Compositional surface diversity in the trans-Neptunian objects

knowledge of the physical and chemical properties of trans-Neptunian object s (TNOs) is still incomplete and confused. To investigate their physical pr operties, we are continuing the TNO observational program started in 1997 a t ESO in La Silla, Chile with the 3.5 m New Technology Telescope. In Februa ry 1999, broadband optical colors were obtained for eight new objects: 1993 FW, 1995 HM5, 1997 CQ(29), 1997 CS29, 1997 CT29, 1997 CU29, 1998 FS144, an d 1998 WH24. Particular attention has been paid to the observations and dat a reduction of these faint objects. These new data increase the available s tatistical sample and will help us to understand the surface properties and the mechanisms of the surface modification of the TNOs. The observed objec ts present a wide spread of colors. The color distribution does not show an y bimodality. Knowledge of the colors of a large number of these objects is important to understand this population, which represents an important res ervoir of primordial material.