Eris (minor planet designation 136199 Eris) is the most massive and second-largest known dwarf planet in the Solar System. Because Eris appeared to be larger than Pluto, NASA initially described it as the Solar System’s tenth planet. Eris was discovered by the team of Mike Brown, Chad Trujillo, and David Rabinowitz [1]http://web.gps.caltech.edu/~mbrown/planetlila/
With a radius of about 722 miles (1,163 kilometers), Eris is about 1/5 the radius of Earth. Eris, like Pluto, is a little smaller than Earth’s Moon. If the Earth were the size of a nickel, Eris would be about as big as a popcorn kernel. From an average distance of 6,289,000,000 miles (10,125,000,000 kilometers), Eris is about 68 astronomical units away from the Sun. One astronomical unit (abbreviated as AU), is the distance from the Sun to Earth. From this distance, it takes sunlight more than nine hours to travel from the Sun to the surface of Eris.[2]https://solarsystem.nasa.gov/planets/dwarf-planets/eris/in-depth/
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.