Eccentric Exoplanet Gets Hot Flashes

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But during a stellar encounter that lasts less than a day, the planet swoops in to about ten times closer than Mercury is to the sun.

This means that for a short period the exoplanet is getting 828 times the average amount of heat from its star.

Using the Spitzer Space Telescope, Laughlin and colleagues measured continuous changes in the planet's temperature over a 30-hour period that included a close approach.

The team found that the planet's atmosphere jumps from about 980 degrees Fahrenheit (527 degrees Celsius) to almost 2,240 degrees Fahrenheit (1,227 degrees Celsius).

What's more, the atmosphere reaches these extreme temperatures extremely fast, the scientists report in this week's issue of the journal Nature.

"It's very, very responsive to the dose of heat it's getting from its star," Laughlin said. "This tells us that the planet's atmosphere absorbs starlight very high up where the air is thin.

"If Jupiter was on an orbit like this, it would probably respond in a similar way, but it wouldn't heat up quite so rapidly," he added.

"Earth would have a much more sluggish response, because the sunlight penetrates to a deeper level."

Planet Detectives

According to CfA's Knutson, the study adds to evidence for why some gas giant planets—which are very distant from the sun in our solar system—orbit so close to their parent stars in other systems.

"As we understand the properties of extrasolar planets, we can do detective work to find out where they came from," Knutson said.

The current theory is that hot Jupiters start forming farther away from their stars and slowly migrate inward.

"The fact that this planet has such an eccentric orbit means something odd happened in this system," she said of HD 80606b.

Knutson and Laughlin are both excited that the Spitzer observations also showed the planet passing behind its host star as seen from Earth. This allowed Laughlin's team to calculate a 15 percent chance it will pass in front of, or transit, the star on February 14.

During a transit, the planet blocks some of its host star's light, allowing astronomers to take a more direct measurement of the object's size.

In addition, some of the starlight gets filtered through the planet's atmosphere. Astronomers can then read signals in the light that indicate the types of gases present.

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