If you were on Mercury you would see the sun three times bigger than on Earth, but you would not care, because you would already be dead. The planet closest to the Sun is also the least explored among those with a rocky composition – the list is completed by Venus, Earth and Mars – in part by the brutal contrasts between the light zones, where 450 degrees are reached, and gloomy, with about 170 below zero.
BepiColombo is launched on October 20 and will be the first European mission to this world slightly larger than the Moon. So far only two ships have visited the planet. The Mariner 10 NASA flew over and took the first photographs of the body in 1974, while its successor Messenger It was the first to orbit it between 2011 and 2015.
Messenger raised many questions that must now answer BepiColombo, a name that pays homage to the Italian mathematician Giuseppe Bepi Colombo, who explained the strange orbital behavior of Mercury and proposed the trajectory of Mariner 10 to fly over the planet using the gravitational assistance of Venus for the first time.
The mission is going to enter into a planet very different from ours. A day in Mercury lasts 59 Earth days, but it is so close to the Sun – almost three times more than the Earth – that it takes just 88 days to spend a year, that is, to go around the star. Messenger He discovered frozen water deposits in areas of perpetual shade and a valley longer than the Colorado River and deeper than the Rift that formed because the planet is shrinking, literally.
Unlike Earth, Mercury has only one spherical tectonic plate under which there is a nucleus of unknown composition, but which is proportionally huge, occupying 85% of the body. This core is cooling slowly, in part because of the slow loss of its original heat, partly because the gravitational pull of the Sun diminishes as the star consumes its atomic fuel and the planet moves away from it. Because of all this, the crust of Mercury has lost seven kilometers of radius since its formation, and that has created the valleys, faults and stepped cracks that Messenger discovered.
BepiColombo includes two orbiter, one that will analyze the surface and the interior of the planet built by the European Space Agency (ESA) and another to study the magnetosphere developed by the Japanese space agency. Among the scientific objectives is to determine the exact composition of the interior of the planet.
"This is the most complex mission that ESA has ever launched," explains engineer Santa Martinez, coordinator of the scientific processing of the mission, whose headquarters will be the ESA space center in Villanueva de la Cañada, near Madrid. "Thanks to the fact that we send two satellites, we can clarify the origin and structure of the planet's magnetic field and confirm if the anomalies are due to the fact that there is more liquid inside than we thought," he points out. The BepiColombo will orbit the planet at a height of between 1,500 kilometers and 500 kilometers. It will pass closer than any other by the regions near the South Pole, which will make "the highest resolution map" of the body to date, explains Martinez.
Another enigma of Mercury that BepiColombo can explain is its chemical composition, which in turn would reveal its origin. "The amount of volatile compounds is much higher than it should be due to the situation of the planet, so it is possible that it was formed beyond Mars and then migrate to its current position, "explains Mauro Casale, another of the mission's scientific leaders.
Before arriving at their destination, the ships will travel 9,000 million kilometers. Bepi, like Messenger, is going to look at an orbit around the planet, a challenge due to the enormous gravitational pull of the Sun. "In order to be fixed in an orbit around Mercury we have to move at a speed very similar to the own rotation of the planet ", Casale points out, and for that it is necessary to accelerate and to brake using the gravity of other bodies. After takeoff, the two probes, attached to the transfer module and the heat shield, will begin an odyssey that will take them over the Earth once, Venus twice, and finally complete six turns of Mercury until they are embedded in its orbit on December 5, 2025. Scientific operations will begin in 2026.
"85% of BepiColombo is new technology", made specifically for the mission, says Casale. The European probe carries 11 scientific instruments on board. In addition to studying Mercury, which in turn can clarify the origin of the rest of terrestrial planets, one of the instruments, the MORE, developed by Italy, is "the most advanced interplanetary tracking system ever built", according to ESA . The Earth and Mercury are at an average distance of 77 million kilometers and the device will be able to indicate the position of the probe with a margin of error of 15 centimeters. Thanks to this instrument it will be possible to test Einstein's general theory of relativity "at a level of unprecedented precision".
Spain has contributed 8% of the mission. Companies in this country have developed key components, such as the half-gain antenna that will be the link between the ship and the Earth during the trip to Mercury. The deep space antenna of the ESA in Cebreros (Ávila) will be the one that receives and sends commands during the entire mission.
The mission will be short. "Due to the high degradation of the probes we must optimize the time", highlights Martinez. BepiColombo will last a year with the possibility of extending one more year. One of its most innovative components are the four electric propulsion engines that use xenon gas as fuel. There will come a time when both the Japanese and the European probe will run out of fuel. When this happens, both will crash against the surface of Mercury, the same fate that ran its US predecessor in 2015.
BepiColombo will be the first European mission to Mercury, one of the most unknown planets in the solar system due to the enormous challenges of orbiting the planet closest to the Sun. The ship will orbit the planet for one year, expandable to another, and withstanding temperatures of 450 degrees and down to 170 below zero in shaded areas. Make the most complete map of the planet (it will pass only 500 km from the south pole), determine if it contains a molten core and study its composition. It has cost 2,400 million and involved 12 countries, including Spain. It is launched on October 20 at 3.45 (Spanish time) from the European spaceport in Kourou (French Guiana).