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posted by cmn32480 on Saturday October 22 2016, @04:23PM   Printer-friendly
from the weebles-wobble-but-they-don't-fall-down dept.

Arthur T Knackerbracket has found the following story:

The massive hypothetical object, which supposedly looms at the edge of our solar system, has been invoked to explain the strange clustering of objects in the Kuiper belt and the unusual way they orbit the Sun.

Now Planet Nine predictors Konstantin Batygin and Mike Brown of Caltech, along with graduate student Elizabeth Bailey, offer another piece of evidence for the elusive sphere's existence: It adds "wobble" to the solar system, they say, tilting it in relation to the sun.

"Because Planet Nine is so massive and has an orbit tilted compared to the other planets, the solar system has no choice but to slowly twist out of alignment," lead author Bailey said in a statement.

Before we go any further, a caveat about Planet Nine: It's purely theoretical at this point. Batygin and Brown predict its existence based on unusual perturbations of the solar system that aren't otherwise easily explained. (This is the same technique scientists used to find Neptune.) But the history of astronomy is rife with speculation that is never borne out: The same guy who correctly predicted the existence of Neptune also believed that a planet he called Vulcan was responsible for the wobble of Mercury. That "discovery" caused the astronomy world to waste years looking for something that wasn't there. (Mercury's wobble was eventually explained by the theory of general relativity.)

But the evidence offered by Batygin and Brown is compelling. When the pair announced their find in January, planetary scientist Alessandro Morbidelli of the Côte d'Azur Observatory in Nice, France, told The Washington Post: "I don't see any alternative explanation to that offered by Batygin and Brown."

"We will find it one day," he added. "The question is when."

Planet Nine's angular momentum is having an outsized impact on the solar system based on its location and size. A planet's angular momentum equals the mass of an object multiplied by its distance from the sun, and corresponds with the force that the planet exerts on the overall system's spin. Because the other planets in the solar system all exist along a flat plane, their angular momentum works to keep the whole disk spinning smoothly.

Planet Nine's unusual orbit, however, adds a multi-billion-year wobble to that system. Mathematically, given the hypothesized size and distance of Planet Nine, a six-degree tilt fits perfectly, Brown says.


Original Submission #1; Original Submission #2

 
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  • (Score: 2) by takyon on Saturday October 22 2016, @07:18PM

    by takyon (881) <reversethis-{gro ... s} {ta} {noykat}> on Saturday October 22 2016, @07:18PM (#417635) Journal
    • There is no agreement that Earth-Moon is a binary/double system [wikipedia.org], and there are a few arguments against it.
    • Do moons or binaries make the detection that much harder? I guess it could by lowering the temperature of both compared to a single, larger gas planet. What it could do is make diameter estimates inaccurate, especially if the imagery has a low resolution.
    • Large binaries are possible [space.com], but so are collision and ejection.

    The possibility of a Planet Nine with moons is interesting since it could allow its mass to be determined with more accuracy, and if Planet Nine is a mini-Neptune, it gives us a new opportunity to find large moons close to home. The largest known satellite is Ganymede, and it has just 2.5% of Earth's mass. Tidal heating could mean that moons around a Planet Nine might have underground oceans.

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  • (Score: 2) by bzipitidoo on Monday October 24 2016, @10:07PM

    by bzipitidoo (4388) on Monday October 24 2016, @10:07PM (#418301) Journal

    I expect Planet 9, whether single or binary, to have lots of moons, same as our gas giants.

    We haven't settled on a definition for binary planet. Very popular is "barycenter is not within the larger body", but that has problems. Would like a definition that does not change the status of a binary system as it evolves, and the barycenter of Earth-Moon is moving as the Moon moves outward, and will eventually be outside Earth's body. Also would like a definition that is independent of position in a solar system and size of the star orbited. Binary star system is easy in part because star is fairly easy. A red dwarf orbiting a blue hypergiant is still a binary star system. Relative mass can make a simple definition. If the mass of the smaller body is at least some significant percentage of the mass of the larger body, then it's a double planet. Just what that percentage should be is a problem-- 50%? 10%? Suppose Earth was in orbit about Jupiter, would that demote Earth to the status of a moon? Suppose Ganymede was in orbit about the sun, would it be a planet then? Ganymede is larger diameter than Mercury, however, Mercury is much denser and has more mass. At any rate, if relative mass an acceptable way to define double planet, that percentage can be decided almost independently of the definition of a planet.