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The Closest Gas Giant

  1. Sep 25, 2003 #1

    Nim

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    How I understand it, the four inner planets are rocky planets because the Sun boiled off most of their atmospheres, while the planets past Mars retained theres.

    I was wondering if the reason why Jupiter is so big is because it is the closest planet to Mars, so it caught most of the atmosphere that was boiled away by the Sun. Plus, the planets get smaller and smaller after Jupiter. Although maybe that has more to do with the density of the disc near the edges when the planets were forming.
     
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  3. Sep 26, 2003 #2

    russ_watters

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    My guess would be its the density of the disc. Not sure though.
     
  4. Sep 26, 2003 #3

    FZ+

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    I believe the current theory to the creation of the gas giants relies on turbulence developing in the disc, swirling some gases into clumps. In this case, the fact that Jupiter is the innermost is probably because Jupiter was a disturbance that started in a patch of high density gases.

    I don't think the atmosphere of mars is a significant factor.
     
    Last edited: Sep 26, 2003
  5. Sep 27, 2003 #4
    Actually, Nim, it is held that planets have to be very large, in order to produce enough gravity to hold in lighter gases. Earth is only large enough (IIRC) to hold in Oxygen and heavier gases/elements.

    So, the atmospheres were not blown off of other planets onto gas giants, but rather each planet developed it's own atmosphere as it was forming, and the bigger ones could hold in lighter gases.

    Jupiter, btw, is considered to be a "brown dwarf" star, which is star that never "ignited".
     
  6. Sep 27, 2003 #5

    drag

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    Nope, as far as I remember it'll have to be 8-10 times
    more massive for that.

    Peace and long life.
     
  7. Sep 27, 2003 #6

    Nereid

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    Close. The inner planets formed in a region where the volatiles (water, methane, ammonia, etc) had been 'boiled off' while the proto-solar system disk was collapsing; their atmospheres came later, from comets (tho' not the Earth's oxygen Mentat, that came much later, from plants).

    All the planets were formed by collisions (rocky planets) or gravitational accretion (gas planets) of planetesimals.
    Jupiter, like the other gas giants, could grow bigger than the rocky planets because there was much more material from which it could form (all those volatiles).

    The planets get smaller and smaller after Jupiter because of the way the remaining gas, dust, and planetesimals were swept up by the growing planets.

    Here's a link that gives a good overview:
    http://www.pha.jhu.edu/~akir/Seminar/seminar.html
    No, it's still a planet. Although the terminology is somewhat inconsistenly applied, the star/planet distinction refers to the formation process, not the mass, nor whether ignition took place or not. Stars form by the collapse of a gas/dust cloud; planets by accretion.
     
    Last edited: Sep 27, 2003
  8. Sep 28, 2003 #7

    drag

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    Greetings !

    We have to remember that that's the way things happened
    in our solar system, but we've already seen many that
    acted otherwise.
    Well, isn't that more of a relative definition, after all
    a star can also be orbiting other stars/objects as well
    as turning aroung the galaxy center and a planet can
    also form individualy without anything nearby to rotate
    around, if the amount of gas is too small. Right ?

    Live long and prosper.
     
  9. Sep 28, 2003 #8

    Nereid

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    Definitions can be somewhat arbitrary. Among those who work together, or otherwise form a community, you usually find that the terms they use settle down to have fairly narrow ranges of meanings (unless they're politicians, of course!).
    That's what astronomers generally mean when they use the terms 'star' and 'planet'. Certainly, stars may form in pairs (the collapse of two blobs of gas, or a cloud which formed two centres), and may form in a galaxy or globular cluster.

    An object which forms from a very small gas cloud would be called a brown dwarf. A number of isolated brown dwarfs have been observed, though it's not always clear if they formed in isolation, or were ejected from a binary.
     
  10. Sep 28, 2003 #9
    So the fact that Jupiter gives off lots more heat, then it gets from the Sun, seems to, in your mind, not have anything to do with the distinction 'tween stars and planets, Huh?
     
  11. Sep 28, 2003 #10

    LURCH

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    In fact, these other systems have caused us to re-evaluate the current model. Many of the extrasolar planets so far discovered are planets several timea the size of Jupiter with orbits smaller than Venus. This has lead to the idea of planetary migration, which proposes that Jupiter and possibly the other gas giants formed close to the Sun and then moved outward much later.

    I don't really buy that theory yet, but it is gaining credibility. Personally, I think the inner planets are rocky because of the composition of the protosolar accretion at the very beginning. The disk was formed buy gravitational attraction, and so it would seem (to me, at least) to make sense that the heavier elements were closer to the center, sort-of "settled to the bottom". Meanwhile, the lighter elements that we normally think of as gasses would float to the top, leaving them out near the edge. I am hoping that the mission to Pluto will help confirm this idea.
     
  12. Sep 29, 2003 #11

    Nereid

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    Just telling it like it is!

    Who sets the rules for how language is used? Let's all vote for Mr. Robin Parsons!

    :wink: First order of business, Madame Chair (of the International Astronomical Union), motion to refer all questions of nomenclature to Mr. Robin Parsons for his esteemed, absolute ruling. :wink:
     
  13. Sep 29, 2003 #12
    To whom it might/and/or/does concern, I would respectfully desist from the nomination, as it is deleterious to my current reputation :wink: to have such a nominator at hand.
    Thanks, one and all!
     
  14. Sep 29, 2003 #13

    Nereid

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    And did you know, those perfidious astronomers, they wanted to demote Pluto! They had this totally :wink: unreasonable, :wink: irrational idea that just 'cause
    - there are lots and lots of satellites that are bigger
    - it's merely the largest of a class of objects, numbering >1,000 (the Plutinos, EKB objects, SDOs, ... take your pick)
    - Ceres* doesn't get to be called a planet
    - etc, etc, etc
    it didn't deserve to be called a planet. I mean, just look at it - doesn't it look like a planet to you?

    Girl, they sure know how to hurt a planet's feelings.

    *the largest asteroid. Like the planets, asteroids orbit the Sun. The main belt asteroids' orbits lie between Mars and Jupiter. >200,000 have been observed (only ~10,000 have names). If Ceres isn't a planet, why should Pluto be?
     
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