  The past decade has welcomed the emergence of cosmic neutrinos as a new
messenger to explore the most extreme environments of the universe. The
discovery measurement of cosmic neutrinos, announced by IceCube in 2013, has
opened a new window of observation that has already resulted in new fundamental
information that holds the potential to answer key questions associated with
the high-energy universe, including: what are the sources in the PeV sky and
how do they drive particle acceleration; where are cosmic rays of extreme
energies produced, and on which paths do they propagate through the universe;
and are there signatures of new physics at TeV-PeV energies and above? The
planned advancements in neutrino telescope arrays in the next decade, in
conjunction with continued progress in broad multimessenger astrophysics,
promise to elevate the cosmic neutrino field from the discovery to the
precision era and to a survey of the sources in the neutrino sky. The planned
detector upgrades to the IceCube Neutrino Observatory, culminating in
IceCube-Gen2 (an envisaged $400M facility with anticipated operation in the
next decade, described in this white paper) are the cornerstone that will drive
the evolution of neutrino astrophysics measurements.
