The European Space Agency (ESA), together with the Japanese space agency (JAXA), will launch the BepiColombo mission on October 20. After a journey of more than seven years, will unravel the secrets of the first world of the Solar System.

Mercury is the planet closest to the Sun and the one that takes less time to complete a round around him. As it is so fast, the Babylonians baptized him as Nabu, in honor of the messenger of the gods of his mythology, and then the Greeks and the Romans knew him as Hermes and Mercurius, respectively. But the truth is that this emissary of the gods has not yet transmitted his message. So far only two spacecraft, the Mariner 10 and the MESSENGER, both from NASA, have flown to Mercury, but these opened more questions than they solved. In fact, this world is still a pending subject to understand how the Solar System was formed, how the planets work and whether Einstein’s Relativity is valid.

For these reasons, the European Space Agency (ESA), together with the Japanese Agency for Aerospace Exploration (JAXA) and other institutions, have invested 1,650 million euros in BepiColombo, a sophisticated mission to explore the planet Mercury. More than 2,000 scientists and engineers from eight countries have worked for 20 years so that, at 06.45 on October 20, the BepiColombo probe will be launched from the Kuru spaceport in French Guiana. It will become the third ship to explore Mercury and will be the culmination of the most complex mission undertaken by ESA in its entire history. In addition, BepiColombo will have a special interest because it will explore one of the most unknown planets in the Solar System.


Appearance that the ship BepiColombo will have on its journey to Mercurio – ESA / ATG medialab

“Mercury is the planet of mysteries,” explained Mauro Casale, an ESA astrophysicist involved in the mission, at a press conference held this week at the European Space Astronomy Center (ESAC) in Madrid. “It’s the most unknown planet in the Solar System, so it’s very interesting to go back there because we still have a lot of things to investigate.”

Mercury has only been explored in two NASA missions, so it is the least studied rock world. In March 1974, Mariner 10 was placed in the orbit of the Sun and flew over the planet three times, revealing a surface full of craters and, to the surprise of astronomers, the existence of a magnetic field. Already between 2008 and 2015, the MESSENGER probe managed to put itself in orbit around Mercury. He found signs of water and organic compounds in the shadow craters of the north pole, and drew a detailed topographic and photographic map of the surface.

A double mission to radiograph Mercury

BepiColombo will be responsible for taking the witness of these two missions. It is composed of two different probes: a ship designed by ESA and called “Planetary Mercury Orbiter” (MPO) and a part designed by JAXA and called “Mercury Magnetospheric Orbiter” (MMO). That’s why Sara de la Fuente, an ESA engineer, said that, in reality, “BepiColombo are two missions in one”.

The two probes will fly together to Mercury assembled to a segment of the ship that will function as a driver and which is called the “Mercury Transfer Module” (MTM). This is equipped with solar panels that have a wingspan of 30 meters and a propulsion system. When they are there, these three blocks will separate and the two orbiters will begin their work in different areas of the planet. The two will go into an orbit that will make them pass through the poles and sweep the entire planet as Mercury turns on itself.

The different modules of the ship BepiColombo. From bottom to top: transfer module, European orbiter, protective shield and Japanese orbiter – ESA

The two ships have three main objectives: to study the origin and evolution of Mercury, analyze the properties of its surface and its interior and learn about its magnetic field and its atmosphere.

But the two probes do not have the same characteristics. The European orbiter (MPO), is equipped with 11 instruments and weighs 1,230 kilograms, like a car. It will map the surface of Mercury, take high-resolution images, analyze the composition of the soil materials (something unknown at the moment) and analyze the magnetic field of this planet.

The Japanese orbiter (MMO), for its part, weighs only 255 kilograms and carries four scientific instruments. It has an octagon shape and is covered by mirrors. Your objective will be to study the magnetic field, the presence of dust particles and the nature of Mercury’s dim atmosphere.

