Since the discovery of cosmic rays in 1912, we still don't know what the sources of these energetic charged particles are. Cosmic rays are observed via their interactions in the
Earth atmosphere and to identify their sources one needs to determine the cosmic ray composition by measurements of the produced secondary particles. However, the
discovery of cosmic high-energy neutrinos by IceCube has opened a new era, dubbed neutrino astronomy and announced as the “breakthrough of 2013”. Neutrinos are
excellent astrophysical messengers; they only interact weakly and point back to their source. The sources of the cosmic neutrinos still remain a mystery, but one expects that they originate from the same cataclysmic phenomena as the cosmic rays. As such, cosmic high-energy neutrinos will enable us to identify the sources of cosmic rays and obtain insight in the inner engines of cosmic phenomena. The IceCube observations have indicated that to achieve this, one needs to obtain sufficient statistics and also reach out to higher
neutrino energies. Consequently, an extension of the IceCube observatory is foreseen in which also new technologies will be employed.