A Rocky World, Far, Far Away

Sep 16, 2009 7:00am

500 light-years away, in the constellation of Monoceros the Unicorn, European scientists say there is an unremarkable star called CoRoT-7. 

Last year they deduced that there was at least one planet orbiting it.  And today, they report, it is one of the most earth-like worlds they've yet spotted among the 300-plus so-called "exoplanets" they've counted circling other stars.  It's probably rocky, like the Earth, instead of being a giant ball of gas like Jupiter or Saturn.  It is the first confirmed rocky exoplanet; almost all the others spotted so far have appeared to be gas giants.

It may look something like this artist's conception — though it is much too distant to be seen by humans.

They've called the planet CoRoT-7b (CoRoT is the European satellite they used for their observations).  What makes it stand out is its size — unusually small and dense, compared to other known exoplanets.It is probably less than twice the diameter of Earth — on the order of 14,000 miles, in other words.  Its "year" is very short: it goes tearing around its host star in 20.4 hours.  They've done the math and  concluded it is only about 1.5 million miles from its sun (we're 93 million miles from ours), so it's probably a very, very hot, unpleasant place, perhaps covered with lava.
They're calculated its mass with help from a telescope in Chile.  When it passes in front of CoRoT-7, it blocks 1/3,000th of the star's light.  That's not much — but it's enough for instruments to detect, and it's confirmation of the planet's size.  From there they can calculate how dense it is.

By dint of sheer distance, earthbound astronomers have been limited in their ability to spot distant planets that resemble the one we live on.  Until a few years ago, one remarked, an astronomer on Alpha Centauri, looking at our Sun with our technology, would think it only had one planet — Jupiter.  The others were too small to detect.

But technology has changed.  "This is science at its thrilling and amazing best," says a statement from Didier Queloz, leader of the research team. (Image: Artist’s conception of CoRoT-7b.  Courtesy European Southern Observatory.)

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