The emphasis of the session is on all aspects of plasma physics and interactions of solar and stellar wind interactions with planets and exoplanets, including: (a) magnetospheric dynamics, aurorae, and radio emissions (b) potential impact of star-(exo-)planet coupling on habitability, (c) comparative studies between Solar System planets and exoplanets. We welcome contributions relying on space-based or ground-based observations as well as theoretical modelling and simulations.
Gina A. DiBraccio, Norberto Romanelli, Jacob R. Gruesbeck, Jasper Halekas, Suranga Ruhunusiri, Jared Espley, Gangkai Poh, John E. P. Connerney, Shaosui Xu, Tristan Weber, Janet Luhmann, and David Brain
At Mars, recent studies based on a combination of MAVEN data and modeling have determined the Martian magnetotail exhibits a ~45° twist, either clockwise or counterclockwise from the ecliptic plane, away from the nominal interplanetary magnetic field (IMF) draping morphology. An initial study by DiBraccio et al.  employed MAVEN magnetic field measurements, coupled with MHD simulations, to indicate that the twist is likely a result of the sun-planetary interaction. Now with several more years of MAVEN data available, we augment this work using a statistical analysis of MAVEN magnetic field data from November 2014 through November 2019. We utilized ~6000 orbits, requiring that MAVEN observed both the magnetotail and the upstream IMF over a given orbit. For periods when the upstream IMF measurements were not available due to MAVEN’s orbit precession, we utilize an IMF proxy to determine characteristics of the upstream orientation. The location of the magnetotail lobes, identified in the data as the regions of magnetic field behind the planet directed towards and away from Mars, are analyzed as a function of the upstream IMF dawn-dusk component. In the previous DiBraccio et al.  study, this dawn-dusk component was found to be the separating factor in the direction of magnetotail twisting. To quantify the degree of tail twisting for a given scenario, we determine the vector between the center of the towards/away tail lobes and calculate the angle between this vector and the expected direction for nominal IMF draping. This calculated tail twist angle is then assessed as a function of a variety of factors including strong crustal field location, Mars season, and downtail distance. In all cases, we determine that the degree of tail twisting is larger when the IMF is oriented in the duskward direction, suggesting enhanced coupling between the IMF and planetary crustal fields. Furthermore, we demonstrate that the degree of tail twisting exhibits different trends for crustal field orientation under dawnward versus duskward IMF configurations. Seasonal variations indicate that tail twisting may vary over the course of the Martian year, but additional data are needed during the northern fall and winter periods for confirmation. Finally, when assessing the tail twist with downtail distance we find that the degree of twisting increases with distance from the planet. This result is similar to Earth where observations of the magnetotail twist increases away from the planet as the torque exerted by the IMF on the planetary field increases. From these findings we confirm that the tail twist at Mars is likely a result of the direct interaction between the IMF and the planetary crustal fields; however, we find evidence suggesting that the degree of twisting is larger for duskward IMF orientations. This implies that magnetic reconnection on the dayside of Mars, between the IMF and crustal fields, may be favorable under specific IMF configurations.
How to cite:
DiBraccio, G. A., Romanelli, N., Gruesbeck, J. R., Halekas, J., Ruhunusiri, S., Espley, J., Poh, G., Connerney, J. E. P., Xu, S., Weber, T., Luhmann, J., and Brain, D.: MAVEN observations of factors influencing the magnetotail twist at Mars, Europlanet Science Congress 2020, online, 21 Sep–9 Oct 2020, EPSC2020-154, https://doi.org/10.5194/epsc2020-154, 2020.
