2026 ED138: Could Our Solar System Have a Sixth Dwarf Planet?

For years, the official count of dwarf planets in our Solar System has stood at five. That number might be about to change.

On 27 October 2026, the International Astronomical Union's Minor Planet Center announced a large, bright object far beyond Pluto. It has the provisional name 2026 ED138, and scientists at the NSF–DOE Vera C. Rubin Observatory in Chile say it is a strong dwarf planet candidate.

What has been found?

According to Rubin Observatory, ED138 is a trans-Neptunian object, meaning it circles the Sun farther out than Neptune. It is currently about 46 astronomical units away. One astronomical unit (au) is the average Earth–Sun distance, and Pluto's average distance is about 40 au, so this new world is out beyond Pluto right now.

Based on its distance, brightness and how much light its surface probably reflects, the team estimates ED138 is between 600 and 1,500 kilometres wide. Rubin notes that icy bodies this large are expected to be pulled into a round shape by their own gravity, and being round is one of the key tests for a dwarf planet.

If it is confirmed, ED138 would join the five dwarf planets recognised by the IAU: Pluto, Ceres, Eris, Haumea and Makemake.

How was it discovered?

The story starts on the evening of 13 October 2026. Astronomer Matthew Holman of the Center for Astrophysics | Harvard & Smithsonian was running Rubin data through a search program he developed with colleague Kevin Napier. The code compares billions of detections of moving objects and links together the ones that belong to the same body.

ED138 popped out, and its brightness and distance immediately suggested it was unusually large. Holman has said his first reaction was excited disbelief, and that he started checking whether he or the code had made a mistake.

They had not. Rubin's Solar System lead scientist Mario Jurić of the University of Washington searched the observatory's catalogues and found more sightings. In total, Rubin's telescope had observed ED138 30 times on 20 nights between 4 March and 11 July 2026. Older images from the Dark Energy Camera in Chile pushed the record back to 2016, giving more than ten years of orbit tracking.

Why nobody spotted it before

This is the most surprising part. Something this big and bright should have been found long ago. The reason it was missed is its location.

ED138 sits in a part of the sky close to the plane of the Milky Way, a crowded region packed with millions of stars. To most telescopes, it was lost in the background. A note on the Rubin community forum adds that earlier surveys either avoided this crowded area or covered it only shallowly.

Rubin is different. It scans the entire southern sky again and again, and its software sifts through huge numbers of points of light to find the few that are moving. That combination is what pulled ED138 out of the crowd.

A tilted, disturbed orbit

According to Rubin Observatory, ED138's orbit is tilted almost 25 degrees compared with the flat plane where most planets travel. That places it in a group called hot-classical objects and suggests that, long ago, gravity from Neptune pushed it off its original path.

The forum post gives more detail: an orbital tilt of about 24.4 degrees, and an orbit that may be linked to a 12:7 rhythm with Neptune, similar to dwarf planet Haumea, though that link is not settled yet. It also notes that ED138 is the brightest such object found since 2013.

Is it officially a dwarf planet now?

Not yet. The size estimate depends on how reflective the surface is, and that is still unknown. Rubin says infrared observations are needed to pin down the exact size and confirm what it really is. Until then, it remains a candidate.

Why this matters

Objects like ED138 are leftovers from the birth of the Solar System. Studying their size, makeup and orbits helps scientists understand how the giant planets moved around early in our system's history and how smaller bodies got scattered.

It is also a sign of things to come. Rubin's main ten-year survey, the Legacy Survey of Space and Time, began in June 2026. Even before that, in April, the team submitted observations of more than 11,000 new asteroids, including roughly 380 new objects beyond Neptune. Holman has said that because Rubin will keep imaging the southern sky for ten years, other large worlds hiding in places earlier surveys skipped are now within reach.

The Globitz take

We often think the map of our Solar System is finished. ED138 shows it is not. A world possibly hundreds of kilometres wide was sitting in plain sight, hidden only by a crowd of stars. If infrared telescopes confirm it, school textbooks may soon need a new line.