The Kuiper Belt (sometimes referred to as the Kuiper-Edgeworth Belt) is an area of the outer solar system that is estimated to stretch across 20 astronomical units (AU) of space. It contains small solar system bodies made mostly of ices. The ices are frozen volatiles (gases) such as methane, ammonia, nitrogen and water. It also is home to the known dwarf planets Pluto, Haumea, Sedna, and Makemake.
The Kuiper-Edgeworth Belt is named for the astronomers Gerard Kuiper, who theorized about a disk of material in the outer reaches of the solar system, and Kenneth Edgeworth, who had the idea that the outer solar system contained a number of small bodies, perhaps left over from the formation of the Sun and planets. This region of space is cold enough to support the existence of volatiles more easily than areas closer to the Sun.
Kuiper Belt Location
The Kuiper Belt extends from roughly the orbit of Neptune (at 30 AU out to about 55 astronomical units from the Sun. The main body of this belt covers much of this region, ranging from nearly 40 AU to 48 AU. It is thick in most places and astronomers have described it as being more torus-shaped than a belt would be. Other regions of the Kuiper Belt include a disk of scattered objects that are part of a population of worlds called Trans-Neptunian Objects.
Facts about the Kuiper Belt
1. The Kuiper Belt could contain hundreds of thousands of icy bodies that range in size from small chunks of ice to worldlets larger than 100 kilometers across.
2. Astronomers have tracked most short-period comets from their origins in the Kuiper Belt. These are comets with orbital periods of 200 years or less.
3. There could be more than a trillion comet nuclei in the main body of the Kuiper Belt.
4. The largest Kuiper Belt Objects are Pluto, Quaoar, Makemake, Haumea, Ixion, Sedna, and Varuna. These are often also referred to as Trans-Neptunian Objects (TNOs).
5. The first mission to the Kuiper Belt and beyond flew by Pluto in July 2015. It’s called New Horizons and surveyed Pluto, Charon and the other four Plutonian moons before heading out to study other Kuiper Belt Objects in the future.
6. Astronomers have found structures similar to our Kuiper Belt around at least nine other stars. Hubble Space Telescope imaged discs around the stars HD 138664 in the constellation Lupus, and HD 53143 in the constellation Carina.
The Kuiper Belt (also known as the Kuiper-Edgeworth Belt) is a disk-shaped region found in the outer solar system, past the orbit of Neptune. It extends from the orbit of Neptune at around 30 Astronomical Units (AU) out to around 50 AU from the Sun and contains hundreds of millions of small icy bodies that are thought to be left over material from the formation of the outer planets.
What is the Kuiper Belt?
The Kuiper Belt is similar to the asteroid belt found between the orbits of Mars and Jupiter, but it is 20 times as wide and somewhere between 20-200 times more massive. The ices are frozen volatiles that are made up of methane, nitrogen, ammonia and water.
At least three dwarf planets are located in the Kuiper belt: Pluto, Haumea and Makemake. Also, some of the solar system’s moons are thought to have originated there, such as Neptune’s Triton and Saturn’s Phoebe.
The belt is thick in most places and is described as being more torus-shaped than a belt would be. The Kuiper belt shouldn’t be confused with the hypothesized Oort cloud, which is a thousand times more distant.
The objects within the belt, along with the members of the scattered disc and any potential Hill cloud or Oort cloud objects are known collectively as trans-Neptunian Objects (TNO).
Kuiper Belt facts
• The Kuiper belt contains millions of icy objects ranging in size from small lumps of ice to large objects of 100 km in diameter or more.
• It is estimated that there are around 35,000 Kuiper belt objects that are larger than 100 km in diameter. This is several hundred times the number and mass of objects found in the asteroid belt.
• There may be as many as 100 million small and faint objects in the belt, with a diameter of 20 km or less. These findings by Anita Cochran and a team of astronomers could not be confirmed by a follow-up Hubble Space Telescope observation though.
• The largest object in the Kuiper belt is the dwarf planet Pluto. Its status as part of the belt is what caused the planet to be reclassified as a “dwarf planet” in 2006.
• Eris is larger than Pluto, however, is located in the scattered disc – although it is believed that it was originally found in the Kuiper belt.
• Neptune’s moon Triton is also larger than Pluto and is believed to have been captured from the Kuiper belt due to gravitational encounters.
• The first mission to the Kuiper belt and beyond is NASA’s New Horizons which flew past Pluto in July 2015. It surveyed Pluto, Charon, and the other moons before continuing its course to the other objects in the belt and beyond.
• Pluto is named after the Greek god of the underworld.
This is a later name for the more well-known Hades and was proposed by Venetia Burney an eleven-year-old schoolgirl from Oxford, England.
• Pluto was reclassified from a planet to a dwarf planet in 2006.
This is when the IAU formalized the definition of a planet as “A planet is a celestial body that (a) is in orbit around the Sun, (b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape, and (c) has cleared the neighborhood around its orbit.”
