[meteorite-list] The Sound of Philae's Touchdown on Comet 67P/Churyumov-Gerasimenko

[Ron Baalke]

http://blogs.esa.int/rosetta/2014/11/20/the-sound-of-touchdown/

The Sound of Touchdown
European Space Agency
November 20, 2014

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.


[Audio File]
Audio file credit: ESA/Rosetta/Philae/SESAME/DLR - USAGE: This file is 
copyright protected and is NOT now available under any CC licensing. It 
may be used only for non-profit, education or personal use. For any other 
use, please contact DLR, Institute of Planetary Research, Asteroids and 
Comets, Berlin, Klaus Seidensticker.

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