What Makes a Dwarf Planet
On 27 October 2026 astronomers using the new Vera C. Rubin Observatory announced 2026 ED138, an icy body perhaps 1,000 kilometres across, about 46 times farther from the Sun than Earth: if confirmed, the sixth recognised dwarf planet and among the largest and brightest bodies known beyond Neptune. This film explains how a moving dot is found among billions, why its size is still uncertain, the three tests the International Astronomical Union set for a planet in 2006 and the vote that made Pluto a dwarf planet, why big bodies pull themselves round, the five recognised dwarf planets from Ceres to Eris, and the crowded, cold Kuiper belt where more are probably waiting.
Round, orbiting, and not alone
A new world, and an old argument.
A moving dot
Stars stay put. Worlds in the solar system move.
What is a planet?
A definition written in 2006.
Round and crowded
Big enough to be round, too small to clear its path.
The five
One near, four far.
The Kuiper belt
A cold, crowded ring of leftovers.
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