BepiColombo probes separate on Mercury approach

BepiColombo's European and Japanese probes separated from their transfer module on Thursday, completing a key step in the spacecraft's high-risk arrival phase at Mercury after an eight-year journey.

The European Space Agency said the autonomous operation went to plan. The spacecraft cut four mechanical struts connecting the orbiters to the module, and spring mechanisms pushed them apart at about 40 centimetres per second.

The signal confirming the separation reached ESA's control centre in Darmstadt, Germany, at 1353 GMT, nearly two hours after the operation because of the distance from Earth.

BepiColombo launched from Earth in 2018 and travelled more than 10 billion kilometres, using nine flybys to adjust its speed and trajectory toward Mercury. ESA has described the arrival as one of its most operationally challenging planetary arrival sequences.

Mercury's weak gravity compared with the Sun's pull makes the planet difficult for spacecraft to approach without being lost or damaged. On Thursday, Mercury was about 63 million kilometres from the Sun and 200 million kilometres from Earth, creating about a 30-minute delay between checks and commands from the ground.

The probes are due to enter Mercury's orbit on November 21. Another difficult phase is expected on December 9 and 10, when the two probes separate into their respective orbits.

From April, ESA's Mercury Planetary Orbiter is expected to study Mercury from as close as 480 kilometres above the surface. The Japanese Mercury Magnetospheric Orbiter, called Mio, will focus on the planet's space environment and magnetic field from an elliptical orbit reaching as far as 11,000 kilometres away.

Mercury is the least studied of the four rocky inner planets. The €1.7 billion mission carries 16 instruments and is intended to investigate unresolved questions about Mercury's magnetic field, iron core and surface.