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Astrophysics Colloquium

Searching for CH4 Source Regions on Mars Using a GCM: Application to the MSL-PFS Spike in June 2013
Presented by Sébastien Viscardy
Royal Belgian Institute for Space Aeronomy

Thursday, August 1, 2019
11:00 A.M. in 169-336

The story of methane on Mars has been highly controversial over the last 15 years. Recently, Giuranna et al. (Nature Geosc., 2019) reported the detection of 15.5 ± 2.5 ppbv of methane above Gale Crater in June 2013, by the Planetary Fourier Spectrometer (PFS) onboard Mars Express. This detection was recorded one day after the observation of a spike (5.78 ± 2.27 ppbv) by Curiosity and constitutes the first independent confirmation of the presence of methane on Mars.

Searching for the potential CH4 sources on Mars is a crucial step toward a better understanding of the origin of the released gas. Several model studies demonstrated the capabilities of GCMs to understand processes forming atmospheric CH4 plumes from local outgassing events. Nevertheless, those investigations are largely inconclusive because many combinations of release locations and release scenarios can explain observations. Indeed, such problems are weakly constrained given the sparsity of observational data. In addition, the use of release patterns (either instantaneous or continuous) in previous studies has not been supported by methane emissions on Earth. The information about emission patterns (strength and duration) from terrestrial analogs can provide guidance for GCM simulations, so that values used are within reason for the geological systems on Mars in the vicinity of any methane detections. In this context, instead of supporting the available methane observations with one consistent numerical experiment, we developed a statistical approach considering a large number of realistic release scenarios and applied a statistical analysis to this sample. Such a study is made possible taking advantage of the additivity of tracers. Emission events can be viewed as a sequence of stochastic gas fluxes generated by combining tracers released successively and scaled randomly in order to mimic the time variability of typical methane seepage observed on Earth. Hence, a probability can be attributed to the given emission site in terms of the number of scenarios consistent with the observations. As a result, comparing the probabilities associated with all potential emission sites within a predetermined region indicates the most plausible sites. This statistical analysis was applied using the GEM-Mars GCM to identify a potential source location of the methane detected by MSL and PFS in June 2013, and pointed to a region east of Gale Crater.

JPL Contact: Renyu Hu (4-6090)

SVCP Astrophysics

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