A risky journey began this Friday, 19 October. Launched from Guyana with the heavy-lift launch vehicle Ariane 5, the BepiColombo mission is setting out to discover one of the least-known planets in our solar system: Mercury. Though it has been identified for millennia, this little planet remains a mystery for astronomers. And for good reason: it is closest to the sun, which makes its exploration particularly dangerous. First, because if one misses its gravity field, one is pushed directly into the Sun. But also because its proximity to the star makes the environment of Mercury very hostile: on its surface, the temperature varies from -180 ° C to 430 ° C, and a day is equivalent to 59 Earth days.Cartography and studying the magnetic field To protect BepiColombo's satellites, it was therefore necessary to use many technological innovations: up to 50 layers of titanium, ceramic and aluminum ... At least 70% of the technologies used on this exceptional mission are new. After leaving Earth, BepiColombo will begin a journey of seven years and 9 billion kilometres. It will pass twice near Venus, to take advantage of its gravitational assistance and save fuel, before heading back to Mercury and reaching the planet’s orbit in 2027. From there, the two probes will be placed in two different orbits. The Japanese spacecraft will remain at a distance, and will be mainly used to study Mercury’s magnetic field. The European probe will approach a little more to study the surface more thoroughly and fully map the planet. The satellites have been designed to remain at least two years in Mercury's orbit, but their mission could be extended if need be. However, sooner or later, the heat will catch up with them: ‘Our time is limited, Mercury is an extremely difficult environment,’ confirms Johannes Benkhoff, an ESA physicist who worked on the project. Discovering an unknown planet This new mission, led by European space agencies (ESA) and Japan (JAXA), is only the third expedition for Mercury’s further study and the second to enter its orbit. In 1974, the American mission Mariner 10 had indeed flown over Mercury before devoting itself to the study of Venus. It made it possible to map the planet and detect its magnetic field. Along with the Earth, Mercury is the only other telluric planet to have an intrinsic magnetic field. At the time, Giuseppe Colombo, professor at the University of Padua, had been very involved in the project. Nicknamed Bepi, it is in his honor that the mission bears his name. Then in 2011, NASA placed the Messenger probe in orbit around Mercury. The mission confirmed the observations of Mariner 10, but was also able to detect volcanic activity and an active heart. Short on fuel, it unfortunately crashed on Mercury’s surface in April 2015. Besides the technological prowess and the difficulty of the expedition, BepiColombo is also the result of a long and complex gestation. Designed in the 90s, this mission gives scientists not only the hope of understanding our neighbor a little bit better, but also to learn more about our solar system, its formation and its evolution.