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Researchers Find Evidence Of Distant Outer Planet
Mongo
post Jan 20 2016, 04:58 PM
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Free to view paper:

Evidence for a Distant Giant Planet in the Solar System

Konstantin Batygin and Michael E. Brown

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Abstract

Recent analyses have shown that distant orbits within the scattered disk population of the Kuiper Belt exhibit an unexpected clustering in their respective arguments of perihelion. While several hypotheses have been put forward to explain this alignment, to date, a theoretical model that can successfully account for the observations remains elusive. In this work we show that the orbits of distant Kuiper Belt objects (KBOs) cluster not only in argument of perihelion, but also in physical space. We demonstrate that the perihelion positions and orbital planes of the objects are tightly confined and that such a clustering has only a probability of 0.007% to be due to chance, thus requiring a dynamical origin. We find that the observed orbital alignment can be maintained by a distant eccentric planet with mass gsim10 m⊕ whose orbit lies in approximately the same plane as those of the distant KBOs, but whose perihelion is 180 away from the perihelia of the minor bodies. In addition to accounting for the observed orbital alignment, the existence of such a planet naturally explains the presence of high-perihelion Sedna-like objects, as well as the known collection of high semimajor axis objects with inclinations between 60 and 150 whose origin was previously unclear. Continued analysis of both distant and highly inclined outer solar system objects provides the opportunity for testing our hypothesis as well as further constraining the orbital elements and mass of the distant planet.


QUOTE
6. SUMMARY

To date, the distinctive orbital alignment observed within the scattered disk population of the Kuiper Belt remains largely unexplained. Accordingly, the primary purpose of this study has been to identify a physical mechanism that can generate and maintain the peculiar clustering of orbital elements in the remote outskirts of the solar system. Here, we have proposed that the process of resonant coupling with a distant, planetary mass companion can explain the available data, and have outlined an observational test that can validate or refute our hypothesis.

We began our analysis with a re-examination of the available data. To this end, in addition to the previously known grouping of the arguments of perihelia (Trujillo & Sheppard 2014), we have identified ancillary clustering in the longitude of the ascending node of distant KBOs and showed that objects that are not actively scattering off of Neptune exhibit true orbital confinement in inertial space. The aim of subsequent calculations was then to establish whether gravitational perturbations arising from a yet-unidentified planetary-mass body that occupies an extended, but nevertheless bound, orbit can adequately explain the observational data.

The likely range of orbital properties of the distant perturber was motivated by analytic considerations, originating within the framework of octupole-order secular theory. By constructing secular phase-space portraits of a strictly planar system, we demonstrated that a highly eccentric distant perturber can drive significant modulation of particle eccentricities and libration of apsidal lines such that the perturber's orbit continuously encloses interior KBOs. Intriguingly, numerical reconstruction of the projected phase-space portraits revealed that, in addition to secular interactions, resonant coupling may strongly affect the dynamical evolution of KBOs residing within the relevant range of orbital parameters. More specifically, direct N-body calculations have shown that grossly overlapped, apsidally anti-aligned orbits can be maintained at nearly Neptune-crossing eccentricities by a highly elliptical perturber, resulting in persistent near-colinearity of KBO perihelia.

Having identified an illustrative set of orbital properties of the perturber in the planar case, we demonstrated that an inclined object with similar parameters can dynamically carve a population of particles that is confined both apsidally and nodally. Such sculpting leads to a family of orbits that is clustered in physical space, in agreement with the data. Although the model proposed herein is characterized by a multitude of quantities that are inherently degenerate with respect to one another, our calculations suggest that a perturber on an a' ~ 700 AU, e' ~ 0.6 orbit would have to be somewhat more massive (e.g., a factor of a few) than m' = 10 m⊕ to produce the desired effect.

A unique prediction that arises within the context of our resonant coupling model is that the perturber allows for the existence of an additional population of high-perihelion KBOs that do not exhibit the same type of orbital clustering as the identified objects. Observational efforts aimed at discovering such objects, as well as directly detecting the distant perturber itself constitute the best path toward testing our hypothesis.


So about the size of Neptune, if their hypothesis is correct.
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scalbers
post Jan 20 2016, 05:29 PM
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This sounds familiar, perhaps written about recently in Sky and Telescope?

http://www.skyandtelescope.com/astronomy-n...int-ofplanet-x/

EDIT: I found the 2014 article above online - though I probably read a similar thing in the magazine.


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Steve G
post Jan 20 2016, 05:43 PM
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Help me out here on the math. If they are mentioning 700 AU (correct me if I'm wrong please) and Voyager 1 is currently 133.8 AU, and is considered to be in interstellar space, and this is 5 times more distant, is it really a planet or an interstellar companion?




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Explorer1
post Jan 20 2016, 05:45 PM
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scalbers: I recall that would have been about the 2014 results for the first KBO grouping; the second grouping being exactly where the models predict seals the deal as far as the paper is concerned. Exciting stuff.
It still needs to be actually spotted, of course (and then work can start on New Horizons 2 for real this time!).
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JRehling
post Jan 20 2016, 06:19 PM
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QUOTE (Steve G @ Jan 20 2016, 10:43 AM) *
Help me out here on the math. If they are mentioning 700 AU (correct me if I'm wrong please) and Voyager 1 is currently 133.8 AU, and is considered to be in interstellar space, and this is 5 times more distant, is it really a planet or an interstellar companion?


