Philae’s SESAME-CASSE ‘listened’ to a lander’s MUPUS instrument produce a aspect of Comet 67P/Churyumov-Gerasimenko final November. Martin Knapmeyer from a German Aerospace Centre, DLR, tells us more.
SESAME-CASSE is a Cometary Acoustic Surface Sounding Experiment located in a lander’s feet. It takes a form of 3 accelerometers, any of that annals acceleration in 3 directions (one straight and dual horizontal). MUPUS comprises a Multi-Purpose Sensors for Surface and Subsurface Science – including a MUPUS penetrator that was activated towards a finish of Philae’s initial scholarship method on 14 Nov 2014.
It was famous early in a credentials of both experiments that a hammering resource of MUPUS, that drives a thermal examine into a comet’s surface, would offer as an acoustic source for ‘sounding’ a subsurface with CASSE. The integrity of a propagation quickness of sound would concede scientists to demeanour during probable layering in a comet’s aspect and subsurface materials, critical for bargain a evolution.
The CASSE instrument listened to a hammering of MUPUS for 2h 15 min. Due to memory limitations, CASSE was not means to take continual recordings, though usually a few seconds during a time. Several watchful durations were also enclosed to give MUPUS time to strech inlet of 10 cm, 20 cm, and 30 cm. A sum of 15 produce strokes were recorded, and one of a recordings contains dual signals (the initial sound, left, is listened during about 3 and 9 seconds respectively). The time between a strokes matches a assign time of a produce resource approaching during that time, so this sold recording proves that CASSE was unequivocally recording produce strokes.
The second sound record (below) contains produce cadence no. 129 (as dynamic from a MUPUS housekeeping catalogue), that was available on Philae’s +Y foot. This cadence was executed during a top appetite turn of a produce system. All 3 channels of a +Y feet are churned into a sound file, that is presented during genuine playback speed, in stereo. The signals on a other dual feet were, in this case, most weaker and their recordings would especially supplement to a credentials noise.
By looking during a strength and peculiarity of a signals perceived by any foot, conclusions could be drawn about a course of Philae on a aspect of a comet. Signal peculiarity differs between feet, though several strokes were available on all 3 feet. From this a CASSE group concludes that all 3 feet of Philae have automatic tie to a surface.
The CASSE group can also sequence out that signals propagated by a structure of a lander only, given we see attainment time delays of several milliseconds between a particular feet, while delays due to asymmetries in a lander would volume to reduction than a sampling interlude (i.e. microseconds). Signals roving by Philae’s structure would so arrive synchronously during all feet rather than feet by foot.
“The CASSE listening examination has valid to be a initial active seismic examination conducted on a astronomical physique given a lunar seismic profiling examination carried out by Apollo 17 astronauts on a Moon in 1972,” says Martin.
He adds: “The geological interpretation of a comet information is still ongoing. We performed unequivocally low call propagation velocities, standard for loose, rarely porous materials though we still have to analyse what clues on layering we have in sequence to determine this with a inability of MUPUS to significantly dig a ground.”
Source: Rosetta blog