BepiColombo


BepiColombo is a joint mission of the European Space Agency and the Japan Aerospace Exploration Agency to the planet Mercury. The mission comprises two satellites launched together: the Mercury Planetary Orbiter and Mio. The mission will perform a comprehensive study of Mercury, including characterization of its magnetic field, magnetosphere, and both interior and surface structure. It was launched on an Ariane 5 rocket on 20 October 2018, with Mercury orbit insertion planned for November 2026, after a flyby of Earth, two flybys of Venus, and six flybys of Mercury. The total cost of the mission was estimated in 2017 as US$2 billion.

Names

BepiColombo is named after Giuseppe "Bepi" Colombo, a scientist, mathematician and engineer at the University of Padua, Italy, who first proposed the interplanetary gravity assist manoeuvre used by the 1974 Mariner 10 mission, a technique now used frequently by planetary probes.
Mio, the name of the Mercury Magnetospheric Orbiter, was selected from thousands of suggestions by the Japanese public. In Japanese, Mio means a waterway, and according to JAXA, it symbolizes the research and development milestones reached thus far, and wishes for safe travel ahead. JAXA said the spacecraft will travel through the solar wind just like a ship traveling through the ocean. In Chinese and Japanese, Mercury is known as the "water star" according to wǔxíng.

Scientific objectives

The main objectives of the mission are:
Mercury is too small and hot for its gravity to retain any significant atmosphere over long periods of time, but it has a "tenuous surface-bounded exosphere" containing hydrogen, helium, oxygen, sodium, calcium, potassium and other trace elements. Its exosphere is not stable as atoms are continuously lost and replenished from a variety of sources. The mission will study the exosphere composition and dynamics, including generation and escape.
The orbiters are equipped with scientific instruments provided by various European countries and Japan. The mission will characterize the solid and liquid iron core and determine the size of each. The mission will also complete gravitational and magnetic field mappings. Russia provided gamma ray and neutron spectrometers to verify the existence of water ice in polar craters that are permanently in shadow from the Sun's rays.

Mission overview

The mission involves three components, which will separate into independent spacecraft upon arrival at Mercury.
  • Mercury Transfer Module for propulsion, built by ESA.
  • Mercury Planetary Orbiter built by ESA.
  • Mercury Magnetospheric Orbiter or Mio built by JAXA.
During the launch and cruise phases, these three components are joined to form the Mercury Cruise System.
The stacked spacecraft will take eight years to position itself to enter Mercury orbit. During this time it uses solar-electric propulsion and nine gravity assists, flying past the Earth and Moon in April 2020, Venus in 2020 and 2021, and six Mercury flybys between 2021 and 2025.
Expected to arrive in Mercury orbit in November 2026, the Mio and MPO satellites will separate and observe Mercury in collaboration for one year, with a possible one-year extension. Although originally expected to enter orbit in December 2025, thruster issues discovered in September 2024 before the fourth Mercury flyby resulted in a delayed arrival of November 2026.
ESA is responsible for the overall mission, the design, development assembly and test of the propulsion and MPO modules, and the launch. The two orbiters are operated by mission controllers based in Darmstadt, Germany. The spacecraft operations manager of BepiColombo was Elsa Montagnon until 2021, and is now Ignacio Clerigo. ESA's Cebreros, Spain ground station is the primary ground facility for communications during all mission phases.

Mission timeline

Before launch

The BepiColombo mission proposal was selected by ESA in 2000. A request for proposals for the science payload was issued in 2004. In 2007, Astrium was selected as the prime contractor, and Ariane 5 chosen as the launch vehicle. The initial target launch of July 2014 was postponed several times, mostly because of delays on the development of the solar electric propulsion system. The mission was approved in November 2009, after years in proposal and planning as part of the European Space Agency's Horizon 2000+ programme; it is the last mission of the programme to be launched.

Launch

The two orbiters were successfully launched together on 20 October 2018. The launch took place on Ariane flight VA245 from Europe's Spaceport in Kourou, French Guiana.

