A Journey of Eight Years to Mercury
Embarking on an eight-year journey only to arrive back at the starting point may seem paradoxical. However, this is precisely the case for BepiColombo. This ambitious mission, a collaborative effort between the European Space Agency (ESA) and the Japan Aerospace Exploration Agency (JAXA), commenced its voyage in October 2018 and has since been traversing the inner solar system. It is now entering a critical phase that will enable its instruments to orbit Mercury, aiming to unravel some of the most pressing mysteries surrounding the planet closest to the Sun.
The initial milestone has been successfully achieved. On 3rd September, while approximately 3.3 million kilometres from Mercury, BepiColombo detached from the Mercury Transfer Module (MTM) — the module responsible for providing energy and propulsion throughout its journey. The ESA confirmed the successful separation via signals received from its deep-space antennas, indicating that all systems are functioning normally.
Reaching this juncture required the spacecraft to execute a series of nine planetary flybys: one of Earth, two of Venus, and six around Mercury itself. This intricate trajectory allowed for gradual adjustments to its path and speed, facilitating BepiColombo’s eventual capture by Mercury’s gravitational pull. Since its departure in October 2018, mission instruments have collectively covered between 9,000 and 10,000 million kilometres, illustrating the complexities involved in reaching other planets. Notably, if the journey could be undertaken in a straight line during a close approach between the two worlds, it would only necessitate a distance of around 77 million kilometres.
The Beginning of a New Phase
The separation from the MTM marks merely the onset of an arrival phase that will unfold over the next seven months. For the time being, the two orbiters involved in the mission, Mio and MPO, will remain attached as they continue their approach to Mercury. On 21st November, they are scheduled to enter a broad orbit around the planet together. The separation of the two orbiters is planned for between 9th and 10th December, while the scientific phase is set to officially commence on 6th April 2027.
A Historic Mission to Mercury
The BepiColombo mission signifies the return of a spacecraft to orbit around Mercury after more than a decade. The previous mission, MESSENGER, operated by NASA, orbited the planet from 2011 to 2015, until its fuel was depleted, ultimately leading to its crash landing on the surface. This initiative, spearheaded by the ESA and JAXA, stands as the second mission in history to establish an orbit around Mercury, and it is the first to study the planet using two orbiters simultaneously.
BepiColombo carries two dedicated observatories. The Mercury Planetary Orbiter (MPO), developed by the ESA, is primarily tasked with investigating Mercury itself. Its instruments are equipped to map the planet’s surface, analyse its composition, measure its topography, study its internal structure, and characterise its magnetic field. Additionally, it will observe the faint layer of particles enveloping Mercury, known as its exosphere.
Exploring Mercury’s Surroundings
The second orbiter, Mio, developed by JAXA, will focus on the space surrounding Mercury. It will measure the magnetic field, charged particles, plasma waves, dust, and the interactions between Mercury and solar wind. The capability to conduct simultaneous measurements from two distinct regions will facilitate a level of study of Mercury’s magnetosphere that has never been accomplished before by prior missions.