bluuebunny/crossref_metadata_2025 huggingface dataset:
Modeling magma oceans in mantle convection simulations
Authors: Sanchis Enrique , Noack Lena , Golabek Gregor J.
Published: September 2022

Magma oceans play a fundamental role in the thermal evolution of rocky planets and moons. Most of these objects are thought to experience a magma ocean phase at least at their very early ages. Right after the formation of a planet or moon, its temperatures are expected to be very high mainly due to radiogenic heating from fast-decaying isotopes, and the release of energy due to the gravitational contraction of the object. Therefore, it is very likely that most, if not all, of these bodies, have or have hosted magma oceans. In addition, it is also possible to find, long after their formation, very hot planets or moons that contain large magma oceans in their interior. Perhaps the most famous example is Io, the innermost of the Galilean moons orbiting Jupiter. Due to strong tidal interactions with Jupiter and its moons, Io suffers from extreme tidal heating, strong enough to melt large regions of its interior.

On the other hand, mantle convection simulations are crucial to understanding the long-term thermal evolution of rocky planets and moons. These simulations are tailored to solid convection in the mantle, thus when considerable fractions of melt are present or are generated in the interior of the planet, the contrasting properties of the solidus and liquidus phases become too large for the simulations to handle. Properties such as the viscosity and the thermal conductivity are several orders of magnitude different between solidus and liquidus. As consequence, the time steps of the simulation become too short, and the simulation ends up 'frozen' in time. Besides, these large differences pose numerical restrictions that make the codes unstable and prone to crash. Due to these limitations, simulating the interior thermal evolution of hot rocky planets and moons with mantle convection codes turns out to be extremely challenging.

In this work, we apply our magma oceans modeling to Io, since it is an appropriate test case in the Solar System with evidence of hosting large amounts of magma in its interior (e.g., Khurana et al. 2011). We use the CHIC convective code (Noack et al. 2015) to model Io's interior thermal evolution. We then apply and expand an approach, originally developed by Golabek et al. 2011, in which the effective local properties are altered wherever melt is present or produced. Our modeling can be applied to any rocky planet with hot interiors, as could be the case of the innermost Trappist-1 planets, or many of the rocky exoplanets known.
The Pursuit of A Meticulous Chemical Survey of Exoplanets
Authors: Edwards Billy , Changeat Quentin , Tsiaras Angelos , Tinetti Giovanna , Lagage Pierre-Olivier
Published: September 2022

Thousands of exoplanets have now been discovered with a huge range of bulk parameters. However, the essential nature of these planets remains largely mysterious. We have poor observational insights into how the chemistry of a planet is linked to its formation environment, or how the host star drives the processes controlling the planet's birth and evolution.

Current facilities have begun the reconnaissance of exoplanetary atmospheres. HST has been utilised to conduct observations of tens of worlds. These data have allowed for the first “population” studies of exoplanet atmospheres to be undertaken. WFC3 G141, which provides sensitivity to water in these atmospheres, has been central to these efforts and has characterised planets in both transmission and emission.

I will discuss the latest outcomes of homogenous population studies with HST WFC3, highlighting the key results and findings in the search for chemical trends. Furthermore, the limitations of current approaches will be presented, including data quality, the potential biases in the current analysis methods, and lack of rigorous population-level target selection.

In the next few years, the quality and quantity of space-based data will drastically increase thanks to JWST, Twinkle and Ariel. These new facilities will probe the atmospheres of hundreds of planets in unprecedented detail, triggering a substantial shift in our understanding of planetary science. However, to maximise the science yield of these missions we must learn lessons from the currently available datasets.

I will discuss how we can use the results and, at times, failings of these previous endeavours to develop clear strategies for target selection. Additionally, I will present projects which seek to understand the key capabilities and niches of these observatories, to help develop strategies to exploit the synergies and complementarities between different facilities in an attempt to construct a meticulous chemical survey of exoplanet atmospheres.
The ELF project: Performance of an extreme adaptive optics system compensating for atmospheric turbulence, cophasing a diluted pupil and performing dark hole coronography in order to reach high contrast exoplanet direct detection
Authors: Langlois Maud , Graf Camille , moretto Gil , Kuhn Jeff , Lewis Kevin , Rebolo Rafael , Lodieu Nicolas , Zhou Ye , cunnygham Ian
Published: September 2022

