J.-P. Lebreton

Titan from Cassini-Huygens

Preface.- Chapter 1 Overview.- Chapter 2 Earth-based Perspective and pre-Cassini-Huygens Knowledge of Titan.- Chapter 3 The Origin and Evolution of Titan.- Chapter 4 Titans Interior structure.- Chapter 5 Geology and Surface Processes on Titan.- Chapter 6 Composition of Titans Surface.- Chapter 7 Volatile Origin and Cycles: Nitrogen and Methane.- Chapter 8 High-altitude Production of Titans Aerosols.- Chapter 9 Titans Astrobiology.- Chapter 10 Atmospheric Composition and Structure.- Chapter 11 Composition and Structure of the Ionosphere and Thermosphere.- Chapter 12 Aerosols in Titans Atmosphere.- Chapter 13 Atmospheric Dynamics and Meteorology.- Chapter 14 Seasonal Change on Titan.- Chapter 15 Mass loss processes in Titans Upper Atmosphere.- Chapter 16 Energy Deposition Processes in Titans Upper Atmosphere and Its Induced Magnetosphere.- Chapter 17 Titan in the Cassini-Huygens Extended Mission.- Chapter 18 Titan Beyond Cassini-Huygens.- Chapter 19 Mapping Products of Titans Surface.- Appendix.

Little or no solar wind enters Venus' atmosphere at solar minimum.

Venus has no significant internal magnetic field, which allows the solar wind to interact directly with its atmosphere2,3. A field is induced in this interaction, which partially shields the atmosphere, but we have no knowledge of how effective that shield is at solar minimum. (Our current knowledge of the solar wind interaction with Venus is derived from measurements at solar maximum.) The bow shock is close to the planet, meaning that it is possible that some solar wind could be absorbed by the atmosphere and contribute to the evolution of the atmosphere. Here we report magnetic field measurements from the Venus Express spacecraft in the plasma environment surrounding Venus. The bow shock under low solar activity conditions seems to be in the position that would be expected from a complete deflection by a magnetized ionosphere. Therefore little solar wind enters the Venus ionosphere even at solar minimum.

Electromagnetic wave propagation in the surface-ionosphere cavity of Venus

The propagation of extremely low frequency (ELF) waves in the Earth surface-ionosphere cavity and the properties of the related Schumann resonances have been extensively studied in order to explain their relation with atmospheric electric phenomena. A similar approach can be used to understand the electric environment of Venus and, more importantly, search for the evidence of possible atmospheric lightning activity, which remains a controversial issue. We revisit the available models for ELF propagation in the cavity of Venus, recapitulate the similarities and differences with other planets, and present a full wave propagation finite element model with improved parameterization. The new model introduces corrections for refraction phenomena in the atmosphere; it takes into account the day-night asymmetry of the cavity and calculates the resulting eigenfrequency line splitting. The analytical and numerical approaches are validated against the very low frequency electric field data collected by Venera 11 and 12 during their descents through the atmosphere of Venus. Instrumentation suitable for the measurement of ELF waves in planetary atmospheres is briefly addressed.

Plasma energization in the shuttle wake region during beam injection from Spacelab 1

Abstract As part of the PICPAB experiment a high energy pulsed electron beam was emitted from Spacelab 1. Probe results showed that the shuttle wake zone had a significant influence on the electron distribution near the shuttle, both during and between the pulses. A population of suprathermal electrons developed during the beam injection, creating a non-thermal probe current which appears to depend critically on the shuttle attitude. The highest suprathermal electron currents were observed in the wake zone. We therefore conclude that the suprathermal electrons in the wake region were not energized by charging effects, but rather by processes related to the dynamics of the wake zone.

Laboratory model of a Tethered Satellite: Current collection upon and sheath formation around a charged body in a drifting magnetoplasma

Abstract The I–V characteristic and the sheath of a Tethered Satellite laboratory model are investigated in a simulated ionospheric plasma environment with particular emphasis on magnetic field effects. The current collection in the ion regime can be described by a power law: I∝V 0.85 and no magnetic field effect is observed. Strong magnetic field effects are observed in the electron current collection regime which cannot be described by a single power law. In the presence of a magnetic field transverse to the plasma flow, the wake of a highly positively charged body is found sideways the body rather than downstream.

Atmospheric Planetary Probes and Balloons in the Solar System

A primary motivation for in situ probe and balloon missions in the solar system is to progressively constrain models of its origin and evolution. Specifically, understanding the origin and evolution of multiple planetary atmospheres within our solar system would provide a basis for comparative studies that lead to a better understanding of the origin and evolution of our own solar system as well as extra-solar planetary systems. Hereafter, the authors discuss in situ exploration science drivers, mission architectures, and technologies associated with probes at Venus, the giant planets and Titan.