WASHINGTON, June 15 (Xinhua) -- The dwarf planet Pluto, formerly known as planet Pluto, was demoted yet again, when U.S. scientist determined it no longer even reigns as king of the dwarf planets.

Michael Brown and Emily Schaller at California Institute of Technology reported in the June 15 issue of journal Science that Pluto's neighbor Eris, another dwarf planet in the same Kuiper belt, is about 27 percent more massive than Pluto.

They determined that Eris is now the largest, most massive known dwarf planet. Eris, which got Pluto demoted from planet status, takes another blow to the poor former ninth planet.

After researchers discovered Eris close to Pluto in 2006, the International Astronomical Union defined the term planet and created the category of dwarf planet for objects including Eris and Pluto.

At the time, Pluto was generally thought to be the largest known dwarf planet. Then, astronomers found Dysnomia, Eris' satellite, and they have now used it, the Hubble Space Telescope and the Keck Observatory, to find the orbit and the density of Eris.