Woonsocket Call

Search for an­cient life on Mars gets boost

- By SARAH KA­PLAN

In puffs of gas from rocks more than 3 bil­lion years old dug up by one of NASA’s ro­botic ex­plor­ers on Mars, sci­en­tists have iden­ti­fied sev­eral com­plex or­ganic mol­e­cules – pos­si­ble build­ing blocks for an­cient life.

It’s not aliens. (It’s never aliens.)

But it is “consistent with the past pres­ence of bi­ol­ogy,” said Ken Wil­li­ford, an as­tro­bi­ol­o­gist at NASA’s Jet Propul­sion Lab­o­ra­tory. “And it makes us more con­fi­dent that if biomark­ers” – or di­rect ev­i­dence of bi­o­logic ac­tiv­ity – “are there, we might find them.”

In two stud­ies pub­lished Thurs­day in the jour­nal Sci­ence, this new find­ing from NASA’s Cu­rios­ity rover is paired with an­other dis­cov­ery: The planet’s meth­ane – an­other or­ganic mol­e­cule usu­ally (but not al­ways) pro­duced by liv­ing be­ings – varies with the sea­sons. In the past, sci­en­tists have seen plumes and patches of this in­trigu­ing sub­stance, but this is the first time they’ve been able to dis­cern a pat­tern in its pres­ence. The re­sult could pave the way for fu­ture mis­sions to pin down the meth-

ane’s source.

“The closer we look, the more we see that Mars is a com­plex, dy­namic planet that – par­tic­u­larly early in its his­tory – was more con­ducive to life than we might have pre­vi­ously imag­ined,” said Wil­li­ford, who was not in­volved in ei­ther study.

A re­minder: Or­ganic mol­e­cules aren’t nec­es­sar­ily pro­duced by or­gan­isms; they’re just chem­i­cal com­pounds that con­tain car­bon. But they’re of in­ter­est to as­tro­bi­ol­o­gists be­cause they are the es­sen­tial ingredient­s in all the chem­istry that drives life on Earth.

Mars’s Gale Crater, where Cu­rios­ity has been trolling around for the past six years, is a par­tic­u­larly in­ter­est­ing place to look for those mol­e­cules. About 3.5 bil­lion years ago, re­search sug­gests, this pock­mark on the Mar­tian sur­face was brim­ming with wa­ter.

But the wa­ter van­ished when most of the Mar­tian at­mos­phere was stripped away by bru­tal so­lar winds. And, given the in­ten­sity of the ra­di­a­tion bom­bard­ing the planet’s sur­face, it wasn’t clear whether any relics from that warm, wet pe­riod could still be pre­served in mud­stones on the lake’s dried-up floor.

Us­ing Cu­rios­ity’s Sam­ple Anal­y­sis at Mars in­stru­ment – which heats soil and rock sam-

ples to ex­am­ine their con­tents – as­tro­bi­ol­o­gist Jen­nifer Ei­gen­brode and her col­leagues were able to iden­tify an ar­ray of in­ter­est­ing or­ganic mol­e­cules: Ring struc­tures known as aro­mat­ics, sul­fur com­pounds and long car­bon chains. Even more com­pelling was the fact that these com­pounds seemed to have bro­ken off even big­ger, more com­plex “macro­molecules” – sub­stances found on Earth in coal, black shale and other an­cient or­ganic re­mains.

“What we have de­tected is what we would ex­pect from a sam­ple from an an­cient lake en­vi­ron­ment on Earth,” said Ei­gen­brode, of NASA’s God­dard Space Flight Cen­ter.

There are some non-bi­o­log­i­cal ex­pla­na­tions for the de­tec­tion – this com­bi­na­tion of com­pounds has also been found in me­te­orites. But that ex­pla­na­tion, too, sug­gests a provoca­tive pos­si­bil­ity; even if the or­ganic mol­e­cules didn’t come from life, they are ex­actly what life likes to eat. Per­haps the me­te­orite-de­liv­ered mol­e­cules pro­vided fuel for an­cient alien or­gan­isms.

