BepiColombo has begun its final approach to Mercury after eight years in flight

After eight years and billions of kilometers of interplanetary cruising, the European Space Agency’s BepiColombo mission has entered the arrival phase of its journey to Mercury. On September 3, 2026, the spacecraft shed the transfer module that had powered it since launch in 2018, the first of several high-stakes maneuvers that will end with two science orbiters settling into orbit around the solar system’s innermost planet in November. Mission controllers report the spacecraft is healthy, but the most demanding operations of the entire mission still lie ahead.

A Separation Confirmed 200 Million Kilometers from Earth

Mission controllers confirmed that BepiColombo’s Mercury Transfer Module (MTM) successfully separated from the rest of the spacecraft stack on September 3, kicking off what the team calls the mission’s “arrival phase.” Confirmation came through two of ESA’s deep-space tracking antennas, located in Spain and Argentina, which picked up telemetry validating the separation. That telemetry showed every system functioning normally, with the Mercury Planetary Orbiter’s solar panels already charging the spacecraft’s batteries. The maneuver carried real risk: it took place more than 200 million kilometers from Earth, a distance that ruled out any real-time troubleshooting and forced mission teams to plan every contingency months in advance. ESA has described the entire arrival sequence as one of the most operationally challenging planetary arrivals it has ever attempted, and separation was only the opening step.

Nine Planetary Flybys Across an Eight-Year Cruise

BepiColombo launched from Europe’s spaceport in Kourou, French Guiana, on October 20, 2018, beginning a roundabout route rather than a direct shot toward the sun. To shed enough orbital energy to be captured by Mercury’s weak gravity, the mission flew past Earth once, Venus twice, and Mercury itself six times before the spacecraft was finally positioned for orbit insertion. That circuitous path is why a trip covering a relatively short distance in solar-system terms has taken the better part of a decade, with the transfer module’s ion thrusters firing for long stretches to fine-tune the trajectory between each flyby. For most of that cruise, the spacecraft flew as a single stack, with the transfer module’s solar wings extending roughly 30 meters from tip to tip to power the ion engines, while the planetary orbiter’s own 7.5-meter solar array remained folded against the stack alongside the smaller Japanese orbiter, which stayed shielded from the sun’s heat until closer to Mercury.

Two Orbiters Named for the Mathematician Who Solved Mercury’s Spin

The mission is named after Giuseppe “Bepi” Colombo, an Italian mathematician and engineer who was the first to recognize that Mercury rotates on its axis three times for every two trips it makes around the sun, an unusual resonance that had puzzled astronomers. Colombo also proposed to NASA how a gravity-assist flyby of Venus could place the Mariner 10 spacecraft on a trajectory that let it pass Mercury three times in 1974 and 1975. His namesake mission consists of two science orbiters flying together: the European Space Agency’s Mercury Planetary Orbiter (MPO) and the Japan Aerospace Exploration Agency’s Mercury Magnetospheric Orbiter, nicknamed Mio. It is the first mission built to send two spacecraft to Mercury for complementary, simultaneous measurements, and only the second mission of any kind to enter orbit around the planet, after NASA’s MESSENGER spacecraft did so in 2011.

From November’s Orbit Insertion to a 2027 Start for Science

Separation from the transfer module is only the first of several milestones packed into the closing months of 2026. The joined MPO and Mio spacecraft, still traveling together with MPO providing power and propulsion for the pair, are due to enter orbit around Mercury on November 21, 2026. The two orbiters will then separate from each other on December 9 and 10, sliding into their own distinct orbits, with MPO maneuvering into a dedicated polar orbit while Mio settles into its own polar science orbit. Even after both spacecraft reach their final positions, engineers plan an extended checkout period before instruments are switched on in earnest; the mission’s science operations are not scheduled to begin until April 2027, more than eight and a half years after launch.

Why Mercury Needs Two Spacecraft Working at Once

Mercury’s proximity to the sun makes it a difficult environment to study from a single vantage point, since the planet’s surface, weak magnetic field, and the way the solar wind interacts with that field all change on fast timescales. MPO is built to map Mercury’s surface composition, topography, and interior structure, while Mio focuses on the planet’s magnetosphere and its interaction with the solar wind. Studying both simultaneously, rather than sequentially the way NASA’s earlier MESSENGER mission did, is intended to let scientists connect surface features to the space environment shaping them in real time. Getting both instruments into position without a mishap during a sequence ESA has called one of the most operationally challenging planetary arrivals it has ever attempted is the task now facing controllers over the next several months, culminating in the two orbiters’ final separation and the long-awaited start of routine science observations in 2027.

This article was produced with the assistance of AI and reviewed by Morning Overview editors prior to publication.