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posted by Fnord666 on Wednesday July 10 2019, @02:27AM   Printer-friendly
from the Ogden-Nash's-fleas dept.

Moons that Escape their Planets Could Become "Ploonets":

Meet ploonets: planets of moonish origin.

In other star systems, some moons could escape their planets and start orbiting their stars instead, new simulations suggest. Scientists have dubbed such liberated worlds "ploonets," and say that current telescopes may be able to find the wayward objects.

Astronomers think that exomoons — moons orbiting planets that orbit stars other than the sun — should be common, but efforts to find them have turned up empty so far (SN Online: 4/30/19). Astrophysicist Mario Sucerquia of the University of Antioquia in Medellín, Colombia and colleagues simulated what would happen to those moons if they orbited hot Jupiters, gas giants that lie scorchingly close to their stars (SN: 7/8/17, p. 4). Many astronomers think that hot Jupiters weren't born so close, but instead migrated toward their star from a more distant orbit.

As the gas giant migrates, the combined gravitational forces of the planet and the star would inject extra energy into the moon's orbit, pushing the moon farther and farther from its planet until eventually it escapes, the researchers report June 29 at arXiv.org.

[...] Some ploonets may be indistinguishable from ordinary planets. Others, whose orbits keep them close to their planet, could reveal their presence by changing the timing of when their neighbor planet crosses, or transits, in front of the star. The ploonet should stay close enough to the planet that its gravity can speed or slow the planet's transit times. Those deviations should be detectable by combining data from planet-hunting telescopes like NASA's TESS or the now-defunct Kepler, Sucerquia says.

Ploonethood may be a relatively short-lived phenomenon, though, making the worlds more difficult to spot. About half of the ploonets in the researchers' simulations crashed into either their planet or star within about half a million years. And half of the remaining survivors crashed within a million years.

What to call a celestial body that orbited a moon? — moonmoon? moo-oon?

M. Sucerquia et al. Ploonets: formation, evolution, and detectability of tidally detached exomoons. arXiv:1906.11400.


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  • (Score: 2) by c0lo on Wednesday July 10 2019, @03:19AM (2 children)

    by c0lo (156) Subscriber Badge on Wednesday July 10 2019, @03:19AM (#865271) Journal

    Your best bet is: "Soon** to be dead. Like Zed". Because the configuration is unstable even for simple cases [wikipedia.org]

    ...Moreover, the motion of three bodies is generally non-repeating, except in special cases.[5]

    On the other hand, in 1912 the Finnish mathematician Karl Fritiof Sundman proved that there exists a series solution in powers of t1/3 for the 3-body problem.[6] This series converges for all real t, except for initial conditions corresponding to zero angular momentum. (In practice the latter restriction is insignificant since such initial conditions are rare, having Lebesgue measure zero.)

    ** At astronomical time scales.

    --
    https://www.youtube.com/watch?v=aoFiw2jMy-0 https://soylentnews.org/~MichaelDavidCrawford
    • (Score: 1, Informative) by Anonymous Coward on Wednesday July 10 2019, @11:08AM (1 child)

      by Anonymous Coward on Wednesday July 10 2019, @11:08AM (#865337)

      Mathematical difficulty does not necessarily translate into physical instability. Even so, the general three-body problem is not necessary to determine the stability of orbits. Our solar system is not just a three-body problem, but a couple of hundred body problem (much more if you count asteroids and comets rather than just the Sun, planets, and moons) and yet the Earth and the Moon have been orbiting peacefully for billions of years.

      Moons orbit planets, planets orbit stars, stars orbit galaxies (or occasionally other stars), galaxies can orbit other galaxies. A submoon (or the silly name of moonmoon) is just going from three to five levels of orbits to four to six. The real question is whether there is a stable orbit that is far enough from the moon to not crash, but close enough to not end up orbiting the planet instead. While there are no known submoons in our solar system, they are possible - if the host moon is massive enough and far enough from its planet. Ironically, a more massive host planet is actually better, because it can host moons farther out, where its tidal forces are weaker.

      Conditions for stable submoons have been calculated [arxiv.org].

      An exomoon candidate about the size of Neptune was recently announced. This exomoon, if it is real, is so massive that I would consider submoons quite likely. Of course, these are not possible to discover with current telescopes.

      • (Score: 2) by c0lo on Wednesday July 10 2019, @12:07PM

        by c0lo (156) Subscriber Badge on Wednesday July 10 2019, @12:07PM (#865349) Journal

        Mathematical difficulty does not necessarily translate into physical instability.

        Difficulty like in "Hard to find solution"? Never said it is.
        A Lebesgue measure of zero? That guarantees a probability on encountering such things so small it's practically impossible to expect one will find it in nature.

        Moons orbit planets, planets orbit stars,

        True, for values of "orbits" observable at humanity experience scale; reasonable to extrapolate for astronomical durations.

        stars orbit galaxies

        Ahem... I think this is a misuse for "orbit".

        galaxies can orbit other galaxies

        Theoretically? Yes. Demonstrable that happens in reality? At best undecidable.

        Conditions for stable submoons have been calculated [arxiv.org].

        That's a nice find, thanks. Something I'll have to find time to read over the weekend.

        --
        https://www.youtube.com/watch?v=aoFiw2jMy-0 https://soylentnews.org/~MichaelDavidCrawford
  • (Score: 3, Funny) by archfeld on Wednesday July 10 2019, @03:46AM (1 child)

    by archfeld (4650) <treboreel@live.com> on Wednesday July 10 2019, @03:46AM (#865276) Journal

    What if... A super giant planet, had a moon, that had a moon itself ? or what if the same occurred around a binary star ? Things could get more confusing than a family tree in Arkansas.

    --
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    • (Score: 2) by c0lo on Wednesday July 10 2019, @04:30AM

      by c0lo (156) Subscriber Badge on Wednesday July 10 2019, @04:30AM (#865283) Journal

      What if... A super giant planet, had a moon, that had a moon itself ?

      You know Europa, Jupiter's moon? It doesn't have a moon itself, no, but tidal heating [wikipedia.org] is enough to keep almost all its water in liquid state and there's fucking plenty of it.
      Imagine what these forces will do to an Europa's moon, assuming such a moon would exists.

      Things could get more confusing than a family tree in Arkansas.

      Heh, I tried to understand the above.
      Ironically, this [wikipedia.org] gives higher chances to NE states to experience "confusing family trees".

      --
      https://www.youtube.com/watch?v=aoFiw2jMy-0 https://soylentnews.org/~MichaelDavidCrawford
  • (Score: 0) by Anonymous Coward on Wednesday July 10 2019, @05:25PM

    by Anonymous Coward on Wednesday July 10 2019, @05:25PM (#865434)

    How could this article not have been submitted by the "that's-no-moon" department? I feel bad now.

  • (Score: 2) by darkfeline on Thursday July 11 2019, @03:07AM

    by darkfeline (1030) on Thursday July 11 2019, @03:07AM (#865647) Homepage

    I guess Pluto is a plunet then?

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