Generally, if somebody describes planetary activity as ‘recent’ they mean on geological timescales: a few hundred thousand years or so. So the BBC headline announcing ‘recent’ water flow on Mars perhaps sounds less impressive than when you discover it means in the last seven years. Although not conclusive, comparisons of two photographs taken seven years apart strongly suggest water flow in the intervening period. The team leader called the possibility of liquid water ‘high, but not extremely high’, although some are apparently calling it ‘a squirting gun’. It seems increasingly likely that there’s water not far under the surface, and it escapes occasionally in flash floods then immediately boils in the low atmospheric pressure. Two immediate thoughts:

• On Earth at least, where there’s water there’s life.
• A base on Mars just became much more feasible.

The evidence comes from a photograph taken by the Mars Global Surveyor, but unfortunately the probe was so surprised at the discovery that it promptly died. Not bad for a ten year old machine, though. The newly-arrived Mars Reconnaissance Orbiter, with its amazing 1-2 meter-per-pixel resolution camera, will presumably be asked to take a closer look.

The best coverage, as ever, comes from Bad Astronomy.