FANTINA instrument suite: A payload proposed to measure the asteroid's structure from deep interior to regolith

Our knowledge of the internal structure of asteroids is, so far, indirect - relying entirely on inferences from remote sensing observations of the surface, and theoretical modeling. What are the properties of the regolith and deep interior? And what are the physical processes that shape their internal structures? Is it a rubble pile or a monolith? In the first case: what is the size distribution of constituent blocks, and the spatial distribution of voids? Direct measurements are needed to provide answers to these fundamental questions that will directly improve our ability to understand the geologic context of the asteroid from which the returned samples will be collected. After a review of the science objectives, this paper presents the FANTINA instrument suite, proposed to instrument Marco Polo R mission and specifically designed to help to answer these questions and support sample acquisition and analysis. The FANTINA science package, in the form of a lander with a radar component onboard the orbiter, is aimed at understanding the physical structure and evolution of the building blocks of the planets at various scales. FANTINA will use radar sounding, a penetrating geophysical technique, to investigate the internal structure of the asteroid. A bistatic radar, FANTINA-B, utilizes a separate transmitter and receiver (on orbiter and lander, similar to the CONSERT radar on ROSETTA) to conduct tomographic investigations of the global deep interior. On the lander this method will be used in combination with a visible imaging system (Camera, FANTINA-C) and accelerometer (Accelerometric sensor, FANTINA-A) to characterize the structure and physical properties of the near surface. A monostatic radar (FANTINA-M, a WISDOM-like instrument) accommodated onboard the orbiter will probe the first ten meters of the regolith and provide an understanding of the transition from the surface environment, where samples are collected, to the deep interior.