The galaxy may swarm with billions of wandering planets

By Phil Plait | May 18, 2011 11:15 am

A new result from astronomers who have spent years peering toward the center of the Milky Way has led to a startling conclusion: there may be billions of Jupiter-sized planets wandering the space between the stars, unbound by the gravity of a parent sun. In fact, there may be nearly twice as many of these free floating planets as there are stars themselves in our galaxy, and they may even outnumber planets orbiting stars!

The study, published in Nature, is the result of the Microlensing Observations in Astrophysics (MOA) project. Instead of looking for tell-tale blips of light near stars, or the effect of planets on their parent stars, microlensing looks for the effect of the planet on background stars that are far more distant than the planet itself.


Warped view

It’s a little weird, and is due to gravity warping space. Imagine me sitting on a flat floor, rolling marbles away from me in all directions. If you’re sitting a few meters away, you can only catch the marbles that are aimed at you. But if there’s a dip in the floor between us, some of the marbles I roll that might have otherwise passed you will get their path diverted toward you as they curve around the dip. You get more marbles!*

The same thing with light and gravity. A star emits light in all directions, but we only see the small amount of light headed our way. If a massive object like a planet gets between us and the star, the gravity of that planet can warp space, causing light we otherwise wouldn’t see to bend toward us. We see more light: the star gets brighter! This is called a gravitational lens. If that massive object is a planet moving in space, then we the starlight get brighter as the planet moves between us and the star, and then fainter as the planet moves on. The way the light changes is predicted by Einstein’s equations of relativity, and can be used to find the mass of the planet doing the warping.


OGLEing a MOA

So the astronomers with MOA sat down and stared at a patch of sky near the center of the Milky Way. In fact, they looked at an astonishing 50 million stars near the galactic bulge — stars are densely packed there, maximizing the chance of seeing a rare event. The lensing of starlight by a passing planet only lasts for a couple of days, so they took images every 10 – 50 minutes to make sure they caught as many as possible. The amount of data they amassed is fiercesome.

And even with all that, in a year of observations (from 2006 – 2007) they only caught about a thousand events. At first that sounded like a lot to me, but it’s only one lensing event per 50,000 stars! Yikes. Anyway, of those 1000, a bit less than half were solid enough observations to use in the study. And of these, only 10 — ten — had that magic characteristic time of about 2 days, indicating the lens was a planet with about the mass of Jupiter. Stars are more massive, and the lensing effect can take weeks from start to finish; only a planet can make such a short event.

Being careful, the astronomers took those 10 events and asked the folks using a different survey (OGLE, for Optical Gravitational Lensing Experiment; acronyms using "GL" tend to be somewhat droll) to see if they saw them as well. OGLE caught 7 of the 10 seen by MOA, confirming their results.

So what makes the astronomers think these are free-floating planets, and not ones orbiting stars like Earth does? Well, the lensing events themselves show only a single rise and fall of the background starlight. If the planets were orbiting stars, those stars would also act like lenses, and their effect would be seen. They weren’t. Now, it’s possible that if a planet were on really wide orbit, the parent star would be too far away to have a significant lensing effect. However astronomers can determine statistically how often that should happen, and the likelihood is only about 25%, meaning a significant number of the events must have been caused by planets without stars.


Goose! Eject! Eject!

Amazing! But where did these planets come from?

Since they’re floating free in space, they either formed like stars, directly from the collapse of interstellar gas clouds, or they formed in solar systems like our own and somehow got tossed out.

The first case — that these objects form like stars — makes a definite prediction on the distribution of masses of the objects (in other words, how many will have a mass 0.1 times Jupiter, how many 0.5 times, and so on). The mass distribution seen doesn’t fit the predictions at all, making that unlikely.

So that leaves them forming in solar systems like our planets did. But how does a planet get ejected from a star? Actually, this comes about naturally, and in fact may be common.

I’ve long suspected this was the case; it makes sense. We see lots of massive planets huddling close in to their parent stars, far closer than any reasonable model can predict. Most likely, these planets form farther out in their native solar system and then migrate inwards toward the star as they plow through the material left over from their formation. Any planet between them and their star will be affected; some will shift orbit, dropping toward the star themselves, others will get flung into wide orbits, and others still will be tossed out of the system entirely.

It’s those last that are so interesting. If the inward-moving planet is, say, five times the mass of Jupiter, it can gravitationally eject a smaller planet, even one as massive as Jupiter. And we do see lots of very massive planets orbiting close in to their stars. This strongly implies that for every "hot super-Jupiter" we see, there is one or more planet that got kicked out of the system, sent out into the galaxy at large á la Space: 1999.


Living la vida interstellar

The MOA results seem to confirm this idea: the statistics imply that there may be twice as many Jupiter-mass free-floating planets in the galaxy as there are stars! Just to let you know, there are hundreds of billions of stars in the galaxy, so there must be many, many billions of planets floating in the vast, empty regions between stars.

Billions. Wow. In fact, these free-floaters may outnumber "regular" planets by a factor of 1.5 or so. There are more of them than there are of us!

Mind you, the MOA survey is sensitive to planets with masses about that of Jupiter. They can’t see smaller planets, which should in fact be more common.

These planets, surprisingly, may not be frozen solid as you might expect. Jupiter and Saturn, for example, give off more energy than they receive from the Sun. The centers of both planets are still warm from a number of heat sources, including radioactive decay as well as having trapped a considerable amount of the tremendous heat generated when they formed 4.6 billion years ago. Any free-floating planet in the galaxy may be presumed to contain as much heat, keeping them gaseous despite the intense cold of interstellar space.

You may be wondering about any potential habitability of these nomads. The planets found are gas giants, not Earth-like at all. But they might have moons orbiting them that could be heated by tides the same way Jupiter’s Io and Saturn’s Enceladus are. It seems unlikely that any moon could stay orbiting a planet ejected from a solar system — I would think they’d get stripped from their parent planet in the process — but nature has surprised us before. Like, say, it’s doing now with this whole "wandering planet" thing. I’d love to see some studies of that.

Also, while there may be an even greater number of smaller planets out there, these likely would be frozen through and through. Too bad. The view would be cool.

So to speak.


Conclusion

The MOA study in question is pretty interesting to me scientifically. The results look pretty good, and come from only a year’s worth of data; as the astronomers look at more data they’re bound to find more of these suckers. I expect to see their statistics get better with time. They seem to have done their work carefully and skeptically; it’s a fascinating result and I’m glad they sought out OGLE observations to back them up.

Personally, too, this is exciting. Imagine, a galaxy full of roaming planets! It’s not like they present a navigational hazard were we to fly starships through space; the galaxy is vast indeed and even a hundred billion planets would be spread pretty thinly. But it sparks my imagination to think of these planets — dark, cold, lonely — plying their way through the blackness of interstellar space. If we ever could voyage to one, what would we find?

It’s thoughts like that which make me glad to be an astronomer, especially one living now. Just when you think the Universe is running low on surprises, it reminds us it’s a lot more clever than we are.

Artwork credit: Dan Durda; NASA/JPL-Caltech


* While I slowly lose mine, of course.


Related posts:

Motherlode of potential planets found: more than 1200 alien worlds!
How many habitable planets are there in the galaxy?
Gallery of exoplanets: real pictures of alien worlds

CATEGORIZED UNDER: Astronomy, Cool stuff, Pretty pictures

Comments (127)

  1. MariaPeron
  2. Gark

    doesn’t the word ‘Planet’ come from the greek word for ‘Wanderer’? more apt than even initially thought, i should say.

  3. Great! More stuff to fear collisions with! Someone should totally write a book about that.

    Very cool, though.

  4. Charlie

    Is there any way to estimate the distance to the closest one to us? What kind of error bars would you be looking at if you did such an estimate?

  5. Arlyaq

    I don’t know of any research into the ability of Jupiter-sized planets to retain moons following gravitational ejection, but a 2007 paper by Debes and Sigurðsson in The Astrophysical Journal Letters suggested that some 5% of terrestial planets might retain Earth’s Moon-sized moons.

