Mercury is the least well-known of the planets in our solar system. This is largely because its proximity to the Sun makes sending space probes there challenging. To learn more about Mercury, the European BepiColombo mission launched two probes in October 2018—MPO (Mercury Planetary Orbiter) and a Mercury Magnetospheric Orbiter, renamed Mio by JAXA—to reach orbit late in 2025. MPO will map the entire surface of the planet and study its inner composition and structure, while Mio will analyse its magnetic field and magnetosphere (the layer of a planet’s atmosphere where physical characteristics are governed by the magnetic field). Data gathered will provide new insights into the formation and evolution of ‘inner’ planets—planets orbiting close to their star—like our Earth.

The MPO probe was developed by ESA and the Mio probe by JAXA. CNES oversaw development of the French instruments on BepiColombo for all of the research laboratories involved in the mission—eight in all (IAS, IPGP, IRAP, LAM, LATMOS, LESIA, LPC2E and LPP), who helped to design six of the 16 instruments.