Astronomers have found a lake on Mars

THERE is no shortage of water on Mars. Astronomers reckon that at least 5m cubic kilometres of ice is locked up beneath the planet's dusty regolith. Whether any of it is liquid is a trickier question. In the 19th century Percival Lowell, an American astronomer, popularised the idea that there were canals criss-crossing the Martian surface, carrying water from the poles to feed a thirsty desert civilisation. Better telescopes, and the arrival of space probes in the 1960s, revealed the canals as a...