Category Archives: exoplanets

astronomy, exoplanets, Kepler mission, Kepler-7b, spitzer space telescope

Exoplanet Cloud Atlas

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Patchy Clouds on a Distant World

Even though it’s not doing any more planet-searching due to an equipment failure, the Kepler telescope (along with the Spitzer Space Telescope) have returned data about a distant exoplanet called Kepler-7b that show it has clouds in its atmosphere. The data allowed astronomers to create an atlas of cloud forms over this planet, ranging from high clouds and clear skies in the western to somewhat clearer regions elsewhere. This is the first time that a “reflective signature” (that is, data that indicate reflectivity of an object in space) has been seen.

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. Image credit: NASA/JPL-Caltech/MIT
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. Image credit: NASA/JPL-Caltech/MIT

Kepler-7b planet radiates much more heat than most giant planets that Kepler scientists have found and its reflectance definitely implies clouds. It lies much too far away from its star to account for the light scientists see being reflected by the planet. That almost certainly suggest that there are clouds floating in this world’s upper atmosphere.

During its mission, Kepler identified planets by fixing its gaze at a specific point in the sky and 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 slightly less than five days, giving it a very short year.

Kepler’s partner in the observations of Kepler-7b, the Spitzer Space Telescope, can focus on one part of the sky for long periods of time, just as Kepler was designed to do. Spitzer is sensitive to infrared light which means it can “see” the heat coming from a distant object and take its temperature. During its observation, Kepler detected a temperature for Kepler-7b somewhere between 1,500 and 1,800 degrees Fahrenheit. Much hotter than most household ovens.

Using the two of these telescopes together to observe distant worlds gives astronomers a new way to study planets that lie far away circling other stars. It also allows astronomers to fine-tune their search for clouds on smaller, Earth-like worlds. (If you’re interested in more details you can read more about this discovery here.)

Now that Kepler is no longer actively looking for planets, scientists are turning their attention to the immense amount of data Kepler sent back, and using telescopes such as Spitzer (and ground-based instruments) to do observations on already known planet candidates.

I find it amazing that we can see these clouds on such a distant world (it lies trillions of miles from Earth). But, I find really impressive is that even though Spitzer can no longer do the most sensitive observations (due to its losing its instrument coolant), it can definitely still show us some amazing things in the cosmos. There are many more planet candidates discovered by Kepler that scientists will be studying, so look for more Kepler-based announcements in the foreseeable future.

exoplanets, exploration

A Realm of Planets

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More Exoplanet Discoveries

An artist’s concept of the seven planets possibly found orbiting Gliese 667C. Three of them (c, f and e) orbit within the habitable zone of the star. Click to get a larger version. Image courtesy Rene Heller.

The search for exoplanets (also known as extrasolar planets) is a painstaking one. You have to tease out “signals” from the planets, and by that I mean you have to look for evidence of planets in the light from distant stars. If a planet orbiting a star passes in front of its “primary” (its star), that passage dims the light a tiny fraction of a percent. And so, you need a very sensitive light meter attached to your telescope to catch that signal. Likewise, as a planet orbits its primary, it can cause the apparent motion of the star to “wiggle” a bit, and that “signal” shows up in the light streaming from the star. To tease out the wiggles and signals, astronomers break starlight into its component wavelengths (i.e., they take a spectrum) and look for changes in that spectrum. Specific kinds of changes may mean that a planet is affecting the star’s orbit, or causing it to dim down a tiny bit.

There are, however other things that can cause a star to appear to dim down or wiggle in its orbit. For example, it could be a variable star whose light intensity varies a tiny but—just enough to make it seem like a planet is passing between us and the star. Or, the star could be experiencing gravitational perturbations from another nearby star, enough to make it wiggle in its motion. The data not only tell that a planet possibly exists at the star, but also gives astronomers a good idea of what its minimum mass could be.

So, looking for these distant worlds is a complex science. Along the way, astronomers have discovered many new variable stars and even the occasional stellar black holes that affect a star’s light as they pass by. But, often enough, astronomers also find planets. And, that’s when the fun begins. Ground-based observers using large telescopes (larger than you have in your backyard) train their instruments on distant stars with planet candidates and begin the lengthy (often years-long) observations it takes to confirm that a planet is actually orbiting those stars.

Just today, an international team of astronomers, led by Guillem Anglada-Escudé of the University of Göttingen, Germany, and Rory Barnes of the University of Washington announced that they’ve found three “Super-Earth” type planets in the s0-called “habitable zone” of a nearby star. Incredibly enough, this world was previously thought to host two or three planets already, so that brings its possible world count to six or seven. “Super-Earths” are planets that are what they sound like—not more than 10 times more massive than Earth. This is the first time that so many of them have been found orbiting in one system.

The name of the star is GJ 667C, and its actually part of a three-star system that lies in the S-shaped constellation Scorpius. GJ 667C is an M-dwarf star, somewhat fainter than the Sun, and has about a third of the mass that our star does. A star this faint has a habitable zone—the region around it where liquid water could exist on a world—that is very close.  Because the habitable zone is so close to the star, the each planet’s year is much shorter than Earth’s is. They range from 20 and 100 days to go once around the star.  The planets are also very likely “tidally locked,” which means the same hemisphere always faces the star. Luckily astronomers know that life can exist under such conditions.

Since such low-mass stars are inherently faint, their habitable zones—the swath of space that would allow an orbiting rocky planet to sustain liquid water on its surface—lie much closer to the star. The closeness of the habitable zone then makes it easier to find potentially habitable rocky planets around low-mass stars.

In the past few years, astronomers have confirmed at least two planets orbiting this star, and possibly a third one that is still being confirmed. More observations allowed the team to find the new planet candidates. The next steps are to do more observations and detailed study in order to prove that these really are planets. If they are, then there’s a very good chance that this realm of planets will feature worlds with solid surfaces and maybe even atmospheres similar to Earth’s.

That’s the exciting part about planetary searches around other stars. While no one has yet found an Earth analog where life is teeming in oceans or on the surface, the time is drawing near when such a world could be found. It surely does lie out there, somewhere, waiting to be discovered and confirmed.