Martian methane releases are rare, episodic, and often debated, but scientists have discovered evidence of a methane emission in June 2013, which constitutes the first confirmation of a methane release on Mars.
Planetary Science Institute Senior Scientist Dorothy Z. Oehler is an author on two new papers on methane detections in the Martian atmosphere. The first is “Methane spikes, background seasonality and non-detections on Mars: A geological perspective” that appears in Planetary Space and Science. Giuseppe Etiope, of the National Institute for Geophysics and Volcanology in Italy, is lead author. The second is “Independent confirmation of a methane spike on Mars and a source region east of Gale Crater” appearing in Nature Geoscience, on which Marco Giuranna, of the National Institute for Astrophysics in Italy, is lead author.
“These two papers add insight into the geologic potential for episodic methane emissions from the subsurface on Mars. Because methane is generally at very low concentrations in the Martian atmosphere, the results also emphasize that methane spikes or pulses on Mars are likely to be detected only occasionally – when rovers, landers or orbiters happen to be at the right place at the right time,” Oehler said.
“The Planetary and Space Science paper provides geological insight into patterns of methane seepage on Earth that could explain episodic methane releases on Mars from the subsurface,” she said. “The Nature Geoscience paper provides new orbital evidence from the Planetary Fourier Spectrometer (PFS) on Mars Express for a Martian methane degassing event in June of 2013. That event was also measured by the Curiosity rover, and the new PFS evidence represents the first confirmation of a methane release on Mars. That paper also reports atmospheric circulation modelling and geological analyses that independently highlight a region approximately 500 kilometers east of Gale Crater as a likely subsurface provenance for the detected methane.
“This is an unexpected and exciting result, as two separate lines of inquiry indicated the same region as the most likely provenance for the methane. And locating the source of methane emissions on the planet will be a first step to future investigations aimed at understanding the origin and significance of the methane,” Oehler said.
Methane on Mars is of great interest, as subsurface accumulations could provide a resource for future exploration activities and it can enhance habitability. Methane could also be a signature of microbial, methane-generating life, though life is not required to explain these detections because methane can also be produced by abiotic processes. Nevertheless, reports of methane spikes and pulses in the Martian atmosphere have been intensely debated, and, until the Giuranna et al. paper, no detection had been confirmed with independent measurements.
The Giuranna et al. paper reports a firm detection of 15.5 ± 2.5 parts per billion by volume of methane in the Martian atmosphere above Gale Crater on June 16, 2013, by the PFS onboard the Mars Express orbiter, one day after the in-situ observation of a methane spike by the Curiosity rover. Methane was not detected in other orbital passages, indicating the episodic nature of the methane release and the generally low concentrations of atmospheric methane, before and after that release.
More information on the papers may be found at https://authors.elsevier.com/a/1Yj4s7IbIigAi or https://www.nature.com/articles/s41561-019-0331-9
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