Tuesday, January 19, 2016

Is Planet Nine a "planet"?

In 2006, when the International Astronomical Union codified what we mean when we say the word "planet," I was quoted multiple times saying something like, "That's it. That's the end of planets. We get eight in this solar system and that will have to be enough. Since 1845 there have been no new ones to discover."

I was wrong.

We think that Planet Nine is between 5 to 10 times the mass of the Earth (some evidence that we are continuing to examine suggests that it might even be closer to 20 times the mass of the Earth; Konstantin is optimistic; I'm skeptical; such tensions are what keep collaborations like ours honest). That puts it at a little smaller than Neptune.

But is it a planet? The IAU definition of planet includes the clunky phrase that it has to "clear its orbit." Really, this phrase is just an attempt to explain the concept that planets are the gravitational dominant things of planetary system and that one of the ways they display their gravitational dominance is by pushing around everything in their path. Overly literal critics of the IAU definition will insist that because Jupiter has asteroids which co-orbit with it (the Jupiter Trojans) that Jupiter is not a plane by this definition, etc. etc., but that is simply a problem with the clunkiness of the statement of the definition, not of the underlying concept.

Is Planet Nine gravitationally dominant? I think it is safe to say that any planet whose existence is inferred by its gravitational effects on a huge area of the solar system is gravitationally dominant.

If that is not good enough for you, though, astronomer Jean-Luc Margot at UCLA has recently written a nice paper finally quantifying what the phrase "clear its orbit" really means. To clear an orbit, an object has to be a certain size, given its distance. I've taken the key figure from his paper, which shows the planets of the solar system and compares them to the "planet" criterion (note that all of the planets are well above the planet line, while the 3 dwarf planets are well below it; this wide separation between planets and dwarf planets is another indicator of how solid the concept of gravitational dominance in the solar system is). If we extend this figure out to the distance and mass of Planet Nine, we find that it, too, is above the planet line for all of our considered cases.



(technical note: Margot has several different criteria for clearing; we prefer the "clear the feeding zone in 4.5 billion years" criterion, which is the line that we have extended).

For for much of the predicted range and size of Planet Nine it is comfortably above the line, at its most distant possible orbit and its smallest possible mass, Planet Nine just barely scrapes by as a planet by this calculation. However, we believe that if it really is on the most distant of possible orbits it is probably on the more massive side. Why? Because if it is going to have the effects that we have seen, it needs to be even more massive if it is further away. In short: no matter where it is, the one thing we know for sure about Planet Nine is that it is dominating the outer edge of the solar system. That is enough to make it a planet by anyone's calculation.

69 comments:

  1. there are many powerful telescopes out there which can look far deeper in the space then why it took so much time to find this ninth planet in our own solar system ? I may be wrong but its a prediction that there might be a big planet, there hasn't been any discovery so far ?

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    1. I would guess because we aren't sure where to point those telescopes. To find this planet with a telescope would would need to know precisely where to find it. While it is easy to observe distant stars because of their light, this mysterious planet is dark and cold. So hopefully with this recent hypothesis, we will be able to point a telescope precisely where we predict we will find this planet, and determine the truth.

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  2. David Rothery of the Open University just mentioned this 1999 prediction of a large planet in a FB study group I'm in http://m.mnras.oxfordjournals.org/content/309/1/31.short
    Abstract

    Aphelion distances of long-period comets show a slight excess around 30 000 to 50 000 au from the Sun. Positions of cometary aphelia within these distance limits are aligned along a great circle inclined to both the ecliptic and the Galactic plane. This paper examines one of the possible explanations for this non-random clustering: that it is due to orbital perturbations by an undiscovered object orbiting within the above-mentioned distances.

    It is very unlikely that you don't know of it, but I thought I'd pop the info here anyway.

    MNRAS (1999) 309 (1): 31-34. doi: 10.1046/j.1365-8711.1999.02806.x First published online October 1, 1999

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    1. Replying to my own comment, this issue about comets is dealt with (and discounted) in the 24 January update here.

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  3. And this
    http://m.mnras.oxfordjournals.org/content/335/3/641.short

    MNRAS (2002) 335 (3): 641-654. doi: 10.1046/j.1365-8711.2002.05649.x First published online September 21, 2002

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  4. Wonder about the long stability of the Pluto:Neptune 3:2 resonance to this?

