I dont have trouble with thought-experiments like "Panspermia" but why is this discovery being touted here (and in an above comment) as en example of such over the excedingly far more likely terrestrial origins of bacteria?
This planet is TEEMING with bacteria. You could say its "lousy" with them. Everywhere you look there are bacteria just "moldering away".
Consider that the bacteriological taxonomic archives only list several thousand named species of bacteria. This is primarily because of our historical reliance on culturing methods as the only means of bacterial identification. However, recent estimates based on DNA squencing have suggested that 1 in 100 to 1 in 1000 species of bacteria are unculturable with today's culturing technology.
One study using DNA sequencing identified 10 new species and 2 new genera of bacteria in the human mouth. If an environment as familiar as the mouth can have undiscovered bacterial species lurking, then the prospects of finding bacteria elsewhere is promising.
Have faith my brothers and sisters in this planets ability to support life in all manner of inhospitable (to humans) environments!
If you want job-security, become a bacterilogist! There is easily another 500 years worth of bacterial species to be discovered and named.
~Flatlander