A Milestone 200 Million Kilometers Away
The BepiColombo mission, a collaboration between the European Space Agency (ESA) and the Japan Aerospace Exploration Agency (JAXA), reached a new milestone on its long journey to Mercury. On September 3, 2026, the spacecraft completed the separation of its Mercury Transfer Module (MTM), a key component that accompanied it for nearly eight years of travel.
The maneuver was executed autonomously over 200 million kilometers from Earth. Due to the distance, radio signals took about 11.5 minutes to reach our planet, so confirmation was received approximately two hours later via the Deep Space Network antennas in Spain and Argentina.
A Journey of Nearly 10 Billion Kilometers
BepiColombo launched in October 2018 from Kourou (French Guiana) aboard an Ariane 5 rocket. Since then, it has traveled about 10 billion kilometers, with nine planetary flybys (one of Earth, two of Venus, and six of Mercury) to slow down and align with the small planet's orbit.
The journey was not without setbacks: the degradation of the solar panels forced a delay in the orbit insertion, originally planned for December 2025, until November 2026. This delay added an extra cost of 15 million euros for ESA.
Two Orbiters, One Goal
The mission carries two scientific spacecraft:
- MPO (Mercury Planetary Orbiter, ESA): will study the surface, composition, topography, and interior of the planet.
- Mio/MMO (Mercury Magnetospheric Orbiter, JAXA): will analyze the space environment, magnetosphere, and exosphere.
During the journey, Mio was protected by the MOSIF, a sunshield that will be released in December. The MTM, now separated, has fulfilled its role and is history.
Next Steps: Orbital Insertion
The planned timeline is as follows:
| Date | Event |
|---|---|
| November 21, 2026 | Orbital insertion (gravitational capture) |
| December 9-10, 2026 | Separation of Mio and MPO |
| December 16, 2026 | Release of the sunshield (MOSIF) |
| March 10, 2027 | MPO reaches its final orbit |
| April 2027 | Start of the scientific phase |
The final orbits will be: MPO at 480×1,500 km and Mio at 590×11,640 km, both with an inclination of 90°. The mission will last one year, with a possible one-year extension.
Mercury: The Planet of Extremes
Mercury is the smallest planet and the closest to the Sun. Its surface temperature exceeds 427 °C during the day, and at its poles there are permanently shadowed craters that harbor ice. Only two previous missions have visited it: Mariner 10 (NASA, 1974) and MESSENGER (NASA, 2011-2015).
Among the mysteries BepiColombo will try to solve are:
- Its iron core, which represents about 65% of its mass (compared to 32% for Earth).
- The strange surface depressions called "hollows", with no equivalent on other planets.
- The presence of graphite, water, and organic compounds detected by MESSENGER.
- Its magnetic field, still poorly understood.
A Theory Connecting Mercury to the Moon
One of the most fascinating hypotheses suggests that Mercury may have lost its outer crust after a collision with a planetesimal about 4.5 billion years ago. The ejected material could have contributed to the formation of the Moon, Earth, or Venus.
A recent study by the Southwest Research Institute and the University of Arizona, published in Astrophysical Journal Letters, proposes that the Moon could have formed in just five hours after the impact of Theia with Earth, rather than in a slow process. The lead author, Adeene Denton, explained: "Everything depends on the temperature of Earth and Theia before the collision. The impact could destroy Theia and produce a large debris disk that would eventually form the Moon. However, when I use the same parameters as in the original impact model, a nearly intact Moon forms in about five hours".
Additionally, Dirk Schulze-Makuch, from the Technical University of Berlin, suggested that the Moon could be partly composed of material lost from Mercury.
Mission Voices
ESA scientists were enthusiastic. Geraint Jones, the project's lead scientist, called the moment "a brilliant moment". Santa Martínez Sanmartín, the mission director, highlighted: "How tiny Mercury is, and yet it harbors some of the greatest mysteries of our solar system". She added: "For the first time in space exploration, we are going to take two spacecraft to the vicinity of the planet and put them into orbit".
For his part, Ignacio Tanco, operations manager, compared the challenge to "working with a very hot pizza oven turned on right at your back". Johannes Benkhoff, project scientist, explained the chemical anomaly of potassium and thorium: "Potassium evaporates very quickly in a hot environment, while thorium survives even at very high temperatures. But on Mercury we see much more potassium than expected".
Finally, Frank Budnik, flight dynamics manager, clarified why the mission took such a long route: "You can reach Mercury faster if you take a direct route. But the problem is that we want to insert into an orbit relative to Mercury. You have to bring the spacecraft to the same speed as Mercury, and this transfer requires a lot of energy".
With the separation of the MTM, BepiColombo begins the final stretch of its journey. In less than three months, the spacecraft will become the first to orbit Mercury with two scientific orbiters, opening a new era in the exploration of the planet closest to the Sun.