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  6. This may sound a little naive; but could Planet 9 be something else with mass, like a wormhole, or other anomaly? I'm basing this purely on having seen Interstellar and an over active imagination currently being fed with enthusiasm ignited by you exciting announcements/research.

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    1. No. It would have to have significantly more mass than the prediction, say a million times more massive. Stop watching fantasy and believing it to be real or anything close to scientifically accurate.

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    2. I'm definitely in the "scientifically literate but not a scientist" camp, but I don't get why it would need to be a million times more massive.

      If it were a black hole with 10 Earth masses, sure, it would have an event horizon with a 3.5" radius, but it will still have the mass and gravitational effect of a 10 Earth mass object.

      Since it has only been observed by its gravitational effects, really it could be most any object out there - planet, black hole, alien mega-structure, giant space hamster, whatever - as long as the mass was in the proper range.

      Now, I don't think it's a wormhole or anything extreme like that either. It's assumed to be a planet because the only sort of object that would naturally exist with that sort of mass and that sort of orbit is a planet (and let's not even get into unnatural explanations). But a black hole/wormhole/any kind of hole wouldn't need to be millions of times more massive to have that effect, it would need to have the same mass range to have that same gravitational effect. At least as I understand it.

      An artificially created Interstellar-like wormhole with the mass of 10 Earths would have the same gravitational effect. Not sure how effective of a wormhole it would be with an event horizon of about 7 inches across - maybe combine Interstellar and Fantastic Voyage and shrink down Matthew McConaughey or something. :)

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    4. Chickenkiller,

      The first part of your answer was useful, thank you; the second part no so much. I'm not a complete idiot, just an idiot with an imagination.

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  7. Well I think ladies and gentlemen that the myth of Planet X or Nibiru has just been confirmed. My imagination is going crazy right now.

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  8. typo "not a plane by this definition" (missing t). feel free to delete this comment.

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  9. HAHA! what about these 5 facts about planet 9 :P
    https://t.co/DjpVyLeFUa

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  10. Dr. Brown (wow, sounds like it's BackToTheFuture, am I number 3334 coming up with that joke? :-) ),

    thanks for that clarification. May I ask a question (you have probably already answered in some publication, that one can read in the web?)? Many proponents of Pluto-Planet-Eris-Planet etc. concept tend to, rather than arguing on what exactly means "clearing its orbit", state that "gravitational dominance" in any form is not an appropriate classification factor for a planet at all. And that the internal structure is what matters here (usually closely related to the mass and usually resulting in a spherical-nonspherical shape). And just as it is "fusion (at least in the past) -> star", it should be "active tectonics -> planet". Then Pluto will definitely be a planet. An obvious exception are of course huge planet satellites (it's anyway all about gravitational dominance in this case), but these are usually easy to tell :-)

    You've obviously considered that concept, and you have most probably (being The Pluto Killer) found it wrong. Why?

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  12. the highly controversial IAU planet definition was adopted by just four percent of its members, most of whom are not planetary scientists but other types of astronomers

    I'm a geologist who looks at rocks, not computer screens. I spent a long time pushing for the "rounded by self gravity" criterion. BUT I recently read Hal Levison's "hand waving" argument on dynamics (Google it; it's on SWRI.EDU). This tightens the "clear it's orbit" argument. I note that NONE of the Levison-criterion-planets are non - round.
    From a DYNAMICs point of view, I see the point. (And I'll be reading the linked article shortly) But this RockSniffer accepts the IAU definition. Reluctantly, but I accept it.
    Pluto isn't a planet.

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  13. Rank amateur here. I understand that each of the known planets have their rotational axes pointing in different directions, and that these axes shift over time, according to axial precession. For example, Earth's north pole currently points towards Polaris, but over a period of 26,000 Earth years, that direction rotates around. Each planet has its own rate of precession and period. I found the link below from 2011, which lists the planets’ various rates. It points out that Venus' rate is way off from what is predicted (because it's more sensitive to perturbations). So, would Planet Nine, being massive and significantly off the ecliptic, have a measurable effect on axial precessions, such as Venus', which were not previously predicted, as well as having effects on the Kuiper belt objects? If Venus' (or some other planets') precessions had resonances aligned with the Kuiper belt objects, might that somehow help predict the location of Planet Nine?

    http://farside.ph.utexas.edu/teaching/336k/Newtonhtml/node115.html

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    1. As it turns out, space is big.

