On Solar System's edge, Taiwan astronomers find 'missing puzzle piece'

Taipei, July 15 (CNA) Taiwanese astronomers have discovered "a missing piece of the puzzle" in the search for a ninth planet at the edge of the Solar System's known frontier.

An international team led by Wang Shiang-yu (王祥宇) and Chen Ying-tung (陳英同) of the Institute of Astronomy and Astrophysics, Academia Sinica (ASIAA) found that "Ammonite" -- a newly discovered "Sedna-like object" -- orbited in the opposite direction from its three neighbors.

For years, astronomers had hypothesized that Sedna-like objects' shared orbits were caused by gravitational influence from a speculated "Planet Nine," located far beyond Neptune.

But Ammonite's orbital divergence points to any potential planet being twice as far away as earlier estimates, Wang told CNA.

This suggests that the outer Solar System may be far more diverse and dynamic than previously thought, Wang said.

The team discovered Ammonite using the powerful Subaru Telescope in Hawaii in 2023, and then spent a year observing and analyzing its orbit, Wang added.

Chen, meanwhile, described the team's work as "like discovering a missing piece of the puzzle at the Solar System's frontier."

The discovery is part of the international research initiative Formation of the Outer Solar System: An Icy Legacy (FOSSIL), involving scientists from Taiwan, Japan, South Korea, Canada, and China.

The full research paper, "Discovery and Dynamics of a Sedna-like Object with a Perihelion of 66 au," was published in Nature Astronomy on July 14, 2025.