    And especially if they do have a moon to provide tidal heating, David Stevenson provided a model in Nature back in 1998 that showed radioactive decay and a thick, hydrogen-rich atmosphere (which could persist in the absence of a solar wind) might provide conditions sufficient to keep a rogue terrestrial planet warm even in the cold dark of interstellar space.

  6. See! There is a conspiracy. We all know that one fo those is name Nibiru and is heading straight at us! :D

    In all seriousness, this is really cool stuff. I am looking forward to hearing and reading more about this.

  7. dcwarrior

    How much mass would these planets account for? Any appreciable % of the “dark matter” problem?

  8. In before the Nemesis/Nibiru theorizers start barreling in.

    Regardless, the prospect that a wandering planet’s path could cross with ours fascinates me. Makes me wonder if any planets in our solar system were “adopted”. Though I imagine that there’d be tell-tale signs of planet capture like unique orbits or inconsistent mineral composition.

    Great read!

    @dcwarrior Good call! Would be interesting to know

  9. ceramicfundamentalist

    i’ve often wondered why we think full blown stars are the only objects out there roaming independently around the galaxy. we know from observation that there are relatively few giant stars, a few more merely big stars, a healthy smattering of average stars like our sun, and lots and lots of small stars. is there any reason to believe that a collapsing dust cloud can foresee that it is collapsing into a mass too small to ignite nuclear fusion and call the whole thing off? shouldn’t we be expecting to find smaller mass interstellar objects perhaps an order of magnitude more often than we see the dimmest fusion powered objects?

  10. Wow, yet another incredible discovery! A galaxy full of freely floating planets. But would moons be stripped away as the gas giant planet was ejected from its solar system? I’m not totally sure they would be, as the mass of the planet would be still there no matter where it was in space. The moons are orbiting the mass of the planet not the star, surely. But I suppose it depends on the manner of the cosmic eviction.

    We used to think that water was absolutely essential for life, well not any more, just a liquid solvent and that solvent may not be water. We also used to think sunlight was essential for life, well that’s gone out the window too, just an energy source needed, and it doesn’t have to be sunlight. If there are moons still in orbit around evicted gas giants and they’re being internally heated by the mass of the planet, just like Europa, then even in these dark places could life be possible? It’s an amazing thought, and would rack up even more the possible places for life in the Galaxy.

  11. Yojimbo

    @ dcwarrior – That was my first thought, too. If they are as common as the top-end suggestion Phil mentioned, that would be a… massive amount of mass. Enough to be cosmically significant?

  12. Tony

    What is really interesting, I think, is that these wanderers could be very big trouble makers as well. While probably a rare occurrence ( or maybe not ) they could occasionally be ‘adopted’ by other stars, which may have their own planets already causing some of those to possibly get ejected. Maybe it will end up being more common for stars to adopt planets than have their own even. That would be really interesting.

  13. Rick

    Is there any way this could be related to dark matter? I realize dark matter outnumbers “normal” matter in the universe by nearly a whole magnitude – but since most of the experiments involve assuming the mass of the objects involved and subtracting the observable mass to get the difference (through rotational speeds of galaxies, weak gravitational lensing, etc), is it possible stuff like these free-floating planets could be throwing off our assumptions about observable mass? And even though these planets could potentially outnumber stars in the galaxy, I also realize that doesn’t mean they out-weigh them – it’s just curious that this method of detection is so similar to that used to detect distant dark matter.

    Or vice versa: could these “microlensing” events be caused by local dark matter instead of the assumed free-floating planets? I know the theory about hot Jupiters tossing out smaller planets is strong (and just plain makes sense), but as Phil says, nature has surprised us before.

  14. Patrick Ley

    This is really fantastically cool. I am in awe.

  15. Robert S-R

    Stupid question, but it will probably be asked eventually: even billions of wandering planets wouldn’t account for the gravitational discrepencies solved by dark matter theory, right? I can see how one could think, “Oh there are invisible planets out there, huh? That must the dark matter everyone’s been talking about!” But surely there’s wayyy more dark matter than rogue planets, right?

  16. Roger

    I was going to ask the same thing as dcwarrior. Would that account for any missing mass in the galaxy and perhaps other galaxies? Don’t know if missing is the right word but you get the idea.

  17. mike burkhart

    OK just one question Could what happened in the scifi novels When Worlds Collide, (and movie) and its sequel After Worlds Collide happen ? For those who havent read eather or seen the movie this is the plot: Before worlds collide : Astronomers discover that two planets have entered the solar system called Broson Alpha and Beta (after there discover) Alpha is on a collsion course with Earth but Beta will settle into Earths orbit after the collsion two space craft are built called ark 1 and 2 (form Noahs ark in the Bible) lift off with a small number of people and land on Beta After Worlds Collide The survivors form a colony on Beta but discover that they are not alone there are other space craft that were built and launched form Earth and a dictator and his army want to rule all the survivors on Beta.

  18. J. Rich

    Given that the low-mass end of the IMF is not very well understood/constrained, this doesn’t seem like an unexpected result. Interesting and difficult science.

    Makes it even more fun to try to explain a continuum of objects with no hard boundaries to people who like sharp cutoffs. Like grant panels and time allocation committees.

  19. Runi Sørensen

    Good question Rick. Even though all these free-floating planets wouldn’t have nearly enough mass to explain dark matter, dark matter has already been shown to exists as shown by the gravitational lensing of two clusters of stars interacting. Still, how would one distinguish free-floating planets from small local pockets of dark matter, assuming it exists without the presence of ordinary matter.

  20. “wandering planet” :) Nice

  21. Tim

    Always thought it would be a cool sci-fi movie idea to find such a rogue (terrestrial) planet headed near/through our solar system…with the frozen remains of an ancient civilization on its surface. Now the idea is a little more “sci”.

  22. Pasander

    Long time ago (say 20+ years) when I played with a simple point mass gravity simulator, if I put in more than two masses it would inevitably lead to ejection or wide elliptical orbit(s) for one or more of the masses. Already back then I wondered how come planets in our solar system have managed to acquire stable orbits. Of course the point mass simulation doesn’t simulate collisions but near misses are probably more common than direct hits anyway. I wouldn’t be at all surprised if the interstellar space was full (relatively speaking) of all kinds of leftovers from star and planet formation processes.

  23. These interstellar planets cannot make up for dark matter: say there were 200 billion stars, then there would be 400 billion planets. If we assume these interstellar planets have on average the mass of Jupiter, and stars have on average about half the mass of the sun (or ~500 Jupiter masses), the planets still sum up to only 2/500 = 1/250 of the mass of the stars, or 0.4%. A far cry from the ~700% that would be needed to explain dark matter.

    But what I wonder: if interstellar planets of Jupiter mass are really twice as abundant as stars, and each of these planets was ejected from a star – wouldn’t that mean that every star, on average, ejects two planets of Jupiter mass? Okay, its a little bit less, because some stars have died since the formation of the galaxies, while their planets have not, but think of it: thats an awfully large number of ejections! And if not all stars have planets, but, say, just 50% of them, we would need *four* ejections per star to get such a high number of interstellar planets. Isn’t that a bit excessive? Our sun had no ejections (otherwise, the solar system would look rather different), but still, we only have one Jupiter-mass planet to eject… And then, most stars are red dwarfs, and these are known to be quite ineffective in producing planets in the first place.

    Either, this means that virtually every star must form planets, and still in most systems, the majority of planets are ejected. Or, a majority of planets is ejected from high-mass star systems that produce and eject dozends of planets, compensating for the low numbers ejected from red dwarf systems. Or, maybe, some of these planets really do form directly in interstellar space (starforming regions).

    What an exciting time to live in!

  24. Michel

    So the more of these planets we find the less dark matter matters?
    I mean we never knew about these masses and we had some serious shortage on mass.

  25. CB

    @ Robert S-R:

    These wandering planets are without a doubt some of the “dark matter”. Dark Matter was originally just a term for the discrepancy between observed gravitational behavior and observed, visible mass. One of the first and most obvious hypothesis was that the “dark matter” was literally just matter that was too dark to see, and even though now it’s thought that this can’t explain all of the dark matter, certainly some of it is.

