Keith's note: In a Mars Science Laboratory pre-launch press conference today, NASA's Doug McCuistion said "MSL is seeking signs of life but this is not a life detection mission". NASA is still confused as to what this mission is about - or at least its PR people are confused. If you are seeking "signs of life" then it is not impossible that those "signs of life", if detected, might also be an indication of extant life. So I guess if NASA detects life on Mars it won't say anything since it is not looking for life to begin with? It is this sort of confusing verbiage that makes PR problems for NASA. Remember the Kepler story last year wherein a project scientist referred to "earth-like" planets but stumbled (days later) to say that he did not really mean that they were "earth-like"?
On one official NASA MSL website at JPL ( http://mars.jpl.nasa.gov/msl/ - NASA seems to need more than one official website) says "The rover's onboard laboratory will study rocks, soils, and the local geologic setting in order to detect chemical building blocks of life (e.g., forms of carbon) on Mars and will assess what the martian environment was like in the past.". That could include extant life too, based on how this is written. If MSL CANNOT detect existing life then NASA should say so. If it can, then NASA should say so.
Oh yes, the official NASA MSL website at NASA.gov (which does not link to the JPL MSL website above) links to another MSL website at JPL - http://marsprogram.jpl.nasa.gov/msl instead. NASA seems to be incapable of having one place where it describes this mission, thus compounding public confusion.