The ExoLife Finder telescope concept combines elements of a fixed pupil telescope with an interferometer in order to achieve very large apertures, high angular resolution and high contrast. The Small ELF (SELF) project is a precursor instrument under construction in the Canary Islands. By combining 15x50cm off-axis parabolic primary segments with 15 off-axis elliptical secondaries in a circular ring SELF achieves the angular resolution of a  3.5m diameter telescope allowing in addition direct “dark hole” coronagraphy by applying specific phase displacements to the subapertures to create nulling in a small area of the field of view. Wavefront sensing and control is done using machine learning observations of simultaneous speckle images in combination with a Mach-Zehnder wavefront sensing for high order wavefront control. Extreme adaptive optics (XAO) systems have severe difficulties to cope with the diluted apertures, and to meet the high contrast requirements: high speed and high accuracy (~ 10 nm) at 5-10 cm spatial scale. An innovative high order adaptive optics system using a self-referenced Mach-Zehnder wavefront sensor has been proposed to counteract these limitations. In this paper, we report on our numerical simulations of the SELF XAO system and on the experimental results obtained for such configuration on our bench dedicated to high contrast. The XAO system delivers high strehl ratio (>95%) while operating in synergy with focal plane wavefront sensing to support cophasing and dark hole coronography in order to reach very high contrast performances.
Effects of regolith porosity on exospheric gas release and retention
Authors: Sarantos Menelaos , Tsavachidis Spiridon , Prem Parvathy
Published: September 2022

The release of gases from regolith is studied with a Monte Carlo model in order to improve models of surface-boundary exospheres in the inner solar system. This kinetic model quantifies the competition between adsorption, desorption, and Knudsen and surface diffusion in three-dimensional granular media. The regolith is simulated as a computer-generated sphere packing with grain size distributions selected from lunar samples, whose voids present realistic paths for mass transport of trapped gases. In this work previous studies of exemplary gas-surface systems (argon, water, sodium) are extended by building sphere packings of varying macroporosity (0.4-0.6). Furthermore, the new calculations include light scattering and heat transfer. Results quantify the effect of regolith porosity on 1) gas residence time, 2) gas angular distribution, and 3) the magnitude of grain-to-grain temperature variations in vacuum. The findings are useful for understanding measurements from laboratory experiments as well as spaceborne measurements (e.g., LADEE, MESSENGER, Bepi Colombo).
Radial distribution of plasma at comet 67P and implications for cometary flyby missions
Authors: Edberg Niklas J. T. , Johansson Fredrik Leffe , Eriksson Anders I. , Vigren Erik , Henri Pierre , De Keyser Johan
Published: September 2022

The Rosetta spacecraft followed comet 67P/Churyumov-Gerasimenko (67P) for more than two years, at slow walking pace (about 1 m/s) within 1500 km from the nucleus. During one of the radial movements of the S/C in the early phase of the mission the radial distribution of the plasma density could be estimated, and the ionospheric density was found to be inversely proportional to the cometocentric distance r from the nucleus (a 1/r-distribution). In this study we characterise the radial distribution of plasma around 67P throughout the mission further, and expanding on the initial results. We also investigate how a 1/r-distribution can be perceived during a flyby with a fast (10's km/s) spacecraft, such as the upcoming Comet Interceptor mission, when there is also an asymmetry introduced to the outgassing over the comet surface. We use data from the Rosetta Plasma Consortium (RPC) Langmuir probe (LAP) and Mutual Impedance (MIP) instruments during six  intervals throughout the mission, when Rosetta moved radially with respect to the comet, to determine the radial distribution of the plasma. We then simulate what radial distribution a fast flyby mission would actually observe during its passage through a coma when there is a 1/r plasma density distribution but also an asymmetric outgassing introduced. The plasma density around comet 67P is found to roughly follow a 1/r dependence, although significant deviations occur in some intervals. If normalizing all data to a common outgassing rate (or heliocentric distance) and combining the intervals to cover a the full radial range of 10-1500 km, a 1/r^1.19 average distribution is found. The simulated observed density from a fast S/C flying through a coma with a 1/r-distribution but with an asymmetric outgassing can in fact appear as both a 1/r-distribution, a 1/r^2-distribution, or an even steeper distribution, due to the combined effect of the radial variation in plasma with the variation in density arising from the spacecraft moving over an asymmetrically outgassing body.

