Mars Simulation Measurements (MSM)

A ubiqutous oxidant has long been proposed as being responsible for destruction of organic compounds on Mars, and the inability of Viking, Phoenix, and Curiosity, to detect organics. The discovery of perchlorate (ClO4-) in 2008 by the Wet Chemistry Lab (WCL) on Phoenix, and the recent confirmation by the Sample Analysis at Mars (SAM) instruments on the Curiosity rover, provides a possible mechanism by which the detection of organics may have been thwarted. Although perchlorate salts are stable under ambient Mars conditions, when heated to the high temperatures required for thermal detection techniques, they becomes powerful oxidizers and would destroy any organic molecules present.  

The presence of perchlorate in the martian soil also strongly points to the existence of oxidizing intermediary oxychlorines (ClOx-) and radicals that would likely be produced during the UV oxidation of chloride to perchlorate in the martian environment [1,2].  For example, intermediary species such as chlorite (ClO2-) and hypochlorite (ClO-) can oxidze simple organic molecules, however, radicals such as ClO-, O2-, •OCl, •Cl, and •OH can oxidize and destroy organic compounds to form H2O and O2. On Earth production of perchlorate occurs photochemically in the atmosphere and possibly on mineral surfaces.  On Mars, the depleted levels of chlorine precursors in the present atmosphere leads to the hypothesis that perchlorate may instead be primarily produced on chloride containing mineral surfaces including rocks, regolith, and dust particles. Such an on-going formation of oxychlorines on a global scale in the past and present [3], could lead to surface materials on Mars depleted or even devoid of organics. Understanding the formation of perchlorate on the surface of Mars and the processes by which it and/or its intermediates destroy or alter organic compounds is key to understanding the preservation of fossils, modern organics, life detection, and the safety of future human explorers.

Perchlorate Production on Mars

Our research goals are to determine:
(1) mechanisms leading to formation of ClO4- & highly oxidizing ClOx- intermediates & radicals;
(2) diffusivity of ClOx- intermediates in regolith;
(3) effects presence of ClO4- and intermediaries, such as ClO-, ClO2-, ClO3- and ClO2(g), have on survivability of martian organic compounds;
(4) extent and stability of chlorinated organic compounds produced by oxidation via ClOx-;
(5) possible synergistic and/or catalytic interactions of ClOx- species with minerals in the martian soil and determine effects on survivability of organics; and
(6) if destruction of organics is due mainly to UV radiation, ClOx-, or to both.

The Mars Simulation Chamber (MSC):

The MSC consists of a stainless steel cylindrical chamber with a depth of 45 cm and an internal diameter of 60 cm.  Samples are staged on a 25 cm diameter cold-plate at the bottom of the chamber.  The temperature of the cold-plate is controlled by an FTS RC210C0 Ultra Low Temperature recirculating cooler that can maintain temperatures as low as -80° C.  A Mars gas mixture (CO2 95.3%, N2 2.8%, Ar 1.8% and O2 0.10%) is delivered by a mass-flow controller and pressure in the chamber can be maintained anywhere from 1000 mbar to 0.1 mbar.

Mars UV-VIS-NIR radiation:

A very highly accurate Mars solar radiation intensity and spectrum are produced by a 1000W xenon-arc lamp and delivered, via a system of filters and beam turners, through a 22 cm fused silica port on the top of the MSC. Because the output of the lamp varies over time the levels of UVC, UVB and UVA radiation (190-400 nm) are monitored periodically using a Spectrawiz UV spectrometer in order to correlate exposure time in the MSC to equivalent Mars UV irradiation dosages.

Mars Chamber

[1] "Evidence of Martian Perchlorate, Chlorate, and Nitrate in Mars Meteorite EETA79001: Implications for Oxidants and Organics”, S. P. Kounaves, B. L. Carrier, G. D. O'Neil, S. T. Stroble, and M. W. Clair, Icarus, 2014, 229, 206-213, doi:10.1016/j.icarus.2013.11.012 Full Text

[2] "The Origins of Perchlorate in the Martian Soil" B. L. Carrier and S. P. Kounaves, Geophys. Res. Lett., 2015, 42, 3746-3754, doi:10.1002/2015GL064290 Full Text

[3] "Evidence for the Distribution of Perchlorates on Mars" B. C. Clark and S. P. Kounaves, Int. J. Astrobiol., 2016, 15, 311-318, doi:10.1017/S1473550415000385 Full Text



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Last Updated: 05/30/2018