Space Weather monitoring with BepiColombo and JUICE during their cruise phases

The space environment is known to be populated by highly energetic particles that may be hazardous for the health of missions and impact planetary environments. The effects of these particles are commonly known as Space Weather. Monitoring interplanetary Space Weather in the Solar System is currently a challenging but essential activity that requires a good knowledge of the Sun and solar wind conditions, the local space environments (including solar wind-magnetosphere-ionosphere coupling), and the interaction of each spacecraft with its local environment. Consequently, understanding the chain of processes that control Space Weather at any planet or spacecraft on various time scales is important to accurately forecast and prevent hazardous conditions for a mission, and ultimately humans, throughout the Solar System.These energetic particles originate from three main sources: (1) Galactic Cosmic Rays (GCRs), a low flux of protons (90%), heavy ions, and to some extent electrons, with energies up to 10E21 eV, arriving from outside of the Solar System; (2) Solar Energetic Particles (SEPs), sporadic and unpredictable bursts of electrons, protons, and heavy ions, travelling much faster than the space plasma, accelerated in Solar Flares and Coronal Mass Ejections; and (3) planetary trapped particles, a dynamic population of protons and electrons trapped around planetary magnetospheres first discovered at Earth by Van Allen. Solar activity is responsible for transient and long-term variation of the radiation environment. These three components of radiation in space combine into a hazardous environment for both manned and unmanned missions and are responsible for several processes in planetary bodies. Therefore, it is important to monitor and comprehend the dynamics of energetic particles in space.BepiColombo and JUICE are two planetary missions from the European Space Agency that are currently travelling to their final destinations, i.e., Mercury and the Jovian system, respectively. Both of them have very long cruises within the Solar System. For BepiColombo, the journey is of 7 years (2018-2025) and for JUICE of 8 years (2023-2031). These long trips provide not only exceptional measurements for cross-calibration of instrumentation, but also for unique science opportunities including collaborations with other solar missions, such as Parker Solar Probe and Solar Orbiter that are characterising the plasma environment within the Solar System. Additionally, JUICE and BepiColombo can also act as upstream solar wind monitors for other planets such as Venus, Earth, Mars and Jupiter.BepiColombo has a large suite of instruments dedicated to plasma and solar physics, most of them operating on regular basis during the cruise phase, such as the Solar Intensity X-Ray and Particle Spectrometer (SIXS), the BepiColombo Environmental Radiation Monitor (BERM), the Solar Particle Monitor (SPM), and the BepiColombo Planetary Magnetometer (MPO-MAG). Some instruments are operated on specific solar wind campaigns. In the case of JUICE, only the RADiation hard Electron Monitor (RADEM) is in continuous operation, the other instruments operate twice per year for a health check, during planetary swingbys, and potentially for longer periods in the second part of the cruise, once JUICE is further away from the Sun, and closer to its final destination.In this work, we report on the solar energetic particle observations detected by both missions and the interplanetary magnetic fields (for the case of BepiColombo only), and how this unique opportunity for cruise observations is significantly helping the planetary and heliophysics communities to characterise Space Weather in the inner Solar System.