Glow of alien planets detected for first time

The discoveries were to be presented at a NASA press conference Tuesday afternoon. The HD 209458b study is discussed in a paper to be published online Wednesday by the journal Nature, according to NASA. The TrES-1 finding will be detailed June 20 in the Astrophysical Journal.

From the new detection, astronomers learned both planets are at least 1340 Fahrenheit (727 degrees Celsius) and have circular orbits.

That reopens a mystery.

Previous observations had found HD 209458b to have a very puffed-up atmosphere, which astronomers thought might have been caused by the tug of another, unseen planet. Were there another planet, then the orbit of HD 209458b would be noticeably non-circular.

"We're back to square one," said Sara Seager, a Carnegie Institution researcher involved in Deming's study. "For us theorists, that's fun."

First photo?
HD 209458b is arguably the most well studied extrasolar planet. Previous work by Charbonneau and others revealed oxygen and other gases in its atmosphere. It is so hot and close to its star that it is rapidly losing its atmosphere, according to another study.

Astronomers are still waiting for the first definite image of an extrasolar planet. The pictures may already have been taken, of a world orbiting a failed star known as a brown dwarf.

Those observations, by the European Southern Observatory and the Hubble Space Telescope, await confirmation. And the planet, if it is one, is unusually massive, with perhaps five times the heft of Jupiter. Imaging it -- as a point of light -- was possible because brown dwarfs do not create the overwhelming glare of a normal star.

The infrared-emitting planets discussed Wednesday are in many ways more interesting to astronomers because of their Jupiter-like dimensions and the fact that they orbit full-blown regular stars not unlike our Sun. And there's no doubt they are planets.

"Now we have our first genuine detection of light from a planet around a solar-like star," Boss said.

Next steps
Five other planets are known to transit in front of normal stars. But they are all too far away to be probed by Spitzer, which is operated by Caltech and NASA's Jet Propulsion Laboratory. A handful of other targets for Spitzer are likely to be found in coming years.

Meanwhile, more might be learned about HD 209458b and TrES-1. Each is thought to rotate in synch with its orbit, so that it always shows the same face to the star. That creates a tremendous heat imbalance between the two sides of the planet.

"It may also be possible to measure winds on these planets," Deming told SPACE.com. "This asymmetric heating should drive strong winds which attempt to redistribute the heat."

There are currently about 140 known worlds beyond our solar system. The first true photographs of extrasolar planets around normal stars are not expected for a few years, until NASA flies a new telescope devoted to the task.

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