An updated set of goals and objectives for the Mercury Gamma and Neutron Spectrometer (MGNS) are presented based on the most recent findings of the MESSENGER mission. The updated design of MGNS with the new CeBr₃ crystal for detection of gamma-ray along with its benefits for the detection of ⁴⁰K and K/Th ratio are discussed. MGNS will then be capable of measuring the elemental composition of shallow subsurface in order to empirically evaluate the fittest model on the origin of Mercury, as well as the presence of possible water ice deposits on the permanently shadowed polar craters on the planet. We present the results of the first measurements in space performed during the instrument commissioning phase and during the first Earth flyby which occurred in April 2020.

The results obtained by experimentally studying gamma rays emitted by samples prepared as analogs of planetary matter and irradiated with thermal neutrons are presented. The intensities of spectral lines of gamma rays emitted by such samples differing in chemical composition are compared. These results will be used in processing data on gamma-ray spectra of the Moon and Mercury from measurements performed onboard spacecrafts with the aim of studying the composition of the surface of these celestial bodies.