Science

William Seger

(11,620 posts) Thu May 15, 2025, 10:41 AM Thursday

Have astronomers found Planet Nine?

https://www.astronomy.com/science/have-astronomers-found-planet-nine/

Science textbooks may be in for another revision. Our solar system shrank from nine planets to eight after the International Astronomical Union demoted Pluto in 2006. But there may yet be another world lurking beyond Neptune — and astronomers may have just found it.

In 2016, astronomers proposed that our solar system could harbor a stealthy ninth planet based on a strange clustering of orbits they detected among distant Kuiper Belt objects. They suggested the unseen world may be gravitationally tugging on those objects with the heft of five to 10 Earth masses. So far, there’s no direct evidence that Planet Nine exists.

Is this the one?

A new study, however, identifies a possible candidate. A separate team of astronomers compared 1983 data from the Infrared Astronomical Satellite (IRAS) with 2006 data from Japan’s AKARI mission in search of faint sources that moved slightly over the intervening 23 years — the kind of slow motion you’d expect from a massive, faraway planet.

“Observing in the far-infrared is advantageous because a distant planet would be extremely faint at optical wavelengths but may emit detectable thermal radiation in the infrared,” says Terry Long Phan, an astronomy graduate student at National Tsing Hua University in Taiwan, who led the study. By eliminating stationary objects and any pairs that moved too much or too little to be the theorized world, they winnowed down from 2 million objects to just 13 possible pairs. “Most of these turned out to be false positives, typically caused by high background noise or potential stationary sources that were not detected but present in the image,” Phan says. “However, we identified one promising candidate that is consistent with the expected properties of Planet Nine.”