Category Archives: Kepler mission

european southern observatory, exoplanets, extrasolar planets, Kepler mission

One Star, Two Planets, Big News

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What Are They Like?

This artist’s concept illustrates the two Saturn-sized planets discovered by NASA’s Kepler mission. The star system is oriented edge-on, as seen by Kepler, such that both planets cross in front, or transit, their star, named Kepler-9. This is the first star system found to have multiple transiting planets. Credit: NASA/Ames/JPL-Caltech

It has been almost 20 years since the first extrasolar planets (worlds around other stars) were discovered.  Astronomers suspected they existed, but since tiny worlds can get lost in the glare of their stars’ light, we had to wait until we had the right kinds of instruments to observe distant worlds circling other stars. Today, the number of confirmed exoplanets lies at just under 500, and that number changes almost daily.

The latest news in planet-hunting circles is the discovery of two planets orbiting a star called Kepler-9.  The planets showed up in data taken by the Kepler mission, which is tasked to search for extrasolar planets in an area of the sky in the direction of the constellation Cygnus the Swan (which is high in the northern hemisphere sky these evenings).

Now, there have been lots of extrasolar planets discovered, but this is the first time two have been confirmed orbiting the same star. The planets, named Kepler-9b and Kepler-9c, have masses that are almost that of Saturn in our own solar system. Kepler-9b is the larger of the two and it orbits the star once every 19 days. The smaller Kepler-9c lies farther away and takes 38 days to make a trip around the star.

The Kepler spacecraft observed this system to tack down the precise length of each planet’s orbit around the parent star. This isn’t the only such system that the spacecraft has data for, but it’s the first to be confirmed — a big milestone for the team and the spacecraft.

The planets were discovered as the Kepler spacecraft’s camera measured tiny decreases in the star’s brightness–decreases that occur when a planet moves between us and the star. And yes, even something so small as a planet can have an effect on the star’s brightness, and Kepler is sensitive enough to detect those little dips in the star’s light.  In addition, the distance between each planet and the star can be calculated by measuring the time between successive dips as the planet orbits the star. Small changes in the regularity of these dips can help astronomers determine the masses of planets and detect other non-transiting planets in the system. In fact, the data seem to indicate that there may be at least one other planet in the system–a world about 1.5 times the Earth’s radius that follows a scorchingly short 1.6-day orbit around the star. Kepler scientists are still taking data to make sure that this is another planet and not an anomaly in the data.

The artist’s concept of the two confirmed planets show that these are gas giant-like worlds, so they’re not likely to be places where life is going to exist — at least life as we know it. And, if there IS another planet that’s closer to Earth-size? Well, it’s not likely to be a very hospitable place either. It’s likely a scorchingly hot place with little opportunity for life to take hold.

Kepler’s discovery is the second in a pair of exoplanet finds reported this week. The European Southern Observatory announced earlier that it has found a star that may have at least five planets orbiting around it. Astronomers used the HARPS spectrograph attached to the ESO’s 3.6-meter telescope in Chile to search for the existence of planets in the system. Unlike the Kepler mission, which checks for dips in light intensity of stars with planets in orbit around them, the HARPS insrtrument looks for stellar motions that indicate the existence of planets. The amount of motion tells them the mass of the planets that may exist, and helps them deduce the orbits of those distant worlds. The measurements correspond to planets with masses between 13 and 25 Earth masses. They appear to orbit  the star with periods ranging from about 6 to 600 days. These planets lie between 0.06 and 1.4 times the Earth–Sun distance from their central star. This is actually pretty well-populated system with five massive planets located within 1.4 AU.  By comparison, the Sun has only four planets — and small ones at that — in roughly the same space.

The science of planetary detection is a major growth area in astronomy. With Kepler’s ongoing mission and the ground-based work being done at places such as ESO, I think it’s only a matter of time before the community of worlds that we can detect will be well over a thousand. Now… if we could only find one with life on it!

astronomy, exoplanets, exploration, Kepler mission

Kepler Detects the Atmosphere of a Distant World

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Media Misses the Story

As my bud Phil Plait would say, “Holy Exoplanet!” The Kepler mission team today announced that their orbiting planet hunter has detected the atmosphere of a known gas giant planet that lies about a thousand light-years from us in the direction of the constellation Cygnus, the Swan.

This is a pretty big story and it should have been mentioned on the evening news, or at least as a headline on places like CNN. But, it wasn’t. What’s it take to get the press excited these days? A scan of CNN headlines shows me that they care about Obama’s grades six months into his presidency (which, by the way, has been a “top” story for two days now), lawmakers whinging about military uniforms, a story about whether anybody is flipping out over Twitter being down for a while earlier today, and a “lifestyle” story about the booming sales at dollar stores. Apparently news of an atmosphere on another planet — a very tough, rare and important discovery, just doesn’t make the cut. Actually, very little science has been making the news, despite the fact that there have been some hot stories and gorgeous images released lately. It’s as if the media don’t give a damn about science if it doesn’t bleed, lead, or bleat about political figures. No wonder so many citizens of the United States are verging science illiteracy — our media don’t bother to report science discoveries very much or very well. Which is sad.

