An eight-year gravitational obstacle course
Getting to Mercury is one of the more counterintuitive challenges in spaceflight. Despite being the closest planet to the Sun, reaching it requires shedding enormous amounts of velocity to avoid being pulled into a solar orbit. To manage this, the ESA–JAXA BepiColombo spacecraft — launched in October 2018 from Europe's Guiana Space Centre on an Arianespace rocket — executed a carefully choreographed sequence of nine planetary flybys: one past Earth, two past Venus, and six past Mercury itself, each shaving off speed and reshaping the trajectory.
On 3 September 2026, the culmination of that long approach began. Flight controllers at the European Space Operations Centre (ESOC) in Darmstadt, Germany, monitored the opening manoeuvres of the orbital insertion phase in real time. ESA broadcast the session live, allowing the public to follow a mission milestone eight years in the making. Operating close to Mercury brings its own engineering demands: solar flux at that distance is roughly ten times stronger than what spacecraft in Earth orbit typically experience, placing intense thermal stress on the onboard systems.
Two orbiters, one shared journey
BepiColombo is not a single spacecraft but a composite stack of two separate science orbiters that have travelled together since launch. The Mercury Planetary Orbiter (MPO), built under ESA's leadership, is designed to map the planet's surface in detail and characterise its geochemical makeup. The Mercury Magnetospheric Orbiter (MMO), developed by JAXA and known as Mio, will focus on Mercury's magnetic field and its dynamic relationship with the solar wind.
Once orbital capture is complete, the two modules will separate and drift into their individual working orbits. This dual-spacecraft configuration is unprecedented for a Mercury mission and will enable simultaneous measurements from two distinct vantage points around the planet — a significant advantage for cross-referencing scientific data that no previous mission could offer.
Questions Mercury has held for decades
Mercury remains one of the least understood bodies in the Solar System. NASA's MESSENGER probe, which orbited the planet between 2011 and 2015, delivered the first comprehensive orbital dataset, but many fundamental questions were left unanswered. BepiColombo aims to go further on several fronts: explaining why Mercury possesses a magnetic field at all — a feature difficult to account for given the planet's small size — investigating the suspected water-ice deposits locked away in permanently shadowed polar craters, and tracing the geological evolution of this iron-rich world over billions of years.
Firm scientific results are still some way off. The nominal science phase will not begin until months after orbital capture, once both orbiters have settled into stable trajectories and their instruments have been fully calibrated. Nevertheless, 3 September 2026 marks a clear turning point: the end of an interplanetary voyage and the beginning of sustained scientific observation at the Solar System's innermost planet. Europe and Japan now have a foothold at Mercury.
