Solar Orbiter's encounter with the tail of comet C/2019 Y4 (ATLAS): Magnetic field draping and cometary pick-up ion waves

ontext. Solar Orbiter is expected to have flown close to the tail of comet C/2019 Y4 (ATLAS) during the spacecraft’s first perihelion in June 2020. Models predict a possible crossing of the comet tails by the spacecraft at a distance from the Sun of approximately 0.5 AU. Aims. This study is aimed at identifying possible signatures of the interaction of the solar wind plasma with material released by comet ATLAS, including the detection of draped magnetic field as well as the presence of cometary pick-up ions and of ion-scale waves excited by associated instabilities. This encounter provides us with the first opportunity of addressing such dynamics in the inner Heliosphere and improving our understanding of the plasma interaction between comets and the solar wind. Methods. We analysed data from all in situ instruments on board Solar Orbiter and compared their independent measurements in order to identify and characterize the nature of structures and waves observed in the plasma when the encounter was predicted. Results. We identified a magnetic field structure observed at the start of 4 June, associated with a full magnetic reversal, a local deceleration of the flow and large plasma density, and enhanced dust and energetic ions events. The cross-comparison of all these observations support a possible cometary origin for this structure and suggests the presence of magnetic field draping around some low-field and high-density object. Inside and around this large scale structure, several ion-scale wave-forms are detected that are consistent with small-scale waves and structures generated by cometary pick-up ion instabilities. Conclusions. Solar Orbiter measurements are consistent with the crossing through a magnetic and plasma structure of cometary origin embedded in the ambient solar wind. We suggest that this corresponds to the magnetotail of one of the fragments of comet ATLAS or to a portion of the tail that was previously disconnected and advected past the spacecraft by the solar wind

IMPALAS: Investigation of MagnetoPause Activity using Longitudinally-Aligned Satellites—a mission concept proposed for the ESA M3 2020/2022 launch

The dayside magnetopause is the primary site of energy transfer from the solar wind into the magnetosphere, and modulates the activity observed within the magnetosphere itself. Specific plasma processes operating on the magnetopause include magnetic reconnection, generation of boundary waves, propagation of pressure-pulse induced deformations of the boundary, formation of boundary layers and generation of Alfvén waves and field-aligned current systems connecting the boundary to the inner magnetosphere and ionosphere. However, many of the details of these processes are not fully understood. For example, magnetic reconnection occurs sporadically, producing flux transfer events, but how and where these arise, and their importance to the global dynamics of the magnetospheric system remain unresolved. Many of these phenomena involve propagation across the magnetopause surface. Measurements at widely-spaced (Δ ˜ 5 RE) intervals along the direction of dayside terrestrial field lines at the magnetopause would be decisive in resolving these issues. We describe a mission carrying a fields and plasmas payload (including magnetometer, ion and electron spectrometer and energetic particle telescopes) on three identical spacecraft in synchronized orbits. These provide the needed separations, with each spacecraft skimming the dayside magnetopause and continuously sampling this boundary for many hours. The orbits are phased such that (i) all three spacecraft maintain common longitude and thus sample along the same magnetopause field line; (ii) the three spacecraft reach local midday when northern European ground-based facilities also lie near local midday, enabling simultaneous sampling of magnetopause field lines and their footprints

The Electron Temperature and Anisotropy in the Solar Wind. I. Comparison of the Core and Halo Populations

© 2016, Springer Science+Business Media Dordrecht. Estimating the temperature of solar wind particles and their anisotropies is particularly important for understanding the origin of their deviations from thermal equilibrium and the effects this has. In the absence of energetic events, the velocity distribution of electrons reveals a dual structure with a thermal (Maxwellian) core and a suprathermal (kappa) halo. This article presents a detailed observational analysis of these two components, providing estimations of their temperatures and temperature anisotropies, and decoding any potential interdependence that their properties may indicate. The dataset used in this study includes more than 120 000 of the distributions measured by three missions in the ecliptic within an extended range of heliocentric distances from 0.3 to over 4 AU. The core temperature is found to decrease with the radial distance, while the halo temperature slightly increases, clarifying an apparent contradiction in previous observational analyses and providing valuable clues about the temperature of the kappa-distributed populations. For low values of the power-index kappa, these two components manifest a clear tendency to deviate from isotropy in the same direction, which seems to confirm the existence of mechanisms with similar effects on both components, e.g., the solar wind expansion, or the particle heating by the fluctuations. However, the existence of plasma states with anticorrelated anisotropies of the core and halo populations and the increase in their number for high values of the power-index kappa suggest a dynamic interplay of these components, mediated, most probably, by the anisotropy-driven instabilities.Manuscript submitted to Solar Physics (26.02.2016)status: publishe

The Radio & Plasmas Waves instrument on the Solar Orbiter mission : science objectives and capabilities

