Towards New Comet Missions

The Rosetta observations have greatly advanced our knowledge of the cometary nucleus and its immediate environment. However, constraints on the mission (both planned and unplanned), the only partially successful Philae lander, and other instrumental issues have inevitably resulted in open questions. Surprising results from the many successful Rosetta observations have also opened new questions, unimagined when Rosetta was first planned. We discuss these and introduce several mission concepts that might address these issues. It is apparent that a sample return mission as originally conceived in the 1980s during the genesis of Rosetta would provide many answers but it is arguable whether it is technically feasible even with today’s technology and knowledge. Less ambitious mission concepts are described to address the suggested main outstanding scientific goals

GPR, a ground‐penetrating radar for the Netlander mission

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/95485/1/jgre1563.pd

The Thermal, Mechanical, Structural, and Dielectric Properties of Cometary Nuclei After Rosetta

The physical properties of cometary nuclei observed today relate to their complex history and help to constrain their formation and evolution. In this article, we review some of the main physical properties of cometary nuclei and focus in particular on the thermal, mechanical, structural and dielectric properties, emphasising the progress made during the Rosetta mission. Comets have a low density of 480±220 kgm−3 and a low permittivity of 1.9–2.0, consistent with a high porosity of 70–80%, are weak with a very low global tensile strength −1m−2s−1/2 that allowed them to preserve highly volatiles species (e.g. CO, CO2, CH4, N2) into their interior since their formation. As revealed by 67P/Churyumov-Gerasimenko, the above physical properties vary across the nucleus, spatially at its surface but also with depth. The broad picture is that the bulk of the nucleus consists of a weakly bonded, rather homogeneous material that preserved primordial properties under a thin shell of processed material, and possibly covered by a granular material; this cover might in places reach a thickness of several meters. The properties of the top layer (the first meter) are not representative of that of the bulk nucleus. More globally, strong nucleus heterogeneities at a scale of a few meters are ruled out on 67P’s small lobe

A porosity gradient in 67P/C-G nucleus suggested from CONSERT and SESAME-PP results: an interpretation based on new laboratory permittivity measurements of porous icy analogues

The Rosetta spacecraft made a rendezvous with comet 67P/Churyumov-Gerasimenko (67P) in 2014 August, soon after the Philae module landed on the small lobe of the nucleus on 2014 November 12. The CONSERT instrument, onboard Rosetta and Philae, sounded the upper part of the interior of 67P with radiowaves at 90 MHz and determined an average of the real part of the permittivity (hereafter ) equal to about 1.27. The SESAME-PP instrument, onboard Philae, sounded the near-surface of the small lobe in the 400–800 Hz range and determined a lower limit of equal to 2.45. We use a semi-empirical formula obtained from measurements of performed in the laboratory at 243 K on water ice and ice-basaltic dust mixtures, with a controlled porosity in the 31–91 per cent range and a dust-to-ice volumetric ratio in the 0.1– 2.8 range, to interpret the results of the two instruments, taking into account the temperature and frequency dependences. A graphical method is proposed to derive ranges of porosity and dust-mass fraction from a value of derived from observations. The non-dispersive behaviour of below 175 K, allows us to compare the values of obtained by CONSERT and SESAME-PP. We show that the porosity of the small lobe of 67P increases with depth. Based on new measurements of analogues of complex extraterrestrial organic matter, the so-called tholins, we also suggest that, for the dust component in the cometary material, the presence of silicates has more effect on than organic materials

Exploring the Martian Subsurface with Ma_MISS EXOMARS 2022

International audienc

Performances of the WISDOM GPR Designed for the Shallow Sounding of Mars

WISDOM (Water Ice and Subsur-face Deposit Observations on Mars) is a Ground Pene-trating Radar (GPR) that is one of the panoramic in-struments selected to be part of the Pasteur payload onboard the Rover of the ExoMars mission. These Pas-teur Panoramic Instruments (the wide angle camera PANCAM, the infrared spectrometer MIMA and WISDOM) will perform large-scale scientific investi-gations at the sites the Rover will visit. Among these instruments, WISDOM is the only one that can provide information about the subsurface structure prior to drilling. WISDOM has been designed to characterize the shallow subsurface structure of Mars. It will give access to the geological structure, electromagnetic na-ture, and, possi-bly, to the hydrological state of the shallow subsurface by retrieving the layering and prop-erties of the buried reflectors. In addition, the data it will provide will be used to determine the most promis-ing locations at which to obtain underground samples with the drilling system mounted on board the rover. This paper describes the WISDOM instrument particular attention is paid on its antennas design as well as on its operations during the mission. Eventually the first measurements performed with a WISDOM prototype on Earth are presented. They show very promising results to well below 2-meter depth

Etude des situations météorologiques donnant lieu à des phénomènes de trajets multiples

Le travail présenté s'inscrit dans le programme d'étude des trajets multiples et de leurs effets sur les liaisons radioélectriques engagé au RPE depuis 1982. Il s'agit ici d'estimer l'importance potentielle des variations horizontales de l'indice de réfraction atmosphérique. Nous nous sommes servis pour notre étude de mesures radiométéorologiques obtenues par un avion instrumenté de la Météorologie Nationale au cours de l'expérience PACEM 3 (Propagation en Air Clair et Météorologie). Après quelques rappels sur les phénomènes étudiés (chapitre II), une présentation de l'expérience (chapitre ni) et une description du traitement des données (chapitre IV), toujours très important dans les études radiométéorologiques, nous nous livrons à deux études de cas pour lesquels il a été possible de reconstituer avec une vraisemblance raisonnable la structure bidimensionnelle de l'indice de réfraction (chapitres V et VI). Ayant ainsi des données quantitatives concernant les gradients d'indice, tant horizontaux que verticaux, on a pu interpréter correctement, à l'aide de simulations par tracés de rayons, les observations radioélectriques concomitantes (chapitres VII et VIII). Cette étude montre que si les gradients verticaux sont nécessaires à l'occurrence de trajets multiples, la prise en compte dès gradients horizontaux peut être nécessaire à une description fine des observations. Dans le dernier chapitre, nous étendons ces résultats en regardant par simulation quels paramètres de la structure de l'indice atmosphérique sont les plus susceptibles d'affecter la propagation.132 pages, figure