What Vera Rubin observatory’s first new dwarf planet means

Back in 2006, the International Astronomical Union controversially demoted Pluto.

As part of that process, they officially defined “planet” and “dwarf planet” for the first time.

Dwarf planets all:

• orbit the Sun,
• aren’t moons,
• achieve hydrostatic equilibrium,
• but don’t clear their orbits.

Therefore, sufficiently massive asteroids like Ceres,

Kuiper belt objects like Pluto, Eris, Makemake, and Haumea,

and Oort cloud objects can achieve dwarf planethood.

Trans-Neptunian objects, ice-rich in composition, require estimated diameters of 400 km to likely achieve hydrostatic equilibrium.

Currently, the Vera C. Rubin Observatory surveys the visible southern skies every 3-4 nights.

Through successive imagery, it uncovers faint, distant, migrating Solar System objects.

Helped by automated code, Rubin scientists identified a remarkable object 2026 ED138.

“Precovery” images were spotted going back 10 years, enabling an orbital determination.

Based on its distance, brightness, and estimated reflectivity, it’s definitely a Trans-Neptunian object.

Its estimated size — between 600 km and 1500 km — places it firmly in dwarf planet territory.

However, no new dwarf planets have been officially recognized by the IAU since 2006.

2026 ED138, nicknamed “Ed“, becomes the 103rd known Trans-Neptunian object 400+ km in diameter.

The 14th brightest Trans-Neptunian object, future occultations should reveal its size.

Mostly Mute Monday tells an astronomical story in images, visuals, and no more than 200 words.

This article is featured on Big Think.