BepiColombo has completed the first step of a tightly sequenced Mercury-arrival campaign: on 3 September, ESA confirmed successful jettison of the Mercury Transfer Module (MTM), leaving ESA’s MPO and JAXA’s Mio bound together for orbital insertion. The remaining operations—capture, separation, and 16 orbit-lowering manoeuvres—are mission-critical before routine science can begin in April 2027. 5

• Journey and milestone: Launched in October 2018, BepiColombo used one Earth, two Venus, and six Mercury gravity-assist flybys—nine in all—to reduce its solar-orbit energy enough to rendezvous with Mercury. Its cruise covered more than 10 billion km. 23

• What happened on 3 September: The MTM, which supplied solar-electric propulsion during cruise, separated successfully more than 200 million km from Earth. With no possibility of real-time control, the event required pre-programmed, precise navigation and commanding; MPO’s solar arrays now power the still-attached MPO–Mio stack. 5

• The major technical setback: A 2024 electrical problem limited power available to the MTM’s solar-electric propulsion system. ESA redesigned the trajectory and operational plan, extending the trip and moving the planned Mercury arrival from December 2025 to November 2026. The successful MTM separation means that cruise-propulsion issue no longer governs the spacecraft’s next phase. 35

• Orbital insertion: On 21 November 2026, the composite MPO–Mio spacecraft is scheduled to fire MPO’s chemical propulsion system to be captured by Mercury. This is not the final science orbit: it begins a months-long campaign to shrink and reshape the initially highly elliptical orbit. 5

• Deployment and orbit shaping: Mio is expected to separate from MPO around 9–10 December. The two orbiters will then execute 16 manoeuvres through early 2027 to reach their distinct polar science orbits: MPO for close planetary observations and Mio for the magnetosphere. 5

• Why arrival is operationally difficult: Mercury’s strong solar gravity requires a large velocity reduction for capture, while proximity to the Sun imposes severe thermal and power constraints—temperatures can exceed 350°C. Coordinating two spacecraft, their separations, propulsion burns, attitudes, communications, and thermal limits makes this ESA’s most complex planetary-arrival sequence. 56

• Science phase: Routine science is planned to start on 6 April 2027, after commissioning and orbit acquisition. Across the two orbiters, 16 instruments will investigate Mercury’s surface composition and geology, its origin and interior—including its large iron-rich core—and its magnetic field, magnetosphere, exosphere, and interaction with the solar wind. Simultaneous measurements from MPO and Mio are central to separating planetary processes from changing space-weather conditions. 56

The dates after 3 September are planned milestones rather than completed events, so they remain contingent on successful capture, deployments, and manoeuvres.

BepiColombo has completed the first step of a tightly sequenced Mercury-arrival campaign: on 3 September, ESA confirmed successful jettison of the Mercury Transfer Module (MTM), leaving ESA’s MPO and JAXA’s Mio bound together for orbital insertion. The remaining operations—capture, separation, and 16 orbit-lowering manoeuvres—are mission-critical before routine science can begin in April 2027. 5

• Journey and milestone: Launched in October 2018, BepiColombo used one Earth, two Venus, and six Mercury gravity-assist flybys—nine in all—to reduce its solar-orbit energy enough to rendezvous with Mercury. Its cruise covered more than 10 billion km. 23

• What happened on 3 September: The MTM, which supplied solar-electric propulsion during cruise, separated successfully more than 200 million km from Earth. With no possibility of real-time control, the event required pre-programmed, precise navigation and commanding; MPO’s solar arrays now power the still-attached MPO–Mio stack. 5

• The major technical setback: A 2024 electrical problem limited power available to the MTM’s solar-electric propulsion system. ESA redesigned the trajectory and operational plan, extending the trip and moving the planned Mercury arrival from December 2025 to November 2026. The successful MTM separation means that cruise-propulsion issue no longer governs the spacecraft’s next phase. 35

• Orbital insertion: On 21 November 2026, the composite MPO–Mio spacecraft is scheduled to fire MPO’s chemical propulsion system to be captured by Mercury. This is not the final science orbit: it begins a months-long campaign to shrink and reshape the initially highly elliptical orbit. 5

• Deployment and orbit shaping: Mio is expected to separate from MPO around 9–10 December. The two orbiters will then execute 16 manoeuvres through early 2027 to reach their distinct polar science orbits: MPO for close planetary observations and Mio for the magnetosphere. 5

• Why arrival is operationally difficult: Mercury’s strong solar gravity requires a large velocity reduction for capture, while proximity to the Sun imposes severe thermal and power constraints—temperatures can exceed 350°C. Coordinating two spacecraft, their separations, propulsion burns, attitudes, communications, and thermal limits makes this ESA’s most complex planetary-arrival sequence. 56

• Science phase: Routine science is planned to start on 6 April 2027, after commissioning and orbit acquisition. Across the two orbiters, 16 instruments will investigate Mercury’s surface composition and geology, its origin and interior—including its large iron-rich core—and its magnetic field, magnetosphere, exosphere, and interaction with the solar wind. Simultaneous measurements from MPO and Mio are central to separating planetary processes from changing space-weather conditions. 56

The dates after 3 September are planned milestones rather than completed events, so they remain contingent on successful capture, deployments, and manoeuvres.