The NASA Kepler Mission has discovered a new exoplanet similar in size to Earth but with a temperature nowhere near the habitable zone.

The planet, designated Kepler-21b, is only about 6 million kilometers away from its parent star. Mercury, the planet closest to the sun, which has a period of 88 days and a distance from the sun of 57 million km.

The research team led by Steve Howell of NASA's Ames Research Center, found that one of the brightest stars in the Kepler star field has a planet with a radius only 1.6 that of Earth's radius and a mass no greater that 10 Earth masses, circling its parent star every 2.8 days.

To support and confirm their Kepler observations, the team of more than 65 astronomers, including David Silva, Ken Mighell and Mark Everett of the National Optical Astronomy Observatory, used multiple telescopes on the ground including the 4-meter Mayall telescope and the WIYN telescope at Kitt Peak National Observatory.

Thus, Kepler 21b is far hotter than any place humans could venture, calculated at about 1900 K, or 2960 F. While this temperature is nowhere near the habitable zone in which liquid water might be found, the planet's size is approaches Earth's.

Kepler 21b's parent star, HD 179070, is quite similar to Earth's sun with a mass of 1.3 solar masses and radius of 1.9 solar radii. However, its age, based on stellar models, is 2.84 billion years, a bit younger than the sun's 4.6 billion years.

According to researchers, HD 179070 is spectral type F6 IV, a little hotter and brighter than the sun. By astronomical standards, HD 179070 is fairly close, at a distance from the sun of 352 light years.

The Kepler mission team observed this field for over 15 months and combined the observations to detect this tiny, periodic signal. The also relied on spectroscopic and imaging data from a number of ground-based telescopes.

The findings been accepted for publication in the Astrophysical Journal.