However, Brown notes that even though it might approach or exceed Earth in size, should such an object be found it would still be a "dwarf planet" by the current definition, because it would not have cleared its neighbourhood sufficiently. [78] Kuiper cliff and "Planet Ten" [ edit ] On average, it lies about 1.8 billion miles (2.9 billion kilometers) away from the Sun, but at their closest approach to one another, they are separated by approximately 1.6 billion miles (2.6 billion kilometers). On the flip side, they can be as far away as 1.98 billion miles (3.2 billion km). It takes Uranus 84 years to complete one trip around the Sun. Walter Baade (1934). "The Photographic Magnitude and Color Index of Pluto". Publications of the Astronomical Society of the Pacific. 46 (272): 218. Bibcode: 1934PASP...46..218B. doi: 10.1086/124467.

Than, Ker (18 June 2008). "Large 'Planet X' May Lurk Beyond Pluto". Space.com . Retrieved 18 July 2016. Note: It’s VERY important you are all using the same game code, as this will determine the randomised location of each object in the sky. A different code means different locations. Although some astronomers, such as Renu Malhotra and David Jewitt, have cautiously supported these claims, others, such as Alessandro Morbidelli, have dismissed them as "contrived". [63] Malhotra & Volk (2017) [83] argued that an unexpected variance in inclination for KBOs farther than the cliff at 50AU (7.5billionkm; 4.6billionmi) provided evidence of a possible Mars-sized planet, possibly up to 2.4 M Earth, residing at the edge of the Solar System, which many news sources began referring to as "PlanetTen". [84] [83] [85] [86] Shortly after it was proposed, Lorenzo Iorio showed that the hypothetical planet's existence cannot be ruled out by Cassini ranging data. [87] Renu Malhotra (1998). "Orbital Resonances and Chaos in the Solar System" (PDF). Solar System Formation and Evolution ASP Conference Series. 149: 37. Bibcode: 1998ASPC..149...37M.a b James W. Christy & Robert S. Harrington (August 1978). "The Satellite of Pluto". Astronomical Journal. 83 (8): 1005–1008. Bibcode: 1978AJ.....83.1005C. doi: 10.1086/112284.

In December 2015, astronomers at the Atacama Large Millimeter Array (ALMA) detected a brief series of 350GHz pulses that they concluded must either be a series of independent sources, or a single, fast moving source. Deciding that the latter was the most likely, they calculated based on its speed that, were it bound to the Sun, the object, which they named "Gna" after a fast-moving messenger goddess in Norse mythology, [97] would be about 12–25 AU distant and have a dwarf planet-sized diameter of 220 to 880km. However, if it were a rogue planet not gravitationally bound to the Sun, and as far away as 4000 AU, it could be much larger. [98] The paper was never formally accepted, and has been withdrawn until the detection is confirmed. [98] Scientists' reactions to the notice were largely sceptical; Mike Brown commented that, "If it is true that ALMA accidentally discovered a massive outer Solar System object in its tiny, tiny, tiny, field of view, that would suggest that there are something like 200,000 Earth-sized planets in the outer Solar System ... Even better, I just realized that this many Earth-sized planets existing would destabilize the entire Solar System and we would all die." [97] Constraints on additional planets [ edit ] Both the Oort cloud and the proposed location of Planet 9 are far too distant for direct observation. However, the Vera C. Rubin Observatory (VRO) in Chili, which came online in 2021, will begin a ten-year survey of the sky in 2022. This is expected todetect thousands more Kuiper belt objects. A close examination of their orbits may be able toconfirm or deny the existence of Planet 9 and provide clues as to its origin and location. Using public data on the orbits of the extreme trans-Neptunian objects, it has been confirmed that a statistically significant (62σ) asymmetry between the shortest mutual ascending and descending nodal distances does exist; in addition, multiple highly improbably (p < 0.0002) correlated pairs of orbits with mutual nodal distances as low as 0.2AU at 152AU from the Solar System's barycentre or 1.3AU at 339AU have been found. [103] Both findings suggest that massive perturbers may exist at hundreds of AUs from the Sun and are difficult to explain within the context of a uniform distribution of orbital orientations in the outermost Solar System. [104] After 1978, a number of astronomers kept up the search for Lowell's PlanetX, convinced that, because Pluto was no longer a viable candidate, an unseen tenth planet must have been perturbing the outer planets. [44] a b Tom Standage (2000). The Neptune File: A Story of Astronomical Rivalry and the Pioneers of Planet Hunting. New York: Walker. p. 188. ISBN 978-0802713636.Even without gravitational evidence, Mike Brown, the discoverer of Sedna, has argued that Sedna's 12,000-year orbit means that probability alone suggests that an Earth-sized object exists beyond Neptune. Sedna's orbit is so eccentric that it spends only a small fraction of its orbital period near the Sun, where it can be easily observed. This means that unless its discovery was a freak accident, there is probably a substantial population of objects roughly Sedna's diameter yet to be observed in its orbital region. [77] Mike Brown noted that During this phase, players will have a chance to submit theories as to where they think objects are located on the board. Each player can submit one theory in Standard Mode and up to two in Expert Mode. C. de la Fuente Marcos & R. de la Fuente Marcos (1 January 2024). "Past the outer rim, into the unknown: structures beyond the Kuiper Cliff". Monthly Notices of the Royal Astronomical Society Letters. 527 (1): L110–L114. arXiv: 2309.03885. Bibcode: 2024MNRAS.527L.110D. doi: 10.1093/mnrasl/slad132 . Retrieved 28 September 2023.

Marc W. Buie; William M. Grundy & Eliot F. Young (July 2006). "Orbits and photometry of Pluto's satellites: Charon, S/2005 P1, and S/2005 P2". Astronomical Journal. 132 (1): 290–298. arXiv: astro-ph/0512491. Bibcode: 2006AJ....132..290B. doi: 10.1086/504422. S2CID 119386667. There are a couple of other game points, which keep things interesting. Every few moves you get to submit theories based on what you know, and there are conferences where the app gives all players more information about the location of Planet X – this can be a real leveller! a b "The Discovery of Pluto". Monthly Notices of the Royal Astronomical Society. 91 (4): 380–385. February 1931. Bibcode: 1931MNRAS..91..380.. doi: 10.1093/mnras/91.4.380. As an aside, Sir William Herschel is credited with discovering and cataloging an additional "800 double stars and 2,500 nebulae." Moreover, "he was the first astronomer to correctly describe the spiral structure of our Milky Way Galaxy."

But the massive body did not turn up in the data from WISE, which scans the heavens in infrared rather than visual light. Since both new studies turned up relatively distant brown dwarfs, they should have had an easier time spotting a companion close enough to the sun to disturb the Oort Cloud, but neither did. a b Dennis Rawlins (1973). "Mass and Position Limits for an Hypothetical Tenth Planet of the Solar System". Monthly Notices of the Royal Astronomical Society. 162 (3): 261–270. Bibcode: 1973MNRAS.162..261R. doi: 10.1093/mnras/162.3.261. Rawlins also took into account Pluto's stellar occultation failure as reported by Halliday, I.; Hardie, R.; Franz, O.; Priser, J. (1966). "An upper limit for the diameter of Pluto". Publications of the Astronomical Society of the Pacific. 78 (461): 113–124. Bibcode: 1966PASP...78..113H. doi: 10.1086/128307. S2CID 121483531. Venkatesh Ketakar" redirects here. For the sociologist, see Shridhar Venkatesh Ketkar. Percival Lowell, originator of the Planet X hypothesis