Earth-like exoplanet yet
BY DR EMILY BALDWIN
Posted: 03 February, 2009
The CoRoT space telescope has detected an exoplanet less than twice the size of Earth orbiting a Sun-like star, and with a surface you could walk on, astronomers speculate.
COROT-Exo-7b was detected as it orbited its parent star once every 20 hours, dimming light from the star as it made its transit across the star’s face. Over 330 exoplanets have been discovered so far, most of which are gas giants with characteristics similar to Jupiter and Neptune, with very few resembling the terrestrial inner planets of our Solar System. This, however, is largely because small planets are extremely difficult to detect and since many planet-seeking methods are sensitive to the mass of the planet, while CoRoT can directly measure the size of the exoplanet’s surface.
The discovery also benefited from observations from The European Southern Observatory at Paranal and La Silla in Chile, the 80-cm telescope at the Canary Islands Astrophysics Institute, and the Canada-France-Hawaii Telescope on Mauna Kea. The findings will appear in a future edition of the journal Astronomy and Astrophysics.
The new plaet was found using the transit method, which measures the tell-tale dip in stellar brightness as the planet passes in front of its parent star, temporarily blocking some of the star's light. Image: CNES.
"Finding such a small planet was not a complete surprise", says Daniel Rouan of the Observatoire de Paris Lesia). "COROT-Exo-7b belongs to a class of objects whose existence had been predicted for some time. CoRoT was designed precisely in the hope of discovering some of these objects." Indeed, recent measurements had indicated the existence of planets of small masses but their size had remained undetermined until now.
But COROT-Exo-7b is not quite as hospitable as it may first sound, for the new world orbits very close to its parent star, such that its surface is a scolding 1,000–1,500 degrees Celsius. Depending on the density of the planet, temperatures like that suggest the surface could be covered in molten lava or enshrouded in a humid cloud of water vapour. The planet could even be made up of water and rock in almost equal amounts.
The internal structure of COROT-exo-7b is also of extreme interest, since iCOROT-Exo-7b could represent an ‘ocean planet’, a kind of planet whose existence has, so far, never been proved. In theory, such planets would initially be covered partially in ice and they would later drift towards their parent star, causing the ice to melt and flood the planet with liquid.
"This discovery is a very important step on the road to understanding the formation and evolution of our planet," says Malcolm Fridlund, ESA's CoRoT Project Scientist. "For the first time, we have unambiguously detected a planet that is 'rocky' in the same sense as our own Earth. We now have to understand this object further to put it into context, and continue our search for smaller, more Earth-like objects with CoRoT.”
Finding Earths is also the mantra for the forthcoming Kepler mission, scheduled for launch on 5 March.