Planetary magnetic fields act as protective barriers, shielding a planet’s atmosphere and surface from energetic charged particles originating from its parent star and outer space. During its fourth flyby of Mercury on 4 September 2024, the ESA/JAXA BepiColombo mission passed within just 165 km of the planet’s surface. This close approach coincided with the elevated fluxes of high-energy charged solar particles, providing an opportunity to study shielding processes of a planet in close proximity to its star. Here, utilizing observations from the Solar Intensity X-Ray and Particle Spectrometer (SIXS) onboard BepiColombo, we investigate the penetration of high energy particles from the Sun into Mercury’s magnetosphere. The variations in energetic particle fluxes depend on the particle type, direction and energy. Our analysis reveals that the disappearance of protons is related to magnetic shadowing by the planet, while electrons dropouts occur due to a wide magnetic loss cone. These findings show that sustained high-energy particle precipitation can occur during solar energetic particle events on weakly magnetized rocky planets orbiting close to their parent star. Such processes probably play a significant role in regolith alteration and exospheric variability, with broader implications for surface geochemistry and potential habitability.

The BepiColombo Environment Radiation Monitor (BERM) is a housekeeping instrument onboard the BepiColombo mission, capable of measuring electron, proton, and heavy-ion fluxes. Due to its quasi-continuous data acquisition throughout all mission phases, BERM provides valuable contributions to both mission operations and scientific analysis of the space radiation environment. This study presents the calibration methodology applied to the electron and proton channels of BERM, along with its validation and cross-calibration with the solar intensity and X-ray spectrometer (SIXS), also onboard of BepiColombo mission. The bow–tie method was employed to calibrate each channel by determining its effective energy and geometric factor enabling the conversion of count rates into physical fluxes. The calibration validation with SIXS data of BERM proton channels P1 to P5 result in a mean deviation in the flux lower than 6%. BERM calibrated channels proved to be consistent with SIXS measurements, enhancing the relevance of BERM to the analysis of the space radiation environment, and in particular to Solar Energetic Particles (SEP) events.

Context. The SPEARHEAD (specification, analysis, and re-calibration of high-energy particle data) project, funded by the European Union’s Horizon Europe programme, enhances the accuracy and usability of high-energy particle measurements. It investigates particle acceleration, release, and transport during solar eruptions by refining instrument response functions and cross-calibrating datasets. This effort supports in-depth analyses of solar energetic particle (SEP) events and provides public data products.

Aims. We present a comprehensive catalogue of > 100 MeV proton events identified from May 1996 to August 2024 using SOHO/ERNE penetrating-particle rates, together with associated solar phenomena derived from multi-instrument observations.

Methods. The SEP events were detected through a systematic scan of ERNE/HED counter data and cross-calibrated with SOHO/EPHIN to derive peak fluxes and fluences. Each event was associated with its likely parent eruption using X-ray (XR) (GOES/XRS, RHESSI, SolO/STIX), radio (Wind/WAVES, STEREO/WAVES, ground-based observatories), and γ-ray (Fermi/LAT) observations, CMEs (SOHO/LASCO), and ground-level enhancements (GLEs) (neutron monitors). Timings and physical properties were systematically compared to investigate the relationships between SEP onset, flare evolution, CME kinematics, and radio signatures.

Results. Associations were established for 96% of CMEs and 76% of X-ray flares; all events exhibited type III radio bursts, while 95% had type II, and 53% type IV. > 100 MeV γ-rays were identified in 65 events, and 22 were linked to GLEs or sub-GLEs. Statistical analyses reveal that most SEP releases closely follow flare and CME onsets, with moderate SEP-XR-CME correlations, and a strong SEP-GLE fluence link. These results indicate that high-energy SEP events are typically associated with strong solar activity signatures, with the observed intensities and timings strongly modulated by magnetic connectivity and coronal conditions.

Conclusions. This catalogue provides the most extensive reference to date for high-energy SEP events over solar cycles 23–25, establishing a unified framework for future investigations of extreme particle acceleration.