  Context. The trans-neptunian region of the Solar System is populated by a
large variety of icy bodies showing great diversity in orbital behavior, size,
surface color and composition. One can also note the presence of dynamical
families and binary systems. One surprising feature detected in the spectra of
some of the largest Trans-Neptunians is the presence of crystalline water-ice.
This is the case for the large TNO (136 108) Haumea (2003 EL61). Aims. We seek
to constrain the state of the water ice of Haumea and its satellites, and
investigate possible energy sources to maintain the water ice in its
crystalline form. Methods. Spectro-imaging observations in the near infrared
have been performed with the integral field spectrograph SINFONI mounted on UT4
at the ESO Very Large Telescope. The spectra of both Haumea and its larger
satellite Hi'iaka are analyzed. Relative astrometry of the components is also
performed, providing a check of the orbital solutions and equinox seasons.
Results. We describe the physical characteristics of the crystalline water-ice
present on the surface of Haumea and its largest satellite Hi'iaka and analyze
possible sources of heating to maintain water in crystalline state: tidal
dissipation in the system components vs radiogenic source. The surface of
Hi'iaka appears to be covered by large grains of water ice, almost entirely in
its crystalline form. Under some restricted conditions, both radiogenic heating
and tidal forces between Haumea and Hi'iaka could provide the energy sufficient
to maintain the ice in its crystalline state.
  Based on observations collected at the European SouthernObservatory, Paranal,
Chile - 60.A-9235
