This newly found object, which measures around 380 kilometers across, was spotted by the Subaru Telescope at the Mauna Kea Observatory in Hawaii. Researchers have nicknamed it ‘Ammonite’ due to its preserved features that offer clues to the early days of our solar system.
Ammonite is now the fourth known member of a rare group of space objects called sednoids. These small celestial bodies have unusual, elongated orbits that keep them on the outer edges of our solar system. Scientists describe it as a kind of space ‘fossil’ that carries ancient memories from the solar system’s early formation.
A research paper from 2021 explained that Sedna likely formed during the earliest phase of the solar system’s creation. Its orbit appears to have shifted due to powerful dynamic forces that occurred when the Sun was still surrounded by a dense cluster of other stars.
Other possibilities for the orbit’s change include a past close encounter with another star—like Scholz’s star, which passed by about 70,000 years ago—or that Sedna originally came from a low-mass star before entering our solar system.
“In recent years, spacecrafts have been sent to various small bodies in the Solar System for close observation and sample collection. However, these spacecrafts have only explored limited regions of the Solar System,” said Dr. Fumi Yoshida, who leads the FOSSIL project—short for Formation of the Outer Solar System: An Icy Legacy. Dr. Yoshida is affiliated with both the University of Occupational and Environmental Health and the Chiba Institute of Technology.
“Most of the vast Solar System remains unexplored. Wide-field observations with the Subaru Telescope are steadily pushing back the frontier,” the scientist added, highlighting just how important wide-field telescopes like Subaru are in these efforts.
After spotting the object, the team searched through archived data and discovered Ammonite had actually been seen before. They traced sightings back to 2021, 2014, and even as far back as 2005 when it was captured by the Kitt Peak National Observatory. These earlier observations helped verify the new findings.
One of the surprising discoveries was that Ammonite follows an orbit that’s unlike the other known sednoids. This could be a sign that the outer solar system is more varied and complex than astronomers had previously believed. It also puts some doubt on the theory that a giant, hidden planet—often referred to as Planet Nine—is controlling these unusual orbits.
That Planet Nine theory was developed to explain why some icy and distant space objects seem to cluster in a specific way. Ammonite’s different path now calls that explanation into question.
Adding to this, Dr. Yoshida noted: “Ammonite was found in a region far away where Neptune’s gravity has little influence. 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.”
“Understanding the orbital evolution and physical properties of these unique, distant objects is crucial for comprehending the full history of the Solar System.”