    But yeah, there’s a lot more dark matter out there than there is planets. Right now, dark matter is supposed to make up a larger percentage of the mass-energy of the universe than normal, visible matter. But these planets total mass is relatively tiny: Jupiter is 1/1000th the mass of our sun, so with only twice as many of these planets as stars in the galaxy, the total contribution of these planets to our galaxy’s mass is small compared to that of the stars. But we need to explain many times more mass than that of our stars.

  26. Joseph G

    WOW.
    Just… wow.
    The potential number of planets in the galaxy doubles or triples just like that.
    Just when you think all the surprises are out of the way, eh? :)

    Did anyone ever read that short story by Fritz Lieber, “A Pail of Air”? One of my favorites, an oldie but a goodie. It’s about the few humans surviving after the earth was ejected from the solar system.

    I always figured that, sure, there may be a couple of planets wandering around out there, star-less, galaxy as big as it is, but that it’d be relatively common? Pure science-fiction… so I thought.

    Edit: You can read “A Pail of Air” here. It’s short, and worth the read.

  27. davidlpf

    oh my god it’s full of planets.

    How does this affect the Drake equation, does this add another term or ups the percentage of the number of planets found around stars.

  28. It’s also sobering to realize that if the Milky Way is this flush with extra planets, every other galaxy you see has them, too.

  29. Regner Trampedach

    Re: accounting for dark matter.
    Several points to make:
    A) Jupiter’s mass is about 1/1000th of the Sun’s. Assuming a similar mass-distribution among ejected planets as among stars (just shifted to lower masses) means that [total mass ratio] = [# planets/# stars]/1000 and therefore unlikely to be a major player.
    B) The fraction of ordinary (baryonic) matter is fixed by conditions during the very early Universe – and those models predictions of hydrogen, helium and lithium (and their isotopes) agree well with observations – that’s why we believe in the 4.5% ordinary matter content of the Universe prediction.
    C) Dark matter is per definition not baryonic (ordinary) and constitutes about 22% of the Universe (by energy, incl rest mass). No planets, stars, neutron stars, black holes, gas clouds, etc., known or unknown, can account for these 22%.
    D) We have had a hard time coming up (from observations) with the 4.5% baryonic matter, but now it seems most of it lie in the dilute but expansive inter-galactic gas. The roaming planets of this news-item does, of course, also add (a little) to the baryon count.
    Cheers, Regner

  30. Robert S-R

    Thanks for the response, CB. I wasn’t sure the mass of the planets would even make up a significant portion of “dark matter” at all, but it’s interesting to consider that we have a tiny fraction of the missing gravity puzzle solved, even if the bulk of the mystery still remains.

  31. Nemo

    As I’ve posted here before, the word is “fearsome”, not “fiercesome”.

  32. Joseph G

    @#5 Arlyaq: I don’t know of any research into the ability of Jupiter-sized planets to retain moons following gravitational ejection, but a 2007 paper by Debes and Sigurðsson in The Astrophysical Journal Letters suggested that some 5% of terrestial planets might retain Earth’s Moon-sized moons.

    And especially if they do have a moon to provide tidal heating, David Stevenson provided a model in Nature back in 1998 that showed radioactive decay and a thick, hydrogen-rich atmosphere (which could persist in the absence of a solar wind) might provide conditions sufficient to keep a rogue terrestrial planet warm even in the cold dark of interstellar space.

    You could get even more tidal heating on a terrestrial moon orbiting one of these gas giants. And without solar wind, you wouldn’t have the radiation hazard that you get from the magnetic field of an in-system gas giant like Jupiter.
    How strange would life be on a planet like that, if it were possible? I’m picturing seaweeds around geothermal hot spots that use temperature gradients for energy, land plants that use radiant heat from lava flows, and extremely energy-efficient, slow critters (that can see in the far infrared) that feed on them :) Such creatures wouldn’t be able to see the stars, though.
    If intelligence every arose, what would they think of the universe that they live in?

    Of course, if you’re willing to go all out and accept the possibility of science-fiction-ey cryogenic life that breathes methane and drinks ammonia, then we’ve just expanded the possible habitats for such life by several hundred percent :)

  33. Georg
  34. RodneyFett

    Thinking of if the wandering planets may retain their moons. If a star were to pass close to our star(the sun) it would possibly disrupt the kuiper belt and Oort cloud without disturbing the planets. I would think the same may apply with moons of planets ejected from their parent star. Some outer moons my be disrupted but not all of them especially the inner ones.

  35. Joseph G

    @27 Nemo: What if the subject of the adjective is only somewhat fierce? Couldn’t it then be fierce-some? :)

    @53 Davidlpf: Hmm. I guess it depends on how you look at it. The Drake equation does seem to be constructed under the assumption that all planets orbit stars. I tend to think that the “percent of stars with planets” variable is just a way to estimate the number of planets; and until recently, there was practically no information available on just how common planets were.
    We’re still mostly in the dark, but at least we’re starting to get an idea…
    Of course, it’s still a good bet that the best place to look for life is in a star’s habitable zone, though if life is ever found on Europa, that’d certainly expand the parameters we’re looking at quite a bit!

  36. This is by far the most interesting thing I’ve ever had no previous knowledge of. I don’t know why I’d never imagined ejected planets when I’ve been so aware of rogue stars shooting around galaxies tossed from binary pairs. It seems to me that any planets in a system that ultimately became a binary pair would get thrown out fairly quickly as well… or swallowed up.

    Still… to think about just standing on some rocky frozen planet or moon zipping along through a galaxy in permanent darkness… you could set up the best infrared telescope! I wonder what speeds they could obtain? It would depend on how it’s ejected – but I imagine they could get moving pretty quickly.

    Who wants to take bets on news sites picking this up and touting it at the next doomsday? Especially with all that “Nemesis” talk out there. Of course if we had even the smallest planet-sized object coming at us we’d pretty much have absolutely no chance whatsoever of surviving it or diverting it.

  37. St4rg4z3r

    If intelligent life does exist in such planets, imagine how their thought process would be.. They wouldn’t know how life would be if their planet was orbiting a star.. there wouldn’t be a day/night cycle..

    They would view the universe in a completely different perspective. It is mind-blowing to think about..

  38. Jim Johnson

    Although it’s not a terribly groundbreaking notion, I would like to point out that these planets are both “dark” and “matter”…

  39. jearley

    Poul Anderson wrote several stories featuring Rogue Planets, such as ‘Satan’s World’ and at least one the the Dominic Flandry novels used a rogue planet as a plot driver.
    If I remember correctly, Maria Osorio’s group found a number of these out towards the Orion Nebula too: http://www.spaceref.com/news/viewpr.html?pid=2762

  40. Jose

    “It seems unlikely that any moon could stay orbiting a planet ejected from a solar system — I would think they’d get stripped from their parent planet in the process — but nature has surprised us before.”

    I guess it could be something difficult, but how about a planet that “gets” it’s moon AFTER being ejected? maybe something similar to the way we got our moon… just wondering. Very interesting article anyway!

  41. Chris A.

    @Nemo (#26):
    “As I’ve posted here before, the word is “fearsome”, not “fiercesome”.”

    Unless, that is, you’re trying to coin a word, and/or are writing playfully, both of which our dear Bad Astronomer has been known to do on occasion.

  42. I agree, it’s ‘fearsome’. The alternative, that Phil sometimes makes puns, is too horrible to contemplate.

  43. Grimbold

    I have my doubts. I mean, people say there ought to be a lot of interstellar comets as well; enough that we should have seen some pass through the Solar System by now, but we haven’t.

    @Joseph G- Yes, A Pail of Air is a terrific story. It’s always been one of my favourites.

  44. Dragonchild

    I don’t find this surprising at all. Privately, I’ve maintained this was a strong possibility for years. It first came up as a possible candidate for dark matter, but IIRC the main counterarguments against that hypothesis is that the amount of baryonic matter to prove the MACHO hypothesis should be easy to detect through interaction with stars (it hasn’t been, as this study shows), and inconsistent with the Big Bang model.

    But that never meant interstellar planets don’t exist! Even though the MACHO hypothesis didn’t pan out, I was too geeked about the thought of rogue planets to let go of the idea. There could be a hundred interstellar planets for every star. As far as dark matter’s concerned, the stars would still be the dominant percentage of the galaxy’s mass — laughably so. But what’s unexciting about the possiblity of billions of rogue planets?

