A search for polycyclic aromatic hydrocarbons over the Martian South Polar Residual Cap

J.D Campbell,P Sidiropoulos,J-P Muller

doi:10.1016/j.icarus.2018.03.008

J.D Campbell, P Sidiropoulos + Show 1 more

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https://doi.org/10.1016/j.icarus.2018.03.008

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Journal: Icarus	Publication Date: Apr 4, 2018
Citations: 7	License type: cc-by

Affiliation: University College London

Abstract

We present our research on compositional mapping of the Martian South Polar Residual Cap (SPRC), especially the detection of organic signatures within the dust content of the ice, based on hyperspectral data analysis. The SPRC is the main region of interest for this investigation, because of the unique CO2 ice sublimation features that cover the surface. These flat floored, circular depressions are highly dynamic, and we infer frequently expose dust particles previously trapped within the ice during the wintertime. Here we identify suitable regions for potential dust exposure on the SPRC, and utilise data from the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) on board NASA's Mars Reconnaissance Orbiter (MRO) satellite to examine infrared spectra of dark regions assumed to be composed mainly of dust particles to establish their mineral composition, to eliminate the effects of ices on sub-pixel dusty features, and to look for signatures indicative of Polycyclic Aromatic Hydrocarbons (PAHs). Spectral mapping has identified compositional differences between depression rims and the majority of the SPRC and CRISM spectra have been corrected to minimise the influence of CO2 ice. Whilst no conclusive evidence for PAHs has been found within the detectability limits of the CRISM instrument, depression rims are shown to have higher water content than regions of featureless ice, and there are possible indications of magnesium carbonate within the dark, dusty regions.

Highlights

Mars has long been the subject of scientific exploration, with a focus on investigations of conditions on ancient Mars, evidence of life, and the search for habitable environments (Fairén et al, 2010)
The Regions of interest (ROIs) incorporate all pixels intersected or covered by the polyline or rectangle
Polycyclic Aromatic Hydrocarbons (PAHs) are crucial to theories of abiogenesis, and despite their ubiquitous presence in space, their detection on planetary bodies remains a primary objective for the field of planetary science

Summary

Introduction

Mars has long been the subject of scientific exploration, with a focus on investigations of conditions on ancient Mars, evidence of life, and the search for habitable environments (Fairén et al, 2010). The lack of a significant atmosphere on present-day Mars means that the surface is exposed to high levels of UV radiation, which would have a deleterious effect on any biological material on the planetary surface (Cockell et al, 2000); the annual, seasonal sublimation and deposition of CO2 ice on the SPRC leads to an unique surface feature known broadly as ‘Swiss Cheese Terrain’ (SCT), characterised by flat floored, circular depressions that can intersect to form intricate patterns reminiscent of Emmental Swiss Cheese (Malin et al, 2001). The dynamic nature of the SPRC has been established by comparing current maps made from CTX imagery to earlier images from the Mars Orbital Camera (MOC) on Mars Global Surveyor, and by comparing images obtained during different orbits from the High Resolution Imaging Science Experiment (HiRISE) on board MRO (Thomas et al, 2005; Pommerol et al, 2011) (Fig. 1).

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