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Thread: Is Planet Nine almost certain, probable, possible or unlikely?

  1. #91
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    Quote Originally Posted by George View Post
    Wouldn't Jupiter spoil any long-lasting satellite orbit for dwarfs in the asteroid belt?
    Did not think of that. The Hill Sphere equation allows for only the object around which the object of interest orbits, not for additional influences. According to this:

    https://en.wikipedia.org/wiki/Hill_s...rther_examples

    Ceres should have space for satellites, but none have ever been detected. Tiny asteroids can have close satellites, for oddly not Ceres. I thought the spacecraft would have spotted one by now.

  2. #92
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    I have to ask some dumb questions: if planet nine is a super earth, then does that not imply it formed in close orbit? And then if it was disturbed by a Jupiter or saturn because of a non harmonic orbit, and got flung outwards, would that not imply an extreme elliptical orbit like a giant comet? And if that is possible then at some period of many thousands of years it would cause major changes to all planet orbits as it approached the sun? And its orbit would be shifted too at close approach.?
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  3. #93
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    Quote Originally Posted by profloater View Post
    I have to ask some dumb questions: if planet nine is a super earth, then does that not imply it formed in close orbit? And then if it was disturbed by a Jupiter or saturn because of a non harmonic orbit, and got flung outwards, would that not imply an extreme elliptical orbit like a giant comet? And if that is possible then at some period of many thousands of years it would cause major changes to all planet orbits as it approached the sun? And its orbit would be shifted too at close approach.?
    Amateur take: If there can be hot Jupiters there can be cold Terrestrials. But, we can't be sure of its orbit without seeing it in motion. And if it came close enough to disrupt inner planets we'd probably have seen evidence of that in our current planetary orbits.


    It could have been flung out eccentrically by Jupiter and then redirected by Uranus or Neptune. If I were creating this system I'd use that as an excuse for why Uranus' axis is so wonky.
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  4. #94
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    Brief piece on current state of the search for Planet Nine.

    https://www.space.com/42177-when-wil...anet-nine.html

    When Will We Find Planet Nine?
    By Mike Wall, Space.com Senior Writer | October 18, 2018 07:30am ET

  5. #95
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    If I read this right, Planet X might be larger than we think, and farther out than we can detect it. Help me out here.


    https://arxiv.org/abs/1810.09771

    Mass of the Kuiper Belt

    E. V. Pitjeva, N. P. Pitjev (Submitted on 23 Oct 2018)

    The Kuiper belt includes tens of thousands of large bodies and millions of smaller objects. The main part of the belt objects is located in the annular zone between 39.4 au and 47.8 au from the Sun, the boundaries correspond to the average distances for orbital resonances 3:2 and 2:1 with the motion of Neptune. One-dimensional, two-dimensional, and discrete rings to model the total gravitational attraction of numerous belt objects are considered. The discrete rotating model most correctly reflects the real interaction of bodies in the Solar system. The masses of the model rings were determined within EPM2017---the new version of ephemerides of planets and the Moon at IAA RAS---by fitting spacecraft ranging observations. The total mass of the Kuiper belt was calculated as the sum of the masses of the 31 largest trans-neptunian objects directly included in the simultaneous integration and the estimated mass of the model of the discrete ring of TNO. The total mass is (1.97 ± 0.30)⋅10^−2 m⊕. The gravitational influence of the Kuiper belt on Jupiter, Saturn, Uranus and Neptune exceeds at times the attraction of the hypothetical 9th planet with a mass of ∼10 m⊕ at the distances assumed for it. It is necessary to take into account the gravitational influence of the Kuiper belt when processing observations, and only then to investigate residual discrepancies to discover a possible influence of a distant large planet.

