Diurnal Variation Of The O2 Singlet-delta Emission And The H2O And HDO Column Densities Near Mars’ Aphelion

Details Diurnal Variation Of The O2 Singlet-delta Emission And The H2O And HDO Column Densities Near Mars’ Aphelion Diurnal Variation Of The O2 Singlet-delta Emission And The H2O And HDO Column Densities Near Mars’ Aphelion

Oct 2010

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010dps....42.4203n&link_type=abstract

American Astronomical Society, DPS meeting #42, #42.03; Bulletin of the American Astronomical Society, Vol. 42, p.1041

Astronomy and Astrophysics

Astronomy

Scientific paper

On Mars, O2 in the excited singlet-Delta state originates from the photolysis of ozone. This metastable state is quenched by carbon dioxide at low altitudes, but radiative decay predominates above 20 km. Since ozone and water are anti-correlated in abundance, the O2 singlet-Delta emission also tests the abundance of water above 20 km. Near Mars’ aphelion, the atmosphere cools and lowers the hygropause below 20 km altitude, permitting increased ozone abundance above the hygropause and thus increased singlet-Delta emission. We report detection of this effect along with near simultaneous detections of H2O and HDO.
On April 3, 2010 (Ls = 72o), we positioned the slit of CSHELL (NASA-IRTF) East-West on Mars centered on the sub-Earth point (14oN). We accumulated data between 5:00 and 9:00 UT as the sub-Earth longitude went from 264o to 322o W (from Isidis Planitia through Syrtis Major). We continuously took data at O2 singlet-Delta (7908 cm-1), HDO (2772 cm-1), and H2O (2996 cm-1) settings. For each setting, we integrated on Mars for four minutes giving an E-W map of the emission or column density across Mars. Over the four-hour terrestrial time period, 12 sets of O2/HDO/H2O data were obtained. We thus trace specific geographical locations on Mars through a local time of 3.8 hours (sols). The data extracted from these observations show the O2 singlet-Delta emission peaking at mid-day and the HDO and H2O column densities increase during the morning hours. Column densities of H2O and HDO are greater over Isidis Planitia (elevation -3 km) than over Syrtis Major (+2 km). The difference in elevation between these two regions does not affect the O2 singlet-Delta emission.
We acknowledge support from NSF RUI-Program (AST-0505765 and AST-0805540) and thank the administrators and the staff of the NASA-IRTF for use of the telescope to acquire the data.

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