The BepiColombo probe has completed its third fly-by of Mercury and sent home some striking snaps of the tiny world’s dark side.

The probe was launched in 2018 on a complex path that saw it fly by Earth (twice) and Venus (once) and calls for six encounters with Mercury before settling into orbit. All the manoeuvring takes time because, as the European Space Agency explains here, entering orbit around the planet is difficult thanks to the Sun’s gravity accelerating any spacecraft’s velocity.

BepiColombo had already made its passes past Earth and Venus, plus a pair of Mercury visits.

On Tuesday it made its third approach to the planet on a trajectory planned to bring it within just 236km of the surface. This pass saw BepiColombo visit Mercury’s nightside, which as the planet’s day lasts 176 terrestrial turnarounds sees a lot of darkness.

The swoop went as planned, and BepiColombo has already beamed back three snaps of the dark side. Here’s the closest the ESA has to a close-up of Mercury.

“Rising out of the nightside this shadowy view … accentuates the heights of snaking tectonic scarps and the depths of craters,” the ESA tweeted.

On its site, the European agency revealed the probe spotted a previously unobserved 218 km-wide peak-ring impact crater that’s been named “Manley” in homage to Jamaican artist Edna Manley (1900-1987).

The flyby also captured images of “Beagle Rupes”, described as “a slab of Mercury’s crust that has been thrust westwards by at least 2 km over the adjacent terrain.”

BepiColombo will again pass Mercury in September 2024, then again in December of the same year, followed by a sixth visit in January 2025. In December 2025 it will arrive in Mercury orbit and split into two craft - the Mercury Magnetospheric Orbiter (MMO) and the Mercury Planetary Orbiter (MPO). Japan’s Aerospace Exploration Agency (JAXA) developed the MMO.

The two orbiters are expected to spend around a year gathering data it’s hoped will advance theories of how Mercury evolved, the nature of its interior and composition, the extent and disposition of its magnetosphere, and the processes that formed its surface.

ESA and JAXA boffins will also use the visit to test Einstein’s Theory of General Relativity by measuring the spacecraft’s orbit and position. ®

https://www.theregister.com//2023/06/21/bepicolombo_third_mercury_flyby/