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.