I was just looking around to see if something has been happening with the Cassini imaging of Titan (nothing obvious) when I saw that NASA has a separate astrobiology page . This site looks really full of goodies!
I clicked onto the headliner, Water from a stone and had a look. Scientists looking for evidence of (past) life on Mars need information about the climate and water history of a particular spot. A promising source for this kind of local information would be as the magnesium sulfate deposits observed by the Viking and later missions. Magnesium sulfates can retain varying amounts of water in their alternative crystal structures. In fact, the relative abundance of different crystal forms of magnesium sulfate is a sensitive indicator of how humid conditions were at the time of the rocks' formation. However, that same sensitivity makes it very difficult to transport these minerals back to Earth without risking transformation between forms or amorphization (loss of crystal structure), driven by the humidity and pressure in transit. To avoid this risk, the scientists would like to equip a future mars lander with an X-Ray diffractometer, which can distinguish the various forms of magnesium sulfate on rocks right on site. Finding a combination that suggests (relatively) warm and wet formation conditions would highlight that locale as a place to search for evidence of life.
I think right now the smart money's on bacterial forms buried well below the surface, where they would be/would have been shielded from temperature extremes and radiation, and might have/have had access to water reservoirs.
As a molecular biologist, I just want to see if those extraterrestrial beasties have DNA! Does anyone else think it's cheesy that almost every character in Star Wars has two eyes and two nostrils? Even Jabba the Hut has a face and a dorsal spinal cord, meaning his ilk has neural crest cells just like earth vertebrates. Hmmmm.... better than Star Trek though.