Gravity assist maneuvers

The stacked spacecraft left Earth with a hyperbolic excess velocity of. Initially, the craft was placed in a heliocentric orbit similar to that of Earth. After both the spacecraft and Earth completed one and a half orbits, it returned to Earth to perform a gravity-assist maneuver and was deflected towards Venus.
Following its Earth flyby in April 2020, BepiColombo was briefly mistaken for a near-Earth asteroid, receiving the provisional designation.
Two consecutive Venus flybys reduced the perihelion near to the Sun–Mercury distance with almost no need for thrust. A sequence of six Mercury flybys lowered the relative velocity to. After the fourth Mercury flyby in 2024, the spacecraft is in an orbit similar to that of Mercury and remains in the general vicinity of the planet.

Science during Venus flybys

After the potential biomarker phosphine has been tentatively discovered in the Venusian atmosphere in September 2020, ESA scientists suggested that BepiColombo might be able to detect the compound during its two Venus flybys in 2020 and 2021. However, it was not clear if the spacecraft's instruments were sufficiently sensitive and there has been no announcement of such detection since.
During the first Venus flyby in October 2020, seven science instruments and a radiation monitor onboard the Mercury Planetary Orbiter, and three instruments onboard Mio, were active and gathering data. The observations were coordinated with JAXA's Akatsuki, the only active spacecraft orbiting Venus at that time, as well as Earth-based observatories.
The second Venus flyby in August 2021 happened only 33 hours after another interplanetary spacecraft by ESA, Solar Orbiter, completed its gravity assist at the same planet. Both spacecraft used their science instruments to study the magnetic, plasma, and particle environment around Venus during their flybys, offering unique multipoint datasets. The MPO's MERTIS instrument captured high resolution spectra of the Venus atmosphere and the Mercury Transfer Module's three monitoring cameras captured a series of black-and-white images of the planet, documenting the various phases of the flyby.

Science during Mercury flybys

During the first Mercury flyby in October 2021, the spacecraft captured its first images of the target planet using the M-CAM monitoring cameras on the Mercury Transfer Module. Some of the scientific instruments on both orbiters were also active during the flyby, exploring the magnetic and particle environment around Mercury and measuring the planet's gravity.
During the second flyby in June 2022, the M-CAM cameras imaged, among other targets, the crater Heaney with a candidate volcano, an important target for the spacecraft's primary mission. This crater has been recently named after Seamus Heaney following a request from the M-CAM team. Some of the scientific instruments have been again active, measuring the magnetic, plasma, and particle environment around the spacecraft.
During the third flyby in June 2023, the MPPE suite of instruments on Mio was used to map the magnetosphere of Mercury. Based on these data, scientists described various expected features of the magnetosphere, but also made new discoveries: 1) a low latitude layer containing particles with much broader energy range than ever observed on Mercury, 2) energetic hydrogen ions trapped at low latitude and near the equator, and 3) cold plasma ions of oxygen and sodium, as well as signatures of potassium, which were probably ejected from the planet's surface by micrometeorites or the solar wind. Mio's observations during this flyby also identified the chirping-like discrete whistler-mode emission waves previously observed in Earth's magnetosphere but so far unknown from Mercury.
In May 2024, computers on BepiColombo reported a sharp increase in the number of memory errors, coinciding with a massive solar flare from the active region AR3664, at that time facing away from Earth. The event was also observed in detail by ESA's Solar Orbiter.
During the fourth flyby in September 2024, the spacecraft had, for the first time, a clear view of Mercury's south pole. The M-CAM 2 and 3 cameras provided images of the polar region, as well as the Vivaldi crater and a crater newly named Stoddart after Margaret Olrog Stoddart following a request from the M-CAM team.
During the fifth flyby in December 2024, using the MERTIS instrument, BepiColombo became the first spacecraft ever to observe Mercury in mid-infrared light. During the sixth and final Mercury flyby in January 2025, the M-CAM 1 camera imaged the permanently shadowed craters Prokofiev, Kandinsky, Tolkien, and Gordimer near the planet's north pole.