At a press conference today, scientists announced that they may be once step closer to determining whether water--an essential ingredient for life--exists on Mars. NASA's Mars Reconnaissance Orbiter has detected "dark, finger-like features" appearing on Martian slopes in the planet's southern hemisphere during late spring and summer and then fading in winter when the weather turns colder. The most plausible explanation is that these streaks are a "kind of salty water that is running on or just below the Martian surface," The Washington Post's Marc Kaufman explains. If that theory's confirmed, he adds, it "would strongly support the widely held theory that the planet was once far more wet and warm and offer "our best target yet for finding possible life beyond Earth." NASA Administrator Charles Bolden added that the discovery "reaffirms Mars as an important future destination for human exploration" (which might be a boon for NASA now that its space shuttle program has ended).

The image above shows the streaks in question, and you can see the streaks appear and disappear instantly across the seasons here. This NASA handout shows a view of the apparent water flows on a slope as they would be seen from a helicopter inside Mars' Newton crater (the Mars-like sky is synthetic)