Astronomers Find Weird, Warm Spot on an Exoplanet

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Whitney Clavin 818-354-4673
Jet Propulsion Laboratory, Pasadena, Calif.
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NEWS RELEASE: 2010-340 Oct. 19, 2010

Astronomers Find Weird, Warm Spot on an Exoplanet

The full version of this story with accompanying images is at:
http://www.jpl.nasa.gov/news/news.cfm?release=2010-340&cid=release_2010-340

PASADENA, Calif. -- Observations from NASA's Spitzer Space Telescope reveal a
distant planet with a warm spot in the wrong place.

The gas-giant planet, named upsilon Andromedae b, orbits tightly around its star, with
one face perpetually boiling under the star's heat. It belongs to a class of planets termed
hot Jupiters, so called for their scorching temperatures and large, gaseous constitutions.

One might think the hottest part of these planets would be directly under the sun-facing
side, but previous observations have shown that their hot spots may be shifted slightly
away from this point. Astronomers thought that fierce winds might be pushing hot,
gaseous material around.

But the new finding may throw this theory into question. Using Spitzer, an infrared
observatory, astronomers found that upsilon Andromedae b's hot spot is offset by a
whopping 80 degrees. Basically, the hot spot is over to the side of the planet instead of
directly under the glare of the sun.

"We really didn't expect to find a hot spot with such a large offset," said Ian Crossfield,
lead author of a new paper about the discovery appearing in an upcoming issue of
Astrophysical Journal. "It's clear that we understand even less about the atmospheric
energetics of hot Jupiters than we thought we did."

The results are part of a growing field of exoplanet atmospheric science, pioneered by
Spitzer in 2005, when it became the first telescope to directly detect photons from an
exoplanet, or a planet orbiting a star other than our sun. Since then, Spitzer, along with
NASA's Hubble Space Telescope, has studied the atmospheres of several hot Jupiters,
finding water, methane, carbon dioxide and carbon monoxide.

In the new study, astronomers report observations of upsilon Andromedae b taken across
five days in February of 2009. This planet whips around its star every 4.6 days, as
measured using the "wobble," or radial velocity technique, with telescopes on the ground.
It does not transit, or cross in front of, its star as many other hot Jupiters studied by
Spitzer do.

Spitzer measured the total combined light from the star and planet, as the planet orbited
around. The telescope can't see the planet directly, but it can detect variations in the total
infrared light from the system that arise as the hot side of the planet comes into Earth's
field of view. The hottest part of the planet will give off the most infrared light.

One might think the system would appear brightest when the planet was directly behind
the star, thus showing its full sun-facing side. Likewise, one might think the system
would appear darkest when the planet swings around toward Earth, showing its backside.
But the system was the brightest when the planet was to the side of the star, with its side
facing Earth. This means that the hottest part of the planet is not under its star. It's sort of
like going to the beach at sunset to feel the most heat. The researchers aren't sure how this
could be.

They've guessed at some possibilities, including supersonic winds triggering shock waves
that heat material up, and star-planet magnetic interactions. But these are just speculation.
As more hot Jupiters are examined, astronomers will test new theories.

"This is a very unexpected result," said Michael Werner, the Spitzer project scientist at
NASA's Jet Propulsion Laboratory, Pasadena, Calif., who was not a part of the study.
"Spitzer is showing us that we are a long way from understanding these alien worlds."

The Spitzer observations were made before it ran out of its liquid coolant in May 2009,
officially beginning its warm mission.

Other authors of the study are Brad Hansen of UCLA; Joseph Harrington at the
University of Central Florida, Orlando; James Y-K. Cho of Queen Mary, University of
London, United Kingdom; Drake Deming of NASA's Goddard Space Flight Center,
Greenbelt, Md.; Kristen Menou of Columbia University, New York, N.Y.; and Sara
Seager of the Massachusetts Institute of Technology, Boston.

JPL manages the Spitzer Space Telescope mission for NASA's Science Mission
Directorate, Washington. Science operations are conducted at the Spitzer Science Center
at the California Institute of Technology, also in Pasadena. Caltech manages JPL for
NASA. For more information about Spitzer, visit http://spitzer.caltech.edu/ and
http://www.nasa.gov/spitzer .

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