Glow of alien planets detected for first time

By Robert Roy Britt

Senior science writer

updated 2:20 p.m. ET March 23, 2005

The glow of planets outside our solar system have been spotted in the first direct detections of light emitted by alien worlds.

The two planets were detected in infrared light, an emission of heat that is not visible to the human eye. There are no conventional photographs, but astronomers are ecstatic nonetheless.

The gas giant worlds, each around a different star, were discovered previously by indirect methods. Both are roughly Jupiter-sized and hot, orbiting very close to their stars. Each completes a "year" in less than four days.

The observations, called a milestone by one analyst, were a surprising and serendipitous convergence of work by two separate teams.

"It's an awesome experience to realize we are seeing the glow of distant worlds," said David Charbonneau, a researcher at the Harvard-Smithsonian Center for Astrophysics (CfA) who led the investigation of TrES-1, a planet a bit less massive than Jupiter that was found last year with the help of a backyard telescope.

Close scrutiny
The new technique, using NASA's Spitzer Space Telescope, allows astronomers to probe the temperatures, atmospheres and emissions of planets, Charbonneau told SPACE.com. It might even let them measure wind for the first time on a planet around another star.

TrES-1 and its star are about 500 light-years from Earth.

The other planet, named HD 209458b, is slightly lass massive than Jupiter and a bit larger. It is about 150 light-years from Earth. These observations were led by Drake Deming of NASA's Goddard Space Flight Center.

In each system, the planet is in a direct line of sight in relation to the star, so that the planet moves across the star and then is eclipsed as it orbits around the star's back side. By comparing the total infrared emission from the reduced amount when the planet is eclipsed, Spitzer revealed the planet's exact emissions.

Using a variant of this "transit" method, astronomers have previously measured the visible light of a star, then noted how much it dimmed when a planet crossed in front. That provides an indirect measure of the planet's size but does not record light coming from the planet itself.

'Major milestone'
Alan Boss, a planet-formation theorist at the Carnegie Institution of Washington, said directly detecting extrasolar worlds is one of the most significant moments in planet hunting since the first extrasolar worlds were discovered a decade ago. Boss, who was not involved in the new work, said 1995 and 2005 will be remembered as historical years in the ongoing search for planets like our own.

"It really is a major milestone," Boss said in a telephone interview.

Each planet was probed with a different Spitzer instrument recording different wavelengths of infrared light. Charbonneau and Deming knew of each other's projects, but their competitive natures kept them from discussing their progress.

"We had no idea where they were at," Charbonneau said.

After Charbonneau submitted his group's paper for publication, he notified NASA. He then learned of a remarkable coincidence.

"We had submitted the papers on the same day, not having known about each others' results," Charbonneau said. He and Deming then exchanged papers and met later to discuss their similar findings. They were amazed that they'd accomplished the same long-sought task using different instruments.

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