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Title: Using ChemCam LIBS data to constrain grain size in rocks on Mars: Proof of concept and application to rocks at Yellowknife Bay and Pahrump Hills, Gale crater

Abstract

Grain size in martian sedimentary rocks can be constrained using point-to-point chemical variabilities in Laser Induced Breakdown Spectroscopy (LIBS) data from the ChemCam instrument on the Mars Science Laboratory (MSL) Curiosity rover. The diameter of each point ablated by the ChemCam laser is in the range of medium to coarse sand in size. Thus, rocks with grains significantly smaller than the laser spot size produce bulk rock compositions at each LIBS point and low point-to-point chemical variability among LIBS points. In contrast, analyses of rocks with grains about the size of the spot or larger contain contributions from individual grains at each point and often have high point-to-point chemical variability. Here the Gini index, a statistical parameter, was used to calculate the point-to-point chemical variability in major-element oxide compositions derived from the ChemCam LIBS data. First, the total range of each LIBS major-element oxide composition was normalized from 0 to 1 across all LIBS observations. Then the Gini index was calculated for each oxide in each LIBS observation. Finally, the Gini indices of each oxide were averaged to derive a Gini index mean score, G MEAN, for each LIBS observation. A correlation between G MEAN and grain size was validatedmore » using sedimentary rocks of various grain sizes from the Yellowknife Bay formation and the Pahrump Hills member of the Murray formation in Gale crater. Overall, finer-grained rocks had smaller G MEAN than coarser-grained rocks. To calibrate G MEAN to grain size, grain size estimates based on visual assessment of high-resolution images were compared to G MEAN values for the same targets to create a calibrated scale. This calibrated scale was used to infer the grain size of rocks with unknown grain size. Overall, the grain sizes predicted for rocks with unknown grain size overlapped with those of known grain size from the same units and/or bedrock targets. The grain sizes inferred using the G MEAN based on ChemCam LIBS data are complimentary to those determined from images and both techniques can be used to improve interpretations of the depositional environments of rocks analyzed by Curiosity and future Mars missions with LIBS, such as the Mars 2020 rover.« less

Authors:
ORCiD logo [1]; ORCiD logo [2];  [3];  [4]; ORCiD logo [5]; ORCiD logo [6];  [7];  [2];  [3]; ORCiD logo [5]; ORCiD logo [8];  [5]
  1. Univ. of California, Davis, CA (United States). Dept. of Earth and Planetary Sciences; Dartmouth College, Hanover, NH (United States). Dept. of Earth Sciences
  2. Univ. of California, Davis, CA (United States). Dept. of Earth and Planetary Sciences
  3. Univ. of Nantes (France). Lab. of Planetology and Geodynamics
  4. California Inst. of Technology (CalTech), Pasadena, CA (United States). Jet Propulsion Lab.
  5. Univ. of Toulouse (France). Research Inst. in Astrophysics and Planetology (IRAP)
  6. Univ. of New Mexico, Albuquerque, NM (United States). Inst. of Meteoritics. Dept. of Earth and Planetary Sciences
  7. Univ. of Florida, Gainesville, FL (United States). Dept. of Geological Sciences
  8. Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
Publication Date:
Research Org.:
Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
Sponsoring Org.:
USDOE; National Aeronautic and Space Administration (NASA); National Centre for Space Studies (CNES) (France)
OSTI Identifier:
1482015
Report Number(s):
LA-UR-18-28846
Journal ID: ISSN 0019-1035
Grant/Contract Number:  
AC52-06NA25396
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
Icarus
Additional Journal Information:
Journal Volume: 321; Journal ID: ISSN 0019-1035
Publisher:
Elsevier
Country of Publication:
United States
Language:
English
Subject:
58 GEOSCIENCES; Planetary Sciences

