Thursday's separation near Mercury starts BepiColombo's months-long arrival sequence, with ESA calling it one of its most operationally challenging planetary arrivals ever attempted.
At 200 million km from Earth and with a roughly 30-minute command delay, the spacecraft must autonomously release the two probes from the transfer module using spring mechanisms.
Mercury's weak gravity and extreme heat near the Sun make the maneuver unusually risky, while thermal, propulsion and attitude-control systems are being used in this environment for the first time.
The mission has already absorbed a 2024 thruster glitch and still faces another key step in December, when the probes separate into their final orbits before science operations begin in April.
With 16 instruments and a 1.7 billion-euro budget, ESA's MPO and JAXA's Mio aim to deliver the most detailed study yet of Mercury's surface, core and magnetic environment.