Terrestrial Gamma-ray Flashes (TGFs) are submillisecond bursts of photons with energies up to several tens of MeV originating from thunderstorms and lightning, and are the manifestation of the most energetic natural particle acceleration processes occurring on Earth. TGFs were first discovered in the early 90s by the BATSE instrument onboard the Compton Gamma-Ray Observatory, and later observed by the RHESSI, AGILE and Fermi missions, all of them devoted to high-energy astrophysics. These missions provided all TGF observational evidences from space until the launch of the Atmosphere-Space Interaction Monitor (ASIM) mission.
ASIM is a mission of the European Space Agency (ESA) dedicated to the observation of optical and high-energy transient emissions associated to thunderstorm and lightning activity: Transient Luminous Events (TLE) and Terrestrial Gamma-ray Flashes (TGF). ASIM overall main science goals are the understanding of the physics of TLEs and TGFs, their relation to lightning and their global impact to the high-altitude atmosphere and the geospace. ASIM was launched on April the 2nd 2018 and installed on the external facility of the Columbus module of the International Space Station, and is in nominal operations since June 2018.
In this presentation I will first set the stage on TGF science and observations, and show how high-energy astrophysics mission became major players in a scientific field far away from the original main science goals of these missions. Then I will review the ASIM payload and mission objectives and present the key scientific results of the mission after 18 months of nominal operations concerning TGF morphology and imaging, and the TGF / lightning / TLE relationship.
