Rosina – Rosetta Orbiter Spectrometer for Ion and Neutral Analysis

The Rosetta Orbiter Spectrometer for Ion and Neutral Analysis (ROSINA) will answer important questions posed by the mission’s main objectives. After Giotto, this will be the first time the volatile part of a comet will be analyzed in situ. This is a very important investigation, as comets, in contrast to meteorites, have maintained most of the volatiles of the solar nebula. To accomplish the very demanding objectives through all the different phases of the comet’s activity, ROSINA has unprecedented capabilities including very wide mass range (1 to >300 amu), very high mass resolution (m/Δ m > 3000, i.e. the ability to resolve CO from N₂ and ¹³C from ¹²CH), very wide dynamic range and high sensitivity, as well as the ability to determine cometary gas velocities, and temperature. ROSINA consists of two mass spectrometers for neutrals and primary ions with complementary capabilities and a pressure sensor. To ensure that absolute gas densities can be determined, each mass spectrometer carries a reservoir of a calibrated gas mixture allowing in-flight calibration. Furthermore, identical flight-spares of all three sensors will serve for detailed analysis of all relevant parameters, in particular the sensitivities for complex organic molecules and their fragmentation patterns in our electron bombardment ion sources.     

Role of ionospheric effects and plasma sheet dynamics in the formation of auroral arcs

At the ionospheric level, the substorm onset (expansion phase) is marked by the initial brightening and subsequent breakup of a pre-existing auroral arc. According to the field line resonance (FLR) wave model, the substorm-related auroral arc is caused by the field-aligned current carried by FLRs. The FLRs are standing shear Alfvén wave structures that are excited along the dipole/quasi-dipole lines of the geomagnetic field. The FLRs (that can cause auroral arc) thread from the Earthward edge of the plasma sheet and link the auroral arc to the plasma sheet region of 6–15 R _E. The region is associated with magnetic fluctuations that result from the nonlinear wave-wave interactions of the cross-field current-instability. The instability (excited at the substorm onset) disrupts the cross-tail current which is built up during the growth phase of the substorms and results in magnetic fluctuations. The diversion of the current to polar regions can lead to auroral arc intensification. The current FLR model is based on the amplitude equations that describe the nonlinear space-time evolution of FLRs in the presence of ponderomotive forces exerted by large amplitude FLRs (excited during substorms). The present work will modify the FLR wave model to include the effects arising from magnetic fluctuations that result from current disruption near the plasma sheet (6–15 R _E). The nonlinear evolution of FLRs is coupled with the dynamics of plasma sheet through a momentum exchange term (resulting from magnetic fluctuations due to current disruption) in the generalized Ohm's law. The resulting amplitude equations including the effects arising from magnetic fluctuations can be used to study the structure of the auroral arcs formed during substorms. We have also studied the role of feedback mechanism (in a dipole geometry of the geomagnetic field) in the formation of the discrete auroral arc observed on the nightside magnetosphere. The present nonlinear dispersive model (NDM) is extended to include effects arising from the low energy electrons originating from the plasma sheet boundary layer. These electrons increase the ionospheric conductivity in a localized patch and enhance the field-aligned current through a feedback mechanism. The feedback effects were studied numerically in a dipole geometry using the the NDM. The numerical studies yield the magnitude of the field-aligned current that is large enough to form a discrete auroral arc. Our studies provide theoretical support to the observational work of Newell et al. that the feedback instability plays a major role in the formation of the discrete auroral arcs observed on the nightside magnetosphere.     

WHISPER, A RESONANCE SOUNDER AND WAVE ANALYSER: PERFORMANCES AND PERSPECTIVES FOR THE CLUSTER MISSION

The WHISPER sounder on the Cluster spacecraft is primarily designed to provide an absolute measurement of the total plasma density within the range 0.2–80 cm^-3. This is achieved by means of a resonance sounding technique which has already proved successful in the regions to be explored. The wave analysis function of the instrument is provided by FFT calculation. Compared with the swept frequency wave analysis of previous sounders, this technique has several new capabilities. In particular, when used for natural wave measurements (which cover here the 2–80 kHz range), it offers a flexible trade-off between time and frequency resolutions. In the basic nominal operational mode, the density is measured every 28 s, the frequency and time resolution for the wave measurements are about 600 Hz and 2.2 s, respectively. Better resolutions can be obtained, especially when the spacecraft telemetry is in burst mode. Special attention has been paid to the coordination of WHISPER operations with the wave instruments, as well as with the low-energy particle counters. When operated from the multi-spacecraft Cluster, the WHISPER instrument is expected to contribute in particular to the study of plasma waves in the electron foreshock and solar wind, to investigations about small-scale structures via density and high-frequency emission signatures, and to the analysis of the non-thermal continuum in the magnetosphere.     

