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Beyond Neptune’s orbit, a diverse collection of thousands of dwarf planets and other relatively small objects live in a region called the Kuiper Belt.
These often untouched remnants of our solar system’s formative days are called Kuiper Belt Objects, or Trans-Neptunian Objects. NASA’s upcoming James Webb Space Telescope will examine an assortment of these icy bodies in a series of programs called Guaranteed Time Observations shortly after its launch in 2021. The goal is to learn more about how our solar system was formed.
“These are objects found in the cemetery of the formation of the solar system,” explained Jonathan Lunine of Cornell University, a Webb interdisciplinary scientist who will use Webb to study some of these objectives. “They’re in a place where they could last billions of years, and there aren’t many places like that in our solar system. We’d like to know what they are like.”
By studying these bodies, Lunine and her colleagues hope to find out which ices were present in the early solar system. These are the coldest worlds to show geological and atmospheric activity, so scientists are also interested in comparing them to planets.
Kuiper belt objects are very cold and faint, however they glow in infrared light, which is wavelengths beyond what our human eyes can see. Webb is specifically designed to detect infrared light. To study these distant objects, scientists will primarily use a technique called spectroscopy, which divides light into its individual colors to determine the properties of materials that interact with that light.
A large assortment
Kuiper belt inhabitants come in various shapes and sizes. Some reside in pairs or multiples, while others have rings or moons. They exhibit a wide range of colors, which can indicate different training histories or different exposure to sunlight.
“Some appear redder, others are bluer. Why?” said Heidi Hammel, a Webb interdisciplinary scientist for solar system observations. He is also vice president of science at the Association of Universities for Research in Astronomy (AURA) in Washington, DC. “By using Webb, we will be able to obtain information on surface chemistry that may be able to give us some clues as to why we it’s these different populations in the Kuiper belt. “
Expelled from the club
Between Jupiter and Neptune, and crossing the orbit of one or more giant planets, there is a different population of objects called centaurs. These are small solar system bodies that have been ejected from the Kuiper belt. In addition to observing current Kuiper belt objects, these Webb programs will study solar system bodies that have been “kicked out of the club.” These former Kuiper belt objects have orbits that have been dramatically disturbed, bringing them significantly closer to the Sun.
“Centaurs are short-lived because they travel through the orbits of Neptune, Uranus and Saturn. So they are typically only around 10 million years,” explained John Stansberry of the Space Telescope Science Institute in Baltimore, Maryland. Stansberry is leading a different team that will use Webb to study Kuiper Belt objects. “At that point, they have an interaction with one of the major planets which is very strong, and they are thrown into the Sun or ejected from the solar system.”
Another body that Webb will study is Neptune’s moon, Triton. The largest of the ice giant’s 13 moons, Triton shares many similarities with Pluto. “Even though it is Neptune’s moon, we have evidence to suggest that it is a Kuiper belt object that got too close to Neptune at some point in its past, and was caught in orbit around Neptune,” he said. Hammel. “Triton was studied by the Voyager 2 spacecraft in 1989. The data from the spacecraft will provide us with a very important ‘fundamental truth’ for our Webb observations of Kuiper belt objects.”
A sampling of the objectives
Here is a small sample of some of the dozen current and previous Kuiper Belt objects that Webb will observe:
Pluto and Charon: The dwarf planet Pluto and its largest moon, Charon, are two of the best-known residents of the Kuiper Belt. Pluto boasts an atmosphere, haze and seasons. It has geological activity on its surface and may have an ocean in it. In addition to Charon, it is home to four other moons: Nix, Hydra, Styx, and Kerberos. The Webb data will complement the observations made by NASA’s New Horizons spacecraft when it flew from the Pluto system in 2015.
Eris: Nearly the size of Pluto, Eris is the second largest known dwarf planet in the solar system. At its furthest point, the mysterious Eris is more than 97 times further away from the Sun than Earth. Due to its distance, it is difficult to observe, but Webb will tell scientists quite a lot what types of ice are on its surface.
Sedna: With its deep red hue, Sedna actually lies beyond the main Kuiper belt. It takes about 11,400 years to complete one orbit and it is estimated that the furthest point of that highly elongated orbit is 940 times the distance of the Earth from the Sun.
Haumea: This large, rapidly rotating body is egg-shaped, and scientists would like to know why. In addition to moons, it also appears to have a ring system. With Webb, scientists hope to learn more about how those rings formed.
Chariklo: The largest centaur, Chariklo is also the first asteroid found to have a ring system. It was the fifth ring system found in our solar system – after Saturn, Jupiter, Uranus and Neptune. The rings are believed to be between two and four miles wide.
Another program, called Target of Opportunity, will observe a Kuiper belt object pass in front of a star if that alignment were to occur during Webb’s first two years of life. Called occultation, this type of observation can reveal the size of an object.
The few spacecraft that flew Kuiper Belt objects could only study these intriguing objects for a very short period of time. With Webb, astronomers can aim at multiple Kuiper belt objects for an extended period of time. The result will be new insights into the early history of our solar system.
The James Webb Space Telescope will be the world’s premier space science observatory when it launches in 2021. Webb will solve the mysteries of our solar system, look beyond distant worlds around other stars, and probe the mysterious structures and origins of our universe and the our place inside. Webb is an international program led by NASA with its partners, the European Space Agency (ESA) and Canadian Space Agency.
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