I'm a real pushover for all the cool photos and geologic discoveries coming from Mars. Now, there's something new from the UA HiRISE camera on the Mars Reconnaissance Orbiter.
Tomorrow's issue of Science has an article by a team including Randolph Kirk at the USGS Astrogeology Branch in Flagstaff and Alfred McEwen at the UA Lunar & Planetary Lab, documenting sets of sedimentary layers that are interpreted as evidence of 100,000 year cyclical climate changes over a multi-million year period early in Martian history.
The one-million-year cycle corresponds to a known pattern of change in Mars's obliquity caused by the dynamics of the solar system. [right, sequences of cyclic sedimentary rock layers exposed in an unnamed crater in Arabia Terra, Mars. Credit, topography, Caltech; HiRISE Images, NASA/JPL/University of Arizona]