Results from the First Field Tests of the WISDOM GPR (2018 ExoMars Mission)

International audienceIntroduction: The WISDOM (Water Ice Subsur- face Deposit Observation on Mars) Ground Penetrating Radar (GPR) is one of the instruments that have been selected as part of the Pasteur payload of ESA’s 2018 ExoMars Rover mission[1]. The Pasteur payload actu- ally consists of two different sets of instruments: the Panoramic Instruments, which include a wide angle camera and the WISDOM radar, that will be used to perform large-scale scientific investigations of the landing site and the Analytical Laboratory Instruments that will analyze the core samples obtained by the sub- surface drill. WISDOM will help identify the location of sedimentary layers, where organic molecules are the most likely to be found and well-preserved. WISDOM has been designed to investigate the near subsurface environment down to a depth of ~2-3 m with a vertical resolution of a few centimeters [2]. WISDOM is a step frequency radar operating over a wide frequency band between 0.5 and 3 GHz. Particular attention was paid to the design of the antenna system, which needs to be able to conduct polarimetric measurements over the whole bandwidth without significant distortion [3]

CONSERT suggests a change in local properties of 67P/Churyumov-Gerasimenko's nucleus at depth

International audienceAfter the successful landing of Philae on the nucleus of 67P/Churyumov-Gerasimenko, the Rosetta mission provided the first opportunity of performing measurements with the CONSERT tomographic radar in November 2014. CONSERT data were acquired during this first science sequence. They unambiguously showed that propagation through the smaller lobe of the nucleus was achieved. Aims. While the ultimate objective of the CONSERT radar is to perform the tomography of the nucleus, this paper focuses on the local characterization of the shallow subsurface in the area of Philae’s final landing site, specifically determining the possible presence of a permittivity gradient below the nucleus surface.Methods. A number of electromagnetic simulations were made with a ray-tracing code to parametrically study how the gradient of the dielectric constant in the near-subsurface affects the ability of CONSERT to receive signals.Results. At the 90 MHz frequency of CONSERT, the dielectric constant is a function of porosity, composition, and temperature. The dielectric constant values considered for the study are based on observations made by the other instruments of the Rosetta mission, which indicate a possible near-surface gradient in physical properties and on laboratory measurements made on analog samples. Conclusions. The obtained simulated data clearly show that if the dielectric constant were increasing with depth, it would have prevented the reception of signal at the CONSERT location during the first science sequence. We conclude from our simulations that the dielectric constant most probably decreases with depth

Habitability on Early Mars and the Search for Biosignatures with the ExoMars Rover

The second ExoMars mission will be launched in 2020 to target an ancient location interpreted to have strong potential for past habitability and for preserving physical and chemical biosignatures (as well as abiotic/prebiotic organics). The mission will deliver a lander with instruments for atmospheric and geophysical investigations and a rover tasked with searching for signs of extinct life. The ExoMars rover will be equipped with a drill to collect material from outcrops and at depth down to 2 m. This subsurface sampling capability will provide the best chance yet to gain access to chemical biosignatures. Using the powerful Pasteur payload instruments, the ExoMars science team will conduct a holistic search for traces of life and seek corroborating geological context information. Key Words: Biosignatures—ExoMars—Landing sites—Mars rover—Search for life. Astrobiology 17, 471–510

Findings from the PP-SESAME experiment on board the Philae/ROSETTA lander on the surface of comet 67P

International audienceThe Permittivity Probe (PP-SESAME [1]) on-board the Philae Lander of the ROSETTA mission was designed to constrain the complex permittivity of the first 2 meters of the nucleus of comet 67P/Churyumov-Gerasimenko and to monitor its variations with time. Doing so, it is meant to provide unique insight into the composition (and activity if data could have been acquired longer) of the comet. In this paper, we present the analysis of the PP-SESAME measurements acquired during the first science sequence, on November 13, 2014, on the surface of the comet

The WISDOM Radar: Unveiling the Subsurface Beneath the ExoMars Rover and Identifying the Best Locations for Drilling

The search for evidence of past or present life on Mars is the principal objective of the 2020 ESA-Roscosmos ExoMars Rover mission. If such evidence is to be found anywhere, it will most likely be in the subsurface, where organic molecules are shielded from the destructive effects of ionizing radiation and atmospheric oxidants. For this reason, the ExoMars Rover mission has been optimized to investigate the subsurface to identify, understand, and sample those locations where conditions for the preservation of evidence of past life are most likely to be found. The Water Ice Subsurface Deposit Observation on Mars (WISDOM) ground-penetrating radar has been designed to provide information about the nature of the shallow subsurface over depth ranging from 3 to 10 m (with a vertical resolution of up to 3 cm), depending on the dielectric properties of the regolith. This depth range is critical to understanding the geologic evolution stratigraphy and distribution and state of subsurface H2O, which provide important clues in the search for life and the identification of optimal drilling sites for investigation and sampling by the Rover's 2-m drill. WISDOM will help ensure the safety and success of drilling operations by identification of potential hazards that might interfere with retrieval of subsurface samples