63,000 AU is one light year, and is approximately the radius of the Sun's Hill sphere. This is therefore only about 1% of the size of the largest orbits that are possible around the Sun, and only 0.25% of the distance to the nearest other star. So this doesn't seem very interstellar to me. On the interstellar scale, this object (if it exists) is right next to the Sun.

Perhaps more to the point, the observed dynamic, if it exists, depends upon the object having made many orbits around the Sun, not being something out there floating in its own orbit around the galaxy.
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Gerald
post Jan 20 2016, 06:35 PM
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That far out the Hill sphere of an object should be rather large. Therfore I'm wondering - provided the analysis isn't based on observational bias - whether there couldn't exist kind of a miniature globular cluster made of planetesimals, or a small version of a protoplanetary disk, of the same mass as the presumed planet, but without having formed an actual planet.
The simulations - as far as I understood - assume a certain point mass, but not necessarily united to one planet.
Or - if there is one population of KBOs - why not a second one, forming a Kozai-like resonance with the observed population.
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stevesliva
post Jan 20 2016, 06:42 PM
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QUOTE (scalbers @ Jan 20 2016, 12:29 PM) *
This sounds familiar, perhaps written about recently in Sky and Telescope?


Mike Brown's blog hinted that he was trying to explain Sedna's weird orbit. This would be that, but I don't think the details have been previously explained.
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katodomo
post Jan 20 2016, 06:56 PM
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QUOTE (Steve G @ Jan 20 2016, 06:43 PM) *
If they are mentioning 700 AU

700 AU is given as an example semi-major axis of a perturber, with from a cursory glance their possible range laying at 400 to 1500 AU semi-major axes. The minor planets cited as grouped by resonance with the hypothetical objext have semi-major axes of 150-600 AU.

What NASA used as definition for the solar system for Voyager is the heliosphere, i.e. the extend to which the stellar wind of the Sun interferes with the interstellar medium; an object with aphelion (such as most long-period comets) beyond basically dips in and out of this bubble. The IAU definition of a planet does not have any distance limitation.

The referred-to Hill Sphere of the Sun, being its gravitational influence zone, is probably the most appropriate measure when considering "interstellar companions" though.
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Gladstoner
post Jan 20 2016, 10:54 PM
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I recall reading somewhere about an observed (possible) clustering of long-period cometary orbits that could have resulted from a distant massive planet or even a brown dwarf (which has since been ruled out). It would be interesting to compare these with the findings of Batygin-Brown.
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Holder of the Tw...
post Jan 20 2016, 11:35 PM
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QUOTE (Mongo @ Jan 20 2016, 10:58 AM) *
"our calculations suggest that a perturber on an a' ~ 700 AU, e' ~ 0.6 orbit would have to be somewhat more massive (e.g., a factor of a few) than m' = 10 m⊕ to produce the desired effect."

So about the size of Neptune, if their hypothesis is correct.


Neptune has a mass about 17.15 earths, so a factor of "a few" time ten earths sounds to me like something bigger than Neptune, even if "a few" means three or four.

Neptune would have been visible to WISE out to 700 au. Saturn, at 95 earth masses, out to 10,000 au. This hypothesized planet somewhere in between. So... just how eccentric an orbit are we talking here?
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0101Morpheus
post Jan 20 2016, 11:37 PM
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Gladstoner.

I was under the impression that the such ruled out any brown dwarf or massive planets currently around the sun. There could have been one out there once and was since lost. Or maybe an interstellar interloper made a close pass to the solar system and went on its way.
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elakdawalla
post Jan 21 2016, 12:34 AM
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Most of the answers to all of your questions can be found on Brown and Batygin's blog.


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scalbers
post Jan 21 2016, 12:43 AM
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QUOTE (stevesliva @ Jan 20 2016, 06:42 PM) *
Mike Brown's blog hinted that he was trying to explain Sedna's weird orbit. This would be that, but I don't think the details have been previously explained.


I believe what I had read about in Sky and Telescope magazine is the clustering of arguments of perihelion of KBO's. It was suggested in 2014 in an online S&T article these correlations of perihelia could be consistent with a distant planetary perturbation (a super-Earth around 250AU distant). I'm a bit unclear on whether what I'd read was in Emily's S&T print article from Feb 2014 or more likely another writeup a bit more recently. I added a relevant link into post #2. Explorer1 summarizes this also in post #4.


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Phil Stooke
post Jan 21 2016, 05:15 AM
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I'm waiting until I can make a map of it before I accept it as real.

Phil


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tfisher
post Jan 21 2016, 06:46 AM
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QUOTE (katodomo @ Jan 20 2016, 01:56 PM) *
700 AU is given as an example semi-major axis of a perturber, with from a cursory glance their possible range laying at 400 to 1500 AU semi-major axes.


Wow. If we launch a probe that goes at similar speed to voyager 1, it takes over 100 years to reach 400 AU. From the blog site, it sounds pretty likely this thing is sitting out near its aphelion. Seems like a multi-generation effort is needed to explore this.

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