Previous models have had difficulty producing the expected ratio between scattered disk objects and outer Oort cloud objects. The binary capture model offers significant improvement and refinement, which is seemingly obvious in retrospect: most sun-like stars are born with binary companions." Govert Schilling (2009). The Hunt for Planet X: New Worlds and the Fate of Pluto. New York: Springer. ISBN 978-0387778044.

Clyde W. Tombaugh (1946). "The Search for the Ninth Planet, Pluto". Astronomical Society of the Pacific Leaflets. 5 (209): 73–80. Bibcode: 1946ASPL....5...73T. A. Brunini & M.D. Melita (2002). "The existence of a planet beyond 50 AU and the Orbital Distribution of the Classical Edgeworth–Kuiper-Belt Objects". Icarus. 160 (1): 32–43. Bibcode: 2002Icar..160...32B. doi: 10.1006/icar.2002.6935. hdl: 11336/37037. Achenbach, Joel; Feltman, Rachel (2016-01-20). "New evidence suggests a ninth planet lurking at the edge of the solar system". The Washington Post . Retrieved 2016-01-20. The instructions are very clear, so you can get up and running in minutes. TIP: You may find it helpful to start as we did, working together on a one player game to help each other learn tactics. Schwamb, Megan (2007-09-18). "Searching for Sedna's Sisters: Exploring the inner Oort cloud" (PDF). Caltech. Archived from the original (PDF) on 2013-05-12 . Retrieved 2010-08-06.

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If you get any of these answers wrong, the app will simply say ‘incorrect’, the game will continue. You can then make another guess on a future turn. If you’re right, finish your turn and move to the ‘End Of The Game’. Game Theory Something still didn't quite add up though. Even after the discovery of Neptune, the unique orbits of some dwarf planets and other small, icy objects in the Kuiper Beltcouldn't be fully explained. These tend to follow orbits that cluster together. Analyzing the orbits has led some astronomers to suggest the possibility that a large, yet-to-be-discovered planet may be lurking far beyond Pluto. What do we know? Matese, John J.; Whitmire, Daniel P. (2011). "Persistent evidence of a jovian mass solar companion in the Oort cloud". Icarus. 211 (2): 926–938. arXiv: 1004.4584. Bibcode: 2011Icar..211..926M. doi: 10.1016/j.icarus.2010.11.009. S2CID 44204219.

The app also offers the useful option of providing players with different amounts of starting info, allowing for the option of a handicap system if some players are more experienced than others. But experience can come with another peril than just game balance: despite the fact each game will have a fresh setup to solve, doing so feels much the same every time. With limited ways to glean information, replayability is dependent on enjoying solving variants of that same puzzle. The presence of an object with a mass similar to that of Mars in a circular orbit at 60AU (9.0billionkm; 5.6billionmi) leads to a trans-Neptunian object population incompatible with observations. For instance, it would severely deplete the plutino population. [82] Astronomers have not excluded the possibility of an object with a mass similar to that of Earth located farther than 100AU (15billionkm; 9.3billionmi) with an eccentric and inclined orbit. Computer simulations by Patryk Lykawka of Kobe University have suggested that an object with a mass between 0.3~0.7 M Earth, ejected outward by Neptune early in the Solar System's formation and currently in an elongated orbit between 101 and 200AU (15.1 and 29.9billionkm; 9.4 and 18.6billionmi) from the Sun, could explain the Kuiper cliff and the peculiar detached objects such as Sedna and 2012 VP 113. [82]Two weeks after Christmas and whilst our other board game gifts are learned, loved and added to our regular play list, my wife has resolutely avoided The Search for Planet X. 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. Clavin, Whitney; Harrington, J.D. (7 March 2014). "NASA's WISE Survey Finds Thousands of New Stars, But No 'Planet X' ". NASA . Retrieved 7 March 2014. In 2014 astronomers at the Universidad Complutense in Madrid suggested that the available data actually indicates more than one trans-Neptunian planet; [71] subsequent work further suggests that the evidence is robust enough but rather than connected with Ω and ω, semi-major axes and nodal distances could be the signposts. [72] [73] Additional work based on improved orbits of 39 objects still indicates that more than one perturber could be present and that one of them could orbit the Sun at 300-400 AU. [74] Whitney Clavin (2011-02-18). "Can WISE Find the Hypothetical 'Tyche'?". NASA/JPL . Retrieved 2011-02-19.

Patryk S., Lykawka; Tadashi, Mukai (2008). "An Outer Planet Beyond Pluto and the Origin of the Trans-Neptunian Belt Architecture". The Astronomical Journal. 135 (4): 1161–1200. arXiv: 0712.2198. Bibcode: 2008AJ....135.1161L. doi: 10.1088/0004-6256/135/4/1161. S2CID 118414447. Once one player has located Planet X, each other player gets one more chance to submit theories or to guess the location of Planet X, after which you score. The biggest bonuses are for locating Planet X, with more points for doing it first, but you can also gain points for correct theories on other sectors, and for being the first to do so in each sector where you were correct—so you can still win even if you’re not the first to find the mystery planet. Iorio, Lorenzo (2017). "Is the recently proposed Mars-sized perturber at 65–80 AU ruled out by the Cassini ranging data?". Frontiers in Astronomy and Space Sciences. 4: 28. arXiv: 1407.5894. Bibcode: 2017FrASS...4...28I. doi: 10.3389/fspas.2017.00028. S2CID 26844167.

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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! The need for the app isn’t as bad as you might imagine, and one of the biggest added benefits from its inclusion is the fact that you can play solo. Sure, you only play against one opponent, but the game you play is exactly the same game as you’ll play against human opponents, so it’s the perfect way to practice or to get a learning game in ahead of teaching it at your local game night.