The BepiColombo mission, a joint endeavor by the European Space Agency (ESA) and the Japan Aerospace Exploration Agency (JAXA), has once again provided groundbreaking insights into Mercury, the least-explored rocky planet in the solar system. On December 1, 2024, the spacecraft conducted its fifth flyby of the planet, unveiling unprecedented details about Mercury’s surface using mid-infrared imaging technology. This marks a significant milestone in planetary science, as no previous spacecraft has observed Mercury in this spectrum of light. The new findings highlight variations in the planet’s surface composition, temperature, and roughness, shedding light on mysteries that have long puzzled scientists.
This flyby was another crucial step in BepiColombo’s eight-year journey to Mercury, which began with its launch in 2018. The spacecraft is scheduled to enter Mercury’s orbit in late 2026, but its latest encounter has already offered a tantalizing glimpse of what’s to come, demonstrating the potential of its cutting-edge instruments, including the Mercury Radiometer and Thermal Infrared Spectrometer (MERTIS).
Unraveling Mercury’s Composition and Temperatures
The flyby provided new insights into Mercury’s unique geological features, with the MERTIS instrument playing a pivotal role. Unlike previous missions, such as NASA’s Messenger, which focused on visible light imaging, MERTIS captured data in mid-infrared wavelengths, a spectrum particularly suited to identifying minerals and understanding temperature variations on the planet’s surface. These observations revealed which regions of Mercury shine more brightly in mid-infrared light, offering clues about their mineral composition and surface roughness.
“With MERTIS, we are breaking new ground and will be able to understand the composition, mineralogy, and temperatures on Mercury much better,” said Harald Hiesinger, principal investigator for the instrument from the University of Münster, Germany. The new data covers a range of features, including parts of the Caloris Basin, one of the largest impact basins in the solar system, and volcanic plains in Mercury’s northern hemisphere.
By observing Mercury in mid-infrared light, MERTIS also unveiled new details about the Bashō Crater, a well-documented impact site previously studied by the Mariner 10 and Messenger missions. The crater, known for its contrasting light and dark materials in visible light, displayed distinct characteristics in the mid-infrared spectrum, providing fresh insights into its composition.
A Breakthrough Decades in the Making
The development of MERTIS represents over two decades of meticulous planning, testing, and innovation. The instrument was designed to withstand the extreme temperatures of Mercury’s surface, which can soar to 420°C (788°F) on its sunlit side. Its ability to distinguish minerals in this hostile environment is a testament to the ingenuity of the scientists behind the project.
“After about two decades of development, laboratory measurements of hot rocks similar to those on Mercury, and countless tests of the entire sequence of events for the mission duration, the first MERTIS data from Mercury is now available. It is simply fantastic!” said Jörn Helbert, co-principal investigator of MERTIS from the German Aerospace Center (DLR) in Berlin.
For the researchers analyzing the data, the results were nothing short of awe-inspiring. “The moment when we first looked at the MERTIS flyby data and could immediately distinguish impact craters was breathtaking! There is so much to be discovered in this dataset – surface features that have never been observed in this way before are waiting for us,” remarked Solmaz Adeli, a planetary researcher at the DLR and project lead for the flyby. “We have never been this close to understanding the global surface mineralogy of Mercury with MERTIS ready for the orbital phase of BepiColombo.”
Decoding Mercury’s Unique Surface Chemistry
One of the most intriguing aspects of Mercury is its unusual surface chemistry. Unlike other rocky planets, Mercury’s surface is surprisingly poor in iron despite its disproportionately large iron-nickel core. This anomaly has long puzzled scientists and prompted extensive laboratory simulations to replicate the planet’s conditions.
“Because Mercury’s surface is surprisingly poor in iron, we have been testing natural and synthetic minerals that lack iron,” Adeli explained. “The materials tested include rock-forming minerals to simulate what Mercury’s surface might be made of.” These experiments are helping researchers interpret the MERTIS data and piece together a clearer picture of Mercury’s composition. By comparing laboratory results with MERTIS observations, scientists aim to uncover the chemical processes that shaped Mercury’s surface over billions of years.
A New Era of Exploration
BepiColombo’s mission is far from over. While its flybys offer invaluable glimpses of Mercury, the spacecraft’s full potential will be realized once it enters orbit in 2026. At that point, MERTIS will generate high-resolution maps of the planet’s mineral distribution, providing unprecedented insights into its geological history and evolution.
Reflecting on the significance of the current findings, Helbert and his team are optimistic about the future. “The best is yet to come – when we enter orbit around Mercury in 2026, MERTIS will be able to exploit its full potential,” said Harald Hiesinger. Until then, the data from the recent flyby serves as a powerful preview of the transformative discoveries that lie ahead.