Re­gard­less, the de­tec­tion is a tech­ni­cal achieve­ment, said Wil­li­ford, be­cause it demon­strates that or­ganic mol­e­cules can per­sist near Mars’s sur­face for bil­lions of years. If sci­en­tists keep drilling deeper and more widely, as they plan to do with the Euro­pean and Rus­sian space agen­cies’ Ex­oMars rover and NASA’s Mars 2020 mis­sion,

who knows what they might find? (Wil­li­ford is deputy project sci­en­tist for Mars 2020.)

The meth­ane study, spear­headed by JPL at­mo­spheric sci­en­tist Chris Web­ster, is also in­trigu­ing for as­tro­bi­ol­o­gists. On Earth, 1,800 out of ev­ery bil­lion mol­e­cules in the at­mos­phere is meth­ane, and 95 per­cent of it comes for bi­o­log­i­cal sources: Burn­ing fos­sil fu­els, de­com­pos­ing de­bris, burp­ing cows. Some of our planet’s ear­li­est or­gan­isms may have been methanogen­s – mi­crobes that eat or­ganic mol­e­cules and ex­hale meth­ane gas.

Sev­eral space­craft in­clud­ing Cu­rios­ity have de­tected whiffs of this gas that “de­fied ex­pla­na­tion,” Web­ster said. Meth­ane is quickly bro­ken down by ra­di­a­tion, so it must be re­plen­ished by some source on the planet. One ex­pla­na­tion “that no one talks about but is in the back of ev­ery­one’s mind,” as God­dard plan­e­tary sci­en­tist Mike Mumma­put it to Sci­ence last win­ter, is that methanogen­s be­neath the Mar­tian sur­face were breath­ing it out.

“You’d ex­pect life to be sea­sonal,” Mumma noted. But it was also pos­si­ble that puffs of meth­ane were de­liv­ered to the desert world by crash­ing me­te­orites or other less thrilling sources.

By ex­am­in­ing data span­ning nearly three Mar­tian years (six Earth years), Web­ster and his col­leagues dis­cerned the first

re­peat­ing pat­tern in Mar­tian meth­ane. Dur­ing the sum­mer months, lev­els of the gas de­tected by Cu­rios­ity rose to about 0.7 parts per bil­lion; in win­ter, they fell to roughly half that. They sug­gest that warmer con­di­tions might re­lease the gas from reser­voirs be­neath the sur­face.

The re­sults don’t ex­plain shorter-lived spikes in meth­ane lev­els – as high as 45 parts per bil­lion – that have been de­tected. And even if the reser­voir ex­pla­na­tion is cor­rect, it re­mains to be seen what’s feeding them.

To de­ter­mine whether the meth­ane is bi­o­log­i­cal, Web­ster said, sci­en­tists can weigh the kinds of car­bon atoms it con­tains (life prefers the lighter ver­sions).

Fu­ture mis­sions might also seek places where there’s “sig­nif­i­cant seep­age” and at­tempt to fig­ure out its source.

In a com­men­tary for Sci­ence, as­tro­bi­ol­o­gist Inge Loes ten Kate of the Utrecht Univer­sity in the Nether­lands, ex­plained what makes these two stud­ies so com­pelling:

“Cu­rios­ity has shown that Gale crater was hab­it­able around 3.5 bil­lion years ago, with con­di­tions com­pa­ra­ble to those on the early Earth, where life evolved around that time,” she wrote. “The ques­tion of whether life might have orig­i­nated or ex­isted on Mars is a lot more op­por­tune now that we know that or­ganic mol­e­cules were present on its sur­face at that time.”

 ?? NASA/JPL-Cal­tech/MSSS ?? A self-por­trait taken by NASA’s Cu­rios­ity rover in the Gale Crater.
NASA/JPL-Cal­tech/MSSS A self-por­trait taken by NASA’s Cu­rios­ity rover in the Gale Crater.

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