BepiColombo

BepiColombo is a space mission by the European Space Agency (ESA) and the Japan Aerospace Exploration Agency (JAXA) to study the planet Mercury. The mission uses two satellites that fly together: the Mercury Planetary Orbiter and Mio, also called the Mercury Magnetospheric Orbiter. These satellites help scientists learn about Mercury's magnetic field, its magnetosphere, and its inside and surface.

The mission began when it was launched on an Ariane 5 rocket on 20 October 2018. Before reaching Mercury, it flew by Earth, Venus, and Mercury several times. It is planned to enter Mercury’s orbit in November 2026. The mission cost about US$2 billion when it was estimated in 2017.

Names

BepiColombo is named after Giuseppe "Bepi" Colombo, a scientist, mathematician, and engineer from the University of Padua, Italy. He was the first to suggest a special space travel method used by the 1974 Mariner 10 mission. This method is now commonly used by space probes.

Mio, the name of the Mercury Magnetospheric Orbiter, was chosen from ideas sent in by people in Japan. In Japanese, Mio means a waterway. It stands for the steps taken in making the spacecraft, and hopes for a safe journey ahead. The spacecraft will travel through the solar wind like a ship moving through the ocean. In Chinese and Japanese, Mercury is called the "water star" (水星) according to wǔxíng.

Scientific objectives

The main goals of the BepiColombo mission are to learn about Mercury, the smallest planet in our solar system. Scientists want to understand how Mercury formed and changed over time, what it is made of, and how its surface looks.

The mission will also study Mercury's thin layer of gases around it, called an exosphere, and its magnetic field. By doing this, scientists hope to test a big idea in physics called Einstein’s theory of general relativity. The two satellites carry special tools from many countries to help explore Mercury’s interior and map its gravity and magnetic fields.

Mission overview

The BepiColombo mission has three parts that will separate when they reach the planet Mercury. These parts are:

• The Mercury Transfer Module (MTM) for moving, built by the European Space Agency (ESA).
• The Mercury Planetary Orbiter (MPO) built by ESA.
• The Mercury Magnetospheric Orbiter (MMO), also called Mio, built by the Japan Aerospace Exploration Agency (JAXA).

During the journey, these three parts travel together as the Mercury Cruise System (MCS). It will take eight years to get to Mercury, using special engines and flying by Earth, the Moon, and Venus several times.

The mission was planned to arrive in December 2025, but because of problems with its engines found in September 2024, it will now arrive in November 2026. Once there, the Mio and MPO satellites will study Mercury together for one year, maybe longer. ESA manages the mission and the two satellites are controlled from Darmstadt, Germany. The main communication station is in Cebreros, Spain.

Mission timeline

Before launch

The BepiColombo mission was chosen by the European Space Agency (ESA) in 2000. In 2007, a company called Astrium was picked to build it, and a rocket called Ariane 5 was chosen to launch it. The mission was approved in 2009 but had many delays, especially with its solar electric propulsion system. It was the last mission in its program to be launched.

Launch

Both orbiters were launched together on October 20, 2018, from Europe's Spaceport in Kourou, French Guiana, using an Ariane 5 rocket.

Gravity assist maneuvers

After leaving Earth, the spacecraft traveled in an orbit similar to Earth's. It returned to Earth in 2020 for a gravity-assist maneuver, which helped it head toward Venus. Two flybys of Venus adjusted its path closer to Mercury. Six flybys of Mercury slowed it down until it was in an orbit close to Mercury's.

Science during Venus flybys

In 2020, scientists thought BepiColombo might detect a special gas in Venus's atmosphere during its flybys in 2020 and 2021, but no announcement of such detection was made. During the first Venus flyby in October 2020, several instruments collected data, working with another spacecraft called Akatsuki. The second flyby in August 2021 happened shortly after another ESA spacecraft, Solar Orbiter, also flew by Venus. Both used their instruments to study Venus's environment.

Science during Mercury flybys

During its first flyby of Mercury in October 2021, the spacecraft took its first pictures of Mercury. Some instruments were also active, studying Mercury's magnetic field and gravity. In June 2022, it imaged a crater named after poet Seamus Heaney. In June 2023, instruments mapped Mercury's magnetosphere and discovered new details about particles around the planet. In May 2024, the spacecraft had computer issues during a big solar flare. In September 2024, it got its first clear view of Mercury's south pole. In December 2024, it observed Mercury in a new kind of light for the first time. The final flyby in January 2025 imaged shadowed craters near Mercury's north pole.

Thruster issues

In May 2024, ESA reported that the spacecraft's thrusters were not working at full power. This caused a change in the flight plan, adding 11 months to the travel time. The new arrival date is now November 2026.

Future

In November 2026, the spacecraft will be captured by Mercury and placed into an orbit around the planet. The two orbiters will then separate and adjust their positions using small engines.

Trajectory

As of January 2025, here is the mission schedule for BepiColombo:

Animation of BepiColombo's path from 20 October 2018 to 2 November 2025
   BepiColombo ·   Earth ·   Venus ·   Mercury ·   Sun
For more detailed animation, see this video

Animation of BepiColombo's path around Mercury

Planned paths for Mio and MPO, the two probes of the BepiColombo mission

Mission components

Mercury Transfer Module

The Mercury Transfer Module (MTM) is a part of the spacecraft that carries two science orbiters to the planet Mercury. It has a mass of 2,615 kg, including fuel, and is placed at the base of the spacecraft stack. The MTM uses a special kind of engine called solar electric propulsion to move through space. This engine uses sunlight and works very efficiently, though it provides a gentle push over long periods.

The MTM also provides power to the two orbiters while they are resting, using large solar panels that stretch 14 meters long. These panels catch sunlight to create electricity.

Mercury Planetary Orbiter

The Mercury Planetary Orbiter (MPO) is one of the two main science spacecraft. It weighs 1,150 kg and has solar panels that can collect enough power even when close to the hot Sun. The MPO carries many tools to study Mercury, including cameras and instruments that can look at different kinds of light and measure magnetic fields.

The MPO has a large antenna to send data back to Earth. It will send information using radio waves, sharing about 1,550 gigabits of data each year.

Mio (Mercury Magnetospheric Orbiter)

Mio, also called the Mercury Magnetospheric Orbiter (MMO), was built mostly by Japan. It is shaped like a short octagon and weighs 285 kg, including its science tools. Mio will spin slowly to stay steady and will orbit Mercury in a path that goes over the poles. It has its own solar panels and antenna to send data to Earth.

Mio carries tools to study Mercury’s magnetic field and the particles around the planet.

Magnetospheric Orbiter Sunshield and Interface

Mio needs extra protection from the Sun’s heat during its journey to Mercury. The European Space Agency made a special sunshield for Mio to keep it cool.

Mercury Surface Element (cancelled)

The plan for a small lander called the Mercury Surface Element was stopped in 2003 because of money problems. This lander would have been about 44 kg and would have studied the surface of Mercury for about one week. It would have used airbags to land gently and would have carried tools to take pictures, measure heat, and study the soil.