Closed System Chemistry inside Massive Ice Deposits at Meridiani Planum

Introduction: The discoveries made by the Opportunity rover at Meridiani Planum have provided a new view of the chemistry of the martian surface. These results have also spawned a number of different interpretations. These different interpretations of the chemistry of the Meridiani sulphate-bearing rocks can be categorized into two main groups. The first model suggests that the rocks are sedimentary and composed of a mixture of two components – a heavily weathered sili-cate component and an evaporite salt component [1]. The second model suggests the rocks are volcano-clastic and were weathered in place by sulphur rich gases [2]. We propose a third model [3] which suggests that individual grains or agglomerates of grains were weathered inside of a large dust/ice deposit, and were re-deposited into eolian sediments after the ice had been removed by sublimation. This hypothesis explains the available data better than the others for the following reasons: 1) The Meridiani sediments have basaltic ca-tion compositions despite the fact that many of the ca-tions are now associated with secondary weathering products such as sulfate[4]; 2) Only small variations in chemical composition are observed in the Meridiani sediments across the 16 km traverse of the Opportunity rover, and these changes are in MgSO 4 content alone, with little or no change in Fe, Ca, Na, or K [4]; 3) The cation composition of the Meridiani sediments shows a strong resemblance to the composition of the bright soils observed at the Pathfinder, Spirit, and Opportunity landing sites [4]. Model Description: This new model [3] for the provenance of the sediments at Meridiani Planum is based in principal on geochemical ideas pioneered by Burns [5], and sedimentological ideas proposed by Tanaka [6]. In our model, the sediments now located at Meridiani Planum were sourced from a nearby, massive dust/ice deposit that was located adjacent to Me-ridiani Planum. This massive dust/ice deposit formed through precipitation of ice around dust grains and aerosols during a period of high obliquity, and resembled the polar layer deposits that exist today in the martian north and south polar regions. Suspended dust in a Noachian atmosphere provided nucleation points for ice crystals to form which is an important driver for the precipitation of water ice in the present day polar caps [7] and would have been more prevalent on ancient Mars. Exposure of the ice deposits to sunlight during the summer seasons allowed for radiant heating of dark …