Media briefing: BepiColombo's next milestone towards Mercury

Meta Title: BepiColombo Nears Mercury Arrival as Transfer Module Separation Approaches
Meta Description: ESA and JAXA’s BepiColombo mission is preparing for a key 2026 milestone: separating its Mercury Transfer Module ahead of orbit insertion and science operations at Mercury.
URL Slug: bepicolombo-mercury-transfer-module-separation-2026
Excerpt: BepiColombo is entering its final approach to Mercury. ESA and JAXA are preparing to separate the spacecraft’s Mercury Transfer Module before planned orbit insertion in November 2026, followed by the deployment of two dedicated Mercury orbiters.

## BepiColombo Enters Its Final Approach to Mercury

The joint European-Japanese BepiColombo mission is approaching one of the most demanding phases of its long journey: arrival at Mercury.

During an ESA media briefing on 31 August 2026, mission specialists outlined preparations for the scheduled separation of BepiColombo’s Mercury Transfer Module, or MTM, on 3 September. The event is a major transition for the spacecraft, which has spent years using solar-electric propulsion and a series of planetary flybys to gradually reshape its orbit around the Sun.

According to ESA, the mission is then expected to proceed toward Mercury orbit insertion in November 2026. If the arrival sequence goes as planned, the two spacecraft carried by BepiColombo — ESA’s Mercury Planetary Orbiter (MPO) and JAXA’s Mercury Magnetospheric Orbiter, known as Mio — are scheduled to separate in December 2026.

These dates were presented as planned milestones in the ESA briefing. The source material does not provide confirmation that the MTM separation, Mercury orbit insertion, or orbiter deployment have already occurred.

## Why Reaching Mercury Is So Difficult

Mercury is the closest planet to the Sun, but that does not make it the easiest destination in the Solar System. In fact, orbital missions to Mercury are exceptionally challenging.

A spacecraft launched from Earth already travels around the Sun at high speed. To reach Mercury and enter orbit around it, the spacecraft must lose a large amount of heliocentric velocity — its speed relative to the Sun. Simply heading inward is not enough. Without a carefully controlled trajectory, a spacecraft would pass Mercury too quickly to be captured by the planet’s gravity.

BepiColombo has addressed this challenge through a combination of gravity-assist flybys and low-thrust solar-electric propulsion. The mission has used flybys of Earth, Venus and Mercury itself to alter its path while conserving propellant. Its electric thrusters have supplied continuous, efficient acceleration over long periods.

The approach has taken years, but it allows the spacecraft to reach Mercury at a manageable speed. The upcoming MTM separation marks the end of the transfer stage that made this complex journey possible.

## What Is the Mercury Transfer Module?

The Mercury Transfer Module is the propulsion section that has carried BepiColombo through interplanetary space. It includes large solar arrays and four ion thrusters, which generate low but highly efficient thrust by accelerating electrically charged particles.

This system was essential because conventional chemical rockets would require an impractically large amount of fuel to slow a spacecraft enough for Mercury arrival. Solar-electric propulsion, powered by sunlight, enabled the mission to steadily modify its orbit while minimizing propellant use.

Once the spacecraft reaches the final stages of arrival, the MTM will no longer be needed. Its separation reduces the spacecraft configuration to the orbiters and their associated protective structures, preparing the mission for Mercury orbit insertion and later deployment.

The maneuver must be performed carefully. BepiColombo has travelled as a tightly integrated spacecraft stack, with the two science orbiters protected during cruise. The separation sequence is one part of a broader arrival campaign involving navigation, propulsion, thermal control and communications.

## Two Orbiters, Two Views of Mercury

BepiColombo is not a single spacecraft but a paired mission designed to study Mercury from complementary perspectives.

ESA’s Mercury Planetary Orbiter will focus primarily on the planet itself. Its instruments are intended to investigate Mercury’s surface, composition, interior structure, gravity field, magnetic environment and extremely thin atmosphere, known as an exosphere.