  6. #96
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    More newly discovered TNOs that make everyone think Something Big Is Out There. We shall see...


    https://arxiv.org/abs/1810.10084

    Dynamical Analysis of Three Distant Trans-Neptunian Objects with Similar Orbits

    T. Khain, et al. (Submitted on 23 Oct 2018)

    This paper reports the discovery and orbital characterization of two extreme trans-Neptunian objects (ETNOs), 2016 QV 89 and 2016 QU 89, which have orbits that appear similar to that of a previously known object, 2013 UH 15. All three ETNOs have semi-major axes a≈172 AU and eccentricities e≈0.77. The angular elements (i,ω,Ω) vary by 6, 15, and 49 deg, respectively between the three objects. The two new objects add to the small number of TNOs currently known to have semi-major axes between 150 and 250 AU, and serve as an interesting dynamical laboratory to study the outer realm of our Solar System. Using a large ensemble of numerical integrations, we find that the orbits are expected to reside in close proximity in the (a,e) phase plane for roughly 100 Myr before diffusing to more separated values. We then explore other scenarios that could influence their orbits. With aphelion distances over 300 AU, the orbits of these ETNOs extend far beyond the classical Kuiper Belt, and an order of magnitude beyond Neptune. As a result, their orbital dynamics can be affected by the proposed new Solar System member, referred to as Planet Nine in this work. With perihelion distances of 35-40 AU, these orbits are also influenced by resonant interactions with Neptune. A full assessment of any possible, new Solar System planets must thus take into account this emerging class of TNOs.

  7. #97
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    Good news for spacecraft trying to get to PLANET 10. It's dancin' time!

    https://phys.org/news/2018-10-team-b...aign=item-menu

    Team makes breakthroughs studying Pluto orbiter mission

    October 24, 2018, Southwest Research Institute

    A Southwest Research Institute team using internal research funds has made several discoveries that expand the range and value of a future Pluto orbiter mission. The breakthroughs define a fuel-saving orbital tour and demonstrate that an orbiter can continue exploration in the Kuiper Belt after surveying Pluto. These and other results from the study will be reported this week at a workshop on future Pluto and Kuiper Belt exploration at the American Astronomical Society's Division for Planetary Sciences meeting in Knoxville, Tennessee.

    Associate Vice President and planetary scientist Dr. Alan Stern leads the SwRI study. The team first discovered how numerous key scientific objectives can be met using gravity assists from Pluto's giant satellite, Charon, rather than propellant, allowing the orbiter to change its orbit repeatedly to investigate various aspects of Pluto, its atmosphere, its five moons, and its solar wind interactions for up to several years. The second achievement demonstrates that, upon completing its science objectives at Pluto, the orbiter can then use Charon's gravity to escape the system without using fuel, slinging the spacecraft into the Kuiper Belt to use the same electric propulsion system it used to enter Pluto orbit to then explore other dwarf planets and smaller Kuiper Belt bodies.

    "This is groundbreaking," said Stern. "Previously, NASA and the planetary science community thought the next step in Kuiper Belt exploration would be to choose between 'going deep' in the study of Pluto and its moons or 'going broad' by examining smaller Kuiper Belt objects and another dwarf planet for comparison to Pluto. The planetary science community debated which was the right next step. Our studies show you can do both in a single mission: it's a game changer."

  8. #98
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    These estimates of Kuiper belt mass makes me wonder if Lowells prediction of Pluto using residuals in the Uranus orbit can now be explained. Or is it policy that Lowells work is to be regarded as a fluke upon pain of exclusion from the modern astronomy community for anybody who thinks differently

  9. #99
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    Quote Originally Posted by peteshimmon View Post
    These estimates of Kuiper belt mass makes me wonder if Lowells prediction of Pluto using residuals in the Uranus orbit can now be explained. Or is it policy that Lowells work is to be regarded as a fluke upon pain of exclusion from the modern astronomy community for anybody who thinks differently
    Recent estimate of the mass of all bodies in the Kuiper Belt, from http://adsabs.harvard.edu/abs/2018CeMDA.130...57P:

    0.02 Earth masses

    Lowell's guess at the mass of Planet X, which he used to compute its predicted position (taken from http://adsabs.harvard.edu/abs/1931ApJ....73....1N:

    0.94 Earth masses

    Even if all the Kuiper-belt objects were clumped together into a single body, which they are most certainly NOT, they have far too little mass to explain the residuals in Neptune's positions.