International audienceWe will review the science objectives of the Radio & Plasmas Waves (RPW) instrument on the Solar Orbiter mission. Among those the study of the connectivity between the solar corona and the inner Heliosphere as close as from 0.3 AU and the kinetic behavior of the Solar Wind are of prime importance. We present then the RPW technical capabilities which will allow in-situ and remote sensing measurements of both electrostatic and electromagnetic fields and waves in a broad frequency range, typically from a fraction of Hertz to a few tens of MHz

The ISL Langmuir probe experiment processing onboard DEMETER: Scientific objectives, description and first results

International audienceThe DEMETER Langmuir probe experiment, called “Instrument Sonde de Langmuir” (ISL), has been designed for in situ measurements of the bulk parameters of the ionospheric thermal plasma. The ISL instrument is comprised of two sensors: (i) a classical cylindrical sensor and (ii) a spherical sensor with its surface divided in seven segments: six spherical caps electrically isolated and the rest of the sphere which is used as a guard electrode. The two main parameters measured by ISL are the electron density and temperature; they are obtained with a 1 s time-resolution. In addition, the ion density and its variation can be derived from the current-voltage characteristics of the probe, but it requires an a-priori knowledge of the ion composition and a more sophisticated processing than the one currently implemented. The novel design for the spherical sensor has been called the segmented Langmuir probe (SLP). The SLP current can be measured individually on each of the seven segments, thus providing angular sensitivity to the ram direction of the incoming ion flow. The SLP was flown for the first time onboard the DEMETER satellite for in-flight validation of this novel concept, but the main sensor used routinely during the mission is the cylindrical probe. The design of the instrument and the analysis technique for the cylindrical probe are described. A brief description of the SLP and of its capabilities is provided. An overview of the currently available ISL data products on the DEMETER Mission Science Data Centre is given. Selected examples of some “classical” ionospheric features as being observed by ISL are discussed

Destabilizing effects of the suprathermal populations in the solar wind

© ESO 2015. Context. Suprathermal populations are ubiquitous in the solar wind, indicating plasma states out of thermal equilibrium, and an excess of free energy expected to enhance the kinetic instabilities. However, recent endeavors to disclose the effects of these populations on the electromagnetic instabilities driven by the temperature anisotropy do not confirm this expectation, but mainly show that these instabilities are inhibited by the suprathermals. Aims. In an attempt to clarify the effect of the suprathermals, we propose to revisit the existing models for the anisotropic velocity distributions of plasma particles and to provide an alternative comparative analysis that unveils the destabilizing effects of the suprathermal populations. Methods. Suprathermal tails of the observed distributions are best fitted by the Kappa power laws (with the bi-Kappa variant to model temperature anisotropies), which are nearly Maxwellian at low speeds (thermal core) and decrease as a power law at high speeds (suprathermal halo). To unveil the destabilizing effects of the suprathermal populations, the existing methods (A) compare Kappa and Maxwellian distributions of the same effective temperature, while the alternative comparative method (B) proposed in this paper allows for an increase of the effective temperature with increasing the suprathermal populations. Both of these two methods are invoked here to quantify and compare the effects of suprathermal electrons on the electromagnetic electron-cyclotron (EMEC) instability, driven by the temperature anisotropy T e ;⊥ > T e ; of the electrons (where ; ⊥ are directions with respect to the magnetic field). Results. Only the Maxwellian limit of lower effective temperature shapes the Kappa model at low energies (method B), enabling a realistic comparison between the Maxwellian core and the global best-fitting Kappa, which incorporates both the core and suprathermal tails. In this case, the EMEC instability is found to be markedly and systematically enhanced by the suprathermal populations for any level of the temperature anisotropy. The results of the present study may provide valuable premises for a realistic description of the suprathermal populations and their destabilizing effects for the whole spectrum of kinetic instabilities in the solar wind.status: publishe

Performances and First Results from the RPW/Search Coil Magnetometer onboard Solar Orbiter

International audienceThe Search Coil Magnetometer (SCM) onboard Solar Orbiter is part of the Radio and Plasma Waves (RPW) experiment. It measures magnetic field fluctuations in the frequency range from a few Hz to 50 kHz on three axes and between 1 kHz and 1MHz in one axis. RPW has been working nearly continuously and SCM has recorded many interesting features, including whistler and other types of waves as well as local characteristics of turbulence. We will provide an overview of these observations as well as a description of the in flight performances of SCM

Performances and First Results from the RPW/Search Coil Magnetometer onboard Solar Orbiter

International audienceThe Search Coil Magnetometer (SCM) onboard Solar Orbiter is part of the Radio and Plasma Waves (RPW) experiment. It measures magnetic field fluctuations in the frequency range from a few Hz to 50 kHz on three axes and between 1 kHz and 1MHz in one axis. RPW has been working nearly continuously and SCM has recorded many interesting features, including whistler and other types of waves as well as local characteristics of turbulence. We will provide an overview of these observations as well as a description of the in flight performances of SCM