Soon, a small aircraft laden with sensors and a high-speed datalink could be flying over the mountains of Mars – the first aircraft to fly over the terrain of another world. Called Ares (Aerial Regional-scale Environmental Survey of Mars), it could, if all goes well, be flying over the Red Planet’s southern uplands in just five years’ time. After a successful series of half-scale tests, the US space agency (Nasa) has ordered a full-scale prototype to be built. Ares is in competition with three other Mars exploration proposals for a Nasa launch in 2007. The final selection of one, or possibly two, missions will be made later this year.