  10. #100
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    Another new paper with relevance to the search for Planet Nine.

    https://arxiv.org/abs/1804.06859

    Shepherding in a Self-Gravitating Disk of Trans-Neptunian Objects

    Antranik A. Sefilian, Jihad R. Touma (Submitted on 18 Apr 2018 (v1), last revised 25 Nov 2018 (this version, v2))

    A relatively massive and moderately eccentric disk of trans-Neptunian objects (TNOs) can effectively counteract apse precession induced by the outer planets, and in the process shepherd highly eccentric members of its population into nearly-stationary configurations which are anti-aligned with the disk itself. We were sufficiently intrigued by this remarkable feature to embark on an extensive exploration of the full spatial dynamics sustained by the combined action of giant planets and a massive trans-Neptunian debris disk. In the process, we identified ranges of disk mass, eccentricity and precession rate which allow apse-clustered populations that faithfully reproduce key orbital properties of the much discussed TNO population. The shepherding disk hypothesis is to be sure complementary to any potential ninth member of the Solar System pantheon, and could obviate the need for it altogether. We discuss its essential ingredients in the context of Solar System formation and evolution, and argue for their naturalness in view of the growing body of observational and theoretical knowledge about self-gravitating disks around massive bodies, extra-solar debris disks included.

  11. #101
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    If this works it will be interesting to see what turns up as "formerly interstellar".


    https://arxiv.org/abs/1811.09632

    Identifying Interstellar Objects Trapped in the Solar System through Their Orbital Parameters

    Amir Siraj, Abraham Loeb (Submitted on 23 Nov 2018)

    The first interstellar object, `Oumuamua, was discovered in the Solar System by Pan-STARRS in 2017, allowing for a calibration of the abundance of interstellar objects of its size and an estimation of the subset of objects trapped by the Jupiter-Sun system. Photographing or visiting these trapped objects would allow for learning about the conditions in other planetary systems, saving the need to send interstellar probes. Here, we explore the orbital properties of captured interstellar objects in the Solar System using dynamical simulations of the Jupiter-Sun system and random initial conditions. We compare the resulting distributions of orbital elements to those of the most similar population of known asteroids, namely Centaurs, to search for a parameter space in which interstellar objects should dominate and therefore be identifiable solely by their orbits. We find that there should be hundreds of `Oumuamua-size interstellar objects identifiable by Centaur-like orbits in polar or retrograde motion. We note four known objects that may be of interstellar origin. Finally, we estimate that LSST will be able to detect several tens of these objects.

  12. #102
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    What used to take one person years to do is now done in a vastly shorter time, with many more results. Interested in seeing if any of these new TNOs contribute to the discovery of Planet 9 from analyses of their orbits.


    https://arxiv.org/abs/1811.10724

    Astrometry and Occultation predictions to Trans-Neptunian and Centaur Objects observed within the Dark Energy Survey

    Martin Banda-Huarca, et al. (Submitted on 26 Nov 2018)

    Transneptunian objects (TNOs) are a source of invaluable information to access the history and evolution of the outer solar system. However, observing these faint objects is a difficult task. As a consequence, important properties such as size and albedo are known for only a small fraction of them. Now, with the results from deep sky surveys and the Gaia space mission, a new exciting era is within reach as accurate predictions of stellar occultations by numerous distant small solar system bodies become available. From them, diameters with kilometer accuracies can be determined. Albedos, in turn, can be obtained from diameters and absolute magnitudes. We use observations from the Dark Energy Survey (DES) from November 2012 until February 2016, amounting to 4292847 CCD frames. We searched them for all known small solar system bodies and recovered a total of 202 TNOs and Centaurs, 63 of which have been discovered by the DES collaboration until the date of this writing. Their positions were determined using the Gaia Data Release 2 as reference and their orbits were refined. Stellar occultations were then predicted using these refined orbits plus stellar positions from Gaia. These predictions are maintained, and updated, in a dedicated web service. The techniques developed here are also part of an ambitious preparation to use the data from the Large Synoptic Survey Telescope (LSST), that expects to obtain accurate positions and multifilter photometry for tens of thousands of TNOs.

