  All magnetized planets are known to produce intense non thermal radio
emissions through a mechanism known as Cyclotron Maser Instability (CMI),
requiring the presence of accelerated electrons generally arising from
magnetospheric current systems. In return, radio emissions are a good probe of
these current systems and acceleration processes. The CMI generates highly
anisotropic emissions and leads to important visibility effects, which have to
be taken into account when interpreting the data. Several studies showed that
modeling the radio source anisotropic beaming pattern can reveal a wealth of
physical information about the planetary or exoplanetary magnetospheres that
produce these emissions. We present a numerical tool, called ExPRES
(Exoplanetary and Planetary Radio Emission Simulator), which is able to
reproduce the occurrence in time-frequency plane of CMI-generated radio
emissions from planetary magnetospheres, exoplanets or star-planet interacting
systems. Special attention is given to the computation of the radio emission
beaming at and near its source. We explain what physical information about the
system can be drawn from such radio observations, and how it is obtained. These
information may include the location and dynamics of the radio sources, the
type of current system leading to electron acceleration and their energy and,
for exoplanetary systems, the magnetic field strength, the orbital period of
the emitting body and the rotation period, tilt and offset of the planetary
magnetic field. Most of these parameters can be remotely measured only via
radio observations. The ExPRES code provides the proper framework of analysis
and interpretation for past (Cassini, Voyager, Galileo), current (Juno,
groundbased radiotelescopes) and future (BepiColombo, Juice) observations of
planetary radio emissions, as well as for future detection of radio emissions
from exoplanetary systems.
