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Number of homeless planets

  1. Feb 24, 2012 #1
    Number of "homeless" planets

    So I stumbled upon this article and wanted to get others opinions of it. The short and long of it is it is claiming that there are roughly 100,000 X as many planets wandering about our galaxy (not attached to a star) as there are stars in our galaxy. Seems a little high to me.
    Further can anyone make an estimation on how much mass this would be (percentage wise) of our galaxy? The article has some information that would be helpful.

    p.s. I was exagerating when I said a little.
  2. jcsd
  3. Feb 27, 2012 #2
    Re: Number of "homeless" planets

    I think if this were true there would be better/more stories and at least one picture of this discovery.

    "Strigari also says there is a slight chance that two nomad planets could collide, flinging bacterial debris into other solar systems."

    I've learned (correct me if I'm wrong) that when galaxies collide that there's not even a slight(not a unit of measurement either) chance of 2 stars colliding. Also, I think it is playing alot of the "life out there" hype.
  4. Feb 27, 2012 #3


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    Re: Number of "homeless" planets

    That number seems really high, and the one I'm familiar with is ~2x freely floating planets as bound planets (and the number of bound planets is ~ the number of stars).

    See: http://arxiv.org/abs/1105.3544v1

    These microlensing studies have a very small population of detections (only 11!), from which they infer a population of hundreds of millions of planets, so I'm somewhat skeptical of the results (but their statistical analysis appears to be sound).
  5. Feb 29, 2012 #4
    Re: Number of "homeless" planets

    Just a minor correction. The arxiv link you gave says there are twice as many Jupiter size planets as stars (actually the same thing my article said).
    From your link
    "Here, we report the discovery of a population of unbound or distant Jupiter-mass objects, which are almost twice (1.8_{-0.8}^{+1.7}) as common as main-sequence stars"

    So it leaves open how many smaller planets could be out there. I am skeptical that there are 50,000 X as many smaller planets as Jupiter sized planets, unless someone has a link to that.
    Also it does seem to be a very small sample size as you said.
  6. Mar 7, 2012 #5
    Re: Number of "homeless" planets

    First, a correction. Strigari et al aren't claiming to have proven the numbers, merely giving an upper bound based on current observational data and the mass of the Galaxy that's not bound up in stars. The 100,000/1 ratio is based on extrapolating the mass-function of brown dwarfs down to Pluto-mass objects. And, surprisingly, the observational limits are consistent with the high figure. In true scientific spirit, the researchers suggest ways of making the numbers harder based on piggy-back observations - using data from other large-scale observational studies.
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