JuRa: the Juventas Radar on Hera to fathom Didymoon

Abstract:

The ESA Hera mission approved by the last ESA council Sapec19+ will be launched in 2024 to deeply investigate the Didymos binary system. In 2022, DART/NASA will impact the moonlet to quantify the mechanical response of the body, mainly from ground-based observation. Five years later, Hera is a unique opportunity to observe in detail the bodies, the crater and the ejecta in order to better constraints mechanical models. Hera will provide a global characterization of the binary system: shape, density, dynamic properties, thermal properties, composition,

Onboard the Juventas small platform, the JuRa radar will fathom Didymoon and provide the first direct observation of an asteroid deep interior. The JuRa instrument is a monostatic radar, BPSK coded at 60MHz carrier frequency and 20MHz bandwidth,

The first objective of JuRA is to characterize the moonlet’s interior, to identify internal geological structure such as layers, voids, sub-aggregate, to bring out the aggregate structure and to characterize its constituent blocks in terms of size distribution and heterogeneity at different scales (from submetric to global).

The second objective is to estimate the average permittivity and to monitor its spatial variation in order to retrieve information on its composition and porosity, especially in the area of the impact crater. Radar bypasses the near surface alteration by space-weathering and thermal-cycling as observed with optical remote sensing.

The same characterization applied to the main asteroid of the binary system is among the secondary objectives, to detect differences in texture and composition and to support the modeling of the binary system’s formation. Supporting shape modeling and the determination of the dynamic state through radar ranging are other secondary objectives.

Thus, the observation of the structure and composition of moonlet will provide constraints on the mechanical model of the impact process. By When compared to the observation of the main body, it will constraint the model of binary system formation to discriminate between progressive versus catastrophic process and more generally on the stability condition of the system.