Astronomers Eye Faint Smudge Beyond Neptune in Hunt for Planet Nine

BEYOND NEPTUNE — The long search for the putative Planet Nine, a world said to lurk far past Neptune, has produced what one digest describes as a tantalizing if controversial new lead. According to a summary of reporting by David Freeman, astronomers at Tsing Hua University have identified a possible candidate consistent with a planet of 7 to 17 times the mass of Earth.

The object is said to orbit between 500 and 700 astronomical units from the sun, roughly 16 to 23 times the distance of Neptune. Such a body, the summary notes, would be responsible for the odd clustering seen among the orbits of distant Kuiper-belt objects.

The evidence is modest. Observations from two infrared space telescopes reportedly picked out a possible object that appeared to shift across the sky by less than one degree. Researchers are now seeking a third observation that might turn what the digest calls a suggestive smudge into a proper orbit. Until then, the matter remains open.

Freeman also surveys an older and less fortunate idea: Nemesis, a dim stellar companion to the sun. Its orbit of some 26 million years was hypothesized to disturb the Oort Cloud and send comets toward Earth, to the considerable inconvenience of the dinosaurs, among others. Freeman traces the notion from reports in 1936 to the celebrated 1984 papers by Davis and colleagues.

The theory has since weakened, the summary says, owing to doubts about the stability of so large an orbit and to surveys that found no suitable companion. NASA's WISE results are said to have ruled out a Saturn-sized body within 10,000 AU and a Jupiter-sized one within 26,000 AU, which the digest describes as the popping of a speculative bubble.