Something old, something new

Posted by Rich Talcott
on Friday, May 11, 2007
 
The Spitzer Space Telescope imaged a hot
spot on the exoplanet HD 189733b. It marks
the first feature ever seen on an exoplanet.
NASA/JPL-Caltech/H. Knutson (CfA)

When you talk about beauty in the universe, the conversation almost always begins with Saturn. For many people, the discussion also ends there. But odds are, if you're an astronomy buff, you could chat up hundreds, if not thousands, more attractive sights.

Last week, a whole new category of beauty was born when astronomers released the first images of a planet circling another star. If you take a look at Saturn, and then at the new planet, you're sure to say beauty is in the eye of the beholder. But who thought, even 15 years ago, that we'd be turning up new planets faster than Alex Rodriguez hits home runs? Now, we're seeing the first detail on these planets.

Heather Knutson of Harvard University led the team that mapped the planet. It orbits the star HD 189733, which lies about 60 light-years from Earth in the constellation Vulpecula. While the star is slightly smaller and cooler than the Sun, the planet (designated HD 189733b) is slightly larger than Jupiter. This "hot Jupiter" circles its host star every 2.2 days at a distance of 3 million miles.

The astronomers, who reported their findings yesterday in Nature, used the Spitzer Space Telescope to zero in on the infrared radiation emitted by the gas-giant planet. "We felt a little like Galileo must have felt when he first glimpsed Jupiter through the eyepiece of his telescope," says Knutson. At the infrared wavelengths recorded by Spitzer, the star doesn't overwhelm the planet's light.

The images reveal a single "hot spot" in the planet's atmosphere about twice as large as Jupiter's Great Red Spot. While the Red Spot exists at a temperature of about –200° Fahrenheit, some 30° warmer than its surroundings, the hot spot on HD 189733b is a broiling 1,700° F — 500° hotter than its surroundings. Surprisingly, the hot spot doesn't lie directly beneath its sun, but is offset by about 30° of longitude. The researchers speculate that high-speed winds redistribute the planet's heat.

Spitzer can map only large, hot worlds — not the kind that might possess liquid water. But the upcoming James Webb Space Telescope (JWST), slated to launch in 6 years, may be able to do the trick. And while JWST won't give us exoplanet images to rival those of Saturn, I think it's fair to say any image revealing water on another world would rank among the most beautiful ever seen.

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