  13. #103
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    Proposal for a new way to hunt for Planet X and beyond.

    https://arxiv.org/abs/1812.08701

    Planet X in CMB and Optical Galaxy Surveys

    Eric J. Baxter, Bhuvnesh Jain, Cullen Blake, Gary Bernstein, Mark Devlin, Gil Holder (Submitted on 20 Dec 2018)

    We consider the possibility of detecting and tracking the hypothesized Planet 9 or other unknown planetary-mass distant solar system members, generically called Planet X, with a combination of CMB and optical imaging surveys. Planets are detectable via thermal emission in CMB surveys and via reflected sunlight in optical surveys. Since the flux from reflected light falls off faster with distance, the signal-to-noise of planetary observations with optical surveys falls off faster than for CMB surveys. A promising approach to detecting new solar system planets with future surveys such as the Simons Observatory, CMB-S4 and LSST, is for a detection in CMB data followed by tracking in the synoptic imaging survey. Even if the parallax were not detected in CMB data, point sources consistent with thermal spectra could be followed up by LSST. In addition to expanding the Planet X discovery space, the joint datasets would improve constraints on key orbital and thermal properties of outer solar system bodies. This approach would work for a Neptune-like planet up to distances of a few thousand AU, and for an Earth-like planet up to several hundred AU. We discuss the prospects for the next decade as well as nearer-term surveys.

  14. #104
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    SHARKS (crossed out) MONGEESE (sic) WITH FRICKIN' LASER BEAMS ATTACHED TO THEIR HEADS

  15. #105
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    Quote Originally Posted by Tom Mazanec View Post
    I thought this bit was the most interesting:
    And there's still another problem with both models: in order to produce the observed effect, the Kuiper Belt needs a collective gravity of at least a few Earth masses.

    Current estimates, however, put the mass of the Kuiper Belt at just 4 to 10 percent of Earth's mass.

    But, according to Solar System formation models, it should be much higher; and, Sefilian notes, it's hard to view the entirety of a debris disc around a star when you're inside it, so it's possible that there's a lot more to the Kuiper Belt than we're able to see.

    "While we don't have direct observational evidence for the disc, neither do we have it for Planet Nine, which is why we're investigating other possibilities," Sefilian said.

    "It's also possible that both things could be true - there could be a massive disk and a ninth planet. With the discovery of each new TNO, we gather more evidence that might help explain their behaviour."
    So even if there isn't a single Planet Nine, there should be a lot more mass out there that has yet to be observed.
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  16. #106
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    It sounds like a classic application of Occam's razor. We have observations that seem to require explanation, and we may be able to explain them with one planet nine, or with a different Kuiper belt than we thought we had (one that includes more mass and more TNOs than we thought), or with a combination of both. These may be quite difficult to distinguish, and indeed even if a planet nine is actually seen, it's possible that its attributes will still be uncertain enough that all these possibilities will remain on the table. So what we will regard as the explanation for the data will be whatever requires some combination of the most plausible values of the fewest free parameters. I'm guessing it will not be a slam dunk no matter how this shakes out.

  17. #107
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    I assume the combo model would reduce the size (and magnitude) of Planet 9, thus helping explain its shyness.
    We know time flies, we just can't see its wings.

  18. #108
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    Quote Originally Posted by Roger E. Moore View Post
    Another new paper with relevance to the search for Planet Nine.

    https://arxiv.org/abs/1804.06859

    Shepherding in a Self-Gravitating Disk of Trans-Neptunian Objects

    Antranik A. Sefilian, Jihad R. Touma (Submitted on 18 Apr 2018 (v1), last revised 25 Nov 2018 (this version, v2))

