Constraining the preservation of organic compounds in Mars analog nontronites after exposure to acid and alkaline fluids

Abstract

The presence of organic matter in lacustrine mudstone sediments at Gale crater was revealed by the Mars Science Laboratory Curiosity rover, which also identified smectite clay minerals. Analogue experiments on phyllosilicates formed under low temperature aqueous conditons have illustrated that these are excellent reservoirs to host organic compounds against the harsh surface conditions of Mars. Here, we evaluate whether the capacity of smectites to preserve organic compounds can be influenced by a short exposure to different diagenetic fluids. We analyzed the stability of glycine embedded within nontronite samples previously exposed to either acidic or alkaline fluids (hereafter referred to as “treated nontronites”) under Mars-like surface conditions. Analyses performed using multiple techniques showed higher photodegradation of glycine in the acid-treated nontronite, triggered by decarboxylation and deamination processes. In constrast, our experiments showed that glycine molecules were preferably incorporated by ion exchange in the interlayer region of the alkali-treated nontronite, conferring them a better protection against the external conditions. Our results demonstrate that smectite previously exposed to fluids with different pH values influences how glycine is adsorbed into their interlayer regions, affecting their potential for preservation of organic compounds under contemporary Mars surface conditions.

A Review of the Phyllosilicates in Gale Crater as Detected by the CheMin Instrument on the Mars Science Laboratory, Curiosity Rover

“…Phyllosilicate-bearing layers are desirable targets for investigation on Mars given their potential to enhance the preservation of organics [13][14][15][16][17][18] and serve as indicators of wetter surficial conditions in the past [2,4,10,13,[19][20][21][22][23][24][25]. To investigate the phyllosilicates in Gale crater, drilled rock powders and scooped samples of loose sediment are measured by the Chemistry and Mineralogy (CheMin) X-ray diffractometer.…”

Raman spectroscopic peculiarities of Icelandic poorly crystalline minerals and their implications for Mars exploration

“…It is difficult to determine the type of molecule adsorbed in the interlayers with Raman setups of laser spot size larger than the grain size of the minerals analyzed. However, from our previous works centered on the study of clay minerals, we know that its combination with IR spectroscopy can give satisfactory results 15 , 61 , providing the Raman technique powerful information on the surface state and the IR on the molecules adhered in the interlayer.…”

Science Drivers for the Future Exploration of Ceres: From Solar System Evolution to Ocean World Science

“…Laboratory studies have also shown that organic molecules (e.g., tholins, chondritic organics) are transformed in aqueous alteration experiments (Kebukawa et al 2013(Kebukawa et al , 2020Brassé et al 2017;Vinogradoff et al 2018;Danger et al 2021), producing numerous new soluble molecules and insoluble OM as a function of time and temperature. The nature and extent of OM evolution likely depends on the nature of the initial molecules, the interaction with minerals, and the fluid properties (Gil-Lozano et al 2020;Haas et al 2020;Vinogradoff et al 2020). The spatial co-occurrence of OM with phyllosilicates and carbonates observed at the surface of Ceres (Raponi et al 2017;De Sanctis et al 2019) suggests a close genetic relationship between these phases and a possible coevolution during hydrothermal processing.…”