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Life on the Red Planet? Methane results boost hopes

Dec. 9, 2009
Courtesy Imperial College London
and World Science staff

Very little meth­ane gas can come to Mars from me­te­orites, sci­ent­ists have found. That leaves mi­crobes, they say, as one of just two re­main­ing pos­sible ex­pla­na­tions for me­thane’s ab­und­ance on the red plan­et.

Meth­ane, some­times al­so called marsh gas, is a flam­ma­ble, odor­less gas pro­duced by a range of bac­te­ria. The gas con­sists of car­bon atoms each of which has four smaller hy­dro­gen atoms cling­ing to to it.

Meth­ane con­cen­tra­tions in the north­ern Martian at­mo­s­phere. Red shows ar­eas of high­er con­cen­tra­tion (up to about 30 parts per bil­ion); vi­ol­et-blue in­di­cates low­er con­cen­tra­tion. (Im­age cour­te­sy NA­SA) 
Sci­en­tists an­a­lys­ing da­ta from tel­e­scop­ic ob­serva­t­ions and un­manned space mis­sions have found that Mars has meth­ane that is con­stantly re­plen­ished by an un­known source. With­out this re­plen­ish­ment, meth­ane would quickly van­ish from Mars be­cause a chem­i­cal re­ac­tion in the at­mos­phere, caused by sun­light, de­stroys it.

Re­search­ers had thought me­te­orites might be re­spon­si­ble for Mar­tian meth­ane be­cause when the rocks en­ter the plan­et’s at­mos­phere they un­dergo in­tense heat, caus­ing a chem­i­cal re­ac­tion that re­leases meth­ane and oth­er gas­es.

But the new stu­dy, by re­search­ers from Im­pe­ri­al Col­lege Lon­don, found that the vol­umes of meth­ane that could be re­leased in this way are too low to ex­plane the meth­ane hang­ing around the Mar­tian at­mos­phere. Pre­vi­ous stud­ies had al­so ruled out that the meth­ane might be de­liv­ered through vol­can­ic ac­ti­vity.

This leaves only two plau­si­ble the­o­ries, ac­cord­ing to the Im­pe­ri­al Col­lege re­search­ers: ei­ther re­ac­tions be­tween vol­can­ic rock and wa­ter cre­ate the meth­ane, or mi­crobes do so, probably as a byprod­uct of their me­tab­o­lism.

“As Sher­lock Holmes said, elim­i­nate all oth­er fac­tors and the one that re­mains must be the truth. The list of pos­si­ble sources of meth­ane gas is get­ting smaller and ex­cit­ing­ly, ex­tra­ter­res­tri­al life still re­mains an op­tion,” said study co-author Mark Seph­ton.

The find­ings are pub­lished Dec. 9 in the re­search jour­nal Earth and Plan­e­tary Sci­ence Let­ters.

The team say their study will help NASA and Eu­ro­pe­an Space Agen­cy sci­en­tists who are plan­ning a joint mis­sion to Mars in 2018 to search for the source of meth­ane. Now these agen­cy sci­en­tists can fo­cus on just two op­tions, the re­search­ers said.

The team used a tech­nique called Quantitative Pyrolysis-Fourier Trans­form In­fra­red Spec­tros­co­py to re­pro­duce the same sear­ing con­di­tions ex­pe­ri­enced by me­te­orites as they en­ter the Mar­tian at­mos­phere. The team heat­ed the me­te­or­ite frag­ments to 1000 de­grees Cel­si­us and meas­ured the gas­es re­leased us­ing an in­fra­red beam.

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Scientists say they have ruled out the possibility that methane comes to Mars from meteorites, raising fresh hopes that microbes might be making the gas on the red planet. Methane, sometimes also called marsh gas, is a flammable, odorless gas produced by a range of bacteria. The gas consists of carbon atoms each of which has four smaller hydrogen atoms clinging to to it. Scientists analysing data from telescopic observations and unmanned space missions have found that Mars has methane that is constantly replenished by an unknown source. Without this replenishment, methane would quickly vanish from Mars because a chemical reaction in the atmosphere, caused by sunlight, destroys it. Researchers had thought meteorites might be responsible for Martian methane because when the rocks enter the planet’s atmosphere they undergo intense heat, causing a chemical reaction that releases methane and other gases. But the new study, by researchers from Imperial College London, found that the volumes of methane that could be released in this way are too low to explane the methane hanging around the Martian atmosphere. Previous studies had also ruled out that the methane might be delivered through volcanic activity. This leaves only two plausible theories, according to the Imperial College researchers: either reactions between volcanic rock and water create the methane, or microbes do so, probably as a byproduct of their metabolism. “As Sherlock Holmes said, eliminate all other factors and the one that remains must be the truth. The list of possible sources of methane gas is getting smaller and excitingly, extraterrestrial life still remains an option,” said study co-author Mark Sephton. The findings are published Dec. 9 in the research journal Earth and Planetary Science Letters. The team say their study will help NASA and European Space Agency scientists who are planning a joint mission to Mars in 2018 to search for the source of methane. Now these agency scientists can focus on just two options, the researchers said. The team used a technique called Quantitive Pyrolysis-Fourier Transform Infrared Spectroscopy to reproduce the same searing conditions experienced by meteorites as they enter the Martian atmosphere. The team heated the meteorite fragments to 1000 degrees Celsius and measured the gases released using an infrared beam.