    Intergalactic space probably isn’t all that empty, either. They’d be damn near impossible to detect, but who knows how many expelled (hypervelocity) red dwarfs, white dwarfs, brown dwarfs and unbound planets are zipping through the void between galaxies?

    I’m thrilled to see some astrophysicists latched onto the idea of rogue planet research even after the MACHO hypothesis was abandoned.

  45. Thomas Siefert

    Why is BA’s use of the word ‘fiercesome’ discussed? It is clear from his article that he not just lost his marbles, but is actively rolling them away…

  46. Thorne

    “Luke, I am your father”…

  47. Sam H

    I didn’t react to this quite as enthusiastically as I did when the BA announced the 1,235 Kepler results a few months back, but damn. :o If these calculations are correct (and my mental math is correct), there’s around a 1000 planets out there for every single person on earth-in our galaxy alone. Just…imagine…the POSSIBILITIES:D
    And amen to anyone who ever said that truth is stranger (and far more wondrous), especially science fiction. Aside from that I’m just blissfully speechless right now, with a smile on my face and a beautiful tune (plus many dreams) in my head. Too sad that we probably never get to see them.
    -unless, of course Roddenberry, Alcubierre and every other starry-eyed visionary were right about interstellar travel – and while I know how unlikely THAT is, I hope to God they’re right.
    Speaking of which, anybody ever heard of Heim theory?? :)

  48. Ron

    I also immediately wondered what dcwarrior asked, if the presence of these exo-planets could account for any of the gravitational behavior that led to the dark matter theory? I suppose a mass of exo-planets would qualify as “dark matter,” though!

  49. Off Colfax

    @48 Sam H.

    “Speaking of which, anybody ever heard of Heim theory??”

    Wasn’t that the one disproven by the Feldman Hypothesis? No… Wait. I’m thinking of the Haim Theory of Corey Interaction. Never mind.

  50. Chief

    Any thoughts on this being a possible solution to the difference in the orbit of pluto and neptune being tilted 93%. A near wanderer affecting the orbits.

    Are there any results on the speeds of the planets, do they eventually assume the same speed of the rotation of the galaxy or continue more or less at the speed of ejection from the parent star.

  51. Chris Winter

    Tim wrote (#22): “Always thought it would be a cool sci-fi movie idea to find such a rogue (terrestrial) planet headed near/through our solar system…with the frozen remains of an ancient civilization on its surface. Now the idea is a little more “sci”.”

    Indeed it would. I’m unaware of such a movie, but that doesn’t mean it hasn’t been done.

    As far as novels, it has — and one was mentioned by Mike Burkhart, though he didn’t mention that aspect. In After Worlds Collide, the refugees find alien artifacts on Bronson Beta.

  52. Paul

    mike burkhart writes:

    The survivors form a colony on Beta but discover that they are not alone there are other space craft that were built and launched form Earth and a dictator and his army want to rule all the survivors on Beta.

    At the end of the movie version, if you watch as the camera pans across the new landscape, you can see scifi-esque towers. In the book, did the planet have inhabitants before humans? And did the author give any thought to the fact that the planet’s atmosphere would just be starting to thaw after being away from a star for so long?

  53. Chris Winter

    Heim Theory purports to be the answer to several puzzles in physics: the origins of elementary particles, a way to unite relativity and quantum mechanics, and a possible method of achieving warp drive.

    http://en.wikipedia.org/wiki/Heim_theory

    As I recall, John Baez poured cold water over the mathematics of it. This was several years ago. I’m sure there’s a lot more information out there on the Web.

  54. Don´t Panic

    I´m sure they are already tracking those roques to see which of them are on a dangerous trajectory.

  55. Dragon

    I utterly fail to see how an absolute lower limit of the size of bits created in a stellar nursery would be limited to viable stars. We already know that brown dwarfs are the most common sorts of stars, and while it seems that dust clouds do contain a lot of dust, that fact that stars start life in such clouds implies that there is no upper limit to the size of that “dust” either. And when a blue giant’s solar wind clears out the area around it what happens to the stuff “cleared” and what limits how big that could be. Dust concentrations thick enough to block out the stars behind would not have to be the only dust, and since micro lensing brightens the star behind if the lens is big enough, would not smaller lenses simply make such scattered “dust” invisible?

    While dark matter may have a very different source, would it not obscure such sub stellar “dust” in any calculation?

  56. Steve D

    Science fiction author Poul Anderson featured “rogue planets” (planets without stars) regularly in his stories.

  57. Jeffrey Cornish

    #57,

    Um, I hate to bring some reality to you concept that ‘I’m sure they are already tracking those roques(sic)”

    First, these were detected by having the planet cross some bit of space between the Earth (where our telescopes are) and a distant background star.

    Imagine looking at a distant street lamp. You notice that something dims it, as if an object had passed between it and you.

    Question 1> How far away is it?
    Question 2> What direction is it going?

    Your answer, given the information presented, should be “I don’t know”

    We have no idea how far away or what direction if travel these 10 extrastellar planets are going in.

    Even better we aren’t seeing the light of the star dimmed, we are seeing the planets feeble gravity bend the light to brighten it.

    Now that does give us a possible way to estimate the distance. Figure for a Jovian mass body what the lensing effect would be to cause the estimated amount of brightening.

    One thing that is for sure is that we are only going to detect by gravitational lensing bodies that are pretty far away.

  58. Lots of commenters have mentioned dark matter, but only one (@Dragonchild, #45) has mentioned MACHO. Hmm. I would have said MACHO is something one really must mention in order to put this story into its proper historical context.

  59. Messier Tidy Upper

    Awe & wonder-evoking finding and excellent write-up there, thanks BA. :-)

    @ 42. Chris A. Says:

    @Nemo (#26): “As I’ve posted here before, the word is “fearsome”, not “fiercesome”.”
    Unless, that is, you’re trying to coin a word, and/or are writing playfully, both of which our dear Bad Astronomer has been known to do on occasion.

    Actually, I thought they were *both* legitimate words with very similar but subtlely different meanings one from ‘fierce’ and one from ‘fear’.

    Something living can be ‘fierce’ such as a lion can be ‘fiercesome.’

    Something inanimate such as a landscape ( vast desert, rugged hostile mountains etc ..) can be ‘fearsome’ or evoking the emotion of fear.

    Isn’t that right?

  60. Messier Tidy Upper

    @18. mike burkhart :

    OK just one question Could what happened in the scifi novels When Worlds Collide, (and movie) and its sequel After Worlds Collide happen ? For those who havent read eather or seen the movie this is the plot: Before worlds collide : Astronomers discover that two planets have entered the solar system called Broson Alpha and Beta (after there discover) Alpha is on a collsion course with Earth but Beta will settle into Earths orbit after the collsion …

    &

    @27. Joseph G Says:

    Did anyone ever read that short story by Fritz Lieber, “A Pail of Air”? One of my favorites, an oldie but a goodie. It’s about the few humans surviving after the earth was ejected from the solar system. I always figured that, sure, there may be a couple of planets wandering around out there, star-less, galaxy as big as it is, but that it’d be relatively common? Pure science-fiction… so I thought. Edit: You can read “A Pail of Air” here. It’s short, and worth the read.

    &

    @40. jearley :

    Poul Anderson wrote several stories featuring Rogue Planets, such as ‘Satan’s World’ and at least one the the Dominic Flandry novels used a rogue planet as a plot driver.

    Thanks. :-)

    I’ve read some of those but not all of them. Cheers! :-)

    Another good one featuring a “rogue planet” that’s been captured which I’d recommend is ‘Starhammer’ ( Arrow books, 1986) by Christopher Rowley. The wandering planet there Baraf in this case is one that’s had it’s star destroyed but has been captured by one of the bright stars in the Plieades – Pleione I think.

    Such supermassive, blue white B type stars have deep gravity wells and while they are short-lived and less likely to form planets I do like tehidea that they could capture wandering “rogue” planets into orbit. Anyone know how likely that is?