 
Exploring the diversity in pyroclastic deposits and volcanic vents on Mercury with machine learning techniques
Authors: Leon-Dasi Mireia , Besse Sébastien , Doressoundiram Alain
Published: September 2022

Evidence of explosive volcanism on the surface of Mercury has been identified in the form of vents and pyroclastic deposits using images and spectral data acquired by the MESSENGER mission (Goudge et al. 2014, Thomas et al. 2014, Jozwiak et al. 2018, Pegg et al. 2021). Understanding the history of the volcanic eruptions forming these features provides an insight in the geological and thermal evolution of the planet. To this end, it is important to constrain the characteristics of each vent and, correlating them with the environment, classify the features according to their age and geological conditions. An individual analysis of a selection of vents has been carried out by Barraud et al. 2021 and Besse et al. 2015, providing new insights on the size, volcanic content and spectral properties of these features. However, performing a global analysis presents further challenges.  The collection of volcanic features identified presents a wide variety of characteristics in terms of morphology (simple vent, pit vent, vent-with-mound etc.), shape (circular, elliptical, curved), location (crater centre, crater rim, inter-crater plain), distribution (isolated or compound) and spectral properties of the pyroclastic deposit. This introduces a large number of variables that complicate the characterisation and timing of volcanic eruptions. 

The vast amount of data returned by the MESSENGER mission offers both a challenge and an opportunity in the methodology to solve this problem. While the combination of a large number of observations from different instruments can complicate the physical interpretation of a given process, it opens the door to the use of machine learning techniques. These methods rely on the identification of patterns on the input data without considering the associated physics, with the aim to reveal underlying correlations that can then be related to physical and chemical phenomena. This technique has been applied to the entire dataset collected by the Mercury Atmospheric and Surface Composition Spectrometer (MASCS), to classify the visible-near-infrared reflectance spectra into three categories (D'Amore et al. 2022). 

In this work, we investigate the application of machine learning to explore the differences amongst the pyroclastic deposits and volcanic vents, with the aim of improving the understanding on the evolution of explosive volcanism in Mercury. In this methodology we combine data from the MASCS and the Mercury Laser Altimeter (MLA) instruments with other properties of the vent surroundings (e.g., crustal thickness). By treating unrelated physical variables together as components of the same input vector, the outcome is a set of dimensions that have no direct physical meaning but can uncover underlying structures to be later physically or chemically interpreted. 
High-inclination NEAs as meteor stream parent bodies
Authors: Christou Apostolos , Georgakarakos Nikolaos
Published: September 2022

Recent meteor radar surveys have uncovered a subpopulation of meteoroids with high orbital inclination and at a=1 au, in the form of a grouping of radiants within the southern toroidal source of sporadic meteors (Brown et al, Icarus, 2010;  Pokorny et al, Icarus, 2014). Many of these showers are so far not detected in optical surveys (Jenniskens et al, PSS, 2018; Bruzzone et al, PSS, 2020), implying a meteoroid population deficient in large particles, such as might result from the gradual, size-sorting action of P-R drag.

Here we consider that the source of this population is one or more Near-Earth Asteroids (NEAs) in similar, high inclination orbits. We test this hypothesis by numerical integration of test particles ejected from a selection of suitable NEAs and evolving under the influence of radiation forces. We pay particular attention to the role of dynamical resonances near Earth's orbit as well as the Kozai mechanism in confining the meteoroids, countering the dispersive action of drag forces and gravitational scattering.

We will report on the outcome of our simulation runs at the meeting.
Characteristics of Lunar Photoelectrons and Backscattered Electrons
Authors: Xu Shaosui , Poppe Andrew , Szabo Paul , Harada Yuki , Halekas Jasper , Chamberlin Phil
Published: September 2022

Introduction: Electrons emitted from the lunar surface include photoelectrons, cold secondary electrons, and backscattered electrons, all of which contribute to the surface-charging environment. Among these electron populations, secondary electrons have been well characterized by previous studies but not so much for the other two populations that make up the high-energy tail. Recently, we reported of oxygen Auger electron observations at the Moon by the ARTEMIS (Acceleration, Reconnection, Turbulence, and Electrodynamics of the Moon's Interaction with the Sun) spacecraft, which provides a unique feature to identify photoelectrons emitted from the lunar surface. This Auger feature allows for the creation of empirical templates for photoelectrons and backscattered electrons to disentangle these two populations and examine their characteristics separately.