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

International audienc

Une diversité de radars conçus pour révéler et caractériser les structures cachées des petits corps et planètes du système solaire

International audienceSince the very first observations of the Moon from the Earth with radar in 1946, radars are more and more frequently selected to be part of the payload of exploration missions in the Solar System. They are, in fact, able to collect information on the surface structure of bodies or planets hidden by opaque atmospheres, to probe the planet subsurface or even to reveal the internal structure of a small body comet nucleus.A brief review of radars designed for the Solar System planets and bodies’ exploration is presented in the paper. This review does not aim at being exhaustive but will focus on the major results obtained. The variety of radars that have been or are currently designed in terms of frequency or operational modes will be highlighted.Depuis les premières observations radar de la Lune depuis la Terre en 1946, les radars font de plus en plus fréquemment partie de la charge utile des missions d’exploration du système solaire. Ils sont, en effet, capables de recueillir des informations à la fois sur la structure superficielle d’un corps ou d’une planète à travers une atmosphère optiquement opaque, de sonder le sous-sol d’une planète, ou encore de révéler la structure interne d’un petit corps.Une revue non exhaustive des radars scientifiques développés pour l’exploration des planètes et autres corps du système solaire est présentée dans cet article. Quelques résultats majeurs sont présentés. L’accent est mis sur la variété des radars qui ont été et sont actuellement conçus en terme de fréquence ou de mode opératoire en fonction des contraintes de la mission et des objectifs visés

Exploring the hidden structures and properties of the Solar System's planets and bodies with radars

International audienceDepuis les premières observations de la Lune depuis la Terre avec un radar en 1946, les radars font de plus en plus fréquemment partie de la charge utile des missions d'exploration du système solaire. Ils sont, en effet, les seuls instruments à pouvoir recueillir, à partir de plateformes en orbite des informations sur la structure superficielles d'un corps ou d'une planète à travers des atmosphères opaques (mission MAGELLAN pour Venus et mission CASSINI pour Titan), ou sonder le sous-sol d'une planète a travers sa surface (radar MARSIS de la mission MarsExpress et SHARAD de la mission Mars reconnaissance Orbiter pour Mars). Très récemment la mission Rosetta a permis de mettre en oeuvre le radar bistatique CONSERT qui a été conçu pour étudier la structure interne du noyau de la comète 67P/Churyumov-Gerasimenko. Les prochaines missions ExoMars (ESA/Roskosmos, 2018) et Mars2020 (NASA, 2020) poseront chacune à la surface de Mars un véhicule équipé d'un radar à pénétration de sol. Des informations capitales pour comprendre l'histoire géologique des sites d'atterrissage seront fournies par ces GPR. Une revue des résultats obtenus par ces différents radars scientifiques sera présentée dans cet article

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

Evaluation of the first simulation tool to quantitatively interpret the measurements of the ExoMars mission's Wisdom GPR

The Water Ice Sub-surface Deposits Observation on Mars (WISDOM) (500MHz - 3GHz) GPR is one of the instruments that have been selected as part of the Pasteur payload of ESA's 2018 ExoMars Rover mission. One of the main scientific objectives of the mission is to characterize the nature of the shallow sub-surface on Mars and WISDOM has been designed to explore the first 3 meters of the sub-surface with a vertical resolution of a few centimetres. Laboratory and field tests using the prototype developed for the ExoMars mission by LATMOS (Laboratoire Atmosphère, Milieux, Observations Spatiales) in collaboration with the AOB (Bordeaux) and the university of Dresden (Germany) are regularly performed to assess and improve the radar performances. In order to quantitatively interpret the experimental data obtained, we developed a simulation tool based on ray-tracing. This code proves to be a fast practical way even if simplified to help radargrams interpretation. The WISDOM GPR, unlike most traditional GPRs, is operated approximately 30 centimetres above the surface. This configuration implies that the propagation between the antenna and the surface cannot be neglected especially because the instrument's aim is to characterise the very shallow subsurface. As a consequence, while we can draw advantage of this specific configuration by using the surface echo's amplitude to retrieve information about the top layer's roughness and permittivity value, precise location of buried reflector becomes more complicated. Indeed, the signature distinctive of individual reflectors buried in the sub-surface is not more an exact mathematical hyperbola. When the individual reflector is buried deep enough in the subsurface, the adjustment by an hyperbolic function still allows the retrieval of the reflector's location and the permittivity value of the surrounding medium. But in case of a reflector closer to the surface, the approximation is no longer valid. We propose a robust model adjustment that can be used for any reflector's depth. The physical assumptions taken into account are presented. Finally, results for different configurations and the validation of the limit conditions for which this adjustment method is reliable are shown. Preliminary analyzes on real data show the good performance of the method developed. Other modelling techniques will be considered to complete a full data interpretation taking the best from the instrument capacitie