Sunday, February 19, 2012 at 11:00
Seasonal Carbon Dioxide Snowfall on Mars"
Abstract: One of the more interesting and unusual aspects of the present-day Martian
climate is the seasonal condensation of the atmosphere during polar winter. Heat cannot
be transported from lower latitudes rapidly enough by the thin CO2 atmosphere to offset
radiative cooling within the polar night, and the air cools to the CO2 frost point. Pressure
changes recorded by the Viking landers indicate that about one third of the atmosphere is
exchanged with the seasonal polar caps each year through the condensation/sublimation
cycle. Does it snow? I will present recent infrared observations by the Mars Climate
Sounder (on NASA's Mars Reconnaissance Orbiter), which reveal the distribution and
behavior of polar CO2 clouds for the first time, elucidating the role of snowfall in
forming the seasonal polar caps. A ~300-km snow cloud persists over the south polar
residual cap (SPRC) for the entire winter season, making it the snowiest place on
Mars.We find that CO2 snowfall contributes at least 7-15% of seasonal deposition at the
SPRC, and the granularity of the snow deposits may enable their interannual preservation
by enhancing their summertime albedo. Thus, the mode of deposition may be a key to
buffering the Martian atmosphere against complete sublimation on interannual time
scales.