New “Fossil” World Discovered in Solar System’s Outer Edge

Astronomers have discovered a mysterious new object in the outer solar system, nicknamed Ammonite. Found by the Subaru Telescope in Hawaii, Ammonite is estimated to be 220–380 kilometers wide and follows a unique, distant orbit. It’s only the fourth known “sednoid”, a group of icy objects with strange orbits far beyond Neptune.

Sednoids have intrigued scientists since Sedna was discovered in 2003. These bodies are believed to carry clues about the early days of the solar system. “Ammonite was found in a region far away where Neptune’s gravity has little influence,” said Dr. Fumi Yoshida, leader of the FOSSIL project. “The presence of objects with elongated orbits and large perihelion distances in this area implies that something extraordinary occurred during the ancient era when Ammonite formed.”

Researchers compiled 19 years of data, tracing Ammonite’s orbit back to sightings as early as 2005. This long record has helped improve the accuracy of its orbit.

However, Ammonite’s orbit differs significantly from other sednoids. “The fact that Ammonite’s current orbit does not align with those of the other three sednoids lowers the likelihood of the Planet Nine hypothesis,” said Dr. Yukun Huang of the Center for Computational Astrophysics. Some now speculate that a planet once existed but was ejected from the solar system.

“In recent years, spacecrafts have been sent to various small bodies in the Solar System… However, these spacecrafts have only explored limited regions,” Dr. Yoshida noted. She hopes discoveries like Ammonite will “help draw a complete picture of the history of the Solar System.”