Strofio is a unique mass spectrometer that is part of the SERENA suite of instruments that will fly on board the European Space Agency’s BepiColombo/Mercury Planetary Orbiter (MPO) spacecraft. Strofio will determine the chemical composition of Mercury’s surface, providing a powerful tool to study the planet’s geological history. Strofio is funded by NASA as a Discovery Mission of Opportunity.

The SERENA instruments include two Neutral Particle Analyzers (Strofio and ELENA) and two Ion Spectrometers (MIPA and PICAM). Together they will investigate the complex particle environment that surrounds Mercury called the “exosphere.” The exosphere is different from an atmosphere. In an atmosphere the molecules constantly collide and change their velocity. In the collision-free exosphere, the particles move due to gravity and, if present, sunlight pressure. Particles escape from Mercury’s surface and flow out into the exosphere, then either return to the surface or are lost in planetary space.