Using a planet-hunting space telescope called CoRoT, astronomers have discoverd the most Earth-like world – one that has a rocky surface. Every 20.4 hours, the planet eclipses a small fraction of the light of the star for a little over one hour by one part in 3000.
This planet, designated CoRoT-7b, is only 2.5 million kilometers away from its host star, or 23 times closer than Mercury is to the Sun. It has a radius that is about 80% greater than the Earth’s.
With a mass much closer to that of Earth than, for example, ice giant Neptune’s 17 Earth masses, CoRoT-7b belongs to the category of “super-Earth” exoplanets. About a dozen of these bodies have been detected, though in the case of CoRoT-7b, this is the first time that the density has been measured for such a small exoplanet. The calculated density is close to Earth’s, suggesting that the planet’s composition is similarly rocky. CoRoT-7b earns another distinction as the closest known exoplanet to its host star, which also makes it the fastest — it orbits its star at a speed of more than 750,000 kilometers per hour, more than seven times faster than the Earth’s motion around the Sun. “In fact,CoRoT-7b is so close that the place may well look like Dante’s Inferno, with a probable temperature on its ‘day-face’ above 2000 degrees and minus 200 degrees on its night face. Theoretical models suggest that the planet may have lava or boiling oceans on its surface. With such extreme conditions this planet is definitively not a place for life to develop,” says one of the co-discoverers.
Doorstep Astronomy: The parent star, now known as CoRoT-7, is and 11th magnitude star located in the constellation of Monoceros (the Unicorn) (see starchart above) at a distance of about 500 light-years. Slightly smaller and cooler than our Sun, CoRoT-7 is also thought to be younger, with an age of about 1.5 billion years. It is faintly visible through a backyard telescope, but you can easily find its location in the eastern early morning sky with the naked eye located between the bright star-like Venus and the brilliant constellation Orion.
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