By European Space Agency (ESA) December 15, 2024
Collected at: https://scitechdaily.com/bepicolombo-unmasks-mercurys-hidden-surface-with-infrared-breakthrough/
On December 1, 2024, BepiColombo completed its fifth flyby of Mercury. During this encounter, it became the first spacecraft to observe Mercury in mid-infrared light. These groundbreaking images revealed differences in temperature and surface composition across the planet’s heavily cratered terrain.
Mercury is the least-explored rocky planet in the Solar System. BepiColombo is only the third mission ever to visit Mercury, and in 2026, it will become the second mission to enter the planet’s orbit. The first two missions were NASA’s Mariner 10, which made three flybys between 1974 and 1975, and NASA’s Messenger, which orbited Mercury from 2011 to 2015.
BepiColombo is on an eight-year journey to Mercury, using the gravity of Earth, Venus, and Mercury to adjust its path and reduce its speed. On December 1, 2024, at 15:23 CET, it completed a flyby just 37,628 km (23,381 miles) above Mercury’s surface.
Groundbreaking Mid-Infrared Observations
During this flyby, BepiColombo gathered valuable data about Mercury and its environment. In addition to capturing standard images and measuring particles and electromagnetic fields, the mission achieved a groundbreaking first: capturing Mercury’s surface in mid-infrared wavelengths of light.
The instrument making this flyby unique is the German-led Mercury Radiometer and Thermal Infrared Spectrometer, MERTIS for short.
“With MERTIS, we are breaking new ground and will be able to understand the composition, mineralogy, and temperatures on Mercury much better,” notes Harald Hiesinger, the instrument’s principal investigator from the University of Münster, Germany.
Jörn Helbert, who helped develop and supervise the instrument as co-principal investigator at the German Aerospace Center (DLR) in Berlin, is delighted: “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!”
The greyscale background image (upper image) shows the surface of Mercury as observed by NASA’s Messenger mission.
MERTIS’s view during this flyby covers part of the largest impact crater on Mercury, called the Caloris Basin. The zoom panel shows a close-up of the area around the Bashō impact crater. Messenger’s visible light images show that Bashō impact crater exhibits both very dark and very bright material. The MERTIS flyby observations reveal that the crater also stands out in infrared light.
The lower right shows the flyby coverage projected on the Mercury globe. The flyby MERTIS data shown in grey is overlaid on the global mosaic of a topography map based on Messenger data.
Credit: MERTIS/DLR/University of Münster & NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington
Unveiling the Mysteries of Mercury
MERTIS’s first Mercury image reveals which parts of the surface shine more brightly in mid-infrared light more than others, with a ground resolution of around 26–30 km (16-19 miles). It covers a part of the Caloris Basin, and parts of a large volcanic plain in the northern hemisphere.
The brightness of the surface depends on temperature, surface roughness, and what minerals the cratered surface is made of. The imaging spectrometer is sensitive to mid-infrared light with wavelengths of 7–14 micrometers, a range known to be particularly suitable for distinguishing rock-forming minerals.
The image highlights the Bashō impact crater, a feature seen already by Mariner 10 and observed in detail by Messenger. Visible light images show that the Bashō impact crater contains both very dark and very bright material. The MERTIS flyby observations reveal that the crater also stands out in infrared light.
“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. We have never been this close to understanding the global surface mineralogy of Mercury with MERTIS ready for the orbital phase of BepiColombo,” says Solmaz Adeli from DLR’s Institute of Planetary Research in Berlin, who was instrumental in planning the current flyby as project lead.
Analyzing Mercury’s Surface
What the little planet’s surface is made of is one of Mercury’s many mysteries. MERTIS and other instruments on BepiColombo’s Mercury Planetary Orbiter will provide better accuracy and resolution of the elemental composition compared to the Messenger data.
Messenger revealed that the surface has relatively little iron in it, despite the planet’s iron-nickel core being unusually large. The mission also revealed that although Mercury orbits close to the Sun, some chemical elements that easily evaporate are present in unusually high concentrations.
A related mystery is why the planet looks so dark. At a first glance, Mercury’s crater-ridden dusty surface may look similar to the Moon, but its surface reflects only about two-thirds as much light as the Moon does.
Preparing for In-Orbit Studies
To be able to interpret MERTIS’s measurements, one needs to know exactly how different minerals glow in mid-infrared light, and how this varies with temperature. The sunlit side of Mercury can get very hot: the MERTIS radiometer measured temperatures up to 420 °C during the flyby.
In preparation for BepiColombo arriving at Mercury in 2026, the MERTIS team has been testing out many different materials and mineral mixtures in the lab, heating them to different temperatures and measuring how they glow in mid-infrared wavelengths.
“Because Mercury’s surface is surprisingly poor in iron, we have been testing natural and synthetic minerals that lack iron,” explains Solmaz. “The materials tested include rock-forming minerals to simulate what Mercury’s surface might be made of.”
MERTIS was built at DLR with participation from German industry. The MERTIS team consists of numerous scientists from several European countries and the USA, who are jointly studying the data from the flyby. “It is really a pleasure to work together with a fantastic team on evaluating the data. And the best is yet to come – when we enter orbit around Mercury in 2026, MERTIS will be able to exploit its full potential,” says Harald.
After orbit insertion, MERTIS will provide a global map of the distribution of minerals on Mercury’s surface with a resolution down to 500 m.
A Clever Sneak Peek
The fact that MERTIS could already carry out observations at this early stage of the mission was only made possible by clever reprogramming of the instrument software. MERTIS was designed to observe Mercury through its so-called ‘planet port’ and to calibrate this data by looking out into cold space with its ‘space port’.
But until BepiColombo arrives at Mercury in 2026, the spacecraft’s parts are ‘stacked’ together, and MERTIS’s planet port is blocked. Thanks to the reprogramming, its space port could now be used to generate data on the way to Mercury during this flyby. This has already proven successful during flybys of the Moon and Venus, allowing the team to test the instrument and to calibrate the data it produces.
“These fascinating and valuable results from the MERTIS instrument are only a tantalizing hint of the great results we’re expecting from the entire BepiColombo science payload once both orbiters are operating in orbit around Mercury,” says Geraint Jones, BepiColombo Project Scientist at ESA.
About BepiColombo
Launched on October 20, 2018, BepiColombo is a joint mission between ESA and the Japan Aerospace Exploration Agency (JAXA), executed under ESA leadership. It is Europe’s first mission to Mercury.
The mission comprises two scientific orbiters: ESA’s Mercury Planetary Orbiter (MPO) and JAXA’s Mercury Magnetospheric Orbiter (Mio). The European Mercury Transfer Module (MTM) carries the orbiters to Mercury.
After arrival at Mercury in late 2026, the spacecraft will separate and the two orbiters will maneuver to their dedicated polar orbits around the planet. Starting science operations in early 2027, both orbiters will gather data during a one-year nominal mission, with a possible one-year extension.
All M-CAM images are publicly available in the Planetary Science Archive.
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