Blog: The Search Continues for Methane on Mars

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13th July 2011.

In 2004 three research teams reported finding the spectral signature of methane in the atmosphere of Mars. Their data was collected using ground-based telescopes and an instrument flying onboard the Mars Express spacecraft called the Planetary Fourier Spectrometer (PFS). The PFS scientists also reported seasonal and even daily variations in methane abundance, with peaks spotted in late spring in the northern hemisphere. In 2009 this variation appeared to be confirmed by further analysis and observation by of one of the ground-based telescope teams.

The methane detections were very low level, only a few tens of parts per billion by volume (ppbv), but even so the results were cause for interest. The lifetime of methane in the martian atmosphere is just a few hundred years; if methane did indeed persist, there had to be a current – or very recent – source of the gas. Given that there is no atmospheric source, and based on our understanding of the martian environment, it would most likely be generated by one of two processes: a hydrological mechanism called serpentinization, or the metabolism of (hypothetical) methanogenic microbial life in the subsurface.

(Release of the gas by clathrate hydrates has also been suggested; however these crystalline solids are not a source in and of themselves, but rather a mechanism of sequestration and release. If clathrates were shown to be linked to the episodic release of methane, the point of genesis would remain to be found.)

One of the most recent advances in the debate was made in a paper which appeared in late 2010. It called into question the ground-based observations, citing confusion with spectral signatures found in Earth’s atmosphere which, the authors suggested, were recorded as the telescopes looked towards Mars.

Until these concerns are addressed, that leaves the PFS data. Terrestrial contamination is not an issue for measurements taken from martian orbit, and so the available observations appear to be consistent with a trace amount of methane in the atmosphere of Mars, somewhere in the order of 10–15 ppbv. This is very close to the detection limit of the PFS instrument, and so the scientific community is being understandably cautious.

The hypothesis that methane is currently being produced by life is understandably an enticing one. Life here on Earth began in an anoxic environment, and current thinking is that methanogenic microbes were amongst the first to evolve around 3.7 billion years ago. If on Earth, then why not on Mars?

There are two missions planned which should be able to answer the question one way or the other: the Mars Science Laboratory, recently rechristened Curiosity, due for launch later on this year; and following that in 2016 will be the ExoMars Trace Gas Orbiter, which is designed to, amongst other things, answer the methane question once and for all.

Selected references:

Formisano, V., S. Atreya, et al. (2004). “Detection of methane in the atmosphere of Mars.” Science 306(5702): 1758.

Zahnle, K., R. S. Freedman, et al. (2010). “Is there methane on Mars?” Icarus 212(2): 493-503.

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Methane on Mars

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18th December 2014.

Is there life on Mars?  New data from NASA’s Curiosity rover, published in Science, has energised the debate.  Methane is so interesting to those seeking evidence of life on Mars because on Earth the overwhelming majority of the gas is produced by living things. The measurements were taken by the Tunable Laser Spectrometer over a period of twenty months, and record a mean background level of atmospheric methane of 0.69 ppbv.  However, at the end of 2013 and start of 2014, four consecutive measurements reached values of 7.2 ppbv.  This spike showed no correlation with relative humidity, atmospheric pressure, ground temperature, air temperature, or radiation levels.  The authors suggest that there may be a negative correlation with column measurements of water vapour and oxygen abundance, but point to a lack of data to fully accept or refute this hypothesis.

The observed high concentrations appeared to be spatially restricted; all the high measurements were taken within 200-300 m of each other, yet were not found after the rover moved 1 km away.  Due to the fact that the spike was sustained for two months before suddenly dropping, the authors conclude that the origin of the methane is likely to be local production or release, with concentrations quickly dipping as the production mechanism ceases.

A MethaneNet article from 2013 discussed some of the possible mechanisms that could lead to atmospheric methane on Mars, which include both biological and physical processes.  Lead author of the paper, Christopher Webster from the Jet Propulsion Laboratory said: “It’s equally likely to be geophysical or biogenic… The fact that we’ve seen it, in a sense, argues that the stock in a possible biogenic source went up.”

MethaneNet spoke to Dr Manish Patel at the Open University, for his thoughts on the latest news.  Dr Patel’s research interests include astrobiology and the modelling of sudden releases of methane from subsurface clathrates.  He said: “This result is a nice confirmation that the methane is there.  There has been a lot of scepticism about martian methane over the last few years, so it is great to get confirmation that what we are seeking to measure is indeed there.”  Dr Patel is also involved as a Co-PI in constructing NOMAD (Nadir and Occultation for MArs Discovery) for the ExoMars Trace Gas Orbiter project in 2016.  Dr Patel said: “NOMAD is led by the Belgian Institute for Space Aeronomy, and is going to map in even more detail the trace gases such as methane in the martian atmosphere using a suite of spectrometers.”

Whether or not the observed martian methane turns out to be of biotic or abiotic origin, it certainly seems an exciting time for research into the atmosphere of Mars.

Reference: Mars methane detection and variability at Gale crater. 2014. Webster, C.R., Mahaffy, P.R., Atreya, S.K., et el. Science, DOI 10.1126/science.1261713

India Launches Mission to Mars

MarsSunset

5th November 2013.

On November 5th, The Indian Space Research Organisation (ISRO) successfully launched the Mars Orbiter Mission (MOM).  If all goes according to plan, the MOM will reach Mars orbit in September 2013, thus making the ISRO the fourth space agency to send a craft to the red planet.  The scientific payload of the craft consists of five instruments, one of which is a Fabry-Perot Etalon sensor to detect the presence of methane in the Martian atmosphere, and to map any potential sources.

Methane was first detected in the atmosphere of Mars in 2003 as large plumes seemingly being emitted from discrete regions.  The largest plume was estimated to contain 19000 tonnes of methane.  This first measurement was backed up by additional reports of methane using both ground-based and space-based observations.

Various processes could account for the Martian methane, such as hydrothermal or volcanic production (unlikely due to a lack of activity), inputs from comet and meteorite impacts, the actions of microorganisms (should they exist), or production using hydrogen (produced abiotically) via Fischer–Tropsch synthesis (reactions between H2 and CO/CO2 that produce hydrocarbons).  Because methane in the atmosphere would be quickly degraded by UV radiation and chemical reactions, its presence implies a continuous source.

However, in September 2013, it was announced that NASA’s Curiosity rover failed to detect substantial methane concentrations on Mars, after analysing six atmospheric samples between October 2012 and June 2013.  The suggested upper limit was 1.3 parts per billion.  It seems that more research is required to get a definitive answer to the question of whether methane exists on Mars, and how it might be produced.  Hopefully the ISRO’s Mars Orbiter Mission will be the next step towards this answer.

References:

Formisano, V., et al., 2004. Detection of methane in the atmosphere of Mars. Science, 306, 1758-1761.

Mumma, M.J., et al., 2009. Strong release of methane on Mars in northern summer 2003. Science, 323, 1041-1045.

Krasnopolsky, V.A., et al., 2004. Detection of methane in the Martian atmosphere: evidence for life? Icarus, 172, 537-547.

Keppler, F., et al., 2012. Ultraviolet-radiation-induced methane emissions from meteorites and the Martian atmosphere. Nature, 486, 93-96.

Image: Martian sunset: Spirit at Gusev crater. NASA.