Presentation #506.06 in the session “Mars Atmospheric Dynamics”.
Since its commissioning in 2017, we have used iSHELL to search for organic molecules (such as CH4, CH3OH, H2CO, C2H6, C2H2, C2H4) in the atmosphere of Mars. We have identified methane and have obtained upper limits for the other molecules listed. We took data using the L3 setting on iSHELL on January 29-31, 2018 (Ls~122°). This setting consists of ten spectral orders ranging from 3.20–3.48 mm, and includes absorption bands of the molecules listed above along with bands of water and ozone. Data were continuously taken with the slit positioned N/S on Mars along the meridian (~14:20 Local Time) as the planet rotated under the slit. The longitude range covered was from 156°W to 256°W. Approximately thirty minutes of data were stacked for this presentation. The Mars atmospheric spectrum was isolated from the solar and terrestrial spectra, including terrestrial signatures of H2O, CH4, O3, and related species. Extracts were taken at 0.6 arc-sec intervals in the latitudinal direction. Simulations based on atmospheric models generated for Mars were created to match the observed spectrum. Column densities for CH4 and H2O were determined - Mars O3 was not detected. For other molecules listed above, upper limits were measured. Results for the column density of water are consistent with other measurements, such as NOMAD-TGO, for the same season and location. Retrieved column densities of methane varied from a peak of 25 ppb (at 255°W, 8°N) to the detectible limit (2 ppb) (at 203°W, 8°N). These values are consistent with previously detected column densities of methane. (Mumma et al., Science, 2009). Column density maps for both methane and water will be presented over the range156° to 256°W, 72°S to 88°N. This work was partially funded by a grant from NASA’s Mars Fundamental Research Program (11-MFRP11-0066) to RN. NASA’s Mars Exploration Program supported this work under WBS 604796.01.12.01.03 to MJM. We thank the administration and staff of the NASA-IRTF for awarding observing time and for coordinating our observations.