ESA and JAXA’s BepiColombo mission has entered one of the most important stages of its eight-year journey to Mercury. On September 3, 2026, mission controllers confirmed the successful separation of the Mercury Transfer Module, the propulsion stage that carried the spacecraft stack through interplanetary space. The two science orbiters are now continuing toward Mercury, where the combined spacecraft is scheduled to enter orbit on November 21, 2026.
The milestone marks the beginning of BepiColombo’s final arrival phase and sets up a carefully choreographed series of events that will eventually place two specialized spacecraft around the closest planet to the Sun. If the remaining steps go as planned, ESA’s Mercury Planetary Orbiter and JAXA’s Mio will separate from each other in December, with full science operations expected to begin in April 2027.
What Happened on September 3?
BepiColombo was launched in October 2018 as a stacked spacecraft made up of several major elements. During the long cruise to Mercury, the Mercury Transfer Module, or MTM, provided electric propulsion and helped guide the mission through a complicated route across the inner Solar System.
ESA reported that the MTM separation was successfully confirmed on September 3. Deep-space antennas at Cebreros in Spain and Malargüe in Argentina acquired the spacecraft signal, and telemetry showed that the remaining systems were operating normally. ESA also reported that the solar arrays on the Mercury Planetary Orbiter were charging the spacecraft’s batteries after separation.
This was not simply a routine hardware release. The separation took place more than 200 million kilometers from Earth, meaning mission controllers could not intervene in real time. Commands had to be planned in advance and the spacecraft had to execute the sequence autonomously before the result could be verified through radio signals received on Earth.
What Happens Next?
The September separation is only the first major step in a months-long arrival sequence. ESA’s current mission timeline lists several key milestones:
- September 3, 2026: Mercury Transfer Module separation.
- November 21, 2026: the combined spacecraft is scheduled to enter orbit around Mercury.
- December 9–10, 2026: ESA’s Mercury Planetary Orbiter and JAXA’s Mio are scheduled to separate.
- April 2027: the main science phase is expected to begin.
During the period between orbital insertion and the start of science operations, teams will configure the two orbiters, check their instruments and maneuver them toward their intended scientific orbits.
Why Is Mercury So Difficult to Reach?
Mercury may be much closer to Earth than the outer planets, but reaching it is surprisingly difficult. A spacecraft traveling around the Sun with Earth already carries a large amount of orbital energy. To move inward toward Mercury, it must reduce that energy while also surviving the increasingly intense solar environment.
That is why BepiColombo followed a long, carefully designed trajectory instead of simply flying directly toward Mercury. Its journey used planetary flybys and solar-electric propulsion to gradually reshape its orbit around the Sun. The mission’s long cruise is a reminder that distance alone does not determine how difficult a destination is to reach.
Mercury also presents an extreme thermal environment. JAXA notes that sunlight at Mercury is far stronger than at Earth and that the planet experiences enormous temperature swings. Spacecraft operating there must be designed to tolerate intense heat while still keeping scientific instruments and electronics within safe temperature limits.
Why BepiColombo Uses Two Orbiters
BepiColombo is unusual because it is designed to place two science spacecraft around Mercury at the same time. The two orbiters have different scientific roles and will observe the planet from complementary perspectives.
ESA’s Mercury Planetary Orbiter (MPO) is focused on the planet itself. Its investigations include Mercury’s surface, composition, geology, internal structure, gravity field and magnetic field. JAXA’s Mio, originally known as the Mercury Magnetospheric Orbiter, is designed primarily to study Mercury’s magnetic field, magnetosphere, plasma environment and interaction with the solar wind.
Operating both spacecraft simultaneously should allow researchers to connect processes occurring at Mercury’s surface and interior with changes occurring in the surrounding space environment. That combination is particularly valuable because Mercury possesses a global magnetic field despite being the smallest planet in the Solar System.
Why Mercury Still Matters
Only two previous missions have studied Mercury up close: NASA’s Mariner 10 and MESSENGER. Those missions transformed scientists’ understanding of the planet, but major questions remain about how Mercury formed, why it contains such a large metallic core, how its magnetic field is generated and how its surface has evolved under constant exposure to the Sun.
BepiColombo is designed to investigate many of those questions with a broader set of instruments and two complementary orbiters. The mission may also help scientists understand the formation of rocky planets in general. Because Mercury formed in an extreme region close to the young Sun, its composition and internal structure preserve clues about conditions in the early Solar System.
A Major Milestone, but the Hardest Part Is Not Over
The successful separation of the Mercury Transfer Module is an important achievement, but BepiColombo has not yet completed its arrival. Orbit insertion in November remains a critical event, followed by the separation and commissioning of the two science orbiters.
For now, however, the mission has completed the first major step of its final approach exactly where it needed to. After nearly eight years and billions of kilometers of travel, BepiColombo is no longer simply cruising toward Mercury. It is beginning the transition from interplanetary traveler to a two-spacecraft scientific observatory around one of the Solar System’s least explored planets.
Sources
- European Space Agency — Latest updates: BepiColombo’s arrival at Mercury, updated September 3, 2026.
- European Space Agency — BepiColombo mission overview.
- Japan Aerospace Exploration Agency — BepiColombo / Mio mission information.
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