Proof of ‘Planet Nine’ may be sewn into medieval tapestries

Posted: May 5, 2018 by oldbrew in History, research, solar system dynamics
Tags: ,

Room for one more? [image credit: NASA]

There’s a suspicion of confirmation bias, or seeing what you wanted to see, in stories like this. But we’ll look for any merits in the ideas anyway. Claims that Planet 9 can’t hide much longer haven’t proved correct so far.

Observations made a thousand years ago could help modern scientists find the theoretical “Planet Nine” in the outer reaches of the solar system, says Live Science.

The far reaches of the outer solar system may be home to an icy giant — a hypothetical planet scientists have dubbed “Planet Nine.”

Meanwhile, archives back on Earth are home to dozens of medieval records documenting the passage of comets through the heavens. Now, two researchers from Queen’s University Belfast in Northern Ireland are hoping to use these old scrolls and tapestries to solve the modern astronomical mystery of Planet Nine.

“We have a wealth of historical records of comets in Old English, Old Irish, Latin and Russian which have been overlooked for a long time,” said university medievalist Marilina Cesario, one of the leaders of the project. “Early medieval people were fascinated by the heavens, as much as we are today.”

The records include dates and times, Cesario said, which makes them useful to modern-day astronomers.

Finding Planet 9

Planet Nine, if it exists, would have about 10 times the mass of Earth and orbit 20 times farther from the sun than Neptune does. (Planet Nine is not Pluto, which was once considered the ninth planet but was demoted to mere “dwarf planet” in 2006. Nor is it Nibiru, the completely fictional “rogue planet” that conspiracy theorists sometimes claim is about to destroy the Earth.)

Scientists suspect the existence of Planet Nine because it would explain some of the gravitational forces at play in the Kuiper Belt, a stretch of icy bodies beyond Neptune. But no one has been able to detect the planet yet, though astronomers are scanning the skies for it with tools such as the Subaru Telescope on Hawaii’s Mauna Kea volcano.

Medieval records could provide another tool, said Pedro Lacerda, a Queen’s University astronomer and the other leader of the project.

“We can take the orbits of comets currently known and use a computer to calculate the times when those comets would be visible in the skies during the Middle Ages,” Lacerda told Live Science. “The precise times depend on whether our computer simulations include Planet Nine. So, in simple terms, we can use the medieval comet sightings to check which computer simulations work best: the ones that include Planet Nine or the ones that do not.”

Continued here.

  1. Book by guy called Donnelly suggests that a large object from a super nova with a gravitational pull came through it smashed “planet 9” with the ice becoming the 40 days and 40 nights of rain. But ist also pulled the Earths surface causing major changes and also moving the poles etc. Antarctica

    I go to Torque Parcal North of Malaga this is rocks which were on the Sea bottom millioms of years back now over a 1,000 mtrs above sea level.

    Also the Med sea was originally more a swamp until the Straits of Gib appeared and also the Bosphorous. thinking being that this part of the Earths surface was closest to this massive asreroid.

  2. oldbrew says:

    In 2020 the Bayeux tapestry is due in the UK.

    Let’s hope there are no post-Brexit customs issues over it 😉

  3. E.M.Smith says:

    As I’ve noted before, the “clears it’s environment” rule makes it hard to call this “Planet 9”. It is supposedly either in the outer fringes of the Kuiper Belt or some think it wanders through the Oort Cloud. In either case the environment is NOT cleared.

    That means it must either be “not a planet” but a “Dwarf Planet” (which will then get into the anomaly of the size being large but the definition not letting it be a “Planet”) or we must accept that “clear the neighborhood” is just a damn stupid rule (even Jupiter has Trojans…) and eliminate that rule, at which time Pluto would return as Planet 9 and this “whatever” would need to be Planet 10 (or higher depending on what i done with Sedna and Makemake and Ceres and…)

    Calling it “Planet 9” is in all cases going to be wrong. (Unless there is some bizarre orbit outside the Kuiper Belt, inside of the Oort Cloud, yet still able to gravitationally perturb both so much as to give the anomalous orbits and / or stimulate comet storms.

