Eris (dwarf planet)

Eris is a very heavy world.

It is a dwarf planet. It stays far away from the Sun. It is even farther than Pluto.

Eris has one small moon. This moon is named Dysnomia. The moon orbits around the big world.

People found Eris in 2005. They used a big telescope to see it. It moves very slowly in the sky.

Eris is very large and heavy. It is heavier than Pluto. But Pluto is a little wider.

Finding Eris helped us learn about space. It changed how we name planets. It is a very special world.

Eris is a very heavy dwarf planet.

It is the most massive dwarf planet in our Solar System. This means it has more mass than Pluto. Pluto is a little wider, but Eris is much heavier.

Eris stays very far from the Sun. Its path is also very tilted. Most planets move in a flat line. Eris moves at a steep angle. It has one moon named Dysnomia. Scientists studied how the moon moves. This helped them find the mass of Eris.

A team led by Mike Brown found Eris in 2005. They used a large telescope in California. Eris moves very slowly across the sky. The team had to look at old images to find it.

Finding Eris changed how we think about space. At first, NASA called it the tenth planet. This caused a big debate. Experts had to make a new rule for planets. Now, Eris is a dwarf planet. This group includes Pluto and Ceres.

Eris is a very heavy dwarf planet in our Solar System.

It is the most massive dwarf planet we know. While Pluto is slightly wider in size, Eris has more mass. In fact, Eris is 27% more massive than Pluto. It is the ninth-most massive object orbiting our Sun.

This tiny world is also the largest object that no spacecraft has ever visited. Its surface area is quite large, similar to the size of South America or Russia.

Eris follows a very unusual path around the Sun. This path is called a high-eccentricity orbit. This means the shape of its path is not a perfect circle. It also has a high inclination, which means its path is tilted at a steep 44-degree angle. Most planets move in a flat line, but Eris moves at a tilt.

It stays very far away from the Sun. In February 2016, it was more than three times further away than Neptune or Pluto. It even has one large moon named Dysnomia that orbits it.

A team of scientists found Eris in January 2005.

Mike Brown led the team from the Palomar Observatory in California. They used the 1.2 meter Samuel Oschin Schmidt telescope to look at the stars. Eris was hard to find because it moves very slowly across the sky. The team had to look back at old images from October 21, 2003. They found it by re-analyzing data with new software. This helped them see the slow motion of the object.

The discovery of Eris caused a big change in science.

Because Eris looked larger than Pluto, NASA first called it the tenth planet. This led to a big debate among experts. To solve this, the International Astronomical Union made a new rule in August 2006. They created a new group called dwarf planets. Eris, Pluto, and Ceres all belong to this new group. This changed the number of main planets back to eight.

The name Eris comes from a Greek goddess.

She was the goddess of strife and discord. The discovery team chose this name because the discovery caused a lot of arguments. Before it had an official name, some people called it Xena. This was a nickname from a popular TV show. The team wanted a name that sounded like the other planets. They chose a name from mythology to honor its importance in space.

Eris is a massive dwarf planet located in the far reaches of our Solar System.

It is classified as a trans-Neptunian object (TNO) within the scattered disk. This means it orbits the Sun beyond the planet Neptune. Eris is the most massive dwarf planet known to astronomers.

While Pluto has a slightly larger volume, Eris is 27% more massive than Pluto. It is the ninth-most massive object orbiting the Sun. It also holds the title of the sixteenth-most massive object in the entire Solar System when counting moons. Eris is a significant world because it is the largest known object that no spacecraft has ever visited.

The movement of Eris through space is quite unusual compared to the major planets. It follows a high-eccentricity orbit, meaning its path is a stretched-out oval rather than a circle.

Its orbit is also highly inclined, tilted at an angle of about 44 degrees relative to the ecliptic. The ecliptic is the flat plane where most planets orbit. Eris also travels a vast distance from the Sun. In February 2016, its distance was more than three times that of Neptune or Pluto. Its orbital period lasts 561 years. This long journey takes it from a closest point of 38.4 AU to a furthest point of 97.7 AU.

Eris is accompanied by one large known moon named Dysnomia.

Scientists were able to determine the mass of Eris by observing the orbit of this moon. In June 2007, calculations showed Eris had a mass of approximately 1.66 × 10^22 kg. This mass is 0.28% that of the Earth. The surface area of Eris is quite large. It is comparable in size to the continents of Russia or South America. The two bodies, Eris and its moon, were the most distant known natural objects in the Solar System until 2018. This distinction remained until the discovery of Sedna and 2012 VP113.

The discovery of Eris began with images taken on October 21, 2003.

A team led by Mike Brown, Chad Trujillo, and David Rabinowitz used the 1.2 m Samuel Oschin Schmidt telescope at Palomar Observatory. They initially missed Eris because it moved very slowly across the sky. Their automatic software excluded objects moving at less than 1.5 arcseconds per hour to avoid false positives. After the discovery of Sedna, the team re-analyzed old data by eye with a lower motion limit. This re-analysis revealed Eris in January 2005. The discovery was officially announced on July 29, 2005, alongside the discovery of the dwarf planet Makemake.

This discovery led to a major change in how we define space objects. Because Eris appeared larger than Pluto, NASA initially called it the tenth planet.

This created a debate about what should be called a planet. In response, the International Astronomical Union (IAU) met to create a formal definition. On August 24, 2006, the IAU approved a new rule. They classified Eris, Pluto, and Ceres as "dwarf planets." This decision reduced the number of recognized planets in our Solar System back to eight. This was the same number that existed before Pluto was discovered in 1930. The discovery team expressed approval of this new scientific classification.

The naming of Eris was a long and careful process.

Before it had an official name, the discovery team used the informal nickname "Xena." This was inspired by the character from the television series *Xena: Warrior Princess*. The team wanted a name that reflected the object's importance. They eventually proposed the name Eris, after the Greek goddess of strife and discord. This name was chosen because the discovery had caused much debate among astronomers. The IAU officially assigned the name on September 13, 2006. The name has two common pronunciations in English: one with a "long" e and one with a "short" e.

Eris connects to broader studies of how our Solar System formed. It is a scattered-disk object, which is a type of TNO. These objects were likely scattered from the inner edge of the Kuiper belt into distant orbits. This happened due to gravitational interactions with Neptune during the formation of the Solar System. Studying Eris helps scientists understand the history of these distant, icy worlds. It also helps us understand the complex gravitational dance that shapes our cosmic neighborhood.