BepiColombo is Europe's first mission to Mercury. Launched on 20 October 2018, it is on a seven-year journey to the smallest and least explored terrestrial planet in our Solar System. When it arrives at Mercury in late 2025, it will endure temperatures in excess of 350 °C and gather data during its one-year nominal mission, with a possible one-year extension. The mission comprises two spacecraft: the Mercury Planetary Orbiter (MPO) and the Mercury Magnetospheric Orbiter (Mio). BepiColombo is a joint mission between ESA and the Japan Aerospace Exploration Agency (JAXA), executed under ESA leadership.
BepiColombo has been designed to provide the measurements necessary to study and understand the composition, geophysics, atmosphere, magnetosphere and history of Mercury. In particular, the mission has the following scientific objectives:
- Investigate the origin and evolution of a planet close to the parent star
- Study Mercury as a planet: its form, interior structure, geology, composition and craters
- Examine Mercury's vestigial atmosphere (exosphere): its composition and dynamics
- Probe Mercury's magnetized envelope (magnetosphere): its structure and dynamics
- Determine the origin of Mercury's magnetic field
- Investigate polar deposits: their composition and origin
- Perform a test of Einstein's theory of general relativity
BepiColombo is named after Professor Giuseppe (Bepi) Colombo (1920-1984) from the University of Padua, Italy, a mathematician and engineer of astonishing imagination. He was the first to see that an unsuspected resonance is responsible for Mercury's habit of rotating on its axis three times for every two revolutions it makes around the Sun. He also suggested to NASA how to use a gravity-assist swing-by of Venus to place the Mariner 10 spacecraft in a solar orbit that would allow it to fly by Mercury three times in 1974-5.
ESA's Science Programme Committee decided at its meeting in Naples in 1999 to name the Mercury cornerstone mission in honour of Giuseppe Colombo's achievements.
The BepiColombo mission is based on two spacecraft: the ESA-led Mercury Planetary Orbiter (MPO), a three-axis stabilised and nadir pointing spacecraft with an instrument suite of 11 experiments and instruments, and the JAXA-led Mercury Magnetospheric Orbiter, or Mio, a spinning spacecraft carrying a payload of five experiments and instruments. A summary of the spacecraft characteristics is given in the table below.
|Mercury Planetary Orbiter (MPO)||Mercury Magnetospheric Orbiter (Mio)|
|Stabilisation||3-axis stabilised||15-rpm spin-stabilised|
|Orientation||Nadir pointing||Spin axis at 90° to Sun|
|Orbit||Polar orbit, period of 2.3 h
480 × 1500 km
|Polar orbit, period of 9.3 h
590 × 11 640 km
|Spacecraft Mass||4100 kg (at launch)
1150 kg (in Mercury orbit)
|275 kg (in Mercury orbit)|
|Payload Mass||80 kg||45 kg|
|Payload Power||100-150 W||90 W|
|Data volume (downlink)||1550 Gbits/year||160 Gbits/year|
|Equivalent average data rate||50 kbits/s||5 kbits/s|
|Antenna||High-temperature resistant 1.0 m X/Ka-band high-gain steerable antenna||0.8 m X-band phased array high-gain antenna|
|Operational lifetime||> 1 year||> 1 year|
The Mercury Planetary Orbiter carries a sophisticated payload of 11 instruments, comprising cameras, spectrometers (IR, UV, X-ray, γ-ray, neutron), radiometer, laser altimeter, magnetometer, particle analysers, Ka-band transponder, and accelerometer. Of these, ten have been provided by Principal Investigators through national funding by ESA Member States and one from Russia.
The Mercury Magnetospheric Orbiter carries a payload of five advanced scientific experiments, including a magnetometer, ion spectrometer, electron energy analyser, cold and energetic plasma detectors, plasma wave analyser, and imager. These have been provided by nationally funded Principal Investigators, one European and four from Japan. Significant European contributions have also been made to the Japanese instruments.
Launch, journey and orbit
The BepiColombo trajectory employs a solar electric propulsion system so that a combination of low-thrust arcs and flybys at Earth, Venus and Mercury are used to reach Mercury with low relative velocity. The solar-electric propulsion is provided by the Mercury Transfer Module (MTM), which will separate from the two orbiters after arriving at Mercury. A brief summary of the key stages in the journey to Mercury are given here:
- Launch on Ariane 5 on 20 October 2018
- Cruise trajectory with solar electric propulsion – the MTM provides up to 290 mN of thrust – plus nine gravity assists: Earth, Venus (twice) and Mercury (six times)
- Approximately 7.2 year cruise phase to Mercury
- The MTM is jettisoned shortly before arrival at Mercury
- Capture and insertion by chemical propulsion engines onboard the MPO
- Upon reaching its operational orbit, Mio is released
- MPO is inserted into final orbit using thrust from its chemical propulsion engines
- For MPO and Mio: one Earth-year (equivalent to 4 Mercury years) operations in Mercury orbit with optional one year extension
Key mission dates
|20 October 2018||Launch|
|10 April 2020||Earth flyby|
|15 October 2020||First Venus flyby|
|11 August 2021||Second Venus flyby|
|1 October 2021||First Mercury flyby|
|23 June 2022||Second Mercury flyby|
|20 June 2023||Third Mercury flyby|
|5 September 2024||Fourth Mercury flyby|
|2 December 2024||Fifth Mercury flyby|
|9 January 2025||Sixth Mercury flyby|
|5 December 2025||Arrival at Mercury|
|14 March 2026||MPO in final orbit|
|1 May 2027||End of nominal mission|
|1 May 2028||End of extended mission|
Ground control: ESA is responsible for the overall mission design, and for the operation of the composite spacecraft up to the insertion of the MPO and Mio into their orbits. During the cruise, the European Space Operations Centre (ESOC) in Darmstadt, Germany, will coordinate the operation of the full composite spacecraft by using the Cebreros 35 m antenna in Spain. The ISAS/JAXA Sagamihara Space Operation Centre, using the Usuda 64 m antenna (Japan), will take over the operation of Mio once it is in orbit around Mercury, while ESOC will remain in charge of the MPO spacecraft.
Science operations: ESA is responsible for the mission and scientific operation of the MPO. The BepiColombo Science Operation Centre is located at the European Space Astronomy Centre (ESAC) in Villafranca, near Madrid, Spain. It defines and coordinates the scientific observations, and assists the teams in operating their instruments.