Space scientists have scrapped a $40 million mission to a distant comet because astronomers have lost it. Nasa were due to send their Deep Impact spacecraft to intercept Comet Boethin as it headed through the solar system in December next year.

But astronomers cannot find any trace of their target and speculate that it might have broken up into tiny pieces.

Now Nasa have approved a plan to send the unmanned probe, which is already in space, to another comet instead. Their new target is called Comet Hartley 2 after Malcolm Hartley, the British astronomer who discovered it.

The new encounter for the mission, which has been renamed Epoxi, will happen two years later than originally planned. The spacecraft will rendezvous with Comet Hartley on October 11, 2010.

In 2005, the Deep Impact probe scored a spectacular success when it attacked another comet, Tempel 1, with a missile. The resulting explosion blew a crater the size of Wembley stadium and was visible back on Earth.

Epoxi will also point the larger of its two telescopes at nearby stars to observe other solar systems. It will be able to detect planets as small as three times the size of the Earth and may detect rings and moons too.

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