    A relatively massive and moderately eccentric disk of trans-Neptunian objects (TNOs) can effectively counteract apse precession induced by the outer planets, and in the process shepherd highly eccentric members of its population into nearly-stationary configurations which are anti-aligned with the disk itself. We were sufficiently intrigued by this remarkable feature to embark on an extensive exploration of the full spatial dynamics sustained by the combined action of giant planets and a massive trans-Neptunian debris disk. In the process, we identified ranges of disk mass, eccentricity and precession rate which allow apse-clustered populations that faithfully reproduce key orbital properties of the much discussed TNO population. The shepherding disk hypothesis is to be sure complementary to any potential ninth member of the Solar System pantheon, and could obviate the need for it altogether. We discuss its essential ingredients in the context of Solar System formation and evolution, and argue for their naturalness in view of the growing body of observational and theoretical knowledge about self-gravitating disks around massive bodies, extra-solar debris disks included.
    Here was the original paper questioning the Planet Nine hypothesis.

  19. #109
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    More on Neptune's resonance effects on the Scattered Disk, which includes Eris and the "snowman", Ultima Thule.

    https://arxiv.org/abs/1901.06040

    Neptune's resonances in the Scattered Disk

    Lei Lan, Renu Malhotra (Submitted on 18 Jan 2019)

    The Scattered Disk Objects (SDOs) are thought to be a small fraction of the ancient population of leftover planetesimals in the outer solar system that were gravitationally scattered by the giant planets and have managed to survive primarily by capture and sticking in Neptune's exterior mean motion resonances (MMRs). In order to advance understanding of the role of MMRs in the dynamics of the SDOs, we investigate the phase space structure of a large number of Neptune's MMRs in the semi-major axis range 33-140 au by use of Poincaré sections of the circular planar restricted three body model for the full range of particle eccentricity pertinent to SDOs. We find that, for eccentricities corresponding to perihelion distances near Neptune's orbit, distant MMRs have stable widths that are surprisingly large and of similar size to those of the closer-in MMRs. We identify a phase-shifted second resonance zone that exists in the phase space at planet-crossing eccentricities but not at lower eccentricities; this second resonance zone plays an important role in the dynamics of SDOs in lengthening their dynamical lifetimes. Our non-perturbative measurements of the sizes of the stable resonance zones provide an explanation for the prominence of the N:1 sequence of MMRs over the N:2, N:3 sequences and other MMRs in the population statistics of SDOs, yield a theoretical understanding of the outer boundary of SDOs at perihelion distance near 36 au, and also provide a tool to more easily identify resonant objects.

  20. #110
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    We will be talking about this forever. The mystery planet doesn't exist in my opinion.

  21. #111
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    Quote Originally Posted by Roger E. Moore View Post
    More on Neptune's resonance effects on the Scattered Disk, which includes Eris and the "snowman", Ultima Thule.

    https://arxiv.org/abs/1901.06040

    Neptune's resonances in the Scattered Disk

    Lei Lan, Renu Malhotra (Submitted on 18 Jan 2019)

    The Scattered Disk Objects (SDOs) are thought to be a small fraction of the ancient population of leftover planetesimals in the outer solar system that were gravitationally scattered by the giant planets and have managed to survive primarily by capture and sticking in Neptune's exterior mean motion resonances (MMRs). In order to advance understanding of the role of MMRs in the dynamics of the SDOs, we investigate the phase space structure of a large number of Neptune's MMRs in the semi-major axis range 33-140 au by use of Poincaré sections of the circular planar restricted three body model for the full range of particle eccentricity pertinent to SDOs. We find that, for eccentricities corresponding to perihelion distances near Neptune's orbit, distant MMRs have stable widths that are surprisingly large and of similar size to those of the closer-in MMRs. We identify a phase-shifted second resonance zone that exists in the phase space at planet-crossing eccentricities but not at lower eccentricities; this second resonance zone plays an important role in the dynamics of SDOs in lengthening their dynamical lifetimes. Our non-perturbative measurements of the sizes of the stable resonance zones provide an explanation for the prominence of the N:1 sequence of MMRs over the N:2, N:3 sequences and other MMRs in the population statistics of SDOs, yield a theoretical understanding of the outer boundary of SDOs at perihelion distance near 36 au, and also provide a tool to more easily identify resonant objects.
    A layperson's summary of this would be nice to have.

