For most space missions, launches are the headline news. For BepiColombo, the real milestone came a few years later. After nearly eight years traveling through the inner solar system, the European-Japanese spacecraft is now approaching the goal it was designed to do from the beginning. According to the European Space Agency, Mercury is expected to finally capture the spacecraft into orbit in November 2026, ending one of the longest and most carefully managed journeys to the planet in history. This waiting is deliberate, not accidental. Traveling to the planet closest to the sun requires a different approach than almost any other destination in space, requiring repeated gravity assists and constant adjustments rather than direct flight. Once BepiColombo is in orbit, scientists will begin a new chapter in the exploration of Mercury, a planet that remains surprisingly alien despite its location in Earth’s cosmic neighborhood.
Why Mercury remains one of the least explored planets
Mercury has never attracted the steady stream of missions that Mars or even Venus has. Its close proximity to the sun makes each visit technically demanding, leaving astronomers with only a handful of close encounters in the past five years.The first was launched in the mid-1970s via NASA’s Mariner 10 spacecraft. These flybys provided humanity’s earliest detailed observations of the charred world, but were never intended to put a spacecraft into orbit. Decades later, NASA’s MESSENGER mission orbited Mercury from 2011 to 2015, changing understanding of Mercury’s geology, magnetic field and chemical composition.BepiColombo now becomes the third mission to reach Mercury, and the second designed to orbit the planet, making its arrival an important addition to a surprisingly short history of exploration.
An unusual path to the solar system’s innermost planets
On a map of the solar system, Mercury may appear closer than Mars, but distance alone doesn’t tell the story. Any spacecraft flying inward toward the sun gathers tremendous speed as the sun’s gravity pulls it closer. The extra speed becomes a major obstacle.Rather than heading straight for Mercury, Bepi Colombo has been doing pretty much the opposite for years. The mission was repeatedly slowed down through a carefully planned series of planetary encounters. Flybys of Earth, two close flybys of Venus, and six encounters with Mercury gradually slowed the spacecraft. At the same time, its ion propulsion system provides a continuous but gentle push, making small corrections over thousands of hours, rather than relying on powerful bursts.The result is a journey defined by patience rather than speed.
How BepiColombo was designed
While BepiColombo is often described as a single spacecraft, its mission actually begins with a stack of three connected vehicles.The Mercury Transfer Module performs missions in interplanetary space while providing the ion propulsion required for long-distance cruises. Attached above it are two separate science orbiters that will eventually separate once Mercury completes its mission.The European-built Mercury Planetary Orbiter will focus on Mercury itself, examining its surface, internal structure and geological history. Beyond that, Japan’s Mio spacecraft has a different mission. Instead of looking down at Mercury, it will investigate Mercury’s magnetic environment and study the interactions between Mercury, the solar wind and surrounding charged particles.Simultaneous operations give scientists the opportunity to observe planets and the space around them simultaneously, something that was not possible with previous missions.
How engineers keep missions on track
The original arrival timetable has not remained unchanged.During 2024, engineers discovered an unexpected degradation in the performance of the spacecraft’s electric propulsion system. An investigation found the problem was due to an electrical current affecting the power distribution system connected to the spacecraft’s solar arrays.The reduced thrust means that existing flight plans can no longer put the spacecraft into Mercury’s orbit as planned. Mission experts redesigned the remainder of the orbit to use more of Mercury’s own gravity to compensate for weaker propulsion during later flybys.The revised route preserved the mission’s scientific objectives, although it delayed orbit entry by nearly a year. BepiColombo is currently expected to complete the process in November 2026, rather than arriving in late 2025.
How BepiColombo will get into orbit
In 2026, the mission passed another major milestone, completing a major phase of ion-powered cruise.Unlike the mission of using a large chemical engine to perform dramatic braking maneuvers, Bepi Colombo’s arrival was much slower. Small adjustments in propulsion continued as Mercury’s gravity slowly took over. The spacecraft will enter a temporary polar orbit before the transfer module is jettisoned.Only then will the two science orbiters separate and begin moving toward their respective paths around Earth. Their full science program is expected to begin in 2027 upon completion of commissioning and orbital adjustments.
Mercury still has many unanswered questions
Despite decades of study, Mercury still baffles planetary scientists.Its massive iron core occupies a much larger proportion of Earth than any other rocky world in the solar system. The cause remains uncertain, with several competing theories trying to explain how this unusual internal structure formed.Despite its relatively small size, Mercury also has a global magnetic field. Exactly how magnetic fields persist for billions of years remains an active area of ​​research.Perhaps the biggest surprises lie near the poles. Although Mercury has the highest surface temperatures in the solar system, permanently shadowed craters appear to preserve water ice because sunlight never reaches their surface. Understanding the origin and stability of these frozen deposits is one of the goals that awaits once scientific observations of BepiColombo begin.
