Three research teams have recently reported detecting the gas methane in the martian atmosphere, at the low concentration of about 10 parts per billion. Most methane (CH4) on Earth is produced in biological processes, both contemporary production by microbes and as underground natural gas formed by earlier generations of microbial life. Since methane is relatively short-lived once it is released into the oxidizing atmospheres of either Earth or Mars, its presence has long been considered a biomarker – a chemical that signals the presence of biological processes. Is the methane discovered on Mars evidence for contemporary life on the Red Planet?

Identification of a biomarker on Mars would qualify as one of the most important discoveries of astrobiology and space exploration. It is thus important to try to understand whether methane in such small quantities is a real biomarker, or whether it might be produced in non-biological processes on Mars.

The new detections were all made remotely using spectroscopy. They come from a team lead by Michael Mumma of NASA Goddard (who is also an Astrobiology Institute team leader), from another group of astronomers led by V. Krasnopolsky of the Catholic University of America, and from a Planetary Fourier Spectrometer (PFS) on the European Space Agency’s Mars Express spacecraft (Vittorio Formisano, PI). The abstracts from the two astronomy teams and the ESA press release are reproduced at the end of this article, along with links to related information.

The production of methane on Earth is dominated by biological processes. Most of the methane is produced by relatively simple microbes (called anaerobic, methanogenic archaea) that have flourished on Earth for billions of years. Many of these microbes live today in the digestive systems of animals, especially cows (famously referred to by Carl Sagan in terms of “bovine flatulents”). We are pretty sure that there are no cows on Mars, but methanogenic microbes are not impossible there, even today.

There are also non-biological sources of methane on Earth. Deep sources of methane are taped by volcanoes and are vented in volcanic eruptions. Mars also has volcanoes, although none seem to be active today. Methane is also produced on Earth through natural reactions of liquid water and iron-bearing minerals, especially in the warm areas such as hydrothermal systems ( hot springs).

The amount of methane detected on Mars is about a factor of 100 less than the estimates of current production on Earth by non-biological means. Because the amounts are so small, it seems reasonable to consider non-biological processes. Precisely because the discovery of active methanogenic microbes on Mars would be so exciting, scientists first try to evaluate possible non-biological sources before claiming these results as biomarkers.

If the methane is being produced on Mars by subsurface reactions involving warm liquid water (which seems like the least likely non-biological process there), that would be a dramatic result in itself. Such evidence for liquid water would rival the recent results from the Mars Exploration Rovers, which have found outcrops of sedimentary rock formed in ancient martian seas. Finding liquid water today on Mars, even below the surface, would greatly enhance the prospects for extant life on that planet. There is an electromagnetic sounding experiment also on the Mars Express orbiter, which may be able to detect levels of subsurface water – a prospect that seems more likely now, with this finding of atmospheric methane on Mars.
AAS/DPS 35th Meeting, 1-6 September 2003


M. J. Mumma (NASA’s GSFC), R. E. Novak ( Iona College), M. A. DiSanti (NASA’s GSFC), B. P. Bonev (Univ. Toledo/NASA’s GSFC)

CH4 and its oxidation products (H2CO, CH3OH, C2H6) on Mars have received both observational (1) and theoretical attention (2, 3), but have not been firmly detected. Owing to its short photochemical lifetime (~ 300 years), the existence of significant methane would indicate underline{recent} release from sub-surface reservoirs; a quantitative measure of the release rate could be inferred from its present atmospheric abundance. Sub-surface methane could be primordial (reduced cosmogonic carbon) (1) or biotic in origin (4); local enhancements are expected if methane is released from discrete regions. The presence of sub-surface hydrogen concentrations on Mars has been inferred from local-enhancements in epithermal neutron fluxes measured on Mars Odyssey (5), however, independent evidence is required to establish its likely chemical form (e.g., water vs. hydrocarbons) in low-latitude sites (Amazonia Planitia, and Schiaparelli-Cassini). We suggest that enhanced methane there could test whether sub-surface hydrogen is chemically bound in hydrocarbon moieties. In any case, a quantitative measure of methane production would provide a key for assessing models of biogenic vs. primordial origins.

We conducted a deep search for methane on Mars using state-of-the-art infrared spectrometers. The R0 and R1 lines in the u3 vibrational band near 3.3 mum were searched using CSHELL at the NASAIRTF (Jan. and March 2003), and Phoenix at Gemini South (May 2003). Details will be presented along with preliminary results.

This work was supported by NASARTOP 344-32-30-10 to MJM, and NSFRUI Grant AST-0205397to REN.

