Moons of Haumea - Orbital Characteristics

Orbital Characteristics

Hiʻiaka orbits Haumea in a nearly circular path every 49 days. Namaka orbits Haumea in 18 days in a highly elliptical, non-Keplerian orbit, and as of 2008 is inclined 13° from the larger moon, which perturbs its orbit. Since the impact that created the moons of Haumea is thought to have occurred in the early history of the Solar System, over the following billions of years it should have been tidally damped into a more circular orbit. Current research suggests that Namaka's orbit has been disturbed by orbital resonances with the more massive Hiʻiaka, due to converging orbits as the two moons move outward from Haumea due to tidal dissipation. The moons may have been caught in and then escaped from orbital resonance several times; they currently are in or at least close to an 8:3 resonance. This resonance strongly perturbs Namaka's orbit, which has a current precession of the argument of periapsis by about -6.5° per year, implying a precession period of 55 years.

At present, the orbits of the Haumean moons appear almost exactly edge-on from Earth, with Namaka periodically occulting Haumea. Observation of such transits would provide precise information on the size and shape of Haumea and its moons, as happened in the late 1980s with Pluto and Charon. The tiny change in brightness of the system during these occultations will require at least a medium-aperture professional telescope for detection. Hiʻiaka last occulted Haumea in 1999, a few years before discovery, and will not do so again for some 130 years. However, in a situation unique among regular satellites, the great torquing of Namaka's orbit by Hiʻiaka will preserve the viewing angle of Namaka–Haumea transits for several more years.