This image, snapped by Cassini as it passed over Saturn's moon Titan, shows the biggest liquid system ever found on any world other than Earth.

Scientists have observed lakes and streams on Titan before, but this river is by far the largest yet: it measures over 320 kilometres in length. That's still twenty times shorter than the Nile, but makes the the Titan river the largest body of liquid ever observed away from Earth.

Unlike our planet, though, this river doesn't flow with water: instead, it's a swirling mass of liquid hydrocarbons such as methane and ethane, which take a liquid state on the moon's -170C surface. Sorry, that means waterskiing is out. [NASA via Wired]

Image by NASA