1. Biosignatures 2 November 2016

2. 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

3. 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.

4. 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

5. 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.

6. 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

7. Curiosity Rover On Mars

8. 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

11. 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