Researchers Find Evidence Of Distant Outer Planet Options

[Mongo]

Free to view paper:

Evidence for a Distant Giant Planet in the Solar System

Konstantin Batygin and Michael E. Brown

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.

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.

[Mongo]

Would that mean dear Pluto is back as a planet ? Whooopie !

Nope. Pluto is far too small to have any significant gravitational effect on other objects in similar orbits. It's merely one of numerous bodies of similar or slightly smaller size in its region of the Solar System, none of which are gravitationally significant. The dominant mass in its region is Neptune, which does control which orbits around it are occupied and which are empty, through resonances. The possible "Planet Nine", on the other hand, would count as a full planet because of its huge gravitational impact on everything in its region of the Solar System.

[scalbers]

On the other hand, planet 9 would be near the borderline of planethood, based on the graph we've seen in the 2015 Margot paper and in this blog:

http://www.findplanetnine.com/2016/01/is-p...ine-planet.html

[HSchirmer]

On the other hand, planet 9 would be near the borderline of planethood, based on the graph we've seen in the 2015 Margot paper and in this blog:

http://www.findplanetnine.com/2016/01/is-p...ine-planet.html

The graph mentioned above illustrates an interesting point, " a planet clearing its orbit" IS actually a function of time AND mass. So the smaller bodies just take longer to BECOME planets.

It seems like Planet-9's current location would be the result of Jupiter or Saturn clearing IT out of THEIR orbit.
INSTABILITY-DRIVEN DYNAMICAL EVOLUTION MODEL OF A PRIMORDIALLY 5 PLANET OUTER
SOLAR SYSTEM
http://arxiv.org/pdf/1111.3682v1.pdf

Several runs of Nice Model simulations suggest that an ice giant between Saturn and Uranus would be the
most likely planet to be ejected.
Rather odd, then, that it WAS NOT a planet when it was being ejected from the orbital path of a gas giant,
then it becomes a planet when it clears out the area where it has been ejected to.

[JRehling]

This paper, Trujillo and Sheppard (2014), is so important to the discussion, that it should be read by anyone trying to understand the new work:

http://home.dtm.ciw.edu/users/sheppard/pub...heppard2014.pdf

It gives details of the key observation, that among minor planets with q>30 AU, the 12 objects with a>150 AU show common orbital characteristics that are not seen among the larger population of objects with q>30 AU and a<150 AU. 12 is sufficient to show statistical significance, so, simply put, there is something here that needs to be explained.

I think we need to see more work considering alternative explanations before a planetary perturber stands out as the only good explanation. Some things the two papers note:

1) Observational biases may exist, but can't explain all of the orbital similarities.
2) An origin based solely in the initial conditions of the outer solar system would not survive gigayear exposure to torques caused by the known outer planets.

Remaining models consist of various combinations of one or more perturbing objects orbiting the Sun combined possibly with some close stellar interaction in the past.

A difficulty is that the number of possible combinations of those models is wildly unconstrained. Finding a model that matches the observations pretty well isn't going to eliminate the infinite number of possible explanations that weren't considered. So, I think we're a long way from being able to duplicate the success of Neptune's discovery, where careful analysis gives astronomers a pinpoint location in the sky where the unseen object must exist.

[JRehling]

Funny, yet thought-provoking:

Possible Undiscovered Planets

http://xkcd.com/1633/

[vossinakis]

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.

Are you referring to this??? Arguments for the presence of a distant large undiscovered Solar system
planet http://astro.u-szeged.hu/ismeret/murray.pdf

[Floyd]

The latest Scientific American has an article on the search for planet X---by Michael Lemonick. Article good as background for this thread.

[TheAnt]

Oh yes I did run into that SciAm article also, before reading it I considered this to be one interesting idea but one that might have other explanations.
However when seeing this graphic with orbits of KBO's that are far from the ecliptic I began to understand why they find this such an tantalizing possibility.

