Ero­sion on Mars re­veals very thick de­posits of ice

Honolulu Star-Advertiser - - NEWS - By Amina Khan

Thanks to ero­sion wear­ing away sur­face rock on Mars, sci­en­tists us­ing NASA’s Mars Re­con­nais­sance Or­biter have spot­ted thick de­posits of ice in the planet’s mid-lat­i­tudes that ex­tend hun­dreds of feet deep. The dis­cov­ery, de­scribed in the jour­nal Science, could of­fer re­searchers a tan­ta­liz­ing new spot to sam­ple our dusty, rusty neigh­bor.

“This ice is a crit­i­cal tar­get for science and ex­plo­ration: It af­fects mod­ern ge­o­mor­phol­ogy, is ex­pected to pre­serve a record of cli­mate his­tory, in­flu­ences the planet’s hab­it­abil­ity, and may be a po­ten­tial re­source for future ex­plo­ration,” the study au­thors wrote. In spite of its dry ap­pear­ance, about a third of the Red Planet ac­tu­ally holds shal­low ground ice. But while that frozen wa­ter’s ex­tent is fairly well known, other cru­cial de­tails — how thick it is, what its lay­ers look like, and how pure it is — largely re­main un­known. If future ex­plor­ers want to be able to draw down th­ese wa­ter sources, sci­en­tists are go­ing to have to learn much more about them.

The de­posits de­scribed in this new pa­per of­fer a po­ten­tial win­dow into some of those mys­ter­ies. The re­searchers ex­am­ined eight dif­fer­ent ex­posed ice de­posits on the planet spot­ted by the or­biter’s HiRISE cam­era. Seven of them are pole-fac­ing scarps (that is, steep banks or slopes) in the south­ern hemi­sphere; one is a clus­ter of scarps in the north­ern hemi­sphere, in Mi­lankovic Crater.

Th­ese ice de­posits could start just 1 to 2 me­ters be­neath the sur­face but ex­tend more than 100 me­ters deep. They’re capped with a layer of rock and dust that’s been ce­mented with ice. Th­ese de­posits seem to be pretty pure in terms of com­po­si­tion — not a lot of dust or dirt mixed in — which was not what sci­en­tists orig­i­nally ex­pected.

The re­searchers think the ice de­posits started out as snow or frost that fell, was com­pacted and then re­crys­tal­lized.

That’s not all that dif­fer­ent from glaciers on Earth, which form from snow be­ing com­pacted over hun­dreds, thou­sands and even mil­lions of years. Here, glaciers are a cru­cial tool for un­der­stand­ing our planet’s at­mo­spheric his­tory. Each layer of snow laid down over time records a dif­fer­ent epoch — and the deeper the lay­ers, the older the epoch. Air pock­ets trapped in the ice pro­vide tiny, pre­his­toric sam­ples of air that can be an­a­lyzed.

Sim­i­larly, th­ese Mar­tian ice de­posits could of­fer sci­en­tists a frozen trove of in­for­ma­tion just wait­ing to be sam­pled and stud­ied up close.

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