Orbits and Masses of the Satellites of the Dwarf Planet Haumea = 2003 EL61

TL;DR

This study precisely determines the orbits and masses of Haumea's satellites using Hubble and Keck data, revealing complex interactions and a history of giant collision, with implications for their tidal evolution and mutual events.

Contribution

First detailed orbital and mass measurements of Haumea's satellites using a fully-interacting three-body model, revealing their dynamical state and collision history.

Findings

Orbits of Haumea's satellites are nearly coplanar.

Mass of Haumea and Hi'iaka are well constrained.

Namaka's mass is marginally detected.

Abstract

Using precise relative astrometry from the Hubble Space Telescope and the W. M. Keck Telescope, we have determined the orbits and masses of the two dynamically interacting satellites of the dwarf planet (136108) Haumea, formerly 2003 EL61. The orbital parameters of Hi'iaka, the outer, brighter satellite, match well the previously derived orbit. On timescales longer than a few weeks, no Keplerian orbit is sufficient to describe the motion of the inner, fainter satellite Namaka. Using a fully-interacting three point-mass model, we have recovered the orbital parameters of both orbits and the mass of Haumea and Hi'iaka; Namaka's mass is marginally detected. The data are not sufficient to uniquely determine the gravitational quadrupole of the non-spherical primary (described by $J_2$). The nearly co-planar nature of the satellites, as well as an inferred density similar to water ice, strengthen the hypothesis that Haumea experienced a giant collision billions of years ago. The excited eccentricities and mutual inclination point to an intriguing tidal history of significant semi-major axis evolution through satellite mean-motion resonances. The orbital solution indicates that Namaka and Haumea are currently undergoing mutual events and that the mutual event season will last for the next several years.