Methodology:  By utilizing the Auger electron feature, we identify cases that are separately dominated by either photoelectrons or pure backscattered electrons and then create energy spectral templates for each population, when the Moon is immersed in the solar wind. With such templates, we then fit the total measured electron spectrum from the lunar surface as observed by ARTEMIS from mid-2012 to the end of 2020 and determine the relative contributions of the two populations.

Results:  For photoelectrons, we find that (1) Auger electron fluxes are correlated with solar X-ray photon fluxes as expected; and, (2) there is a dawn-dusk asymmetry in Auger electron fluxes, caused by a selection bias as downward electrons are mainly halo electron on the dusk side, lower in flux than strahl electrons on the dawn side. For backscattered electrons, we find the backscattering ratio (the flux ratio of backscattered electrons and downward electrons at the same energy) varies geographically due to different proportions of surface backscattered electrons and non-adiabatic magnetic scattering by crustal magnetic fields. In addition, for surface backscattering, the backscattering ratio decreases with increasing energies, ranging from <20% at 50 eV to <10% at 500 eV. Lastly, comparing the two populations, within the solar wind, backscattered electron fluxes are mostly higher than photoelectron fluxes and, thus, photoelectrons are not so frequently observed when the Moon is in the solar wind. 

 
Laboratory Research on Ice Rheology in support of Ocean World Exploration
Authors: McCarthy Christine , Zaman Maheenuz , Singh Vishaal , Skarbek Rob
Published: September 2022

Understanding the rheology of ice in the outer shells of ocean worlds is important for a variety of reasons. The mechanical behavior has long been studied to make sense of intriguing surface morphologies, some of which bear striking resemblance to rocky features on Earth and other bodies, some of which are totally unique. The mechanical behavior of planetary ice also is used to provide possible answers to questions related to transport and conveyance of melt and/or chemical species, which in turn addresses potential habitability. Finally, in the era of ocean world exploration, knowledge of the mechanical behavior of very cold and moderately impure ice provides critical information needed to manage expectations and inform protocols for future missions. In this presentation I will share results from experiments conducted in our lab on ice and ice-mixtures that are designed to measure the mechanical behavior at planetary conditions. In particular we use a custom cryogenic, servo-controlled biaxial apparatus to measure frictional response of ice sliding on ice to explore faulting behavior in the upper, brittle portion of an icy shell. Moving beyond simple Coulomb analysis, we measure fault stability as a function of temperature and velocity, which point to a predicted source region for icequakes at depth, a so-called “seismogenic zone” for icy worlds. We employ rate- and state- dependent frictional properties determined from experiments in numerical models to describe a variety of fault and boundary types, including thrust, subduction, and strike-slip faulting. We explore the nature of unstable frictional behavior by analyzing laboratory stick-slip events for frequency-magnitude, or recurrence, relations. Such information can inform expected seismic activity and be useful for planning instrument sensitivity and can be used ultimately to interpret results from a lander-based seismometer. Additionally we will present results from performance testing of communications hardware that may be deployed in the vicinity of such active faults. We will share mechanical and optical results from a series of shear-testing experiments on fiber optic communication tethers embedded in ice and will articulate the feasibility of their use in future probe missions that will descend into an icy shell. The experimental work coming out of our lab seeks to unravel the dynamic properties of ice on icy moons, identify challenges that may arise when spacecraft interact with it, and develop the technology required for assessing the habitability of ocean worlds.
Pristine Solar Wind Deep in the Collisional Atmosphere of Mars
Authors: Girazian Zachary , Halekas Jasper , Ruhunusiri Suranga , Fowler Christopher
Published: September 2022

At Mars, the solar wind is usually decelerated and heated at the bow shock, then diverted around the planet by the induced magnetosphere. Recently, however, Crismani et. al. (2019) presented MAVEN (Mars Atmosphere and Volatile EvolutioN) observations of an interesting event, where near-pristine solar wind was observed in the collisional atmosphere below 200 km. We searched through seven years of MAVEN SWIA (Solar Wind Ion Analyzer) observations to determine how often these types of events occur. We found at least 15 orbits during which near-pristine solar wind was observed below 200 km. In this presentation, we will discuss the occurrence rate of the events and characterize the planetary and solar wind conditions under which they are observed. Finally, we will discuss the implications of solar wind having direct access to the collisional atmosphere, which may include localized (1) ionization that alters the structure of the ionosphere, (2) heating of the thermosphere, (3) energization of ions to escape speeds, and (4) patchy proton aurora.

