Two years of observations with the JUICE mission radiation monitor, RADEM.

Jupiter and its icy moons—Europa, Ganymede, and Callisto—are among the most intriguing targets in the Solar System for studying habitability and searching for life. Substantial evidence suggests that these moons harbor subsurface water oceans beneath their icy crusts, with conditions that may support the development and sustainability of life. To investigate this, the European Space Agency (ESA) has launched the JUpiter ICy moons Explorer (JUICE) on April 14^th, 2023.

The Jovian radiation environment is extremely hazardous for space exploration. High-energy electrons trapped in the Jovian system can penetrate thick shielding walls and accumulate large doses in electronic components and materials reducing their operational lifespan significantly. High energy particles can also disassociate biological molecules that migrated from the icy moons’ oceans to the surface hindering the detection of biosignatures from orbit.

For these reasons, JUICE carries a RADiation hard Electron Monitor (RADEM), with a novel design, capable of measuring high energy electrons, protons, and ions. RADEM is an engineering instrument, that is continuously operated throughout the mission including its cruise phase, but that can also contribute significantly to scientific investigations of the Jovian system. The same is true for the cruise phase. JUICE joins an increasing but still limited Solar fleet that includes STEREO-A, Solar Orbiter, Parker Solar Probe, BepiColombo, and near-Earth spacecraft, having already observed dozens of Solar Energetic Particle events.

In this work, we will take a deep dive into the two first years of RADEM observations, calibration activities, and scientific highlights, including a cosmic ray calibration campaign, cross-calibrations with STEREO-A and SOHO, and observation of the Van Allen belts during JUICE’s world first Lunar-Earth Gravity Assist.