Charles Bowers, James Slavin, Gina DiBraccio, Gang Kai Poh, Shaosui Xu, David Brain, Jared Espley, and David Mitchell
Here we analyze magnetic flux ropes in the ionosphere of Mars in order to understand their formation mechanism and contribution to atmospheric escape. Detected at objects throughout the solar system, flux ropes are a well-documented magnetic field phenomenon characterized by a filament of highly twisted magnetic field with a strong axial core and weaker outer helical wraps. The ubiquity of flux rope observations despite the diversity of plasma environments in which they form along with the subsequent properties of the flux ropes (radius, orientation etc.), suggests that a variety of plasma physics processes may form these magnetic field structures. Planetary flux ropes at intrinsic magnetospheres are commonly thought to form at the dayside magnetopause due to reconnection between the IMF and the global intrinsic magnetic field or in the cross-tail current sheet when the magnetic fields in the two lobes reconnect. However, flux ropes are also observed at planets in which intrinsic magnetic fields are absent (i.e. Venus) or localized (i.e. Mars). Flux rope formation in the Martian magnetosphere is of particular interest due to the localized crustal magnetic anomalies. In the southern hemisphere, the crustal anomalies are strong (100-1000 nT at the surface) protruding into space creating a “mini-magnetospheric” interaction between the IMF and the crustal anomalies similar to the dayside magnetopause of magnetized planets. In the northern hemisphere, the crustal anomalies are weaker, and do not inhibit the IMF flux tubes from penetrating deep into the ionosphere, creating a plasma environment similar to Venus.
Flux ropes play a role in two classes of fundamental processes at Mars: (1) the rapid reconfiguration of magnetospheric magnetic fields and the acceleration of charged particles, and (2) atmospheric and magnetospheric mass loss through plasma channeling and entrainment in their helical wraps and escape down the magnetotail. While case studies of flux ropes have been carried out at Mars, a comprehensive survey of ionospheric flux ropes and their formation mechanisms is required to better understand the solar-wind magnetospheric interaction at the planet. Here, we present the first survey of flux ropes at Mars with evidence for the flux ropes having been formed by 3 distinct formation mechanisms: External Reconnection (ER) between the draped IMF and crustal anomalies, Internal Reconnection (IR) between the crustal anomalies themselves, and Boundary Wave Instabilities (BWI) similar to those believed to operate at Venus.
We identified 171 magnetic flux ropes observed in the Mars Atmosphere and Volatlie EvolutioN (MAVEN) measurements. Using magnetic field data taken by the magnetometer (MAG) instrument, we applied Minimum Variance Analysis (MVA) to identify flux ropes by their characteristic increase in total field magnetic field strength coinciding with the inflection point of a bipolar signature created by the surrounding helical wraps (Figure 1). These flux ropes display a wide range in core field intensity (5 - 110 nT), location in latitude (-70° - +70°), and solar zenith angle (15°- 140°). The Solar Wind Electron Analyzer (SWEA) instrument onboard MAVEN measures superthermal (>1eV) electrons at a 4 second cadence. We use the fluxes of these electrons compared to the local magnetic field orientation to parameterize the likelihood of a presence of a loss cone. This parameter is known known as a pitch angle distribution (PAD) score. The energy distribution of the electrons is compared to an expected distribution for the photoelectrons at Mars to parameterize the likelihood that the measured electrons are composed of primarily photoelectrons or solar wind electrons; this is known as the shape parameter. These two parameters combine to provide an estimation of the local magnetic topology at the spacecraft. We performed this analysis on our collection of flux ropes and the surrounding environment to determine the formation mechanism of the flux rope.
In the ER flux rope formation mechanism, the draped IMF and a crustal anomaly undergo multiple X-line reconnection. If a flux rope were formed via the ER mechanism, the flux rope would contain both solar wind electrons and photoelectrons, and it would be surrounded by open magnetic field lines, as shown in Figure 2. Thus, a flux rope that were created by the ER mechanism would show an open topology score surrounding the flux rope, with a mixture of solar wind and photoelectron shape parameters inside the structure. 49 (29%) flux ropes are consistent with this formation mechanism. In the IR formation mechanism, a crustal magnetic field loop is distorted due to an increase in solar wind pressure. This distortion may lead to the crustal fields overlapping and reconnecting on themselves in a single X-line as seen in Figure 3. In this case, the flux rope would be found downstream of the subsolar point, surrounded by closed magnetic topology, and contain exclusively photoelectrons.
Figure 4 shows an example of an IR formation mechanism flux rope consistent with this topology projected onto a model of the crustal magnetic fields of Mars. We can see the flux rope axis (red arrow) points perpendicular to radial streamlines emanating out from the subsolar point (yellow triangle) to the flux rope detection point (red diamond), which is also in agreement with the schematic shown in Figure 3. 88 (51%) of flux ropes are consistent with this formation mechanism. The development of large-amplitude waves, most probably Kelvin-Helmholtz (KH), on the boundary between the fast tailward flows in the magnetosheath and the much more slowly moving ionospheric plasma may also form flux ropes at Mars. We characterize this type of flux rope as formed through the BWI mechanism. They contain primarily solar wind electrons, and occur near the draped magnetic topology found in the magnetosheath. 16 (9%) of flux ropes are consistent with this this formation mechanism.
