Philaeâ€™s SESAME-CASSE instrument â€˜listenedâ€™ to the landerâ€™s MUPUS instrument hammer the surface of Comet 67P/Churyumov-Gerasimenko last November.
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** SESAME-CASSE is the Cometary Acoustic Sounding Surface Experiment located in the landerâ€™s feet in the form of three accelerometers, each of which records acceleration in three directions (one vertical and two horizontal)
** MUPUS comprises the Multi-Purpose Sensors for Surface and Subsurface Science â€“ including the MUPUS penetrator that was activated towards the end of Philaeâ€™s first science sequence on 14 November 2014
It was recognized early in the preparation of both experiments that the hammering mechanism of MUPUS, which drives a thermal probe into the cometâ€™s surface, would serve as an acoustic source for sounding the subsurface with CASSE. The determination of the propagation velocity of sound would allow scientists to look at possible layering in the cometâ€™s surface/subsurface materials, important for understanding its evolution.
The CASSE instrument listened to the hammering of MUPUS for 2 hours and 15 minutes. Due to memory limitations, CASSE was not able to take continuous recordings, but only recorded a few seconds in one go.
A total of 15 hammer strokes were recorded; this audio file contains two signals. The time between the two strokes fits to the charge time of the hammer mechanism expected at that time, thus this particular recording proves that CASSE was really recording hammer strokes.
When recorded, the Philae lander and the comet were about 510 million kilometres from Earth.
Credit: ESA/Rosetta/Philae/SESAME/DLR (CC BY-SA IGO 3.0)
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