The dynamics of the Jovian magnetosphere is controlled by the interplay of the planet’s fast rotation, its main iogenic plasma source and its interaction with the solar wind. Magnetosphere-Ionosphere-Thermosphere (MIT) coupling processes controlling this interplay are significantly different from their Earth and Saturn counterparts. At the ionospheric level, they can be characterized by a set of key parameters (ionospheric conductances, electric currents and fields, exchanges of particles along field lines, Joule heating and particle energy deposition) from which one can determine (1) how magnetospheric currents close into the ionosphere, and (2) the net deposition/extraction of energy into/out of the upper atmosphere associated to MIT coupling. We present a new method combining Juno multi-instrument data (MAG, JADE, JEDI, UVS, JIRAM and Waves) and modelling tools to estimate these key parameters along Juno’s trajectories. We first apply this method to two southern hemisphere main auroral oval crossings to illustrate how the coupling parameters are derived. We then present a first statistical analysis of the morphology and amplitudes of these key parameters for eight among the first nine southern perijoves. Our method aims at being extended to more Juno orbits to progressively build a comprehensive view of Jovian MIT coupling along the main auroral ovals.

Observing planetary auroral radio emission is the most promising method to detect exoplanetary magnetospheres and magnetic fields,  the knowledge of which will provide valuable insights into the planet’s interior structure, atmospheric escape, and habitability.

We present LOFAR (LOw-Frequency ARray) Low Band Antenna (LBA: 10-90 MHz) circularly polarized beamformed observations of three exoplanetary systems which are usually considered to be among the best candidates for exoplanetary radio emission. We tentatively detect circularly polarized bursty emission from the τ Boötis system in the range 14-21 MHz with a statistical significance of 3σ. Assuming the detected signal is real, we discuss its potential origin. A possible explanation is radio emission from the exoplanet τ Boötis b via the cyclotron maser mechanism. Assuming a planetary origin, we derived limits for the planetary polar surface magnetic field strength, finding values compatible with theoretical predictions. 

Follow-up observations will allow to confirm this possible first detection of an exoplanetary radio signal. We will discuss such follow-up observations that have recently been performed on LOFAR-LBA, NenuFAR and UTR-2.

The prominent component of Jovian decametric (auroral) emissions is induced by Io. Io decametric emissions (Io-DAM) have thus been monitored on a regular basis by Earth- or Space-based radio observatories for several decades. They display a typical arc-shaped structure in the time-frequency plane which results from the motion of the Io flux tube relative to the observer convolved with the anisotropic radio emission cone. Remote determination of the Io-DAM beaming pattern was used to check the emission conditions at the source (e.g. Queinnec & Zarka, 1998). It has been done at several occasions using various models of magnetic field/lead angles which introduce significant uncertainties. Nevertheless, Io-DAM arcs were shown to be consistent with oblique emissions triggered by the Cyclotron maser Instability from loss-cone electron distributions of a few keVs (Hess et al., 2008). The CMI validity for Jovian DAM and the prominence of loss cone electron distributions has been later confirmed by Juno in situ measurements (e.g. Louarn et al, 2017). In this study, we took advantage of simultaneous radio/UV or bi-point stereoscopic radio measurements provided by Juno/Waves, the Nançay Decameter Array and the Hubble Space Telescope to unambiguously derive the beaming pattern of several Io-DAM arcs and compare it with theoretical expectations. We then assess the energy of CMI-unstable auroral electrons at the source and discuss our results at the light of similar independent studies reaching different conclusions.