    Basically the present definition of planet is bogus and causes so much special pleading and hand waving around issues that it is just dumb. It also means “Planet 9” can’t be the 9th planet…

    Personally, I’d just fix a mass or diameter that was defined as the “cut off” and be done. Want Pluto in? Make it a 2000 km diameter. What Pluto out? Make it 2500 km diameter. Then all the “issues” just evaporate in all the other cases.

    (What is the most silly aspect of the definition? It means that MOST and perhaps ALL “planets” are not planets for all of the early part of their existence, as they are busy sucking up local debris. Maybe a Billion years worth? Then there’s an ambiguous period where they got most of it, but not all, and what are they? Then some ill defined time later, they ‘suddenly’ become a planet as enough debris is “cleared”. The Earth gets regular Taurid impacts along with millions of other minor impacts per year. So has Earth “cleared the neighborhood”? If so, why are we sill having a rain of debris?

    Does this look “clear” to you?

  4. oldbrew says:

    EMS – If Pluto is ‘in’, why not Eris with similar size and mass?

    Eris (minor-planet designation 136199 Eris) is the most massive and second-largest dwarf planet in the known Solar System.
    . . .
    Eris is the ninth most massive object directly orbiting the Sun, and the 16th most massive overall, because seven moons are more massive than all known dwarf planets.
    . . .
    Eris’s mass is about 0.27% of the Earth mass, about 27% more than dwarf planet Pluto, although Pluto is slightly larger by volume.
    – – –
    So has Earth “cleared the neighborhood”?

    Nothing of any significance (except the Moon) has a similar orbital distance from the Sun.
    But look at the Plutinos (near 40 AU)…these are only the large ones. Lots of smaller ones not shown.

  5. E.M.Smith says:


    I take no position on Pluto IN vs OUT. As for Eris (and Sedna and even Ceres and…) that would depend on what size limit were chosen (and diameter vs mass – mass being easier to estimate for things you can’t see well but can observe influencing orbits).

    Note that at one time Ceres WAS defined as a planet. We’ve been through this planet demoting circus before…

    As for Eris: Mean radius 1163 km. Want it “in”, make your limit 2000 km diameter. Want it “out”, make your limit 2500 km diameter.

    Yes, you get a choice of a lot more planets (small diameter like 2000 km) or fewer (large diameter like 2500 km or 4000 km or whatever pleases the voters in the pool.)

    As for Earth “clearing the neighborhood” you have a statistical issue that is NOT addressed. (Part of the problem I pointed out above). How often or what percentage is “cleared”? Note that this is NOT stated in the definition. Nor is “any significance” in the definition.

    The definition says cleared of “planetesimals”.

    A planet is an astronomical body orbiting a star or stellar remnant that is massive enough to be rounded by its own gravity, is not massive enough to cause thermonuclear fusion, and has cleared its neighbouring region of planetesimals.

    While the name is always applied to small bodies during the process of planet formation, some scientists also use the term planetesimal as a general term to refer to many small Solar System bodies – such as asteroids and comets – which are left over from the formation process. A group of the world’s leading planet formation experts decided at a conference in 2006[4] on the following definition of a planetesimal:

    A planetesimal is a solid object arising during the accumulation of planets whose internal strength is dominated by self-gravity and whose orbital dynamics is not significantly affected by gas drag. This corresponds to objects larger than approximately 1 km in the solar nebula.

    So anything in the NEOs that’s bigger than 1 km? Why, yes…

    As Anonymous said, the largest Near Earth Object is 1036 Ganymed (yes, it was named after the same god that Jupiter’s moon Ganymede was named after. Ganymed is the German spelling of the god’s name).

