First results from the DORN experiment onboard the Chang’E 6 mission

The DORN instrument is an alpha spectrometer that was deployed to the surface of the Moon aboard the Chang’E 6 spacecraft in June 2024, in the Apollo crater within the South Polar Aitken Basin, at a latitude of -41.6°S. Its purpose was to measure the concentration of radon and polonium released from the lunar regolith, to study the origin and dynamics of the lunar exosphere and the physical and thermal properties of the regolith. It consisted of 16 silicon detectors, organised in 8 Detection Units and 2 Fields of view, covering the near and far fields, and measuring charged particles in the 0.6 to 12 MeV energy range. The instrument was switched on several times during the mission. First, during the Chang’E 6 Earth-Moon transfer (for 10 hours), then in an ellipitical orbit (for 32 hours) and in a circular orbit at an altitude of ~200 km (for 111 hours), in the wake of a strong solar storm. After Chang’E 6 landing, it collected 19 hours of data and was switched off a few hours before the liftoff of the ascent module. We will present the results obtained by this instrument and compare them with previous measurements of radon and polonium made from the orbit and with simulations obtained by a global model of radon transport in the lunar subsurface and exosphere.