SNIFFING for puffs of radioactive radon gas could be the easiest way to find water lurking metres beneath the Martian soil.
We already know there should be plenty of water on Mars. Probes have found water vapour in the Martian atmosphere and ice on the surface at the poles. And NASA’s Mars Odyssey spacecraft recently detected traces of hydrogen, almost certainly bound up in ice near the surface.
But Mars Odyssey’s sensors could only peek into the top metre of soil, and although the European Space Agency’s Mars Express – due to reach the planet in December – has surface-penetrating radar that can spot water, it…
