Astronomy and Astrophysics – Astronomy
Scientific paper
Sep 2009
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009dps....41.5406n&link_type=abstract
American Astronomical Society, DPS meeting #41, #54.06
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. As Mars approaches 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 for the first time.
We obtained diurnal maps (emission rate versus local time) of the O2 singlet-Delta emission (1.27 microns) on three dates spanning the pre-aphelion season on Mars: Ls = 357o (Jan 16, 2006), Ls = 20o (Jan 19, 2008), and Ls = 50o (Mar 27, 2008). The data were collected using CSHELL at the NASA-IRTF. The slit was positioned North-South on Mars, and spectral/spatial data were taken at 1.0 arc-sec increments stepped East-West across the planet. At Ls = 357o and Ls = 20o, emissions were strong in the polar-regions, but not detected at middle to low latitudes. For Ls = 50o, strong emissions were detected at all latitudes. Models (e.g., Sandor et al. 1997, JGR,102,D7,9013-9028) predict that ozone formed during the night is rapidly destroyed at sunrise; it is then reformed during the daylight hours, peaks near noon local time and is reduced in the late afternoon. All detected emissions show this strong diurnal variation. The strong emission at mid-latitudes in the pre-aphelion season (Ls = 50o) is consistent with a lower hygropause altitude, as predicted by current models (Nair et al.1994, Icarus,111,124-150).
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.
Hewagama Tilak
Mumma Michael J.
Novak Robert E.
Sanstead Paul
Villanueva Geronimo
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