      I did some more digging, and it appears I conflated two kinds of precession in my post yesterday. Axial precession is distinct from perihelion precession, which is the topic at the U Texas link. At this point I have more questions than there are questions.

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  14. How does (if at all) the discovery of a new planet affect the current data about the solar system and it’s bodies’ angular momentum, mass or orbital periods? Would we need to for example recalibrate Jupiter’s mass or orbital period. What if it had been an inner planet discovery?

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    1. P9 dominates the angular momentum budget of the solar system. We're studying what the implications of that might be!

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  15. Amateur rank here as well. I've noticed that the predicted orbit for this new planet would be well beyond the heliosphere. How would the extremely high flow of cosmic rays alter the planet's characteristics?

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  16. Would this planet pull earth? I'm hearing it would on March 26th but that doesn't make any since due to how far it is.

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    1. This planet has less of an effect on the earth than all of the other planets combined.

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    2. This planet does not exist. You have no direct evidence and even your indirect evidence is suspect. You need to stop talking about it like it's a fact already. As a "scientist" you should be the first to exercise caution in how you represent your findings. It's going to be embarrassing enough when this turns out to be wrong, but even more so since you are talking about it as if it's fact.

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    4. Mike, it was scientists in the day that thought the Earth was flat. The Bible affirms and always has affirmed that it is spherical. In fact, the Bible also affirmed that the stars were innumerable when science claimed there were only thousands. The Bible affirmed that stars were different in kind from one another when scientists claimed they were all the alike. Medical Science in the day thought that you needed to bleed people to get rid of diseases when the Bible said the blood is the life.

      And as far as respected scientists go, Si Isaac Newton is recognized as one of the greatest scientists of all time and guess what? He was a young earth creationist. So, maybe if someone that intelligent says something, people should stand up and take notice. You for instance.

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    6. "Sir Issac Newton had no knowledge of modern day geology so he can be excused for being naive about the age of the Earth and universe;"

      Actually, he should be commended for understanding the truth whereas you can not be excused considering the preponderance of evidence "against" billions of years.

      "there's nothing wrong with being religious per se and I'm sure Newton was intelligent enough to understand that the laws of physics which he helped to define ARE God's laws of this universe."

      Indeed he was, as he said things like the following:

      “This most beautiful system of the sun, planets and comets, could only proceed from the counsel and dominion of an intelligent and powerful Being.”

      But he also knew that God could be trusted and it's God's word in the Bible that tells us that the universe did not start as a big bang billions of years ago.

      "Using the Bible as a "book of science" is naive beyond comprehension!"

      I never said it was a science book. I merely pointed out a few facts from the Bible that show how the Bible was correct and science was wrong. If you believe that you can refute the truth of those statements then please try. And when you come to the conclusion that you can't, because facts are facts, then please explain how the Bible authors knew things that scientists didn't. Coincidence? I think not.


      "If this universe were only a paltry few thousand years old, it would be nothing but a gravity well--a small, incredibly dense black hole--at best or maybe a radioactive waste zone (of nothing but incredibly dangerous, concentrated energy) at worst!"

      You assume that if the universe were only 6,000 years old then that it would mean it was an "evolving" thing instead of created as-is just for the purpose it serves.

      "There are too many stars, too many galaxies to cram within a 6,000 light-year radius of Earth to avoid one of these two catastrophic scenarios."

      No one ever said it was a 6,000 light year radius. You are obviously referring to the light-travel problem. Horizon Problem anyone? Oh, inflation solves that? Right, a fictional scenario invented to solve a problem that proves the big bang false. Science at its best.

      "Again, have fun at your Flat Earth Society meeting--or whatever whack-job meeting you attend regularly!"

      The irony is that your beliefs are the ones crazier than flat-earth ideas. Not mine.

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    8. "You clearly have NO understanding of the universe and no understanding of the laws that govern it so you're utterly unqualified to contribute any intelligent comments to this forum."

      Stating that does in no way prove it. It only demonstrates that you have no intelligent response to the things I stated.

      "Please, go out, purchase a gun, put it up to the side of your head, and pull the trigger!"

      Now you are advocating I kill myself or rather that you'd like to see me dead. That is a typical response from someone who probably believes there is no purpose to life and that we are only evolved ape-like creatures. It also shows you still have no response to the statements I put forth.

