The trans-Neptunian object (42355) Typhon: composition and dynamical evolution

Context. The scattered disk object (42355) Typhon shows interesting features in visible and near-infrared spectra, in particular, the visible spectrum shows evidence of aqueously altered materials. Aims. This article presents a possible origin for absorption features on the surface of (42355) Typhon based on an episode of aqueous alteration, and it seeks to understand this event in the context of its dynamical evolution. Methods. We observed (42355) Typhon at the ESO/Very Large Telescope using FORS2 and ISAAC on telescope unit 1 and SINFONI on telescope unit 4. We compared these data with those previously published, in order to confirm features found in the visible and near infrared spectra and to study possible surface heterogeneities. We interpreted the surface composition using the Hapke radiative transfer model on the whole available spectral range " 0.5# 2.4 µm. To complete the portrait of (42355) Typhon, we followed its dynamical evolution using the code EVORB v.13 for 20 Myr. Results. We confirm detection of a subtle absorption feature in the visible at " 0.6 µm, which we interpret as caused by water-altered silicates. In the near infrared, we confirm the presence of water ice by the 2.0 µ ma bsorption feature. The best-f it models to our data point the presence of water ice. Conclusions. (42355) Typhon is too small to have su! ered water alteration, but this event could happen in a larger parent body from which (42355) Typhon is a remnant after a catastrophic disruption.