Open Archive TOULOUSE Archive Ouverte ( OATAO ) OATAO is an open access repository that collects the work of Toulouse researchers and makes it freely available over the web where possible. This is an author-deposited version published in: http://oatao.univ-toulouse.fr/ Eprints ID: 17283 To link this article: http://dx.doi.org/10.1016/j.pss.2011.10.016 To cite this version : Dehant, Veronique and Banerdt, Bruce and Lognonné, Philippe and Grott, Matthias and Asmar, Sami and Biele, Jens and Breuer, Doris and Forget, François and Jaumann, Ralf and Johnson, Catherine and Knapmeyer, Martin and Langlais, Benoit and Le Feuvre, Mathieu and Mimoun, David and Mocquet, Antoine and Read, Peter and Rivoldini, Attilio and Romberg, Oliver and Schubert, Gerald and Smrekar, Sue and Spohn, Tilman and Tortora, Paolo and Ulamec, Stephan and Vennerstrøm, Susanne Future Mars geophysical observatories for understanding its internal structure, rotation, and evolution. (2012) Planetary and Space Science, vol. 68 (n° 1). pp. 123-145. ISSN 0032-0633 Any correspondence concerning this service should be sent to the repository administrator: [email protected] Future Mars geophysical observatories for understanding its internal structure, rotation, and evolution Veronique Dehant a,n, Bruce Banerdt b, Philippe Lognonne´ c, Matthias Grott d, Sami Asmar b, Jens Biele e, Doris Breuer d, Franc-ois Forget f, Ralf Jaumann d, Catherine Johnson g,h, Martin Knapmeyer d, Benoit Langlais i, Mathieu Le Feuvre i, David Mimoun j, Antoine Mocquet i, Peter Read k, Attilio Rivoldini a,l, Oliver Romberg m, Gerald Schubert n, Sue Smrekar b, Tilman Spohn d, Paolo Tortora o, Stephan Ulamec e, Susanne Vennerstrøm p a Royal Observatory of Belgium, Belgium b Jet Propulsion Laboratory, USA c Institut de Physique du Globe, Sorbonne Paris Cite´, Univ. Paris Diderot, France d Institute of Planetary Research, DLR, Germany e German Space Operations Center/GSOC, DLR, Germany f Laboratoire de Me´te´orologie Dynamique, Paris, France g Department of Earth and Ocean Sciences, University of British Columbia, Vancouver, Canada h Planetary Science Institute, Tucson, USA i Laboratoire de Plane´tologie et Ge´odynamique, UMR 6112, Universite´ de Nantes, Nantes Atlantique Universite´s, CNRS, France j Universite´ de Toulouse, ISAE/Supaero, Toulouse, France k Atmospheric Oceanic and Planetary Physics, Oxford Physics, UK l Universite´ catholique de Louvain, Earth and Life Institute (ELI), Georges Lemaˆıtre Centre for Earth and Climate Research (TECLIM), Belgium m Institute of Space Systems (DLR), Bremen, Germany n University of California, Los Angeles, USA o University of Bologna, Italy p National Space Institute, Technical University of Denmark, Denmark abstract Our fundamental understanding of the interior of the Earth comes from seismology, geodesy, geochemistry, geomagnetism, geothermal studies, and petrology. For the Earth, measurements in those disciplines of geophysics have revealed the basic internal layering of the Earth, its dynamical regime, its thermal structure, its gross compositional stratification, as well as significant lateral variations in these quantities. Planetary interiors not only record evidence of conditions of planetary accretion and differentiation, they exert significant control on surface environments. Keywords: We present recent advances in possible in-situ investigations of the interior of Mars, experiments Interior structure and strategies that can provide unique and critical information about the fundamental processes of Rotation terrestrial planet formation and evolution. Such investigations applied on Mars have been ranked as a Magnetic field high priority in virtually every set of European, US and international high-level planetary science Heat flow Seismology recommendations for the past 30 years. New seismological methods and approaches based on the Mars cross-correlation of seismic noise by two seismic stations/landers on the surface of Mars and on joint Atmosphere seismic/orbiter detection of meteorite impacts, as well as the improvement of the performance of Very Habitability Broad-Band (VBB) seismometers have made it possible to secure a rich scientific return with only two simultaneously recording stations. In parallel, use of interferometric methods based on two Earth–Mars radio links simultaneously from landers tracked from Earth has increased the precision of radio science experiments by one order of magnitude. Magnetometer and heat flow measurements will complement seismic and geodetic data in order to obtain the best information on the interior of Mars. n Corresponding author. Tel.: þ322 373 0266; fax: þ322 374 9822. E-mail addresses: [email protected], [email