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posted by martyb on Tuesday June 05 2018, @01:41PM   Printer-friendly
from the Planet-Nine-from-Outer-Space dept.

Collective gravity, not Planet Nine, may explain the orbits of 'detached objects'

Bumper car-like interactions at the edges of our solar system—and not a mysterious ninth planet—may explain the the dynamics of strange bodies called "detached objects," according to a new study. CU Boulder Assistant Professor Ann-Marie Madigan and a team of researchers have offered up a new theory for the existence of planetary oddities like Sedna—an icy minor planet that circles the sun at a distance of nearly 8 billion miles. Scientists have struggled to explain why Sedna and a handful of other bodies at that distance look separated from the rest of the solar system. [...] The researchers presented their findings today at a press briefing at the 232nd meeting of the American Astronomical Society, which runs from June 3-7 in Denver, Colorado.

[...] [Jacob] Fleisig had calculated that the orbits of icy objects beyond Neptune circle the sun like the hands of a clock. Some of those orbits, such as those belonging to asteroids, move like the minute hand, or relatively fast and in tandem. Others, the orbits of bigger objects like Sedna, move more slowly. They're the hour hand. Eventually, those hands meet. "You see a pileup of the orbits of smaller objects to one side of the sun," said Fleisig, who is the lead author of the new research. "These orbits crash into the bigger body, and what happens is those interactions will change its orbit from an oval shape to a more circular shape." In other words, Sedna's orbit goes from normal to detached, entirely because of those small-scale interactions.

Also at Popular Mechanics, where Planet Nine proposer Konstantin Batygin disputes the findings:

Batygin, of Caltech, tells Popular Mechanics that any sufficiently strong gravitational encounter could detach an object from Neptune's embrace, but for the distant small bodies of the Kuiper belt to have done so through "self-gravity"—as the CU model proposes—there would need to be about five to ten times the mass of Earth in the outer parts of the Kuiper belt. There isn't.

"Unfortunately, the self-gravity story suffers from the following complications," Batygin says. "Both observational and theoretical estimates place the total mass of the Kuiper belt at a value significantly smaller than that of the Earth [only 1 to 10 percent Earth's mass]. As a consequence, Kuiper belt objects generally behave like test-particles enslaved by Neptune's gravitational pull, rather than a self-interacting group of planetoids."

Planet Nine.

Related: Planet Nine's Existence Disfavoured by New Data
Medieval Records Could Point the Way to Planet Nine
Another Trans-Neptunian Object With a High Orbital Inclination Points to Planet Nine
Outer Solar System Origins Survey Discovers Over 800 Trans-Neptunian Objects
LSST Could be the Key to Finding New Planets in Our Solar System


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  • (Score: 0) by Anonymous Coward on Wednesday June 06 2018, @05:40AM (1 child)

    by Anonymous Coward on Wednesday June 06 2018, @05:40AM (#689198)

    Sedna is at 1.4×1010 km from the sun. The gravitational acceleration from the sun for an object at that distance is something like 6.8×10-7 m/s2. The mass of Sedna is still unknown at this time, but it is not unreasonable to estimate it at 1021 kg (less than Pluto or Eris). An object about, say, 500,000 km from it (of the order of the distance from the earth to the moon), also experiences an acceleration due to Sedna's gravity comparable to what it is getting from the sun, roughly 3×10-7 m/s2. Think of what that means for a second: a body like Sedna has about as much influence over the trajectories of objects somewhat close to it as the sun does. It's easy to see how smaller KBOs close to Sedna might have dynamics that look like them periodically congregating in crowds to "annoy Sedna" and then later disperse as their altered trajectories fling them away. With a relatively large object out there with a gravitational influence comparable to the sun's at that distance they'd definitely not just be drifting about in neat, orderly Keplerian orbits!

    An even bigger body like the hypothetical Planet 9 would be a really noticeable influence on objects close to it out there. If, as hypothesised, it had ten earth masses, it would be able to exert accelerations of 0.02 m/s2 on bodies half a million kilometres from it (roughly as much as that experienced by a body at 0.5 AU from the sun, just a little further than Mercury's orbit). In contrast, at 700 AU (planet nine's hypothesised distance), the sun's influence on those objects close to it would be a measly 1.2×10-8 m/s2.

  • (Score: 2) by c0lo on Wednesday June 06 2018, @07:47AM

    by c0lo (156) Subscriber Badge on Wednesday June 06 2018, @07:47AM (#689216) Journal

    It's easy to see how smaller KBOs close to Sedna might have dynamics that look like them periodically congregating in crowds to "annoy Sedna" and then later disperse as their altered trajectories fling them away.

    I can accept that the dynamics may allow smaller KBO to show a "congregation"-like behaviour (being fling after the encounter with altered objects, or having some of them even accreting them on Sedna). I doubt though that we can observe a periodicity - because those objects will likely be thrown from their orbit and there's no guarantee that others with similar distribution space/velocity distribution will be available for a "future annoying encounter"; it's more likely to assist to a dynamic (deterministic) chaos of such events; at least until Sedna clears its orbit (the smaller KBO objects need to be close to Sedna to speak about meaningful n-body conditions, thus it's likely those objects will be in the close neighbourhood)

    --
    https://www.youtube.com/watch?v=aoFiw2jMy-0 https://soylentnews.org/~MichaelDavidCrawford