What Astronomers Know About Possible Dwarf Planet ED138

What is ED138?

ED138 is the provisional name for a newly spotted, distant object in our solar system. It is described as icy and is beyond Pluto. Its full provisional designation is 2026 ED138. ²

The object was noticed earlier in October while scientist Matthew Holman examined data from the Simonyi Survey Telescope at the Vera C. Rubin Observatory. Mario Jurić and colleagues contributed additional observations, according to the report of the discovery. ²

For now, the careful description is “dwarf planet candidate.” That means astronomers think it may meet the definition, not that it has already been accepted as one.

How big is ED138?

One report gives an early estimated diameter of 600 to 1,500 kilometers. That is a broad range, so it should not be treated as a precise measurement. ³

Another report says initial measurements put ED138 among the largest dwarf planet candidates found beyond Neptune. The supplied reports do not explain the measurement method or provide a final size. ²

Objects this far away are difficult to measure directly. Astronomers therefore need more observations to narrow the estimate and learn whether the body is large enough, and shaped in the right way, to fit the dwarf-planet category.

What makes an object a dwarf planet?

The International Astronomical Union’s definition requires a dwarf planet to orbit the Sun, be nearly round because its own gravity has shaped it, and not have cleared other objects from its orbital neighborhood. It also cannot be a moon. ²⁴

Being large does not automatically settle the question. A candidate’s shape matters, and astronomers must also distinguish a dwarf planet from other small bodies that orbit the Sun.

The recognized list is small. One supplied report names Pluto, Ceres, Eris, Haumea and Makemake as the five recognized dwarf planets. ² The exact treatment of some borderline objects can vary: the supplied reference material notes that definitions and practical classification have not always been applied consistently. ⁴

How will astronomers confirm ED138’s status?

First, astronomers need to keep observing it. Repeated observations help establish its path around the Sun and support a more reliable record of where it is. The available reports say additional observations were made, but do not set out a specific timetable for confirmation. ²

They also need stronger evidence about its physical size and shape. If it is large enough for gravity to make it nearly round, and it meets the other parts of the definition, that would support classifying it as a dwarf planet. ²⁴

The sources do not describe a single test or say that a decision has been made. ED138’s current status should therefore remain provisional until evidence is sufficient and its classification is settled.

Why was ED138 found now, and why does it matter?

ED138 turned up in early observations from the Rubin Observatory, using the Simonyi Survey Telescope. The discovery shows how new survey data can help astronomers find faint objects against a crowded background of stars. ²³

Finding another candidate would help researchers study the distant, icy population beyond Neptune and test how many bodies there may be that are large enough to become rounded by gravity. The number of dwarf planets in the solar system is not known; estimates and classification approaches differ. ⁴

For the public, the main point is that ED138 is an interesting new candidate, not a newly confirmed member of the dwarf-planet list. Its size and final classification remain open questions.