After an 8-Year, 10 Billion-Kilometer Journey, BepiColombo Reaches Mercury’s Toughest Stage

BepiColombo has entered the most difficult part of its journey to Mercury after spending eight years and traveling more than 10 billion kilometers. On Sept. 3, its two linked probes successfully detached from the transfer module that had propelled them across space.

The spacecraft is expected to enter orbit around Mercury on Nov. 21. In December, the probes will separate and move into different orbits for their scientific missions. The approach has required a winding route since BepiColombo launched from Earth in 2018, including nine planetary flybys to adjust its speed and trajectory so Mercury’s weak gravity could capture it.

Mercury is only slightly larger than the Moon, and its small mass gives it much weaker gravity than the Sun. That makes it difficult for a spacecraft to approach and enter orbit. During its final flyby in January 2025, BepiColombo captured clear images of impact craters and volcanic plains. As of Sept. 3, it remained about 3.3 million kilometers from its destination.

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a tricky task

The European Space Agency described the arrival procedure as one of the most challenging planetary operations in its history. Because the spacecraft was about 200 million kilometers from Earth, the system had to autonomously cut four mechanical supports connecting the probes to the transfer module. Springs then gently pushed the components apart at 40 centimeters per second. ESA officials called it “a tricky task,” but Germany’s control center received confirmation of success about two hours later.

The European Mercury Planetary Orbiter will begin detailed observations next spring from an orbit as close as 480 kilometers above the surface. Japan’s Mercury Magnetospheric Orbiter, or Mio, will follow an elliptical orbit reaching about 11,000 kilometers from Mercury while studying the planet’s magnetic field and surrounding space environment. Mercury can reach 427 degrees Celsius, yet permanently shadowed polar craters are extremely cold and contain ice. ESA officials compared operating a probe there to working with “a blazing pizza oven running behind you.”

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a blazing pizza oven running behind you