Once upon a time, Mars was awash in surface water: river systems, lakes, and maybe even oceans. This required an atmospheric pressure that was not much different than what we have on Earth (to date, about 1 bar). Alas, Mars gravity was too puny to hang on to its own atmosphere, most of which had escaped to space by roughly 4 billion years ago. Any critters around at the time would have rooted for global warming. Gone, essentially, was the abundant surface water. We see today what is left: an atmosphere that is dominated by a meager 6 mbar of carbon dioxide. Water vapor is present in the atmosphere in trace amounts, but as water ice it dominates the composition of the polar caps and is also found in the shallow subsurface at mid to high latitudes. Mars has become an icy world that even with a tenuous atmosphere undergoes significant climate change. It does so by experiencing Milankovitch Cycles “on steroids.” These are periodicities in a planet’s orbital and rotation properties that on Earth cause glacial and interglacial periods in the present Ice Age. On Mars, the same phenomena occur. The tilt of the spin axis (obliquity) is more pronounced than on Earth, plus it has a strong chaotic component. Given Mars’ thin atmosphere, obliquity variations can lead to sublimation of the entire north polar water ice cap and the deposition of that material at mid-latitudes, where water-ice glaciers form. More recently, a sounding radar has discovered a massive solid carbon dioxide (dry ice) deposit in the south polar cap, indicating that, driven by obliquity variations, the atmosphere completely vanishes from time-to-time. To top that, dry-ice glaciers flow downhill from high points in the cap. This talk will emphasize the role of sounding radars in unraveling the mysteries of the current Martian climate.
No Denying Climate Change on Mars
Roger J. Phillips, Institute Scientist, Southwest Research Institute, Boulder CO; Director Emeritus, McDonnell Center for the Space Sciences and Professor Emeritus, Department of Earth and Planetary Sciences, Washington University in St. Louis
April 15, 2015 - 7:00pm
Whitaker Hall, Room 100