Reference: Crismani, M. M. J., Deighan, J., Schneider, N. M., Plane, J. M. C., Withers, P., Halekas, J., et al. (2019). Localized ionization hypothesis for transient ionospheric layers. Journal of Geophysical Research: Space Physics, 124, 4870–4880. https://doi.org/ 10.1029/2018JA026251
Salty SeaFreeze: new experimental efforts toward a comprehensive thermodynamic representation for icy moons hydrospheres.
Authors: Journaux Baptiste , Brown J. Michael , Pakhomova Anna , Powell-Palm Matthew , Vance Steve , Bollengier Olivier , Tobie Gabriel
Published: September 2022

The water-rich layer of icy moons of the outer solar system contains a variety of organic (e.g. CH4, NH3, CO2) and inorganic (e.g. NaCl, MgSO4, Na2SO4, MgCl2) solutes detected by robotic mission like NASA Cassini and Galileo probes. Many of the geological processes on these moons, like cryovolcanisms, tectonics, oceanic evolution, involves processes of partial melting and fractional crystallization that are controlled by  the stability of solid phases (ices and hydrates) and their eutectic. The ices and pure water thermodynamic are now accurately constrained at the high pressure and low temperature found inside these moons by the SeaFreeze numerical representation. However, the thermodynamics and equilibria in salty aqueous systems relevant for icy moons remains underexplored. SeaFreeze is used broadly in the planetary science community and beyond, the next logical step is the representation of the effect of salts (e.g. anti-freeze effects, eutectics, density, formation of hydrates, water activity), that requires important experimental effort. We will discuss new results from sound speed measurements, isochoric freezing and in-situ single crystal X-Ray diffraction experiments at high pressure and low temperatures that allowed us to constrain the equilibria (eutectics and phases stability) as well as solution thermodynamics in the H2O-(Na-,Cl+,Mg2+,SO42-) systems. We will present how these new data are implemented into SeaFreeze to allow for a comprehensive representation of water-salts systems from the cryogenic conditions at the surface to the incredible pressures found in icy worlds. We will discuss the implication for chemical physics/mineralogy as well as for the upcoming exploration of icy worlds of our solar system by NASA and ESA robotic space missions.
Optimization of future multi-filter surveys towards asteroid characterisation
Authors: Klimczak Hanna , Kotłowski Wojciech , Oszkiewicz Dagmara , DeMeo Francesca , Kryszczyńska Agnieszka , Wilawer Emil , Kwiatkowski Tomasz
Published: September 2022

Colors have been commonly used by researchers to assign taxonomic class to asteroids. Furthermore, the optical design of future space surveys should account for a large number of incidental asteroid observations that they will likely make. It is thus crucial to consider a use of an optimal filter setup for asteroid taxonomic classification. Following the work from Klimczak et al. 2021 which compared different machine learning algorithms (Naive Bayes, Logistic Regression, Support Vector Machine (SVM), Gradient-boosting, Multilayer Perceptrons) on two different parameter sets: principal component directions (PCA) and reflectance values spaced 0.05μm in the 0.45-2.5μm range and spectral slope, we extend this analysis to reflectance colors.  We aim to study the most efficient way to link colors to the Bus-DeMeo taxonomy and obtain a set of narrow band filters that should be used to correctly detect the taxonomic type of an object. 

The set of features used in this work consists of 35 reflectance colors that were selected across the wide range of spectroscopic measurements. All aforementioned machine learning methods are trained to predict taxonomic types on this set, and Feature Selection is performed to assess the importance of individual features and decrease the redundancy of the set. 

We find that Multilayer Perceptron and Support Vector Machines provide the best results on the whole feature set, with 85% balanced accuracy for taxonomic types and 93% for complexes. These results slightly outperform the results from our previous work. Furthermore, we find that satisfactory results can be obtained by reducing the feature set to top 5 features for taxonomic types (retaining 80% balanced accuracy), and top 3 features for complexes (retaining 89% balanced accuracy).

