Listen to the ESA/JAXA BepiColombo spacecraft as it flew past Mercury on 8 January 2025. This sixth and final flyby used the little planet’s gravity to steer the spacecraft on course for entering orbit around Mercury in 2026.
What you can hear in the sonification soundtrack of this video are real spacecraft vibrations measured by the Italian Spring Accelerometer (ISA) instrument. The accelerometer data have been shifted in frequency to make them audible to human ears – one hour of measurements have been sped up to one minute of sound.
BepiColombo is always shaking ever so slightly: fuel is slightly sloshing, the solar panels are vibrating at their natural frequency, heat pipes are pushing vapour through small tubes, and so forth. This creates the eerie underlying hum throughout the video.
But as BepiColombo gets closer to Mercury, ISA detects other forces acting on the spacecraft. Most scientifically interesting are the audible shocks that sound like short, soft bongs. These are caused by the spacecraft responding to entering and exiting Mercury’s shadow, where the Sun’s intense radiation is suddenly blocked. One of ISA’s scientific goals is to monitor the changes in the ‘solar radiation pressure’ – a force caused by sunlight striking BepiColombo as it orbits the Sun and, eventually, Mercury.
The loudest noises – an ominous ‘rumbling’ – are caused by the spacecraft’s large solar panels rotating. The first rotation occurs in shadow at 00:17 in the video, while the second adjustment at 00:51 was also captured by one of the spacecraft’s monitoring cameras.
Faint sounds like wind being picked up in a phone call, which grow more audible around 30 seconds into the video, are caused by Mercury’s gravitational field pulling the nearest and furthest parts of the spacecraft by different amounts. As the planet’s gravity stretches the spacecraft ever so slightly, the spacecraft responds structurally. At the same time, the onboard reaction wheels change their speed to maintain the spacecraft’s orientation, which you can hear as a frequency shift in the background.
This is the last time that many of these effects can be measured with BepiColombo’s largest solar panels, which make the spacecraft more susceptible to vibrations. The spacecraft module carrying these panels will not enter orbit around Mercury with the mission’s two orbiter spacecraft.
The video shows an accurate simulation of the spacecraft and its route past Mercury during the flyby, made with the SPICE-enhanced Cosmographia spacecraft visualisation tool. The inset that appears 38 seconds into the video shows real photographs taken by one of BepiColombo’s monitoring cameras.
Credits: ESA/BepiColombo/ISA & MTM
Acknowledgements: Sonification and SPICE-enhanced Cosmographia spacecraft visualisation by Carmelo Magnafico (IAPS/INAF)
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