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.

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. 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. S. C. Tegler & W. Romanishin (2001). "Almost Planet X". Nature. 411 (6836): 423–424. doi: 10.1038/35078164. PMID 11373654. S2CID 5135498.

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When Sedna was discovered, its extreme orbit raised questions about its origin. Its perihelion is so distant (approximately 76AU (11.4billionkm; 7.1billionmi)) that no currently observed mechanism can explain Sedna's eccentric distant orbit. It is too far from the planets to have been affected by the gravity of Neptune or the other giant planets and too bound to the Sun to be affected by outside forces such as the galactic tides. Hypotheses to explain its orbit include that it was affected by a passing star, that it was captured from another planetary system, or that it was tugged into its current position by a trans-Neptunian planet. [64] The most obvious solution to determining Sedna's peculiar orbit would be to locate a number of objects in a similar region, whose various orbital configurations would provide an indication as to their history. If Sedna had been pulled into its orbit by a trans-Neptunian planet, any other objects found in its region would have a similar perihelion to Sedna (around 80AU (12billionkm; 7.4billionmi)). [65] Excitement of Kuiper belt orbits [ edit ]

Helhoski, Anna. "News 02/16/11 Does the Solar System Have Giant New Planet?". The Norwalk Daily Voice . Retrieved 10 July 2012. NASA's Solar System Exploration: Multimedia: Gallery: Pluto's Symbol". NASA. Archived from the original on 2006-10-01 . Retrieved 2007-03-25.There's both evidence that Planet 9 formed alongside the other planets in our solar system billions of years ago, and that it just passed through long enough to shake things up before disappearing once more.