A presentation to be given at the Lunar and Planetary Science Conference in Houston next month argues that mysterious blotches [right, credit NASA/JPL-Caltech/University of Arizona/Max Planck Institute] that appeared on the Phoenix Mars Lander legs shortly after it landed, and grew in size over the ensuing weeks, may have been the first liquid water ever seen on Mars.
Thanks to NewScientist which has a good analysis of the report and comments from other planetary scientists.