  61. Messier Tidy Upper

    Thinking captured planets I can’t resist noting that a variation of this theme is provided by one of my all-time favourite novel trilogies – the Helliconia series by Brian Aldiss. In this fictional system a sunlike star and its habitable planet have both been captured into orbit by a white supergiant :

    http://en.wikipedia.org/wiki/Helliconia#Astronomy

    resulting in a fascinating binary star and planetary system with the sunlike stars long eccentric orbit around the white supergiant resulting in centuries long seasons of extreme cold, heat and temperate climate ecosystems. Aldiss goes into a fair bit of good (ish?) astronomy and has created some wonderful bits of world building. It’s a great read. :-)

    Wonder how probable it and suchlike fictional systems actually exist in reality?

    It does seems logical that more massive (& brighter) stars would be more likely to capture such wandering orphan exoplanets – but offsetting that they also have extremely short stellar lifespand and, too, gravitational capture is highly improbable. Still … even if they’re exceedingly rare, it’s fun to imagine it could – and given the sheer numbers of both stars and planets out there may well have – happen(ed). :-)

    PS. That ‘Starhammer’ novel I mentioned according to Wikipedia :

    http://en.wikipedia.org/wiki/Starhammer

    apparently inspired the computer game ‘Halo’ to some extent. I haven’t played that game myself to tell how much however.

  62. Messier Tidy Upper

    Wasn’t the suggested Oort cloud superjovian planet “Tyche” that some astronomers think just *might* possibly have been found in the WISE data meant to have (perhaps?) been captured into orbit around our Sun?

    Do I recall correctly reading suggestions that some of the Edgeworth-Kuiper Cometary Belt /Oort Cloud / Scattered Disk bodies – ice dwarf planets and some comets could have been captured from interstellar space where they’d been wandering or very loosely bound to other stars and subsequently stolen by our sun passing close to them – with our daytime star also having distant objects stolen in exchange or in turn also?

    Would wandering rogue exoplanets (or ‘Planemos’* or whatever they get named – by arbitrary IAU fiat “planets” have to orbit stars by – in my view atrociously bad – definition.) gravitationally “steal” or capture ice dwarfs and comets on the fringes of various star systems making them into moons of their own?

    ——————

    * ‘Planemos’ being a suggested title for these wandering / “rogue” / “star-challenged” (in PC speak! ;-) ) worlds – a contraction of planetary mass objects.

  63. Pete Jackson

    If the number of Jupiter-sized bodies are only twice as many as the number of stars, then the nearest one is probably a couple of light years away. Hence, close encounters with them, as with stars, are going to be very unlikely. Like Jupiter, they may emit in the infrared with a temperature of about 100K, but even the most sensitive infrared surveys would have a hard time picking these up at that distance.

    Sooner or later we will probably see small asteroid-sized bodies passing through or near our solar system at hyperbolic velocities.

  64. This is a very interesting proposal in that it is observation based rather than theory based. It seems to me that by using the presently accepted models of stellar and planetary formation it would seem very difficult to model the creation of so many rogue planets by ejection. Instead brown dwarfs that never acquired enough mass to ignite as a star would seem more likely a possibility than rogue planets ejected from solar systems. Also only closer white dwarf stars are observable so it could also seemingly include a portion of these. No present mainstream model that I know of can explain such large quantities of rogue planets as the source of these lensing anomalies but I’m sure they will now try to model the mechanics that might allow for large quantities of rogue planets.

    Of course such lensing aberrations may include some or all of the above, but as others have pointed out even all of these still may not make a dent in explaining dark matter.

    Other cosmological models of a much older universe have proposed large quantities of both black dwarf stars and stellar sized black holes within galaxies which could make a dent in the dark matter question if they existed in such quantities — or another gravitational model that does not require dark matter, or any combination of the above along with many other possible theoretical entities.

  65. Whomever1

    Thank you, Messier. As you say, these large round things floating in interstellar space cannot–by definition–be planets.

  66. Michael Simmons

    About planets passing though our solar system, grab a copy of Universe Sandbox and try throwing different mass object though our solar system.

    My observation that you can throw a small brown dwarf though our solar system between Saturn and Jupiter and chances are that unless it happens to pass close to a outer planet (unlikely) or it is travelling very slowly it will hardly be noticed.
    The biggest risk is the disturbance to the huge population of asteroids and the numbers that might be thrown inward towards the inner planets.
    Given this I think its highly likely this has happened many times though out the life of the solar system.
    The result is highly dependant on how fast you think the object will pass thought the solar system.

    re moons surviving the ejection.. I think that’s highly likely so long as they are well within the hills radius of the planet. Again Universe Sandbox can give you a feel for this.

  67. Tracy

    Ok, ok So what would you call a large “moon” that lost its host star and planet? For whatever reason. I think you see where I’m going with this. Without history can you define an object?

  68. amphiox

    Either, this means that virtually every star must form planets, and still in most systems, the majority of planets are ejected. Or, a majority of planets is ejected from high-mass star systems that produce and eject dozends of planets, compensating for the low numbers ejected from red dwarf systems.

    AFAIK, the planetary formation models often show systems starting out with at least an order of magnitude more protoplanets than actually end up in stable orbits at the end of the formation process, the rest either being ejected, or merging in collisions, so it seems that it is positively likely that some star systems could well eject more planets than the number they actually retain.

    It also occurs to me that a super-Jupiter spiraling inwards and ejecting smaller planets in the process might not end up in a tight close orbit. It could also fall all the way into the star itself. Alternately, it could end up in a highly elliptical orbit and then later be stripped from its parent star by interaction with another star on close approach (perhaps more likely where stars are denser). So it is also possible that a star currently without planets might have also ejected planets in its past.

  69. amphiox

    I utterly fail to see how an absolute lower limit of the size of bits created in a stellar nursery would be limited to viable stars. We already know that brown dwarfs are the most common sorts of stars, and while it seems that dust clouds do contain a lot of dust, that fact that stars start life in such clouds implies that there is no upper limit to the size of that “dust” either.

    Well, as a cloud of gas collapses and its density increases, so does it’s temperature, and this will result in an outward pressure that will resist further collapse. If there is not enough mass in the gas cloud for its gravity to overcome this, then the collapse process will halt, so there ought to be some theoretical lower limit to how small an object can possibly form from the core collapse process.

    As I understand it, a more sophisticated version of this argument is the reason why the very first stars in the Universe (the Population I stars) are believed to all have been over 100 solar masses in size. In the early universe before there were any stars, when all the gas was hydrogen, helium and a trace of lithium, only stars with that much mass had sufficient gravity to overcome this heat resistance and continue collapsing. After the formation of heavy element nuclei by the first generation stars, these nuclei absorbed and radiated away heat more efficiently, allowing gas clouds containing them to continue to collapse with smaller masses, allowing smaller stars to form.

  70. amphiox

    An earth sized rocky planet that is ejected from its parent solar system should presumably retain the heat of its formation and any heat created by radioactive decay. Since the earth itself is still geologically active 4.5 billion years after its formation, such an wandering ejected planet should maintain a molten core and mantle for several billion years at least. If it had any significant water, this would freeze, but one could envision subsurface lakes and oceans, melted by local hydrothermal processes, and insulated from the cold of interstellar space by all the frozen ice on top of them.

  71. Johnny Carson

    Weird. Weird, wild, wacky stuff.

  72. jess tauber

    Well, some of our more bible-math loving citizens have determined that the earth will experience worldwide earthquakes starting in two days, gratis from a fast moving wandering superjuper. And the Rapture will be caused by its gravity stripping away those with higher levels of coupling to Mass (thanks be to J. Higgs C.).

    A few months later, after it swings around the sun again, it’ll smash into us, and the world will end in fire, which means I won’t have to sit once again through yet another season of ridiculous presidential pre-election posturings, and I won’t have to tell Rush Limbaugh where to go, cause he’ll already be there.

  73. flash

    Forever alone

  74. Joseph G

    @Messier Tidy Upper: Yet again you make me expand my reading list. I’m glad I got an e-reader recently :P
    Regarding the binary star/planetary system, I got curious about that awhile back – I don’t recall the specifics, but the gist of what I read was that you can indeed have an earth-like planet at around one AU from one star, and a binary star that can come close enough to be “interesting,” without destabilizing said planet’s orbit (something like 10 or 20 AUs?)
    Seeing as how the luminosity of a star increases quite quickly with mass, and that gravity and radiation both follow the inverse square law, it actually seems more plausible that a higher-mass star could affect a binary companion’s planet’s climate without getting close enough to destabilizing its orbit.
    That’s assuming everything formed in place, though.
    IIRC, doesn’t capture normally involve 3 objects? A primary, the captured body, and another body that absorbs the balance of momentum?