      "The collective IQ of the human race will only go up a small amount but at least it will go up!"

      I have a a 3.97 GPA in college and have tested quite well on I.Q. tests. So, your outright ad hominem attack is just that.

      "Shame on me for getting baited into a trap set by an utter simpleton!!!!!!!!!!!!!!"

      Shame on you for believing the lies that have been spoon fed to you by people who reject God. When you can actually refute what I've stated, please come back and give it a shot.

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    10. Anyone reading your responses can only conclude that "you" are the one babbling mindlessly. I stated some facts and you came back not with refutations, but ad hominems and wishing I'd kill myself. Why don't you at least try to show us how intelligent you are. Please explain how there can be comets in our solar system if the solar system is billions of years old? If you say the Oort cloud then please provide the rock-solid, observational evidence that such a cloud actually exists.

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    12. You can't argue with the truth. I can understand your frustration though. It can be infuriating to believe something your whole life only to find out it's all been a lie. No one wants to be the fool. But the truth is that it's easier to fool someone then to convince them they've been fooled.

      More baseless accusations? I've never taken drugs nor do I drink.

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    14. If I'm such a simpleton, why am I the only one in this conversation willing to discuss the issue and you are the one making baseless accusations and slinging ad hominems? It's no wonder you've deleted your other responses. You know it makes you look bad.

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    16. Well, I can see why you'd want me to delete this because it makes you look like a whiny brat throwing a temper tantrum because he can't verbalize a coherent response. I know that's a bit harsh, but your responses really are quite childish.

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    18. Mike Post said: "I was expecting too much from a simpleton. Go flatter yourself somewhere else...unbelievable!"

      I'll make sure to post what you said every time now before responding. So people can see your responses even though you are deleting them.

      Now, about that comet problem. Can you please explain, please so we can see that you are not the simpleton that you claim I am?

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    20. Mike Post said: "I only have conversations with intelligent people who have intelligent things to say, simpleton! Again, go flatter yourself somewhere else!"

      I think the issue of comets is a good topic to discuss. It's a big problem for those who believe the solar system is billions of years old. There is currently no actual scientific evidence to explain why they are still around. I'm asking you to provide some scientific evidence for how they can still exist. And you don't think this is a worthy topic?

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    21. Well, it is up to our hosts, but in my experience, the best comment communities are those that can self-moderate. With that in mind, I humbly suggest that the two of you bickering and name-calling adds nothing to the discussion about this possible planet. So if you want to debate further, I would personally suggest taking it to email. I'm guessing our hosts would prefer a more mature and productive level of discourse here. If they think I have overstepped my bounds, I apologize, but it would be nice to not have a precedent set of comments devolving to this level.

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    22. I agree, Ken. I would be happy to engage in a mature and productive discussion. Do you not see that I am willing to do that, but Mike Post is not? Isn't it obvious from his responses that he is the one causing the issue here? You may not agree with my position, but I think you can agree that my side of the discussion has been an attempt to actually have a mature discussion. I admit I responded to his childish remarks and called him out on it a little harshly, but yeah, I'm human and it gets frustrating when I try to have a mature discussion and someone just attacks me with baseless accusations and ad hominems.

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    24. Mike Post said: "Let's do everyone a favor and delete this entire line of rubbish postings, shall we?"

      Why can't we just have a mature discussion? Let's talk about how the solar system can't be billions of years old. There are many scientific evidences that point to a young solar system with comets being one of them. The reason the topic is relevant is because in order for this Planet 9 theory to be correct, it requires millions of years in order for the orbits of the TNOs to be perturbed in the way suggested.

      So, if anyone can provide scientific proof to explain the existence of comets in our "supposedly" old solar system, then please do so. And as I've already stated, the Oort Cloud cannot be used as a proof since it has never been observed and there is indeed no direct evidence for its existence. In fact, the only "evidence" for its existence is that it "must" exist for the solar system to be as old as claimed, which is obviously circular reasoning. Claiming something "must" exist because you are assuming your belief is correct to begin with is not science. So, please provide actual scientific evidence for why comets can exist in an old solar system.

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  17. What is up with your obession with denying dwarf planets inclusion as a subcategory of planet. Most cashews consumed worldwide are dwarf cashews. Why is it that no one bothers to call them dwarfs? Maybe because they have a life. The sun is a dwarf sun. There are dwarf owls. Dwarf rhinoceri. Dwarf possums. Dwarf humans. Neptune is actually number nine. Pluto is number ten. Charon is number eleven. Shall I go on?