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Entre décembre 2015 et janvier 2016, 3 éjections de masse coronale
(CME) ont impacté la magnétosphère terrestre (Akhavan-Tafti et
al., 2020). La deuxième éjection a traversé la magnétosphère du
19 décembre (arrivée) au 26 décembre. Elle était constituée d’un
choc, d’une gaine et d’un nuage magnétique et est celle qui a
produit la plus forte activité au sein de la magnétosphère
terrestre (indice SYM-H &lt; - 150nT). Les propriétés du plasma
contenu dans le nuage magnétique étaient  assez proches de celles
qui règnent dans l’environnement de Mercure (Beta, le rapport de
la pression thermique sur la pression magnétique entre 0.05 et 1, et
le nombre de Mach Alfvénique, rapport de la vitesse du plasma sur la
vitesse d’Alfvén entre 1 et 4). La mission MMS a capturé un
événement de reconnexion magnétique à la magnétopause le 21
décembre associé au passage de cette CME. Ses données à hautes
résolutions temporelle et spatiale permettent d’étudier le
processus de reconnexion à l’échelle de la dynamique des
électrons; elles peuvent être comparées à celles mesurées lors
d’événements non liés à l’impact d’une CME. La réponse
plus globale de la magnétosphère peut être étudiée à partir des
données fournies par la mission Cluster également située côté
jour lors de l’événement et des données de la mission THEMIS
évoluant dans la queue géomagnétique. Enfin, l’activité
aurorale peut également être suivie à partir des images des
caméras plein ciel du réseau sol relié à la mission THEMIS.
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Decametric emission induced by interactions between the Galilean moons and the Jovian magnetosphere: in-situ measurements by Juno.

Authors: C. K. Louis, P. Louarn, F. Allegrini, W. S. Kurth, J. Szalay, C. Jackman, M. Blanc, Y. Wang
At Jupiter, part of the auroral radio emissions are controlled by the Galilean moons Io, Europa and Ganymede. Until now, they have been remotely detected, using ground-based radio-telescope, or electric antenna aboard spacecraft. The polar trajectory of the Juno orbiter leads to cross the magnetic flux tube connected to these moons, or their tail, and gives a direct in-situ measurements of the characteristics of these decametric moon induced radio emissions (such as the electron population, size of the source, and beaming angle and growth rate of the emission). In this study, we focus on a few typical example of the Io, Europa and Ganymede flux tube crossings. The study of Juno/JADE-E (particle) and Juno/Waves (radio) data leads to an estimation of the source size, the electron population energy and the emission beaming angle, and brings us new constrains on the generation process (the so-called Cyclotron Maser Instability).

Q. Nenon, A. R. Poppe, A. Rahmati and J. P. McFadden, Space Sciences Laboratory, U. C. Berkeley

Phobos is a small airless moon that orbits 6000 km above the Martian surface. Its surface is altered by space plasma ions, including not only solar wind ions (protons, alphas), but also heavy ions escaping the atmosphere of the red planet (O+, O2+, and CO2+ ions). The existence, distribution, and time dynamics of these ion populations along Phobos' orbit are driven by the coupling between the Martian atmosphere-ionosphere and the solar wind.

In this presentation, we use four years of in-situ measurements of ions conducted at Phobos' altitude by NASA's MAVEN spacecraft to determine the ion environment that weathers Phobos' surface. Two ion-induced surface weathering processes are then discussed: (1) neutral sputtering, which we find is equally produced by solar wind ions and by Martian heavy ions on Phobos, (2) implantation of exogenous atoms that come from the atmosphere of Mars. We reveal the near-side/far-side asymmetry in ion bombardment and surface alteration at Phobos. One implication of the implantation of Martian atmospheric atoms in Phobos' soil is that Phobos' regolith contains a unique record of the lost atmosphere of Mars. From there, we draw recommendations for the future sampling site of JAXA's MMX mission, which will bring back Phobos' samples to Earth.

Authors:

Moa Persson (presenter), IRAP, CNRS-UPS-CNES, Toulouse, France

Y. Futaana, Swedish Institute of Space Physics, Kiruna, Sweden

R. Ramstad, LASP, University of Boulder Colorado, Boulder, CO, USA

A. Schillings, Department of Physics, Umeå University, Umeå, Sweden

K. Masunaga, LASP, University of Boulder Colorado, Boulder, CO, USA

H. Nilsson, Swedish Institute of Space Physics, Kiruna, Sweden

A. Fedorov, IRAP UPS CNRS, Toulouse, France

S. Barabash, Swedish Institute of Space Physics, Kiruna, Sweden

Abstract

The atmosphere of Venus is today very dry and thick, but Venus might have been covered with several hundreds of meters of water on its surface in its early history. One of the mechanisms that could be responsible for the loss of the water is atmospheric escape to space. One of the largest escape channels at Venus at present day is non-thermal ion escape through the magnetotail. The interaction between the solar wind and the Venusian ionosphere causes an energy transfer from the solar wind to the ionospheric particles. When the ionospheric ion reaches above escape energy (~8 eV for O+) it escapes to space. It has been shown that the escape of oxygen ions at Venus increases as the energy in the upstream solar wind increases. In this study, we extend the previous escape study by further investigating how much of the solar wind energy that are transferred to the escaping particles and how the energy transfer changes with the upstream conditions. 

