Top images reveal Mercury's mysteries during BepiColombo's sixth flyby

Top images reveal Mercury's mysteries during BepiColombo's sixth flyby
by Erica Marchand
Paris, France (SPX) Jan 10, 2025

On January 8, 2025, the ESA/JAXA BepiColombo mission made its sixth flyby of Mercury, completing the final gravity assist needed to position itself for orbit insertion around the planet in late 2026. During this maneuver, the spacecraft flew just 295 kilometers above Mercury's night side before capturing stunning images of the sunlit northern regions.

At 06:59 CET, BepiColombo passed over Mercury's cold, dark side. Minutes later, it soared directly above the planet's north pole, unveiling views of shadowed craters and expansive volcanic plains bathed in sunlight. These images were shared during ESA Director General Josef Aschbacher's Annual Press Briefing on January 9.

This flyby marked a significant milestone for the mission. It was the last opportunity for the spacecraft's monitoring cameras (M-CAMs) to capture close-up views before the module carrying them separates from BepiColombo's two orbiters-ESA's Mercury Planetary Orbiter and JAXA's Mercury Magnetospheric Orbiter-prior to orbit insertion.

Insights from Mercury's craters and volcanic plains

BepiColombo's monitoring camera 1 (M-CAM 1) provided a rare glimpse into Mercury's permanently shadowed polar craters, including Prokofiev, Kandinsky, Tolkien, and Gordimer. These regions are among the coldest in the Solar System, and previous evidence suggests they may harbor frozen water. Investigating the presence of water in these craters will be a key focus of BepiColombo's orbital mission.

The Borealis Planitia volcanic plains, located near the north pole, also featured prominently in M-CAM 1's images. These smooth plains, formed by ancient lava flows around 3.7 billion years ago, exhibit surface wrinkles caused by planetary contraction as Mercury's interior cooled. The images highlighted craters like Henri and Lismer, whose interiors were reshaped by these lava flows.

Another image captured the expansive Caloris basin, Mercury's largest impact structure, which spans over 1,500 kilometers. The basin's surface displays linear troughs radiating outward, hinting at the force of the impact that formed it. A distinct bright lava flow within the basin raises intriguing questions about its origin and movement, which BepiColombo aims to address in its primary mission phase.

Young features bring Mercury's history to light

Despite its dark appearance, Mercury's surface features bright patches associated with younger geological activity. The Nathair Facula, visible in M-CAM 2's imagery, exemplifies explosive volcanic activity. This bright deposit spans 300 kilometers and includes a 40-kilometer-wide volcanic vent that experienced at least three major eruptions.

Nearby, the Fonteyn crater, formed about 300 million years ago, stands out due to its bright ejecta-a clear indication of its relatively recent formation. Understanding the composition of these bright features will provide critical insights into Mercury's geological history and evolution.

A successful campaign

"This is the first time that we performed two flyby campaigns back-to-back. This flyby happens a bit more than a month after the previous one," said Frank Budnik, BepiColombo Flight Dynamics Manager. "Based on our preliminary assessment, everything proceeded smoothly and flawlessly."

Geraint Jones, BepiColombo's Project Scientist at ESA, added, "BepiColombo's main mission phase may only start two years from now, but all six of its flybys of Mercury have given us invaluable new information about the little-explored planet. In the next few weeks, the BepiColombo team will work hard to unravel as many of Mercury's mysteries with the data from this flyby as we can."