One of the major outcomes of recent studies on the formation of the Solar System is the reconnaissance of the fundamental importance of processes which took place during the first 10 thousands to 2 or 3 millions years of the lifetime of the Sun and its accretion disk. Astrophysical observations in the optical to infrared wavelengths of circumstellar disks around young stars have shown the existence in the inner disk of high-temperature processing of the dust. X-ray observations of T-Tauri stars revealed that they exhibit X-ray flare enhancements by several orders of magnitude. The work we have performed over the last years on the isotopic analysis of either solar wind trapped in lunar soils or of Ca-, Al-rich inclusions and chondrules from primitive chondrites, has allowed us to link some of these astrophysical observations around young stars with processes, such as irradiation by energetic particles and UV light, which took place around the T-Tauri Sun. The aim of this project is to make decisive progress in our understanding of the early solar system though the development of in situ high-precision isotopic measurements by ion microprobe in extra-terrestrial matter. The project will be focused on the exploration of the variations in the isotopic composition of O and Mg and in the concentration of short-lived radioactive nuclides, such as 26Al and 10Be, with half-lives shorter than 1.5 millions years. A special emphasis will be put on the search for nuclides with very short half-lives such as 32Si (650 years) and 14C (5730 years), nuclides which have never been discovered yet in meteorites. These new data will bring critical information on, for instance, the astrophysical context for the formation of the Sun and the first solids in the accretion disk, or the timing and the processes by which protoplanets were formed and destroyed close to the Sun during the first 2 million years of the lifetime of the Solar System.