"Long before it's in the papers"
January 27, 2015


Mars rock called possible evidence of biological activity

Dec. 3, 2014
Courtesy of École Poly­tech­nique Fédérale de Lau­sanne
and World Science staff

Did Mars ev­er have life? Might it still? A me­te­or­ite iden­ti­fied as com­ing from Mars has re­ig­nit­ed the old de­bate. A study pub­lished this month ar­gues that the rock con­tains traces of car­bon with a likely bi­o­log­i­cal or­i­gin, like coal, which comes from re­mains of long-ago plants. 

The Tissint meteorite. (© Alain Herzog / EPFL)

“So far, there is no oth­er the­o­ry that we find more com­pel­ling,” said study co-author Phi­lippe Gil­let, stress­ing that he’s open to being pro­ven wrong.

Gillet and col­leagues from Chi­na, Ja­pan and Ger­ma­ny ar­gue that the car­bon could have got­ten in­to the rock through con­tact with flu­id rich in or­gan­ic ma­te­ri­al. The study appears in the jour­nal Me­te­or­it­ic and Plan­e­tary Sci­ences.

Thrown off Mars af­ter an as­ter­oid hit its sur­face, the me­te­or­ite, named Tissint, fell on the Mo­roc­can des­ert on July 18, 2011, in view of sev­eral wit­nesses, the sci­en­tists said. Stud­ies found the rock had small fis­sures filled with or­gan­ic, car­bon-con­tain­ing mat­ter.

The re­search­ers car­ried out sev­eral anal­y­ses to con­clude that the rock did­n’t or­i­ginate on Earth and that the car­bon got in­to it be­fore it left Mars. They took is­sue with a pre­vi­ous pro­pos­al that the car­bon traces or­i­ginated through the high-temperature crys­tall­iz­a­tion of mag­ma, or mol­ten rock. Gillet and col­leagues ar­gue that more prob­a­bly, liq­uids con­tain­ing or­gan­ic com­pounds of bi­o­log­i­cal or­i­gin in­fil­trat­ed Tiss­in­t’s “moth­er” rock at low tem­per­a­tures, near the Mar­tian sur­face.

These con­clu­sions are sup­ported by sev­eral prop­er­ties of the me­te­or­ite’s car­bon, such as its lev­els of so-called car­bon-13 com­pared to car­bon-12, they ex­plained. This was found to be sig­nif­i­cantly low­er than the ra­tio of car­bon-13 in the car­bon di­ox­ide of Mars’s at­mos­phere, pre­vi­ously meas­ured by the Phoe­nix and Cu­ri­os­ity rovers. More­o­ver, this dif­fer­ence cor­re­sponds per­fectly with what is seen on Earth be­tween a piece of coal and the car­bon in the at­mos­phere, the sci­en­tists ar­gue. 

The re­search­ers say the or­gan­ic mat­ter could al­so have reached Mars when very prim­i­tive me­te­or­ites, called car­bonated chon­drites, fell there, but probably not, be­cause such me­te­or­ites con­tain very low levels of or­gan­ic mat­ter.

“In­sist­ing on cer­tain­ty is un­wise, par­tic­u­larly on such a sen­si­tive top­ic,” said Gillet,  who directs the Earth and Plan­e­tary Sci­ences Lab­o­r­a­to­ry at the École Poly­tech­nique Fédérale de Lau­sanne, a Swiss in­sti­tute of tech­nol­o­gy. “I’m com­pletely open to the pos­si­bil­ity that oth­er stud­ies might con­tra­dict our find­ings. Howev­er, our con­clu­sions are such that they will re­kin­dle the de­bate as to the pos­si­ble ex­ist­ence of bi­o­log­i­cal ac­ti­vity on Mars – at least in the past.”

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Did Mars ever have life? Does it still? A meteorite identified as coming from Mars has reignited the old debate. A study newly published in the journal Meteoritics and Planetary Sciences argues that the rock contains traces of carbon with a likely biological origin, like coal, which comes from long-ago plants. “So far, there is no other theory that we find more compelling,” said Philippe Gillet, director of the Earth and Planetary Sciences Laboratory at the École polytechnique fédérale de Lausanne, a Swiss institute of technology. Gillet and colleagues from China, Japan and Germany analyzed the traces and argue that the carbon could have gotten into the rock through contact with fluid rich in organic material. Ejected from Mars after an asteroid crashed on its surface, the meteorite, named Tissint, fell on the Moroccan desert on July 18, 2011, in view of several witnesses, the scientists said. Studies found the rock had small fissures filled with organic, carbon-containing matter. The researchers carried out several analyses to conclude that the rock didn’t originate on Earth and that the carbon got into it before it left Mars. They took issue with a previous proposal that the carbon traces originated through the high-temperature crystallization of magma, or molten rock. Gillet and colleagues argue instead that more probably, liquids containing organic compounds of biological origin infiltrated Tissint’s “mother” rock at low temperatures, near the Martian surface. These conclusions are supported by several properties of the meteorite’s carbon, such as its levels of so-called carbon-13 compared to carbon-12, they explained. This was found to be significantly lower than the ratio of carbon-13 in the carbon dioxide of Mars’s atmosphere, previously measured by the Phoenix and Curiosity rovers. Moreover, this difference corresponds perfectly with what is seen on Earth between a piece of coal and the carbon in the atmosphere, the scientists argue. The researchers say the organic matter could also have reached Mars when very primitive meteorites, called carbonated chondrites, fell there, but probably not, because such meteorites contain very little organic matter. “Insisting on certainty is unwise, particularly on such a sensitive topic,” warns Gillet. “I’m completely open to the possibility that other studies might contradict our findings. However, our conclusions are such that they will rekindle the debate as to the possible existence of biological activity on Mars – at least in the past.”