On The Look-Out for Extrasolar Planets
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We’re so used to thinking about other planets… around other stars… in other galaxies… that it’s difficult to believe the existence of extrasolar planets (“exoplanets”) was unconfirmed until 1992. The first published “discovery” was actually made four years earlier by astronomers Bruce Campbell, G.A. Walker, and S. Yang of a planet orbiting the binary system Gamma Cephei, but it was unconfirmed until 2003. In 1992, three planets were discovered (and confirmed) orbiting the pulsar PSR B1257+12. This is considered to be the first true discovery, along with 51 Pegasi b in 1995 as the first exoplanet orbiting a main-sequence star.
This is an artistic impression of the planets orbiting PSR B1257+12:
Image: Artist conception Extrasolar Visions II, some rights reserved
Of course, you’re familiar with 51 Peg b and know it to be the archetype of a new class of planets, the “hot Jupiter”.
As of November 2009, there have been 405 confirmed exoplanet discoveries. That may not seem like a lot, until you stop to think about what it actually takes to find them. We’re used to looking at stars or orbiting bodies within our own solar system. Stars are easy; they’re shiny. Very shiny. Bodies in our own solar system, besides being very close, are shiny, too. They reflect the sun’s light. When you back up and look at a solar system 40 – 50 light years out, the planets aren’t very shiny anymore. What little sparkle they may reflect is completely absorbed in the fierce, blazing glow of the star.
So, how do you find them?
There are several methods which can be used, depending upon where, and at what, you’re looking, but there are two methods which have so far produced the best results. The first is radial velocity, which measures the Doppler shift in a star as it is acted on by the gravity of the orbiting planet. The second method is by measuring the dip in brightness of the star when a planet passes (transits) in front of it. As you can imagine, the changes measured by either of these methods are tiny. NASA has programs earmarked for future funding which will greatly increase our ability to locate exoplanets by both indirect and direct methods; much like the Kepler Space Observatory will do.
With our current instruments and methods, it’s only really possible to confirm very large planets; a “super” Jupiter, or a “super” Earth. Every small improvement made in locating exoplanets will reap huge advances in our knowledge. I find the amount of information astronomers can get now to be fantastic… just imagine what we’ll know in ten more years.
Image: NASA/ESA Hubble Space Telescope
This, by the way, is Fomalhaut b, the first exoplanet discovered by direct imaging (inferred in 2005, located in 2008), the first imaged planet since Neptune to have been predicted prior to discovery, first planet to have been correctly placed based on interaction with a debris disc, and is thought to be the coolest, low-mass object ever imaged outside our solar system.
Now THAT is a big deal.
how did they come up with the way to predict the discovery of this planet
Great question, Paul! They were able to infer the presence of the planet by the way it acted on the debris disc. If you look at the image, the “dust belt” is the bright, outer ring that gives the image the appearance of an eye (what you see imaged inside the ring is the “noise” from the scattered starlight). You can see that the dust belt is not centered on the star, meaning that “something else” with respectable mass is acting upon it. Also, the inner margins of the ring are quite a bit sharper than you might expect, again indicating the action of “something else” upon the dust ring.
thank you for the information,do you think you’ll be talking about “brown dwarfs” particularly about the newly discovered “stb213 jo41757″ double brown dwarfs they say are the coolest and faintest so far
Oh, yes, we certainly will! It’s a discussion in and of itself on how they currently differentiate between large mass planets and small mass brown dwarfs (the division is the limiting mass for thermonuclear fusion of deuterium). Certainly makes you give Jupiter a few thoughtful glances, doesn’t it?
yes it does,lol they say there some where between a “hot Jupiter and a red dwarf”and one way to determain the makeup of one is by the amount of lithum it still retains,mwell i hope you bring it soon ,i would luve to know more on them.thank you,happy Thanksgiving
marian,i was also wondering are there any known planets tha orbit a dwarf?
Yes, there are two of them known to orbit brown dwarfs, and either of them make for some interesting reading: 2M1207b and MOA-2007-BLG-192Lb (that’s a mouthful; often found shortened to “MOA-192b”).
I just think it’s great that it’s been confirmed that other stars have planets. It was long assumed that they must (Tom recently helped me out on a project involving a German astronomer who wrote in 1744 that every “fixed star” must have planets), and the idea has long been standard in science fiction, but we just didn’t *know*.
There was a counter-theory for a while that planets were formed by one star passing another so closely that material was drawn by gravity out of both, which would condense into planets. This would happen so seldom that planets would be extremely rare. The planets in our solar system (and presumably one belonging to the star that passed us) might be the only planets in this half of the galaxy. Fortunately, it’s looking as though planet formation is much more common and less catastrophic than that.
Well Dwight, planet formation may be more common than once thought, but I’m not too sure about the less catastrophic part. My understanding is that astrophysicists currently believe our own Sun and solar system was formed from the debris cloud left from an earlier star going supernova. Hard to imagine many things more catastrophic than that!
where were the planets about Oct 1st 2009 to Dec 5th 2009 My energy was not good and I had trouble getting a handle on my personality. The energy was too high and It effected me emotionally.
Arlene
Hi,folks:
Will we be able to measure these larger planets we discover for similar perterbations in their radial velocity, dips in brightness, or the “other methods” you referred to, and so infer the likely presence of smaller planets in the system?