Astronomers have discovered Kepler-10b, the smallest planet outside our solar system. It is about 560 light-years away, and has a surface temperature hotter than molten iron.

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. Kepler-10b is the first rocky planet the spacecraft has picked up.

As Kepler-10b orbits its host Sun-like star so closely, the planet could not harbor life and it is furiously hot -- about 2,500 degrees Farendheit, or 1,370 degress C. That is hot enough to melt and cast bronze. The planet orbits its sun once every 0.84 days or 20 hours, and is more than 20 times closer to its star than Mercury is to our Sun.

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.

All of Kepler's best capabilities have converged have converged for this discovery yielding the first solid evidence of a rocky planet orbiting a star other than our Sun. Our knowledge of Kepler-10b is only as good as the knowledge of the star it orbits, said Natalie Batalha, Kepler's deputy science team lead at NASA's Ames Research Center in Moffett Field, California.

As 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 is the analysis that really allowed us to pin down Kepler-10b's properties, Batalha added.

The spacecraft's ultra-precise photometer detects a slight decrease in the star's brightness 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.

To confirm this dips in brightness, the Kepler team gathered transiting data from the spacecraft for eight months, starting in May 2009, and sent the information to astronomers at the Keck telescope in Hawaii. Scientists waiting for a signal to confirm Kepler-10b as a planet were not disappointed.

The telescope was able to measure small changes in the star's spectrum, called Doppler shifts, caused by the telltale tug exerted by the orbiting planet on the star. Fron the shifts astronomers measured its radial velocity.

This planet-detection technique relies on the fact that stars wobble back and forth as their planets circle around, tugging on them like children. As a star moves toward us, the color of its light shifts to shorter, or bluer, wavelengths. As the star heads away, its light stretches into longer, or redder, wavelengths. The same principle, called the Doppler effect, causes sound from a speeding train to lower in pitch as it passes by.

By measuring changes in the wavelength of light from a star, astronomers can track changes in the star's velocity that arise from circling planets. By measuring the speed of the star and the period of the wobble, they can determine the mass and distance of the unseen planet, respectively.

Measurements of unprecedented precision have shown that the planet, Kepler 10b, has a diameter 1.4 times that of Earth with a mass 4.6 times higher and an average density of 8.8 grams per cubic centimeter -- similar to that of an iron dumbbell.

The discovery of Kepler-10b, a bone-fide rocky world, 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.

Key facts about Kepler Mission

-- The Kepler Mission is a NASA space observatory designed to discover Earth-like planets orbiting other stars. The mission is named in honor of German astronomer Johannes Kepler.

-- The spacecraft was launched on March 7, 2009 aboard a Delta II rocket from Cape Canaveral Air Force Station, Florida. The mission's planned lifetime is least 3.5 years.

-- The mission's life-cycle cost is estimated at $600 million, including funding for 3.5 years of operation.

-- Kepler is a mission under NASA's Discovery Program of low-cost, focused science missions.

-- Ames Research Center manages Kepler's ground system development, mission operations and science data analysis. NASA's Jet Propulsion Laboratory in Pasadena, California managed Kepler mission development.

-- Ball Aerospace & Technologies Corp. was responsible for developing 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.

-- The Kepler mission's first main result announced on January 4, 2010. Among the notable results are one of the least dense planets yet found, and two low-mass white dwarf stars that were initially reported as being members of a new class of stellar objects.

-- Kepler uses a photometer developed by NASA to continuously monitor the brightness of over 145,000 main sequence stars in a fixed field of view.

-- Most of the extrasolar planets detected so far by other projects are giant planets, mostly the size of Jupiter and bigger. Kepler is designed to look for planets 30 to 600 times less massive, closer to the order of Earth's mass (Jupiter is 318 times more massive than Earth).

-- Kepler is not in an Earth orbit but in an Earth-trailing solar orbit so that Earth does not occlude the stars which are observed continuously and the photometer is not influenced by stray light from Earth.

Kepler Mission Discoveries

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