  Aims. We seek to constrain the surface composition of the Trans-Neptunian
Object (90482) Orcus and its small satellite Vanth, as well as their mass and
density. Methods. We acquired near-infrared spectra (1.4-2.4 {\mu}m) of (90482)
Orcus and its companion Vanth using the adaptive-optics-fed integral-field
spectrograph SINFONI mounted on Yepun/UT4 at the European Southern Observatory
Very Large Telescope. We took advantage of a very favorable appulse (separation
of only 4") between Orcus and the UCAC2 29643541 star (R = 11.6) to use the
adaptive optics mode of SINFONI, allowing both components to be spatially
resolved and Vanth colors to be extracted independently from Orcus. Results.
The spectrum of Orcus we obtain has the highest signal-to-noise ratio to date,
and we confirm the presence of H2O ice in crystalline form, together with the
presence of an absorption band at 2.2 {\mu}m. We set an upper limit of about 2%
for the presence of methane, and 5% for ethane. Because the methane alone
cannot account for the 2.2 {\mu}m band, the presence of ammonia is suggested to
the level of a couple of percent. The colors of Vanth are found slightly redder
than those of Orcus, but the large measurement uncertainties forbid us from
drawing conclusions on the origin of the pair (capture or co-formation).
Finally, we reset the orbital phase of Vanth around Orcus, and confirm the
orbital parameters derived by Brown et al. (2010, AJ 139).
