Geologists poring over the latest images from Mars keep on turning up new and tantalising evidence that water once flowed freely on the planet’s surface — and may still flow from time to time. If their interpretation is right, underground aquifers or ice layers should be commonplace on the planet. Yet no spacecraft flown so far has been capable of identifying them. All that should change in a few years, however, with the first European missions to the Red Planet. The European Space Agency’s Mars Express followed by the Netlanders, lead by the French space agency, CNES, will be the first missions capable of prospecting directly for underground water on Mars.