P087-07
Localizing Methane Emission Sites on Mars from Inverse Modeling

Wednesday, 16 December 2020: 19:39
Virtual
Michael Mischna1, Yangcheng Luo2, Yuk L Yung3, John C Lin4 and Benjamin Fasoli4, (1)NASA Jet Propulsion Laboratory, Pasadena, CA, United States, (2)California Institute of Technology, Division of Geological and Planetary Sciences, Pasadena, CA, United States, (3)California Institute of Technology, Pasadena, CA, United States, (4)University of Utah, Atmospheric Sciences, Salt Lake City, UT, United States
Recorded Presentation
Abstract:
Methane has been detected in the Martian atmosphere by both remote sensing and in-situ observations by the MSL Tunable Laser Spectrometer (TLS). During its surface operation, TLS has observed six methane spikes with concentrations up to ~21 ppb. These spikes have been interpreted as the result of discrete methane emission events that occurred nearby. Localizing these emission sites can guide future Mars exploration of this intriguing methane signal. A common localization approach has been to simulate the Martian winds with general circulation models (GCMs), release passive tracers from local grid points, transport them while stepping forward in time using the bulk wind, and observing the resulting plume distribution. This forward modeling approach is inefficient and spatially coarse, limited by the resolution of the underlying GCM.

Here we adopt a novel method of inverse modeling, in which we transport methane plumes backwards in time from where they are detected, map out the upstream regions that are potentially methane emission sites, and quantify the influence of the upstream regions on the detected methane concentrations. We demonstrate that this approach overcomes most shortcomings inherent in the forward modeling approach, and present preliminary ‘footprints’ of the methane emission source regions responsible for the TLS observations, both inside the Gale crater and over a larger, ~3000-km-wide region. The approach employs MarsWRF, a Mars GCM, to simulate the Martian winds during the season of each of the methane spikes. Using the nested mode of MarsWRF with a 4-km resolution at Gale crater, we can resolve the local atmospheric circulation at Gale crater. We then use the terrestrial Stochastic Time-Inverted Lagrangian Transport (STILT) model, adapted to Mars, to trace, backwards in time, upstream locations from where surface emissions can exert influence on the detected methane concentration.

Our analysis for the methane spike observed by TLS in at Ls = 336.12° in MY 31 shows that inside Gale crater, the crater floor to the northwest of Mount Sharp has the strongest influence on methane concentration (left panel). Over a broader, 3000-km-wide spatial scale, the region to the northwest of Gale crater has the strongest influence on the detected methane concentration (right panel).

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