Conventional wisdom has it that one of two things might explain the lack of air and water on Mars. First is the idea that it simply leaked away over the eons, dribbling away into space as the solar wind stripped molecules from the top of the planet's atmosphere. Another more colourful theory has it that some catastrophic impact blasted the atmosphere away in one titanic event. Either way, the planet now shows little sign of either water or air, though a recent set of photographs snapped from orbit did offer the tantalising possibility that water may still occasionally flow over the surface. Measurements taken previously have suggested the ongoing loss was quite rapid, but new observations from the European Space Agency's Mars Express orbiter are throwing those measurements out, though not necessarily with the bathwater, because that still seems to be there in potentially vast quantities. New figures from Mars Express put the rate of leakage at 20 grams per second of oxygen and CO2, which is 1% of the measured rate by the 1989 Phobos 2 mission. If correct, and extrapolating backwards into its history, it means that Mars has lost a lot less water than air than previously calculated, perhaps only in the region of a few centimetres of water. This is very exciting news, because based on observations of geological formations on the surface, it has been estimated there was once enough water on Mars to fill oceans half a mile deep! So if Mars hasn't lost its water and air, where is it? The only real possibility is underground, which returns us to the fascinating discovery of what looked like a very recent (in the region of years) outpour of water on Mars. Was this little dribble the tip of a huge iceberg buried beneath the Martian sands? Could be, but don't forget the other possibility that a giant asteroid blew away the atmosphere sometime in the distant past. But it certainly is a food for thought (or should that be water to glug and air to breath) because if it is there, locked away beneath the surface, we have even more reason to get a human presence on Mars as soon as possible.