Tags: Planet.
28978 Ixion is a plutino (an object that has a 2:3 orbital resonance with Neptune). It is very likely to be a dwarf planet although the IAU has not officially classified it as such. Light-curve-amplitude analysis shows only small deviations which suggests that Ixion is a spheroid with small albedo spots and hence a dwarf planet. Tancredi (2010) thinks that Ixion is probably a dwarf planet. Its diameter of 650 km estimated by Spitzer makes it about the fifth largest plutino.