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  22. #112
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    Quote Originally Posted by Swift View Post
    So even if there isn't a single Planet Nine, there should be a lot more mass out there that has yet to be observed.
    Which is more probable, I wonder? I'm inclined to agree with Mike Brown (from his findplanetnine website):

    ...

    So, is Planet Nine really just an eccentric inclined ring of icy bodies?

    As happy as I am to see alternative hypotheses, and as correct as I think the underlying physics of this paper is, I think it is utterly unlikely that our solar system has a massive eccentric inclined ring of material. There are two major reasons why this seems somewhere between implausible and impossible to me. First, the ring needs to contain something like 10 times the mass of the Earth. Current estimates of the amount of material in the Kuiper belt are about 100-500 times smaller than that. Could we be wrong by a factor of 100-500? Sure. There are always ways to conspire to hide things in the outer solar system, but that is an awful lot of mass to hide.

    Second, it is critical to ask: why would there be a massive eccentric inclined ring of material in the distant solar system in the first place? The new paper doesn’t address this question at all. It simply shows that if such a carefully arranged ring is put into place by fiat it can stabilize itself (Konstantin doesn't think such a disk is stable over the age of the solar system, but that's beyond my pay grade; the new paper doesn't realistically address the question so it's hard for me to know) and can cause the same effects that Planet Nine would. But I can’t think of any remotely plausible reason such a disk would be there in the first place. Basically the answer to “why do we see a disk of distant eccentric inclined Kuiper belt objects?” is “because there is a much more massive disk of even more distant eccentric inclined Kuiper belt objects keeping it in place.”

    ...

    The Planet Nine hypothesis, on the other hand, explains the observations and is considerably simpler. One planet, scattered into the outer solar onto a eccentric inclined orbit, explains a host of otherwise unexplainable phenomenon. As breathtaking as the idea that there might be a new planet out there is, the steps to get there are really rather mundane. This new alternative is a much more complicated answer to the same question. Usually in science we prefer the simpler solution. Again, this doesn’t guarantee that it is true, but that there needs to be some compelling reason to believe that the simpler explanation is wrong and the more complicated one is correct. I can’t see any such reason.

    The good news, though, is that a ring of bodies is significantly easier to find than a single planet. While I would argue that it should already have been found if it existed, at least we can all agree that something remains out there to be found...
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  23. #113
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    Quote Originally Posted by A.DIM View Post
    I'm inclined to agree with Mike Brown (from his findplanetnine website):

    ...
    Second, it is critical to ask: why would there be a massive eccentric inclined ring of material in the distant solar system in the first place? ...
    Well, something had to knock over one of our ice giants. What would have went with the debris? Maybe it goes all Ulysses when Scholz's star passes through and that torques the belt, with some...er...ah... precession over time---flailing here mind you....
    Last edited by publiusr; 2019-Feb-05 at 11:10 PM.

  24. #114
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    More detail on what and where Planet Nine might be.

    https://arxiv.org/abs/1902.10103

    The Planet Nine Hypothesis

    Konstantin Batygin, Fred C. Adams, Michael E. Brown, Juliette C. Becker (Submitted on 26 Feb 2019)

    Over the course of the past two decades, observational surveys have unveiled the intricate orbital structure of the Kuiper Belt, a field of icy bodies orbiting the Sun beyond Neptune. In addition to a host of readily-predictable orbital behavior, the emerging census of trans-Neptunian objects displays dynamical phenomena that cannot be accounted for by interactions with the known eight-planet solar system alone. Specifically, explanations for the observed physical clustering of orbits with semi-major axes in excess of ∼250 AU, the detachment of perihelia of select Kuiper belt objects from Neptune, as well as the dynamical origin of highly inclined/retrograde long-period orbits remain elusive within the context of the classical view of the solar system. This newly outlined dynamical architecture of the distant solar system points to the existence of a new planet with mass of m 9 ∼5−10M ⊕ , residing on a moderately inclined orbit (i 9 ∼15−25° ) with semi-major axis a 9 ∼400−800 AU and eccentricity between e 9 ∼0.2−0.5 . This paper reviews the observational motivation, dynamical constraints, and prospects for detection of this proposed object known as Planet Nine.

