Revision 1

Accepted · first revision · record

Title: Is there an undiscovered planet beyond Neptune?
Plain: Some very distant icy bodies have orbits that seem lined up in a way that a hidden planet several times Earth's mass could explain. Others argue the alignment is an accident of where telescopes looked.
Precise: Determine whether the apsidal and nodal clustering of distant trans-Neptunian objects (semimajor axis above about 250 au, perihelion above about 40 au) is statistically significant after correcting for survey selection, and whether it requires an undetected planet of roughly 5 to 10 Earth masses on an eccentric orbit at a few hundred au. An answer is a detection, or an exclusion of the proposed parameter space by direct search and by unbiased orbital statistics.
Settled by: Direct detection by deep wide-field surveys, or a large, well-characterized sample of distant objects from the Rubin Observatory survey showing no significant clustering.
Kind: well-posed
Answer type: yes-no
References: (empty)
Literature status: contested
Status note: No detection as of 2026; the Rubin Observatory, whose first images were released in 2025, is expected to enlarge the distant-object sample substantially.
Posed since: 2016