After almost eight years of travel, BepiColombo has just abandoned the part of the spacecraft that carried it to Mercury’s doorstep.
On September 3, the mission’s transfer module successfully separated more than 200 million kilometers from Earth. Until then, it had provided the energy and propulsion needed for the journey. The two scientific probes, which make up its payload, are now continuing their journey together toward Mercury.
Separation of BepiColombo’s transfer module
Credit: ESA/ATG medialab; Mercury: NASA/JPL.
The confirmation was not immediate. At this distance, ground teams cannot directly observe the maneuver or intervene in real time. An initial change in the radio signal indicated that the separation had probably taken place. Later, two antennas located in Spain and Argentina received signals confirming the success of the operation.
BepiColombo is actually a mission made up of several elements. The European MPO probe will mainly study Mercury itself, particularly its surface and interior. The Japanese Mio probe will focus primarily on the planet’s space environment. Until now, both had been stacked on the European transfer module.
Exploded view of BepiColombo’s four elements: Mio, its shield, MPO and the MTM transfer module.
Credit: ESA / ATG medialab.
The latter had a very specific function: ensuring the long interplanetary journey. Launched in October 2018, the mission did not travel directly to Mercury. It made nine planetary flybys to gradually modify its trajectory and speed.
MPO now provides the electrical power and handles the maneuvers with its own thrusters. The two scientific probes remain attached to each other for the next major stage.
This stage is scheduled for November 21, 2026. BepiColombo will then have to enter orbit around Mercury. Heading toward a planet so close to the Sun is not simple. The Sun’s strong gravitational pull instead makes it difficult to slow down enough to remain in orbit around Mercury rather than fly past it.
BepiColombo’s interplanetary journey toward Mercury, with the gravitational flybys used during the mission.
Credit: ESA / ATG Europe — CC BY-SA 3.0 IGO.
MPO and Mio will then separate on December 9 and 10. They will gradually reach their respective working orbits around the planet. BepiColombo will then become the first mission to study Mercury simultaneously with two probes placed in orbit.
Regular scientific observations will not begin immediately. The teams will first have to check the probes and their instruments, then complete their positioning around Mercury. The scientific phase is expected to begin in April 2027, with complementary measurements of the planet, its magnetic field and its environment.