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Thread: Planets and "Free-floaters"

  1. #1 Planets and "Free-floaters" 
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    Objects determined to be only somewhat larger than Jupiter, and well below the deuterium burning threshold for brown dwarfs have been detected over the past decade in star-forming regions of large molecular clouds, unassociated with any particular star. These have been referred to as "planet size objects" This brings us to the question of what is a planet, especially regarding large gas giants like Jupiter and Saturn.

    I believe the most recently discovered free-floater is an object with a mass calculated at 3X Jupiter, found in the sigma Orionis star cluster and the smallest so far. This is probably only at the present lower limit of of detectability and has nothing to do with the minimum size object that can form at the centers of collapsing protostellar discs which brings us to the first question.

    Are these objects, roughly the same size as Jupiter and probably of the same or similar composition planets because Jupiter happens to be a planet or are they something else. And from this, what defines a planet.

    Is a planet determined by constraints on intrinsic characteristics of mass, size, and shape alone. Is it determined only by position and behavior, orbiting a star in a stable orbit. Or is it a combination of the two. Perhaps Jupiter, and even Saturn should be thought of first as sub-stars (brown dwarfs being semi-stars) that happen also to be planets because they were captured by the sun early in its history.


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  3. #2  
    Time Lord
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    I'd class Jupiter a solar system product - and proper planet - because it formed in the centrifuge of our stellar accretion disc. Bodies formed singly in clouds will simply incorporate every nearby element... normally that would be mainly water ice for the small stuff (comets), and then hydrogen and helium as growth (or mutual accretion?) enables.


    A pong by any other name is still a pong. -williampinn
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  4. #3  
    Universal Mind John Galt's Avatar
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    Definitions of planets and their distinction from other astronomical objects is wholly artificial: classification systems are human constructs. Consequently the question lacks meaning.

    One small correction - Jupiter and Saturn were not 'captured' by the sun, they formed from the collapse of the same cloud.
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  5. #4 From whence Jupiter 
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    Quote Originally Posted by Pong
    I'd class Jupiter a solar system product - and proper planet - because it formed in the centrifuge of our stellar accretion disc. Bodies formed singly in clouds will simply incorporate every nearby element... normally that would be mainly water ice for the small stuff (comets), and then hydrogen and helium as growth (or mutual accretion?) enables.
    I agree the Jupiter is certainly a planet because it behaves as a planet in that it orbits a star (the Sun) and that it is within certain size constraints -- massive enough to be spheroidal but not massive enough to produce hydrogen fusion. It, along with Saturn, may very well have formed from the proto-solar disk. That is no doubt the over riding opinion. However with the recent discovery of unattached objects not much larger than Jupiter in such places as the sigma orionis association I question whether this can be said for sure.
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  6. #5 Re: From whence Jupiter 
    Universal Mind John Galt's Avatar
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    Quote Originally Posted by John M
    It, along with Saturn, may very well have formed from the proto-solar disk. That is no doubt the over riding opinion. However with the recent discovery of unattached objects not much larger than Jupiter in such places as the sigma orionis association I question whether this can be said for sure.
    As a scientist you know that nothing should ever be said for sure. However, the origin of Jupiter and Saturn from the accretion disc is supported by a mass of interlocking astronomical, astrophysical, geochemical and orbital dynamics observations, further confirmed by detailed FEA simulations of the evolving disc. If they have an alternative origin it is remarkably well concealed by data that point in an entirely different direction.
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