Still when considering a planet like Neptune it should have an atmosphere that's gaseous even in the cold realm so far from the Sun. One such should show an IR excess for one or another reason, latent heat released when gas turning liquid and rain down for example. Now actually finding it might depend where this putative planet is located in its orbit, if it's anywhere of the furthest part of the orbit right now, the distance and very small proper motion might make it very difficult to detect. So yes, perhaps, they might be onto something here - yet, saying 'evidence' is stretching the meaning of the word a little bit to far yet.

[jasedm]

I agree. Evidence there isn't (as yet)

[fredk]

Agreed. Possibly "indirect evidence" or "circumstantial evidence", with the caveat already mentioned here that an "unobvious bias" may also explain the observations. "Theoretical evidence" also doesn't make sense, since theories aren't observations and so can't provide evidence!

In my business, we'd probably call it a "hint".

[Habukaz]

It's easy for a definition of the word evidence to be circular:

a) evidence is something which shows that something exists
b) we know that something exists because we have evidence for its existence

So in order to know if something counts as evidence towards something, we first have to know if that something is real, and in order to know if something is real, we need evidence..


I think I'd rather put it this way: evidence is an observation consistent with a hypothesis, regardless of whether we assume the hypothesis to be true or false.

(now, you could say that evidence is part of what convinces you that something is real, but the subjectivity of this would make the definition problematic)

So I'd finally say that there is evidence - "inconclusive" evidence - for a fifth giant planet in the solar system. The consensus would also appear to be that not (good) enough evidence has been presented yet for this case in order to get really excited about it.

[Floyd]

We have the original data in the orbital parameters of several KBOs. Trying to explain the unusual clustering of these orbits, the idea of a 9th planet seemed a possibility. Much experimentation with computer modeling found a planet 9 mass and general orbit that could cause such clustering. Now there is a hypothesis. To test the hypothesis requires new data(KBOs) or spotting planet 9. The original data for a hypothesis can't be used as evidence for that hypothesis--must get new data.

[HSchirmer]

It's easy for a definition of the word evidence to be circular:
...
I think I'd rather put it this way: evidence is an observation consistent with a hypothesis, regardless of whether we assume the hypothesis to be true or false.
...

There are a few other definitions, the one I'm familiar with is logic/legal.

Evidence is anything that helps to prove or disprove an ultimate fact.

In much the same way that you have equations and variables, you also have law (hypothesis) and facts.
Facts are usually variables, unknowns that can be established or measured.
A series of facts, combined with an argument, eventually gets you to a proof.

[nprev]

MOD NOTE: Enough with the semantics, please.

[Gerald]

Citing this article:

The 0.007% chance that the clustering of the six objects is coincidental gives the planet claim a statistical significance of 3.8 sigma—beyond the 3-sigma threshold typically required to be taken seriously, but short of the 5 sigma that is sometimes used in fields like particle physics.

The range between 3 and 5 sigma is usually called "evident", greater or equal 5 sigma is called "definitive". 3 < 3.8 < 5. That's all.

The question is essentially, whether the numerical experimental settings leading to these 3.8 sigma confidence level are consistent with the way astronomers would have looked for the KBOs, hence whether the observational bias is considered appropriately.

One issue might be, that the same arguments preventing the direct observation of a possible planet 9 prevented observations of KBOs, e.g. the densely crowded Milky Way background.
Another issue might be an adjustment of the observation and detection methods to the first observed KBO of the presumed cluster. This disturbs the independence of the individual finds, as assumed in most randomized statistical tests, hence modifies inferred probabilities, and eventually the confidence level.

Edit: Another example: The probability of six objects randomly found in the same predefined 0.203 fraction of the sky is 7e-5 (the 3.8 sigma); the probability of six objects randomly found in the same predefined 0.379 fraction of the sky is 3e-3 (3.0 sigma). Hence another uncertainty is the size of the region of the sky the six observations are assigned to.