    As for consequences, the Chicxulub crater was caused by a meteor that is estimated to be about 10 km in diameter. It was the cause of the Cretaceous–Paleogene extinction event. I am afraid that if a meteor 22 km across hit the earth, nothing would live through it.

    Fortunately, Ganymed does not cross earth’s path and will never hit us. But there are plenty of asteroids out there that can do a lot of devastation,so we do need to do out best to find them all and track them.

    1036 Ganymed is the largest near-Earth asteroid, at approximately 33 kilometers in diameter. It was discovered by Walter Baade on October 23, 1924. It has a very well determined orbit, and its next pass of the Earth will be at a distance of 0.374097 AU (55,964,100 km; 34,774,500 mi) on 13 October 2024. It is an Amor asteroid, and also a Mars-crosser asteroid, and will pass 0.02868 AU (4,290,000 km; 2,666,000 mi) from Mars on 16 December 2176.

    We are still getting hit with “big ones” from time to time, so by definition we’ve not cleared the neighborhood of planetesimals.

    So now you end up in a statistical argument about how often is ‘not often enough’ to count… another of the problems with a definition that is ill suited. just like what happens when something perturbs the orbit of 1036 Ganymed such that it does cross Earth. Or we end up with a definition that must ASSUME all orbits are stable forever (a known fallacy).

    So BY DEFINITION (but with an asterisk about some missing statistical parts) the Earth is NOT a planet(!)… Or we must ASSUME a bunch of things into the definition that are not in evidence…

    BAD definitions put you in this kind of no-mans-land of squabbles and non-defined things. GOOD definitions do not suffer these problems.

    So I advocate for “Pick a SIZE limit you like” and avoid the whole “when were enough planetesimals soaked up to START being a planet” problems along with avoiding arguing over Pluto and Ceres in / out based on nearby junk and avoid special pleading that Trojans are exempt and all the rest.

    Once you want a definition that says “if there is junk near by” you get into a whole lot of more issues with what junk, how big, how often, WHEN, etc….

    Do remember that at some early point in the solar system formation, the existing Planets were undergoing much more regular bombardment, but were also QUITE large. The present definition says something the size of Saturn (as Jupiter was at one point in the accretion) was NOT a planet, until a little later when it suddenly was…. At that time it, too, had a lot of planetesimals near it (by definition).

  6. oldbrew says:

    EMS – if you include the ‘crossers’ nothing has any chance of clearing anywhere, not even Jupiter.

  7. I think the book Dark Matter, Missing Planets & New Comment , Paradoxes Resolved Origins illuminated by Tom Van Flandern has been mentioned several times on this site. Van Flandern says that there is a good chance that a planet exploded between Earth and Jupiter leaving behind mars and causing the rotation of Venus to go the other way and even that Mercury was a moon of Venus which was knocked off. He also speculates that there was another planet further out which exploded and left behing the dwarf planets Pluto etc and affected the orbit of Neptune.Van Flandern ( ) was a respected astronomer and based his book on factual information for which he gives an extensive reference list.

  8. E.M.Smith says:


    Yup, that’s one of the problems. Definition does NOT say “excluding crossers”…

    So all those sticky little Oh Crap issues just go away if you state:

    Self rounding is defined as FOO size. ( I’d pick 2000 km diameter, but negotiable as a fiat definition)

    A Planet is defined as orbiting the central star (our sun), never going retrograde in orbit (sun concave orbit) and “self rounding”.

    Then just stop. Find a rock bigger than 2000 km orbiting the sun, it’s a planet. Find something bigger orbiting Jupiter and sometimes the orbit is convex to the sun (retrograde motion) as it spins past Jupiter, then it’s a moon.

    Do note: This definition would also resolve some of the issues with the Moon. It doesn’t really orbit the Earth so much as the two of us co-orbit the sun. The lunar orbit is always solar concave and never goes retrograde. We end up as a binary planet system and all the kibutzing over how big our moon is compared to Earth and no other moon being like that just evaporates. No lunar special pleading needed either….

