A MARTIAN AND LUNAR VERY BROAD BAND SEISMOMETER S.Tillier (1) , S. de Raucourt (1) , P. Lognonné (1) , T. Nébut (1) , O.Robert (1) , T.Gabsi (1) , B.Lecomte (1) , O.Pot (1) , J. Gagnepain-Beyneix (1) , D.Mimoun (2) (1) PRES Paris-Cité, Institut de Physique du Globe de Paris, Planetary and Space Geophysics, Paris – FRANCE, Email: tillier@ipgp.fr (2) DEOS, ISAE, Toulouse – FRANCE ABSTRACT The very broad band seismometer (VBB) is a seismic sensor being developed by the Institut de Physique du Globe de Paris (IPGP) in France, under the founding of CNES, the French national space agency. It is part of a planetary seismometer being developed by an international consortium, which is currently a unit of the core payload for the Martian project GEMS- 2 from JPL (Jet Propulsion Laboratory, USA), but also for the SELENE-2 Japanese Lunar project (ISAS– JAXA). The VBB development relies on a solid technical heritage of a series of aborted Martian projects. But for the Moon’s conditions and environment, some design adaptations and performances enhancement have been required, ultimately leading to a new VBB design. 1. SCIENCE OBJECTIVES The main goal for planetary seismometers is to study the seismic activity of a planet and the meteorite flux at the planet’s surface. These seismic events are characterized by their approximate distance and azimuth, and their magnitude. The seismometer allows for the characterization of shallow and deep interior of the planet, and especially the deep subsurface layering structure, the crustal thickness of the landing site, the core size and the mantle structure. The power of seismology derives from the enormous amount of information encoded in a seismic signal. The vibrations detected by a seismometer reflect the characteristics of the original source, the geometry of the path taken from the source to the receiver (and thus the structure of the planet) and the physical properties of the material through which it has passed. The magnitude value of a seism is directly linked to the seismic signal frequency: the higher the magnitude, the lower the frequency. Therefore, the sensor bandwidth is linked to the type of signal to measure. Since one of the scientific goals of a planetary seismometer instrument is to measure deep quakes at low frequencies, a Very Broad Band (VBB) sensor is needed. 1.1. Mars In order to understand how a telluric planet is geologically evolving, a detailed knowledge of its interior structure, of the mineralogy and temperature of its mantle, of the amount of energy released during accretion (and therefore of the size of the main units of the planet: crust, mantle, core), of the heat flux and possibly of the large-scale convective structure is required. We also need to monitor its present geological activity and have a detailed view of its crust and subsurface. The level of present seismicity gives a measure of the contemporary level of tectonic and perhaps volcanic activity, both in terms of intensity and geographic distribution. Estimates of seismicity depend on thermal calculations or extrapolation of historical faulting. Thus the measurement of seismicity, regardless of the actual number of events detected, provides fundamental information about Mars’ dynamics. Regarding impacts, the unique characteristics of the seismograms they produce, characterized by a relatively low cutoff frequency, allow them to be differentiated from marsquakes. These seismograms can thus provide a direct measure of the current rate of impacts. Figure 1 gives an example of a prediction of the seismicity map of Mars that has been determined by the Monte Carlo simulation of seismic activity and releases a cumulated moment of 6x10 17 Nm per year. The epicenter location probability is provided by the density of observable surface faults (Knapmeyer, M., J. Oberst, E. Hauber, M. Waehlisch, C. Deuchler, R. Wagner, 2006). Figure 1 – Seismicity map of Mars ’ _________________________________________________ ‘14th European Space Mechanisms & Tribology Symposium – ESMATS 2011’ Constance, Germany, 28–30 September 2011 501