The smallest exoplanet ever seen is less than twice the size of Earth, and orbits a star similar to our sun 390 light years away. Astronomers recently spotted this world, the most Earth-like planet yet discovered, with the COROT satellite.

"For the first time, we have unambiguously detected a planet that is

'rocky' in the same sense as our own Earth,” said Malcolm Fridlund, ESA

COROT project scientist.

For all its similarity to our own globe, though, it is still a far cry away from a habitable Earth-twin. For one thing, it is so hot — between 1,830 and 2,730 degrees Fahrenheit — that scientists think it might be covered in lava. It orbits extremely close to its sun and whips around the star once every 20 hours.

Nonetheless, the discovery takes us one step closer to finding another world that could host life. The newly found planet, dubbed COROT-Exo-7b, is distinct from most of the roughly 330 exoplanets so far discovered, which are by and large gas giants like Jupiter. This planet, however, is a terrestrial world like Earth, and seems to have a density similar to that of our own planet.

"Finding such a small planet was not a complete surprise," Daniel Rouan, an astronomer at the Observatoire de Paris Lesia, said in a press release. "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."

Terrestrial planets are so hard to find because they are small, and their low mass makes it tough to detect their gravitational pull on parent stars (a common way of discovering exoplanets). COROT (Convection, Rotation and Planetary Transits), a European Space Agency spacecraft, instead hunts for exoplanets by searching for changes in a star’s brightness caused by a planet passing in front of it. The drop in light of COROT-Exo-7b’s star as the planet moves in front can be seen in the graph above. This technique is particularly successful with planets that orbit close in to their star, even if they are small.

“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," Fridlund said.

The researchers announced the finding today at a COROT symposium in Paris.

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Image: CNES