• Pluto was discovered on February 18th, 1930 by the Lowell Observatory.
For the 76 years between Pluto being discovered and the time it was reclassified as a dwarf planet it completed under a third of its orbit around the Sun.
• Pluto has five known moons.
The moons are Charon (discovered in 1978,), Hydra and Nix (both discovered in 2005), Kerberos originally P4 (discovered 2011) and Styx originally P5 (discovered 2012) official designations S/2011 (134340) 1 and S/2012 (134340) 1.
• Pluto is the largest dwarf planet.
At one point it was thought this could be Eris. Currently the most accurate measurements give Eris an average diameter of 2,326km with a margin of error of 12km, while Pluto’s diameter is 2,372km with a 2km margin of error.
• Pluto is one third water.
This is in the form of water ice which is more than 3 times as much water as in all the Earth’s oceans, the remaining two thirds are rock. Pluto’s surface is covered with ices, and has several mountain ranges, light and dark regions, and a scattering of craters.
• Pluto is smaller than a number of moons.
These are Ganymede, Titan, Callisto, Io, Europa, Triton, and the Earth’s moon. Pluto has 66% of the diameter of the Earth’s moon and 18% of its mass. While it is now confirmed that Pluto is the largest dwarf planet for around 10 years it was thought that this was Eris.
• Pluto has an eccentric and inclined orbit.
This takes it between 4.4 and 7.3 billion km from the Sun meaning Pluto is periodically closer to the Sun than Neptune.
• Pluto has been visited by one spacecraft.
The New Horizons spacecraft, which was launched in 2006, flew by Pluto on the 14th of July 2015 and took a series of images and other measurements. New Horizons is now on its way to the Kuiper Belt to explore even more distant objects.
• Pluto’s location was predicted by Percival Lowell in 1915.
The prediction came from deviations he initially observed in 1905 in the orbits of Uranus and Neptune.
Pluto is the second closest dwarf planet to the Sun and from 1930 when it was discovered up until 2006, it was also considered the ninth planet of the solar system. It is also the second largest dwarf planet, with Eris being the most massive known dwarf planet.
On July 14, 2015, The New Horizons mission did a Pluto flyby to capture the first high resolution photographs of the planet and gather incredible data on Pluto and its worlds.
The moons of Pluto
Pluto has 5 known moons. In order of distance from Pluto, these are Charon, Styx, Nix, Kerberos and Hydra. Charon is the largest of the moons and mutually tidally locked with Pluto. This is a gravitational lock that makes one side of an astronomical body always face the another – for example how the same side of the Moon always faces Earth. Charon hovers over the same spot on Pluto – and the same side of Charon always faces Pluto.
Charon is also so large that Pluto-Charon are sometimes considered a double object, a double dwarf planet or a binary system.
Facts about Pluto
• Pluto was discovered on February 18th, 1930 by Clyde Tombaugh of the Lowell Observatory. In the 76 years between its discovery and subsequent reclassification as a dwarf planet, the planet completed under one third of its orbit around the Sun.
• In 2006, Pluto was reclassified from a planet to a dwarf planet. This happened after the IAU formalized the definition of a planet as “A planet is a celestial body that (a) is in orbit around the Sun, (b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape, and (c) has cleared the neighborhood around its orbit.“.
• The planet is named for Pluto, the Roman god of the underworld – the Roman alternative for the Greek god Hades. The name was proposed by an eleven-year-old schoolgirl from Oxford, England by the name of Venetia Burney.
• It takes Pluto 246.04 Earth years to orbit the Sun.
• Pluto has five known moons. These are Charon, Styx, Nix, Kerberos and Hydra. The latter two moons were known as S/2011 (134340) 1 and S/2012 (134340) 1 before they were officially named.
• Pluto is smaller than many moons. When it was first discovered, Pluto’s small size surprised the scientific community who predicted it would be as large as Jupiter. The moons Ganymede, Titan, Callisto, Io, Europa, Triton, and the Earth’s moon are all larger than Pluto. It has 66% of the Moon’s diameter and just 18% of its mass.
• Sunlight on Pluto has the same intensity as moonlight on Earth. This is because it located so far from the Sun in the outer solar system – approximately 5,945,900,000 km.
• Either Pluto or Eris is the largest dwarf planet. The most accurate measurements currently put Eris at an average diameter of 2,326 km with a 12 km margin of error, compared to a 2,368 km diameter with a 20 km margin of error for Pluto. The atmosphere on Pluto makes it difficult to accurately map its size.
• The orbit of Pluto is eccentric and inclined. This means that the orbit takes it anywhere from 4.4 to 7.4 km from the Sun and that periodically Pluto is actually close to the Sun than the eight planet, Neptune.
• The first spacecraft will visit Pluto in July 2015. The New Horizons mission, launched in 2006 did a Pluto flyby on July 14th, 2015, on its way to the distant Kuiper Belt after almost a decade of flight.
