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Astronomers unveil faraway planet of molten rock
Posted: 11 January 2011

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Scientists announced Monday the discovery of a blistered planet not much bigger than Earth, the smallest such object ever confirmed beyond the solar system.

Artist's impression of the molten planet Kepler-10b. Credit: NASA/Dana Berry
Working with NASA's Kepler space telescope and an observatory in Hawaii, astronomers verified the existence of a rocky planet orbiting perilously close to its parent star 560 light years from Earth. The planet is so hot its surface is likely made of molten rock, according to scientists.

The planet is named Kepler 10-b and marks a milestone for the NASA telescope, which was launched in 2009 to find Earth-sized planets around other stars. Kepler is capable of detecting objects in the Goldilocks zone, where planets are just the right distance from a star for life-friendly temperatures, but scientists have not announced any of those discoveries yet.

Measuring about 1.4 times bigger than Earth, Kepler-10b completes an orbit every 20 hours. It is located 20 times closer to its parent star than Mercury is to the sun. With surface temperatures around 2,800 degrees Fahrenheit, the planet is much too hot to support liquid water or an atmosphere.

"All of Kepler's best capabilities have converged to yield the first solid evidence of a rocky planet orbiting a star other than our sun," said Natalie Batalha, Kepler's deputy science team lead at NASA's Ames Research Center. "The Kepler team made a commitment in 2010 about finding the telltale signatures of small planets in the data, and it's beginning to pay off."

Batalha is the primary author of a paper on Kepler-10b accepted by the Astrophysical Journal.

Kepler 10-b orbits a star much like the sun. It was first spotted in July 2009, according to Batalha.

The discovery is based on more than eight months of data collected by Kepler in 2009 and 2010. After Kepler's data captured the interest of scientists, they used the W.M. Keck Observatory in Hawaii to confirm the finding by observing Kepler-10b's gravitational tug on the star.

The Kepler spacecraft stares at a field of more than 150,000 stars in the constellation Cygnus, watching for periodic dips in light that could signal a planet passing in front of the star. Once they declare the discovery of a candidate planet, astronomers turn to ground-based telescopes for follow-up observations.

Scientists calculated the new planet is 4.6 more massive than Earth. Its average density is 8.8 grams per cubic centimeter, similar to that of an iron dumbbell, according to NASA.

"The discovery of Kepler 10-b is a significant milestone in the search for planets similar to our own," said Douglas Hudgins, Kepler program scientist at NASA Headquarters in Washington. "Although this planet is not in the habitable zone, the exciting find showcases the kinds of discoveries made possible by the mission and the promise of many more to come."

Batalha said Kepler-10b is nicknamed Vulcan after the Roman god of fire.

The smallest planet confirmed before Monday was COROT-7b, an object detected by a European space mission and reported in February 2009. That planet is about 1.7 times the size of Earth, and although it is believed to be rocky, scientists say Kepler-10b is the first exoplanet proven to be Earth-like.

Monday's announcement brings Kepler's planet tally to 8, not counting a suspected planet about one-and-a-half times the size of Earth. Named Kepler-9d, the so-called "super-Earth" is part of a multi-planet system announced in August, but officials have not published confirmation of its existence.

Artist's concept of the Kepler spacecraft. Credit: NASA/Wendy Stenzel
Withheld for in-house analysis up to now, a significant chunk of Kepler data will be released to the science community Feb. 1. There could be a flurry of confirmed planet announcements over the next few months, but a NASA spokesperson said there be no further releases before the Feb. 1 data dump.

NASA publicly unveiled the first 43 days of Kepler observations to the science community last year. The data included more than 700 candidate planets, but the Kepler science team kept 400 of the potential discoveries for themselves.

About half of the candidate planets turn out to be false positives, according to William Borucki, Kepler's principal investigator at Ames.

Many of the candidates are believed to be rocky planets between the sizes of Earth and Neptune, so officials anticipate more discoveries soon.

But all of the planets found so far orbit too close to fiery stars to harbor life. Right now, Kepler's observations are limited to planets with orbital periods less than three months.

The spacecraft rotates on its axis every three months, meaning light from a specific star falls on a different set of CCDs inside the telescope's 95-megapixel camera. Kepler scientists will expand their search for planets in the habitable zone once they finish writing an advanced software program to analyze stars over longer periods of time.

A computer progarm has to stitch together observations from each three-month period to find planetary transits occurring at longer intervals.

Planets in more distant orbits would pass in front of the parent star at greater intervals. For example, an extraterrestial telescope elsewhere in the galaxy could only see Earth transit the sun once per year.

The Kepler team's scientific prudence means it could be several years before NASA is prepared to make an Earth-shattering announcement.

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