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Thread: Planet IX?! Is it not still Planet X?

  1. #1
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    Planet IX?! Is it not still Planet X?

    As in unknown?

    Mike Brown recently published a Planet Nine video about his discovery where he says, "everybody's been wrong for 170 years, but we're right," and I chuckled.

    Of course, Planet 9 hasn't been detected directly, even while four candidates turned up in a recent citizen science project. None the less, I couldn't help but revisit some questions and curiosities. Assuming it's there, a large perturber in the outer system would seem to answer or add to multiple questions:

    -sun's axial tilt.
    -solar system's angular momentum
    -long-period cometary "wakes" and periodic bombardment
    -retrograde and resonant motions
    -Uranus on its side
    -Pluto having the same retrograde motion as Triton while also intersecting Neptune's orbit.

    There are probably others but these readily come to mind.

    I wonder if the putative perturber will be found to have satellites, or assuming there's one, could there be more?
    Where the telescope ends, the microscope begins. Which of the two has the greater view?

  2. #2
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    In what way does Pluto have "the same retrograde motion as Triton"?

    -- Jeff, in Minneapolis

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    The amusing thing about this potential planet being called Planet 9 is once found using Roman numerals we will be searching for Planet X again, a label which Planet 9 was designed to avoid. The name Planet 9 worked, but only as long as Planet 9 remains a mystery.

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    I don't care what they call it. In fact, I sort of won't mind too much it they DON'T find it, in a way. If it's not there, then there's another mystery to solve to figure out observations in the Kuiper Belt.

    CJSF
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    OK, yeah, I do hope the find it, really.
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    I thought that X was simply a designation for unknown. Presumably, if we find a planet 11, we will still be on the lookout for Planet X.
    Solfe

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    Pluto does not intersect Neptune's orbit. Yes, Pluto's perihelion is closer to the sun than Neptune, but at the points where the orbits "cross", they're separated by several AU. And due to the 2:3 resonance between their orbits, the two bodies never get closer to each other than about 17 AU.

    This resonance, BTW, does not need any special explanation, nor does the "crossing" orbit. Pluto is not the only body in such a resonance with Neptune; something like 25% of known Kuiper Belt objects are in 2:3 resonant orbits with Neptune. And the orbits of these other bodies (called plutinos) often "cross" that of Neptune in the same way. Similar resonances happen in other parts of the solar system. There's several asteroids that are in resonance with the Earth, for example. And it's likely that some of, if not all, the TNOs that suggest there's a Planet 9 are in some kind of resonance with that body.

  7. #7
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    Quote Originally Posted by Jeff Root View Post
    In what way does Pluto have "the same retrograde motion as Triton"?

    -- Jeff, in Minneapolis
    My mistake: Pluto rotates on its axis retrograde while Triton orbits Neptune retrograde. Indeed, these are not the "same retrograde motion."
    Where the telescope ends, the microscope begins. Which of the two has the greater view?

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    Quote Originally Posted by Solfe View Post
    I thought that X was simply a designation for unknown. Presumably, if we find a planet 11, we will still be on the lookout for Planet X.
    Yes, precisely my point. When Pluto was a planet, X doubled as Ten, but it's Unknown if Planets stop with Nine.
    Where the telescope ends, the microscope begins. Which of the two has the greater view?

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    Quote Originally Posted by dtilque View Post
    Pluto does not intersect Neptune's orbit. Yes, Pluto's perihelion is closer to the sun than Neptune, but at the points where the orbits "cross", they're separated by several AU.
    ...
    And it's likely that some of, if not all, the TNOs that suggest there's a Planet 9 are in some kind of resonance with that body.
    Yes, KBOs and Plutinos too, I'd bet.

    And you're correct, my use of "intersect" was inexact. Pluto's inclined eccentric orbit simply brings it closer to the sun than Neptune; it does not actually cross Neptune in its orbit.

    Planet X (heh), if it's there, could help explain Pluto's inclined eccentric orbit and retrograde rotation, and I think it's likely with some sort of resonance.
    Where the telescope ends, the microscope begins. Which of the two has the greater view?

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  11. #11
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    Quote Originally Posted by A.DIM View Post
    Yes, KBOs and Plutinos too, I'd bet.
    No, it doesn't work that way. Plutinos are already in resonance with Neptune. They can't be in resonance with Planet 9 too. Ordinary cubewanos, that is, KBOs in circular orbits, do not show any sign of being in resonance with another object. Their orbits are too regular. Possibly some of the Scattered Disk objects are, but we won't know until we discover Planet 9.

    Planet X (heh), if it's there, could help explain Pluto's inclined eccentric orbit and retrograde rotation, and I think it's likely with some sort of resonance.
    It's Planet 9, not Planet X. Planet X was a planet hypothesized by Percival Lowell to explain supposed irregularities in Neptune's orbit. The X stood for unknown, not for any number. And it turned out that Pluto was not Planet X because there was no need for such a planet. The irregularities were caused by erroneous measurements of Neptune's position.

    As for Pluto's axial tilt (i.e. the retrograde rotation), I'd say that it's much more likely to be the result of a collision, probably the one that formed Pluto's satellites, rather than gravitational effects of a quite distant planet. Pluto's eccentric orbit is likely the result of it being pushed around by Neptune until it fell into resonance with that planet. Once in resonance, its orbit doesn't change.
    Last edited by dtilque; 2017-Apr-17 at 03:24 AM.

  12. #12
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    Quote Originally Posted by dtilque View Post
    No, it doesn't work that way. Plutinos are already in resonance with Neptune. They can't be in resonance with Planet 9 too. Ordinary cubewanos, that is, KBOs in circular orbits, do not show any sign of being in resonance with another object. Their orbits are too regular. Possibly some of the Scattered Disk objects are, but we won't know until we discover Planet 9.

    It's Planet 9, not Planet X. Planet X was a planet hypothesized by Percival Lowell to explain supposed irregularities in Neptune's orbit. The X stood for unknown, not for any number. And it turned out that Pluto was not Planet X because there was no need for such a planet. The irregularities were caused by erroneous measurements of Neptune's position.

    As for Pluto's axial tilt (i.e. the retrograde rotation), I'd say that it's much more likely to be the result of a collision, probably the one that formed Pluto's satellites, rather than gravitational effects of a quite distant planet. Pluto's eccentric orbit is likely the result of it being pushed around by Neptune until it fell into resonance with that planet. Once in resonance, its orbit doesn't change.
    If Planet X (it's unknown!) exists, it seems certain we'll have to revise formation models for Neptune, Pluto et al. It is, after all, an inferred perturber in the outer solar system. But you're right, we won't know until it's discovered. And when it is, whether we like it or not, we'll still be hypothesizing Planet X.
    Where the telescope ends, the microscope begins. Which of the two has the greater view?

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