Volume: 03, Issue: 06 03/23/2005 
Artist conception of extrasolar planets in visible light (left) and infared light (right). Image courtesy NASA/JPL.
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Collage of photographs taken by Spitzer. Image courtesy NASA/JPL.
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Other Articles in This Issue:
Cassini Detects Atmosphere on Enceladus
Imaging Radar Links Storm Runoff to Coastal Pollution
Shuttle Crew Tests Equipment for Return to Flight
Teach Your Students Through Technology
 

Spitzer Telescope Captures Light from Distant Planets

For the first time, astronomers have detected light from planets that do not orbit our Sun. According to NASA, this discovery by its Spitzer Space Telescope has marked the beginning of a new age of planetary science, in which these extrasolar planets can be directly measured and compared.

Although no actual images were recorded, scientists are thrilled with the discovery.

"It's fantastic," said Dr. David Charbonneau of the Harvard- Smithsonian Center for Astrophysics. "We've been hunting for this light for almost 10 years, ever since extrasolar planets were first discovered."

Spitzer directly observed the warm infrared glows of two previously detected Jupiter-sized planets, designated HD 209458b and TrES-1. These extrasolar gas giants zip closely around their parent stars, from where they can soak up ample starlight and shine brightly in infrared wavelengths.

To distinguish this planet glow from that of the fiery hot stars, the astronomers used a simple trick. First, they used Spitzer to collect the total infrared light from both the stars and planets. Then, when the planets dipped behind the stars as part of their regular orbit, the astronomers measured the infrared light coming from just the stars. This pinpointed exactly how much infrared light belonged to the planets.

"In visible light, the glare of the star completely overwhelms the glimmer of light reflected by the planet," said Charbonneau. "In infrared, the star-planet contrast is more favorable because the planet emits its own light."

The Spitzer data told the astronomers that both planets are at least a steaming 1,000 Kelvin, or 1340 Fahrenheit. Upcoming Spitzer observations using a range of infrared wavelengths are expected to provide more information about the planets' winds and atmospheric compositions.

The findings also reawaken a mystery that some astronomers had laid to rest. Planet HD 209458b is unusually puffy, or large for its mass, which some scientists thought was the result of an unseen planet's gravitational pull. If this theory had been correct, HD 209458b would have a non-circular orbit. Spitzer discovered that the planet does, in fact, follow a circular path.

Spitzer is ideally suited for studying extrasolar planets known to transit, or cross, stars the size of our Sun out to distances of 500 light-years. Of the seven known transiting planets, only the two mentioned here meet those criteria. As more are discovered, Spitzer will be able to collect their light - a bonus for the observatory, considering it was not originally designed to see extrasolar planets. NASA's future Terrestrial Planet Finder coronagraph, set to launch in 2016, will be able to directly image extrasolar planets as small as Earth.

Shortly after its discovery in 1999, HD 209458b became the first planet detected via the transit method. That result came from two teams, one led by Charbonneau. Five years later, TrES-1 was found via the transit method as part of the NASA-funded Trans-Atlantic Exoplanet Survey, a ground-based telescope program established in part by Charbonneau.

Artist's concepts and additional information about the Spitzer Space Telescope are available at http://www.spitzer.caltech.edu/Media .

    
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