This work has been supported by grant No. 2017/25/B/ST9/00740 from the National Science Centre, Poland.
Electric conductivities of Titan’s dusty ionosphere
Authors: Shebanits Oleg , Wahlund Jan-Erik , Waite Hunter , Dougherty Michele
Published: September 2022

Titan's ionosphere has a global presence of dusty (ion-ion) plasma a few hundreds of kilometers below the photoionization peak altitudes. Recent studies have shown that charged dust dramatically alters the electric properties of plasmas, in particular planetary ionospheres. Titan is immersed in magnetospheric plasma and magnetic field of Saturn (most of the time) and the moons ionospheric conductivities define the interaction with its environment.

We present revisited electric conductivities and the conductive dynamo region of Titan’s ionosphere using the full plasma content (electrons, ions+, and ions–/dust–) from 13 years of in-situ measurements by the Cassini mission. We show that the traditional approach of only using the easily detectable electron densities underestimates the Pedersen conductivities at ∼1,100–1,200 km altitude by up to 35%. The Hall conductivities are in general not affected but several cases indicate a reverse Hall effect at closest approach (∼900 km altitude) and below. We also identify a dayside-nightside asymmetry, with dayside conductivities a factor ∼7–9 larger than on the nightside (due to higher plasma densities).

Figure 1 shows the median profiles of the Pedersen, Hall and magnetic field parallel conductivities plotted in altitude and versus the neutral atmosphere, color-coded into dayside, terminator and nightside. First thing to note is that due to the extent of Titan’s atmosphere and ionosphere, plotting versus altitude results in noticeable less organized data due to atmospheric variations. These profiles scale with the plasma densities so their trends propagate – we identify solar cycle effects that match those on the heavy charge carriers.

Figure 1. Sliding median conductivity profiles: Pedersen (panels a1, b1), Hall (panels a2, b2) and Parallel (panels a3, b3). The total medians are in solid black. The colored lines are medians for the dayside (SZA<70), terminator (70≤SZA<100) and nightside (SZA≥100). Adapted from Shebanits et al. (2022).

The study is available in open access and includes the dataset: https://doi.org/10.1029/2021JA029910 .
Formation of a single large moon around a gas giant: Saturn-Titan system
Authors: Fujii Yuri , Ogihara Masahiro
Published: September 2022

Circumplanetary disks are regarded as birthplaces of large moons. While Jupiter has four large satellites known as Galilean moons, Titan is the only large moon around Saturn. N-body simulations using a simple power-low disk suggest a system tend to have multiple moons or loses all the moons due to inward migration. Thus, forming a single satellite system in a disk is known to be difficult. 
 The orbits of moons are continuously affected by the interaction with the disk, and the direction and speed of the migration depend on the disk structures, i.e., surface density and temperature. Therefore, the final configuration of the moon system is determined during the dissipation of the disk. We studied the orbital evolution of moons in various circumplanetary disks to find a way of configuring a single-large-moon system. 
 We model dissipating circumplanetary disks with taking the effect of opacity into account when we calculate the temperature structure. Because of this, our disk has multiple slopes, and thus, the migration speed of a moon varies with the orbital location. Then, we calculate the orbital evolution of Titan-mass moons in the final evolution stage of the disks. We performed N-body simulations with initially many satellites to see whether single-moon systems can form at the end. 
 We found that the radial slope of the temperature structure characterized by the dust/ice opacity produces a patch of orbits where the Titan-mass moons resist inward migration with a certain range of the viscosity. We call such a patch as “safety zone.” The safety zone assists moons initially located in the outer orbits to remain in the disk, while those in the inner orbits migrate toward the planet. When the satellite formation is not very efficient in the outer radii of circumplanetary disks, the system can end up with a single large moon at a distant from the planet while the inner orbits are cleared out. Smaller moons may stay in the inner orbits as their migration speed is slower compared to the Titan-mass ones. We demonstrated the formation of systems with single large moon around gas giants for the first time. 
Modelling the full 2-5 µm Juno JIRAM spectral range with NEMESIS: Zonal Profiles of Jupiter’s Aerosols, Condensables, and Disequilibrium Species
Authors: Melin Henrik , Fletcher Leigh , Irwin Pat , Grassi Davide , Mura Alessandro
Published: September 2022

Since 2016 the Juno spacecraft has been in orbit around Jupiter, gathering unprecedented data from its highly inclined 53-day orbit. The Jupiter Infrared Auroral Mapper (JIRAM) is an imager and spectrograph with spectral coverage between 2 and 5 µm. This region is dominated by reflected sunlight by aerosols and hazes, with distinct absorptions by ammonia, phosphine, germane and other minor species in Jupiter's troposphere, as well as ionospheric H3+ at high altitude. Here, we outline the process undertaken to model the full spectral coverage of JIRAM with NEMESIS, our radiative transfer and retrieval code (Irwin et al., 2008). This includes altering the NH3 aerosol and haze properties, updating the molecular line-list, and testing the sensitivity to the abundance of the molecular species that are within the 2-5 µm range offered by JIRAM. 

