Space telescope being retired
Nasa’s revolutionary planethunting Kepler space telescope has run out of fuel and will be retired, the space agency has announced.
During its nine-year mission, Kepler found more than 2600 planets orbiting stars outside the solar system, including many with the potential for harbouring life.
Thanks to the spacecraft, scientists have learned that the Milky Way galaxy has more planets than stars.
"Before we launched Kepler, we didn’t know if planets were common or rare," said Paul Hertz, director of the National Aeronautics and Space Administration’s astrophysics division in Washington, DC.
Scientists have pored over Kepler’s data and concluded that between 20 and 50 per cent of the stars we can see are accompanied by planets that have much in common with Earth. These planets are about the same size as ours and orbit at a distance where any water that might be on the surface would be stable in liquid form.
Even more common is a type of planet that is missing from our own solar system – so-called super-Earths, larger than our planet but smaller than Neptune.
Kepler has also revealed that many solar systems are far more crowded than our own. One of its most tantalising discoveries was the TRAPPIST-1 planetary system, a mere 39 light years away and home to seven rocky Earthsized worlds. All seven are closer to their star than Mercury is to the Sun.
In April, the US space agency launched the Transiting Exoplanet Survey Satellite (TESS) to look for planets around 200,000 nearby stars.