After 8 Years and 6 Billion Miles, Two Spacecraft Are Finally at Mercury

A Journey Like No Other

The BepiColombo Mercury mission entered its long-awaited arrival phase after an eight-year journey that began in October 2018. On September 3, 2026, a critical milestone was reached: the arrival phase began with the separation of the Mercury Transfer Module from the spacecraft stack. Since launch, the mission has traveled more than 6 billion miles — 10 billion kilometers. That's an almost incomprehensible distance for a destination that, by planetary standards, is practically next door.

BepiColombo is a joint effort between the European Space Agency and the Japan Aerospace Exploration Agency, designed to use two complementary orbiters to reveal insights into how Mercury formed and evolved so close to the sun. The eight-year journey involved six gravity-assist flybys of Mercury, two of Venus, and one of Earth, as well as a critical solar panel issue in 2024 that delayed its arrival. Getting to Mercury is notoriously hard — the sun's immense gravity makes it one of the most difficult places in the inner solar system to reach and stay.

Two Orbiters, One Mission

BepiColombo will be the first mission to orbit Mercury with two spacecraft simultaneously, with ESA's Mercury Planetary Orbiter (MPO) and JAXA's Mercury Magnetospheric Orbiter (Mio) orbiting the planet at the same time. The two craft serve very different but complementary roles. ESA's MPO will descend into a low polar orbit to map the planet's surface topography, elemental composition, and internal structure, while JAXA's Mio will swing into an elongated orbit to analyze the planet's magnetic field and surrounding plasma environment.

The separation of the transfer module occurred 39 million miles from the sun, in an environment where temperatures swing between -180 and 450°C, and solar radiation is up to ten times what we experience on Earth. ESA's Ignacio Tanco, head of inner solar system mission operations, described the operation as equivalent to launching an entirely new spacecraft. The arrival sequence is far from a single dramatic moment. The composite spacecraft will enter orbit around Mercury on November 21, 2026, and MPO and Mio will separate from each other on December 9–10, 2026. MPO is then scheduled to reach its final science orbit on March 10, 2027, with science operations for both spacecraft beginning on April 6, 2027.

Mercury's Big Mysteries

Mercury may be the solar system's smallest planet, but it punches well above its weight scientifically. Just one spacecraft, NASA's MESSENGER, has ever orbited the planet — and it left scientists with more questions than answers. BepiColombo will investigate properties still considered mysterious, including Mercury's unusually high density, the fact that it is the only planet besides Earth with a magnetic field, the much higher-than-expected amount of volatile elements detected by MESSENGER, and the nature of water ice that may exist in permanently shadowed areas at the poles.

The planet's surface appears old and cratered, undisturbed by geologic activity like volcanoes — yet it has a magnetic field, which is normally caused by a molten core that should, in turn, cause surface changes. That contradiction has puzzled scientists for decades. Then there are Mercury's strange "hollows." Scientists are hoping to probe the so-called hollows spotted on Mercury by earlier missions — depressions that look like the surface is being eaten away. Hollows haven't been found elsewhere on planets in our solar system, and with no wind or water to form the thousands of puzzling depressions, scientists want to know what forces sculpted them.

Why This Matters Beyond Mercury

The scientific interest in going to Mercury lies in the valuable information the mission can provide to enhance our understanding of the planet itself as well as the formation of our solar system — information which cannot be obtained with observations made from Earth. In other words, Mercury isn't just a curiosity. It's a time capsule. Understanding how the smallest, innermost planet formed and survived so close to the sun could reshape our understanding of how rocky planets — including our own — came to be.

With the transfer module now jettisoned and both science orbiters on course, the most scientifically productive chapter of BepiColombo's story is still ahead. Once its main science mission begins, the two orbiters will study all aspects of mysterious Mercury from its core to surface processes, magnetic field, and exosphere, to better understand the origin and evolution of a planet close to its parent star. Eight years of travel. Billions of miles. The answers, finally, are within reach.