Discovering a small planet like Earth

The first iron-clad evidence of a rocky planet outside the solar system was found using the Kepler Space Telescope.

" It's a missing planetary link ," said astronomer Geoff Marcy of the University of California-Berkeley, who compared this discovery to penicillin's development and discovered DNA.

So far Marcy and other scientists have found more than 500 extrasolar planets, mostly large gas planets like Jupiter or Saturn. The goal of planet hunters is to find a place like Earth.

Measuring just 1.4 times the size of the Earth, Kepler-10b is like a baseball field, although the planet is too hot for life as we know it. The planet is about 20 times closer to its star than Mercury's orbit around the sun and has a surface temperature of about 2,500 degrees F, close to the melting point of iron.

" Radiation prevents it from keeping the atmosphere, " said Natalie Batalha, a scientist at Kepler.

The planet may be located further in a more crowded area at the same time in its past, or it may have evolved at its current location. Either way, this planet cannot settle at this time, Marcy said.

However, its existence is the first clear evidence that Earth-like worlds exist, scientists say.

This evidence, collected over 8 months, stems from a small but continuous change in the amount of light coming from the parent star, a phenomenon caused by the periodic disappearance of a planet - from the viewpoint Kepler's point - when it orbits its star in the back.

Kepler-10b made a trip around its star for a day, providing a rich amount of measurements for the Kepler team. The planets are located at a distance similar to the distance of the earth to the sun - planets seem to be able to support life - take 365 days to move around their mother stars, so need more many observations.

What makes the study of Kepler-10b so important is that scientists have "captured" the size of the planet - and thus calculated its density - with an unprecedented level of accuracy.