Kepler Kaput: The Planet-Hunter Stops Hunting

Kepler, NASA's prolific planet-hunting space observatory, is wounded.

Kepler-22b, located some 600 light years away from Earth, was in 2011 the first such exosolar planet to be identified. Pointed at a specific region of space containing around 100,000 stars, so far Kepler has found at least 135 planets, with over 3500 possible others yet to be formally identified from analysis of the data collected. Astronomers estimate that there at are least 17 billion Earth-like planets in our Milky Way galaxy, which is just one of billions in the Universe.

Whilst it formally completed its mission last year after the intended three-year spell, the hope was it could continue on for a few more years. However it has now had to give up its day job of planet hunter extraordinaire after NASA engineers were unable to fix the latest problems.

Kepler identifies planets by detecting changes in the light received from stars, specifically the intensity dips as orbiting planets get in the way. This is extremely tricky to do, with the amount of light only changing by fractions of a percent.

To be able to make these measurements, Kepler needs to remain pointed in a particular direction for a sufficient period of time. One of the stabilising wheels broke last year, but Kepler was able to continue with just three. With two now broken this is no longer possible - manoeuvring it is now likened to trying to push a shopping trolley with dodgy wheels in a straight line down a supermarket aisle.

Kepler may still be of some use, and NASA are now looking into such possibilities, but its main role is over. This year the European Space Agency will launch the Gaia space observatory, which will map the stars and in the process should discover thousands more Earth-like planets. And so the search for extraterrestrial worlds continues...