Real science showing evidence for a real atmosphere of a planet a thousand light-years away from us. Courtesy NASA/Kepler mission. Click to embiggen.
Real science showing evidence for a real atmosphere of a planet a thousand light-years away from us. Courtesy NASA/Kepler mission. Click to embiggen.

Well, I’ll tell you about this story. It’s all about light curves — which may have scared off the media. It’s not a pretty picture of the kind they like to put up on the front page.  It’s data and it takes a little explaining — which isn’t hard — but try telling a hardened editor that this is more exciting than yet another story about Michael Jackson’s kids…

So, what’s a light curve? Sometimes stars (or other objects) vary in their brightness. If you chart that variation, you get a curve. It swoops up when the object is bright and then down when the object is dim. Variable stars get brighter and dimmer all the time. So do asteroids — as they tumble through space, they reflect different amounts of sunlight, producing a light curve.

Well, some stars show a changing light curve that has nothing to do with being a variable star. Something is causing those stars to dim just a tiny bit on a regular periodic schedule. What could that be? How about a planet?  Planets circle their stars on regular schedules, and as they pass between us and their stars, the amount of light we (or actually our instruments) see from each of those stars gets a little dimmer. If you chart the dimming and brightening over time, you can get a good idea of how long a planet takes to go around its star.

Well, this is exactly what Kepler is doing — measuring light curves of thousands of stars in a field in the constellation Cygnus. Today, astronomers released the news that one of those light curves of a star about a thousand light-years away showed evidence of a planetary atmosphere. That is spectacular news because 1) it hasn’t been done like this before and 2) it’s based on ten days of test data, where the instruments onboard the spacecraft looked at the amount of light coming from stars in its field of view.

The data were collected after Kepler was launched but before the actual science ops began. Make no mistake about it — finding a planetary atmosphere a thousand light-years away in data taken to test an instrument tells me that this spacecraft is going to be uncovering a bunch of new worlds and telling us MUCH more about the state of newly discovered planets in our galaxy. It’s like pointing your telescope to the sky for the first time and spotting a comet right out of the blue.

The observations are of the planet HAT-P-7, a world astronomers already knew existed from a prior discovery. The planet follows a whoppingly fast 2.2-day orbit around its star and lies about 26 times closer to its star than Earth lies from the Sun. Kepler detected this world as it transited (passed in front of) the star. The repeated transits cause tiny dips in the amount of light that the spacecraft sees coming from the star.

HAT-P-7 is a “hot Jupiter.” It’s so close to its parent star that the heat of its glow is about the same as the red heating element on a stove. The new measurements are so precise they also show a smooth rise and fall of the light between transits caused by the changing phases of the planet, similar to those of our moon. This is a combination of both the light emitted from the planet and the light reflected off the planet. That is, the light curve of the star was changed not just by the transit of the planet, but by the changing phases of the planet.

The rise and fall of light is also punctuated by a small drop in light, called an occultation, exactly halfway between each transit. An occultation happens when a planet passes behind a star. The depth of the occultation and the shape and amplitude of the light curve show that the planet has an atmosphere with a day-side temperature of about 4,310 degrees Fahrenheit. Little of this heat is carried to the cool night side. The occultation time compared to the main transit time shows the planet has a circular orbit. The discovery of light from this planet confirms the predictions by researchers and theoretical models that the emission would be detectable by Kepler.

This new discovery at HAT-P-7 also shows us that Kepler has the precision to find Earth-size planets — which I can guarantee you is going to be pretty exciting when it happens. Of course, it will show up in a light curve and not a pretty picture — but that data will be beautiful in its own right!

What I find interesting to speculate about is that if Kepler were 1,000 light-years away from US and looked back at Earth, it would see similar dips and changes in the  light curve of the Sun as Earth orbits it. That distant Kepler, operated by aliens who want to know if the Sun has any planets with life, would be excited to know that our planet has an atmosphere. And, they’d wonder whether any life was being supported by that atmosphere.  (And, hopefully, their media would be more on the ball about reporting such a discovery.)

If I were you, I’d keep an eye on the Kepler mission via their web site — there’s bound to be more big news coming from this wonderful spacecraft. Heck, it might show us an Earth-like planet soon. But, don’t bet on the media covering that unless there’s something sexy, bloody, or politically banal discovered on the surface of the planet. If it doesn’t bleed, it apparently doesn’t lead.

Update, Monday August 10: I had to laugh last night when I clicked on CNN.com and saw that they were finally headlining this story — late on a Sunday night in the last part of the weekend news cycle.  There’s an interesting twist this time: they posted the story about the NASA mission with an image from the ESA COROT mission about an entirely different  planetary atmosphere discovery made by the COROT satellite. The image CNN used to illustrate their Kepler story is credited to NASA and apparently came from NASA, even though it was first used on the ESA site to illustrate the COROT findings (in  first appeared last year on the it’s clearly stated on the ESA web page that the credit is ESA-C. Carreau.  CNN just put up there what they were given — albeit a few days after the actual news was released.