Beyond Neptune lies a vast ring of icy worlds. It's like the asteroid belt, but around 20 times as wide and far more massive.
Pluto is the best known, but the first other object here wasn't found until 1992. Thousands are known now, and there may be hundreds of thousands more than 100 km wide.
These are untouched leftovers from the birth of the planets, kept in a deep freeze for 4.5 billion years.
In 2019 New Horizons flew past one of them, Arrokoth, a reddish snowman of two lumps that gently stuck together. It's the most distant world ever explored up close.
Many of the comets that swing past the Sun come from out here.
- Where
- About 4.5 to 7.5 billion km from the Sun
- Thought to hold
- Hundreds of thousands of icy bodies over 100 km wide
- Biggest
- Pluto, 2,377 km wide
- Visited
- Once, by New Horizons
