A European spacecraft bound for Mercury cleared a major hurdle on Thursday when it safely separated from its propulsion module that has carried it through deep space since 2018.
BepiColombo now flies on a slimmer stack made of two orbiters and a sunshield. The change marks the end of the mission’s long cruise and the start of its months‑long arrival phase as it closes in on the planet nearest to the sun.
After the separation command at 2 p.m. local time in Germany on Sept. 3, teams waited nearly two hours for radio signals to cross more than 120 million miles of space. Fresh data then revealed the spacecraft in its expected new configuration, with healthy power levels from its remaining solar panel. Dropping the transfer module meant the most important instruments onboard were no longer blocked.
“Finally, we have science cameras,” said Paolo Cappuccio, a European Space Astronomy Centre scientist in Spain. “Let’s go to Mercury.”
The mission will give scientists new insight into Mercury, the least studied planet in the solar system — even less so than dwarf planet Pluto. That’s not because scientists don’t care about it, but because Mercury is the hardest world to reach, mission leaders say. Spacecraft must shed huge amounts of speed to fall inward toward the sun and match Mercury’s tight, fast orbit. Only two missions — NASA‘s Mariner 10 and Messenger — have ever visited Mercury before, and only Messenger orbited it.
Launched in 2018, BepiColombo is a joint mission between the European Space Agency and Japan’s JAXA. Until today, the car‑size Mercury Transfer Module, or MTM, used solar power and ion engines to push the spacecraft through a series of flybys of Earth, Venus, and Mercury.
About six years into flight, the team faced a major crisis when that module’s solar panels began underdelivering on power. That forced engineers to redraw BepiColombo’s path, cut back on the engine firings, adjust the schedule of key maneuvers, and accept a later arrival at Mercury so they could keep the spacecraft healthy.
Credit: ESA infographic
At separation on Thursday, the space-weary BepiColombo was still about 2.1 million miles from its destination, but it had reached the final leg of its journey. Small release devices let the module drift away at roughly 1 mph, while the remaining spacecraft briefly entered a “safe mode” to reset.
The spacecraft separated from the propulsion module because it needed to switch to a lighter setup better suited for steering and doing science in orbit around Mercury.
Before shutting down for good, the module sent its final snapshots from three small cameras. The images show parts of the spacecraft — a solar panel edge, an antenna, and a boom — against the blackness of space. Mercury itself does not appear, both because of camera angles and the fact that the planet is still millions of miles away.
There are no pictures of the actual separation because, once detached, the module had no computer or antenna to continue snapping with the engineering cameras.
Credit: ESA
Want more science and tech news delivered straight to your inbox? Sign up for Mashable’s Light Speed newsletter or get Mashable push alerts today.
Over the next weeks, flight teams will adjust BepiColombo’s trajectory so it arrives at just the right spot — at just the right speed — to let Mercury’s gravity capture it. A key engine burn on Nov. 21 is expected to place the stack into a wide orbit around Mercury.
In December, Japan’s MIO spacecraft will separate into its own high path to study Mercury’s magnetic bubble, while Europe’s orbiter will focus on the planet itself, mapping the surface and probing the interior.
Mercury bakes to more than 750 degrees Fahrenheit in daylight and plunges below minus 290 degrees at night. BepiColombo must survive not only fierce sunlight but also the heat that Mercury’s surface radiates back into space. Engineers built special heat‑resistant coverings and solar panels that can cope with the brutal assault from the sun.
Credit: ESA
Scientists hope the twin orbiters will reveal why this small world has such a large metal core, how its thin cloud of gas changes over time, and how its magnetic field compares with Earth’s when they reach their final paths around March 2027.
When the telemetry from the spacecraft came through at exactly the moment the team expected, Elsa Montagnon, BepiColombo’s spacecraft operations manager, said she felt relief.
“I don’t have words,” Montagnon said. “It has power, it has propulsion, it could reorient itself, and it can communicate with us. We have a mission.”