The Kuiper Belt is an immense donut-shaped cluster of icy objects at the outer edges of our solar system, beyond the orbit of Neptune. Astronomers believe that millions of Kuiper Belt objects (KBOs), which are smaller than planets, are remnants left over from the formation of the solar system.

It is theorized that the icy KBOs might have come together to form planets if they had not been in the area of Neptune. But Neptune's gravity stirred up this region of space so much that the small, icy objects were not able to coalesce into a large planet.

On January 1st 2019, NASA’s New Horizons space probe flew past Arrokoth, the KBO in the photo. At the time of the probe's fly-by, Arrokoth became the most distant and most primitive object ever explored by a spacecraft. Arrokoth's deep red hue and snowman shape were unlike any ever seen, and came as a surprise to the New Horizons researchers.

Another more well-known object is also located in the Kuiper Belt: the ex-planet Pluto. In 2006, the International Astronomical Union pronounced that Pluto would no longer be considered a planet, but rather a 'dwarf planet'. After discovery of dwarf planets larger than Pluto in the Kuiper Belt, a new definition for planets was required. It stated that a planet must "clear out' other objects in the vicinity of its orbit. Sharing an orbit with other KBOs, Pluto no longer qualified as a planet.

The Kuiper Belt was named after Gérard Kuiper, a Dutch-american astronomer.

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