protected] (V. Dehant), [email protected] (B. Banerdt), [email protected] (P. Lognonne´), [email protected] (M. Grott), [email protected] (S. Asmar), [email protected] (J. Biele), [email protected] (D. Breuer), [email protected] (F. Forget), [email protected] (R. Jaumann), [email protected] (C. Johnson), [email protected] (M. Knapmeyer), [email protected] (B. Langlais), [email protected] (M. Le Feuvre), [email protected] (D. Mimoun), [email protected] (A. Mocquet), [email protected] (P. Read), [email protected] (A. Rivoldini), [email protected] (O. Romberg), [email protected] (G. Schubert), [email protected] (S. Smrekar), [email protected] (T. Spohn), [email protected] (P. Tortora), [email protected] (S. Ulamec), [email protected] (S. Vennerstrøm). doi:10.1016/j.pss.2011.10.016 In addition to studying the present structure and dynamics of Mars, these measurements will provide important constraints for the astrobiology of Mars by helping to understand why Mars failed to sustain a magnetic field, by helping to understand the planet’s climate evolution, and by providing a limit for the energy available to the chemoautotrophic biosphere through a measurement of the surface heat flow. The landers of the mission will also provide meteorological stations to monitor the climate and obtain new measurements in the atmospheric boundary layer. 1. Introduction et al., 2006) and more recently to the determination of the core size and state with tidal measurement (Williams et al., 1996, 1.1. Why study Mars? 2001) and modern seismic processing (Weber et al., 2011; Garcia et al., 2011). Subsequently, with the development of seismic By studying other planets, we seek to understand the pro- networks on the Earth, seismology has mapped the structure of cesses that govern planetary evolution and discover the factors core–mantle boundary, density and phase changes in the mantle, that have led to the unique evolution of Earth. Why is Earth the three-dimensional velocity anomalies in the mantle related to only planet with surface liquid oceans, plate tectonics, and sub-solidus convection, and lateral variations in lithospheric abundant life? Mars is presently on the edge of the habitable structure. Additionally, seismic information places constraints zone, but may have been much more hospitable early in its on Earth’s interior temperature distribution and on the boundary history. Recent surveys of Mars suggest that the formation of conditions at the top and bottom of the outer core, which govern rocks in the presence of abundant water was largely confined to the mechanisms of geodynamo operation (e.g., Aubert et al., the earliest geologic epoch, the Noachian age (prior to 3.8 Ga) 2008). Thus physical properties inferred from seismic data are used (Poulet et al., 2005). This early period of Martian history was in almost any modeling of the Earth’s thermal and volatile evolution, extremely dynamic, witnessing planetary differentiation, forma- including the exchange of volatiles among different reservoirs tion of the core, an active dynamo, the formation of the bulk of (McGovern and Schubert, 1989; van Keken and Ballentine, 1999; the crust and the establishment of the major geologic divisions Franck and Bounama, 1997, 2000; Schubert et al., 2001; Guest and (Solomon et al., 2005). Formation of the crust and associated Smrekar, 2007; Smrekar and Guest, 2007), and their impact on the volcanism released volatiles from the interior into the atmo- long term habitability of the planet. sphere (Greeley, 1987; Phillips et al., 2001; Gillmann et al., 2009), The main difference between the Earth and Mars is that the causing conditions responsible for the formation of the familiar latter still preserves many billion year old crustal and potentially signs of liquid water on the surface of Mars, from the abundant mantle structures on a planetary spatial scale (e.g., the heavily channels, phyllosilicate formations and carbonate deposits to cratered southern hemisphere of Mars), while the ocean floor that sulfate-rich layered outcrops (Poulet et al., 2005; Clark et al., covers about two-thirds of the Earth’s surface is younger than 250 2005; Bridges et al., 2001; Ehlmann et al., 2008; Morris et al., million years, due to plate tectonics and associated recycling of 2010). the Earth’s lithosphere. Martian meteorite compositions indicate melting source regions with different compositions that have 1.2. Why study the geophysics of Mars? persisted since the earliest evolution of the planet (Jones, 1986; Borg et al., 1997, 2002). Further, much of the Martian crust dates Studying the geophysics of Mars, focusing on interior pro- to the first half billion years of solar system history (Frey et al., cesses