New Dwarf Planet Candidate 2026 ED138 Likely Found Beyond Neptune in the Kuiper Belt

Summary

In this Science Friday episode Flora Lichtman talks with Dr. Matthew Holman about the discovery of a distant dwarf planet candidate beyond Neptune, 2026 ED138, spotted in the Kuiper Belt by the Vera Rubin Observatory. The discussion outlines how astronomers vet moving objects to rule out false positives, how light from the object informs size estimates, and the methods that could confirm its spherical shape through thermal infrared measurements or occultations. The conversation compares the object to Pluto and touches on what redness implies about surface composition. The host also explores the naming process and invites listener suggestions for the object’s name.

• The object is likely in the Kuiper Belt and may be 600 to 1500 kilometers across.
• Size and mass remain uncertain because we only see reflected light; thermal infrared or occultation measurements could constrain the true size.
• The redness of the surface suggests a composition different from the freshest methane frost seen on larger dwarf planets.
• Names for such objects are proposed by a nomenclature committee, with audience input encouraged.

Overview

The podcast features Flora Lichtman speaking with Dr. Matthew Holman about the detection of a potential new dwarf planet, 2026 ED138, in the Kuiper Belt. The Vera Rubin Observatory is credited with the discovery. The discussion emphasizes the process by which astronomers confirm such detections and distinguish real objects from false positives that commonly arise in that very small subfield of astronomy.

Discovery and Vetting

Holman explains that the initial data come from software that identifies moving objects, but confirmation requires going through various tests to rule out false positives. A key point is that if ED138 is real, it would be relatively large for a Kuiper Belt object, which makes vetting particularly important. He notes the challenge of distinguishing a large, dark body from a smaller, highly reflective one based solely on reflected sunlight, which drives the need for additional measurements.

Two primary methods to determine actual size are discussed: thermal infrared observations to measure the object's own glow and occultations, where the object passes in front of background stars, allowing size estimation from the light curve during the occultation.

Color, Size, and Comparison

The object is described as fairly red, which contrasts with the neutral, highly reflective surfaces of the largest dwarf planets that have fresh frost. Based on current data, ED138’s diameter is estimated to lie between about 600 km and 1500 km, making it smaller than Pluto (roughly 2400 km in diameter) but still a substantial body in the Kuiper Belt.

Why Now and How Many?

Holman discusses why such objects are difficult to find—southern-hemisphere visibility during the object’s sky passage and significant star field noise from the Milky Way make detection challenging. He estimates there are likely one to three objects as bright as ED138 in the Kuiper Belt, with many more distant and fainter bodies awaiting discovery because brightness falls off with distance squared from the Sun.

Naming and Public Involvement

The conversation turns to naming ED138. Holman expresses a reluctance to settle on a name before the object’s true status is confirmed and mentions a past experience naming moons after dances, which was not approved by the nomenclature committee. Flora invites listeners to submit ideas and provides contact details, highlighting a potential theme for naming objects tied to ideas of discovery and things previously hidden. The discussion also covers how names are typically assigned to objects beyond Neptune, often drawing on mythological or cultural figures.

Takeaways and Future Work

The episode closes with reflections on the broader significance of finding new distant worlds. Holman emphasizes that this discovery represents the ongoing exploration of the solar system and the possibility of unveiling even larger, more distant bodies in the Kuiper Belt. He underscores the motivational aspect of continued exploration and the role of public engagement in science naming conventions.