Category Archives: exoplanets

exoplanets, extrasolar planets, planet-forming scenarios, planetary history, planetary science

More Planet Stuff: Here and Abroad

Leave a comment

Perseid Thoughts

So, did you see any Perseids last night?  We went out after midnight and saw maybe 20 before the Moon’s brightness lit the sky up too much.  There were several really bright blue-white ones flaring across the sky and a lot of smaller flashes that went by pretty quickly.  Did you know that each time you see a meteor flare in the sky, you’re seeing the vaporization of something that likely formed well before the planets did?  That may have been the leftovers of a stellar explosion long before our Sun was born?  Meteors are usually always bits of dust and grains thrown off by comets as they round the Sun, or are the crumbs of ancient collisions between asteroids. Those crumbs and bits of dust are scattered along the comet’s path, and occasionally they intersect with Earth. Those that aren’t bounced off the top of the atmosphere come heading straight in. As these bits of cosmic debris blast speed through the air, they get heated and vaporized — giving off light in the process. That’s what we see as a meteor.

There’s debris scattered throughout the solar system, the leftovers from the formation of the planets, moons, rings, and Sun.  Of course, it’s spread very thin — chances are if you were going through interplanetary space you’d encounter little of it, but it’s out there. However, when it encounters Earth, that’s when things get all flashy and bright for these little bits of dust. Think about that the next time you’re out stargazing and see that telltale flash of light go across the sky.  You’re watching the demise of something that’s likely OLDER than this planet.

Planetary Billiards

Artists impression of what the WASP-17 system might look like. Courtesy KASI/CBNU/ARCSEC
Artists' impression of what the WASP-17 system might look like. Courtesy KASI/CBNU/ARCSEC (Click to embiggen.)

Speaking of planetary systems, there’s a new world joining the ever-growing list of exoplanets out there. A team of scientists from the United Kingdom’s Wide Angle Search for Planets (WASP) project and the Geneva Observatory Extrasolar Planet Search program  announced today that they found a giant planet they named WASP-17. It’s orbiting around a star about a thousand light-years away.  That in itself would be sort of ho-hum in these days of “oh, gee, there’s another planet out there — how about finding us an Earthlike one” attitude from the press — but this planet is orbiting is star the “wrong” way. That is, it’s in a retrograde orbit, moving opposite the direction of anything else that’s in orbit around the star. This is a big honkin’ clue that something happened to knock the planet out of the orbit it formed in and send it careening like a billiard ball off in an entirely different orbit.  The best guess is that WASP-17 had a close encounter with an even bigger planet during the often-violent period of planetary formation around the star.  It’s a dangerous time for objects orbiting newly formed stars — things smash into each other, forming larger planets or grinding smaller objects to dust.

Not only is this planet headed the wrong way, but it’s huge — and that’s also a clue to its violent experiences in the past. As it got shoved into its current highly elliptical retrograde orbit, WASP-17 experienced some intense tidal interactions (caused by the gravitational pull of the star, perhaps, and at least by nearby objects). Those tides alternately compress and stretch the planet, which has the density of polystyrene (think foam cups), which heats it up (same as at Io, the volcano world orbiting Jupiter here in our own solar system).  Heating causes bloating, and voila — you get WASP-17.

This discovery doesn’t just tell astronomers about that particular system however — it also gives really good insight into what conditions were like when the Sun and planets formed 4 billion years or so ago.  It wasn’t just a “here’s a Sun, here are some planets, now start evolving” kind of thing. The process is long, drawn out, involves lots of crashes of objects, and apparently, some cosmic billiards!

astronomy, exoplanets, exploration, Kepler mission

Kepler Detects the Atmosphere of a Distant World

7 Comments

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.