Liquid Water on Mars

It's generally accepted that billions of years ago, Mars was a pretty wet place. But over time, Mars lost its atmosphere and its water, and the oceans that probably existed on the surface dried up. With atmospheric pressure at 1% of Earth's, and with temperatures rarely getting above freezing, liquid water on the surface of Mars today seems like an unlikely prospect. But not impossible. In the past few years, space probes have found features called recurring slope lineae, dark streaks that appear in the Martian summer and fade away during the winter. It was suspected that liquid water was forming these features, but the evidence was not there.

As you may have guessed, today NASA announced that the evidence had been gathered, and they could definitively say that the RSL were in fact formed by liquid water. Now, I don't want to overstate the importance of this discovery. The water is filled with a kind of salt called perchlorate, which lowers the freezing point of the water to well below zero. That's good for liquid water, not good for life, as we know of no organism that could live in such an environment. In addition, we're not talking about some big gushing stream running down a crater, but what basically amounts to damp soil. There's not a lot of water available. However, finding any amount of liquid water is fantastic news. Just because life as we know it could not survive there doesn't mean it's completely inhospitable, and any manned missions to Mars could certainly use it. I think it's absolutely incredible that for so long, we assumed that liquid water could only exist on Earth, but we've found it on Europa, on Enceladus, and now, on Mars. That's 4 different planetary systems that we can find liquid water, spread out across a billion miles of space. At this point, I would be more surprised if life did not exist elsewhere in the Solar System then if it did, because with every discovery of liquid water, the odds of finding life improve.