JAXA’s Mio spacecraft is designed to study the space environment around Mercury. It will investigate the planet’s magnetosphere — the region shaped by Mercury’s magnetic field and its interaction with the solar wind.

Together, the two orbiters should provide a more complete picture than either spacecraft could alone. MPO can examine processes at the surface and inside the planet, while Mio can monitor how charged particles and magnetic fields behave around Mercury.

The two-spacecraft approach is particularly valuable because Mercury’s magnetosphere is small and highly variable. It is continually compressed and disturbed by the solar wind, which is much stronger near the Sun than it is at Earth.

## The Science Questions Waiting at Mercury

Mercury is the smallest planet in the Solar System and one of the least explored. NASA’s Mariner 10 made three flybys in the 1970s, and NASA’s MESSENGER spacecraft became the first mission to orbit Mercury in 2011. BepiColombo’s MPO and Mio are expected to become only the second and third orbiters of the planet.

Despite the observations made by MESSENGER, several major questions remain.

One concerns Mercury’s oversized iron-rich core. The planet has an unusually large core relative to its overall size, and scientists are still working to understand how it formed. Measurements of Mercury’s gravity, rotation and magnetic field may help reveal whether parts of the core remain liquid and how the planet’s interior has evolved.

Another question involves Mercury’s surface chemistry. The planet’s crust preserves evidence from the early Solar System, including extensive volcanic plains, impact basins and material altered by billions of years of solar radiation and micrometeoroid impacts.

BepiColombo will also study water ice and other volatile materials in permanently shadowed craters near Mercury’s poles. Although the planet is intensely hot in direct sunlight, some polar regions never receive sunlight and can remain cold enough to preserve ice.

The mission’s measurements may also test aspects of fundamental physics. Mercury’s close orbit around the Sun makes it a useful environment for examining gravitational effects predicted by Einstein’s general theory of relativity.

## Operating Near the Sun Brings Major Risks

Mercury’s proximity to the Sun creates a harsh operational environment. Spacecraft hardware must cope with strong sunlight, high temperatures and significant temperature changes between sunlit and shaded conditions.

Thermal management is therefore central to BepiColombo’s design and operations. The spacecraft’s instruments, electronics, solar arrays and communications equipment must operate within safe temperature limits while the mission continues to maneuver and gather data.

Navigation is also demanding. Mercury has a relatively weak gravitational influence compared with larger planets, and the spacecraft must execute accurately timed maneuvers to enter and maintain the intended orbits.

The orbiters will eventually operate in different trajectories suited to their scientific goals. Their observations will need to be coordinated with spacecraft operations, ground communications and the changing conditions of Mercury’s environment.

## A New Era of Mercury Exploration

The planned MTM separation is important not simply because it removes a propulsion unit. It signals that BepiColombo is moving from its years-long cruise toward its central purpose: scientific exploration of Mercury.

Mercury has often received less public attention than Mars, Jupiter or Saturn, partly because it is difficult to observe from Earth and difficult to reach with spacecraft. Yet it offers a unique record of how rocky planets formed close to a young star.

By comparing Mercury with Earth, Venus and Mars, scientists can better understand why the inner planets developed such different sizes, atmospheres, magnetic fields and geological histories.

If the scheduled arrival sequence proceeds successfully, BepiColombo will give planetary science its most detailed examination yet of the Solar System’s innermost world. The coming months are therefore a critical operational period — and the start of what could be a scientifically transformative mission phase.

## Authority sources (external links):

– [ESA’s BepiColombo mission overview](https://www.esa.int/Science_Exploration/Space_Science/BepiColombo)
– [ESA’s BepiColombo media briefing on the next Mercury milestone](https://www.esa.int/ESA_Multimedia/Videos/2026/08/Media_briefing_BepiColombo_s_next_milestone_towards_Mercury)
– [JAXA information on the Mio