The GEMS-2 Seis Experiment

The objective of the Mars SEIS experiment is the determination of the deep internal structure of Mars. In particular, geophysical parameters of first importance, such as the state (liquid/solid) and size of the core, as far as structure of the mantle and shape of discontinuities will be determined by the experience. It will measure seismic activity in a very broad band of signal, from the tidal frequencies (0.05 mHz) up to the short period frequencies (50 Hz), to address the widest range of scientific questions, from the state of the inner core to the meteoritic rate measurement. The instrument integrates a Very Broad Band 3 axis seismometer, completed by another trihedron of MEMS short period seismometers, and environmental sensors for pressure, wind and temperature. The sensors will be deployed on the Martian ground by a robotic arm and protected by a wind and thermal shield. Long term VBB bias will be protected from both temperature and pressure variations (as well as passively compensated), allowing the sensor to operate in the rough Martian thermal environment. The sensor assembly, which contains all seismic sensors, as well as house-keeping and temperature measurements, will be deployed on the ground, in order to allow the best possible mechanical coupling. Infrasound, which might be associated to dust devils and atmospheric discharge, will be also monitored. The overall mass of the SEIS instrument is about 6 kg, including all sensors, data control processors and installation devices. A dedicated electronics will manage the overall experiment and ultra-low noise, space qualified 24 bits A/D converters will perform the acquisition. The instrument operation is designed to be very simple. It will operate in a “deploy and forget” strategy (with a deployment and closely monitored during the first month however) uploading data and events of interests at each pass of the relay satellite. When relay is not available, the data will be stored on-board. The upload of data will be made on the basis of raw compressed data, plus an excerpt of the high frequency events of the day. The proposed instrument has been developed up to PDR in the frame of the ExoMars Humbold payload. Most critical parts have been tested, including shock tests for pivot, electronics components and displacement sensors. TRL 6 is expected at the end of 2011. SEIS has been proposed onboard the GEMS Mission Proposal, submitted to NASA in the frame of the 2010 Discovery AO.