Dusty Disk Evidence of Planetary Collision

Article written: 24 Sep , 2008
Updated: 24 Dec , 2015
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What astronomers had expected to be a run-of-the-mill protoplanetary disk turned out to be evidence of a much more intriguing story. While observing the sun-like star BD 20 307, a team of astronomers noticed a large disk of dust surrounding the star. Usually, this is evidence of planetary formation around younger stars. The 8 planets (and plutoids…) in our own solar system formed out of just such a disk. Disks like this aren’t generally found around older stars, though, and when the age of the star was calculated to be several billion years old, the source of the dust appears to come from a rare event: it is the resulting debris of two planets slamming into each other.

Using data from the Chandra X-ray Observatory, and taking the brightness using one of Tennessee State University’s automated telescopes in Arizona, the team first discovered BD 20 307 to in fact be part of a close binary pair. Not only that, but the system was much older than previously thought: several billions of years old, rather than a few hundred million. The system is 300 light-years away from Earth in the constellation Ares.

The curiously large amount of dust orbiting BD 20 307 is 1 million times the amount of dust than is found in our own solar system, and orbits at a distance from the star that is similar to the orbits of Earth and Venus around our own Sun. The abundance of dust particles in this orbit – and around such a mature star – led scientists to the conclusion that it was created by the violent collision of two exoplanets.

Benjamin Zuckerman, UCLA professor of physics and astronomy and co-author of a paper on the discovery said, “It’s as if Earth and Venus collided with each other. Astronomers have never seen anything like this before. Apparently, major catastrophic collisions can take place in a fully mature planetary system.” Zuckerman and his team will report their findings in the December issue of the Astrophysical Journal.

Normally, warm disks of dust surround younger star systems, out of which larger and larger structures can form, eventually yielding planets. To find a disk of dust in around a star that is several billions of years old is odd, because the pressure of stellar radiation pushes out the lighter dust over time, and the larger chunks either form planets and asteroids, or break down in collisions and get blown away.

The collision between the planets took place within the past few hundred thousand years, though it is possible that it happened even more recently. Such a colossal collision raises the question of how the orbits of the two planets became destabilized, and whether such a collision could happen in our own solar system.

“The stability of planetary orbits in our own solar system has been considered for nearly two decades by astronomer Jacques Laskar in France and, more recently, by Konstantin Batygin and Greg Laughlin in the U.S.A. Their computer models predict planetary motions into the distant future and they find a small probability for collisions of Mercury with Earth or Venus sometime in the next billion years or more. The small probability of this happening may be related to the rarity of very dusty planetary systems like BD+20 307,” said paper co-author Gregory Henry, astronomer at Tennessee State University (TSU).

Source: EurekAlert


22 Responses

  1. Jorge says

    They weren’t planets: they collided, hence they obviously didn’t have their orbits cleaned, which makes them dwarf planets.

    Oh, wait: they didn’t orbit the Sun, so they weren’t dwarf planets either. They were… er…

    Er…

    OK, let’s try again. Forget the IAU and its silly-silly-übersilly definition. They were obviously big enough to have been rounded by their own gravity? Yes? Allright: you can call them planets. Problem solved.

  2. Sili says

    Well, doesn’t it make a difference the the ‘star’ in question is a binary? I’d imagine that’d make for less stable orbits.

  3. BHC says

    or maybe it was just one planet, the aliens on it reached our tech level, and proceeded to blew their own planet up. 🙂

  4. BHC says

    wow, totally messed up the grammar when i inserted ‘proceeded to’ at the last moment.
    🙁
    would be interesting to see if there was life on what would’ve been the planet. it’s only 300ly away, so hubble & pals should be able to resolve that system pretty clearly, right?

  5. Silver Thread says

    Perhaps binary planets with degrading orbits? Similar to the Earth and the Moon if the moon were scooting closer to earth a little each year. It could take a very long time for it to finally reach the point where the two objects collide aye?

    Or maybe it’s two solar systems on a collision course, now ~that~ would be dramatic.

  6. simcop2387 says

    This is just more evidence of Aliens building a working LHC 🙂

    seriously though, its really neat they’re able to determine that kind of thing.

  7. Jorge says

    Sili:

    I’d imagine that’d make for less stable orbits.

    When a star is a binary you’re a bit more limited in the areas where your orbits are stable, but you can have stable orbits in almost any configuration. You’d just need to have your orbiting bodies either close enough to one of the stars or distant enough from both that any disturbances it suffers aren’t serious and cancel out in the long run. Or if it’s in resonance.

    Take the Pluto system for an example: you have two large bodies in a double system, Pluto and Charon, and yet you have stable orbits for Hydra and Nix, not all that far away from “mom and “dad” :).

  8. Jorge says

    Silver:

    Perhaps binary planets with degrading orbits? Similar to the Earth and the Moon if the moon were scooting closer to earth a little each year. It could take a very long time for it to finally reach the point where the two objects collide aye?