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    1. For the most part your analogies are too simple, if not naive. (For starters, the sun is actually a type G2V yellow dwarf, but it's more than just that.) And just as thermonuclear fusion is the defining characteristic of a star vs a sub-stellar object like a brown dwarf, gravitational dominance is now the defining characteristic of planet vs a sub-planetary object like a dwarf planet. Ceres is a runt and can't even clear out a few chumpy rocks in its vicinity and Pluto is such a runt in its neighborhood that Neptune plays loop-to-loop with Pluto like it's some kind of toy yo-yo or something. That's simplifying the actual celestial mechanics, of course, but maybe that will help you to understand what's going on. There are plenty of intelligent sources online if you wish to educate yourself further on the subject. The IAU definition of planet definitely could use a few tweaks but the gist of what it's saying is dead on target (see my lengthy post below for a suggested tweak or two). Have a great day!

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  18. Mike, you have extended the wrong line for your argument. The upper, dotted line shows clearing in 4,6 billion years which is what you (and all of us) prefer. Unfortunately, it cuts very UNcomfortably right through the box :)

    /Kjell Olauson, Orebro Astronomi, Sweden (info@orebroastronomi.se)

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    1. The figure caption is a bit ambiguous, but, no, we extended the "clearing the **feeding zone** line" not the 5 Hill radius line.

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    2. You are assuming there were billions of years. The universe and everything in it are only about 6,000 years old. Thus, all your assumptions and calculations are based on faulty science and cannot be trusted. Short period comets alone prove the solar system is young. Pluto was shown to be young, various moons and planets also prove it is young. Blue stars prove it is young. The horizon problem proves it is young. And so on.

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    3. OK, got you. The line for 2√3 in 4,6 billion yrs wasn't actually in the diagram but I suppose it pretty much coincided with the dashed line. Thank you for the clarification.

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  19. Astronomer Jean-Luc Margot has tweaked the IAU's "basic" definition of a planet in recent times to include, among other things, exoplanets and an upper mass limit for planets to differentiate them from sub-stellar objects (i.e., brown dwarf vs. giant planet).

    While this is certainly admirable, what's needed (in my humble opinion) is more than one criterion for demonstrating and defining what 'dynamical dominance' can actually mean: 'clearing the neighborhood' of primordial planetesimals using JLM's 'lambda' discriminator (or similar); dominating a belt or zone populated with a multitude of other but much smaller rounded objects (which Ceres doesn't do) by locking said objects in mean-motion resonant orbits (which 'Planet Nine', if it exists, already seems to be doing); or any other measure that says "Hey, I'm the boss around here so get!"

    What's also needed is a simple sub-class for non-player objects (like dwarf planets) and those that don't otherwise fit the dominant-players club of 'planet' (like a terrestrial-size planet (or larger) sitting in the farthest reaches of a solar system below JLM's lamba cut-off point).

    To that end, I propose the following enhanced definition of JLM's already excellent revised IAU planet defintion:

    A planet is a celestial body that...

    (a) is in orbit around one or more stars or stellar remnants;
    (b) has sufficient mass to either...
    (i) clear [or dynamically dominate] the neighborhood around its orbit, i.e., Π ≥ 1; OR, if Π < 1,
    (ii) lock smaller rounded bodies (in hydrostatic equilibrium), with a combined mass ≥ 100x < its standalone mass, into mean-motion resonant orbits;
    (c) has a mass below 13 Jupiter masses, a nominal value close to the limiting mass for thermonuclear fusion of deuterium.

    A subplanet is a celestial body that:

    (a) exhibits one of the following orbital characteristics:(i) is in orbit around one or more stars or stellar remnants
    (and will be sub-classified by mass {e.g., dwarf planet, terrestrial, or other such sub-classification as needed});
    OR (ii) is not in orbit around a star or stellar remnant (and will be sub-classified as a rogue planet or other sub-classification as needed);
    (b) has sufficient mass to overcome rigid body forces to assume hydrostatic equilibrium (roughly rounded shape);
    (c) has a mass below 13 Jupiter masses, a nominal value close to the limiting mass for thermonuclear fusion of deuterium;
    (d) has not cleared the neighborhood around its orbit and has not locked smaller rounded bodies (in hydrostatic equilibrium) into mean-motion resonant orbits;
    (e) is not a satellite.

