Posted on 20/11/2014 by Claudia
The sound of touchdown
Sensors in the feet of Rosetta’s lander Philae have recorded the sound of touchdown as it first came into contact with Comet 67P/Churyumov-Gerasimenko. The instrument, SESAME-CASSE, was turned on during the descent and clearly registered the first touchdown as Philae came into contact with the comet, in the form of vibrations detected in the soles of the lander’s feet.
Image credit: ESA/ATG medialab
Audio file credit: ESA/Rosetta/Philae/SESAME/DLR – CC BY-SA IGO 3.0
Note that this is an actual sound file; i.e. it is a recording of mechanical vibrations at acoustic frequencies. No modification was necessary except for some technical adjustments (e.g. the .wav format requires amplitude normalisation). Actual frequency content and duration are unchanged.
SESAME is the lander’s Surface Electrical Sounding and Acoustic Monitoring Experiment, and comprises three suites of instruments:
- CASSE – the Comet Acoustic Surface Sounding Experiment, which allows mechanical parameters of the surface to be deduced, along with details of the structure of the subsurface;
- DIM – the Dust Impact Monitor, which measures properties of impacting comet grains;
- PP – the Permittivity Probe, which determines one of the key electrical properties of the material beneath Philae, which is linked to the water ice content of the surface.
Klaus Seidensticker from the DLR Institute of Planetary Research says: “Our data record the first touchdown and show that Philae’s feet first penetrated a soft surface layer – possibly a dust layer – several centimetres thick until they hit a hard surface – probably a sintered ice-dust layer – a few milliseconds later.”
Data from the SESAME-DIM instrument meanwhile suggest that current cometary activity at the final landing site is low, while preliminary data from SESAME-PP are consistent with a large amount of water ice under the lander. Combined with additional data from other instruments, the goal is to derive mechanical properties of the comet. However, first impressions already suggest that the surface of 67P/C-G is significantly structured, mixing soft and hard aspects.
Klaus adds: “At the moment, we are also supporting the effort to reconstruct the flight path of the lander after first touchdown, collecting all available data across the various instruments. This is important for SESAME, especially CASSE, as we need to know the speed, impact angle, and rotation rate before the first touchdown, but also the final landing place.”
SESAME Principal Investigators:
CASSE: Klaus Seidensticker (PI for the SESAME consortium), German Aerospace Center, Institute of Planetary Research, Asteroids and Comets, Berlin, Germany
DIM: Harald Krueger, Max-Planck-Institute for Solar System Research, Göttingen, Germany
PP: Walter Schmidt, Finnish Meteorological Institute, Helsinki, Finland