Artist concept of Kepler-10b.
Credit: NASA
The planet, known as Kepler-10b, isn't exactly the ideal vacation spot. One side is probably a magma-melting 1,400°C, while the other is likely to be vacuum-frigid.
Still, it's the first rocky planet yet confirmed.
Kepler-10b orbits an 8 billion-year-old star, 560 light-years from Earth. It's named for the Kepler space telescope, which first spotted it in 2009, using a method called transit photometry.
"Kepler measures the brightness of thousands of stars, very, very precisely," said Natalie Batalha, an astronomer from San Jose State University, San Jose, California, who reported the latest Kepler-10b findings in January 2011, at a meeting of the American Astronomical Society in Seattle, Washington.
What the telescope is searching for, she added, are the very tiny dimmings that occur when a planet passes between the star and the telescope.
A planet like Earth, would cause about a 0.01 per cent reduction in the star's brightness.
"Imagine you have 10,000 light bulbs and you take one away," she said. "That's the change in brightness we're looking for."
From the outset, Kepler-10b was exciting because it removed only 1.5 of those light bulbs, making it not all that much bigger than Earth. But that didn't mean it was rocky.
To learn more, scientists first had to learn more about the star. So they trained a giant Earth-based telescope on it and watched for tiny Doppler shifts in the star's light as the planet (which lies so close to its sun that it completed an orbit every 20 hours) made its circles.
These changes occur because planets don't simply circle their stars, they also tug them slightly back and forth with each revolution.
The magnitude of these nodding motions by the star reveals the relative masses of the sun and planet: a small planet with a big sun produces little effect, while a big planet with a small sun has a larger one.
But these motions aren't huge. In the case of Kepler-10b, the scientists had to be able detect velocity shifts of only three metres per second - about the speed of the average jogger.
On some stars, that might be impossible. But Kepler-10b's sun is old and quiescent, with relatively few flares or sunspots to throw in large, random surface motions that would mask any effect from the planet.
But all that this reveals are the relative sizes of the star and the planet. Next, the scientists had to know exactly how big, and how massive, the star is. To determine that, they looked at tiny, minute-by-minute changes in the star's radiation marked by starquakes - disturbances that make an entire star ring like a bell.
