Back in April, NASA's Curiosity rover found evidence of liquid water on Mars. Still, this is no life-friendly oasis: The water is hyper-salty, ultra-cold, and contained in fleeting layers of sludge trapped beneath the red planet's regolith soil. Nonetheless, it completes the trifecta of requirements for Earth-like life. We now know Mars has soil-bound nutrients, a carbon monoxide energy source for hungry microbes, and liquid water.
The scientists behind the water discovery, including Morten Bo Madsen at the Niels Bohr Institute, say that "finding life on Mars still doesn't look very probable, because it's simply just too cold and/or too dry" on large swaths of the planet. But it certainly looks at least possible that there could be environmental niches, probably connected to one of these [salt-water] brines, where life could thrive."
To Gary King, a microbiologist at Louisiana State University who studies life that survives in extreme environments, this presents humanity with an amazing opportunity. We may never find native Martian microbes, and they may, in fact, be long gone. But because the Red Planet's has that life-friendly trio—the energy sources, nutrients and water—we could grow microbial life there ourselves.