The European and Japanese mission BepiColombo has successfully completed the first of six flybys of the planet Mercury, its scientific target. On October 1, the spacecraft was just 199 kilometers (123 miles) over the surface of the planet, allowing it to take some stunningly detailed images of the smallest planet.
“The flyby was flawless from the spacecraft point of view, and it’s incredible to finally see our target planet,” Elsa Montagnon, Spacecraft Operations Manager for BepiColombo, said in a statement.
BepiColombo's monitoring cameras took the first close-up images of Mercury in over six years, revealing large impact craters and some of the spacecraft's own elements. The last probe orbiting the planet was NASA’s MESSENGER, which came to a scheduled end in 2015 when it slammed into Mercury’s surface at about 14,000 kilometers per hour (8,750 mph) and created its own new crater on the planet’s surface.
BepiColombo's closest point to Mercury was on the planet’s nightside, at 11:34 pm UTC, so it wasn't ideal to take photos then. The images collected started about five minutes after the closest approach when the spacecraft was about 1,000 kilometers (600 miles) away and continued for four hours as it moved further and further from the planet.
“It was an incredible feeling seeing these almost-live pictures of Mercury,” said Valentina Galluzzi, co-investigator of BepiColombo’s SIMBIO-SYS imaging system that will be used once in Mercury orbit. “It really made me happy meeting the planet I have been studying since the very first years of my research career, and I am eager to work on new Mercury images in the future.”
The region below shows part of Mercury's northern hemisphere, including Sihtu Planitia that has been flooded by lava. The Raduki plains, the smooth lighter area around the Calvino crater, can also be seen. The 166-kilometer-wide Lerminotov crater appears brighter than the others because it contains what is known as "hollows", features unique to Mercury where volatile elements are escaping into space. BepuiCollomno will study these in greater detail when it gets there.
Bepi also caught some of Mercury's southern hemisphere, as shown below here. The smooth floor of the largest crater, the 251-kilometer-wide Haydn crater, shows that it was once flooded by lava — as most of the plains were. Some of the bright spots seen on the surface are what is called "faculae", which are thought to be material flung out by volcanic explosions. These were discovered by MESSENGER and BepiColombo will find out more about them.
The two science orbiters on BepiColombo are ESA’s Mercury Planetary Orbiter and JAXA’s Mercury Magnetospheric Orbit. They will map the planet’s surface and analyze its composition, measure its magnetic field and the tenuous layer of particles – its exosphere – around it. This will provide important clues to how Mercury formed and evolved.
Mercury might have lost most of its mass after a major collision, and the mission might provide evidence to confirm or deny that scenario. It will also tell us more about its volcanism and lava flows.
BepiColombo’s main science mission will begin in early 2026, after orbital insertion in December 2025. To slow down enough to get into Mercury’s orbit without the use of an incredible amount of fuel, it will complete nine planetary flybys in total. Four are already in the bag: one at Earth, two at Venus, and now the first one at Mercury. Five more Mercury flybys are set to take place, with the next on June 23, 2022.