What’s Out Tonight?

A general ASTRONOMY site to get you started exploring the night sky

Kuiper Belt

Facts about the Kuiper Belt 

• The Kuiper belt is a left over debris field of ices that starts immediately after Neptune and extend farther than Pluto. 
• Pluto is the largest object in the Kuiper belt.

Diameters: Range from a few feet to 1,433 miles in diameter for Pluto. 
T otal Mass: 0.4 to 4 times that of our Moon. 
Compositions: Ices—frozen methane, ammonia, water and some silicates (rocks).

Distances from Sun: Varies from 2.8 to 5.1 billion miles. Neptune is 2.8 billion miles and Pluto is 3.7 billion miles from the Sun
Revolutions about Sun: Varies from 164 to 300 or more years 
Atmospheres: None of the Kuiper Belt Objects have atmospheres.

Moons: Some larger Kuiper Belt bodies have moons orbiting them. 

Observing with a small telescope: None of the objects in the Kuiper Belt can be seen visually with a small telescope—they are too far and faint.

The Kuiper Belt start immediately after Neptune and has a shape like ​a donut. The very bluish ball on the edge of the belt is Neptune. The object with the reddish orbit is Pluto and appears above the Kuiper Belt but it is part of the Belt.

The Kuiper Belt

The Kuiper Belt is an area of leftover debris from the formation of the solar system that starts immediately after Neptune and extends considerably farther than Pluto. Pluto is a member of the Kuiper belt. This belt is analogous to the asteroid belt between Mars and Jupiter. The main difference between the Kuiper Belt and the Asteroid belt is that the Kuiper belt is much larger in size and more massive (that is, it has more objects) and the objects in the Kuiper Belt are composed largely of various ices compared to the silicates (rocks) and metals of the Asteroid Belt. Pluto is the largest object in the Kuiper Belt. If a Kuiper Belt object came in close to the Sun, it would become a comet. 

In reality, the Kuiper Belt should not have been named in honor of Gerald Kuiper (1905–1973) because he advocated that such a belt would have disperse over time and should therefore not exit anymore. Kuiper died years before the existence of the Kuiper Belt was confirmed. Although Kuiper was an exceptional planetary scientist and made major contributions to astronomy, formulating a hypothesis about a belt of leftover material beyond Neptune was not one of them! So be it for history and those who want to honor those they like. A British astronomer by the name of Edgeworth, in 1943, first suggested the existence of the Kuiper Belt and for this reason, the Kuiper Belt is sometimes referred to as the Edgeworth-Kuiper Belt. 

The discovery and confirmation of the Kuiper Belt had to wait for modern computerized telescopes and digital imagery. However, the first vestiges of the Kuiper belt were the discoveries in 1977 and 1992 of two small ice bodies with orbits between Saturn and Uranus. The question was: Where did they come from? They had to have come from some place nearby because their unstable orbits suggested that they would last but a few million years. Computer simulations indicated that these objects did not come from the outer Oort Cloud of debris that surrounds our solar system at a great distance but from a source much closer in—in the area around Pluto. The astronomers who wrote an article about this simulation had referenced Kuiper in the first sentences of the paper and this is the reason that Kuiper’s name got stuck to this outer debris field. 

In 1988, the search for objects in the Kuiper Belt began but it took until 1992 to find the first and within six months, a second was discovered. In succeeding years, as more and more objects in the Kuiper Belt were discovered, Pluto was demoted to a Dwarf Planet in 2006 and became one of the larger objects within the Kuiper Belt. 

What is the Oort Cloud? Astronomers hypothesis that there is a distant giant spherical debris of ices that surrounds our solar system and may extend halfway to the nearest star or nearly 2 light years away or 12 trillion miles. The closest star to us is a little over 4 light years distant. This Oort Cloud starts at an estimated 1000 times farther than the Kuiper Belt. Some comets are believed to originate from this cloud.

Quaoar, a large Kuiper Belt Object discovered in 2002. It has a diameter around 1,370 miles and is 4 billion miles from the Sun. How do astronomers know that this is not a star? They take photographs on different days and if the star moves, it is most likely an object in our solar system. An orbit can be calculated after several days of movement.