Europe's BepiColombo spacecraft has passed a critical milestone in its eight-year journey to Mercury, jettisoning its Mercury Transfer Module ahead of entering orbit around the planet in November. The manoeuvre, carried out on Thursday, was described by mission officials as equivalent in risk to launching a new spacecraft, since the remaining orbiters had to immediately take over power generation, propulsion and thermal control unaided, in a region of intense heat and solar radiation. Success is essential for the mission, led by the European Space Agency with Japanese and American involvement, to achieve its goal of studying how Mercury formed.

The nearly $2 billion mission launched in 2018 and has relied on plasma propulsion plus nine flybys of Earth, Venus and Mercury to shed enough velocity to be captured by the planet's gravity, a manoeuvre that demands more energy than reaching far more distant worlds such as Pluto. BepiColombo is actually a stack of three spacecraft, and Thursday's separation leaves the European-built Mercury Planetary Orbiter and Japan's Mercury Magnetospheric Orbiter (Mio) travelling together until they part ways in December, shortly after reaching their initial orbit. The discarded transfer module occurred some 39 million miles (63 million kilometres) from the Sun, and its removal will finally expose several key instruments, including the mission's best cameras, which had been obscured throughout the cruise phase.