1. Krasnopolsky, V.A., G.L. Bjoraker, M.J. Mumma, and D.E. Jennings 1997. JGR 102(E3):6525.

2. Wong, Ah-Son, S.K. Atreya, and T. Encrenaz 2003. JGR 108(E4):7-1.

3. Summers, M.E., B.J. Lieb, E. Chapman, and Y. Yung 2002. GRL 29(24):2171.

4. Pellenbarg, R.E., Max, M.D., and Clifford, S.M. 2003. JGR 108(E4):GDS 23-1.

5. Boynton, W.V., W.C. Feldman, et al. 2002. Science 297:81.

European Geophysical Union Meeting, Nice, May 2004



V. A. Krasnopolsky (1), J. P. Maillard (2), T. C. Owen (3)

(1) Catholic University of America, Department of Physics, Washington, DC 20064, USA

(, (2) Institute d’Astrophysique de Paris, CNRS, 75014 Paris, France

(, (3) Institute for Astronomy, University of Hawaii, Honolulu, HI 96822,


Using the Fourier Transform Spectrometer at the Canada-France-Hawaii Telescope, we observed a spectrum of Mars at the P-branch of the strongest CH 4 band at 3.3 µ m with resolving power of 220,000. Summing up the spectral intervals at the expected positions of 18 strongest Doppler-shifted martian lines, we detected the absorption by martian methane at a 3.9 sigma level. The observed CH 4 mixing ratio is 11 ± 4 ppb. Total photochemical loss of CH 4 in the martian atmosphere is equal to 1 . 8 × 10 5 cm − 2 s − 1 , and the CH 4 lifetime is 440 years. Heterogeneous loss of atmospheric methane is probably negligible, while the sink of CH 4 during its diffusion through the regolith may be significant. There are no processes of CH 4 formation in the atmosphere, so the photochemical loss must therefore be balanced by abiogenic and biogenic sources. The mantle outgassing of CH 4 is 4000 cm − 2 s − 1 on the Earth and smaller by an order of magnitude on Mars. The calculated production of CH 4 by cometary impacts is 2.3 per cent of the methane loss. Methane cannot originate from an extinct biosphere, as in the case of “natural gas” on Earth, given the exceedingly low limits on organic matter set by the Viking landers and the dry recent history which has been extremely hostile to the macroscopic life needed to generate the gas. Therefore, methanogenesis by living subterranean organisms is the most likely explanation for this discovery. Our estimates of the biomass and its production using the measured CH 4 abundance show that the martian biota may be extremely scarce and Mars may be generally sterile except for some oases.

ESA news release, 30 March 2004


During recent observations from the ESA Mars Express spacecraft in orbit around Mars, methane was detected in its atmosphere.

Whilst it is too early to draw any conclusions on its origin, exciting as they may be, scientists are thinking about the next steps to take in order to understand more.

From the time of its arrival at Mars, the Mars Express spacecraft started producing stunning results. One of the aims of the mission is analysing in detail the chemical composition of the Martian atmosphere, known to consist of 95% percent carbon dioxide plus 5% of minor constituents. It is also from these minor constituents, which scientists expect to be oxygen, water, carbon monoxide, formaldehyde and methane, that we may get important information on the evolution of the planet and possible implications for the presence of past or present life.

The presence of methane has been confirmed thanks to the observations of the Planetary Fourier Spectrometer (PFS) on board Mars Express during the past few weeks. This instrument is able to detect the presence of particular molecules by analysing their ‘spectral fingerprints’ – the specific way each molecule absorbs the sunlight it receives.

The measurements confirm so far that the amount of methane is very small – about 10 parts in a thousand million, so its production process is probably small. However, the exciting question remains: “Where does this methane come from?”

Methane, unless it is continuously produced by a source, only survives in the Martian atmosphere for a few hundreds of years because it quickly oxidises to form water and carbon dioxide, both present in the Martian atmosphere. So, there must be a mechanism that refills the atmosphere with methane.

“The first thing to understand is how exactly the methane is distributed in the Martian atmosphere,” says Vittorio Formisano, Principal Investigator for the PFS instrument. “Since the methane presence is so small, we need to take more measurements. Only then will we have enough data to make a statistical analysis and understand whether there are regions of the atmosphere where methane is more concentrated.”

Once this is done, scientists will try to establish a link between the planet-wide distribution of methane and possible atmospheric or surface processes that may produce it. “Based on our experience on Earth, the methane production could be linked to volcanic or hydro-thermal activity on Mars. The High Resolution Stereo camera (HRSC) on Mars Express could help us identify visible activity, if it exists, on the surface of the planet”, continues Formisano. Clearly, if it was the case, this would imply a very important consequence, as present volcanic activity had never been detected so far on Mars.

Other hypotheses could also be considered. On Earth, methane is a by-product of biological activity, such as fermentation. “If we have to exclude the volcanic hypothesis, we could still consider the possibility of life,” concludes Formisano.

“In the next few weeks, the PFS and other instruments on-board Mars Express will continue gathering data on the Martian atmosphere, and by then we will be able to draw a more precise picture,” says Agustin Chicarro, ESA Mars Express Project Scientist.

Thanks to the PFS instrument, scientists are also gathering precious data about isotopes in atmospheric molecules such as water and carbon dioxide – very important to understand how the planet was formed and to add clues on the atmospheric escape. The PFS also gives important hints about water-cloud formation on the top of volcanoes, and shows the presence of active photochemical processes in the atmosphere.