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Browsing by Author "Lawrence, David J."

Browsing by Author "Lawrence, David J."

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  • Analysis of MESSENGER Gamma-Ray Spectrometer data from the Mercury flybys 
    Rhodes, Edgar A.; Evans, Larry G.; Nittler, Larry R.; Starr, Richard D.; Sprague, Ann L.; Lawrence, David J.; McCoy, Timothy J.; Stockstill-Cahill, Karen R.; Goldsten, John O.; Peplowski, Patrick N.; Hamara, David K.; Boynton, William V.; Solomon, Sean C. (2011)
    [alpha]bstract<br/>During its three flybys of Mercury, the MESSENGER spacecraft made the first detection of gamma-ray emission from the planet&#39;s surface. With a closest approach distance of ~200 km, the flybys provided ...
  • Chlorine on the Surface of Mercury: MESSENGER Gamma-Ray Measurements and Implications for the Planet s Formation and Evolution 
    Evans, Larry G.; Peplowski, Patrick N.; McCubbin, Francis M.; McCoy, Timothy J.; Nittler, Larry R.; Zolotov, Mikhail Yu; Ebel, Denton S.; Lawrence, David J.; Starr, Richard D.; Weider, Shoshana Z.; Solomon, Sean C. (2015)
    Orbital measurements obtained by the MESSENGER Gamma-Ray Spectrometer have been analyzed to determine the surface abundance of chlorine in Mercury s northern hemisphere. The derived Cl/Si mass ratio is 0.0057 ± 0.001, which ...
  • Constraints on the abundance of carbon in near-surface materials on Mercury: Results from the MESSENGER Gamma-Ray Spectrometer 
    Peplowski, Patrick N.; Lawrence, David J.; Evans, Larry G.; Klima, Rachel L.; Blewett, David T.; Goldsten, John O.; Murchie, Scott L.; McCoy, Timothy J.; Nittler, Larry R.; Solomon, Sean C.; Starr, Richard D.; Weider, Shoshana Z. (2015)
    Mercury&#39;s low surface reflectance and the low surface abundances of iron and titanium have led to the suggestion that carbon (C) may serve as the dominant darkening agent on Mercury&#39;s surface. Estimates of the ...
  • Elemental Mapping by Dawn Reveals Exogenic H in Vesta&#39;s Regolith 
    Prettyman, Thomas H.; Mittlefehldt, David W.; Yamashita, Naoyuki; Lawrence, David J.; Beck, Andrew W.; Feldman, William C.; McCoy, Timothy J.; McSween, Harry Y.; Toplis, Michael J.; Titus, Timothy N.; Tricarico, Pasquale; Reedy, Robert C.; Hendricks, John S.; Forni, Olivier; Le Corre, Lucille; Li, Jian-Yang; Mizzon, Hugau; Reddy, Vishnu; Raymond, Carol A.; Russell, Christopher T. (2012)
    Using Dawn&#39;s Gamma Ray and Neutron Detector, we tested models of Vesta&#39;s evolution based on studies of howardite, eucrite, and diogenite (HED) meteorites. Global Fe/O and Fe/Si ratios are consistent with HED ...
  • Enhanced sodium abundance in Mercury's north polar region revealed by the MESSENGER Gamma-Ray Spectrometer 
    Peplowski, Patrick N.; Evans, Larry G.; Stockstill-Cahill, Karen; Lawrence, David J.; Goldsten, John O.; McCoy, Timothy J.; Nittler, Larry R.; Solomon, Sean C.; Sprague, Ann L.; Starr, Richard D.; Weider, Shoshana Z. (2014)
    Abstract MESSENGER Gamma-Ray Spectrometer measurements demonstrate that the abundance of Na varies across the surface of Mercury. The maximum Na/Si abundance ratio of 0.20 ± 0.03 by weight (~5 wt% Na) is observed at high ...
  • Identification and Measurement of Neutron-absorbing Elements on Mercury&#39;s Surface 
    Lawrence, David J.; Feldman, William C.; Goldsten, John O.; McCoy, Timothy J.; Blewett, David T.; Boynton, William V.; Evans, Larry G.; Nittler, Larry R.; Rhodes, Edgar A.; Solomon, Sean C. (2010)
