The outer part of the Solar system is populated by the so-called trans-Neptunian objects (TNOs), small bodies that describe elliptic orbits with a larger semi-major axis than that of Neptune. They were formed beyond the snow line, where the temperature of the protoplanetary disc was low enough to allow molecules of volatiles (such as water or methane) to survive during this early era of the Solar system. Due to the vast distances to the Sun, the surface materials of TNOs have undergone less chemical processes if compared with other objects of the Solar system; in some sense, these objects are time capsules containing almost intact material from the protoplanetary disc. I will discuss two of the most powerful techniques for the study of the physical properties of these objects using ground-based observations, photometry and stellar occultations, and present some of the latest advances in this area of research.
