Newly found planet so hot it can rain iron

SEATTLE -- Using a new technique that will be used to search for Earthlike planets, astronomers have found a distant extrasolar planet, a bizarre place of torrid heat, with clouds and raindrops made of iron.

A team from the Harvard-Smithsonian Center for Astrophysics found the planet orbiting a star 5,000 light-years away by detecting the slight dimming of light caused as the planet moved between the star and telescopes on Earth.

The sophisticated technique was compared to spotting the shadow cast by a mosquito flying in front of a searchlight two hundred miles away.

More than 100 extrasolar planets -- planets orbiting stars other than the sun -- have been found by measuring a star's wobble caused by the gravity of the planet. The new discovery is the first using the new technique, called a transit search, which looks directly at the dimming light.

"We have found a better way to detect new worlds in our Milky Way galaxy that paves the way for future planetary discoveries," said Dimitar Sasselov, leader of the Harvard-Smithsonian team. He reported on the discovery Monday at the national meeting of the American Astronomical Society.

Sasselov said the new planet was found in orbit of a star in a distant spiral arm of the Milky Way and closer than the sun to the galactic center.

3,100 degrees

The planet is just slightly smaller than Jupiter. It orbits very close to its star, about one-fiftieth the distance between the Earth and the sun. This orbit means the planet whips around the star every 29 hours, in contrast to the yearlong orbit of the Earth about the sun.

This rapid orbit enabled the researchers to repeatedly confirm the presence of the planet, said Sasselov.

Because it is so close to its star, the new planet is thought to have an atmospheric temperature of about 3,100 degrees, enough to vaporize most metals.

"This is the hottest planet that we know about," said Sasselov. "It is hot enough to have an iron fog and to rain hot iron droplets."

He said the new planet would be a place of violence, with a powerful jet stream whipping the clouds and loosing showers of molten iron.

Sasselov said the team has two other candidate extrasolar planet discoveries that have yet to proven by further studies.

The importance of the new finding, he said, is that it proves that the transient technique can be used to find extrasolar planets and supports the possibility that Earth-sized bodies will be found.

NASA is planning a program, called Kepler, that will use an orbiting observatory and the transient technique to search for new Earths.

Kepler's goal is to look for Earth-sized planets that are about the same distance from a star as Earth is from the sun, about 93 million miles. This is in the center of what is known as the habitable zone, a place where there is liquid water and mild temperatures. Planets in such a zone are thought to have the best chance of hosting life.