Astronomers make largest ever discovery of habitable planets （254 words）

By Clive Cookson, Science Editor

-----------------------------------------------------

Astronomers have identified the largest group of potentially habitable planets yet discovered, about 40 light years away from Earth.

An international team led by Liège university in Belgium made the discovery of the planetary system, three of whose seven Earth-sized worlds have conditions in which life could have evolved. Their findings, reached by combining observations from a dozen telescopes on mountaintops and in space, are published in the journal Nature.

The planets orbit a relatively cool red dwarf star called Trappist-1 that has just 8 per cent of the sun’s mass and 0.5 per cent of its light output.

Until now the hunt for planets in the galaxy beyond our solar system, known as exoplanets, has concentrated on sun-like stars, around which more than 3,500 have been detected. The Trappist-1 discovery marks the start of a new search focusing on red dwarfs, which are more plentiful than larger stars.

“The energy output from dwarf stars like Trappist-1 is much weaker than that of our sun,” said Amaury Triaud, a team member at Cambridge university. “Planets would need to be in far closer orbits than we see in the solar system if there is to be surface water. Fortunately, it seems that this kind of compact configuration is just what we see around Trappist-1.”

Because the Trappist-1 system is relatively close to Earth in galactic terms and because its parent star is a dimly shining dwarf, astronomers predict that it will be easier to study than most exoplanets associated with dazzlingly bright sun-like stars.