Our classification of the processes responsible for flux ropes at Mars will further our understanding comprise the complex coupling between the Martian magnetosphere and atmosphere.
How to cite:
Bowers, C., Slavin, J., DiBraccio, G., Poh, G. K., Xu, S., Brain, D., Espley, J., and Mitchell, D.: Evidence of Low-Altitude Magnetic Flux Ropes Formed by Three Distinct Mechanisms Using Observations from MAVEN, Europlanet Science Congress 2020, online, 21 Sep–9 Oct 2020, EPSC2020-413, https://doi.org/10.5194/epsc2020-413, 2020.
Sae Aizawa, Nicolas André, Ronan Modolo, François Leblanc, Elisabeth Werner, and Vincent Génot
The highly compressed magnetosphere (HCM) events at Mercury observed by the MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) spacecraft have been investigated using the global hybrid simulation LatHyS. The HCM events occur due to the interactions with coronal mass ejections (CMEs) or high-speed streams (HSSs) and previous studies indicate that not only the reconnection-driven erosion but also the induced currents in the inner core have an important role in the variation of the dayside magnetosphere of Mercury. However, the effects of the presence of planetary ions on Mercury’s system have not been well discussed. In this study, we mainly focus on the presence of planetary ions that are self-consistently produced from the exosphere by several ionization processes under extreme solar wind conditions and discuss their role on the structure and dynamics of Mercury’s magnetosphere.
How to cite:
Aizawa, S., André, N., Modolo, R., Leblanc, F., Werner, E., and Génot, V.: Global hybrid simulations of highly compressed magnetosphere events at Mercury, Europlanet Science Congress 2020, online, 21 Sep–9 Oct 2020, EPSC2020-257, https://doi.org/10.5194/epsc2020-257, 2020.
Norberto Romanelli, Gina DiBraccio, Daniel Gershman, Guan Le, Christian Mazelle, Karim Meziane, Scott Boardsen, James Slavin, Jim Raines, Austin Glass, and Jared Espley
In this work we perform the first statistical analysis of the main properties of waves observed in the 0.05–0.41 Hz frequency range in the Hermean foreshock by the MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) Magnetometer. Although we find similar polarization properties to the '30 s' waves observed at the Earth's foreshock, the normalized wave amplitude (∼0.2) and occurrence rate (∼0.5%) are much smaller. This suggests significant lower backstreaming proton fluxes, due to the relatively low solar wind Alfvenic Mach number around Mercury. These differences could also be related to the relatively smaller foreshock size and/or more variable solar wind conditions. Furthermore, we estimate that the speed of resonant backstreaming protons in the solar wind reference frame (likely source for these waves) ranges between 0.95 and 2.6 times the solar wind speed. The closeness between this range and what is observed at other planetary foreshocks suggests that similar acceleration processes are responsible for this energetic population and might be present in the shocks of exoplanets.
How to cite:
Romanelli, N., DiBraccio, G., Gershman, D., Le, G., Mazelle, C., Meziane, K., Boardsen, S., Slavin, J., Raines, J., Glass, A., and Espley, J.: Upstream Ultra-Low Frequency Waves Observed by MESSENGER's Magnetometer: Implications for Particle Acceleration at Mercury's Bow Shock, Europlanet Science Congress 2020, online, 21 Sep–9 Oct 2020, EPSC2020-421, https://doi.org/10.5194/epsc2020-421, 2020.
Baptiste Cecconi, Corentin K Louis, Claudio Munoz, and Claire Vallat
The ExPRES code simulates exoplanetary and planetary auroral radio emissions. It could be used to predict and interpret Jupiter’s radio emissions in the hectometric and decametric range. In this study, we model the occultations of the Jovian auroral radio emissions during the Galilean moons flybys by the Galileo spacecraft. In this study, we focus on auroral radio emissions, configuring the ExPRES simulations runs with typical radio source physical parameters. We compare the simulations run results with the actual Galileo/PWS observations, and show that we accurately model the temporal occurrence of the occultations in the whole spectral range observed by Galileo. We can then predict auroral radio emission occultations by the Galilean moons for the Juno and JUICE missions. ExPRES will be used by the JUICE/RPWI (Radio Plasma Waves Investigation) team to prepare its operation planning during the Galilean moon flybys for, e.g., the Galilean moon ionosphere characterization science objective, with passive ionospheric sounding during ingress and egress of Jovian radio source occultations.
