• Plettemeier, D.
• Herique, A.
• Zine, S.
• Krause, C.
• Team, Assert
• Souyris, J.
• Ulamec, S.
• Michel, Patrick
• Prado, J.
• Kofman, W. W.
• Barucci, A.
• Biele, J.
• Ho, T.

Abstract

The internal structure of NEAs remains largely unknown. It is a key point for the understanding of asteroid accretion and dynamical evolution. From a science point of view, the internal structure is also a key point for the understanding of asteroid accretion and dynamical evolution. For risk management and mitigation, it is required to characterize whether a small asteroid will survive the transit through the atmosphere and also to define a deflection policy. There are some indirect evidences that a rubble pile structure is really common at least for objects larger than a few hundreds of meters in diameter. But a more precise characterisation of the internal structure is required, such as the size and the structure of the main blobs and their distribution within the NEAs main body as well as a statistical characterisation of the surface regolith in term of density and size distribution. Radar tomography is the only way to image the internal structure from decimetric to global scale in order to better understand the nature of the primary object and its posterior alterations. It is also a way to estimate the ratio between micro- and macro-porosity. Bistatic radar tomography is an original technique, developed with the CONSERT Experiment (Rosetta / ESA) to image ant characterize the internal structures of 67P/Churyumov-Gerasimeko with a signal transmitted from the Orbiter to the Lander. By regards to a more classical monostatic radar like Marsis (MarsExpress/ESA), this bistatic configuration requires limited resources (mass, power and dataflow) and increases the capacity of deep sounding. So ASSERT (ASteroid Sounding Experiment by Radiowave Transmission) is proposed to instrument a MASCOT-type lander e.g. as payload of the ESA Marco Polo R mission (ESA). The first addressed question is a rubble pile or a monolithic body: For a rubble pile, the tomography will allow to estimate the size distribution of the boulders by direct imaging or statistical analysis of the scattered signal. The estimation of the mean permittivity of the blobs is a way to estimate the macro- versus micro-porosity. Its spatial variations highlight the heterogeneity of the parent bodies and segregation mechanism during reaccretion. - And for a monolithic object, we can expect only micro-porosity. Then images of the body interior and spatial distributions of the permittivity give the heterogeneity. In a further analysis, the characterization of the heterogeneity by statistical or imagery approach is a key point to understand asteroid accretion and evolution: - is this body accreted or re-accreted from the same material or not, from similar parent bodies or not? - is there some evidence of collisional metamorphism with change in the porosity and or mineralogy? - is there some evidence of metamorphism per hydration? This advanced interpretation will be based on the sample return analysis and constitutes a complete recontextualization of the analyzed samples at the global body scale

Topics

• density
• impedance spectroscopy
• surface
• experiment
• tomography
• porosity