Solar System survey casts doubt on mysterious ‘Planet Nine’

By Gabriel Popkin

An analysis of four icy bodies discovered in the outer Solar System reveals no sign that they are being influenced by a large, unseen planet lurking beyond Neptune. The finding chips away at a line of evidence for a ‘Planet Nine’ proposed in 2014 on the basis of the clustering of objects in a region called the Kuiper belt, argues a team of astronomers in a paper1 first posted on the arXiv preprint server on 16 June.

The objects were found by researchers leading the Outer Solar System Origins Survey (OSSOS), which is studying the region of space beyond Neptune. The bodies that piqued the astronomers’ interest dwell in the outer reaches of the Kuiper belt.

Using the 3.6-metre Canada-France-Hawaii telescope on Mauna Kea, Hawaii, the team found four bodies that orbit the Sun in enormous ellipses at least 250 astronomical units (au) wide. An au is equivalent to the distance between Earth and the Sun; Neptune orbits at around 30 au. About 12 large-orbit bodies have been spotted so far, including the four found by OSSOS.

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