Exospheric Sampling of Mercury's Surface Composition

Stefano A. Livi (Southwest Research Institute)

ESA's BepiColombo mission to the planet Mercury includes a comprehensive set of advanced instruments. Strofio, one of the instruments on the SERENA neutral and ionizing particle suite on the Mercury Planet Orbit (MPO), is a high mass resolution, time-of-flight system for low energy neutral particles.

Key questions addressed by Strofio are:

• What are the composition, isotopic abundance, spatial distribution, and temporal variability of the neutral particles in Mercury's exosphere?
• How do the surface, exosphere, and magnetosphere interact?
• What is the chemical composition of Mercury's surface?

The design of the Strofio sensor is driven by the attempt to achieve both isotopic resolving capability (goal is a cross talk of 10^-5 or better between two adjacent masses at the 50% level) and temporal resolution (a full-range spectrum can be collected in as short as 100 ms) within very limited resources (goal is 2 kg, 4W, 1,000 cm³). Laboratory tests on an available prototype show that these goals are within reasonable reach. This instrument is currently being developed as an integral part of the Serena/BepiColombo project, but could be readily adapted to a number of future missions, including missions to study planetary atmospheres and exospheres, cometary missions, and fast flybys.