Radar tomography of asteroid deep interior. JuRa / HERA to DIDYMOS and Ra proposed to APOPHIS

Our knowledge of the internal structure of asteroids relies entirely on inferences from remote sensing observations of the surface and theoretical modeling. Is the body a monolithic piece of rock or a rubble-pile, and how high is the porosity? What is the typical size distribution of the constituent blocks? Are these blocks homogeneous or heterogeneous? Direct measurements of an asteroid’s deep interior structure are needed to better understand asteroid accretion and their dynamic evolution. The characterization of the asteroids’ internal structure is crucial for science, planetary defense and exploration. In orbit Radar sounding is the most mature instruments capable of achieving the objective of characterizing the internal structure and heterogeneity, for the benefit of science as well as for planetary defense or exploration.

This is the goal of JuRa, the Juventas radar, onboard the ESA HERA mission. JuRa is a monostatic radar, BPSK coded at 60MHz carrier frequency and 20MHz bandwidth, inherited from CONSERT/Rosetta. The instrument design is under integration on Juventas cubesat for the ESA HERA mission. HERA will be launched this autumn to deeply investigate the Didymos binary system and especially its moonlet Dimorphos, five years after the DART/NASA impact. The main objective of JuRA is to characterize the asteroid interior, to identify internal geological structure such as layers, voids and sub-aggregates, to bring out the aggregate structure and to characterize its constituent blocks in terms of size distribution from submetric to global scale. 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.

This radar is also proposed to probe Asteroid 99942 Apophis in 2029, a potentially dangerous asteroid which will then approach Earth as close as 32000 kilometers on the DROID JPL/CNES and the RAMSES ESA proposed missions. This radar, which is a modified version of JuRa, will be able to operate in both monostatic and bistatic modes between orbiting or landed CubeSats. The knowledge of Apophis’ internal structure is crucial to improve our ability to study its stability conditions and to model its response to the gravitational constraints induced by Earth close approach. The Multipass processing will allow us to build a 3D tomographic image of the interior at different scales from submeter to global.

In this talk will present the instrument, its status, performances and goals as well as the science objectives in the context of the different targets.