How to cite:
Cecconi, B., Louis, C. K., Munoz, C., and Vallat, C.: ExPRES Modeling of Auroral Radio Source Occultation observed by Galileo Application to JUICE and Juno, Europlanet Science Congress 2020, online, 21 Sep–9 Oct 2020, EPSC2020-962, https://doi.org/10.5194/epsc2020-962, 2020.
Georg Fischer, Ulrich Taubenschuss, and David Pisa
Saturn kilometric radiation (SKR) is thought to be created by the cyclotron maser instability along auroral magnetic field lines, where radio emissions are generated near the electron cyclotron frequency at the source. Using the Wideband Receiver (WBR) of the Cassini Radio and Plasma Wave Science (RPWS) instrument it was possible to create dynamic spectra of high temporal and spectral resolution. They display the radio wave intensity as a function of time and frequency with a temporal resolution of a fraction of a second and a spectral resolution of ~0.1 kHz.
In these dynamic spectra one can find a plethora of various fine structures which we classify in the following way: We first simply distinguish between 0-dimensional structures (dots), 1-dimensional structures (lines), and 2-dimensional structures (areas). For areas we require a minimum extension of 5 seconds in time and 5 kHz in frequency. Our main focus is on the lines, where we again distinguish between the four classes of horizontal lines, vertical lines, and lines with a positive or a negative slope (going to higher or lower frequencies). For the latter two it is thought that they are related to downward or upward moving radiation sources, i.e. bunches of energetic electrons moving down or up along the magnetic field lines. Using these simple 6 classes (DOTS, HORZ, VERT, POSS, NEGS, AREA) it is already possible to classify about 80% of all spectra showing SKR. Unclassified spectra contain no clear linear elements and mostly consist of patchy structures with holes that do not fulfill the minimum size requirement (5 s, 5 kHz) to be classified as areas. Linear elements appear in about one third of the spectra in the frequency range from 100 kHz to 1 MHz. Some spectra can of course be mixed and show dots, lines and areas, but in our classification we prioritize lines over areas and dots.
How to cite:
Fischer, G., Taubenschuss, U., and Pisa, D.: Classification of fine structures of Saturn kilometric radiation, Europlanet Science Congress 2020, online, 21 Sep–9 Oct 2020, EPSC2020-620, https://doi.org/10.5194/epsc2020-620, 2020.
Before to ultimately plunge into Saturn’s atmosphere, the Cassini spacecraft explored between 2016 and 2017 the auroral regions of Saturn’s magnetosphere, where rises the Saturn’s Kilometric Radiation (SKR). This powerful, nonthermal, radio emission analog to Earth’s Auroral Kilometric Radiation, is radiated through the Cyclotron Maser Instability (CMI) by mildly relativistic electrons at frequencies close to the local electron gyrofrequency. The typical SKR spectrum, which ranges from a few kHz to ~1MHz, thus corresponds to auroral magnetic flux tubes populated by radiosources at altitudes ranging from ~4 kronian radii (Rs) down to the planetary ionosphere.During the F-ring orbital sequence, Cassini probed the outer part of both northern and southern auroral regions, ranging from ~2.5 to ~4 Rs altitudes, and crossed several SKR low frequency sources (~10-30 kHz). Their analysis showed that the radiosources strongly vary with time and local time, with the lowest frequencies reached on the dawn sector. They were additionally colocated with the UV auroral oval and controlled by local time-variable magnetospheric electron densities, with importants consequences for the use SKR low frequency extensions as a proxy of magnetospheric dynamics. Along the proximal orbits, Cassini then explored auroral altitudes below ~2.5 Rs and crossed numerous, deeper, SKR sources at frequencies close to, or within the emission peak frequency (~80-200 kHz). Here, we present preliminary results of their survey analysis. Understanding how the CMI operates in the widely different environments of solar system magnetized planets has direct implications for the ongoing search of radio emissions from exoplanets, ultracool dwarves or stars.
