Distant Planet Mapped for First Time, "Hot Jupiter" Features Fierce Winds

Anne Minard
for National Geographic News

May 9, 2007

Giant planets known as hot Jupiters are even hotter, wilder, and more mysterious than scientists expected, two new studies reveal.

The studies include the first rough map ever completed of a planet outside our solar system.

Hot Jupiters are large, typically gaseous planets that orbit their stars much more closely than Jupiter circles the sun. (See an interactive map of the solar system.)

One of the new studies shows that fierce, hot winds on a hot Jupiter 63 light-years away sweep heat from the planet's daylight side to its dark, nighttime side.

(Read related story: "'Hot Jupiters' Could Give Rise to Earthlike Worlds, Study Says" [September 7, 2006].)

The other study suggests that another, even more distant hot giant is as black as coal and absorbs nearly all the light that hits it, re-emitting the energy as extraordinary heat.

The pitch-black world, the smallest known planet outside our solar system, is also one of the hottest: a whopping 3,500 degrees Fahrenheit (1,925 degrees Celsius), the study found.

Both studies appear in this week's issue of the journal Nature.

Keeping the Cool Side Hot

Because hot Jupiters are so close to—and always have one side facing—their stars, most scientists have expected that dramatic temperature differences would exist between the worlds' daylight, or star-facing, sides and their nighttime sides.

To test this theory, Harvard University graduate student Heather Knutson and her colleagues observed a hot Jupiter in the constellation Vulpecula using the Spitzer Space Telescope. They then used that data to develop a temperature map of the planet's surface.

The team found only a relatively minor difference in temperature—about 500 degrees Fahrenheit (280 degrees Celsius)—between the day and night sides.

For the temperature to be so consistent across the planet, "[t]here must be extremely strong winds, similar to the jet stream on the Earth," Knutson explained.

The winds are much stronger than those in Earth's jet stream, however, with speeds up to 9,656 kilometers (6,000 miles) an hour.

The researchers were able to take things a step further and map the temperature variations across the planet.

Over the course of 33 hours, the team mapped the body by measuring its brightness from pole to pole, creating the first such map of an extrasolar planet. (See enlarged photo at left.)

Results revealed that a "hot spot"—an area of the planet that received the most intense heat from the parent star—was far from where it was expected to be, further confirming the presence of winds.

"This is not something we ever expected to be able to do with the current generation of space telescopes," Knutson said.

Superhot Planet

Joseph Harrington of the University of Central Florida and Cornell University is the lead author of the second Nature study.

He calls the Harvard research an "exquisite analysis," though it reveals a very different picture of hot Jupiters than his own work.

Harrington and his colleagues used Spitzer to spy on another extrasolar planet—this one in the constellation Hercules—with a very different result.

Unlike the planet in the Harvard study, which tends to retain and redistribute its heat across its atmosphere, the planet studied by Harrington's team releases its starlight almost immediately as heat, the study found.

Past research has proposed that at least one unusually heavy chemical, titanium oxide, may be present in the planet's atmosphere, which may explain why the world absorbs nearly all the light that hits it.

Based partly on these results, Harrington and others have been promised more access to the Spitzer telescope in order to peer at similar superhot planets.

Knutson's research team will soon map the temperatures of another hot Jupiter, dubbed HD 209458, which was recently found to have water in its atmosphere.

The planet has a "mysteriously puffed-up radius," Knutson said, and her team will be observing it at various wavelengths to yield more thorough pictures of its atmosphere.

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