The Kuiper Belt, a ring of icy bodies in the outer solar system, lies just beyond the orbit of:

The Kuiper Belt is a doughnut-shaped region of icy bodies that lies just beyond the orbit of Neptune, roughly 30 to 50 Astronomical Units (AU) from the Sun. One AU is the average distance between the Earth and the Sun, about 150 million km.

What the Kuiper Belt contains:

• Millions of icy bodies made of frozen water, ammonia and methane, along with rock and dust.
• Several dwarf planets and large objects, such as Haumea and Makemake.
• These objects are leftovers from the formation of the solar system, about 4.6 billion years ago, that never grew into planets.

Naming:

• The belt is named after the Dutch-American astronomer Gerard Kuiper, who in 1951 discussed the possibility of such objects.
• The Irish astronomer Kenneth Edgeworth had suggested a similar idea earlier, so it is sometimes called the Edgeworth-Kuiper Belt.

Importance:

• It is the main source of short-period comets, which take less than 200 years to orbit the Sun.
• Studying its objects helps scientists understand the early solar system.

Exploration:

NASA's New Horizons spacecraft flew past a Kuiper Belt object called Arrokoth in January 2019. It was the most distant object ever explored closely by a spacecraft at that time.

Comparison with the asteroid belt:

• The Kuiper Belt is about 20 times wider and much more massive than the asteroid belt.
• Asteroid belt objects are mainly rocky and metallic, while Kuiper Belt objects are mostly icy.
• Much farther out is the Oort Cloud, thought to be the source of long-period comets.

About Neptune:

• Neptune is the eighth and farthest planet from the Sun.
• It was discovered in 1846 by Johann Galle, based on mathematical predictions by Urbain Le Verrier and John Couch Adams.

Why not the other options?

• ✗Mars, Jupiter and Saturn lie well inside the Kuiper Belt; Neptune is the outermost planet.