RPC-MIP: the Mutual Impedance Probe of the Rosetta Plasma Consortium

The main objective of the Mutual Impedance Probe (MIP), part of the Rosetta Plasma Consortium (RPC), is to measure the electron density and temperature of Comet 67P/Churyumov-Gerasimenko’s coma, in particular inside the contact surface. Furthermore, MIP will determine the bulk velocity of the ionised outflowing atmosphere, define the spectral distribution of natural plasma waves, and monitor dust and gas activities around the nucleus. The MIP instrumentation consists of an electronics board for signal processing in the 7 kHz to 3.5 MHz range and a sensor unit of two receiving and two transmitting electrodes mounted on a 1-m long bar. In addition, the Langmuir probe of the RPC/LAP instrument that is at about 4 m from the MIP sensor can be used as a transmitter (in place of the MIP ones) and MIP as a receiver in order to have access to the density and temperature of plasmas at higher Debye lengths than those for which the MIP is originally designed.     

Analysis of Theories of Fully Ionized Space Plasma

The physical sense of the main ideas, presently used in plasma physics, is discussed. An attempt is made to clarify the concepts, used in plasma physical calculations. The concept of `Coulomb collisions' with the implicitly introduced rapid stochastization plays the main negative role in the physics of fully ionized plasma. Statistical methods, which are adequate for the neutral gas and for the partially ionized plasma, are not applicable for the completely ionized case. It is the cause of large errors in evaluating real plasma parameters. A new concept is considered: a fully ionized space plasma should be treated as a dynamical system with a low level of chaos. Further progress in space physics requires a serious renewal of plasma theory.     

Primordial matter in the outer solar system: A study of its chemical composition from remote spectroscopic analysis

Our knowledge of the primordial matter from the objects of the outer solar system has made a considerable progress over the past years, in spite of the lack of any in situ measurements of these objects at the present time. The recent progress of ground-based instrumentation and the launch of the two Voyager fly-by missions have provided a huge amount of new informations about the origin and the evolution of the primitive Solar System objects.The most significant discoveries concerning the atmospheres of the Giant Planets can be summarized as follows: (1) there does not seem to be any differentiation in the internal structure of Jupiter during the planet's history; thus, the H₂/He ratio measured on Jupiter seems to be representative of the H/He ratio of the Primordial Nebula; (2) there is some evidence for a helium differentiation, relative to hydrogen, in Saturn's interior; (3) there seems to be a carbon enrichment on both Jupiter and Saturn by a factor about 2; this result is consistent with a model in which the planetary core is formed first, and the atmosphere accreted by this core in a second stage; (4) the D/H ratio measured on Jupiter should be representative of the D/H value in the Primordial Nebula, 4.5 billion years ago; this value is 2 to 5 times larger than the mean value measured in the local interstellar medium now; (5) Titan's atmosphere is dominated by nitrogen and contains traces of organic and prebiotic molecules (HCN, C₂N₂, HC₃N); the chemical composition of Titan's atmosphere could be favorable for the early stages of life development.The small bodies of the Solar System — asteroïds and comets — are still very poorly known. However they contain a key information about the physical and chemical properties of dust in the Primordial Nebula and the interstellar medium. With the launch of expected fly-by missions towards Comet Halley and, possibly, towards asteroïds, we may hope to know a new development of our understanding of these objects, comparable to the progress we have known on the Giant Planets over the past ten years.     

On the origin of the grooves on Phobos

L-grooves are the consequence of layered structure of Phobos, which are made up of parallel layers of different composition or hardness.     

L'avion,plateforme d'observations scientifiques

Transition between high altitude manned observatories and unmanned balloon-borne or rocket-borne experiments is achieved with high flying aircrafts, at altitudes above tropopause (>12 km), which became readily available, at reasonable cost and reliability, in the past five or ten years.This paper reviews the development of scientific uses of aircrafts, especially for astronomy and geophysics, with some emphasis placed on infrared problems, closely related to the scale height of the chief infrared absorber, i.e. telluric water vapor.Absorbers distribution vs altitude and spectral characteristics are summarized (Figures 1, 2, 3).Capabilities of various available aircrafts are compared (Table I) and the various ways to consider modifications are discussed: structural modifications or design problems to fit telescopes or light collectors on board. Tables II and III list the advantages of airborne observations, compared to other spatial carriers, and also the specific problems connected with aircrafts. Adopted solutions to these problems are exposed (Figures 4, 5, 6, 7) and costs are briefly discussed.Finally, a few examples of scientific results, gathered in the few past years from aircraft, are given, both in astronomy and in geophysics.