Mars’s oceans AP­PEARED EARLY

New the­ory could ex­plain why Mars’s wa­ter has dis­ap­peared

Sky at Night Magazine - - BULLETIN -

Mars’s oceans could have been around sev­eral hun­dred mil­lion years ear­lier than for­merly be­lieved. A novel sce­nario sug­gests that the oceans formed four bil­lion years ago at the same time as the largest vol­canic struc­ture on Mars, Thar­sis – the vol­canic plateau near the planet’s equa­tor that is home to Olym­pus Mons.

“The as­sump­tion was that Thar­sis formed quickly and early, rather than grad­u­ally, and that the oceans came later,” says Michael Manga from Univer­sity of Cal­i­for­nia, Berke­ley, who took part in the study. “We’re say­ing that the oceans pre­date and ac­com­pany the lava out­pour­ings that made Thar­sis.”

The min­eral com­po­si­tion and to­pog­ra­phy of Mars sug­gest that there was once a huge ocean cov­er­ing its north­ern hemi­sphere. How­ever, sev­eral key ques­tions that chal­lenge this the­ory re­main, such as what hap­pened to all the wa­ter? And why is the sup­posed shore­line not level?

The first of these is­sues is caused by cur­rent es­ti­mates for the oceans’ vol­ume, which are too large. If there had been as much wa­ter on Mars as cur­rently pre­dicted, it would not have had time to com­pletely evap­o­rate into space or freeze into per­mafrost. How­ever, these es­ti­mates are based on the cur­rent land­scape, which is de­formed by the Thar­sis re­gion. If the oceans had formed be­fore or at the same time as the vol­canic struc­ture, they would have been much shal­lower.

The new sim­u­la­tions could also ex­plain why the ge­o­log­i­cal fea­tures thought to be the an­cient shore­line are un­even. On Earth, shore­lines are all at sea level, but those on Mars vary in el­e­va­tion. But if the ocean and its coast formed when Thar­sis was young, the land­scape would have changed as the re­gion grew, de­form­ing the shore­line in the process.

“These shore­lines could have been put in place by a large body of liq­uid wa­ter that ex­isted be­fore and dur­ing the em­place­ment of Thar­sis, in­stead of af­ter­wards,” says Univer­sity of Cal­i­for­nia, Berke­ley grad­u­ate Robert Citron, who led the study.

The cur­rent work is all the­o­ret­i­cal, but the In­Sight lan­der head­ing to Mars this month could help test the con­cept by map­ping the Mar­tian in­te­rior and ex­am­in­ing the planet’s vol­canic past.

“This is a hy­poth­e­sis,” stresses Manga about the study’s find­ings. “But sci­en­tists can do more pre­cise dat­ing of Thar­sis and the shore­lines to see if it holds up.” https://www.berke­

A new the­ory sug­gests Mars’s oceans formed sev­eral hun­dred mil­lion years ear­lier than once thought

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