  25. #115
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    Quote Originally Posted by Roger E. Moore View Post
    More detail on what and where Planet Nine might be.

    https://arxiv.org/abs/1902.10103

    The Planet Nine Hypothesis

    Konstantin Batygin, Fred C. Adams, Michael E. Brown, Juliette C. Becker (Submitted on 26 Feb 2019)

    Over the course of the past two decades, observational surveys have unveiled the intricate orbital structure of the Kuiper Belt, a field of icy bodies orbiting the Sun beyond Neptune. In addition to a host of readily-predictable orbital behavior, the emerging census of trans-Neptunian objects displays dynamical phenomena that cannot be accounted for by interactions with the known eight-planet solar system alone. Specifically, explanations for the observed physical clustering of orbits with semi-major axes in excess of ∼250 AU, the detachment of perihelia of select Kuiper belt objects from Neptune, as well as the dynamical origin of highly inclined/retrograde long-period orbits remain elusive within the context of the classical view of the solar system. This newly outlined dynamical architecture of the distant solar system points to the existence of a new planet with mass of m 9 ∼5−10M ⊕ , residing on a moderately inclined orbit (i 9 ∼15−25° ) with semi-major axis a 9 ∼400−800 AU and eccentricity between e 9 ∼0.2−0.5 . This paper reviews the observational motivation, dynamical constraints, and prospects for detection of this proposed object known as Planet Nine.
    If they know its orbit, then it seems to me that its visual discovery shouldn't be that far away. I saw on Phil's blog that Does Planet 9 Exist? <All signs (still) point to 'yes'>. So it seems that he is in favor of its existence.

    A dumb question what does "∼5−10M ⊕" mean?

  26. #116
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    Quote Originally Posted by bknight View Post
    A dumb question what does "∼5−10M ⊕" mean?
    The mass of the planet is between 5 and 10 times the mass of the Earth. (I would put the error bars a bit wider.)
    Forming opinions as we speak

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    Quote Originally Posted by antoniseb View Post
    The mass of the planet is between 5 and 10 times the mass of the Earth. (I would put the error bars a bit wider.)
    Thanks I have never seen that nomenclature.

  28. #118
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    The farther out you go, the fewer Little Rocks you find. Why? This implies Planet Nine will have interesting cratering.

    https://arxiv.org/abs/1902.10795

    Impact Craters on Pluto and Charon Indicate a Deficit of Small Kuiper Belt Objects

    K. N. Singer, et al. (Submitted on 27 Feb 2019)

    The flyby of Pluto and Charon by the New Horizons spacecraft provided high-resolution images of cratered surfaces embedded in the Kuiper belt, an extensive region of bodies orbiting beyond Neptune. Impact craters on Pluto and Charon were formed by collisions with other Kuiper belt objects (KBOs) with diameters from ~40 kilometers to ~300 meters, smaller than most KBOs observed directly by telescopes. We find a relative paucity of small craters less than approximately 13 kilometers in diameter, which cannot be explained solely by geological resurfacing. This implies a deficit of small KBOs (less than 1 to 2 kilometers in diameter). Some surfaces on Pluto and Charon are likely greater than 4 billion years old, thus their crater records provide information on the size-frequency distribution of KBOs in the early Solar System.

  29. #119
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    3,199
    Pluto turns out to be a complicated, ever-changing world with seasons. Planet Nine is probably complicated, too.

