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Kepler Discovers Rocky Planet

January 10, 2011

NASA’s Kepler mission confirmed the discovery of its first rocky planet, named Kepler-10b. Measuring 1.4 times the size of Earth, it is the smallest planet ever discovered outside our solar system.

The discovery of this so-called exoplanet is based on more than eight months of data collected by the spacecraft from May 2009 to early January 2010.

“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 in Moffett Field, Calif., and primary author of a paper on the discovery accepted by the Astrophysical Journal. “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.”

Kepler’s ultra-precise photometer measures the tiny decrease in a star’s brightness that occurs when a planet crosses in front of it. The size of the planet can be derived from these periodic dips in brightness. The distance between the planet and the star is calculated by measuring the time between successive dips as the planet orbits the star.

Kepler is the first NASA mission capable of finding Earth-size planets in or near the habitable zone, the region in a planetary system where liquid water can exist on the planet’s surface. However, since it orbits once every 0.84 days, Kepler-10b is more than 20 times closer to its star than Mercury is to our sun and not in the habitable zone.

Kepler-10 was the first star identified that could potentially harbor a small transiting planet, placing it at the top of the list for ground-based observations with the W.M. Keck Observatory 10-meter telescope in Hawaii.

Scientists waiting for a signal to confirm Kepler-10b as a planet were not disappointed. Keck was able to measure tiny changes in the star’s spectrum, called Doppler shifts, caused by the telltale tug exerted by the orbiting planet on the star.

“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,” he said.

Knowledge of the planet is only as good as the knowledge of the star it orbits. Because Kepler-10 is one of the brighter stars being targeted by Kepler, scientists were able to detect high frequency variations in the star’s brightness generated by stellar oscillations, or starquakes. This analysis allowed scientists to pin down Kepler-10b’s properties.

There is a clear signal in the data arising from light waves that travel within the interior of the star. Kepler Asteroseismic Science Consortium scientists use the information to better understand the star, just as earthquakes are used to learn about Earth’s interior structure. As a result of this analysis, Kepler-10 is one of the most well characterized planet-hosting stars in the universe.

That’s good news for the team studying Kepler-10b. Accurate stellar properties yield accurate planet properties. In the case of Kepler-10b, the picture that emerges is of a rocky planet with a mass 4.6 times that of Earth and with an average density of 8.8 grams per cubic centimeter — similar to that of an iron dumbbell.

Ames manages Kepler’s ground system development, mission operations and science data analysis. NASA’s Jet Propulsion Laboratory in Pasadena, Calif., managed Kepler mission development.

Ball Aerospace and Technologies Corp. in Boulder, Colo., developed the Kepler flight system and supports mission operations with the Laboratory for Atmospheric and Space Physics at the University of Colorado in Boulder. The Space Telescope Science Institute in Baltimore archives, hosts and distributes the Kepler science data.

Image 1: Kepler-10b is a scorched world, orbiting at a distance that’s more than 20 times closer to its star than Mercury is to our own Sun. The daytime temperatures expected to be more than 2,500 degrees Fahrenheit, hotter than lava flows here on Earth. Intense radiation from the star has kept the planet from holding onto an atmosphere. Flecks of silicates and iron may be boiled off a molten surface and swept away by the stellar radiation, much like a comet’s tail when its orbit brings it close to the Sun. Credit: NASA/Kepler Mission/Dana Berry

Image 2: The daytime temperatures expected to be more than 2,500 degrees Fahrenheit, hotter than lava flows here on Earth, hot enough to melt iron! Many years ago, before Kepler launched, members of what became the Kepler team built a robotic telescope at Lick Observatory to learn to do transit photometry–detecting drops in brightness of stars when planets pass in front of them. We called it the “Vulcan Telescope,” named after the hypothetical planet that scientists in the 1800′s thought might exist between the Sun and Mercury. A planet that might explain the small deviations in Mercury’s orbit that were later explained with Einstein’s theory of general relativity. Vulcan is the god of fire in Roman mythology, a name befitting of a world so close to the Sun. The artist’s rendering of Kepler-10b is reminiscent of that hypothetical planet Vulcan. The Kepler team came full circle in its quest. We know that we’ve only begun to imagine the possibilities. Credit: NASA/Kepler Mission/Dana Berry

Image 3: Kepler-10b orbits one of the 150,000 stars that the Kepler spacecraft is monitoring, a star that is very similar to our own Sun in temperature, mass and size, but older with an age of over 8 billion years, compared to the 4-and-1/2 billion years of our own Sun. It’s one of the brighter stars that Kepler is monitoring and about 560 light years from our solar system, which means when the light from this star began its journey toward Earth, European navigators were crossing the Atlantic Ocean for the first time in search of new horizons. Today, we’re still exploring and our crow’s nest is a space telescope called Kepler. One day, the oceans we cross will be the galaxy itself, but for now, we imagine the worlds we discover by putting all that we’ve learned from our observations and analyses into the fingers of artists. Kepler-10b must be a scorched world, orbiting at a distance that’s more than 20 times closer to its star than Mercury is to our own Sun, with a daytime temperature expected to be more than 2,500 degrees Fahrenheit. The Kepler team has determined that Kepler-10b is a rocky planet, with a surface you could stand on, a mass 4.6 times that of Earth, and a diameter 1.4 times that of Earth. Credit: NASA/Kepler Mission/Dana Berry

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