High clouds in the west, clear skies in the east: That's the weather report for Kepler-7b, a sizzling Jupiter-like world that's quadrillions of miles away.
The scientific world's first map of the clouds on an extrasolar planet has been laid out in a paper accepted for publication in the Astrophysical Journal Letters. It's based on years' worth of readings from NASA's Kepler and Spitzer space telescopes.
"By observing this planet with Spitzer and Kepler for more than three years, we were able to produce a very low-resolution 'map' of this giant, gaseous planet," the paper's lead author, Brice-Olivier Demory of the Massachusetts Institute of Technology, said Monday in a NASA news release.
"We wouldn't expect to see oceans or continents on this type of world, but we detected a clear, reflective signature that we interpreted as clouds."
The Kepler probe discovered Kepler-7b three years ago. Further observations from Kepler showed astronomers that there was a bright spot on the planet's western hemisphere. Then they used Spitzer's infrared observations to determine that the bright spot was due to reflected starlight rather than internal heat.
Demory's reference to low resolution should be emphasized: The "map" is little more than a division between the planet's bright and dark sides. It's not even as detailed as the murky illustration released by NASA on Monday. But it does show how data from two telescopes can be combined to learn something important about alien planets.
Kepler has been observing distant stars for four years, and although the spacecraft went out of service this summer, there are still reams of readings for scientists to pore through. Those readings track the subtle variations in starlight that occur when a planet passes over the disk of its parent star.
Some variations can represent changes in the brightness of a planet such as Kepler-7b changes that might be analogous to phases of the moon or of Venus.
But Demory and his colleagues had to figure out whether the changes in brightness were caused by the planet's hot glow, or by changes in the reflectivity of the planet's surface.
That's where the Spitzer data came in handy. Spitzer, which was launched 10 years ago, is an infrared telescope that can make precise temperature measurements for celestial objects including extrasolar planets. Last year, for example, astronomers relied on Spitzer to take the temperature of a world known as 55 Cancri e, 41 light-years from Earth.
When astronomers checked Spitzer's readings, they estimated that the planet's temperature was 1,500 to 1,800 degrees Fahrenheit (800 to 1,000 degrees Celsius).
That's hot but not hot enough to account for the light levels detected by Kepler. This gave the scientists enough confidence to claim that the
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