This paper describes the methods and results for the localization by triangulation of cosmic gamma-ray bursts (GRBs) independently observed by two space experiments: the Mercury Gamma-ray and Neutron Spectrometer (MGNS) and the High Energy Neutron Detector (HEND). MGNS is onboard the MPO/BepiColombo mission and on a stage of cruise to Mercury whereas HEND is onboard Mars Odyssey mission and in orbit around Mars. An analysis is performed of the accuracy of localization of the GRBs jointly observed by the two instruments at interplanetary distances by comparing their light curves. Notable achievements and scientific opportunities are described also in light of the recent inclusion of MGNS within the program of interplanetary network for gamma-ray burst localization (IPN).

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.