    Yes, it disrupts the “Traditional 9” and it disrupts the “Present 8″… but it is sound physics and both rational and consistent without loose ends.

    When Jupiter was the size of Saturn AND taking lots of impacts while it grew, it WAS a planet. Just a young one still accreeting. Ceres returns as a planet and we no longer need a special pleading that it’s really just an overgrown asteroid. Etc.etc.

  9. oldbrew says:

    A dwarf planet is still a planet 🙂

  10. oldmanK says:

    A comment by EM Smith is academically interesting. Quote: “Fortunately, Ganymed does not cross earth’s path and will never hit us. But there are plenty of asteroids out there that can do a lot of devastation,so we do need to do out best to find them all and track them.”

    But then what? Make a Will? There is absolutely no interest beyond where funding exists. And that ignores the fact that the biggest hazard to humanity is under our feet, as the Holocene clearly provides proof. Few survived the events between 8k2 and 2k. Those did not come from outer space in spite of all ‘impact’ theories. But there is no interest there.

  11. Annie says:

    Oldbrew: There is no need to bring the Bayeux Tapestry to Britain! There is an excellent copy of it in the Reading Museum, made in the 19th century.

  12. Annie says:

    Perhaps I’m being naive here but I rather thought the term ‘planet’ meant a body (in the solar system) that moved around the sky, from our point of view. The word is derived from the Latin ‘planeta’ (wanderer) is it not?

  13. oldbrew says:

    Planets orbit the Sun, whereas moons orbit planets (but by doing so they inevitably orbit the Sun also).

  14. E.M.Smith says:


    If you spot them early enough, very little delta-V is needed to shift the orbit just enough to avoid Earth. We have several ways that it could be done. Ignoring it for the little ones (like recently lit up part of Russia) but doing something about the ones like Tanguska that could nuke somewhere as large as New York City.

    We’re talking a rock about the size of a football field. Big, but when you only need to change it by a meter / minute velocity, not that much total fuel needed…

    I don’t know as we have a firm fix on what caused things like the 8.2 ky event… but yes, we need to ‘smell the coffee’ on those periodic cold events…


    That was the original definition. By that definition given our better telescopes now, we’d have dozens of planets as things the size of Ceres would qualify (and at one time it WAS defined as a planet…) but to avoid an ever larger catalog of planets, the definition has been changed.

    Oh, and in the ancient form, the Moon of Earth was a planet… as it wandered too. Then it became “not a planet” when the sun centered model “won”. But they missed that it is never retrograde orbit and that the Moon / Earth system is really two bodies orbiting the sun. Another “special pleading ‘was made to require the barycenter, or the mutual center of rotation, of a binary planet to be outside the surface of the Earth so the Moon would remain not-a-planet. BUT, the barycenter is close to the surface of the Earth and the moon is slowly receding, so eventually the moon will again “become a planet” as the barycenter moves to above the surface.

    That’s the kind of issue you get with such ersatz definitions. There was a competing definition of binary planet that just had “no retrogade segment / orbit concave to star” but as that would have the Moon / Earth system being a “binary planet” it was rejected (despite being the more correct and NOT having the Moon change from moon to planet at some future date…)


    Would that it were true that a dwarf planet was just defined as a planet of small stature, like “below 4000 km diameter”. I’d be fine with that. Toss Pluto, Ceres, etc. etc. all into the “planet but small enough to ignore when naming all the big planets in 3rd grade” bucket and move on. But it isn’t.

    A dwarf planet is a planetary-mass object that is neither a planet nor a natural satellite. That is, it is in direct orbit of a star, and is massive enough for its gravity to compress it into a hydrostatically equilibrious shape (usually a spheroid), but has not cleared the neighborhood of other material around its orbit.

