A newly discovered object on the outer edge of our solar system is renewing debate over one of astronomy’s most elusive puzzles: the possible existence of a ninth planet.
Nicknamed “Ammonite,” the newly discovered object, officially designated 2023 KQ14, was found by Japanese astronomers using the Subaru Telescope on Maunakea, Hawaii. This discovery marks only the fourth sednoid ever found, joining an exclusive class of mysterious celestial bodies with strange, long orbits far beyond Pluto.
“In recent years, spacecraft have been sent to various small bodies in the Solar System for close observation and sample collection,” Fumi Yoshida of the University of Occupational and Environmental Health and the Chiba Institute of Technology, who leads the FOSSIL project, said in a statement.
“However, these spacecraft have only explored limited regions of the Solar System. Most of the vast Solar System remains unexplored,” Yoshida added. “Wide-field observations with the Subaru Telescope are steadily pushing back the frontier.”
Sednoids: The Search for Trans-Neptunian Objects
Sednoids are distant trans-Neptunian objects named after Sedna, the first of their kind discovered in 2003. These bodies orbit the Sun on highly elliptical paths that never bring them close to the known planets. Unlike Pluto, sednoids remain at great distances, far beyond the typical range of 30–50 astronomical units (AU) from the Sun. Sedna, for instance, swings between 76 AU and 900 AU. Ammonite has a similarly extreme trajectory, ranging from about 66 AU to 252 AU.
“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 National Astronomical Observatory of Japan, who conducted simulations of Ammonite’s orbit.
“It is possible that a planet once existed in the Solar System but was later ejected, causing the unusual orbits we see today,” says Huang.
Astronomers believe that clues hidden in these icy relics from the early solar system may point to the existence of an unseen giant planet. Earlier this year, studies from Taiwan and the U.S. weighed in on the subject, with one team estimating a 40% chance that such a planet exists.
Other Planet Nine Theories: Batygin & Brown
Planet Nine has been the subject of multiple hypotheses over the decades. One of the most prominent in recent years was proposed by Professor of Planetary Science Konstantin Batygin and Michael E. Brown, Professor of Planetary Astronomy, both at the California Institute of Technology (Caltech).
In 2016, Batygin and Brown discovered unusual clustering patterns in the orbits of distant Kuiper Belt Objects (KBOs). Statistical analysis indicated that there was only a 0.007% chance that these alignments were random, suggesting a likely gravitational influence from an unseen source.
In a 2022 interview, Batygin told The Debrief that the hypothetical Planet Nine “is a five to maybe 10 earth mass object that we think orbits the sun with a really long period, about once every 10,000 to 20,000 years.”
“We can see the gravitational influence that it exerts upon the outer solar system, but we have never seen the object directly,” Batygin told The Debrief at the time.
So what makes Batygin think the ninth planet exists at all? For the Caltech astronomer, it really comes down to the structure of the outer solar system, and specific alignments in the debris field known as the Kuiper belt.
“If you go and kind of zoom out, and look at the most distant orbits that we know of in this field of debris, then you will see that they all point [in] one direction,” Batygin told The Debrief in 2022. “ So the things that are kind of pristine, that are not strongly messed up by the other giant planets of the solar system, all point in the same direction.”
“That’s a gravitational one-way sign, if you will, that some more distant object is confining. These orbits, gravitationally, keep them together,” Batygin said.
“Ammonite’s inclination is near the orbital plane, but it does not show clustering with other stable objects,” Batygin told The Debrief in a recent follow-up email that asked how Ammonite’s orbital inclination and perihelion compare to those of other objects.
“Importantly, however, its semi-major axis is below the critical threshold for predicted clustering in our models, placing it in a parameter space where we wouldn’t necessarily expect clustering to occur,” he added.
Ammonite Breaks the Mold
Ammonite was discovered through a survey called FOSSIL (Formation of the Outer Solar System: An Icy Legacy). As the name suggests, it echoes the extinct marine mollusks that vanished 66 million years ago—and this distant world may offer similar ancient insights. After being spotted in 2023, astronomers confirmed its orbit in 2024 using the Canada-France-Hawaii Telescope and traced its path in archival images dating back nearly two decades.
Ammonite introduces a twist to current research. According to Dr. Huang, its orbital orientation doesn’t match that of the other known Sednoids. This misalignment, revealed through orbital simulations, suggests Ammonite may not have been shaped by the same gravitational forces—potentially weakening the case for Planet Nine.
“It’s possible that a planet once existed in the Solar System but was later ejected,” said Dr. Huang. “That could explain the orbits we see today.”
If Planet Nine is real, it may lie farther away than previously thought—or be more elusive than anticipated.
“This object is an intriguing addition to the census of Trans-Neptunian Objects (TNOs),” Batygin recently told The Debrief via email. “While dynamically stable, it does not fit neatly into the main group of perihelion-aligned bodies.”
“At first glance, it might seem to challenge the Planet Nine hypothesis. However, upon closer inspection, its semi-major axis is less than 250 AU — a boundary beyond which orbital clustering becomes prominent in our models,” Batygin said. “Thus, the Planet Nine theory can comfortably accommodate this new find.”
For now, Ammonite offers a tantalizing glimpse into a remote region of the solar system and may help reveal new secrets in the years ahead.
“We stand on the brink of numerous new discoveries,” Batygin added. “With the recent activation of the Vera Rubin Observatory, we anticipate an explosion in the census of distant TNOs over the next few years.”
“All theories and hypotheses, including Planet Nine, will soon face rigorous observational tests,” Batygin said.
The new paper, “Discovery and dynamics of a Sedna-like object with a perihelion of 66 au,” was published in Nature Astronomy.
Chrissy Newton is a PR professional and founder of VOCAB Communications. She currently appears on The Discovery Channel and Max and hosts the Rebelliously Curious podcast, which can be found on YouTube and on all audio podcast streaming platforms. Follow her on X: @ChrissyNewton, Instagram: @BeingChrissyNewton, and chrissynewton.com.