Terrestrial planet forming around a nearby star?

By Phil Plait | October 3, 2007 9:32 am

Some interesting news from Spitzer Space Telescope: astronomers have spotted a disk of material orbiting one of the two stars in the binary system star HD 113766, located a little over 400 light years from Earth. The disk of material is loaded with rocky material, and is at the right distance from the star to be in the "Goldilocks zone", where temperatures are right for a habitable planet.

Artist’s impression of the system HD 113766

While this is an interesting news story, it has the potential to get away from us (I expect to see "Earth-like planet forming nearby!" headlines any second now). Update: I called it.

First, let me be clear: no planet has been seen! The conditions are correct to form one, though. The disk has enough material to form a planet the size of Mars or so; small, but maybe not too small. The system is about 10 million years old, which is favorable as well: a planet forming at that distance from the star won’t have too much hydrogen and helium associated with it, since the star would have blown those lighter elements away by now.

However, I’m not sure such a small body would retain much of that atmosphere anyway; the cores of Jupiter and Saturn are much larger than Mars. When they formed, the planets’ cores were probably bigger than Mars, which is why they had enough gravity to hold onto their dense atmospheres made up of the lighter elements.

Also, given the size of the belt itself, I wonder if that material will be able to to form a planet at all. Mars formed in our solar system, of course, but our planetary disk was much larger than this one. I am not an expert here (anyone here know more about this? Comment!) but it seems likely to me that a disk that thin may not be able to coalesce into a planet; it may stay as an asteroid belt. You need a certain density of material for it to form planets easily, and this disk may not get above that limit. Again, I’m not sure; the paper is not online yet (not even at astro-ph!).

Orbiting much farther out is another belt made of lighter compounds like water ice, which is also interesting. It doesn’t have nearly as much material in it, but could still coalesce into millions of comet-like bodies, equivalent to our own Kuiper Belt out past Pluto. Perhaps gravitational disturbances from the second star in the binary will cause those comets to scream down on the new planet (assuming a planet can form), loading it with water… which is very cool indeed. When we get the technology to start really seeing planets, to resolve their surfaces, I wonder… how many will be smaller planets covered in water? Tiny Mars-like water worlds, circling distant Suns; is that what we’ll find?

Every time we dig a little deeper, probing newly-forming systems, we get surprises. Planets forming farther out than we expect, supermassive planets ten times the bulk of Jupiter orbiting a scant few million kilometers off their parent stars, whipping around them in just days, a tail of boiled off atmosphere streaming behind them

The Universe is a weird place, and we’re only just starting to figure that out. The surprises are the best part!

Comments (26)

Links to this Post

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  1. tacitus

    The Universe is a weird place, and we’re only just starting to figure that out. The surprises are the best part!

    Agreed. It’s going to be fun to watch all the exoplanet discoveries over the next couple of decades.

    One thing that I have noticed is that creationists use these “surprises” to claim that scientists don’t really know what they’re talking about, and that you can’t trust anything they say about astronomy or any of the sciences that contradict their view of the Bible.

    FYI: it seems we’re only a month or so away from the first major results announcement from the COROT telescope:

    http://spaceurope.blogspot.com/2007/10/with-malcolm-fridlund-missions-project.html

    Looks like they’re finding plenty of planets. Can’t wait!

  2. Lurchgs

    I’m wondering… isn’t the current mainstream theory about earth the one that says we’d not be here if it weren’t for an early collision with a mars-sized body that resulted in our moon? Said moon skims off the lighter elements, leaving us with a rather dense, rocky ball – and it’s just right for life.

    Now.. assuming a proto-system similar to what our own was like, if dust/rocks etc were to condense into a planet in an orbit that permits the ice span (freezing/thawing of H2O) , you’d end up with a planet .. what.. 15% more massive? (I’m assuming equal starting masses, and some small but significant mass loss in our own collision) Without a relatively massive moon, would it end up more venus-like than earth-like? The last consensus I read about was that a planet of earth-moon mass, in this orbit, would likely be a hothouse and unlikely to support life.

    On the other hand, if a *Mars* sized body were to coalesce, the lesser mass might allow the solar wind to strip the lighter elements, which might result in a more earthlike planet.

    (I think Mars is actually too small – something like 10% the mass of Earth and 15% the volume.. memory failing. Bring it up to something like 50-70% the mass/volume of the earth/moon system and things might work out for life. All of this is pure, unadulterated, WAG, of course. Others with far more knowledge are struggling with the question. I doubt I’m going to answer it in an off-the-cuff pondering on a blog)

  3. Lurchgs

    A relatively off-topic thought just hit me (OW!!) just after I submitted my post.. If we assume a life-bearing planet that lacks a moon, and if we assume said life is intelligent… without a moon.. how screwed up would their astronomy be? They could almost certainly figure out that their planet was round.. but could they determine that their sun is not the center of the universe? (I would think that if there are other planets, they could eventually determine that they orbit their sun)

  4. Thorin

    Hey Phil (and readers), sorry to clutter up your comments area but I wanted to fwd this link and didn’t have a way to email currently.

