As we approach November, a significant milestone in space exploration is on the horizon. The BepiColombo spacecraft, a collaborative effort between European and Japanese space agencies, is set to achieve a remarkable feat: entering orbit around Mercury, a planet that has eluded close-up observation for most of our solar system's history. This event marks the culmination of nearly a decade of patience and precision, as the spacecraft has been carefully navigating its way towards this elusive planet.
Mercury, often overlooked due to its proximity and small size, is a planet of intrigue. Its oversized iron core, global magnetic field, and potential water ice in permanently shadowed polar craters make it a unique enigma in our solar system. Despite its mysterious nature, only two missions have ever ventured to Mercury, and only one has orbited it, leaving much of its secrets untold.
The Challenge of Reaching Mercury
Mercury sits at the bottom of a gravitational well, making it incredibly difficult to reach. Any spacecraft aimed at Mercury accelerates as it falls towards the Sun, arriving at a speed too great to be captured by the planet's gravity. Slowing down this rapid descent is the key challenge, and BepiColombo has spent eight years doing just that.
The spacecraft has utilized a complex trajectory, looping around Earth, Venus, and Mercury itself multiple times, each close pass acting as a brake. Combined with the gentle thrust of its ion engines, BepiColombo has gradually shed velocity, a process that has taken patience and precision.
A Trio of Spacecraft
What launched in 2018 is actually a stack of three spacecraft. The transfer module, carrying the other two, has been responsible for the ion propulsion and trajectory adjustments. On top of this module are the European Mercury Planetary Orbiter, which will study the planet's surface and interior, and Japan's Mio orbiter, focused on the magnetic field and surroundings.
After arrival, the transfer module will be discarded, and the two orbiters will separate, each taking its own path around Mercury. This arrangement allows for simultaneous study of the planet's surface and magnetic environment, a first for Mercury exploration.
Delayed but Not Derailed
The November arrival date is a slight delay from the original plan. In 2024, an issue with the thrusters reduced their power, causing a reevaluation of the trajectory. The new plan includes closer flybys of Mercury to gain more braking from its gravity, ensuring the full science mission can still be achieved.
The Final Leg of the Journey
The spacecraft's final Mercury flyby was in January 2025, and in June 2026, it completed the main cruise phase of its ion propulsion. Now, it's in the arrival phase, a gradual process due to the low, steady thrust of its engines. A precise sequence of maneuvers will slow BepiColombo just enough for Mercury's gravity to capture it into a polar orbit.
The Rewards of Exploring Mercury
Mercury's oddities make it a fascinating subject for study. Its large iron core, unique among rocky planets, and its ability to sustain a magnetic field despite its small size are intriguing mysteries. The potential presence of water ice in shadowed craters, despite its proximity to the Sun, is a paradox that demands explanation.
Our close-up knowledge of Mercury is limited to NASA's Mariner 10 flybys in the 1970s and the MESSENGER orbiter from 2011 to 2015. BepiColombo, as the third mission and second orbiter, promises to expand our understanding significantly.
What to Expect
In November, we'll witness the capture of BepiColombo into Mercury's orbit, a precise and gradual process. This will be followed by the separation of the two orbiters and the commencement of their science missions in 2027. The answers to long-standing questions about Mercury's core, magnetic field, and polar craters will begin to emerge.
As BepiColombo completes its eight-year journey, Mercury, a planet that has long eluded close inspection, will finally reveal its secrets.
