On Jan. 5, 2005, astronomers at NASA found Eris, the second-largest dwarf planet in the planetary system. Eris is just a little smaller sized than Pluto, and it orbits the sun about three times farther than Pluto. An artists illustration of the dwarf world Eris. (Image credit: ESO/L. Calçada) NASA initially believed that Eris was bigger than Pluto, and they originally explained Eris as the tenth planet in the solar system. But the International Astronomical Union, or IAU, wasnt too thrilled about adding Ceres to the list of planets in the planetary system. Rather, they chose to come up with the first official definition of the word “world,” and that new meaning excluded both Eris and Pluto. Catch up on our whole “On This Day In Space” series on YouTube with this playlist. On This Day in Space Archive! Still insufficient space? Dont forget to examine out our Space Image of the Day, and on the weekends our Best Space Photos and Top Space News Stories of the week. Email Hanneke Weitering at [email protected] or follow her @hannekescience. Follow us @Spacedotcom and on Facebook..