Citation Formats

Rivera-Hernández, Frances, Sumner, Dawn Y., Mangold, Nicolas, Stack, Kathryn M., Forni, Olivier, Newsom, Horton, Williams, Amy, Nachon, Marion, L'Haridon, Jonas, Gasnault, Olivier, Wiens, Roger, and Maurice, Sylvestre. Using ChemCam LIBS data to constrain grain size in rocks on Mars: Proof of concept and application to rocks at Yellowknife Bay and Pahrump Hills, Gale crater. United States: N. p., 2018. Web. doi:10.1016/j.icarus.2018.10.023.
Rivera-Hernández, Frances, Sumner, Dawn Y., Mangold, Nicolas, Stack, Kathryn M., Forni, Olivier, Newsom, Horton, Williams, Amy, Nachon, Marion, L'Haridon, Jonas, Gasnault, Olivier, Wiens, Roger, & Maurice, Sylvestre. Using ChemCam LIBS data to constrain grain size in rocks on Mars: Proof of concept and application to rocks at Yellowknife Bay and Pahrump Hills, Gale crater. United States. doi:10.1016/j.icarus.2018.10.023.
Rivera-Hernández, Frances, Sumner, Dawn Y., Mangold, Nicolas, Stack, Kathryn M., Forni, Olivier, Newsom, Horton, Williams, Amy, Nachon, Marion, L'Haridon, Jonas, Gasnault, Olivier, Wiens, Roger, and Maurice, Sylvestre. Tue . "Using ChemCam LIBS data to constrain grain size in rocks on Mars: Proof of concept and application to rocks at Yellowknife Bay and Pahrump Hills, Gale crater". United States. doi:10.1016/j.icarus.2018.10.023.
@article{osti_1482015,
title = {Using ChemCam LIBS data to constrain grain size in rocks on Mars: Proof of concept and application to rocks at Yellowknife Bay and Pahrump Hills, Gale crater},
author = {Rivera-Hernández, Frances and Sumner, Dawn Y. and Mangold, Nicolas and Stack, Kathryn M. and Forni, Olivier and Newsom, Horton and Williams, Amy and Nachon, Marion and L'Haridon, Jonas and Gasnault, Olivier and Wiens, Roger and Maurice, Sylvestre},
abstractNote = {Grain size in martian sedimentary rocks can be constrained using point-to-point chemical variabilities in Laser Induced Breakdown Spectroscopy (LIBS) data from the ChemCam instrument on the Mars Science Laboratory (MSL) Curiosity rover. The diameter of each point ablated by the ChemCam laser is in the range of medium to coarse sand in size. Thus, rocks with grains significantly smaller than the laser spot size produce bulk rock compositions at each LIBS point and low point-to-point chemical variability among LIBS points. In contrast, analyses of rocks with grains about the size of the spot or larger contain contributions from individual grains at each point and often have high point-to-point chemical variability. Here the Gini index, a statistical parameter, was used to calculate the point-to-point chemical variability in major-element oxide compositions derived from the ChemCam LIBS data. First, the total range of each LIBS major-element oxide composition was normalized from 0 to 1 across all LIBS observations. Then the Gini index was calculated for each oxide in each LIBS observation. Finally, the Gini indices of each oxide were averaged to derive a Gini index mean score, GMEAN, for each LIBS observation. A correlation between GMEAN and grain size was validated using sedimentary rocks of various grain sizes from the Yellowknife Bay formation and the Pahrump Hills member of the Murray formation in Gale crater. Overall, finer-grained rocks had smaller GMEAN than coarser-grained rocks. To calibrate GMEAN to grain size, grain size estimates based on visual assessment of high-resolution images were compared to GMEAN values for the same targets to create a calibrated scale. This calibrated scale was used to infer the grain size of rocks with unknown grain size. Overall, the grain sizes predicted for rocks with unknown grain size overlapped with those of known grain size from the same units and/or bedrock targets. The grain sizes inferred using the GMEAN based on ChemCam LIBS data are complimentary to those determined from images and both techniques can be used to improve interpretations of the depositional environments of rocks analyzed by Curiosity and future Mars missions with LIBS, such as the Mars 2020 rover.},
doi = {10.1016/j.icarus.2018.10.023},
journal = {Icarus},
issn = {0019-1035},
number = ,
volume = 321,
place = {United States},
year = {2018},
month = {10}
}

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