    The term dwarf planet was adopted in 2006 as part of a three-way categorization of bodies orbiting the Sun, brought about by an increase in discoveries of objects farther away from the Sun than Neptune that rivaled Pluto in size, and finally precipitated by the discovery of an even more massive object, Eris. The exclusion of dwarf planets from the roster of planets by the IAU has been both praised and criticized; it was said to be the “right decision” by astronomer Mike Brown, who discovered Eris and other new dwarf planets, but has been rejected by Alan Stern, who had coined the term dwarf planet in April 1991.

    If suffers from the same bogus “cleared the neighborhood” kludge as full sized planets. So again you start racking up the brain warpage. Starting with the very first line.

    A “planetary-mass” that isn’t a planet. Say what? WT Heck does that mean? Oh, it means that when Jupiter was “only” the size of Saturn and a gas giant, it was a “dwarf”… Sheesh.

    This whole thing was just a badly played hand to get all the KBOs knocked out of the Planet definition. There’s a couple of them that are quite large and “someone” just didn’t want to start getting into the business of having 20 or 30 “planets”, so they invented this kludge that doesn’t work well at other times in the evolution of the solar system and doesn’t work all that well now either.

    As of 5 Feb 2018, Brown’s list includes 952 objects, identifying ten known trans-Neptunian objects—the four accepted by the IAU plus 2007 OR10, Quaoar, Sedna, Orcus, (307261) 2002 MS4 and Salacia—as “near certain”, with another 27 “highly likely.” Stern states that there are more than a dozen known dwarf planets.

    Only two of these bodies, Ceres and Pluto, have been observed in enough detail to demonstrate that they actually fit the IAU’s definition. The IAU accepted Eris as a dwarf planet because it is more massive than Pluto. They subsequently decided that unnamed trans-Neptunian objects with an absolute magnitude brighter than +1 (and hence a diameter of ≥838 km assuming a geometric albedo of ≤1) are to be named under the assumption that they are dwarf planets.

    Mercury is 2440 km radius. So about 4880 km diameter. The easiest “fix” would have been to just define an artificial cutoff (no more artificial than ‘clears the neighborhood’…) of 4000 km Diameter for being a planet (or the equivalent rocky mass of about 3 x 10^23 kg if you want a mass basis) and be done. Pluto, Ceres, Eris all out. 8 in.

    Or, if you wanted to keep Pluto in, make the cutoff 2000 km diameter and accept Eris as a Planet also so we get 10. All the other TNOs are under 1000 km pretty much and nobody would mind leaving them out.

    Ceres at 473 km radius 956 km diameter would also stay out so no worries about a “planet” in the asteroid belt.

    Would it really be all that horrible to have a 10th planet “discovered”?

  15. E.M.Smith says:

    Oh, and note that the Moon, at diameter about 3475 km, gets excluded from the Planet Club if a 4000 km diameter cut-off is used, but would stay in if a 2500 km or 2000 km diameter cut-off is used. In the case where it was excluded, we would become a “planet / dwarf-planet binary system” with the removal of the barycenter rule.

  16. oldbrew says:

    EMS – no definitions can be exact when solar systems are as messy as they are, or ours is anyway.

    But if you look at the so-called ‘planets’ of our SS, none of them have another planet or dwarf planet near them (in terms of orbital period / semi-major axis), although they may have one or more large-ish moons.

    But Pluto is relatively small and does have dwarf planet-sized bodies orbiting in very similar periods e.g. Orcus, Ixion, i.e. at about the same average distance from the Sun.

  17. E.M.Smith says:


    So make your cut off for planet to be 4000 km diameter and we can all go home…

    (And that would be exact.)

    Ceres, Pluto,and Eris all remain “dwarf Planets”.

    The Moon remains a moon until the barycenter definition is removed
    (or when it inevitably drifts a bit further out but we won’t be alive then).

    We avoid all the bogus bits caused by having the definition of planet depend on little junk near by that initially and often can not be seen…

    Jupiter as a Saturn sized young acreting planet is not called a dwarf.

    All the other smaller TNOs stay out of the Planet Pool.

