An international team of scientists, using the CoRoT satellite, have discovered a planet only twice as large as the Earth orbiting a star slightly smaller than the Sun. The new discovery is the smallest extrasolar planet (planet outside our solar system) whose radius has ever been measured. Though the composition of planet is not yet certain, scientists believe it is probably composed predominantly of rock and water. It orbits its host star in 20 hours, which is the shortest orbital period of all exoplanets found so far. Astronomers infer its temperature must be so high (over 1000 degrees C) that it should be covered in lava or superheated water vapour.
“Finding such a small planet wasn’t a complete surprise”, said Dr Daniel Rouan, from LESIA in Paris, who announced the discovery at a conference in Paris. Dr Alain Leger from the Institut d’Astrophysique de Marseille, leader of the discovery paper, explains: “It could be an example of a so-called ocean planet, whose existence was predicted some years ago: a Neptune-like planet, made of ice around a rocky core, drifts so close to its star, the ice the melting to form a fluid envelope.”
The international team had to be sure they were not seeing one of many other kinds of objects that can mimic planetary transits, using complementary observations from the ground. This is particularly challenging in the case of such a small planet, as Dr Aigrain from the University of Exeter explains “We ruled out every mimic except for a very improbable, almost perfect chance alignment of three stars. All our data so far is consistent with the transits being caused by a planet of a few Earth masses, though more data are needed for a precise mass estimate.”
The discovery of CoRoT-Exo-7b was announced at the CoRoT Symposium 2009 in Paris and will be the published in a special issue of the journal Astronomy and Astrophysics dedicated to results from CoRoT.
Read the full article here.
Content added 7 February 2009.
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