    World Wide Star Count/Light Pollution Survey
    http://www.windows.ucar.edu/citizen_science/starcount/

  5. Tremant

    One thing that occurs to me (and i don’t think that i could be the only one) is that while we can detect large planets and rings of dust around other stars, our capacity for the detection of a small already exsisting rocky body inside that ring of dust is improbable at this time. not impossible just very unlikely until either better tech or better methods (and i am hoping the methods are all that are needed to be improved to actually see another world as the nasa inferrometers have been canned). Is there any way to rule out a small forming planet already exsisting inside that small inner ring? Is it possible that the ring is so thin because much of the material is collapsing or has already collapsed to a small planet that the exsisting ring of material is feeding? Could there already be a mars size or larger world inside the ring?

    (first time posting and i apollogise for the spelling, doing this from my phone)

  6. Adding to Phils questions: How is the other star in this system going to affect planet formation? Will the other star prevent the material from coalescing? Or will it promote formation by drawing the disk into a bulge? FYI aas.org says the two stars in the system are separated by 170AU.

    @LurchGS: I don’t think that not having a moon would affect their astronomy that much. IMHO Having a moon probably held us back somewhat as the two most prominant objects in the sky obviously revolve around the Earth. With the presence of a second star in their system their environment may be more favourable than ours is.

  7. TAMU Student

    So… we’ve got a planet forming in a binary system?

    Can you say, Tatooine?

    Seriously though, aren’t regular Day/Night cycles believed to have been important in the formation of life on earth?

  8. Chris Reed

    Well, it didn’t take long for the “Earth-like” headline….

    How about “Astonomers See Second Earth in the Making”

    http://www.msnbc.msn.com/id/21114394/

  9. dkary

    Based on Phil’s description here, this system looks more like the sort of late-stage dust-rich disk that we see after most of the disk is gone. If this system is forming like we think our system formed, then most of the mass of the disk is locked up in larger bodies (moon-sized or more) which are invisible with current technology. The 10-million year age for the star fits with this as well.

    By the way, I don’t think the “large moon skims of the volatiles” idea really works any more. That was suggested a few decades ago to explain the differences between Venus and Earth, and Larry Niven used it in his Known Space stories so a lot of people have heard of it. However, the problem is that the Earth has just as much of the carbon that gives Venus it’s thick atmosphere: our’s is mostly locked up in limestone and other carbonate rocks rather than in our atmosphere. I’ve seen the claim that if we turned the rocky mountains (and other large limestone structures) back into CO2, we would have an atmosphere that looks a lot like Venus’.

  10. bumhaskins

    I wonder if being located in a binary system will have any effect on how the planet develops.

  11. Let’s check back in with this system in 4 billion years or so.

    That is if we can still find it after 16 orbits of the galaxy and colliding with Andromeda. :)

  12. andy

    Now compare the picture used with the one given for the release about a disc around stars in a quadruple system. Blatant recycling!

  13. Rev. BigDumbChimp

    Let’s check back in with this system in 4 billion years or so.

    shheesh. Yeah right. Try 6000 years buddy.

  14. TAMU Student

    /That is if we can still find it after 16 orbits of the galaxy and colliding with Andromeda./

    Not to mention the end of the world occuring ;)
    http://www.exitmundi.nl/exitmundi.htm

  15. andy

    Let’s check back in with this system in 4 billion years or so.

    Well, the star in question is a fairly massive and luminous star of spectral type F3, so it would probably have gone or be going through the red giant part of its evolution by then.

  16. linus

    It is interesting that the Earth are inside the freeze limit for water. This limit actually lie outside the asteroid belt so if the current theory is correct the Earth would have no water since it could not stay even liquid on earth when it formed… Huzzah for comets which brought us the water. This implies that even if a planet forms it will probably not have water…

  17. MattFunke

    Lurchgs: If we assume a life-bearing planet that lacks a moon, and if we assume said life is intelligent… without a moon.. how screwed up would their astronomy be? They could almost certainly figure out that their planet was round.. but could they determine that their sun is not the center of the universe?

    Sure. There’s another star in their system, about 170 AU out. If the center of mass of these two stars lies well outside the bodies of either star, they ought to get some really interesting parallax measurements once they start taking them. Realizing that their star is not fixed would certainly help them to realize that they’re not in the center of things.

