Assessing Mercury’s composition using GREF : The BepiColombo MIXS G round RE ference F acility

We report on the design, development and characterisation of the unique ground reference facility (GREF), which is dedicated to supporting the ESA/JAXA BepiColombo Mercury Imaging X-ray Spectrometer (MIXS), arriving at Mercury in 2026. Incorporating MIXS detector qualification model components housed within a vacuum chamber to mimic the space environment, the GREF allows for MIXS hardware calibration alongside verification of data calibration, analysis and reduction techniques. Ultimately, the GREF provides an experimental test-bed within which to perform X-ray fluorescence of known materials in a controlled environment for direct comparison to BepiColombo data, while also verifying the correct operation of the instrument in space. The GREF is thus key to understanding Mercury’s composition, for ground-truthing analyses obtained remotely on Mercury, and data gathered using this facility will underpin all future observations made in space by MIXS.