    I’m probably making no sense, but I’m tired and giddy with science-geekery. I’m going to the Bay Area Maker Faire on Saturday, woooo! :D

    @74Jess Tauber: Haha, win!

    Srsly, two days? That thing must be bookin’! Assuming we could spot a Jovian planet out past the orbit of Pluto, that thing would have to be moving at something like 10% of C to get here inside of two days. Of course, something going that fast would hardly swerve at all. It certainly wouldn’t “swing around” anything short of a neutron star :)

    Sheesh, if religious fundamentalists didn’t frighten/swindle/kill/mislead so many people, I’d find them positively adorable.

    @75 flash: Bahahaha. I so wish we could post images. Forever aloneface planet!

  75. sea of dirac

    at comment 77 I’m late to the party here
    but hear me out I’ve got a doozy
    (deep breath)
    this is possible evidence of intelligent alien life
    stay your cries dammit!
    anyone about the Fusion Candle? anyone?
    anyway its a stupefyingly large tube crammed down the polar axis of a Jovian and set alight
    really not so much a candle as miniature sun as it uses the giants natural stores of hydrogen and helium as a fusion powerplant, this is used to generate heat, light and thrust that could vector the planet from its home system.
    reasonably this would be built by a Kardashev II civilization to solve the most important problem in space travel storage capacity, but going completely nutters and taking their gas giant with them.

    i’m fully aware of the heresy this presents
    and while some may be a freak accident as the author suggests it may in fact be more likely this is some far off intelligence at work.

    —————————————————–
    first brought to my mind in Larry Niven’s a world out of time where earth was whisked away through the strategic use of …(ehh)…Uranus
    http://qntm.org/destroy#sec3 (check #11)
    http://www.schlockmercenary.com/2003-08-03 (comic form!)

  76. molybdenumfist

    It’s a Fleet of Worlds

  77. Paddy

    This inspires a few questions from an astronomical know-nothing:

    How would we best go about looking for more wandering planet-sized objects, particularly within a few light years of the solar system? Might we be able to look for their IR signature by sending a probe outside the heliosheath? (And is any of the Voyager data we might get as they head further out likely to be remotely relevant?)

    Also, on the mechanics of planetary ejection: would they generally be ejected within the plane of the milky way, or could they just as easily be ejected outside of it? EDIT: On the assumption that most incoming objects which might displace them would be coming from elsewhere in the galaxy and thus moving within its plane, I’d guess that the former would be the case, but am I missing something?

  78. Paddy

    On consideration, the second question I asked seems a little dumb – given the close distances needed for such an event to take place, there’s no reason to think that the ejector would be in-plane with the ejectee with respect to the galaxy, especially as solar systems aren’t necessarily in plane (ours isn’t). However, once ejected, I’d expect the general gravitational attraction of its solar system of origin and other nearby objects should tend to pull it back towards said plane.

  79. Stargazer

    Perhaps some of these planets have even been ejected from the Milky Way?

  80. Dark Jaguar

    Attention planet citizens… Planet, Alert! A stray planet is on a collision course with your stray planet!!

  81. jeremy greenwood

    sorry duel post

  82. jeremy greenwood

    Is the MACHO hypothesis really dead? I recently read something about red dwarves in one of the Magellanic clouds being far more common than previously thought. And now rogue planets.
    Surely most of the stars we see are supergiants, which are not only very rare but also very short lived, so should there not be very many more stellar remnants, black holes, neutron stars etc. than there are visible stars? has this been taken into account?

  83. john

    @4. Charlie: If the nearest star is typically 3-5 light years away and there are twice as many planets, the nearest planet ought to be about (3-5)/cube root of 2, that’s about 2.5-4 light years away.
    Error bars would be more fun to calculate. (start with the volume and number of stars in our neighborhood, assume a uniform distribution, calculate. Then try modeling a more accurate distribution, which ought not change the numbers by much.)

  84. Don´t Panic

    @60. Jeffrey Cornish Says
    euh….
    It was a joke.

    *points at nick*

  85. Rick

    Thanks for all the analysis on the dark matter side-theory! I figured the total mass of even a liberal count of these planets would still be inconsequential. And when the result is far less than 1% with two large, Jupiter-magnitude planets for every star, it clearly means this isn’t something that’s going to impact dark matter theories anytime soon. And the early-universe simulations predicting the outcome of mass distribution is yet another nail in the coffin.

    One other thing to think about: the assumption that most star systems out there have large Jupiter-sized planets orbiting close to their star may not be the best assumption to make. I think that’s mainly based on the number of exo-planets that we have *currently* observed, which is limited by our optical power. Right? Or am I way off here again? Anyway, if that assumption is off as well, wouldn’t that mean far fewer than 2 ejected planets per star would be predicted? If, say, we get better optical observations that indicate that star systems with “hot-Jupiters” are rare, then would that throw off the number of 400 billion free-floaters?

    Either way – I think everyone can agree that it’s science like this that keeps us enthusiastic, especially since it’s getting some endorsements as being “good” science. All the talk of sci-fi implications and further research is exactly what good science should do: it keeps us all guessing what fascinating results we’ll be seeing tomorrow. It’s exciting and keeps our imaginations energized.

  86. Brycedavid

    Hmm…doesn’t this recall, I don’t know, something called SPACE:1999? You know, a rogue moon and all.

  87. icemith

    With the previous comments re the presence of many more bodies in Space, relatively speaking, I guess we have to find a new word to describe “Space”, as it is patently a wrong description, a mis-nomer and possibly fraudulent!

    Ivan.

  88. Joseph G

    @89 Rick: One other thing to think about: the assumption that most star systems out there have large Jupiter-sized planets orbiting close to their star may not be the best assumption to make. I think that’s mainly based on the number of exo-planets that we have *currently* observed, which is limited by our optical power. Right? Or am I way off here again? Anyway, if that assumption is off as well, wouldn’t that mean far fewer than 2 ejected planets per star would be predicted? If, say, we get better optical observations that indicate that star systems with “hot-Jupiters” are rare, then would that throw off the number of 400 billion free-floaters?

    Well, it is true that “hot jupiters” are pretty much the easiest planets to find, and the most obvious, under the methods they’ve primarily been using to find exoplanets (the doppler shift and transit methods). So yeah, the abundance of hot gas giants found in exoplanet surveys so far are probably nowhere near what you’d find in an accurate sampling of the average planetary system.

  89. Dave

    Let me mix up some sci-fi and produce a funny hypothesis :-)
    Dark Matter –> Sub space –> FTL –> Time Travel
    And this is what Star Trek people will discover in the coming centuries – that Dark Matter resides in Sub-Space(TM) and allows WarpDrive(TM) and Time Travel.

  90. Matt B.

    Buzz Aldrin’s novel Encounter with Tiber had an account of a frozen rogue gas giant passing Alpha Centauri within the Roche limit 9000 years ago, spurring the natives to come here. Low on plot, but big on sense of wonder.

  91. Messier Tidy Upper

    @70. Tracy :

    Ok, ok So what would you call a large “moon” that lost its host star and planet? For whatever reason. I think you see where I’m going with this.

    Personally speaking I’d call it a rogue exoplanet and then further categorise it based on its composition eg. “rocky rogue planet”, “ice dwarf rogue planet”, “carbon rogue planet”, etc. Although if it’s similar in nature to Titan it could be called a “Free Titan” which has some good mythological allusions! ;-)

    As for the IAU definition for such an object however, well, beats me. According to the IAU (don’t get me started on dumb their definition is!) only our Sun can have planets so technically exoplanets don’t count. ‘Planemo’ (see #65) or ‘sub-stellar’ object have been suggested – but both are clunky and far as I know “unoffical” terms. A broader, more inclusive and reasonable definition of planet that includes such bodies is badly needed in my view. Because I’d say such objects do deserve to be called planets and that’s the term that makes most sense for them. Unbound planets or rogue planets or some other sub-class but planets nonetheless.

