Spectroscopic investigation of the Centaurs

The Centaurs are a peculiar class of objects with chaotic orbits which semimajor axes fall between those of Jupiter and Neptune. It is now believed that they could represent a link between trans neptunian objects and short-period comets. To investigate the nature of these particular objects, we have performed optical spectroscopic observations of 5 Centaurs. The spectral range covered is 0.37-0.75 micron. The spectral slopes are neutral or slightly blue for 2060 Chiron to very red for objects as 7066 Nessus. The investigated objects have not shown any cometary activity. The obtained spectra show a wide types range which implies different surface compositions probably due to evolutionary mechanisms like long-term exposures to cosmic rays and/or solar ultraviolet radiation. These differences are very similar to those obtained also among the Kuiper belt objects. This compositional similarity could confirm that Centaurs are transneptunian objects injected into giant-planet orbits. Even if only Chiron has shown cometary activity until now, the Centaurs are probably transition objects between the trans neptunians, asteroids and cometary nuclei.