    https://arxiv.org/abs/1903.02096

    The CH4 cycles on Pluto over seasonal and astronomical timescales

    T. Bertrand, et al. (Submitted on 5 Mar 2019)

    New Horizons observations suggest that CH4 on Pluto has a complex history, involving reservoirs of different composition, thickness and stability controlled by volatile processes occurring on different timescales. In order to interpret these observations, we use a Pluto volatile transport model able to simulate the cycles of N2 and CH4 ices over millions of years. By assuming fixed solid mixing ratios, we explore how changes in surface albedos, emissivities and thermal inertias impact volatile transport. This work is therefore a direct and natural continuation of the work by Bertrand et al. (2018), which only explored the N2 cycles. Results show that bright CH4 deposits can create cold traps for N2 ice outside Sputnik Planitia, leading to a strong coupling between the N2 and CH4 cycles. Depending on the assumed albedo for CH4 ice, the model predicts CH4 ice accumulation (1) at the same equatorial latitudes where the Bladed Terrain Deposits are observed, supporting the idea that these CH4-rich deposits are massive and perennial, or (2) at mid-latitudes (25°N-70°N), forming a thick mantle which is consistent with New Horizons observations. In our simulations, both CH4 ice reservoirs are not in an equilibrium state and either one can dominate the other over long timescales, depending on the assumptions made for the CH4 albedo. This suggests that long-term volatile transport exists between the observed reservoirs. The model also reproduces the formation of N2 deposits at mid-latitudes and in the equatorial depressions surrounding the Bladed Terrain, as observed by New Horizons. At the poles, only seasonal CH4 and N2 deposits are obtained in Pluto's current orbital configuration. Finally, we show that Pluto's atmosphere always contained, over the last astronomical cycles, enough gaseous CH4 to absorb most of the incoming Lyman-flux.

    ===

    https://arxiv.org/abs/1903.02315

    Pluto's lower atmosphere and pressure evolution from ground-based stellar occultations, 1988-2016

    E. Meza, et al. (Submitted on 6 Mar 2019)

    Pluto's tenuous nitrogen (N2) atmosphere undergoes strong seasonal effects due to high obliquity and orbital eccentricity, and has been recently (July 2015) observed by the New Horizons spacecraft. Goals are (i) construct a well calibrated record of the seasonal evolution of surface pressure on Pluto and (ii) constrain the structure of the lower atmosphere using a central flash observed in 2015. Method: eleven stellar occultations by Pluto observed between 2002 and 2016 are used to retrieve atmospheric profiles (density, pressure, temperature) between ∼ 5 km and ∼ 380 km altitude levels (i.e. pressures from about 10 microbar to 10 nanobar). Results: (i) Pressure has suffered a monotonic increase from 1988 to 2016, that is compared to a seasonal volatile transport model, from which tight constraints on a combination of albedo and emissivity of N2 ice are derived; (ii) A central flash observed on 2015 June 29 is consistent with New Horizons REX profiles, provided that (a) large diurnal temperature variations (not expected by current models) occur over Sputnik Planitia and/or (b) hazes with tangential optical depth of about 0.3 are present at 4-7 km altitude levels and/or (c) the nominal REX density values are overestimated by an implausibly large factor of about 20% and/or (d) higher terrains block part of the flash in the Charon facing hemisphere.

  30. #120
    Join Date
    Sep 2004
    Posts
    3,199
    Pluto might have an ocean? Could Planet Nine have an ocean, too?

    https://arxiv.org/abs/1903.05574

    Reorientation of Sputnik Planitia implies a Subsurface Ocean on Pluto

    F. Nimmo, et al. (Submitted on 13 Mar 2019)

    The deep nitrogen-covered Sputnik Planitia (SP; informal name) basin on Pluto is located very close to the longitude of Pluto's tidal axis[1] and may be an impact feature [2], by analogy with other large basins in the solar system[3,4]. Reorientation[5-7] due to tidal and rotational torques can explain SP's location, but requires it to be a positive gravity anomaly[7], despite its negative topography. Here we argue that if SP formed via impact and if Pluto possesses a subsurface ocean, a positive gravity anomaly would naturally result because of shell thinning and ocean uplift, followed by later modest N2 deposition. Without a subsurface ocean a positive gravity anomaly requires an implausibly thick N2 layer (greater than 40 km). A rigid, conductive ice shell is required to prolong such an ocean's lifetime to the present day[8] and maintain ocean uplift. Because N2 deposition is latitude-dependent[9], nitrogen loading and reorientation may have exhibited complex feedbacks[7].

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