  18. Lurchgs

    Dkary – I read those too, yup. But, from what I’ve been reading (popular press, I’m afraid) and seeing on [I admiti it] Discovery, a variant is back in favor – just skimming the lightest of the volatiles. It plays some other role in the development of life, as I recall, but I’m hoolied if I can remember it, or find it quickly.

    MattFunke – good point. however, it occurs to me that we don’t know the distance between the two stars. I would suggest it’s significant, based on the fact that the dust rings formed at all. Thus, the period is likely to be measured in centuries – paralax may well be a non-issue for them.

    Linus – sure – when the planet *forms*, it won’t have much water, and a bunch of that will probably outgas and blow away as it cools. But, given the ring of water here, I think the BA is right is suggesting a proliferation of comets. It cosmic short order, I think there’ll be plenty of water on that rock.

    What’s interesting from this direction is there doesn’t seem to be any indication of other coalescences in the system (from what I’m reading) and just the one rocky belt – of rather limited mass. So, possibly *one* planet. And lots and lots of loose rocks running around like the drivers in Rome. If life forms, it’s going to be pretty hardy, having to deal with much more frequent bombardment than our ancestors did. I don’t know how many rocks were prevented from reaching the surface of my favorite pile of rock by the other orbiting bodies (moon, mars, etc), but I think the general scientific scientific consensus is “Lots” or maybe “Lots and lots”

    BA – I don’t think it’s fair to put that ‘call’ on the chart with the other gold stars. That prediction was about as difficult as “The sun will come up tomorrow”, or “Lurchgs sleeps until noon on Saturday!”

    Now, if you’d offered finer granularity – say “Wall Street Journal proclaims:” or “National Geographic headlines:”, I’d give you at least a red star. Dwarf.

  19. Lurchgs

    oops – as usual, I goofed a bit –

    MattFunke. I didn’t see the distance ref in your post. Didn’t see it online in other places – but ok.. 170 AU – call it better than 4 times as far as Pluto. I still think the period is going to be too long for intelligent life to make use of paralax. Even if they keep records, how likely is it to be “Oh, those ancients kept crappy records”, rather than accept that they might just be right?

  20. Hi Phil,

    “Update: I called it.”

    Good call – but Meyer et al also did back in Jan 2002.

    Best to see:
    http://www.aas.org/publications/baas/v33n4/aas199/1302.htm
    so not to read out of context but…
    “We report the discovery of a young star that appears to have a very unusual distribution of circumstellar dust. HD 113766…
    A simple model of the excess emission from 4.8 through 60 microns suggests a range of blackbody temperatures from approx. 290 to 440 K… uggest that the dust is being continuously replentished through collisions of planetesimals. The extent of this hypothetical planetesimal belt would be from

  21. StevoR

    Said Lurchgs :

    “If we assume a life-bearing planet that lacks a moon, and if we assume said life is intelligent… without a moon.. how screwed up would their astronomy be? They could almost certainly figure out that their planet was round.. but could they determine that their sun is not the center of the universe? (I would think that if there are other planets, they could eventually determine that they orbit their sun.)”

    See Isaac Asimov’s non-fiction book ‘The Tragedy of the Moon’ (Mercury Press,1972)if youcanfind acopy somewhere. He discussed this & the similar qu. of what the implications for understanding astronomy if our Moon circled Venus instead at considerable & fascinating length. There are a couple of essays on that & a number on other things including ‘The World Ceres’ as in the dwarf planet -he called that too! ;-)

    Well done BA.

    Ah, the media … forever predictable… forever getting it wrong.

  22. StevoR

    Said Lurchgs :

    “If we assume a life-bearing planet that lacks a moon, and if we assume said life is intelligent… without a moon.. how screwed up would their astronomy be? They could almost certainly figure out that their planet was round.. but could they determine that their sun is not the center of the universe? (I would think that if there are other planets, they could eventually determine that they orbit their sun.)”

    See Isaac Asimov’s non-fiction book ‘The Tragedy of the Moon’ (Mercury Press,1972) if you can find a copy somewhere. He discussed this & the similar qu. of what the implications for understanding astronomy if our Moon circled Venus instead at considerable & fascinating length. There are a couple of essays on that & a number on other things including ‘The World Ceres’ as in the dwarf planet -he called that too! ;-)

    Well done BA.

    Ah, the media … forever predictable… forever getting it wrong.

  23. Remember, it wasn’t our Moon going around the Earth which was the convincing argument that the Earth wasn’t the center of the universe. It was observations of other moons going around Jupiter. Something not possible before practical telescopes.

    There are many things which can make people question dogma about astronomical phenomena. Go read about the reasons for dropping the Julian calender, sometime.

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