BepiColombo
What is BepiColombo?
Probes & telescopes· Launched 2018-10-20 – arrival 2026-11-27 planned (cruising). A joint European–Japanese mission to Mercury. Launched in 2018, it has slowed itself with nine planetary flybys and is due to enter orbit around Mercury in November 2026.
Mission timeline
Spacecraft specs
| Launch | 2018-10-20 |
|---|---|
| Orbit insertion | 2026-11-27 (planned) |
| Flybys | Earth×1·Venus×2·Mercury×6 |
Figures are representative approximations. Source: compiled from NASA and IAU public data.
Bepi Colombo, the mathematician who explained Mercury's spin
The spacecraft is named after Giuseppe 'Bepi' Colombo, a mathematician at the University of Padua. In 1965 radar observations showed that Mercury turns once every 59 days. Until then it had been assumed that Mercury, like our Moon, always kept the same face toward the Sun. Colombo was the first to notice that 59 days fits Mercury's 88-day year in an exact 2-to-3 ratio: Mercury spins three times for every two trips around the Sun.
In 1970 Colombo suggested a trick to the Mariner 10 team. If the spacecraft's own orbit around the Sun took exactly twice as long as Mercury's year, it could meet the planet again and again at the same spot. Mariner 10 did just that, passing Mercury three times in 1974 and 1975. That is why a spacecraft that reaches Mercury through repeated flybys carries his name.
The mission in depth
BepiColombo is a Mercury mission made of two orbiters travelling as one. The European orbiter will study Mercury's surface and interior, while Japan's orbiter, Mio, will study the magnetic field around the planet. Together with a propulsion module that carries them, they were launched on 20 October 2018 on an Ariane 5 rocket.
Because Mercury is the planet nearest the Sun, it might seem easy to reach, but it is actually very hard. A spacecraft heading toward the Sun keeps speeding up as the Sun's gravity pulls it in. Arrive too fast and it simply shoots past Mercury. So the craft has to keep braking on the way down, like a car on a steep hill.
BepiColombo braked with nine planetary flybys: one of Earth, two of Venus and six of Mercury. Electric ion engines also trimmed its speed with a gentle, steady push. In April 2024 a problem with the engines' power supply reduced their thrust, and as a result arrival at Mercury was delayed from December 2025 to November 2026.
On arrival the propulsion module is dropped and the two orbiters head into separate orbits. Scientists want to learn how a planet as small as Mercury makes a magnetic field, why its surface has shallow pits called hollows, and why its core is so large for its size. The orbit view shows the eight-year path spiralling in toward the Sun.
Frequently asked
- When did BepiColombo launch?
- BepiColombo was launched on 2018-10-20.
- What is the next milestone for BepiColombo?
- Next for BepiColombo, on 21 Nov 2026: BepiColombo enters Mercury orbit.
- In one line, what is BepiColombo?
- Probes & telescopes — A joint European–Japanese mission to Mercury.
Related
Figures are representative approximations. Simulated positions use J2000 mean elements.