Michael Rowan-Robinson of Imperial College London reports in a paper published on arXiv on 2021-11-11 “A search for Planet 9 in the IRAS data” on a search of data collected by the IRAS spacecraft in the 1980s, which performed an all-sky survey in infrared wavelengths. He examined unidentified sources in the IRAS observations with only a single nearby confirmation detection. This would be the signature of a moving object, in particular a “super-Earth” mass planet nine orbiting in the Kuiper Belt at a distance of 200 to 400 astronomical units (AU, the mean distance of the Earth from the Sun).
A single candidate observation was found, fitting an object between 3 and 5 earth masses at a distance of 225±15 AU. Parameters for a present-day search for this object are computed.