How to cite:
Lamy, L.: The peak frequency source of Saturn’s Kilometric Radiation, Europlanet Science Congress 2020, online, 21 Sep–9 Oct 2020, EPSC2020-1024, https://doi.org/10.5194/epsc2020-1024, 2020.
The characteristic relaxation time of the Uranus magnetosphere is of the order of the planet's rotation period. This is also the case for Jupiter or Saturn. However, the specificity of Uranus (and to a lesser extent of Neptune) is that the rotation axis and the magnetic dipole axis are separated by a large angle (~60°) the consequence of which is the development of a highly dynamic and complex magnetospheric tail. In addition, and contrary to all other planets of the solar system, the rotation axis of Uranus happens to be quasi-parallel to the ecliptic plane which also implies a strong variability of the magnetospheric structure as a function of the season. The magnetosphere of Uranus is thus a particularly challenging case for global plasma simulations, even in the frame of MHD. We present a detailed analysis of MHD simulations of a fast-rotating magnetosphere inspired from Uranus at solstice. At first, a simplified case allows us to explain in detail the formation and the internal structure of a double helix that develops in the magnetotail at solstice. Then we analyse a "real" Uranus simulation with parameters for the solar wind and planetary magnetic field defined from the measurements of Voyager II flyby in 1986.
How to cite:
Griton, L. and Pantellini, F.: How a magnetic helix can develop at solstice in a Uranus-type rotating magnetosphere, Europlanet Science Congress 2020, online, 21 Sep–9 Oct 2020, EPSC2020-731, https://doi.org/10.5194/epsc2020-731, 2020.
During the Archean eon from 3.8 to 2.5 billion years ago, the Earth's upper atmosphere and interactions with the magnetosphere and the solar wind were likely significantly different to how it is today due to major differences in the chemical composition of the atmosphere and the younger Sun being signifcantly more active. Understanding these factors is important for understanding the evolution of planetary atmospheres within our solar system and beyond. While the higher activity of the Sun would have caused additional heating and expansion of the atmosphere, geochemical measurements show that carbon dioxide was far more abundant during this time and this would have led to significantly thermospheric cooling which would have protected the atmosphere from losses to space. I will present a study of the effects of the carbon dioxide composition and the Sun's activity evolution on the thermosphere and ionosphere of the Archean Earth, studying for the first time the effects of different scenarios for the Sun's activity evolution. I will show the importance of these factors for the exosphere and escape processes of the Earth and terrestrial planets outside our solar system.
How to cite:
Johnstone, C.: Earth's thermospheric evolution and implications for planetary habitability, Europlanet Science Congress 2020, online, 21 Sep–9 Oct 2020, EPSC2020-870, https://doi.org/10.5194/epsc2020-870, 2020.
The recent discovery of an Earth-sized planet (TOI-700 d) in the habitable zone of an early-type M-dwarf by the Transiting Exoplanet Survey Satellite constitutes an important advance. In this Letter, we assess the feasibility of this planet to retain an atmosphere – one of the chief ingredients for surface habitability – over long timescales by employing state-of-the-art magnetohydrodynamic models to simulate the stellar wind and the associated rates of atmospheric escape. We take two major factors into consideration, namely, the planetary atmospheric composition and magnetic field. In all cases, we determine that the atmospheric ion escape rates are potentially a few orders of magnitude higher than the inner Solar system planets, but TOI-700 d is nevertheless capable of retaining a 1 bar atmosphere over gigayear timescales for certain regions of the parameter space. The simulations show that the unmagnetized TOI-700 d with a 1 bar Earth-like atmosphere could be stripped away rather quickly (< 1 gigayear), while the unmagnetized TOI-700 d with a 1 bar CO2-dominated atmosphere could persist for many billions of years; we find that the magnetized Earth-like case falls in between these two scenarios. We also discuss the prospects for detecting radio emission of the planet (thereby constraining its magnetic field) and discerning the presence of an atmosphere.
How to cite:
Dong, C., Jin, M., and Lingam, M.: Atmospheric Escape From TOI-700 d: Venus versus Earth Analogs, Europlanet Science Congress 2020, online, 21 Sep–9 Oct 2020, EPSC2020-1001, https://doi.org/10.5194/epsc2020-1001, 2020.
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