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    1. Please forgive any formatting miscues in the following suggested taxonomy that covers all non-clustered celestial objects:

      Stellar Mass Object (SMO)
      Main Sequence Stars - O-B-A-F-G-K-M (classified by surface temperature)
      Stellar Remnants (white/black dwarfs, neutron stars, black holes, pulsars/magnetars, etc.)

      Sub-Stellar Mass Object (SSMO)
      Brown Dwarfs (mass range in Jupiter masses < minimum SMO mass)
      Sub-Brown Dwarfs (>=13 Jupiter masses to minimum brown dwarf mass)

      Planetary Mass Object (PMO) - All roughly rounded celestial objects < ~ 13 Jupiter masses
      Planet (1) orbits one or more stars or stellar remnants;
      (2) cleared the neighborhood of [or is dynamically dominant in] its orbit using a planetary discriminant (e.g., JLM's "pi" or Stern-Levison's "lamba" value); OR,
      demonstrates gravitational dominance using a "non-discriminant standard"
      (e.g., locks other PMOs in mean-motion resonant orbits, etc.).
      Uberplanet (non-dwarf planet)
      (1) orbits one or more stars or stellar remnants;
      (2) has not cleared the neighborhood of its orbit;
      (3) has a mass >= Mercury (or other planetary mass >= "terrestrial").
      Unterplanet (dwarf planet)
      (1) orbits one or more stars or stellar remnants;
      (2) has not cleared the neighborhood of its orbit;
      (3) has a mass < Mercury (or other planetary mass < "terrestrial");
      (4) is not a satellite.
      Rogue planet (free-floating, etc.)
      (1) does not orbit a star or stellar remnant;
      (2) is not a satellite.
      Ubersatellite (superior satellite or regular moon)
      (1) does not directly orbit a star or stellar remnant;
      (2) orbits another planetary mass object (PMO).

      Sub-Planetary Mass Object (SPMO) - All other non-rounded celestial objects
      Untersatellite (inferior satellite or irregular moon)
      (1) does not directly orbit a star or stellar remnant;
      (2) orbits a PMO or another sub-planetary mass object (SPMO).
      Asteroids/planetoids (belt, Trojan, etc.)
      Comets

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    2. Like it or not, the IAU definition of planet formulated in 2006 has withstood at least three "attempts" at revision when the IAU last met in 2009, 2012, and 2015 that all failed. That says something about its legitimacy as a working definition (that's admittedly not perfect). And like it not, the term planet is semantic (and arguably cultural) shorthand for "classical planet", "major planet", "primary planet", and any other term that invokes the notion of a superlative (i.e., the biggest and the baddest "players" in a given solar system). When people ask "How many planets are there?" they're really asking "How many major planets are there?" The term planet is here to stay.

      What's needed is a more practical and intuitive taxonomy that remains simple and consistent and yet allows virtually all celestial objects to be classified in a way everyone can understand. (This system of taxonomy should also be free of sentimentality and petty politics like Stern's planet-happy assertion that Titan and Ganymede are "planets" as well.) This system should also be free of semantic inconsistencies and slippery claims: for instance, that location is a baseless criterion for a system of taxonomy; e.g. 'If the Earth (or Jupiter for that matter) were in the Oort Cloud, it would no longer be planet!' Agreed, not as defined by a taxonomy where 'planet' is a sub-classification that excludes PMOs that don't dominate their orbits. But in that same vein, Earth wouldn't be a 'planet' if it were in orbit around Jupiter! Yet it would still remain a planetary mass object just as if Earth were floating between the stars and would no longer be a planet in that situation either. Like it or not, location IS a valid basis for classification.

      The "MO (mass object)"-based taxonomy I suggested earlier allows all PMOs (round & < 13 Jupiter masses) to be sub-classified more or less according to their distinguishing traits and the system fits in with stellar, sub-stellar, and sub-planetary mass objects as well. Enjoy!

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    3. How to define what a planet is:

      Step 1: Define the minimum dominant mass (MDM) of a solar system

      The mass of the smallest rounded celestial body in orbit around a star (or stellar remnant) that has cleared the neighborhood of [or is dynamically dominant in] its orbit using Jean-Luc Margot's planetary discriminant (where Π ≥ 1).

