Librational response of a deformed 3-layer Titan perturbed by non-keplerian orbit and atmospheric couplings

The analyses of Titan's gravity field obtained by Cassini space mission suggest the presence of an internal ocean beneath its icy surface. The characterization of the geophysical parameters of the icy shell and the ocean is important to constrain the evolution models of Titan. The knowledge of the librations, that are periodic oscillations around a uniform rotational motion, can bring piece of information on the interior parameters. The objective of this paper is to study the librational response in longitude from an analytical approach for Titan composed of a deep atmosphere, an elastic icy shell, an internal ocean, and an elastic rocky core perturbed by the gravitational interactions with Saturn. We start from the librational equations developed for a rigid satellite in synchronous spin-orbit resonance. We introduce explicitly the atmospheric torque acting on the surface computed from the Titan IPSL GCM (Institut Pierre Simon Laplace General Circulation Model) and the periodic deformations of elastic solid layers due to the tides. We investigate the librational response for various interior models in order to compare and to identify the influence of the geophysical parameters and the impact of the elasticity. The main librations arise at two well-separated forcing frequency ranges: low forcing frequencies dominated by the Saturnian annual and semi-annual frequencies, and a high forcing frequency regime dominated by Titan's orbital frequency around Saturn. We find that internal structure models including an internal ocean with elastic solid layers lead to the same order of libration amplitude than the oceanless models, which makes more challenging to differentiate them by the interpretation of librational motion.Comment: 38 pages, 4 figures. Accepted for publication in Planetary and Space Scienc

Drama in education as a method to teach Grade 1 life skills with science as integrating theme

Abstract : When children start their engagement with science content, they lay the foundation for future learning. This study describes the views of Grade 1 teachers and learners on the use of science content to integrate the teaching of the Grade 1 Life Skills curriculum of the third term. The central premise of this study was to develop a programme that will integrate the Grade 1 Life Skills curriculum by using drama in education as an integrating tool and science content as conceptual fodder for the programme. The premise of the inquiry is that learners can benefit from an integrated curriculum as it enables learners to value the content taught and how it connects to other curriculum topics with real world implications. I argue that drama in education conventions can be used as an integrating tool as it allows for active participation and student centred learning experiences. The study proposes that using science content as the driving for the programme allows for early exposure to this neglected learning area in the foundation phase and ensures that concepts are understood before more advanced terminology is learnt in the intermediate phase. The study was conducted at a private primary school in the northern suburbs of Johannesburg. In a design based study, utilising qualitative data in three modalities, the study investigated teachers’ perspective on the way in which Life Skills is currently addressed in Grade 1 and the perceived success of the integrated program. These modes of data collection were individual interviews, observation protocol and video recordings. The unit of sampling was three Grade 1 teachers and 6 Grade 1 learners in this schools. The analysis was done using deductive coding. The pattern that was composed from the data analysis shows, in three themes, that the teachers were aware of the benefits of teaching Life Skills but due to the limited time available for teaching this subject area, they hardly focus on this learning area’s vast variety of content. With this in mind, eleven categories emerged from the analysis of the observations and post interviews with the teachers and learners that indicated that the teachers had positive attitudes towards the integration of the subject area and excitement arose from both the children and teachers when unpacking the success of each activity. The study discusses the data in the framework of third generation Cultural- Historic Activity Theory. This study recommends that FP teachers consider using science-based activities along with drama in education conventions to integrate the teaching of the v Life Skills content. The content taught in Life Skills is essential to the holistic development of learners. By using science content to integrate the teaching of Life Skills content teachers can evoke the learners’ interest in subject matter that improves the development of skills needed for learning in the 21st century. The study concludes that the integrated programme addressed most of the tensions that were identified within the activity and can possibly be used to integrate the Life Skills curriculum.M.Ed. (Childhood Education

Titan's past and future: 3D modeling of a pure nitrogen atmosphere and geological implications

Several clues indicate that Titan's atmosphere has been depleted in methane during some period of its history, possibly as recently as 0.5-1 billion years ago. It could also happen in the future. Under these conditions, the atmosphere becomes only composed of nitrogen with a range of temperature and pressure allowing liquid or solid nitrogen to condense. Here, we explore these exotic climates throughout Titan's history with a 3D Global Climate Model (GCM) including the nitrogen cycle and the radiative effect of nitrogen clouds. We show that for the last billion years, only small polar nitrogen lakes should have formed. Yet, before 1 Ga, a significant part of the atmosphere could have condensed, forming deep nitrogen polar seas, which could have flowed and flooded the equatorial regions. Alternatively, nitrogen could be frozen on the surface like on Triton, but this would require an initial surface albedo higher than 0.65 at 4 Ga. Such a state could be stable even today if nitrogen ice albedo is higher than this value. According to our model, nitrogen flows and rain may have been efficient to erode the surface. Thus, we can speculate that a paleo-nitrogen cycle may explain the erosion and the age of Titan's surface, and may have produced some of the present valley networks and shorelines. Moreover, by diffusion of liquid nitrogen in the crust, a paleo-nitrogen cycle could be responsible of the flattening of the polar regions and be at the origin of the methane outgassing on Titan.Comment: Accepted for publication in Icarus on July 7, 201

Entretien avec le mensuel de l'université "HAL est avant tout un système créé par et pour les chercheurs"

Entretient sur l'archive ouverte HALAvec plus de 100 000 documents disponibles en texte intégral, les "Hyper Archives en Ligne" (HAL), développées dans le cadre du projet des archives ouvertes, sont devenues un outil majeur de communication scientifique pluridisciplinaire. Daniel Charnay revient pour LMU sur l'origine du projet, son actualité, ses perspectives