Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Orphan planets, i.e., planets not in a solar system

  1. Nov 14, 2012 #1


    User Avatar
    Staff Emeritus
    Science Advisor

    Orphan or 'rogue' planets may be common, rather than an exception, at least in the galaxy.

    But how common?
  2. jcsd
  3. Nov 14, 2012 #2
    I'm thinking that the best way to figure out how probable this is, at least without actually observing a large number of rogue planets (which I think would be a waste of effort, seeing as how we would essentially have to aim telescopes into random points in space), would be to determine in what ways a planet could be cast out from its solar system, and then to determine how likely those occurrences are from what we already know.

    Not that I really know anything that would cause something like this to happen other than a large gravitational force, but I don't see how we could figure out the probability of the occurrence of rogue planets any other way.

    Then again, astronomers could possibly focus heavily on one area, and find how many rogue planets are in that given area. Assuming that these planets haven't drifted too far from their solar systems, this could then be applied to other similarly populated areas (in terms of the number of stars).
  4. Nov 14, 2012 #3


    User Avatar
    Science Advisor
    Gold Member

  5. Nov 15, 2012 #4


    User Avatar

    Staff: Mentor

    Do they need a star system to be produced in the first place? If my understanding is right gas giant can be produced just by the small collapsing gas cloud, and the difference between gas cloud collapsing into a star or a gas giant would be only its initial size?

    In the case of other planets (other than gas giants) that's not that easy, as apparently you need a star system for the elements to separate.
  6. Nov 15, 2012 #5


    User Avatar
    Science Advisor
    Gold Member

    That is certainly possible, but, my impression is most are ejected. Free forming bodies are usually termed sub-brown dwarfs.
  7. Nov 15, 2012 #6

    Vanadium 50

    User Avatar
    Staff Emeritus
    Science Advisor
    Education Advisor
    2017 Award

    But we already do this. We call them surveys.
  8. Nov 15, 2012 #7
    Perhaps most rogue planets never orbited primary stars, but formed as pieces of collapsing nebula independent of any stellar formation. Failed protostars.
  9. Nov 15, 2012 #8
    I claimed ignorance in this area of expertise (along with most). I'm certain that there are other ways that they can form besides what I mentioned.

    Regardless, Borek already brought it up:
    I wasn't aware of that, thanks.
  10. Nov 16, 2012 #9
    we are still in the process of plantery discovery. it is amazing how over a decade our view of plantery systems has come along. it is now belived that 'average' 1-5 solar mass stars of which there are plenty have matured planets orbiting them.
    plantery systems are usually in elliptical orbits and over a period of time certain unfavorable resonences will be created that WILL cause oribital migration.
    it will also happen in our system over time as well.
    there are bound to be many many rogue planets.
    but due to the small size they are at the moment unable to be detected.
  11. Nov 16, 2012 #10
    Just saw a presentation that included this very subject last night at the Cleveland Museum of Natural History. It was a talk given by a professor at Vanderbilt. He claimed that estimates are around 1.6 rogue planets per star. That's a lot of planets! Hopefully, none are named Melancholia.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook