Theoretical and experimental studies of electromagnetic resonances in the ionospheric cavities of planets and satellites; instrument and mission perspectives Fernando dos Santos Simoes To cite this version: Fernando dos Santos Simoes. Theoretical and experimental studies of electromagnetic resonances in the ionospheric cavities of planets and satellites; instrument and mission perspectives. Instrumentation and Methods for Astrophysic [astro-ph.IM]. Université Pierre et Marie Curie - Paris VI, 2007. English. NNT : 2007PA066424. tel-00811520 HAL Id: tel-00811520 https://tel.archives-ouvertes.fr/tel-00811520 Submitted on 10 Apr 2013 HAL is a multi-disciplinary open access L’archive ouverte pluridisciplinaire HAL, est archive for the deposit and dissemination of sci- destinée au dépôt et à la diffusion de documents entific research documents, whether they are pub- scientifiques de niveau recherche, publiés ou non, lished or not. The documents may come from émanant des établissements d’enseignement et de teaching and research institutions in France or recherche français ou étrangers, des laboratoires abroad, or from public or private research centers. publics ou privés. THESE DE DOCTORAT DE L’UNIVERSITE PIERRE ET MARIE CURIE Spécialité Physique, ED 389 Présentée par M. Fernando António DOS SANTOS SIMÕES Pour obtenir le grade de DOCTEUR de L’UNIVERSITÉ PIERRE ET MARIE CURIE Résonances des cavités ionosphériques des planètes et de leurs satellites: progrès et perspectives instrumentales Soutenue le 7 de Décembre de 2007 devant le jury composé de: Mme. Laurence REZEAU (Présidente) M. François LEFEUVRE (Rapporteur) M. Christian MAZELLE (Rapporteur) M. Michel HAMELIN (Directeur de thèse) M. Christian BÉGHIN (Examinateur) M. Jean-Jacques BERTHELIER (Examinateur) M. Réjean GRARD (Examinateur) M. Jean-Pierre LEBRETON (Examinateur) Este trabalho é dedicado a todos os homens e mulheres que têm dentro de si uma vontade insaciável de conhecer, de olhar o infinito e tentar transpô-lo. Esta tese é um tributo a todos os que procuram, sabiamente, chegar sempre mais alto e promovem o conhecimento científico como um extraordinário legado da humanidade. Acknowledgments This thesis covers several topics of research and, consequently, many people from various disciplines have made it possible, sometimes anonymously. I express first my thanks to all men and women who have worked for the Cassini- Huygens programme during the last three decades and have contributed to the success of this remarkable mission, which will remain a major legacy to planetary scientists for many years to come. I am grateful to the members of the HASI-PWA-Team for inviting me to participate in the PWA data analysis and to contribute to unveiling the mysteries of Titan. I thank CETP-IPSL (Saint Maur, France) and RSSD/ESA-ESTEC (Noordwijk, The Netherlands) that provided outstanding environments to conduct my research. I thank my supervisor, Michel Hamelin, for his wise coordination and for creating excellent research conditions. A have appreciated very much his friendship and support, especially when my numerical models were not converging. I thank all my CETP colleagues; with a special mention for two of them. I am particularly indebted to Alain Péan for his hardware and software expertise, when additional memory or faster computers were required. I have also appreciated having fruitful discussions with Jean-Jacques Berthelier who had always a clever suggestion every time I was faced with a problem. I thank Christian Béghin of LPCE for his sagacity and his friendly cooperation, and for showing me how analytical and numerical models can be complementary. The subsurface permittivity probe was initially developed at RSSD, ESA-ESTEC, and I want to show my gratitude to those who have contributed to such an achievement. I thank Gerhard Schwehm, head of Planetary Missions Division, for hosting my activities; Jean-Pierre Lebreton for his continuous encouragements and for helping me to obtain the funds required for my research; Agustin Chicarro and Roland Trautner for their efficient supervision; Jo Heida and Bart Butler for their help regarding electronics design and assembling; and Lambert Schipperheijn for mechanical parts manufacturing. I thank Bernd Lehmann and César Gómez Fernández of the Mechanical Systems Laboratory, at ESA-ESTEC, for helping me with instrument calibration and testing. I must emphasize that several of my objectives have been achieved only because they believed that such accomplishments were possible. Several ideas were extensively discussed with these people, in particular Roland Trautner; hence the subsurface permittivity probe is also theirs. Last, but not least, I thank Réjean Grard, who has been involved in several aspects of this thesis, from its inception at ESTEC, until its completion at CETP. Finally, I wish to thank my family and friends for their unconditional support, mainly when they felt that I was living on another planet than Earth. This research was sponsored by the following institutions: Fundação para a Ciência e a Tecnologia and Agência de Inovação, (Portugal); European Space Agency, European Space Research and Technology Centre, (The Netherlands); Centre National d’Études Spatiales (France). I also thank the International Space Science Institute (Switzerland) for hosting and supporting several team meetings. i ii Résume L’étude des ondes d’extrêmement basses fréquences dans les cavités ionosphériques des planètes et satellites dotés d’atmosphère suit une approche similaire à celle suivie pour la Terre. Elle contribue à la caractérisation du circuit électrique atmosphérique, des sources d’énergie associées et des limites interne et externe des cavités. Un modèle numérique à éléments finis a été développé et appliqué à ces corps planétaires en vue d’étudier en particulier les résonances de Schumann. Les paramètres du modèle sont : (a) la géométrie de la cavité, (b) les caractéristiques de l’ionosphère, (c) la réfractivité de l’atmosphère neutre et (d) la permittivité complexe de la proche sub-surface. La simulation donne la fréquence propre et le facteur Q de la résonance ainsi que la distribution spatiale du champ électrique dans la cavité. Les cavités de Vénus et Titan sont étudiées dans le détail. La première est très asymétrique et un dédoublement de la fréquence de résonance est prédit. La seconde a été explorée par la sonde Huygens et, additionnellement la faible conductivité du sol de Titan ouvre la porte à l’étude de la sub-surface. La pertinence d’un modèle de la cavité de Titan a été testée par rapport aux mesures in situ de l’instrument Permittivity, Waves and Altimetry (PWA) à bord de la sonde Huygens. L’instrument PWA a mesuré les profils de conductivité électronique et ioniques grâce aux techniques d’impédance mutuelle (MI) et de relaxation, et a identifié une couche conductrice à une altitude d’environ 60 km. Après atterrissage, la constante diélectrique et la conductivité locales du sol mesurées par la sonde MI sont respectivement ~2 et ~ 10-10-10-9 Sm-1. Aucune évidence d’éclair ou de coup de tonnerre n’a été enregistrée, mais un fort signal à 36 Hz a été reçu pendant toute la descente. Cette émission à bande étroite n’est probablement pas un artefact. On a montré par modélisation avec des paramètres appropriés que le signal peut être une résonance naturelle. L’expérience acquise est appliquée à la conception de nouveaux instruments, ARES et SP2, pour étudier l’atmosphère et le sol de la planète Mars dans le cadre du projet ExoMars et pour d’autres corps lors de futurs projets spatiaux. On propose de tirer profit des caractéristiques polaires de l’eau et d’appliquer la technique MI à la détection de la glace dans le régolithe martien. Mots clés Sciences planétaires; mission Cassini-Huygens; ondes électromagnétiques; résonance de Schumann; électricité atmosphérique; instrumentation spatiale iii iv Theoretical and experimental studies of electromagnetic resonances in the ionospheric cavities of planets and satellites; instrument and mission perspectives Abstract The study of extremely low frequency electromagnetic wave propagation in the ionospheric cavities of celestial bodies in the Solar System follows an approach similar to that developed for Earth. It contributes to the characterization of the atmospheric electric circuit and associated energy sources, and to the identification of the inner and outer cavity boundaries. A wave propagation finite element model is developed and applied to all planets and satellites surrounded by an atmosphere, with the aim of studying, in particular, the Schumann resonance phenomenon. The input parameters of the model are: (a) the geometry of the cavity, (b) the ionized atmosphere characteristics, (c) the neutral atmosphere refractivity and (d) the top subsurface complex permittivity. The simulation yields the eigenfrequency and Q- factors of the resonance and the distribution of the electric field in the cavity. The cavities of Venus and Titan are studied in more detail. The former is highly asymmetric and a significant splitting of the eigenfrequency is predicted. The latter has been explored by the Huygens Probe and, additionally, the low conductivity of Titan’s soil opens the door to subsurface investigations. The validity of a model of Titan’s cavity is scrutinized against the in situ measurements performed by the Permittivity, Waves and Altimetry (PWA) analyzer, onboard the Huygens Probe. The PWA instrument measured the ion and electron conductivity profiles using the Mutual Impedance