BepiColombo and its two orbiters built to study Mercury

Background

BepiColombo is the ESA mission sent to orbit Mercury, the least explored planet of the inner Solar System. ESA calls it the second and most complex mission ever to orbit the planet, because a spacecraft close to the Sun is harder to place than one sent to Saturn. It travelled as three joined parts: the Mercury Planetary Orbiter, the Mercury Magnetospheric Orbiter and the Mercury Transfer Module that carried both. It lifted off on 20 October 2018 on an Ariane 5 from Europe's Spaceport, and has taken years of looping flybys to slow into place. ESA's schedule puts arrival at Mercury in December 2026, with routine science from April 2027. Among the puzzles it is to settle are the ice in the polar craters of a scorched world, why so small a planet has a magnetic field, and what the hollows on its surface are. Mercury is a small desert world and the answers are expected to say something about the whole Solar System.