The Subaru Telescope has spotted a cosmic relic that could rewrite what we know about the early Solar System.
Nicknamed ‘Ammonite’ but officially designated 2023 KQ14, this newly discovered space rock is now the fourth known sednoid, a rare class of distant, icy bodies with highly elongated orbits that dance around the outermost fringes of our cosmic neighbourhood.
What makes Ammonite special? It’s not just its extreme orbit.
It’s a frozen relic from the dawn of the Solar System, offering clues about how our planets formed around the Sun, and whether a mysterious ninth planet still lurks in the darkness.
Finding Solar System fossils
Ammonite’s discovery comes courtesy of FOSSIL (Formation of the Outer Solar System: An Icy Legacy), a project aimed at uncovering ancient remnants of the early Solar System.
By studying relics from the Solar System’s formation, scientists can learn more about what our early cosmic neighbourhood was like.
This sort of science is also conducted by missions like Hayabusa 2 and OSIRIS-REx, which collected samples of asteroids and returned them to Earth for examination under laboratory conditions.
But the scope of such missions is limited to what can physically be reached by spacecraft and safely returned to Earth.
Launched in 2020 and led by an international team primarily from Japan and Taiwan, FOSSIL uses the Hyper Suprime-Cam (HSC) on the Subaru Telescope in Hawaii, one of the most powerful wide-field cameras on Earth.
“In recent years, spacecraft have been sent to various small bodies in the Solar System for close observation and sample collection,” says Dr. Fumi Yoshida of the University of Occupational and Environmental Health and the Chiba Institute of Technology, who leads FOSSIL.
“However, these spacecrafts have only explored limited regions of the Solar System. Most of the vast Solar System remains unexplored.
“Wide-field observations with the Subaru Telescope are steadily pushing back the frontier.”
A two-decade trail of clues
Although official discovery of Ammonite, 2023 KQ14, came in 2023 through Subaru’s observations, astronomers later found it in archived data stretching all the way back to 2005.
That includes images from the Dark Energy Camera and the Kitt Peak National Observatory.
These astronomical breadcrumbs give astronomers 19 years of observational data, enabling them to reconstruct Ammonite’s orbit
Ammonite has maintained a stable orbit around the Sun for at least 4.5 billion years – almost as old as the Sun itself – making it one of the oldest wanderers out there.
What Ammonite tells us about Planet Nine
Ammonite’s orbit doesn’t match those of other sednoids like Sedna, 2012 VP113, and 2015 TG387, which has implications for one of astronomy’s biggest mysteries: Planet Nine.
Some scientists believe the bizarre orbits of sednoids are due to the gravitational pull of an unseen planet far beyond Neptune — a so-called Planet Nine.
Evidence for Planet Nine was announced in a study released in April 2025.
But Ammonite breaks the pattern. Its orbit is different enough that it weakens the case for Planet Nine as it’s currently imagined.
“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,” says Dr. Yukun Huang of the National Astronomical Observatory of Japan, who conducted simulations of Ammonite’s.
“It is possible that a planet once existed in the Solar System but was later ejected, causing the unusual orbits we see today.”
One possibility is that a long-lost planet may have once stirred up the Solar System’s outer regions, only to be ejected, leaving behind scrambled orbits and icy fossils like Ammonite.
A new piece of the Solar System puzzle
The discovery of Ammonite challenges our current models and opens up new possibilities for what shaped the outer Solar System.
“This region is far from the Sun, where Neptune’s gravity has little influence,” says Dr. Yoshida.
“The presence of objects with elongated orbits and large perihelion distances implies that something extraordinary occurred during the ancient era when Ammonite formed.”
With telescopes like Subaru continuing to peer into the deep dark, the FOSSIL project is far from finished.
More discoveries like Ammonite could soon help us piece together the full story of our Solar System, from chaotic beginnings to the (relatively) quiet stability we enjoy today.
Read the full paper at www.nature.com/articles/s41550-025-02595-7