Ariane 5 that will launch the BepiColombo on October 20. Still to assemble the “nose” of the rocket, where the probe is – ESA

In addition, the proximity of Mercury to the Sun will be used by scientists to make an experiment that will try to verify an effect predicted by Einstein’s Relativity: the gravitational lens. This occurs when a large mass, such as the Sun, deforms spacetime and produces an apparent displacement of the star background. The effect would be similar to moving a magnifying glass through a text, and see how the letters are deforming.

The Odyssey to Mercury

Another of the most interesting things about this mission is that the trip to Mercury will be an authentic odyssey. The main problem is that the ship must travel at the same speed as this planet and avoid being accelerated by the immense mass of the Sun. The trip is scheduled to begin on October 20, when it is launched from French Guiana. Although the probe would only need five months to fly to the planet directly, its speed would prevent it from entering the orbit of this world. Therefore, it will have to take a more indirect route, rely on the gravity of other planets and travel 9,000 million kilometers. In total, your journey will last more than seven years and two months.

The ship will make several “gravitational assistance” maneuvers, through which the probe takes advantage of the gravity of the planets to move in the desired way. For this reason, by the way, the mission is called BepiColombo: its name honors the mathematician Giuseppe (Bepi) Colombo (1924-1984), who proposed to take advantage of the gravity of Venus to get to Mercury.

Orbits of the satellite BepiColombo. On the left the Japanese probe (MMO) and on the right the European probe (MPO) – ESA / ATG medialab

In total, the BepiColombo will fly over the Earth once, Venus twice and Mercury in six before it enters the orbit of its destiny planet, on December 5, 2025. It will take advantage of these encounters with the planets to take some measurements of Venus and Mercury and to calibrate the instruments, but fundamentally will do them by needs of the orbit.

As early as March 2026, scientific operations will begin. They are scheduled to last a full year (more than four years on Mercury), and to extend another year. After that, the degradation of the instruments due to the solar wind will make it impossible to continue with the work. The orbit of the BepiColombo will decay naturally and lose its altitude. The Japanese probe will take about three years to crash into Mercury. The European component will do so in six years.

Work under the solar bombardment

Apart from what has already been said, BepiColombo is an extraordinary mission because it will explore a desolate world in a region scorched by the Sun. It will have to work under the incessant bombardment of the solar wind and get the scientific instruments to work near an ambient temperature, although in the outside there are temperatures that go from -180 to 450 ºC. This has required that 85% of all the technology used in the mission be newly created.

For example, the probe is protected with a multi-layer coating and with a special white paint to stop the solar wind. And the solar panels are equipped with a liquid cooling circuit, which help to dissipate the Sun’s heat to a radiator.

In addition, this mission will be the first interplanetary trip of the ESA that will depend on ionic propulsion engines. These take advantage of the energy captured in the solar panels to steal electrons from the xenon, which the BepiColombo has stored in a tank, and in doing so generate the desired propulsion.

However, this new propulsion is one of the points of the mission where it is more likely that there is an error, because the engines already gave problems during the testing phase. Besides that, there are the usual fears that something will fail during the launch from the spaceport, and that the ship will suffer errors in the multiple stages that depend on mechanical devices. For example, the BepiColombo will have to deploy the solar panels and antennas after takeoff, and its four modules (the two probes, the transfer module and a protective shield) will separate when it reaches Mercury. “Everything in this mission is a critical point,” Mauricio Casale joked.

Technological benefits

The positive thing about facing such a complex mission is that it allows us to perfect technology. As explained by María del Pilar Román Fernández, member of the Department of Spatial and Technological Return of the Center for Industrial Technological Development (CDTI), “BepiColombo has been a challenge for all the companies that have participated: it has required changing designs, testing materials and to develop new technologies ».

But what has been a “tremendously complicated mission and a real headache”, according to Román Fernández, has also brought “new opportunities to expand the market and open new doors”. Many of the developments, whose history goes back 20 years, are being used in two future ESA missions: the Solar Orbiter (to the Sun) and the JUICE (to Jupiter). Other projects are being used to improve ground antennas and others will be used to design new and better propulsion systems for future space travel.


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