Space telescopes find patchy clouds on exotic world

Oct 01, 2013
Kepler-7b (left), which is 1.5 times the radius of Jupiter (right), is the first exoplanet to have its clouds mapped. The cloud map was produced using data from NASA's Kepler and Spitzer space telescopes. Credit: NASA/JPL-Caltech/MIT

(Phys.org) —Astronomers using data from NASA's Kepler and Spitzer space telescopes have created the first cloud map of a planet beyond our solar system, a sizzling, Jupiter-like world known as Kepler-7b.

The planet is marked by high clouds in the west and clear skies in the east. Previous studies from Spitzer have resulted in temperature maps of planets orbiting other stars, but this is the first look at cloud structures on a distant world.

"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," said Brice-Olivier Demory of Massachusetts Institute of Technology in Cambridge. Demory is lead author of a paper accepted for publication in the Astrophysical Journal Letters. "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."

has discovered more than 150 exoplanets, which are planets outside our solar system, and Kepler-7b was one of the first. The telescope's problematic reaction wheels prevent it from hunting planets any more, but astronomers continue to pore over almost four years' worth of collected data.

Kepler's visible-light observations of Kepler-7b's moon-like phases led to a rough map of the planet that showed a bright spot on its western hemisphere. But these data were not enough on their own to decipher whether the bright spot was coming from clouds or heat. The Spitzer Space Telescope played a crucial role in answering this question.

Like Kepler, Spitzer can fix its gaze at a star system as a planet orbits around the star, gathering clues about the planet's atmosphere. Spitzer's ability to detect infrared light means it was able to measure Kepler-7b's temperature, estimating it to be between 1,500 and 1,800 degrees Fahrenheit (1,100 and 1,300 Kelvin). This is relatively cool for a planet that orbits so close to its star—within 0.06 astronomical units (one astronomical unit is the distance from Earth and the sun)—and, according to astronomers, too cool to be the source of light Kepler observed. Instead, they determined, light from the planet's star is bouncing off cloud tops located on the west side of the planet.

"Kepler-7b reflects much more light than most giant planets we've found, which we attribute to in the upper atmosphere," said Thomas Barclay, Kepler scientist at NASA's Ames Research Center in Moffett Field, Calif. "Unlike those on Earth, the cloud patterns on this planet do not seem to change much over time—it has a remarkably stable climate."

The findings are an early step toward using similar techniques to study the atmospheres of planets more like Earth in composition and size.

"With Spitzer and Kepler together, we have a multi-wavelength tool for getting a good look at planets that are trillions of miles away," said Paul Hertz, director of NASA's Astrophysics Division in Washington. "We're at a point now in exoplanet science where we are moving beyond just detecting exoplanets, and into the exciting science of understanding them."

Kepler identified planets by watching for dips in starlight that occur as the planets transit, or pass in front of their stars, blocking the light. This technique and other observations of Kepler-7b previously revealed that it is one of the puffiest planets known: if it could somehow be placed in a tub of water, it would float. The planet was also found to whip around its star in just less than five days.

Explore all 900-plus exoplanet discoveries with NASA's "Eyes on Exoplanets," a fully rendered 3D visualization tool, available for download at http://eyes..gov/exoplanets . The program is updated daily with the latest findings from NASA's Kepler mission and ground-based observatories around the world as they search for like our own.

Other authors include: Julien de Wit, Nikole Lewis, Andras Zsom and Sara Seager of Massachusetts Institute of Technology; Jonathan Fortney of the University of California, Santa Cruz; Heather Knutson and Jean-Michel Desert of the California Institute of Technology, Pasadena; Kevin Heng of the University of Bern, Switzerland; Nikku Madhusudhan of Yale University, New Haven, Conn.; Michael Gillon of the University of Liège, Belgium; Vivien Parmentier of the French National Center for Scientific Research, France; and Nicolas Cowan of Northwestern University, Evanston, Ill. Lewis is also a NASA Sagan Fellow.

The technical paper is online at www.mit.edu/~demory/preprints/kepler-7b_clouds.pdf .

Explore further: Understanding clouds as a necessary ingredient in the search for life: The case study of the exoplanet Kepler-7b

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GSwift7
not rated yet Oct 01, 2013
Unlike those on Earth, the cloud patterns on this planet do not seem to change much over time—it has a remarkably stable climate


I wonder if a highly oblique rotation might make it appear this way? Maybe they are looking at the north and south poles; one hemisphere is in winter and the other in summer? That would explain semi-persistent weather patterns on a hemispherical scale. We see this on bodies with tilted rotation in our own solar system, including Earth.
Fleetfoot
not rated yet Oct 01, 2013
I'm not clear which direction is absolute west in the universe so the article isn't clear, but I could understand a cloud remaining in a fixed relationship to the star given the proximity, as we see standing clouds over mountains even when a high wind is blowing.
GSwift7
5 / 5 (1) Oct 02, 2013
I'm not clear which direction is absolute west in the universe so the article isn't clear, but


The usual convention is the "right hand rule". When looking at any star, it rotates in the same direction as the orbits of its planets. If you make a fist with your right hand and place it on the table, with your thumb pointing up, then the direction your fingers point is East, the direction your thumb points is North, and the table top is the ecliptic. This is a self-contained frame of reference for any given star (as defined by common convention, though it's just a naming convention so that everyone can speak simply).

In the case above, we are aligned with the ecliptic (so we can see planetary eclipses). The direction the planets are moving when they eclipse is defined as East.
Fleetfoot
5 / 5 (1) Oct 02, 2013
The usual convention is the "right hand rule". When looking at any star, it rotates in the same direction as the orbits of its planets. If you make a fist with your right hand and place it on the table, with your thumb pointing up, then the direction your fingers point is East, the direction your thumb points is North, and the table top is the ecliptic. This is a self-contained frame of reference for any given star (as defined by common convention, though it's just a naming convention so that everyone can speak simply).


OK, but does that mean "west" is the side facing the star or facing away from it? I assumed the former but it depends on which side of the star the planet is placed.

"light from the planet's star is bouncing off cloud tops located on the west side of the planet. ... the cloud patterns on this planet do not seem to change much over time—it has a remarkably stable climate."
GSwift7
5 / 5 (2) Oct 03, 2013
OK, but does that mean "west" is the side facing the star or facing away from it?


The west side should be the trailing side. I assume this planet is tidally locked, which blows away my idea of seasons. I didn't initially catch the .06 AU orbit distance.

So, a tidally locked gas giant with some kind of stable pattern in the atmosphere.

The wiki page notes that what they are seeing could be something other than clouds, such as incandescence from solar heating. Keep in mind that at the temperature range of this planet, the atmosphere could have silica and iron vapor. If it is a cloud pattern, it's probably not water vapor clouds.

The more I read about Kepler 7b, the stranger it seems. How can it be so puffy? This is a really old system, since the host star is nearing the end of the main sequence. Maybe 7b used to be more massive and it's been evaporating atmosphere? Could we be seeing a coma rather than clouds? Or some other plasma feature near the planet?