BepiColombo begins Mercury arrival after 8-year journey

The European-Japanese BepiColombo spacecraft reached a defining milestone on Thursday, successfully separating its propulsion module and beginning its arrival phase at Mercury after nearly eight years of travel through the inner solar system.

The Mercury Transfer Module, the main power and propulsion system that has ferried the mission's two planetary probes since launch, separated from the spacecraft stack at 12:00 GMT on September 3, with confirmation arriving via ESA's deep space antennas in Spain and Argentina about an hour later. Telemetry indicated all systems were nominal and the solar panels on ESA's Mercury Planetary Orbiter were charging the spacecraft's batteries.esa

"It will basically be a new mission starting today," said Bruno Sousa, ESA's head of operations definition and engineering, during a mission livestream.space

A Long Road to the Innermost Planet

BepiColombo launched aboard an Ariane 5 rocket from French Guiana on October 19, 2018, embarking on a journey that has covered more than 10 billion kilometers. To slow itself enough to reach Mercury's weak gravitational pull — the planet is only slightly larger than the Moon — the spacecraft executed nine flybys of Earth, Venus, and Mercury.bangkokpost+1

The mission was complicated further in April 2024 when a solar panel issue reduced thrust capacity, forcing engineers to devise a lower-power trajectory that delayed Mercury arrival from December 2025 to November 2026.space

"It's one of the most complicated missions we have ever flown," Sousa said.space

Months of Maneuvers Ahead

Thursday's separation does not place BepiColombo in orbit. The two science orbiters — ESA's Mercury Planetary Orbiter and JAXA's Mercury Magnetospheric Orbiter, known as Mio — will navigate toward Mercury ahead of orbital insertion on November 21. Mio is scheduled to separate from the orbiter around December 9, and a sequence of 16 maneuvers will progressively lower and reshape the spacecraft's orbits through early 2027.esa+1

"Arriving to Mercury is not as simple as other missions that do a big maneuver and they are there," said Elsa Montagnon, BepiColombo's operations manager. "In our case, it's going to be six months of continuous activities."space

Science operations are set to begin on April 6, 2027, with 16 instruments studying Mercury's surface composition, geology, interior, and magnetic field. The mission carries a 1.7 billion-euro budget and will deliver what ESA calls "unprecedented views" of the solar system's least-studied rocky planet.bangkokpost+1

"I'm again extremely relieved," Montagnon said after confirming the separation. "That the telemetry comes exactly at the moment we expect it… this is the best case scenario."space