    No need for special pleading about the Trojans.

    No need for statistical hand waving over NEOs and Earth crossers.

    etc. etc.

    It is just fundamentally problematic to define an elephant based on the proximity of mice, fleas, and dung beetles… Just call it what it is: a really big mammal…

  18. E.M.Smith says:

    Oh, and do note that the Earth has a “similar sized planet or dwarf planet” near it in almost the same orbit… The definition was cooked to say “barycenter inside Earth, not a planet” (there WAS an active proposal to make it concave / non-retrograde orbit instead). So slight change of definition, it becomes a planet.

    Or just wait a bit and inevitably it will drift outward enough to suddenly become a planet under our present definition anyway… and they again you will have your example of “a nearby planet in almost the same orbit”. (As will be the case for all binary planets in other solar systems).

    Defining A by what B is near it is a rough, irregular, and painful road….

  19. oldbrew says:

    EMS – what status would Pluto’s binary partner Charon have in your preferred scheme?

  20. E.M.Smith says:

    As it is under 2000 km in mean diameter, in all choices of “Planet Size Limit” of 2000, 2500, or 4000 km (or any size you like larger than the 1616 km diameter size of Charon) it would either be a dwarf planet or a moon of Pluto (depending on how you chose to define moon and where the barycenter of their mutual orbit might be).

    As folks seem dead set against Pluto and Eris being Planets, I would presume folks would choose the 4000 km diameter cutoff, thus making both Pluto and Charon “dwarf planets”. As to “can a dwarf planet have a moon?” and what definition of moon is used for dwarf planets, I have no opinion other than I lean toward all moons being required to have some segment of their orbit be convex toward the sun / retrograde compared to the planet orbit of the sun; as the way to distinguish a binary planet (binary dwarf planet) rather than the barycenter method (due to the barycenter method eventually changing your moons into planets or dwarf planets…

    I have no idea where the barycenter of the Charon / Pluto orbit is (another reason its a bit daft as a method is it isn’t easy to know at vast distances…) so can’t say how they would be defined under the present barycenter rule. But let’s check the wiki:

    The center of mass (barycenter) of the Pluto–Charon system lies outside either body. Because neither object truly orbits the other, and Charon has 12.2% the mass of Pluto, it has been argued that Charon should be considered to be part of a binary system with Pluto. The International Astronomical Union (IAU) states that Charon is considered to be just a satellite of Pluto, but the idea that Charon might be classified a dwarf planet in its own right may be considered at a later date.

    So the IAU, again in a great leap of indecisive confusion, can’t manage to say that the “moon barycenter rule” makes this a binary system (even if of 2 dwarf planets)… Sigh. Idiots. But they might, maybe, get around to thinking about it later…. and for now will call it a “satellite” (most likely has they also haven’t decided if dwarf planets can have moons…)

    OK, with the barycenter known; what I’d do to please everyone:

    Say planets orbit the sun, concave all the way, and have diameter greater than or equal to 4000 km.

    Then we have 8 planets, and a bunch of dwarf planets.

    Leaving he moon definition alone (as just about everyone in the IAU would go ape sh… crazy over us being a binary planet system or a planet / Dwarf planet binary) that would make Pluto / Charon a “Dwarf Planet Binary System”.

  21. p.g.sharrow says:

    It would appear to me that the definitions are drawn from the wrong point of view. There are stellar bodies of all sizes that are basically orbited by smaller bodies or satellites. These are planets and planetoids that are large enough to self round, comets and asteroids. Any body might have satellites of any number or size. A moon is a satellite regardless of size.

    I can at present think of no definition that would fulfill everyone’s desire to differentiate planets by size. You have Gas Planets, verses Stoney Planets but that is just a condition of atmospheric density which could include Venus as a gas planet, Earth as a Stoney. Luna is at least a planetiod. If I were to devise divide of planets from planetiods I would use the ability to retain an Atmosphere with a tropohause is required for a planet which would make Mars, Mercury and Pluto planetoids, Luna, Titan, etc. are plantoids as well as being satellite…pg

  22. oldbrew says:

    Plutinos sharing the same or similar semi major axis as Pluto (39.3 AU):
    These are just the brightest ones.

