End of the blue glow: BepiColombo turns off solar electric propulsion for Mercury arrival

24 CEST on 15 June 2026, a faint blue glow in space was switched off for the last time. After powering BepiColombo 's eight-year journey across the inner Solar System, the spacecraft's solar electric propulsion system completed its final. The institutional report frames the development in practical terms and ties it to the broader mission or observing effort.

That matters because astronomy does not advance on single detections. The field builds confidence by accumulating independent observations across different wavelengths, instruments and epochs until isolated signals become defensible conclusions. What looks convincing in one dataset can dissolve when a second instrument looks at the same target, and what looks marginal can solidify when follow-up campaigns confirm the original reading. The current standard requires that a result survive this triangulation before the community treats it as settled. 24 CEST on 15 June 2026, a faint blue glow in space was switched off for the last time. Since its launch in October 2018, the ESA/JAXA BepiColombo mission to the Solar System’s innermost planet has been on an 8 year-long cruise phase powered by solar electric.

Located in BepiColombo ’s Mercury Transfer Module (MTM), the four QinetiQ T6 solar electric propulsion thrusters use electricity generated by the spacecraft’s solar arrays to. Unlike traditional chemical propulsion, this system uses solar energy to turn xenon gas into an electrically charged stream (plasma), which is then accelerated and fired out at.

Requiring far less propellant and able to adjust its thrust based on the available solar power, SEP is one of the most efficient and flexible propulsion systems flown to date. After a long, challenging cruise phase with nine planetary flybys (one by Earth, two by Venus and six by Mercury), BepiColombo finally closed this chapter last Monday by.

The commands were sent from Earth well in advance to turn off the thrusters at exactly the right moment during the spacecraft’s last thrust arc. On the morning before the scheduled afternoon SEP system shutdown, Neil Wallace - the lead SEP thruster engineer - met with the mission team and industry partners at ESA’s.

What gives the story weight is not just the object itself, but the way the measurement trims the range of plausible physical explanations. Astronomy has accumulated enough cases to know that the most interesting results are rarely the ones that confirm expectations cleanly; they are the ones that confirm some expectations while complicating others, or that open a parameter space that previous instruments could not reach. The scientific community evaluates these contributions by asking whether the new data constrain a model in a way that older data could not, and whether those constraints survive systematic review.

Together, they reviewed the lessons learned from BepiColombo’s SEP, a key step towards the implementation of this system in future space missions. Only when the remaining spacecraft composite (MPO - Mio -MOSIF) reaches the point of Mercury orbit insertion in late November will BepiColombo’s flight control team activate.

Because the account originates with ESA Space Science, it functions best as a primary institutional report that is close to the data and operations, not as independent scientific validation. Institutional communications are produced by organizations with legitimate interests in presenting their work in a favorable light, which does not make them unreliable but does make them partial. Details that complicate the narrative, including instrument limitations, unexpected failures and results below projections, tend to be minimized relative to progress messages. Technical documentation and peer-reviewed publications, where they exist, provide the complementary layer that institutional releases cannot substitute.

The next step is to see whether other instruments and other wavelengths tell the same story. Campaigns with JWST, the VLT, the forthcoming Extremely Large Telescopes and radio arrays will provide the spectral coverage and spatial resolution needed to move from detection to physical characterization. The timeline for that kind of confirmation is typically measured in years, not months, which is worth keeping in mind when reading the current result.

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