Gassy planet a real scorcher


May 10, 2007

HD 149026b is a so-called "hot Jupiter," a gas giant that orbits very close to its star

CHICAGO, Illinois (Reuters) -- It's dense, gassy and a bit of an oddball, but a planet orbiting a star in the constellation Hercules may be the hottest known yet, scientists said Wednesday.

The planet -- HD 149026b -- is smaller than the typical gas giant and its atmosphere is much heavier, contributing to its staggering temperature of 3,700 degrees Fahrenheit, they said.

The discovery comes as astronomers create the first climate map of a more typical gas giant.

Both findings, reported in the journal Nature, will help scientists gain a better understanding of climate on planets outside our solar system.

University of Central Florida's Joseph Harrington describes the hot planet as a black ball with a red spot staring right at its star.

"It looks like the evil eye," he said in a telephone interview.

The planet is a so-called "hot Jupiter," a gas giant that orbits very close to its star.

It is one of 14 planets outside our solar system that passes in front of and behind its parent star as seen by Earth -- known as "transiting" planets.

By measuring changes in the amount of light given off by the star as the planet crosses its path, Harrington and colleagues were able to to deduce its temperature.

"This planet is off the temperature scale that we expect for planets," said Drake Deming of NASA's Goddard Space Flight Center in Greenbelt, Maryland, who worked on the study.

Harrington said for a planet to get so hot, it must be absorbing most of the light that reaches it. That light is radiated back in the form of a dim red glow.

HD 149026b is located 279 light-years from Earth with a light-year being the distance light travels in a year -- about 6 trillion miles.

Exoplanet map

While Harrington and colleagues have found the most extreme of the hot Jupiters, researchers at the Harvard-Smithsonian Center for Astrophysics have created a rough climate map for a more garden-variety gas giant.

Using NASA's Spitzer space telescope, researchers measured changes in infrared light coming from the planet HD 189733b in the constellation Vulpecula some 60 light-years from Earth.

The planet is tidally locked to its star, so that one side always faces the star and the other side is always dark.

What the study revealed is a planet with supersonic winds more than six times faster than those on Jupiter that are distributing heat evenly around the planet, even the side that does not face its sun.

"You've got this big belt of wind that is whipping around the planet," Heather Knutson of the Harvard-Smithsonian Center said in a telephone interview.

Harrington said Knutson's work will come to serve as the model for mapping climate on other planets.

"It's a Rosetta Stone," he said.