Marco Giuranna, Sébastien Viscardy, Frank Daerden, Lori Neary, Giuseppe Etiope, Dorothy Oehler, Vittorio Formisano, Alessandro Aronica, Paulina Wolkenberg, Shohei Aoki, Alejandro Cardesín-Moinelo, Julia Marín-Yaseli de la Parra, Donald Merritt & Marilena Amoroso Nature Geoscience (2019)

• Reports of methane detection in the Martian atmosphere have been intensely debated. The presence of methane could enhance habitability and may even be a signature of life. However, no detection has been confirmed with independent measurements. Here, we report a firm detection of 15.5 ± 2.5 ppb by volume of methane in the Martian atmosphere above Gale Crater on 16 June 2013, by the Planetary Fourier Spectrometer onboard Mars Express, one day after the in situ observation of a methane spike by the Curiosity rover.
• My question. Where does methane occur naturally on Earth? Wetlands are the major natural source of methane produced on Earth. Other important natural sources of methane include termites (as a result of digestive processes), volcanoes, vents in the ocean floor, and methane hydrate deposits that occur along continental margins and beneath Antarctic ice and Arctic permafrost.
• Now, are there wetlands on Mars? Do termites live on Mars? Are there erupting volcanoes on Mars? Are there oceans on Mars comparable with those on Earth? and last but not least how does the measured 15.5 ppb of mathane on Mars compare with the 1.9 ppm in the Earth's atmosphere, hence a factor 123 more on Earth than on Mars.
• Although different types of organic compounds have been found in Martian rocks, the question remains whether they were produced by living organisms (as suggested in the 1990s for the famous Martian meteorite ALH 84001, or more recently for the mudstones found at Gale Crater) or whether they’re of purely chemical origin. Scientists remain skeptical that organics are indigenous to Mars. In the case of Martian meteorites found on Earth, they think that organic compounds are the result of terrestrial contamination after the rocks arrived here. Organic compounds found on Mars were interpreted by them not to have originated there, but to have come from the infall of organic-rich comets and asteroids.
• So is methane on Mars an indication of life or past life on Mars? Give it a try folks.