Lina and her colleagues also observed the direct interaction of the spacecraft with the surrounding space plasma. When the spacecraft is heated by the Sun it cannot detect the colder, heavy ions because the spacecraft itself gets electrically charged and repels them. But as the spacecraft moves through the planet’s nightside shadow, the charging is different, and suddenly a sea of cold plasma ions become visible. For example, it detected ions of oxygen, sodium and potassium, which were likely sent flying from the planet’s surface by micro-meteorite strikes or through interactions with the solar wind.

“It’s like we’re suddenly seeing the surface composition ‘exploded’ in 3D through the planet’s very thin atmosphere, known as its exosphere,” remarks Dominique. “It’s really exciting to start seeing the link between the planet’s surface and the plasma environment.”

“In this rare dusk-to-dawn sweep through the large-scale structure of Mercury’s magnetosphere we’ve tasted the promise of future discoveries,” says Go Murakami JAXA’s BepiColombo project scientist.

“The observations emphasise the need for the two orbiters and their complementary instruments to tell us the full story and build up a complete picture of how the magnetic and plasma environment changes over time and in space,” adds Geraint Jones, ESA BepiColombo project scientist.

“We can’t wait to see how BepiColombo will impact our broader understanding of planetary magnetospheres.”

Meanwhile, scientists are already digging into the data snatched during last month’s fourth close Mercury flyby while flight controllers are readying for the final two back-to-back flybys slated for 1 December 2024 and 8 January 2025, respectively.