An ambitious mission to reveal the secrets of the least explored planet in the inner solar system is about to reach its cosmic destination after a long journey. The BepiColombo mission, a joint effort between the European Space Agency and the Japan Aerospace Exploration Agency, aims to use two complementary orbiters to reveal information about how Mercury formed and evolved so close to the sun. The mission launched on an Ariane 5 rocket from the European Spaceport near Kourou, French Guiana, in October 2018. Since then, it has traveled more than 10 billion kilometers (6 billion miles). BepiColombo is named after the Italian engineer and mathematician Giuseppe “Bepi” Colombo, who studied the peculiar rotation of Mercury and proposed trajectories that enabled NASA’s first flybys of the planet in 1974. Earth is about 10 times closer to Mercury than to Jupiter, but BepiColombo has taken longer to reach the small planet than previous missions like Galileo and Juno that are headed to the largest planet in our solar system. outside. “You can go faster to Mercury if you take a direct path to it,” said Frank Budnik, director of flight dynamics for ESA’s BepiColombo mission. “But the problem is that we want to insert ourselves into an orbit with respect to Mercury. We have to take the spacecraft to the same speed as Mercury, and this is a transfer that requires a lot of energy.” A combination of electric propulsion and gravitational impulses from a total of nine flybys of Earth, Venus and Mercury have helped BepiColombo reach the correct speed on its long cruise. But the great challenges for BepiColombo are not over yet. The Mercury Transfer Module, which has powered the multi-year journey, will separate from BepiColombo’s stack of two scientific orbiters at 8 a.m. ET on Thursday. ESA will host a livestream starting at 7:45 a.m. ET on Thursday to share the separation milestones, and at 9:53 a.m. ET, the agency will conduct a spacecraft safety check to see how BepiColombo has fared so far on its mission. “The separation of the transfer module will take place under extremely challenging conditions and we will have to face considerable risk that things will not go as planned,” said Ignacio Tanco, head of ESA’s Inner Solar System Mission Operations. “It will be equivalent to launching a new spacecraft, only this spacecraft is around a different planet. We are going to see for the first time systems in operation that we have not been able to fully test.” And that is just the beginning of a complex process. “Unlike other missions, the arrival of BepiColombo does not mean a single event,” said Tanco. “We have about half a year of intense operations ahead of us.” Establishing an observing orbit around Mercury is even more difficult than the journey to get there. ESA’s Mercury Planetary Orbiter, or MPO, and JAXA’s Mercury Magnetospheric Orbiter, or MIO, will be captured by Mercury’s gravity and enter orbit around the planet on November 21. The two orbiters will separate from each other between December 9 and 10; The Mercury Planetary Orbiter will enter its orbital position on December 16 and the Mercury Magnetospheric Orbiter will follow on March 10. Science operations will officially begin for both orbiters. in April. “It will be the first time that a mission launches two completely independent and operational spacecraft around a different planet,” Tanco said. The MPO will observe the planet itself, while the MIO will focus on the space environment around Mercury, said Santa Martínez, director of the BepiColombo mission at ESA. Mercury is about 58 million kilometers (36 million miles) from the sun on average and completes one orbit around our star every 88 days, according to NASA. This proximity means that the planet’s surface temperatures can reach about 800 degrees Fahrenheit (430 degrees Celsius) during the day. Mercury’s short distance from the Sun has made it a difficult planet to explore, and is the main driver of BepiColombo’s complexity. Only two previous missions, NASA’s Mariner 10 in 1974 and its MESSENGER mission in 2011, have been in close proximity to the rocky world. Like BepiColombo, it took MESSENGER almost seven years to reach Mercury. “The spacecraft itself has been designed to operate in extremely demanding conditions,” Tanco said. “It’s essentially equivalent to operating with a very hot pizza oven on your back.” Both orbiters are equipped with solar panels to provide them with power and risk overheating so close to the sun. The MIO will rotate 15 times per minute, while the MPO will position its assembly at a nearly edge-on angle to the sun to receive enough sunlight while avoiding solar radiation damage. Putting two spacecraft into orbit around Mercury will provide unprecedented views of the planet and open a new chapter in scientists’ understanding of the solar system, Martínez said. The orbiters will help map the planet in high resolution and answer questions that arose during MESSENGER’s detailed study of Mercury. Each orbiter is equipped with a variety of instruments to explore the structure and composition of Mercury, including craters and evidence of ancient volcanic activity on its surface, as well as the planet’s magnetic field and its exosphere, a thin cloud of gas that surrounds the planet, said Geraint Jones, principal scientist for the BepiColombo project at ESA. One of the mysteries that scientists hope to investigate are the so-called holes discovered on Mercury by Mariner 10 and MESSENGER. “There are depressions in the surface that look like they’re eating it up,” Jones said. “It is possible that we could see changes in these regions over time.” No holes have been found anywhere else on the planets in our solar system, and with no wind or water to form the thousands of puzzling depressions, scientists want to know what forces sculpted them. The orbiters could also help uncover the truth behind why Mercury is so dense for its small size. About 4.5 billion years ago, when planets formed from the debris surrounding the Sun, “Mercury is thought to have started to form, created a modest-sized planet, and then was hit by another large planetesimal, which ripped off its outer crust,” Jones said. “That means the overall density of the material that was left was much higher, and that’s why it has the high density it has now.” Learning more about Mercury’s surface and interior could confirm the theory or provide new answers, Jones said. Subscribe to CNN’s Wonder Theory science newsletter. Explore the universe with news about fascinating discoveries, scientific breakthroughs and more.
