Biosignatures 2 November 2016

Methane on Mars: Methane, an indicator of life? Methane (CH4) is an organic molecule present in gaseous form in the Earth's atmosphere More than 90% of methane on our home planet is produced by living organisms. Methane breaks up in the presence of ultraviolet solar radiation. Methane has a chemical lifetime of about 300-600 years: it must be created now

By analogy with Earth, the biological origin of Martian methane could be explained by the existence of micro-organisms, called methanogens, existing deep under the surface, and producing methane as a result of their metabolism.

If the methane on Mars is biotic, two possibilities: Long-extinct microbes, which disappeared millions of years ago, have left the methane frozen in the Martian upper subsurface, and this gas is being released into the atmosphere today as temperatures and pressure near the surface change, or Some very resistant methane-producing organisms still survive

An alternative explanation is that the methane is geological in origin It could be produced, for example, by the oxidation of iron, similar to what occurs in terrestrial hot springs, or in active volcanoes. This gas could have been trapped in solid forms of water, or 'cages', that can preserve methane of ancient origin for a long time. These structures are known as 'clathrate hydrates'. A geochemical process called serpentinisation could also produce the abiotic methane.

Confirming the presence of methane on Mars is a goal of the ExoMars program This was the part of the Exomars program that succeeded! ESA’s Trace Gas Orbiter went into Mars orbit last month before the lander crashed

Curiosity Rover On Mars

Curiosity Detected Methane variations While exploring its bowl-like landing site in the Gale Crater, Curiosity detected a major spike in methane levels, which quickly dissipated months later. Over the course of four different measurements starting in November 2013, methane levels increased 10-fold before tapering off in July 2014

Summary False negatives: Lack of biosignatures does not mean life does not exist False positives: Finding a biosignature does not require life as a source What to do? Get more information to check for consistency Rule out alternatives