Mars.
Origin of Bounce Rock
On the basis of our ?ndings, we propose that
Bounce Rock is a fragmented rock ejected from an
impact on Mars that was not accelerated suf?ciently to
leave Mars? gravity ?eld. It is a decimeter-sized rock
that is mainly composed of silicates and has chemical
properties characteristic of Mars (e.g., Fe ?Mn ratio).
Therefore, it appears unlikely that Bounce Rock, itself,
is a meteorite. The thin atmosphere on Mars does not
suf?ciently slow incoming objects of such masses to
prevent them from shattering upon impact (Bland and
Smith 2000). In fact, the only ??exotic rocks?? of
200 210 220 230 240 250 260 270 280 290 300
1,9
2,0
2,1
2,2
2,3
2,4
2,5
2,6
2,7
2,8
2,9
??E
Q 
(m
m
/s
)
Temperature (K)
 Glanz2
 Case
 Fips2
 Maggie
Fig. 13. Temperature dependence of the quadrupole splitting
DEQ for the two Fe
2+ doublets assigned to pyroxene in four
different targets on Bounce Rock. Symbols are placed in the
center of each temperature window and horizontal error bars
represent the width of each temperature window. The doublet
with larger DEQ shows a pronounced temperature dependence
whereas the DEQ of the other doublet remains more or less
stable. This feature is consistent with the larger DEQ doublet
arising from Fe2+ in pyroxene M1 positions and the other
doublet arising from Fe2+ in the pyroxene M2 site. Linear
regressions for Glanz2: solid line; Case: dashed; Fips2: dotted;
Maggie: dash-dot.
Bounce Rock 13
T
ab
le
5.
T
em
pe
ra
tu
re
-d
ep
en
de
nt
M
o?s
sb
au
er
pa
ra
m
et
er
s
ob
ta
in
ed
fr
om
fo
ur
ta
rg
et
s
on
B
ou
nc
e
R
oc
k.
T
ar
ge
t
M
B
pa
r.
P
yr
ox
en
e
M
2
T
em
pe
ra
tu
re
bi
ns
(K
)
P
yr
ox
en
e
M
1
T
em
pe
ra
tu
re
bi
ns
(K
)
O
ct
ah
ed
ra
l
F
e3
+
T
em
pe
ra
tu
re
bi
ns
(K
)
20
0?
21
0
21
0?
22
0
22
0?
23
0
23
0?
24
0
24
0?
25
0
25
0?
26
0
20
0?
21
0
21
0?
22
0
22
0?
23
0
23
0?
24
0
24
0?
25
0
25
0?
26
0
20
0?
21
0
21
0?
22
0
22
0?
23
0
23
0?
24
0
24
0?
25
0
25
0?
26
0
G
la
nz
2
da (m
m
s)
1 )
1.
13
1.
13
1.
14
1.
14
1.
14
1.
15
1.
16
1.
16
1.
16
1.
17
1.
16
1.
17
[0
.4
7]
[0
.4
7]
[0
.4
7]
[0
.4
7]
[0
.4
7]
[0
.4
7]
D
E
Q
b
(m
m
s)
1 )
2.
03
2.
03
2.
06
2.
03
2.
03
2.
04
2.
75
2.
75
2.
79
2.
72
2.
74
2.
70
[0
.6
7]
[0
.6
7]
[0
.6
7]
[0
.6
7]
[0
.6
7]
[0
.6
7]
C
c
(m
m
s)
1 )
0.
42
0.
42
0.
44
[0
.4
4]
0.
44
[0
.4
4]
0.
37
0.
39
0.
38
[0
.3
8]
0.
40
[0
.3
8]
[0
.3
5]
[0
.3
5]
[0
.3
5]
[0
.3
5]
[0
.3
5]
[0
.3
5]
A
d
(%
)
67
65
71
67
72
74
31
33
27
32
26
24
2
3
1
1
2
2
C
as
e
da (m
m
s)
1 )
1.
14
1.
14
1.
14
1.
14
1.
15
1.
15
1.
16
1.
16
1.
16
1.
17
1.
20
1.
19
[0
.4
7]
[0
.4
7]
[0
.4
7]
[0
.4
7]
[0
.4
7]
[0
.4
7]
D
E
Q
(m
m
s)
1 )
2.
07
2.
06
2.
06
2.
04
2.
07
2.
03
2.
80
2.
76
2.
78
2.
76
2.
74
2.
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14 J. Zipfel et al.
comparable or larger size encountered in Meridiani
Planum are iron meteorites, e.g., Heatshield Rock,
Block Island, Shelter Island, and Mackinac Island,
which all have much higher strength (Schro?der et al.
2008; Fleischer et al. 2010).
Here, we speculate about the size and location of a
potential source crater. The observation of a shatter-
cone-like surface and the relative weakness of the rock
compared to other basalts on Mars (both of which may
point toward the rock having been shocked) taken
together with its isolated occurrence on the hematite-
rich plains indicate that it was ejected from an impact
crater in the Meridiani region or nearby. Eagle crater
and Endurance crater are about 22?130 m in diameter,
respectively, and are located closest to Bounce Rock.
However, these craters are not the source of Bounce
Rock. In both of these craters, the only rocks exposed
on the crater walls and ?oors are sulfate-rich
sandstones. Although Endurance crater may have
excavated to a depth of several tens of meters?greater
than the current depth of the crater?orbital data
suggest that the sediments at the Meridiani site are
hundreds of meters in thickness (Hynek et al. 2002).
Even Victoria crater, which is several km from Bounce
Rock and approximately 800 m in diameter, does not
appear to have excavated completely through the
Meridiani sediments (Squyres et al. 2009).
