  Jupiter has the most energetic and complex radiation belts in our solar
system. Their hazardous environment is the reason why so many spacecraft avoid
rather than investigate them, and explains how they have kept many of their
secrets so well hidden, despite having been studied for decades. In this White
Paper we argue why these secrets are worth unveiling. Jupiter's radiation belts
and the vast magnetosphere that encloses them constitute an unprecedented
physical laboratory, suitable for both interdisciplinary and novel scientific
investigations: from studying fundamental high energy plasma physics processes
which operate throughout the universe, such as adiabatic charged particle
acceleration and nonlinear wave-particle interactions; to exploiting the
astrobiological consequences of energetic particle radiation. The in-situ
exploration of the uninviting environment of Jupiter's radiation belts present
us with many challenges in mission design, science planning, instrumentation
and technology development. We address these challenges by reviewing the
different options that exist for direct and indirect observation of this unique
system. We stress the need for new instruments, the value of synergistic Earth
and Jupiter-based remote sensing and in-situ investigations, and the vital
importance of multi-spacecraft, in-situ measurements. While simultaneous,
multi-point in-situ observations have long become the standard for exploring
electromagnetic interactions in the inner solar system, they have never taken
place at Jupiter or any strongly magnetized planet besides Earth. We conclude
that a dedicated multi-spacecraft mission to Jupiter's radiation belts is an
essential and obvious way forward and deserves to be given a high priority in
ESA's Voyage 2050 programme.