    That won’t happen. As the two objects get closer, they reach a point, called Roche limit, where the less heavy of the two is torn apart by tidal forces from the other. You get a ring, and probably a long bombardment on the surviving planet by small(ish) fragments of the smaller body, not a collision. That might send some dust into the interplanetary space, I guess, but nothing comparable to a smack on collision.

  9. Trippy says

    Here’s the Arxiv pre-print for the paper the article talks about.

    http://arxiv.org/abs/0804.1799

    If you read it, you’ll find out that the calculations suggest that the stars are orbiting each other with a semi major axis of 4.4 – 4.7 Million km. This is .029-.031 AU or 9 stellar radii to put this in perspective, mercury has a semi major axis of 57 Million km or 0.387 AU.

    In otherwords, if this binary system were within the place of the sun, you’d have two solar masses worth of material within a radius of 9 solar radii.

    The difference in tidal effects between that and a two mass sun is going to be nothing, or next to nothing.

    In fact, most planetary scientests will tell you that the only way planets can form in a binary system is if it happens to be a close binary like this, or a paricularly widely space system.

  10. See this article at Space Review: Can we detect asteroid impacts with rocky extrasolar planets?
    http://www.thespacereview.com/article/761/1
    This one would have been much brighter.

  11. David says

    A planet with an elliptical orbit going round a binary star could experience its aphelion being raised very gradually. Once the aphelion of this planet has become greater than the perihelion of a planet in a larger orbit, then you may have the time bomb ticking away. It depends on the difference in the inclinations of the orbits amongst other things. Both orbits could be said to be stable at the outset.

  12. Vino says

    @BHC
    I would think that the dust surrounding this star will pose problems with actual imaging of the system…rather than aiding us….maybe we can try spitzer….

    The other thought is whether this system harbours anymore exoplanets? Is there a way of detecting them…if so, r they in a stable configuration or are they going to give us a spectacle in near future like Levy -9????

  13. Rey says

    I think we are the next planet with intelligent life to be destroyed 😀 …well, better live your life to the fullest, cuz when they come, were done LOL

  14. Mike says

    Man, I just love this site. The article is great as always.

    KEEP UP WITH THE GREAT JOB, CONGRATS !!!

  15. Helio George says

    Amazing story and another new puzzle.

    [A Sun-like binary star system. What are those two yellow objects in the illustration’s background? :)]

    Any change a billion years of gravity waves from this dance couple could trigger some orbital problems?

  16. Tyler Durden says

    “I think we are the next planet with intelligent life to be destroyed 😀 …well, better live your life to the fullest, cuz when they come, were done LOL”

    Excellent point. This is clearly the work of the Destroyers who are diligent in wiping out all life forms they encounter by destroying the planet they live on.

    Soon the Destroyers will be noticing the EM transmissions from Earth or just sniffing our atmosphere and seeing a habitable biosphere, and some day some astronomers elsewhere will be marvelling at the dust cloud in our solar system..

  17. j.h.wegener says

    I think this event should make us aware that there is good reason to study planets and other “dark” objects, even if we for a moment forget alien life. This reason is obvious: We learn more about the destiny of bodies like earth and ulitmately about our own possible future. Perhaps “worlds” like our often end in ways we hardly imagine yet? Of course such research is more relevant if we or descendants do not destroy ourselves – then there may be some sense in finding out what wonders or dangers are ahead, and, if possible, do prevent or “soften” the latter.

  18. BHC says

    @Helio George

    those are obviously ball-lightning style photon torpedos, just in case the moon-drop doesn’t do in the planet.

    is it too late to rename BD 20 307 to
    Alderaan?

  19. troy says

    “:OK, let’s try again. Forget the IAU and its silly-silly-übersilly definition. They were obviously big enough to have been rounded by their own gravity? Yes? Allright: you can call them planets. Problem solved.”

    Were they? Don’t be draw in by the “”Photo”” it is only an artists depiction.

  20. Dark Gnat says

    Hope neither of those planets were inhabited.

    It would suck to find out that the a planet was inhabited, but just got blasted apart.

    Then again, if there were intelligent being there, they might have realized their fate, and decided to leave or just sent out a message.

    Regardless, it wouldn’t hurt to check out different EM frequencies…just in case.

  21. Jorge says

    Troy:

    Were they? Don’t be draw in by the “”Photo”” it is only an artists depiction.

    Seems they were indeed. This is in today’s Astronomy Photo of the Day, and they talk about Earth / Venus-sized planets there.

    As far as I understood, if the bodies were smaller they’d never generate that much dust. That’s what that team’s interpretation of the data is, anyway. There could be others.

    And, BTW, that’s a good artist’s illustration for a change, even with all that back-lighting coming from nowhere.

  22. Jerry says

    could a binary system with two suns have some sort of evil gravitational effect because each sun might have an opposing gravitational force which might adversely effect the magnetospheres or gravitational equilibrium of the two planets, causing them to collide at perihelion.Would anyone care to comment?

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