לוח שנה משולב

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.