Page "Orbital resonance" Paragraph 59

The next largest body in a similar 2: 3 resonance with Neptune, called a plutino, is the candidate dwarf planet Orcus.

Orcus has an orbit similar in inclination and eccentricity to Pluto's.

However, the two are constrained by their mutual resonance with Neptune to always be in opposite phases of their orbits ; Orcus is thus sometimes described as the " anti-Pluto ".