    Incidentally, far as I know, there is no size limit to moons – if it orbits a planet rather than a star directly then its a moon whether its the size of a small asteroid or whether its larger than the Earth! The largest moons in our solar system are larger than the smallest planets – incl. Mercury as well as Pluto, Eris, Ceres, etc …

    It follows that it’s quite possible for a planet to become a moon. Indeed, our own Moon if not gravitationally bound to Earth would qualify and if Mercury orbited Jupiter or another world instead of being independent it’d be a moon.

    Without history can you define an object?

    Yes. You can define it by mass, composition, morphology (shape) and so forth.

    History (& formation) is one element but is not & should not be the be-all and end all at least as I understand things.

  92. Messier Tidy Upper

    The BA has updated this story and calculated the chances of how near such a rogue planet might be – link here for future reference & thread connection :

    http://blogs.discovermagazine.com/badastronomy/2011/05/19/are-we-in-danger-from-a-rogue-planet/

    Turns out one could possibly be closer to us than the Alpha Centauri triple star – and no, it probably won’t bring down death from the skies! ;-)

  93. @83. Stargazer :

    Perhaps some of these planets have even been ejected from the Milky Way?

    I’d say that’s very probable – although the odds against us actually finding examples are exceedingly high.

    @ 28. davidlpf :

    oh my god it’s full of planets.

    LOL! ;-)

    How does this affect the Drake equation, does this add another term or ups the percentage of the number of planets found around stars.

    I think not too much given that intelligent life at least is highly unlikely to arise on such planets. Then again, I could be wrong.

    @86. jeremy greenwood :

    Surely most of the stars we see are supergiants, which are not only very rare but also very short lived, so should there not be very many more stellar remnants, black holes, neutron stars etc. than there are visible stars?

    Yes & no. Depends what you mean by see – & what equipment or observatory you are using.

    We already know that the vast majority of stars are fainter than our Sun – 70% or so are red dwrafs with another 10% white dwrafs and 15% or so ornage (type K) dwarfs. We see supergiants from much further away as they are cosmic lighthouses but we do know that they’re rare.

    It is true that there are more stellar remannts than supergiants (esp. white dwarfs) and we’ve found that there are more reddwarfs than we used to think and thus more stars in total than we used to think just recently.

    However, this adds a new class of planet – rogue ones – to our inventory but doesn’t change the currently known abundances of stars, I think.

  94. Joseph G

    Shoot, it didn’t let me finish my last post (92).
    I was going to say that on the other hand, many hot Jupiter-type planets may get swallowed up by their primaries, or get so close that their atmosphere gets blown away (eventually). So even a system without an obvious HJP doesn’t rule out some planetary migration and subsequent ejections at some point in its history. And I’m sure even a terrestrial planetoid could eject another terrestrial planetoid, given just the right set of circumstances…

  95. Brian Too

    Well, the best theory available on the formation of the Moon is that Earth got hit by a Mars sized body. While it seems more likely that impactor formed locally, there’s nothing to say it could not have been an interstellar wanderer either. Hmm?

  96. Messier Tidy Upper

    @ 78. Joseph G : Thanks. You’ve added to my reading list as well. :-)

    @ 93. Dave : LOL. Good one. :-D

    @71. amphiox Says:

    … AFAIK, the planetary formation models often show systems starting out with at least an order of magnitude more protoplanets than actually end up in stable orbits at the end of the formation process, the rest either being ejected, or merging in collisions, so it seems that it is positively likely that some star systems could well eject more planets than the number they actually retain. It also occurs to me that a super-Jupiter spiraling inwards and ejecting smaller planets in the process might not end up in a tight close orbit. It could also fall all the way into the star itself. Alternately, it could end up in a highly elliptical orbit and then later be stripped from its parent star by interaction with another star on close approach (perhaps more likely where stars are denser). So it is also possible that a star currently without planets might have also ejected planets in its past.

    Or “eaten” them. I think we already have some evidence for stars devouring some of their worlds.

    Your comment there also reminds me of an article in ‘NewScientist’ magazine (?) suggesting our Solar system may have ejected many worlds from the inner region – many mars-Earthsized ones – out into interstellar space and perhaps also the Cometary belts and spheres beyond Neptune. I’ll have to see if I can find that one again!

    Good comment. :-)

  97. Philip Rhodes

    Is the idea of all these ‘wandering planets’ perhaps a bit premature given the somewhat contradictory way in which the authors couched their findings?

    from the Nature abstract
    ” These planetary-mass objects have no host stars that can be detected within about ten astronomical units by gravitational microlensing. However, a comparison with constraints from direct imaging suggests that most of these planetary-mass objects are not bound to any host star.”

    The first sentence only claims that the discovered objects are > 10 AUs from a star. Well, Jupiter is ~ 5.2 AU , Saturn ~ 9.5 and Uranus ~ 19.2 AU from the sun although Saturn and Uranus have much less mass than Jupiter. However, the next sentence (which I don’t have the expertise to evaluate) pushes the idea that the objects are in fact not bound to a star. Step up to plate astronomers and tell us if you think the second claim is strongly supported or whether the paper may in fact be describing a another way (a quite clever way I would think) to find extra-solar planets. Thanks in advance for any forthcoming clarifications!

  98. two quotes taken out of context from the above report:

    …”And of these, only 10 — ten — had that magic characteristic time of about 2 days, indicating the lens was a planet with about the mass of Jupiter. Stars are more massive, and the lensing effect can take weeks from start to finish; only a planet can make such a short event.”

    ‘The first case — that these objects (might) form like stars — makes a definite prediction on the distribution of masses of the objects (in other words, how many will have a mass 0.1 times Jupiter, how many 0.5 times, and so on). The mass distribution seen doesn’t fit the predictions (of present star formation theory) at all, making that unlikely.”

    (parenthesis added)

    These two “paragraphs” are quotes from the subject conjecture concerning “The galaxy may swarm with billions of wandering planets.”

    The first seems to indicate that this conjecture is based primarily upon 10 observations, 7 of which were confirmed by another study. The second paragraph seems contradictory in that they were primarily looking for events that lasted for 2 days and those shorter than that apparently were not considered in the study yet stellar formation theory accordingly predicts masses less than Jupiter size but such possible observations were not considered in the study.

    Based upon the information above, it does not seem to me that Jupiter sized brown dwarfs were eliminated as the most logical conclusion. These objects theoretically have been thought by present theory to exist in the quantities they have speculated concerning brown dwarfs, but rogue planets until now have not been thought to exist in such large numbers so that greater theoretical changes and speculation would seemingly be required which may turn out to be premature.

    I think in any case 7 confirmed observations no matter how carefully such observations were conducted and the possible conclusions analyzed, that is not enough to get too committed to any particular conclusions other that speculation such as “there could be billions of ……”

    Certainly continued observations will be made and alternative possibilities will continue to be considered.

    — although this possibility is certainly controversial and food for thought.

  99. Phil

    I’m reminded of an old “Twilight Zone” episode where the earth is, for unexplained reasons, doomed to fly toward the sun and burn up. The “twist” revealed at the end is that it was all just a hallucination by a delirious woman. The earth is actually, for unexplained reasons, flying *out* of the solar system into the cold, dark void.

    Sounds pretty fantastic, of course. But play with a N-body gravity simulator and you’ll see how a passing star or large planet really could wreck the solar system. Depending on its mass, trajectory and timing, it could severely perturb the earth’s orbit or eject it entirely from the solar system. And it wouldn’t have to hit anything at all; gravity alone would do all the damage.

    So that “Twilight Zone” nightmare could really happen if one of those stray planets were ever to pay us a close visit. But we’d have decades and probably centuries of warning, so the “Nibiru” nitwits can’t point to this and say they told us so. But I’m sure they’ll try anyway.

  100. Rob

    I’m going to reread Fritz Leiber’s ‘The Wanderer’ tonight!