    No such list can be drawn up for Earth.
    – – –
    By extrapolating from the limited area of the sky so far examined, we have estimated that the number of Plutinos larger than 100 km diameter is 1400, to within a factor of a few, corresponding to a few % of the total.

    Here, Pluto is in the blue (resonant) group just inside the 40 AU line.
    [one page pdf]

    There are at least 70,000 “trans-Neptunians” with diameters larger than 100 km in the radial zone extending outwards from the orbit of Neptune (at 30 AU) to 50 AU. [Pluto is in the middle of that zone]

  23. oldbrew says:

    Dave Jewitt (see above) also notes:
    Some non-resonant KBOs have inclinations much higher than the Plutinos and this is a dynamical surprise, for which no single, clear explanation currently exists.

    That probably brings us back to Planet 9 theories.
    – – –
    For perspective…

  24. oldbrew says:

    Support here for EM Smith’s view:

    Researchers Explain Why Pluto Is a Planet
    Scientists criticized the choice adopted by the convention of the International astronomical Union in 2006.
    – – –
    Again, the problem is: if a different definition were to be adopted, which of the current ‘dwarf planets’ should be promoted to planet, which not, and why (were those criteria used)?

  25. E.M.Smith says:

    I’ve already shown how the use of diameter lets you have the same outcome as now, but with a clean definition. Not one where “little junk” determines what is a planet.

    Over 4000 km = planet; then Pluto, Eris, Ceres etc. ALL stay dwarf planets. So 8 planets.

    Problems kept away.

    Or chose:

    Over 2000 km = planet; then Pluto, Eris are planets, Ceres is not and remains a dwarf planet. We have 10 planets.

  26. E.M.Smith says:

    Oh, and as to “why cut off and why?” the two proposed solutions (or 3 if you want the 2500 km value) are based on:

    1) Self rounding.

    2) Somebody hates planets in the vicinity of KBOs.

    The self rounding is interesting. Clearly for a water droplet it’s about 1 cm. But for gasses even less. For rocks, it takes a lot more gravity. So usually folks talk about “self rounding rocky” but then “which rocks” matters. It’s “about” 2000 km diameter but with things like gravel self rounding at less than that and iron at more. So you want “self rounding” but the exact number will be a cherry pick in any case. Just make it more than 2000 km for most kinds of large rocks.

    Now for #2, if you want Pluto, Eris, and any other KBO found kept out of the planet club just make the definition a big enough diameter to keep Mercury IN and Pluto OUT. That’s 4000 km diameter. Bigger than 2000 km, so definitely self rounding. Big enough it’s hard to say anything that big orbiting a star is NOT a planet. Keeps KBOs out of the club. Unless you found some really big think in the far reaches but then I’d assert an Earth sized KBO really ought to be called a planet anyway.

    For examples of theoretical planet shapes (and why you really just want to pick a diameter or a mass as your cut-off value to avoid messes…) see:

  27. oldbrew says:

    Somebody hates planets in the vicinity of KBOs

    It’s the which-is-which problem 😎

  28. oldbrew says:

    Article written: 10 May, 2018

    These simulations incorporated recent geological evidence from Mars and Earth that indicate that Mars’ formation period was about 1/10th that of Earth’s. This has led to the theory that Mars was left behind as a “stranded planetary embryo” during the formation of the Sun’s inner planets.

  29. oldbrew says:

    The orbit period of this oddball is about 2 years longer than Pluto’s…

    A “Weirdo” Asteroid Has Been Found In The Outer Solar System That Isn’t Supposed To Be There
    09 MAY 2018

    Astronomers say they have detected an asteroid beyond the orbit of Pluto that is in the wrong place. But while odd, it could tell us more about our own beginnings.

