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2015 Annual Science Report

SETI Institute Reporting  |  JAN 2015 – DEC 2015

Characterizing Carbonate Outcrops on Mars

Project Summary

Carbonate-rich rocks have been proposed for decades as a possible sink for a thicker CO2-rich atmosphere on early Mars. We are mapping new detections of carbonates in ancient (Noachian) rocks in several regions of the martian southern highlands. These rocks represent enticing astrobiological targets for understanding paleo-environments, habitability and carbon cycling via in situ study with a future landed mission.

4 Institutions
3 Teams
0 Publications
0 Field Sites
Field Sites

Project Progress

We have completed spectral and associated stratigraphic analysis of carbonate-bearing outcrops primarily in the Huygens crater and northwest Noachis Terra regions of the martian highlands. Laboratory spectra of Fe- and/or Ca-rich carbonates show that these outcrops are distinct from the Mg-rich carbonates identified previously via remote sensing of martian dust and from some of the outcrops surrounding the Isidis basin. The Huygens crater and Noachis Terra carbonate outcrops always co-occur with phyllosilicates, and the overlapping spectral absorptions of these two mineral classes pose challenges for mapping them independently. We speculate that this may have led to an underappreciation of how widespread carbonate outcrops are on Mars.

The Early Noachian age implied by the stratigraphic position of these carbonate outcrops (e.g., underlying Hellas basin ejecta) implies that they record very early conditions of prime astrobiological interest for future missions such as Mars 2020. Burial to depths of several kilometers may have protected them from later acidic surface weathering until relatively recent exposure by impact, tectonics, and erosion.

We have also focused (Co-Investigator Bishop) on global comparisons of martian carbonate spectra and how variations in the absorption band positions indicate a range of cation chemistries. This work was presented at the Astrobiology Science Conference in Chicago.

Wray contributed carbonate spectral analyses to two presentations on potential future landing sites: one on Holden crater led by Ross Irwin at the Mars 2020 Landing Site Workshop, and the other on Huygens basin led by Paul Niles at the First Landing Site / Exploration Zone Workshop for Human Missions to the Surface of Mars.

Figure 1. Carbonate-bearing rocks found on Mars to date, on MOLA topography (modified from Ehlmann et al. [2008]). Green points are Mg-carbonates (reported by Ehlmann et al. [2008], except where indicated), cyan are Fe/Ca-carbonates reported by other authors, while dark blue points are newly reported here (mostly Fe/Ca-carbonates).
Figure 2. Bishop laboratory spectra of various carbonates (top) compared to rescaled CRISM spectra (bottom) from outcrops spread across the martian globe.

Figure 3. Aqueous minerals exposed in the upper wall of Her Desher Vallis. (a) A shallow subsurface layer mapped by Buczkowski et al. [2010, 2013] contains ubiquitous Fe/Mg-phyllosilicates (red), variably mixed with carbonate (yellow). This is overlain by a different hydrous mineral, possibly sulfate (blue). Red is D2300, Green is BDCARB, Blue is SINDEX [Pelkey et al., 2007]; purely green (not yellow) areas are artifacts. CRISM HRL00009B61 overlain on CTX B20_017450_1542, as in (b) Carbonates mapped independently using the CINDEX parameter [Pelkey et al., 2007], tracking their 3.9 µm absorption (red). Note correspondence to all yellow areas in (a) (i.e., spectra both 2.3 and 2.5 µm absorptions), but not areas that are red in (a) (i.e., having only a 2.3 µm band). (c) Enhanced-color view of the transition from hydrous (sulfate?) layer (bright blue to yellow hues) to underlying clay- and carbonate-bearing layers (darker maroon). The darker sub-unit at the top of the clay-bearing horizon extends for at least several kilometers and appears deficient in carbonate relative to the underlying, polygonally fractured outcrop. From HiRISE PSP_007086_1545_IRB.