Dear 100 Hour Board,
Now that Pluto has been demoted to a dwarf planet, has its moon been promoted to a dwarf planet as well? Or is it still just a moon? How many recognized small planets does this astronomical decision add to the solar system?
- Planet Janet
No, Charon is still a moon. It has not yet been decided which objects qualify as "dwarf planets," but clearly, Ceres also qualifies, as does Eris (formerly 2003 UB313, or "Xena"). No others have officially been added by the IAU, but many other objects also fit the listed requirements for dwarf planets: orbiting the Sun, sufficient mass to be rounded, not having cleared its orbit of other debris, and do not orbit another planet. For a quite interesting explanation of the classification, including a list of other objects that seem to fit the requirements, see http://en.wikipedia.org/wiki/Dwarf_planet