A collaboration between ESA and JAXA might reveal some amazing facts about Mercury.

Mercury is the innermost planet of our solar system and has an orbital period of just 87.97 days around the Sun. Quite understandingly, the smallest planet has also the smallest orbital period among all its companions. Similarly, the axis of Mercury exhibits the smallest tilt of any of the solar system’s planets. Just like Venus, Mercury orbits as an Inferior planet and never exceeds the limit of 28^o away from the sun. Given its small size, Mercury is much more difficult to observe than Venus.

The images of Mercury suggest that it has been geologically inactive for billions of years. In terms of appearance, its surface resembles with that of a moon as there are numerous craters on it. Having said that, the planet has no natural satellite of its own. The surface temperatures of Mercury vary diurnally because it has almost no atmosphere to preserve the heat. Consequently, the temperature ranges around 427^o C in the day while they drop to -173^o C at night. However, the temperature at the Polar Regions always stays below -93^o C.

Mercury is tidally locked with the sun in a 3:2 Spin-orbit Resonance. This means that it rotates exactly three times on its axis during every two rotations around the central star of our solar system. As a result, an observer residing on Mercury will get a day every two years. In addition to that, it offers a molten, abnormally large core and generates a magnetic field. Likewise, the presence of unidentified, volatile substances at its surface adds to the mystery of this planet as it is quite close to the sun. In order to answer all these questions, the European Space Agency (ESA) launched a mission, called BepiColombo, to Mercury on 20^th October 2018. It will reach Mercury in 2025.

The launch was executed from the agency’s spaceport in French Guyana. After three days of rotation around the Earth, the BepiColombo is now in an elliptical orbit around the sun. It has come inside the Earth’s orbit to achieve this particular position. However, it will move out of the Earth’s orbit in the early parts of 2019 and will stay there for most of the year before returning back inside. It is expected to come perilously close to the Earth in April 2020.

During that phase, it will make use of the Earth’s gravity to swing itself inwards towards Venus (Gravity-assist Flyby). BepiColombo will follow it up with another gravity-assist flyby of Venus once it reaches there. In 2021, it will once again take help from Venus’s gravity to send the spacecraft towards Mercury. In the coming four and a half years (2021-2025), 6 similar flybys of Mercury will be needed to push the BepiColombo towards the target. Scientists hope that after all these flybys, the spacecraft will arrive at its target at a slow enough speed to enter the Mercurial orbit in December 2025.

25 years ago, a group of scientists proposed ESA to plan a mission for exploring Mercury. 7 years later, the space agency approved the project as a ‘Cornerstone Mission’, which refers to the class of world-class, scientifically excellent missions that need significant improvements in technology. Historically, ESA has successfully executed some Cornerstone missions including the LISA Pathfinder and Rosetta Comet Mission.

ESA collaborated with the Japanese space agency, JAXA, for this extraordinary venture. The mission is named after Giuseppe Bepi Colombo, who was the first man to propose gravity-assist flybys. The spacecraft carries two orbiters (one from each space agency). First one of them is Mercury Planetary Orbiter (MPO), which is a 2-meter long instrument from ESA. It has a mass of more than 1 ton. On the other hand, the Japanese orbiter is smaller in size and weighs only a quarter of its European counterpart.

The original name of this orbiter was Mercury Magnetospheric Orbiter (MMO). However, it was changed to Mio earlier this year in June. It is kept inside a sunshield and is attached to one of the sides of the MPO. The Mercury Transfer Module (MTM) resides on the other side of the European orbiter. It is a propulsion device which is responsible for taking the spacecraft to the Mercurial orbit. It creates thrust by accelerating positively-charged Xenon. The 7.5-meter long wing of solar panels turns the energy from the sun into electricity to power the ‘Ion Drive’, which will be operated in intervals.

Mio will take charge once the spacecraft arrives at Mercury. It spins at 15 revolutions per minute to provide stability, which will be vital for studying the planet. MPO will also examine Mercury from a circular orbit through its camera and other instruments. Last but not the least, both of these orbiters are equipped with a magnetometer which will allow them to report magnetic conditions of two different places simultaneously.

Have a glimpse at the proposed journey of BepiColombo: