Astronomers spot 'Ammonite', a distant world that questions planet nine

The orbit of the newly found dwarf planet ‘Ammonite’ (2023 KQ14, marked in red) is shown alongside the orbits of the other three known sednoids (in white). (Image: NAOJ)

Sky watchers might just have a new favourite. Astronomers have found a mysterious object drifting beyond Pluto. Named Ammonite, it could change how we understand our solar system’s edge.

Spotted After Years, Far Past Pluto

In March 2023, Japan's Subaru Telescope in Hawaii detected a faint, icy body. Now named 2023 KQ14, or Ammonite, it lies well beyond Pluto. The object was uncovered as part of the FOSSIL survey, a project exploring the far reaches of space. Its nickname comes from the spiral fossil of an extinct sea creature. The team behind the find shared their results in Nature Astronomy on 14 July.

Ammonite joins a tiny group of celestial oddities. It's the fourth known sednoid, a type of distant object with an unusual orbit. Sednoids move far beyond Neptune, the outermost known planet. Sedna, the first sednoid found in 2004, gave the group its name. While Sedna ranges between 76 and 900 astronomical units (AU) from the Sun, Ammonite’s orbit stretches from 66 to 252 AU.

A Blow to the Planet Nine Idea

The Planet Nine theory has long puzzled scientists. It suggests a hidden Neptune-sized planet might lurk in deep space. This idea came from noticing strange orbits of small icy bodies in the Kuiper Belt. Many believed a larger planet’s gravity was behind it.

But Ammonite may weaken that belief. Its orbit doesn’t follow the same pattern as the others. In fact, its farthest point lies in the opposite direction. This misalignment could mean there is no giant planet guiding these paths.

Yukun Huang, one of the researchers, explained this shift. He said Ammonite’s orbit lowers the chances of Planet Nine being real. Another team member, Shiang-Yu Wang, noted that the original idea relied on aligned orbits. Ammonite breaks this rule.

What Happens Next in the Search

Still, not all experts are ready to let the idea go. Some suggest a ninth planet may once have existed. Others think it might still be hiding far beyond our reach. Christopher Impey from the University of Arizona remains hopeful. He believes the Rubin Observatory in Chile could soon find answers.

That telescope is expected to scan the night sky in great detail. If a hidden planet is out there, it might not remain hidden for long.

For now, though, Ammonite adds another twist to a space mystery that’s far from solved.