136199 Eris
136199 Eris is a significant celestial body located in the Kuiper Belt, which is a region beyond Neptune filled with icy objects. Discovered by a team led by astronomer Mike Brown at the Palomar Observatory in 2003, Eris was initially known as 2003 UB313. It was confirmed as a dwarf planet in 2006 by the International Astronomical Union (IAU), following a debate that redefined the criteria for what constitutes a planet. Eris has a diameter of approximately 2,326 kilometers (1,445 miles) and is denser than Pluto, indicating it is primarily composed of rocky material with a thin layer of ice.
Eris travels on an unusual, elongated orbit taking 561.37 Earth years to complete, varying in distance from the sun between 38.5 AU and 97.56 AU. Its extreme surface temperatures can range from −217 to −243 degrees Celsius (−359 to −405 degrees Fahrenheit). Eris has one known moon, Dysnomia, which is thought to have formed from debris resulting from a collision involving Eris. The discovery of Eris and other Kuiper Belt Objects (KBOs) has expanded our understanding of the solar system’s formation and the diverse characteristics of its outer regions.
136199 Eris
FIELDS OF STUDY: Sub-planet Astronomy; Cosmology; Observational Astronomy
ABSTRACT: 136199 Eris is a Kuiper Belt object (KBO) that orbits far beyond Neptune. It was found in 2003 and officially classified as a dwarf planet in 2006. Its similarity to Pluto forced the scientific community to determine the characteristics that qualify a space object as a planet. The ensuing debate created a new category of space objects called dwarf planets, and Pluto was demoted from its planetary status.
An Important Discovery
A team of researchers at the Palomar Observatory, a research center operated by the California Institute of Technology (Caltech) outside San Diego, California, imaged 136199 Eris in 2003. Astronomer Mike Brown and his team conducted nightly surveys of the Kuiper Belt, a disk-shaped region of space beyond the orbit of Neptune. This area of space is filled with at least one thousand icy space objects of varying sizes. The team was looking for large space objects that had not yet been identified due to their distance from Earth.
The team first photographed Eris, then called 2003 UB313, on October 21, 2003. They confirmed the discovery in January 2005 and submitted the object to the International Astronomical Union (IAU) for consideration as the tenth planet of the solar system.
The discovery was to have a serious impact on astronomical science. It forced the scientific community to consider seriously the question, "What is a planet?" Astronomers had long known that Pluto, discovered in 1930, differed greatly from the other eight planets of the solar system. At only about 2,390 kilometers (1,485 miles) in diameter, Pluto is smaller than Earth’s moon. Pluto’s location beyond the orbit of Neptune places it billions of miles from the sun, making it a cold, icy place. Additionally, the shape and angle of its orbital path vary from the elliptical orbital path traveled by the other eight planets. The discovery of 2003 UB313, which was then estimated to be about 3,000 kilometers (1,864 miles) in diameter, forced the question. If Pluto were a planet, it seemed logical that 2003 UB313 should qualify, too.
A Dwarf Planet
After intense debate, the International Astronomical Union (IAU) resolved the issue by creating a new class of space objects, dwarf planets, in 2006. This category was meant to distinguish between small, round planetary bodies and the eight regular planets of the solar system. This difference was outlined in IAU Resolution B5.
IAU defined dwarf planets as space objects that orbit the sun, have enough mass and gravity to attain a round shape, and lack the gravitational power to clear other space objects out of their orbit. Additionally, dwarf planets are not satellites, or moons, to other space objects.
Once the dwarf planet category was established, IAU placed 2003 UB313 in it. The IAU named the object Eris after the Greek goddess of conflict, a nod to the debate that followed its discovery. At the same time, IAU demoted Pluto from a full planet to a dwarf planet. (This was a controversial decision for many in the public who did not understand the necessity for the change.) The IAU also designated Ceres, a unique object found in the asteroid belt, as a dwarf planet. Eventually, the IAU added more objects to the dwarf planet category. The group expects the number of known dwarf planets to grow in future as many more of these objects are discovered in the Kuiper Belt.
Characteristics of Eris
Eris travels in the outermost part of the solar system, 97.56 astronomical units (AU) from the sun at its farthest point. Eris is therefore more than ninety-seven times farther from the sun than Earth is. However, Eris also has an unusual, tilted orbit, so its distance from the sun can vary quite a bit. At its closest, Eris is 38.5 AU from the sun. This takes it closer to Earth than Pluto.
Eris’s orbit follows a long path that takes it far beyond Neptune and the Kuiper Belt into a zone of icy debris. In fact, Eris’s orbital path is 561.37 Earth years long. Due to the distance Eris travels, its surface temperatures are extreme. It is very cold, with surface temperatures estimated to be between −217 and −243 degrees Celsius (−359 and −405 degrees Fahrenheit). At its farthest point from the sun, the atmosphere collapses and freezes. When Eris moves closer to the sun, its atmosphere expands.
Eris’s size has been open to debate since its discovery. While early estimates placed the object at about 3,000 kilometers (1,864 miles) in diameter, later research indicated that its diameter is 2,326 kilometers (1,445.3 miles). Thus, Eris is about the same size as Pluto, not larger, as first believed.
Despite the controversy over size, scientists agree that calculations from Eris’s satellite, Dysnomia, prove that Eris has 27 percent more mass than Pluto does. This extra mass makes it the denser of the two dwarf planets. Scientists believe this density is evidence that Eris is composed mainly of a rocky material covered with a thin surface of ice. (Pluto, on the other hand, is less dense and therefore more likely to be made up of ice and rock.) Eris is very bright and reflects nearly all light. Because of this and its color, scientists believe its surface is made of nitrogen ice and solid methane.
Eris’s Satellite
Eris has one known satellite, Dysnomia. It was discovered on September 10, 2005, at the Keck Observatory in Hawaii. This moon is named for the daughter of the goddess Eris who was known for celebrating lawlessness. The moon Dysnomia may be composed of frozen water, but scientists are unsure of this.
Dysnomia is quite small. Astronomers estimate Dysnomia’s diameter at about 150 to 250 kilometers (93 to 155 miles). Dysnomia orbits close to Eris. It is located only about 37,370 kilometers (23,200 miles) from Eris. (By contrast, Earth’s moon is 384,400 kilometers, or 238,855 miles, from Earth.) Its orbit takes sixteen days to complete.
Scientists believe that Dysnomia formed much like Earth’s moon. They hypothesize that Eris collided with a large space object that ejected material into space. That material eventually came together to form Dysnomia.
Vastness of the Solar System
Like Eris and Pluto, Dysnomia is considered a Kuiper Belt object (KBO), which is simply a designation for objects that formed in the region of space beyond Neptune. More than 1,300 KBOs were discovered between 1992, when the belt first was identified, and 2014. These objects are important for several reasons. KBOs are thought to be untouched fragments from the formation of the solar system about 4.6 billion years ago. As such, they may teach scientists much about how the solar system formed and evolved. In addition, KBOs have proven that the solar system is far more vast than previously imagined.
PRINCIPAL TERMS
- dwarf planet: a celestial body that has enough mass to attain a nearly round shape, lacks the gravity to keep its neighborhood free of other space objects, orbits a star, and does not act as a satellite to another space object.
- Kuiper Belt: a disk-shaped region of space beyond the orbit of Neptune, about thirty to fifty-five astronomical units (AU) from the sun. The Kuiper Belt contains a collection of more than a thousand icy space objects that may be untouched material from the formation of the solar system.
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