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Extrasolar Planet Detected Visually
"etphonehome" was the first of many to submit this.
Astronomers at UC-Berkeley measured a star decreasing in brightness as its planet crossed in front of it. This is the first known planet whose orbital plane crosses Earth, making this measurement possible. It's great to see independent confirmation of the "wobble" which until now has been the only evidence of extrasolar planets. There's a splendid artist's rendition on the
astronomers'
webpage; see also the story on
CNN
or the technically-challenged
Washington Post
("the planet had indeed cast a shadow over the star").
They monitor the intensity of light from the star as a function of time. They saw the star dim a little bit just when predicted by the group who discovered the planet. If correct, it will transit (pass in front of the star) again today and people will be looking to confirm this.
What happened is that a very large planet moved in its orbit of the other star into a position between that star and Earth. Thus, it blocked some of the light from the star from reaching earth, making the star appear to dim for a few moments...think of it as a very partial eclipse of that star by one of its planets, much like our moon occasionally gets between us and the sun, causing partial or total eclipses, blocking or dimming it briefly.
This dimming of the star, predicted by the astronomers, proved that they had inferred its orbit coreectly, and that there are indeed other planets. Even if they are obscenely close to thier stars. A 3-4 day orbit means that thing is very very close to its sun - the weird thing is they've detected a lot of planets with about the same distance from various stars...
Where are all the planets that have nice, decent, life supporting orbits? (ok ok , life-as-we-know-it style? I don't want to emigrate to Mercury or its distant kin!!)
What this was probably intended to say was...
Ever since the first extrasolar planet around a sun-like star was discovered (1995) to be in a 4 day orbit, astronomers have theorized that that planet (and recently several others like it) were not massive terrestrial planets, but rather gas giants like Jupiter (but much closer to their parent star). This discovery is the first where we accurately know both the mass and radius observationally. The observations show that this is indeed a gas giant as predicted (for similar type planets) years ago.
The bit about it not forming so close is a little more technical. But basically, we beleive that gas giants begin to for a few AU (distance from Earth to Sun, Jupiter is at 5 AU) from their parent star (based on our estimates of the temperature of the disk and at what distance different elements and molecules will condense). An alternative is that these close massive planets are accutally humoungous rocky planets (like Mercury, Venus, Earth, Mars). While this observation does not prove that it didn't form there, it does prove it's a gas giant. That is a triumph of astrophysical theory.
BTW- Some of the difficulties with forming gas giants at several AU are: How do you move them in to 0.04 AU? Why do they stop right there and not continue to migrate into their parent star?
These telescopes do the most precise photometry ever achieved, working to about 0.001 magnitudes on a night-to-night basis, and about 0.0002 mags for long-term variations. That's ALMOST good enough to montior irradiance changes for stars that vary as little as the Sun does. On a very good night, with lots of overlapping data, these telescopes could almost detect a transit of an Earth-sized planet.
There are two published papers on using these telescopes to look for transits in exoplanet systems. A third has been accepted for publication by the Astrophysical Journal and will come out in the March 10, 2000 issue. (I'm one of the authors.) Preprints of the papers are all available on one of my webpages:
(I'll get the preprint of the 3rd paper up there on Monday.)
It's great to see that a transit has finally been observed! We were starting to get worried... The search for transits is being done in collaboration with a long-term program to better understand the stars they orbit also done at Fairborn and with Mount Wilson's HK Project.
Bob Donahue
Forgive me if I'm missing the point, but why include an artist's rendition of the planet/star system on a page that otherwise contains scientific information? You can disclaim 'til you're blue in the face, yet someone is going to surf on over there and think, "man, those scientists sure can take clear pictures of faraway stuff these days!"
Seems to me that when you expect the unwashed masses to visit your site, you should consider that many folks really don't have a good grasp on the state of the technology. Monitoring the brightness of a star and noticing a 1.7% dip is a lot different from peering through an eyepiece and looking at Saturn's rings. I think in this case, the picture only obfuscates the situation.
But maybe I'm nitpicking...
wcb
The reason it's not called a binary system is that the mass of the "planet" is 0.6 times the mass of Jupiter. This is not massive enough for it to fuse hydrogen or even deuterium. To answer your question, the star is probably about 1.1 to 1.3 times the mass of the sun (not based on careful analysis, only it's spectral type), so the mass ratio is approximately 2000:1.
Of course how massive it is does not necessarily determine how it formed. Indeed, one hypothesis is that it did form by direct gravitational collapse from the protostellar nebula similar to the star it surrounds. However this hypothesis is no longer favored by most astrophysicsts for rather technical reasons related to turbulence in the protostellar disk. Additionally, models (see papers by Alan Boss who favors this approach) have difficulty doing this at less than a few AU (AU=distance from Earth to Sun, Jupiter is at 5 AU, this planet is at 0.045 AU).
(Other hypothesis exist about ways to form a planet at several AU and then migrate the planet to a small distance. I'll answer another question related to this after lunch, so you can read more there.)
In fact current radial velocity surveys could detect Jupiter mass planets out to several AU (AU=distance fom Earth to Sun, Jupiter at 12AU, this planet orbits at 0.045 AU) . In fact some have been detected as far as 3 AU from their star (see Marcy & Butler's list
Just think. Say you have a flashlight pointed at the wall and you put your hand in front of the flashlight; you get a shadow on the wall. Anyone remember that image posted on slashdot with the shadow of moon on the earth. Now we have single planet hundreds of lightyears away casting a shadow for a brief moment; covering our entire solar system, perhaps a lot more. Just think how many star systems are in this planet's shadow! All the many cubic light-years of space, probably millions, in the shadow from a single point in the sky.
***Beginning*of*Signiture***
Linux? That's GNU/Linux to you mister!
Good question. If current theories are correct then they did not form there, but rather migrated after forming at several AU. The fact that one is observed to be a gas giant supports this since gas giants are beleived to form at several AU.
How did they move? At the moment, there are several hypotheses, each with it's own problems. To summarize:
1. Interaction with a gaseous disk to transport angular momentum outward and mass inward by exciting spiral density waves at Lindblad resonances (distance at which the orbital frequency matches the frequency of radial oscilation of the planet in an epicyclic approximation) on both sides of the planet's orbit. Big problems: Effects of additional planets, how to stop the migration right before it falls into the star
2. Interaction with a planetessimal disk in which many small bodies at orbital resonances (where ratio of the two orbital periods is a rational) have their eccentricities excited so they can be kicked out of the system by the planet in a close encounter. Big problems: Effects of additional planets, need a very massive disk for the process to be unstable (and thus significant migration).
3. Interation with other planets so that one planet gets kicked farther out (sometimes out of the system entirely) and another planet closer in, or two collide. Big problems: Can this send enough planets so close to their star to match observations?
4. Interactions with another (more distant) star that induces a long term secular increase in the eccentricity until tidal effects before important and circularize the orbit at a small radius. Big problems: Quadrupole moment of star may limit eccentrity. Some planets are around star with no observed wide binary companion.
If you want references to any of these, I can provide them.