This study builds on previous models for JIRAM spectra in thermal emission (Grassi et al., 2020) and reflected sunlight (Grassi et al., 2021), by attempting to fit the entire 2-5 µm range simultaneously with a single consistent aerosol model.  The model includes two aerosol layers, a NH4SH type layer at 1.3 bars, and a NH3 type layer at 0.7 bars, as well as a tholin type haze layer that extends from the troposphere to the stratosphere. We demonstrate that JIRAM observations of both reflected sunlight and thermal emission cannot be reproduced simultaneously using standard refractive indices available in the literature.  We build a simple model of the refractive indices for the three aerosol layers, adapting the technique of Sromovsky et al. (2010), and demonstrating the improvement in the fits at each step.  As a proof of concept we present the analysis of meridionally averaged zonal profiles, investigating how aerosols, ammonia, and phosphine vary with latitude during the early perijoves of the mission.
Could we observe exomoons around ε Eridani b?
Authors: Kleisioti Evangelia , Dirkx Dominic , Rovira Navarro Marc , Kenworthy Matthew
Published: September 2022

There are more than 200 moons in the Solar System, however no exomoon detection has been confirmed so far. Extrasolar gas giants are expected to host exomoons, which could scale in mass with their parent planet up to Earth radii. Two of the gas giant planet-moon systems are in long-lived mean motion resonances (MMRs) and it is expected that the latter would prevail in extrasolar systems as well. Since tidal dissipation depends on the orbital and physical properties of the system, there is a chance that Tidally Heated Exomoons (THEMs; Peters and Turner 2015) are detectable with MIRI/JWST in infrared (IR) wavelengths.

ε Eridani b is one of the few known exoplanets with mass greater than 1 MJ and angular separation larger than 0.5 arcseconds on the sky. The proximity to Earth makes ε Eridani b a suitable candidate for the search of THEMs in the IR. Taking the Jovian satellites as an archetype for an exomoon system around ε Eridani b, this would mean that an MMR between two or more exomoons could make them detectable for larger timescales.

We explore the parameter space of exomoon orbital and physical properties, conclude which values would make an exomoon around ε Eridani b detectable with MIRI/JWST and investigate the interior structures of the putative exomoon that are consistent with these properties. Our model assumes a layered, radially symmetric moon, consisting of a silicate mantle and a liquid core. We present our results for the Andrade rheology model, different heat transfer mechanisms (mantle convection, heat piping), and constrain feasible interior structures and orbital parameters for several values of (observed) surface heat fluxes.
Formation of primordial atmospheres for growing protoplanetary cores
Authors: Sommeregger Arijane
Published: September 2022

Context. In order to find life outside the Solar System we first need to understand how terrestrial planets form in different environments. Many terrestrial planets are formed by a conversion process, during which planets lose most of their H2-rich (primordial) atmospheres. Primordial atmospheres are formed in the early, disk-embedded phase of planet formation, where a protoplanetary core can accumulate gas from the circumstellar disk into a planetary envelope.
Aim. The aim of this thesis is to simulate the formation process of primordial atmospheres and to analyse their formation as a function of core mass, disk lifetime, and orbital radius. In doing so, this study considers cores that have formed at the start of the embedded phase and do not change their mass during atmosphere formation, as well as cores that grow continuously during the embedded phase.
Methods. The formation of primordial atmospheres are described using the equations of radiation-hydrodynamics, which are solved numerically using the adaptive implicit RHD-code (TAPIR). The discretisation of the physical equations is based on finite volumes on a staggered mesh and advective flows are calculated using the second order van Leer flux limiter.
Results. The study considers primordial atmospheres for orbital radii between 0.387 and 1.524 au, and disk lifetimes in the range of 1 - 10 Myr. The atmospheres get more massive for larger orbital radii, larger core masses, and longer lifetimes of the surrounding disk. Atmospheres of cores more massive than a limitating mass Mc,limit at some point enter a runaway collapse, while atmospheres of less massive cores grow smoothly during their entire formation. The core mass limit Mc,limit shrinks with disk lifetime and orbital radius. The smallest value found is Mc,limit = 0.7 M⊕.
How does the origin of stars in the Milky Way affects the composition of planet building blocks?
Authors: Cabral Nahuel , Guilbert-Lepoutre Aurélie , Bitsch Bertram , Lagarde Nadège
Published: September 2022

Our Galaxy is composed of different stellar populations which are characterized by different chemical abundances. They are thought to imprint the composition of small bodies formed together with planets : planet building blocks (PBB), asteroids and interstellar objects.

