The BepiColombo spacecraft flew past Mercury for the fifth time last week, revealing the planet in mid-infrared light for the first time. The images revealed details of the temperature and composition of the closest planet to the Sun.
BepiColombo launched in October 2018 and is scheduled to arrive at Mercury in November 2026, about a year later than initially planned. BepiColombo pulled off its closest flyby and fourth gravity assist of Mercury in early September, and now, the spacecraft’s fifth pass of the planet has revealed new data about the scorching-hot-by-day, frigid-by-night planet.
The spacecraft collected new data on Mercury using its Mercury Radiometer and Thermal Infrared Spectrometer, or MERTIS. The instrument captured details of Mercury at mid-infrared wavelengths, in which details of the planet’s surface temperatures, roughness, and constituent minerals become apparent.
“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,” said Jörn Helbert, who helped develop the instrument as its co-principal investigator at the German Aerospace Center, in an ESA release. “It is simply fantastic!”
The images show the Bashō Crater, an impact crater previously observed by the Mariner 10 and Messenger missions. In visible light, the crater sticks out as a relatively pronounced pockmark on the planet’s surface. It’s also visible at mid-infrared wavelengths.
“The moment when we first looked at the MERTIS flyby data and could immediately distinguish impact craters was breathtaking,” said Solmaz Adeli, a researcher at the German Aerospace Center’s Institute of Planetary Research, in the same release. “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,” Adeli added.
MERTIS’ data indicated the surface of Mercury was 788° Fahrenheit (420° Celsius) at the time of the flyby. Testing different minerals in lab settings and seeing how they glow at mid-infrared wavelengths could indicate the exact chemical cocktail present in sediments on the planet’s surface.
Though BepiColombo’s arrival in Mercury’s orbit is delayed, the recent observations provide a sneak peek of the up-close-and-personal view of the planet scientists will have in two years’ time.