Model calculations (Head et al. 2002) show that
impactors about 150 m in diameter producing craters of
approximately 3 km may accelerate fragments in the
decimeter size range to velocities higher than the Mars
escape velocity of 5 km s)1. Using fall statistics and
crystallization ages, volume and estimated soil thickness
at an assumed target site, Head et al. (2002) further
inferred that source craters for EETA79001 and the
other shergottites could have been as small as 3?4 km
Fig. 15. Concentrations of P (in ppm) versus Fe (in wt%) in
basalts from Earth, Moon, HEDs, and basaltic shergottites.
Bounce Rock and other basalts analyzed on Mars have
properties that are taken to be typical of Mars as de?ned by
analysis of the Martian meteorites. Data for terrestrial basalts
are taken from GEOROC; data for Moon and HEDs from
BVSP (1981); other data sources are given in Fig. 11.
Fig. 14. Bounce Rock and other rocks on Mars have bulk
Fe ?Mn atomic ratios similar to those of basaltic, olivine-
phyric, and lherzolitic shergottites. Data sources are given in
Fig. 11. Compositions of terrestrial MORB glasses from
basalts with SiO2 between 45 and 52 wt% are shown for
comparison (data source GEOROC at http://georoc.mpch-
mainz.gwdg.de/georoc/).
Fig. 16. Image of Meridiani Planum taken with the thermal
emission imaging system on the Mars Odyssey orbiter. This
image shows the estimated landing ellipse for MER-B at
Meridiani Planum and big craters in the vicinity. Rays of
impact ejecta emanate from Bopolu, the large crater (19 km
diameter) southwest of Eagle crater. Bounce Rock, found
directly next to Eagle crater, falls on the extension of a ray at
about 75 km from Bopolu crater. Bedrock studied by the
rover Opportunity in Victoria, Eagle, and Endurance craters
are S-rich.
Bounce Rock 15
diameter. Such material must have been ejected in close
proximity to the impactor?s edge from within the crater.
Material more distant from ground zero, yet still within
the crater, may have been ejected at spall velocities too
low to leave Mars? gravity ?eld. Therefore, we might
expect a signi?cant fraction of ejected material from
relatively small craters to scatter over the surface of
Mars. As pointed out by Head et al. (2002), the range
in exposure ages and the lack of 2p exposure make it
unlikely that a single crater is the source of all
shergottites.
Bounce Rock?s location within discontinuous rays
of a crater approximately 19 km in diameter and
located 75 km to the southwest at 2.95S and 6.33W
(Fig. 16) makes this crater a possible candidate (Squyres
et al. 2004b). In 2006, this crater was of?cially named
Bopolu. Its size easily exceeds the minimum size of a
crater needed to launch material from Mars (Melosh
1984; Head et al. 2002). Additional evidence that
Bopolu may be the source crater for Bounce Rock
comes from TES data mapping of the hematite
distribution at Meridiani Planum. Unlike its
surroundings, Bopolu crater samples material that is not
hematite rich (Hamilton et al. 2003). These authors
further screened TES data for potential source craters
for Martian meteorites by taking TES spectra of Los
Angeles, Zagami, ALHA77005, Nakhla, ALH 84001,
and Chassigny as representative endmembers. Although
Bopolu did not register as a source match for Los
Angeles or Zagami material in a TES deconvolution,
neither did any other crater on Mars. It is of course
possible that the source rocks for these materials are
distributed on a scale that is below that of TES
resolution. Although the TES results leave the identity
of a potential source crater in question, Bopolu as the
source crater for Bounce Rock is the simplest
interpretation.
CONCLUSIONS
Bounce Rock is unique on the plains of Meridiani
in many respects. At Meridiani, Planum rocks are
typically exposed inside craters and are very S-rich and
of sedimentary origin. The texture, mineralogy, and
chemistry of Bounce Rock, however, indicate an
igneous origin. Bounce Rock has a pyroxene-rich
mineralogy as deduced from Mini-TES and Pancam
spectra, Mo?ssbauer analyses, and APXS bulk
compositional data. Although there is some
disagreement between instrument results about the
composition of pyroxenes in Bounce Rock the pyroxene
content is clearly high, approximately 55 vol%
according to Mini-TES results. Fits to Mini-TES
spectra are consistent with the pyroxene consisting
mostly of Ca-rich clinopyroxene. Mo?ssbauer data, on
the other hand, indicate a predominance of medium- to
low-Ca pyroxene (pigeonite), with subordinate high-Ca
pyroxene (augite), similar to the pyroxene in lithology B
of EETA79001 and QUE 94201. A relationship to these
two basaltic shergottites is strongly indicated by Bounce
Rock?s bulk chemistry determined by the APXS.
Possible shock features support the interpretation that
Bounce Rock is a piece of distal impact ejecta, and
Bopolu crater (19 km diameter), located 75 km to the
southwest, is the most likely source crater. In Bounce
Rock, a rock with the characteristic Martian chemical
?ngerprint (e.g., Fe ?Mn ratio and P concentration) and
a shergottite-like bulk composition has been analyzed
for the ?rst time on Mars. This ?nding provides
additional direct evidence of a Martian origin for the
shergottite meteorites.
Acknowledgments?The authors thank the Meteorite
Working Group and the curator for Antarctic
meteorites, Kevin Righter, for loan of an unpolished
butt of EETA79001. Some of this research was carried
out at and for the Jet Propulsion Laboratory,
California Institute of Technology, sponsored by the
National Aeronautics and Space Administration. This
article has bene?tted greatly from reviews of an earlier
version of the manuscript by Phil Bland, Cyrena
Goodrich, Takashi Mikouchi, Deon van Niekerk, and
Larry Nittler. We also thank M. Schmidt, E. Walton,
and Alan Treiman for their reviews.
Editorial Handling?Dr. Alan Treiman
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