Update to the Robotic Mars Exploration Strategy 2007-2016 (MAPG) (12.17 Mb PDF)
Findings of the Mars Special Regions Science Analysis Group (Astrobiology, Volume 6, Number 5, 2006). Non-subscribers might also note that the publishers of Astrobiology are, for the time being, granting free online access to that entire issue, which contains a couple of other interesting items.