      For example, for our solar system Mercury is the MDM; in the solar system known as Kepler-37, the MDM is Kepler-37b (which has a diameter slightly greater than Earth's moon). See the following link for a more technical explanation of Margot's practical planetary discriminant:

      http://mel.ess.ucla.edu/jlm/publications/Margot15.aj.PlanetDefinition.pdf.

      Step 2: Define the term planet

      A celestial body that...

      (1) orbits one or more stars or stellar remnants;
      (2) is a gravitationally dominant member of its solar system, defined as follows:
      (a) has cleared the neighborhood of [or is dynamically dominant in] its orbit (e.g., Margot's Π ≥ 1)
      OR
      (b) has a mass >= the MDM of its solar system;
      (3) has a mass below 13 Jupiter masses, a nominal value close to the limiting mass for thermonuclear fusion of deuterium.

      With this definition, as long as Earth and Jupiter orbit the sun directly, they will always remain planets regardless of their hypothetical location in the solar system (e.g., a "remote" Jupiter that orbits in the Oort Cloud or a "remote" Earth" that orbits at 100 AUs from the the sun). And with this definition, you don't set an arbitrary cut-off point for planethood for all other solar systems at Mercury but instead use a contextual cut-off point for planethood unique to each solar system (as in the case of Kepler-37).

      Everything less than the MDM will be a dwarf planet or small solar system body (SSSB, or sub-planetary mass object) so there won't be any more Jupiter-like planets potentially mislabeled as "dwarf planets" because of their given location within a solar system. Rogue planets and large rounded satellites will remain separate categories under the classification of planetary mass objects (PMOs).

      In summary, planets are by all rights the dominant players of any given solar system (after their parent star(s) of course). Dwarf planets, large rounded satellites, rogue planets, and SSSBs are, for various reasons, not dominant players of solar systems.

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  20. It seems to me that our best chance for imaging this planet to see if it has any Moons would be to use the New Horizons probe. Are the most likely hiding spots along the New Horizon's current trajectory?

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    Replies
    1. If Planet Nine is indeed near the projected aphelion location, then New Horizons is heading in the near opposite direction. (And New Horizons' camera couldn't see it anyway since it's too far away)

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    2. AV, do you know if there's even a remote possibility of one of the other four probes--Voyager 1, Voyager 2, Pioneer 10, and Pioneer 11--on an interstellar trajectory (assuming each probe is still technically active) might've picked up some bit of "static-type" information inadvertently that could indicate the presence of Planet Nine out and beyond the Kuiper Belt? Thanks in advance!

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    3. New Horizons has a pathetically weak telescope. Hubble would be the way to go.

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  21. According to the Nice Models, in the early Solar System Jupiter and Saturn are theorised to have been in a 2:1 resonance.
    Does that mean, as Saturn was gravitationally dominated by Jupiter, it wouldn't be classified as a planet? That doesn't seem right.

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  22. I like the name Tartarus for this new planet, the Tartarus was a place where the evil people were punished for their sins, maybe this world need justice and retribution, so in my personal opinion the new planet could represent this ideal of victory over the evildoers. Also, we have Pluto and Eris in the outer solar system, Pluto was the god of underworld and Eris promoted a lot of wars and pain between the people, so the correct choice to complete the picture would be a place of final punishment for the evildoers.

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  23. I WILL AGREE,WHY DON'T WE HAVE HUBBLE OR KEPLAR LOOKING FOR IT?WHAT AM I THINKING ,IF THAT HAPPENED,THEN NASA WOULD HAVE TO ADMIT SOMETHING.THAT ISN'T GOING TO HAPPEN.THEN YOU COULD REFER TO THE ANCIENT TEXTS OF THE SUMERIANS AND OTHERS.THEY KNEW MORE ABOUT OUR SOLAR SYSTEM BACK THEN,THAN WE KNOW TODAY.LONG LIVE THE ANUNNAKI.

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  24. If you go to this URL: http://simbad.u-strasbg.fr/simbad/sim-id?Ident=HD+++8556

    and look at this location:

    01 27 52.425, -07 06 16.03

    you will notice a blue semicircle which could be the limb of Planet 9.

    Hope this is correct!

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  25. Is it possible that the 9th so to speak is actually another moon??

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