We used the Ion Mass Analyser (IMA) sensor, part of the ASPERA-4 instrument package on board Venus Express, to investigate the coupling between the net power of the escaping oxygen ions and that of the upstream solar wind. We show that only about 0.01 % of the available solar wind power is transferred to the escaping ions, and that the percentage decreases as the available energy in the upstream solar wind increases. This means that, today, the Venusian induced magnetosphere is very efficient at protecting its atmosphere from being stripped by the solar wind. A comparison with a similar study made at Mars, which has crustal magnetic fields but no intrinsic magnetic field, shows a similar trend to that at Venus, but the energy transfer from the solar wind to the Martian ionospheric ions is more effective. A similar study at Earth, which has an intrinsic magnetic field, showed a different response of its escape to the variations in the energy of the upstream solar wind, than both Venus and Mars. Here, we will show the coupling between the solar wind and oxygen ion escape for Venus, and compare it with the similar studies made at Mars and Earth.

Authors

Yevhen Tkachenko(1, 2), Dimitra Koutroumpa(1), Ronan Modolo(1), Hyunju Connor (3)

1 LATMOS/IPSL, CNRS, UVSQ Paris-Saclay, Sorbonne Université, Guyancourt, France 

2 Université d'Orléans, Orléans, France

3 University of Alaska Fairbanks, Fairbanks, Alaska, USA

Abstract

Current work discusses new steps in the modeling of the X-ray emission produced in the Earth?s magnetosheath due to the Solar Wind Charge eXchange (SWCX) processes. Initially discovered and explained for comets [1, 2], this emission, produced by highly charged solar wind ions (e.g. O7+), has also been observed from interplanetary gas, planets, terrestrial magnetosheath, etc. [3]. SWCX emission in the Earth's magnetosheath will be the target of the future joint ESA and CAS space mission called SMILE (Solar wind Magnetosphere Ionosphere Link Explorer). While the mission will help study various aspects of the interactions of the solar wind and Earth's space environment, it is already possible to estimate the levels of X-ray flux in the Earth's magnetosheath using numerical models and existing theoretical investigations. The goal of the current study is to extend the application of a Test Particle (TP) model to input electric (E) and magnetic (B) fields from MHD (OpenGGCM) [4] simulations, and compare the X-ray emissivity maps to the ones from a pure MHD approach. In the TP approach, we follow numerical test-particles, representing O7+ ions, solving their motion equation as they propagate in the MHD-computed E and B fields, and calculate the probability of them charge exchanging with hydrogen atoms from the Earth?s exosphere. There are two main directions of this extension. First of all, we investigate the impact of the spatial resolution of the model (0.1 Earth radii (Re) and 0.05 Re) to the description of the TP trajectories. This is essential to have smoother MHD-discontinuities surfaces. Second, we transition from static charge exchange cross sections to a dynamic description depending on the interaction velocity. The impact of the dynamic cross sections on the X-ray emissivity may have been underestimated, especially close to electromagnetic barriers where velocity changes are significant, as only static ones have been used before. The work helps to understand the physics of SWCX emissivity based on the existing observations of SW. It is also very useful in the context of the SMILE mission as it provides important synthetic pre-observational results that can be used later as the basis for the data analysis of the Earth's magnetosheath X-ray emissivity.

References

1. Lisse C. M. et al., Science, 274, 205,1996.

2. Cravens T. E., Geophys. Res. Lett., 24, 105-108,1997.

3. Robertson I. P. and Cravens T. E., Geophys. Res. Lett., 30, 1439, 2003 and the references within. 

4. OpenGGCM model, https://ccmc.gsfc.nasa.gov/models/modelinfo.php?model=OpenGGCM