    Called 2004 EW95, the asteroid is unique in that it is rich in carbon – the first such rock found so far from the Sun. It probably formed in the asteroid belt between Mars and Jupiter before being flung out to its current location in the Kuiper Belt.
    . . .
    2004 EW95 is thought to be about 300 kilometers (190 miles) across

  30. oldbrew says:

    Welcome Back, Pluto? Planethood Debate Reignites
    By Mike Wall, Senior Writer | May 11, 2018

    And then there’s the pithy take by California Institute of Technology astronomer Mike Brown, whose discovery of outer-solar-system objects helped spark the rethink of Pluto’s place in the solar system.

    “So, hey, Pluto is still not a planet. Actually, never was. We just misunderstood it for 50 years. Now, we know better. Nostalgia for Pluto is really not a very good planet argument, but that’s basically all there is. Now, let’s get on with reality,” Brown wrote via Twitter, where his handle is @plutokiller.

    Or we could have over 100 ‘planets’ (see link), most of them smaller than the Moon? No thanks.

  31. oldbrew says:

    A New World’s Extraordinary Orbit Points to Planet Nine

    “It’s not proof that Planet Nine exists,” said David Gerdes, an astronomer at the University of Michigan and a co-author on the new paper. “But I would say the presence of an object like this in our solar system bolsters the case for Planet Nine.”
    . . .
    It wasn’t until they added in a ninth planet — a planet with characteristics that perfectly match Batygin and Brown’s predictions — that the wacky orbit finally made sense. “The second you put Planet Nine in the simulations, not only can you form objects like this object, but you absolutely do,” said Juliette Becker, a graduate student at Michigan and the lead author on the new paper. A strong and sustained interaction with Planet Nine appears to be the only way to pump up the object’s inclination, pushing it away from the plane of the solar system. “There is no other reasonable way to populate the Kuiper belt with such highly inclined bodies,” Batygin said. “I think the case for the existence of Planet Nine is now genuinely excellent.”

    Other astronomers aren’t so certain — in part because the early solar system remains a mystery.

  32. p.g.sharrow says:

    @Oldbrew; Slowly but surely “Astrophysics theory” approaches reality. I wonder which will happen first. They accidentally discover Planet 9 or they figure out it’s correct orbit and thereby know where to look for it. My guess is in favor of accidental. 😉 …pg

  33. oldbrew says:

    Other astronomers aren’t so certain — in part because the early solar system remains a mystery.

    If they ever find a Planet 9 it will be even more of a mystery :/

  34. p.g.sharrow says:

    As our sun is a 3rd generation star there could be “other” planets nearby…pg

  35. oldbrew says:

    p.g – it would probably be difficult to work anything precise out about a Planet 9 based on the orbits of a few dwarf planets.

    But if that’s all the evidence there is, might as well give it a go.

  36. oldbrew says:

    Dwarf Planet Pluto Could Be A Giant Comet
    24 May 2018

    Dr. Christopher Glein of SwRI’s Space Science and Engineering division and his team developed what they called “the giant comet cosmochemical model of Pluto formation.”

    Through the model, the team arrived at a conclusion that a previously discovered glacier on Pluto’s surface, the Sputnik Planitia, has the similar nitrogen composition to that of the comet 67P/Churyumov-Gerasimenko.

    “We found an intriguing consistency between the estimated amount of nitrogen inside the glacier and the amount that would be expected if Pluto was formed by the agglomeration of roughly a billion comets or other Kuiper Belt objects similar in chemical composition to 67P, the comet explored by Rosetta,” Glein explained.

  37. p.g.sharrow says:

    A Dirty Snowball model for early planetary/stellar creation would be the best one to pursue. Water electrostatics would provide the best attractant to begin the build before gravity would become great enough to be the dominate attraction force. Once self rounding takes place internal pressures are high enough to cause Melt and heat energy accumulation in the core…pg