The Cu­rios­ity rover has been on Mars over 2,000 sols now but its big­gest rev­e­la­tions may be still to come

Sky at Night Magazine - - A PASSION FOR SPACE - with Dr San­jeev Gupta

Sit­ting atop the Vera Ru­bin Ridge in Gale crater, Cu­rios­ity rover has just cel­e­brated two ma­jor mile­stones. It has now been ex­plor­ing the Red Planet for 2,000 sols – or Mar­tian days – hav­ing tra­versed 18.7km since Au­gust 2012. Which also means it’s been on the planet for three Mar­tian years.

From this van­tage point, Cu­rios­ity’s science team has en­joyed some re­mark­able panoramic im­ages thanks to the rover’s Mast­cam cam­eras. For those of us fa­mil­iar with deserts from field­work, they have a weird Earthly qual­ity, with hills and moun­tain slopes of strat­i­fied sed­i­men­tary rocks that re­sem­ble what you might find in North Africa. But scat­tered here and there are those tell-tale sig­na­tures of a dif­fer­ent world: im­pact craters, holes gouged into the sur­face by col­lid­ing me­te­orites.

Cu­rios­ity’s mis­sion to Mars is first and fore­most an ex­plo­ration of hab­it­abil­ity; to as­sess the Mar­tian sur­face as a po­ten­tial habi­tat for past or present life. Our fo­cus is the an­cient rock suc­ces­sions pre­served in Gale crater that hail back to a time when Mars’s cli­mate may have been more hos­pitable to mi­cro­bial life than to­day’s harsh con­di­tions. This is where my own spe­cial­ity comes into play.


Writ­ten in the rocks

I am a sed­i­men­tary ge­ol­o­gist. Through clues in rocks, I can tell you what a land­scape looked like mil­lions, if not bil­lions, of years ago. But I never imag­ined I would be do­ing this on Mars.

Cu­rios­ity’s trav­els in Gale crater have re­vealed a spec­tac­u­lar ar­ray of sed­i­men­tary rocks which at­test to dy­namic an­cient en­vi­ron­ments. Rivers de­rived from the crater rim built al­lu­vial fans com­posed of rounded peb­ble beds and small un­der­wa­ter dunes. These rivers even­tu­ally built a se­ries of deltas that fed wa­ter and sed­i­ment into a lake that the science team be­lieves filled the cen­tre of the crater. Lake de­posits are bril­liant for as­tro­bi­ol­ogy. They not only rep­re­sent quiet-wa­ter en­vi­ron­ments with good po­ten­tial for the de­vel­op­ment of mi­cro­bial life, but they also in­crease the chances of pre­served ev­i­dence.

Preser­va­tion is a cru­cial fac­tor. Life may have been present, but its traces erased by bil­lions of years on the sur­face of Mars. In Gale crater we found re­mark­able mud­stones made up of mil­lime­tre-thick lay­ers – lam­i­na­tions – that record the set­tling of fine-grained sed­i­ment in a stand­ing body of wa­ter. We’ve driven across hun­dreds of me­tres of such lam­i­nated mud­stones, which sug­gests that this lake ex­isted for hun­dreds of thou­sands, if not mil­lions, of years.

The rocks that make up the Vera Ru­bin Ridge are also finely lam­i­nated mud­stones but with an abun­dance of the iron ox­ide, haematite. We knew about the haematite from or­bital ob­ser­va­tions, but not how it came to be. Was it re­lated to the chem­istry of the lake wa­ter? Was it caused later by flu­ids per­co­lat­ing through the rocks? And what im­pli­ca­tions does it have for pos­si­ble life on an­cient Mars? The Cu­rios­ity science team is grap­pling with these prob­lems at this very minute. Watch this space!

Dr San­jeev Gupta is a co-in­ves­ti­ga­tor on the Cu­rios­ity rover’s Mast­cam team

Mag­gie Aderin-Po­cock is on hol­i­day

The Vera Ru­bin Ridge looks de­cep­tively Earth-like, but its re­mark­able rocks have a hid­den tale to tell

Mar­tian mud­stones found at the base of Mount Sharp in Gale crater

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