Eris observed by James Webb Telescope
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August 29, 2022


As the most powerful telescope with exceptional abilities, James Webb Telescope is targeting Eris (previously known as Xena) for observations this week. Eris is a dwarf planet in our solar system that was discovered by a team of astronomers led by Mike Brown at Palomar Observatory in California in 2003. Eris is named after the Greek goddess of discord, who was the daughter of the sea-god, and the wife of Khrysippus— a second-generation version of the tyrannical father of all Greeks. The discovery of Eris revolutionized our understanding of celestial motion and sparked a fierce debate about its classification as a dwarf planet. The only difference between a planet and a dwarf planet is the area surrounding each celestial body. A dwarf planet has not cleared the area around its orbit, while a planet has. Since the new definition, three objects in our solar system have been classified as dwarf planets: Pluto, Ceres and Eris.

Eris takes 557 Earth years to make one trip around the Sun. The plane of Eris' orbit is well out of the plane of the solar system's planets and extends far beyond the Kuiper Belt, a zone of icy debris beyond the orbit of Neptune. As Eris orbits the Sun, it completes one rotation every 25.9 hours, making its day length similar to ours. Eris has a very small moon called Dysnomia. Dysnomia has a nearly circular orbit lasting about 16 days. This moon is named after Eris' daughter, the demon goddess of lawlessness. Dysnomia and other small moons around planets and dwarf planets allow astronomers to calculate the mass of the parent body. Dysnomia plays a role in determining how comparable Pluto and Eris are to each other.

Dwarf planet Eris is a member of a group of objects that orbit in the Kuiper Belt. This belt is populated with thousands of miniature icy worlds, which formed early in the history of our solar system about 4.5 billion years ago. These icy, rocky bodies are called Kuiper Belt objects, transneptunian objects, or plutoids. Like Pluto, Eris is believed to have a rocky surface with surface temperatures varying from about -359 degrees Fahrenheit (-217 degrees Celsius) to -405 degrees Fahrenheit (-243 degrees Celsius). Eris is often so far from the Sun that its atmosphere collapses and freezes, falling to the surface as snow. As it gets closest to the Sun in its faraway orbit, the atmosphere thaws.

As James Webb Telescope discovers new information about Eris with these observations, we will have new pictures and data released to the public soon. Typically, data and images are released within a few months of the observation once the peer review has been completed. In addition to Eris, James Webb Telescope is observing Nebulae, asteroids and galaxies this week. The entire schedule of weekly James Webb Telescope observations can be found here.