THE MARS SCIENCE LABORATORY believes it has discovered something "earthshaking". Exactly what that something is, they're not saying right now. Check out Nancy Atkinson's account on io9, "Scientists claim to have discovered something “earthshaking” on Mars".
In an interview on NPR today, MSL Principal Investigator John Grotzinger said a recent soil sample test in the SAM instrument (Sample Analysis at Mars) shows something "earthshaking."
Apparently, after an initial discovery of methane was found to be Earth atmosphere that had been trapped within the rover, the scientists are being extra cautious. Religious fundamentalists are probably going to freak out, which is good.