The European Space Agency (ESA) has published an audio recording made from data from the BepiColombo spacecraft. It recorded its encounter with Mercury.
On January 8, 2025, BepiColombo performed its sixth and final gravity maneuver in the vicinity of Mercury. The next encounter with the planet will be as early as November 2026, so the spacecraft will enter a permanent orbit around it this time.
During the Mercury flyby, a number of instruments — including the Italian Spring Accelerometer (ISA) — were activated aboard BepiColombo. It recorded the actual vibrations the vehicle experienced as it flew by the planet. The accelerometer data was frequency shifted to make it audible to the human ear. One hour of measurement was accelerated to one minute of sound. The audio recording is complemented by a video sequence with accurate modeling of the route and position of the spacecraft. The inset, which appears at the 38th second of the video, shows actual photos taken by one of BepiColombo’s cameras.
A constant eerie background hum can be heard on the recording. These are normal spacecraft vibrations that are caused by propellant movement, solar panel vibration, and cooling system operation.
But as BepiColombo approached Mercury, other forces began to act on the vehicle, which also caught on the recording. The most scientifically interesting are tremors, which sound like short, soft thumps. They are caused by the vehicle’s reaction to enter and exit the planet’s shadow when the Sun’s intense radiation is suddenly blocked. One of ISA’s scientific goals is to track the changes in solar radiation “pressure” to which BepiColombo will be subjected in orbit around Mercury.
The loudest sounds are caused by the rotation of the spacecraft’s large solar panels. The first rotation occurs in the planet’s shadow at 00:17 in the video, and the second rotation at 00:51 can also be seen in the instrument’s selfie camera footage.
The faint sounds, similar to the wind noise of a phone call that gets louder around the 30th second of the video, are caused by Mercury’s gravitational field stretching the spacecraft slightly. To keep BepiColombo properly oriented, its flywheel motors have changed their speed, which can be heard as a frequency shift in the background.