The Kepler space telescope, Nasa's iconic mission to find a new Earth outside our solar system, has a problem. A crucial component used to help it orient in space has stopped working and, with little chance of getting it fixed, it looks as though the satellite will have to retire from active duty.

However, on Thursday Nasa tried to remain upbeat. "I wouldn't call Kepler down-and-out just yet," said Nasa associate administrator for space science John Grunsfeld, who as a former astronaut undertook several spacewalks to repair and upgrade the Hubble Space Telescope. Similar in-flight repairs are not an option for the $600m Kepler observatory, since it is in an orbit 40 million miles (60 million kilometres) from Earth.