Watch live: BepiColombo begins its arrival at Mercury

Meta Title: BepiColombo Begins Mercury Arrival Phase With MTM Separation
Meta Description: ESA and JAXA’s BepiColombo mission is set to begin its Mercury arrival phase on 3 September 2026, starting with the separation of its transfer module.
URL Slug: bepicolombo-mercury-arrival-mtm-separation
Excerpt: After nearly eight years in space, the ESA/JAXA BepiColombo mission is preparing for a critical transition at Mercury. ESA plans to livestream the separation of the Mercury Transfer Module from the mission’s two science orbiters on 3 September 2026.

## BepiColombo Approaches a New Phase at Mercury

The European Space Agency’s BepiColombo mission is preparing to enter one of the most important and technically demanding periods of its journey: its arrival phase at Mercury.

According to ESA, the first major milestone is scheduled for 3 September 2026, when the mission’s Mercury Transfer Module, or MTM, will separate from the two spacecraft designed to study the planet itself. ESA plans to broadcast the operation live from its mission control centre, with coverage beginning at 13:45 CEST.

The event marks a transition that has been almost eight years in the making. BepiColombo launched in October 2018 and has followed a long, fuel-saving route through the inner Solar System. Rather than flying directly to Mercury, the spacecraft has used repeated gravity-assist flybys of Earth, Venus and Mercury to gradually reshape its orbit around the Sun.

That method conserves propellant, but it also makes the mission’s final approach exceptionally complex. Mercury orbits close to the Sun and moves quickly along its path, meaning a spacecraft arriving from Earth must shed a substantial amount of orbital energy before it can be captured by the planet’s gravity.

## What Will Happen During the MTM Separation?

BepiColombo is not a single spacecraft in the usual sense. It was launched as a composite mission made up of several major elements.

The Mercury Transfer Module supplied the propulsion needed for the cruise to Mercury. Its solar-electric propulsion system, including ion engines and large solar arrays, was designed to carry the mission through the long interplanetary journey and numerous flybys.

Attached to the MTM are the mission’s two scientific orbiters:

– **Mercury Planetary Orbiter (MPO):** ESA’s spacecraft, intended to investigate Mercury’s surface, internal structure, exosphere and environment.
– **Mercury Magnetospheric Orbiter (Mio):** JAXA’s spacecraft, built to study Mercury’s magnetic field, magnetosphere and interactions with the solar wind.

The planned separation does not mean that the two science orbiters will immediately split apart from one another. Instead, it removes the cruise-stage module whose main role was to transport the scientific spacecraft toward Mercury. The orbiters will remain part of a carefully managed arrival sequence before they can eventually begin their separate science operations.

ESA has described this as the first major step in a highly challenging planetary arrival campaign. The agency’s announcement does not provide every technical detail of the full sequence, including all planned manoeuvres, timings or individual deployment events. What is clear is that discarding the transfer module is a necessary transition from interplanetary travel to Mercury-orbit operations.

## Why Reaching Mercury Is So Difficult

Mercury may be the closest planet to Earth in some orbital configurations, but it is among the hardest destinations in the Solar System to reach.

The problem is the Sun’s gravity. A spacecraft departing Earth already travels around the Sun at high speed. To descend toward Mercury’s orbit, it falls deeper into the Sun’s gravitational well and gains even more speed. Reaching Mercury is therefore not mainly a matter of travelling inward; it is a matter of slowing down enough to match the planet’s rapid orbit.

Mercury circles the Sun at an average speed of roughly 47 kilometres per second. A direct flight from Earth would require an impractically large amount of propellant to brake into orbit. BepiColombo’s solution has been to use gravity assists and electric propulsion over many years.

During a gravity assist, a spacecraft passes near a planet and uses the planet’s motion and gravity to alter its own path. BepiColombo’s flybys have progressively reduced the energy of its solar orbit and aligned its trajectory more closely with Mercury’s.

This extended route helps explain why the mission has taken so long to reach its destination. It also explains why the arrival phase cannot be treated as a simple final step. Every separation, engine operation, spacecraft orientation and communication session must be closely coordinated.

## A Joint Mission to a Poorly Understood Planet

BepiColombo is a partnership between ESA and the Japan Aerospace Exploration Agency, or JAXA. Its name honours Giuseppe “Bepi” Colombo, the Italian mathematician and engineer who helped explain Mercury’s unusual rotation and contributed to the planning of NASA’s Mariner 10 mission in the 1970s.

Mercury remains one of the least explored rocky planets. NASA’s Mariner 10 completed three flybys in the 1970s, while NASA’s MESSENGER spacecraft became the first mission to orbit Mercury in 2011. MESSENGER transformed understanding of the planet, documenting volcanic plains, a global magnetic field, unusual surface chemistry and signs of water ice in permanently shadowed polar craters.

Yet major questions remain.

Scientists are still investigating why Mercury has such a large iron-rich core relative to its size, how its magnetic field is generated, and how the planet’s surface has evolved under intense solar heating and radiation. Mercury’s extremely thin exosphere—an atmosphere-like cloud of atoms released from the surface—also changes in response to sunlight, micrometeoroid impacts and the solar wind.

By operating two orbiters with complementary instrument suites, BepiColombo is intended to examine Mercury as both a planetary body and a world immersed in the Sun’s highly variable space environment.

## What the Two Orbiters Will Study

ESA’s Mercury Planetary Orbiter is designed to focus heavily on Mercury itself. Its instruments include cameras, spectrometers, laser-ranging equipment and radio-science systems. Together, these tools are expected to help researchers map the surface, assess mineral composition, measure topography and probe the planet’s interior.

JAXA’s Mio spacecraft is tailored to the space environment around Mercury. It will study charged particles, plasma waves and magnetic fields around the planet. That work is especially significant because Mercury has a magnetic field despite being much smaller than Earth, and because its magnetosphere is compressed by the powerful solar wind close to the Sun.

Operating both spacecraft at the same time could help scientists connect changes in the solar wind to effects in Mercury’s magnetic environment and at its surface.

The two-orbiter approach is one of BepiColombo’s defining strengths. A single spacecraft can make valuable measurements, but paired observations can provide a more complete picture of the interactions between the planet, its magnetic field and the surrounding solar environment.

## Why the Livestream Milestone Matters

Spacecraft separations are rarely dramatic in the visual sense. Viewers should not expect a conventional camera view of the transfer module drifting away, since the operation takes place far from Earth and under tightly controlled spacecraft conditions.

Instead, ESA’s livestream is likely to offer a look at the operational side of the milestone: mission controllers, engineering updates and confirmation of events as telemetry arrives from the spacecraft.

That is precisely why the broadcast is significant.