  The dwarf planet Haumea has two large satellites, Namaka and Hi'iaka, which
orbit at relatively large separations. Both moons have significant
eccentricities and inclinations, in a pattern that is consistent with a past
orbital resonance (Ragozzine and Brown, 2009). Based on our analysis, we find
that the present system is not consistent with satellite formation close to the
primary and tidal evolution though mean-motion resonances. We propose that
Namaka experienced only limited tidal evolution, leading to the mutual 8:3
mean-motion resonance which redistributed eccentricities and inclinations
between the moons. This scenario requires that the original orbit of Hi'iaka
was mildly eccentric; we propose that this eccentricity was either primordial
or acquired though encounters with other TNOs. Both dynamical stability and our
preferred tidal evolution model imply that the moons' masses are only about one
half of previously estimated values, suggesting high albedos and low densities.
As the present orbits of the moons strongly suggest formation from a flat disk
close to their present locations, we conclude that Hi'iaka and Namaka may be
second-generation moons, formed after the breakup of a past large moon,
previously proposed as the parent body of the Haumea family (Schlichting and
Sari, 2009). We derive plausible parameters of that moon, consistent with the
current models of Haumea's formation (Leinhardt et al, 2010). An interesting
implication of this hypothesis is that Hi'iaka and Namaka may orbit retrograde
with respect to Haumea's spin. Retrograde orbits of Haumea's moons would be in
full agreement with available observations and our dynamical analysis, and
could provide a unique confirmation the "disrupted satellite" scenario for the
origin of the family.
