The 2000s saw a renewed interest in exploring Mars with NASA orbiters, landers, and rovers. None had specifically astrobiological missions, but all contributed to better understanding pathways into the discipline’s goals. The Phoenix lander, for instance, found water ice in the north of Mars, ground-truthing the theory that Mars had substantial ice deposits just under its surface. The MER rovers, Opportunity and Spirit, detected carbonates and other minerals important to understanding the potential for biology in the martian past.
And then came Curiosity, which has had an explicitly astrobiological mission – to determine whether ancient Mars was habitable. The rover does not have the capacity to assess whether the planet was actually once inhabited by microbial life, but the results it has collected have convinced its science team that portions of the Gale Crater landing site were once perfectly capable of supporting life. It was the first formal identification of a habitable environment beyond Earth.
As is always the case with astrobiology, it was a combination of results — gathered by way of geology, geochemistry, minerology, sedimentology, super-high temperature chemistry and precision photography — that led to the conclusion. These findings support the theory that Mars was warmer and much wetter during its earliest days, even though climate modelers can’t figure out how an ancient Mars could have been warm enough, and had an atmosphere thick enough, to keep that water liquid for potentially tens of millions of years.
As technologies and scientific understandings have progressed, astrobiology has entered ever more fields. Moving beyond the astronomical detections of a cosmic menagerie of exoplanets, efforts are now underway to analyze the atmospheres, and ultimately the surfaces, of those bodies.
Carbon dioxide, water, and other compounds have already been detected in exoplanet atmospheres, but the ultimate goal is to find concentrations of oxygen, ozone and perhaps methane – gases which are associated with biology. Because oxygen and ozone quickly bond with other elements, the presence of large reservoirs of elemental oxygen, for instance, would tell scientists that it is constantly being produced. On Earth, the production of oxygen is largely a function of life.