On Thursday, a spacecraft operated by the European Space Agency and Japan made its closest approach yet to Mercury, sending back sharp, black-and-white images of the planet’s barren, speckled surface at sunrise.
The spacecraft, BepiColombo, gave scientists their first clear view of Mercury’s south pole. It also captured several of the planet’s craters, including those with unusual rings of peaks within the basin’s rim.
David Rothery, a volcanologist at the Open University in England, refers to Mercury as “Lord of the Peak Rings.”
The latest flyby “was perfect,” said Dr. Rothery, who is a member of BepiColombo’s science team. “It was exactly what I hoped to see, but better quality, showing more detail than I’d hoped.”
Johannes Benkhoff, the project scientist for BepiColombo at the European Space Agency, wrote in an email that the new images made him “shout for joy.” He added, “It is such a relief when you find out that everything worked as planned.”
A joint mission between the European and Japanese space agencies, BepiColombo launched in 2018. It will go into orbit around Mercury in 2026, about a year after its original arrival time. The delay was prompted by efforts to overcome problems with the spacecraft’s thrusters.
Mercury is the least-studied rocky planet in the solar system. With two orbiters, one more focused on Mercury’s landscape and the other collecting data about its surrounding space environment, scientists hope to use the BepiColombo mission to learn about the planet’s origins and evolution by studying its composition, geology and magnetic field.
Mercury is difficult to get to because flying toward the sun causes spacecraft to pick up speed. A series of flybys of Earth, Venus and Mercury are helping to slow down BepiColombo, which will eventually maneuver the mission into orbit around Mercury. Thursday’s flyby was the fourth of six planned around Mercury, with BepiColombo grazing the planet just 103 miles above its surface.
The images it sends back from these close encounters, Dr. Rothery said, are an added bonus.
He is particularly intrigued by Mercury’s peak ring basins and how their structures could be linked to the planet’s ancient volcanism — which might still be marginally active today, he said. BepiColombo snapped photos of two peak ring basins, Vivaldi and the recently named Stoddart. How exactly these rings were made is still a mystery.
Three monitoring cameras on BepiColombo snapped its latest batch of images. But the mission’s more powerful primary scientific instruments, including a higher-resolution color camera, won’t begin making observations until the spacecraft goes into orbit around Mercury.
The view of Mercury’s south pole is a preview of what is to come, as BepiColombo is expected to collect better data of the southern hemisphere than did NASA’s Messenger spacecraft, which the agency crashed into the planet in 2015 after an 11-year mission.
Mercury is full of secrets. It has a core that is mysteriously oversize compared with the rocky shell surrounding it. Water ice exists on its surface, despite scorching exposure to the sun without an atmosphere to protect it. The planet has an unexpected magnetic field and is rich in volatiles — elements like chlorine, sulfur and potassium — thought to readily evaporate on planets with high temperatures. This could indicate that Mercury once formed farther out in the solar system than where it is today, Dr. Rothery said.
“It’s a paradoxical place,” he said.
After BepiColombo’s remaining flybys, scheduled for December and January, it will spend nearly two years cruising around the sun before settling into orbit around Mercury by the end of 2026.
First proposed in 1993, the mission was set to be launched in 2014, but engineering delays pushed the date four years later. With the efforts to compensate for the spacecraft’s thruster difficulties, scientists face an additional 11-month delay before the orbit of Mercury begins.
Though the delays have been frustrating, Dr. Rothery is glad the team is being patient. “The main thing is that we get there when we get there,” he said. “We want to play it safe.”
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