Today, NASA announced a possible discovery of liquid water on Mars. The evidence takes the form of a seasonally-varying streak on a crater face. The dark patterns start in spring, fade in autumn and winter, and resume the following year. Other similar features have been spotted, but are mostly believed now to be dry flows: landslides caused by freezing and thawing of carbon dioxide in the Martian surface. Unlike those features, the new flows are on warm slopes, which is more consistent with water flows than any other volatile substance (such carbon dioxide — dry ice). The best explanation thus far is salty water from below the surface bubbles up during warm weather, flows while temperatures are suitable, then freezes and dries up during the colder seasons. (See Phil Plait’s far more detailed explanation here.)

Salty water, of course, is like Earth’s oceans, an intriguing possibility. Life on Earth requires both water and salt — many scientists think life may have originated in the oceans, which makes the discovery of salty water on Enceladus that much more exciting. Water — even salty water — by itself is not evidence for life, but the existence of the raw materials of life is tantalizing nevertheless.

Of course it’s too early to say these features are definitely water, and the NASA scientists are careful to say that. Just because we don’t have a good alternative explanation doesn’t mean one doesn’t exist! My scientist’s brain warns me to be cautious; I’ve been disappointed before by possible liquid water discoveries on Mars, and confirmation may be some time in coming. My scientist’s heart, though, is the heart of a child — and that is hopeful. Time will tell which is right, but I think all scientists have both that cautious head and hopeful heart — and the hearts are leading space exploration.

Speaking of space exploration, if conditions hold up, NASA will launch the Juno space probe, heading to Jupiter. I originally intended to write a long post about Juno, because it’s such an exciting mission, but I’m packing to move to a new apartment tomorrow and writing is going to have to wait a few days. (It’s not a long distance away from where I’m currently living, so I’m largely practicing the “shove stuff into boxes and worry about it later” method of packing.) I hope to get back into regular posting soon, and hopefully there will be so many new things to write about that I won’t be able to keep up.