NASA's Mars Reconnaissance Orbiter may have just found flowing water on Mars. It's the closest that scientists have come to finding flowing water on the Red Planet and will help determine if Mars could harbour life.
Remember, frozen water has been found on Mars years ago. But frozen water — ice — in Mars cold temperature stays frozen, life as we know it needs some sort of, uh, non-frozen water to exist.
The evidence NASA found for the liquid water are "dark, fingerlike features" — about half a yard to five yards wide that go on for hundreds of yards with more than thousands appearing in some locations — that appear on Martian slopes in late spring 'til summer and disappear in the winter. The most plausible human explanation that scientists currently have for these stream-like remnants are that they're caused by flowing briny seawater (as saltiness lowers water's freezing temperature). There's our non-frozen water!
The images show flows lengthen and darken on rocky equator-facing slopes from late spring to early fall. The seasonality, latitude distribution and brightness changes suggest a volatile material is involved, but there is no direct detection of one. The settings are too warm for carbon-dioxide frost and, at some sites, too cold for pure water.
It's still no where near 100 per cent confirmed, but NASA believes that this mystery of possible liquid can be solved with more research, observation and experiments. If true, I'd like to volunteer myself to be the first Earthling to drink it. [NASA]
Update: For more information on the possibility of liquid water on Mars and the scientific explanation of "recurring slope lineae", check out io9 who spoke to the scientists behind the discovery. [io9]