Angeles and lead author of a paper presenting the new observations in the Astrophysical Journal. “It’s exciting, and interestingly confusing.”

The planet, called upsilon Andromedae b, was one of the first hot Jupiters — giant planets several times the size of Jupiter that orbit searingly close to their stars — ever discovered. The planet’s orbit is so tight that the same side faces the star at all times. One side boils at 2,700 degrees Fahrenheit, the night side simmers at a mere 1,100 degrees Fahrenheit and the two hemispheres are separated by a zone of perpetual twilight.

Astronomers expected the hottest point on such a planet’s surface to face the sun. A few other planets have shown hot spots that were shifted a bit to one side, which could be explained by fast winds spreading through the planet’s atmosphere.

But upsilon Andromedae b’s hottest point is shifted 84 degrees to the east, almost perpendicular to where astronomers expected to find it.

“That’s a much bigger offset of a hot spot than has been seen for previous planets,” Crossfield said. “It’s going to be fun to try and figure out exactly what is going on on this planet.”

To take the planet’s temperature, Crossfield and colleagues used the Spitzer Space Telescope to measure the amount of infrared light coming from the star and the planet together. Because infrared light is a measure of heat, the pair of objects appears brighter when the planet’s hot side faces the Earth.

The astronomers watched the planet over the course of 5 days, a little more than a year on upsilon Andromedae b, in February 2009. Earlier measurements of how the planet’s gravity tugs the star to and fro gave a detailed picture of how long the planet takes to go around the star — 4.6 Earth days — and when it passes behind the star.

To the team’s surprise, the system appeared brightest when the planet was off to the side of the star, with its twilight edge facing Earth.

Stranger still, the planet showed a sharp temperature contrast between the night and day sides. A hot spot so close to the twilight zone should warm up the night side of the planet considerably, Crossfield said. But that’s not what happened.

“It’s not clear yet what’s responsible or how to reconcile this,” Crossfield said.

At this point, any explanation the team can offer is pure speculation, Crossfield stressed. But some candidates include supersonic winds that spark sonic booms, and currents flowing in the upper atmosphere through atoms so hot they’ve lost their electrons.

“These are things for which there’s not a lot of observational evidence yet, but they can be tested by future observations,” Crossfield said.

“I think this is one of the most intriguing new findings in exoplanet research,” said Adam Burrows of Princeton University, who was not involved in the new study. But “given the extraordinary nature of the conclusions, caution is in order. One should wait for more data and more thinking about exactly what may be going on before concluding that something exotic is happening.”

Video and Image: NASA/JPL-Caltech

See Also:

• Extreme Exoplanet’s Wild Ride
• New Technique Finds Gaseous Metals in Exoplanet Atmospheres
• Ground-Based Telescope Measures Exoplanet Atmosphere For First Time
• Hubble Detects First Organic Molecule Around Exoplanet
• Top 5 Most Extreme Exoplanets

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Authors: Lisa Grossman

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