    MESSENGER} Neutron Spectrometer {(NS)} observations of cosmic-ray-generated thermal neutrons provide the first direct measurements of Mercury&#39;s surface elemental composition. Specifically, we show that Mercury&#39;s ...
  • Major-element abundances on the surface of Mercury: Results from the MESSENGER Gamma-Ray Spectrometer 
    Evans, Larry G.; Peplowski, Patrick N.; Rhodes, Edgar A.; Lawrence, David J.; McCoy, Timothy J.; Nittler, Larry R.; Solomon, Sean C.; Sprague, Ann L.; Stockstill-Cahill, Karen R.; Starr, Richard D.; Weider, Shoshana Z.; Boynton, William V.; Hamara, David K.; Goldsten, John O. (2012)
    Orbital gamma-ray measurements obtained by the MESSENGER spacecraft have been analyzed to determine the abundances of the major elements Al, Ca, S, Fe, and Na on the surface of Mercury. The Si abundance was determined and ...
  • The Major-Element Composition of Mercury s Surface from MESSENGER X-ray Spectrometry 
    Nittler, Larry R.; Starr, Richard D.; Weider, Shoshana Z.; McCoy, Timothy J.; Boynton, William V.; Ebel, Denton S.; Ernst, Carolyn M.; Evans, Larry G.; Goldsten, John O.; Hamara, David K.; Lawrence, David J.; McNutt, Ralph L.; Schlemm, Charles E.; Solomon, Sean C.; Sprague, Ann L. (2011)
    X-ray fluorescence spectra obtained by the MESSENGER spacecraft orbiting Mercury indicate that the planet s surface differs in composition from those of other terrestrial planets. Relatively high Mg/Si and low Al/Si and ...
  • Radioactive Elements on Mercury s Surface from MESSENGER: Implications for the Planet s Formation and Evolution 
    Peplowski, Patrick N.; Evans, Larry G.; Hauck, Steven A.; McCoy, Timothy J.; Boynton, William V.; Gillis-Davis, Jeffery J.; Ebel, Denton S.; Goldsten, John O.; Hamara, David K.; Lawrence, David J.; McNutt, Ralph L.; Nittler, Larry R.; Solomon, Sean C.; Rhodes, Edgar A.; Sprague, Ann L.; Starr, Richard D.; Stockstill-Cahill, Karen R. (2011)
    The MESSENGER Gamma-Ray Spectrometer measured the average surface abundances of the radioactive elements potassium (K, 1150 ± 220 parts per million), thorium (Th, 220 ± 60 parts per billion), and uranium (U, 90 ± 20 parts ...
  • Return to Mercury: A Global Perspective on MESSENGER&#39;s First Mercury Flyby 
    Solomon, Sean C.; McNutt, Ralph L.; Watters, Thomas R.; Lawrence, David J.; Feldman, William C.; Head, James W.; Krimigis, Stamatios M.; Murchie, Scott L.; Phillips, Roger J.; Slavin, James A.; Zuber, Maria T. (2008)
    In January 2008, the MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) spacecraft became the first probe to fly past the planet Mercury in 33 years. The encounter revealed that Mercury is a dynamic ...
  • Variations in the abundances of potassium and thorium on the surface of Mercury: Results from the MESSENGER Gamma-Ray Spectrometer 
    Peplowski, Patrick N.; Lawrence, David J.; Rhodes, Edgar A.; Sprague, Ann L.; McCoy, Timothy J.; Denevi, Brett W.; Evans, Larry G.; Head, James W.; Nittler, Larry R.; Solomon, Sean C.; Stockstill-Cahill, Karen R.; Weider, Shoshana Z. (2012)
    A technique for converting gamma-ray count rates measured by the Gamma-Ray Spectrometer on the MESSENGER spacecraft to spatially resolved maps of the gamma-ray emission from the surface of Mercury is utilized to map the ...

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