  101. Chris Winter

    Someone mentioned Fritz Leiber, which reminded me of his novel The Wanderer. Only in that novel the planets wandered by design: they were fitted with some sort of warp drive and flitted around the galaxy. One showed up in our solar system…

    And just to avoid any possible confusion (which wouldn’t last long in any case), the novel Rogue Moon by Algis Budrys does not concern wandering moons; it’s about an alien installation found on our own Moon. If someone buys this based only on the title, they shouldn’t feel cheated. It’s an excellent story.

  102. icemith

    Seeing poor old Jupiter seems to be a benchmark when relating to all these other bodies, whether they are stars, dwarf stars, planets, dwarf planets etc, etc, does anybody have a link to a graphic site that SHOWS the actual agreed (?) sizes of all these bodies?

    I’m curious because I’m wondering if Jupiter could be similar to the size/mass/composition of say, a dwarf star. These “smaller” stars, having not attained nuclear fission, (or is that, fusion?), seem to be not much different from Jupiter. It could imply that it itself could have been a “wanderin’ star”, that just happened to be caught by our very own Sol.

    Just wonderin” …….. Ivan.

  103. Joseph G

    @109 Icemith: Regarding the first question, Here’s a little image showing a rough size comparison of various bodies.

    Regarding the second question, Jupiter is much, much smaller… (er, lighter) then a brown dwarf.
    It’s complicated by the way that massive objects pack themselves together.
    See, Jupiter is about as large, physically, as a cold (relatively) body of gas can get. If you add mass to Jupiter, it’d actually start to shrink slightly (at least, after the heat caused released by the gravitational collapse of the extra matter radiated away). The pressure at the center of a body this size does some weird things to matter (see “degenerate matter” and “metallic hydrogen”). Jupiter is still slowly contracting, the upper layers of its atmosphere slowly settling. It’s believed to have been about twice the diameter it is now back when it was young and much hotter.
    Basically, a brown dwarf has a degenerate matter core and a normal gas atmosphere, the core being a large percentage of its volume then a gas giant like Jupiter. The lower cut-off for brown dwarfs is considered to be about 13 Jupiter masses, but they can be up to 50 times the mass of Jupiter before hydrogen fusion is initiated and it becomes a very low mass red dwarf.
    As you can see from the image, a brown dwarf isn’t that much larger in diameter then Jupiter, the size being a function of the temperature of the outer (non-degenerate) gas, even though it’s much more massive then Jupiter. Confused yet? I know I am. That’s quantum physics for ya.

    So, in a word, no :)

  104. @icemith,

    “I’m curious because I’m wondering if Jupiter could be similar to the size/mass/composition of say, a dwarf star.”

    your quote above.

    Below is a link from a 2005 study whereby they were looking for exo-planets and were identifying them by a dimming affect that would result as they pass in front of a star. For there to be a magnifying effect like the ones discussed in the above analysis, the planet would need to be about Jupiter size and the distance between the planet to the star must be such that we are at the focal point/ range of the gravitational lensing of the star by the planet.

    One of the objects they discovered in that study discussed in the link below, was believed to be the smallest and minimum possible size of a star which could have nuclear fusion. According to this link, the limit concerning the minimum size of a star is presently thought to be about 75 times the mass of Jupiter. As to the size (diameter) of this small star, it was thought to be only 16% larger than Jupiter but obviously far denser.

    This sparse information leads to a hypotheses. As a planet or proto-star becomes greater in mass than Jupiter its diameter generally does not change much, only its density — up to 75 Jupiter masses.

    http://www.newscientist.com/article/dn7098-planet-search-reveals-smallest-star-ever.html

  105. Wzrd1

    You should’ve saw how horribly CNN mangled that story. First, they reported how scientists were looking at stars, seeing when they BRIGHTENED, due to the object orbiting it.
    ORBITING planets aren’t rouges for starters AND passing in front of the star DIMS it.
    THEN, they mangled the science into something even LESS recognizable as science than biblical science!
    I’m guessing that they asked Bill Nye, the screw-up guy. The guy they interviewed over the Fukushima reactors, yet had zero clue what cesium-137 was and thought boron was a reaction product or used in some other cooling way or something. And he butchered a lot of other interviews after…
    Or, they interviewed a tea party scientist, you remember then, Christian Science Monitor types… ;)

    Forrest, good info. The fact is, DENSITY of the hydrogen is the key for fusion. That can essentially be converted into pressure, as at a given pressure, due to gravity (or other forces), compressing the gas into a certain density that pretty much guarantees fusion (well, temperature is important too, with a bunch of different equations for that one), but again, the pressure generates the temperature at a specific density…
    As for density, THAT is variable in a main sequence star. The core being densest. The outer layers more rarified. That is far more different from a planet, due to the thermonuclear energy input from the core region of the star pressing the remainder of the star outward.
    Again, a buttload of really cool math. Math that I’d butcher, if I didn’t use a computer… :/

  106. Joseph G

    @icemith, forrest: My mistake, you’re right about the mass required for hydrogen fusionbeing more like 75 Jupiter masses.
    I think the actual elemental composition of the body has some effect on the exact threshold as well – as we’ve established, it’s darned complicated.

    Wzrd1: I’m guessing that they asked Bill Nye, the screw-up guy. The guy they interviewed over the Fukushima reactors, yet had zero clue what cesium-137 was and thought boron was a reaction product or used in some other cooling way or something.

    Srsly? Gah. Got a youtube link? :)

  107. Messier Tidy Upper

    @#100 :

    Your comment there also reminds me of an article in ‘NewScientist’ magazine (?) suggesting our Solar system may have ejected many worlds from the inner region – many Mars-to-Earth-sized ones – out into interstellar space and perhaps also the Cometary belts and spheres beyond Neptune. I’ll have to see if I can find that one again!

    Found it! :-)

    This was the cover story no less for the NewScientist issue, 23rd July 2005, titled “How many Planets in the solar System?” with the cover artwork having crossed out ‘9’ and written ’23’ in red over it. It dealt with the “oligarchic theory” of the formation of our solar system and suggested based on claims by Eugene Chiang and Scott Kenyon’s computer models and theorising that there may have been about 60 Mars sized bodies formed early in our solar system’s formation history and many of them were ejected out to now orbit around 1,000 to 10,000 AU. Other such worlds were ejected altogether.

    There’s also a New Scientist issue here of interest if folks can find a copy – the 24th November 2001 issue – that has “Dark Worlds : The strange Planets that Roam Deep Space” as its cover story which is also titled (inside the mag.) “Lost Worlds and written by Marcus Chown featuring these free-floating planets. :-)

  108. Paddy

    Nobody else interested in speculating about how we might do better at spotting these?

  109. Atlas

    I’ve always felt (without any proof) that there are planetary sized objects in interstellar space, this is sort of a nice finding. These “rogue” planets aren’t going to be anything strange, nor will they have life as we know it, to quote one famous skeptic.

    Strangeness comes from not expecting something. I expected this find, it’s not only feasible, but realistically if you extend the Oort cloud out to the nearest stellar bodies, you get gravitational places where even large bodies may form (Lagrange points), and be ejected by the nearest heavier body. The interstellar space is dirty, there are a lot of wandering bodies (planets, in the original sense) out there, but you can’t detect them easily because they are dark, i.e. reflectors. Brown dwarfs we can see in the infrared, but how about rogue Neptunes or less?

  110. Atlas

    Paddy, I’m afraid we need at least two big interferometry telescopes on solar orbit to detect anything like what is required to actually see even the planets on nearest stars. Best would be a fleet of telescopes at Saturn’s orbit.

  111. John Halley

    Pretty typical reporting. For many of us, this is old news. All galaxies must be filled with such planets that are unattached to any star. Most likely there are many in the space between galaxies. It is simply the gravitational process that creates all stars, planets, and other bodies of accumulated mass. Only if there is enough material in the area of accumulation can a body become large enough to ignite into a star. There may well be more free planets than stars for them to orbit, with many have their own mini-solar systems that can not be directly observed because there is no light from them. The fact that these have been detected is fairly recent, but the mass accumulation has long been assumed.

  112. squiggleslash

    OK, so how come these celestial bodies, who aren’t even orbiting a star, get to call themselves “planets” but Pluto doesn’t? Hmmm? Hmmm?

    It’s not fair I tell you!

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