• The term “plutoid” is used to describe objects in the solar system that are rounded and orbit the Sun beyond the orbit of Neptune. There are currently only four recognized plutoids – Pluto, Eris, Haumea and Makemake. Some astronomers believe they are at least 70 more objects that could be plutoids and are awaiting classification.
• Pluto and its moon Charon form a binary system. This means that the center of mass of the two objects is outside of Pluto and Pluto moves in small circles while Charon orbits it.
• The orbit of Pluto is chaotic and unpredictable. Scientists are able to predict the location of Pluto along its orbit path for the next 10-20 million years – beyond that it is unknown.
• It took sunlight over 3 hours to reach the New Horizons mission flying to Pluto.
• Some of the ashes of Clyde Tombaugh, the astronomer who discovered Pluto, are onboard the New Horizons probe that went to Pluto and beyond.
• Scientists believe that Pluto is made up of 50–70% rock and 30–50% ice by mass.
• Pluto is expected to have a solid rocky core, surrounded by a water ice mantle and a frozen nitrogen surface.
• Pluto’s core is predicted to be around 70% of its total diameter. This would put the core at around 1,700 km in diameter (1,000 miles).
• Pluto has an atmosphere sometimes. When Pluto is closer to the Sun on its elliptical orbit path the surface ice thaws and forms a thin atmosphere of nitrogen, methane and carbon monoxide. As it travels away from the Sun this then freezes back into its solid state.
The history of Pluto
Pluto is a dwarf planet that was discovered in 1930 by Clyde Tombaugh, who at the time was working at the Lowell Observatory in Flagstaff, Arizona. Tombaugh discovered Pluto accidentally while looking for an unknown planet called Planet X that was causing disturbances in the orbits of Uranus and Neptune. By comparing two photographs of the night sky taken one week apart, he noticed an unknown faint spot that had possibly moved. Photographs obtained later confirmed the moving object and after receiving suggestions for the new planet’s name from around the world, the name Pluto was announced on May 1, 1930. Later observations of Pluto however showed that it was not the Planet X that astronomers were looking for. In fact, it was later shown that Planet X did not really exist.
Pluto lies within a disc-shaped zone beyond Neptune’s orbit populated by tiny icy objects. This region is called the Kuiper Belt and its inhabitants are referred to as Kuiper Belt objects or trans-Neptunian objects. But in recognition of Pluto’s special place in astronomical history when it was downgraded to a dwarf planet, objects found in this region are also called “plutoids”. This icy region is believed to have formed in the early evolution of the Solar System. Not all plutoids are tiny. Eris, another dwarf planet, is actually more massive than Pluto. Because of its distance, it is difficult to determine what Pluto is made of. But it is believed to be composed of a rocky core, a mantle of water ice and a surface covered with methane ice and frosty nitrogen.
Although Pluto is the second largest dwarf planet in the Solar System (after Eris), its diameter of 2,302 km (1430.4 mi) is only two-thirds that of the Earth’s moon. It has a mass of 1.31 x 1022 kg, which is one-sixth that of the moon. Pluto is smaller than Jupiter’s four largest moons (Io, Ganymede, Europa and Callisto) and the largest moons of Saturn (Titan) and Neptune (Triton).
Pluto’s orbit around the Sun takes 246.02 Earth years. Unlike the eight planets in the Solar System, which have a more or less circular and flat orbit, the dwarf planet’s orbit is elliptical and highly inclined, similar to the dwarf planet Eris. Its perihelion brings it 4.44 x 109 km (2.76 x 106 mi) closer to the Sun, but this is 30 times farther than the Earth is to the Sun. Its aphelion takes it 7.37612 x 109 km (4.58 x 109 mi) away from the Sun, which is 48 times the Earth’s aphelion. When Pluto is close to the Sun, its icy surface melts, rises and forms a thin layer of gaseous atmosphere comprised of nitrogen, methane and carbon monoxide. As the dwarf planet moves farther away, this atmosphere freezes and falls back to the surface. Pluto completes one rotation in 6.39 Earth days. Its rotation is retrograde, meaning it rotates from east to west like the planets Uranus and Venus. Because it has an axial tilt of 122.5°, it actually rotates on its side. This creates extreme variations in its seasons.
In 1978, almost 50 years after Pluto’s discovery, the first moon orbiting the dwarf planet was discovered. Charon is nearly half of Pluto’s size and orbits 19,640 km (12,200 mi) away from it. Photographs taken of these two bodies show that Charon is gray, whereas Pluto is red. This indicates that their surfaces are composed of different materials. In 2005, the Hubble Space Telescope discovered two additional moons orbiting Pluto, which were named Nix and Hydra. These two moons’ orbits are farther away from the dwarf planet than Charon. In 2011 and 2012, two more moons were discovered by Hubble and they are temporarily named P4 and P5.