Possible Dwarf Planet Found Beyond Pluto, Roughly the Size of Texas

Astronomers have found a candidate dwarf planet in the outer reaches of the Solar System, according to New Atlas. Provisionally named 2026 ED138, the icy object turned up in early data from the Vera C. Rubin Observatory in Chile. New Atlas puts its width at somewhere between 600 and 1,500 kilometers (373 and 932 miles), which it compares to the size of Texas.

That size is only a rough estimate, and the object has not been confirmed as a dwarf planet. Here is what is known so far.

What exactly was found?

A chunk of ice and rock, currently about 46 times farther from the Sun than Earth is. For comparison, New Atlas says Pluto's average distance is about 40 times Earth's. The object appears to orbit close to the plane of the Milky Way, where millions of background stars make it hard to pick out faint, slowly moving specks.

Who spotted it, and how?

Harvard & Smithsonian astrophysicist Matthew Holman was processing archived Rubin data with software he developed with colleague Kevin Napier when a signal emerged. The code is designed to connect detections scattered across Rubin's huge collection of observations. Given the distance, the object's brightness suggested something unusually large. Holman described his first reaction as “excited disbelief.”

University of Washington astronomer Mario Jurić then found another 20 observations in Rubin's records that hinted at a possible dwarf planet. Searches of older survey images extended the object's observational history back to 2016, giving astronomers about a decade of evidence to reconstruct its likely orbit. The discovery was announced this week, based on observations gathered while Rubin was still preparing for its main survey.

How big is it, really?

Nobody can say yet. A small object with a shiny surface can reflect as much sunlight as a larger, darker one, so brightness alone leaves plenty of room for interpretation. Until researchers pin down how reflective the surface is, New Atlas says, the diameter should be treated as a ballpark estimate. Observations at longer wavelengths could help by measuring radiation emitted by the object itself rather than sunlight bouncing off it.

What would make it a dwarf planet?

Under the International Astronomical Union's definition, a dwarf planet must orbit the Sun, be massive enough for gravity to pull it into a nearly round shape, and have failed to clear its orbital neighborhood. It also cannot be a moon. New Atlas notes that an icy body within the estimated size range has a good chance of being fairly round, which makes it a promising candidate. If confirmed, it would receive a new name and join Pluto, Eris, Haumea, Makemake and Ceres.

Is this the long-sought Planet Nine?

No. According to New Atlas, 2026 ED138 is far too small and too close to fit the Planet Nine hypothesis, a proposed heavyweight world meant to explain the unusual orbital clustering of some distant objects. The object's orbit is tilted about 25 degrees from the plane of the Solar System, which New Atlas says suggests a gravitational encounter with a massive body such as Neptune may have nudged it off its original path.

Why does it matter?

For general readers, the find is a first glimpse of what the new observatory was built to do. Rubin sits on Cerro Pachón and pairs an 8.4-meter (28-foot) telescope with a 3,200-megapixel camera, described as the largest digital camera ever built. Over its decade-long Legacy Survey of Space and Time, it will repeatedly photograph the southern sky every few nights, producing what New Atlas calls a cosmic movie. By comparing images, researchers can tell objects that move or change brightness from the static background.

That record could reveal new asteroids, hidden comets and exploding stars, offering insights into subjects from dark matter to the history of the Solar System. A faint world that went unnoticed for a decade in older images shows how much data like this can still hold.

Around Prague, based on reporting by New Atlas