Eris (dwarf planet)

Eris is the most massive and second-largest known dwarf planet in our Solar System. It is a special kind of object called a trans-Neptunian object, meaning it orbits the Sun beyond the planet Neptune. Eris was discovered in January 2005 by a team from the Palomar Observatory led by Mike Brown and was named after the Greco–Roman goddess of strife and discord in September 2006.

Eris is very big, with a diameter of about 2,326 kilometers. It is also very heavy—its mass is 27% greater than that of Pluto, even though Pluto is slightly larger by volume. Eris has one large moon named Dysnomia. In February 2016, Eris was about 96.3 astronomical units from the Sun, which is more than three times the distance of Neptune or Pluto from the Sun.

Because Eris seemed larger than Pluto when it was first found, some people called it the tenth planet. This helped lead to a new definition of what a planet is. In 2006, the International Astronomical Union decided that Eris, Pluto, and Ceres are dwarf planets, not regular planets. This brought the number of known planets in our Solar System back to eight.

Discovery

Eris was discovered by a team led by Mike Brown, Chad Trujillo, and David Rabinowitz on January 5, 2005, using images taken on October 21, 2003. The team was searching for large objects in the outer part of our Solar System and had already found several big objects, including dwarf planets like Quaoar, Orcus, and Sedna.

They took pictures on October 21, 2003, at the Palomar Observatory in California, but didn’t notice Eris right away because it moved very slowly across the sky. After finding another object called Sedna, they looked closer at their old pictures and finally spotted Eris in January 2005. They shared their discovery on July 29, 2005, along with another object named Makemake.

Later observations showed that Eris has a small moon named Dysnomia. By studying Dysnomia’s path, scientists figured out that Eris is slightly more massive than Pluto.

Name

Eris is named after the Greek goddess Eris, who stands for strife and discord. The name was suggested by the Caltech team on September 6, 2006 and officially given on September 13, 2006. Before this, the object was known by the temporary name 2003 UB₃₁₃, given by the IAU.

For a while, the object was called Xena by the discovery team. This name came from the TV show Xena: Warrior Princess. The team used this name because they thought the object might be bigger than Pluto, and they wanted a name that sounded strong and mythological. They kept this name secret until a reporter asked about it.

The team finally chose Eris because they felt it was a fitting name for an object that had caused a lot of discussion and debate in the astronomy world.

Classification

Eris is a dwarf planet that orbits far beyond Neptune. It was once thought to be larger than Pluto, which caused some people to call it the "tenth planet." However, in 2006, scientists created a new rule for what counts as a planet, and Eris did not meet all the rules. Because of this, Eris and Pluto were both called dwarf planets instead of regular planets.

Orbit

See also: List of Solar System objects most distant from the Sun

Eris takes about 558 years to go around the Sun. It can be as far away as 97.7 astronomical units from the Sun and as close as 38.4 astronomical units. Eris's path around the Sun is tilted at about 44 degrees compared to the Earth's path. When it was found, Eris and its moon were the farthest known objects in our Solar System, until another object was discovered in 2018.

Eris's orbit is very stretched out, bringing it as close as 37.9 astronomical units to the Sun. This is closer than Pluto but still safe from Neptune. In about 800 years, Eris will be closer to the Sun than Pluto for a while. Eris did not get noticed until 2005 because its tilted orbit made it hard to see from Earth.

Size, mass and density

Eris is a big object in space, almost as large as Earth's Moon but a little smaller than Pluto. Scientists measured its size in 2011 and found it to be about 2,326 kilometers across. Even though it is smaller than Pluto, Eris is heavier, with about 27% more mass than Pluto.

Because Eris is heavier but smaller, it is made of denser materials, mostly rock. Some scientists think Eris might have a hidden layer of liquid water deep inside, kept warm by natural processes. This makes Eris very interesting to learn about and explore.

Surface and atmosphere

Scientists studied Eris using special telescopes and found that its surface has ice made of methane, similar to the surface of Pluto and Neptune's moon Triton. In 2022, the James Webb Space Telescope discovered that Eris also has nitrogen ice on its surface.

Eris looks almost white and uniform, unlike the reddish surface of Pluto. This is because methane ice covers its surface evenly. Because Eris is very far from the Sun, its temperature changes a lot, but sometimes it gets warm enough for some of its ices to turn into a thin atmosphere. This atmosphere is made of methane and nitrogen, which are gases that can easily evaporate in space.

Rotation

Eris does not change much in brightness as it spins, which makes it hard to measure how long it takes to rotate. Studies show that Eris spins in sync with its moon Dysnomia, taking about 15.78 Earth days for one full spin. Dysnomia also spins in sync with Eris, making them a special pair that rotates together, just like Pluto and its moon Charon. Earlier tries to measure Eris's spin gave unclear results because they did not watch Eris long enough. We do not know Eris's tilt, but it might be about 78 degrees, meaning most of its northern part gets sunlight, with some areas always lit in 2018.

Satellite

Main article: Dysnomia (moon)

In 2005, scientists using special telescopes in Hawaii observed Eris and found a small object moving around it. This object is a moon, or natural satellite, of Eris. At first, the scientists called this moon "Gabrielle." Later, when Eris got its official name, the moon was named Dysnomia after a figure from ancient stories who was the daughter of Eris.

Exploration

The spacecraft New Horizons observed Eris from a distance in May 2020. This happened after it had flown by Pluto in 2015. Even though New Horizons was farther from Eris than Earth was, its position allowed scientists to study Eris in a special way.

In the 2010s, scientists thought about future missions to visit the Kuiper belt, and Eris was one of the places they considered. They figured out that a spacecraft could reach Eris in about 24.66 years if it used a big planet's gravity to help it along.