Paper No. 12
Presentation Time: 11:05 AM
THE CHEMCAM INVESTIGATION: COMPOSITIONS AT THE CURIOSITY ROVER LANDING SITE
WIENS, Roger C., Los Alamos National Laboratory, P.O. Box 1663, MS J565, Los Alamos, NM 87545, MAURICE, Sylvestre, Institut de Recherche en Astrophysique et Planetologie, Toulouse, 31028, France and TEAM, MSL Science, Jet Propulsion Laboratory, Pasadena, CA 91101, rwiens@lanl.gov
The Mars Science Laboratory rover, Curiosity, is equipped with an instrument suite named ChemCam, designed for small-footprint elemental composition analysis and context imaging at distances within 7 m of the rover. ChemCam employs laser-induced breakdown spectroscopy (LIBS) to interrogate spots ≤ 0.5 mm diameter at these distances using focused ~15 mJ pulses which ablate material in electronically excited states, emitting photons at wavelengths that are unique for each element. ChemCam’s 240-850 nm spectral range was selected to observe emissions of all elements including H, C, N, and O as well as Li, Be, and B. LIBS is highly sensitive to alkali and alkaline earth elements but has relatively poor sensitivity to halides and sulfur. The Mars atmosphere interferes with C and N observations but does not prevent detection at sufficient (several %) levels.
ChemCam’s LIBS analyses are semi-quantitative, as abundance determinations rely on comparison with training-set spectra and cross calibration with APXS. Key features of the technique as applied to field geology on Mars are the ability to remove surface dust with repeated laser pulses at the same location and to probe samples for surface coatings or weathering rinds. Depth profiling proceeds at a rate of approximately one micron per pulse for many rocks, and ChemCam can profile up to a few cm into unconsolidated soils. Line scans and rasters can be used to determine sample heterogeneity or to walk up a sequence of layers.
Gale Crater was selected as the Curiosity landing site based on the 5 km of sedimentary strata that comprises Mt. Sharp at the center of the crater and based on the evidence for flowing and potentially standing water within and near the landing ellipse. The actual landing site is within 400 m of a junction of several different geological terrains having differing thermal inertias and elevations, suggesting the potential for interesting targets for study early in the mission.
