A characterization of a comet nucleus interior: inversion of simulated radio frequency data

Radio transmission through the nucleus of the comet Wirtanen, as developed in the CONSERT experiment on the ROSETTA mission, is designed to provide in formation on the electrical properties of the cometary interior. In order t o determine what information can most readily be obtained, we first introdu ce an analytical model of the nucleus permittivity. We then use the WKB app roximation to describe the propagation of waves through the nucleus model a ssuming a radio frequency of 90 MHz, the frequency chosen for the experimen t. With one end of the propagation path on the surface of the comet, and th e other in a vehicle orbiting the nucleus, it is shown that the signal at t he orbiting end of the path must be 'back-propagated' to the surface of the nucleus of the comet in order to obtain a correct interpretation of the da ta. We show how the mean permittivity along each propagation path can be ob tained and how this can be used to obtain information about the large scale structure of the nucleus. Finally we discuss how the permittivity distribu tion found can be used to constrain the nature of the material in the inter ior of the nucleus. (C) 1999 Elsevier Science Ltd. All rights reserved.