We investigated the expected PBB composition in different Galactic regions using the ground-based spectroscopic surveys GALAH and APOGEE ; and the stoichiometric condensation model from Bitsch & Battistini (2020). This study has revealed the potential link between the PBB composition and the stellar populations across the Galaxy (Cabral et al, submitted).  

Interestingly, the PBB compositions determined from large observational surveys reveal common trends determined previously with synthetic models. We confirm the PBB composition valley separating the thin disk stars from the thick disk stars (i.e. a bimodal distribution of compositions) already highlighted in our previous study (Cabral et al. 2019) using the Besançon stellar population synthesis model of the Milky Way.

Moreover, we find that metal-poor stars both in the thin and thick disks should host water-rich PBB. Given the importance of water abundance in planet formation simulations (Morbidelli et al. 2015, Ros et al. 2013, 2019), we discuss in a galactic context the potential impact for the early phases of planet formation.

Overall we find that the chemical abundances of host stars should impact the composition of exoplanets, as well as small body populations found around these stars. Our results imply that thick disk stars (which are rather alpha-rich, metal-poor stars) are suitable hosts for ice-rich small bodies (cf. Figure). Whether thick disk stars are suitable for water worlds or/and hycean planets (Madhusudhan et al. 2021) remains matter of debate.

 
Escape and precipitation of planetary ions at Mercury under different solar wind conditions
Authors: Aizawa Sae , Andre Nicolas , Persson Moa , Modolo Ronan , Raines Jim , Leblanc Francois , Chaufray Jean-Yves , Nenon Quentin
Published: September 2022

The escape and precipitation of planetary ions at Mercury under different solar wind conditions have been examined using a global hybrid simulation. The combination of Mercury’s weak intrinsic magnetic field and solar wind conditions at Mercury’s location results in the formation of a relatively small magnetosphere compared to that of Earth. Its magnetosphere is strongly compressed and may disappear when solar wind conditions are extreme. Under these circumstances, the solar wind can directly interact with its exosphere and surface and the escape of planetary ions is expected to be enhanced. By focusing on the dynamic pressure and interplanetary magnetic field dependence, three different solar wind conditions are used in this study. Under the extreme solar wind planetary protons shows the highest escape rates while planetary sodium ions show the smallest, indicating that the distribution of sodium ions around the planet is controlled by the size of the magnetosphere. As the Larmor radius of planetary sodium ions is larger than that of planetary protons, they cannot escape and instead precipitate onto surface during extreme solar wind conditions, when the dayside magnetosphere is well compressed. Precipitation maps of three components (solar wind protons, planetary protons, and planetary sodium ions) show that the flux from planetary plasmas is sometimes higher than solar wind plasmas, suggesting that the precipitation of planetary plasmas should be considered for the space weathering of Mercury’s surface.
Effect of a thermally stratified layer in the outer core of Mercury on its internally generated magnetic field
Authors: Rivoldini Attilio , Deprost Marie-Hélène , Zhao Yue , Knibbe Jurien , Van Hoolst Tim
Published: September 2022

The low intensity and lack of small-scale variations in Mercury’s present-day magnetic field can be explained by a thermally stratified layer blanketing the convective liquid outer core. The presence of a present-day stable layer is supported by thermal evolution studies that show that a sub-adiabatic heat flow at the core-mantle boundary can occur during a significant fraction of Mercury’s history. The requirements for both the likely long-lived Mercury dynamo and the presence of a stable layer place important constraints on the interior structure and evolution of the core and planet.

We couple mantle and core thermal evolution to investigate the necessary conditions for a long-lived and present-day dynamo inside Mercury’s core by taking into account an evolving stable layer overlying the convecting outer core. Events such as the cessation of convection in the mantle may strongly influence the core-mantle boundary heat flow and affect the thickness of the thermally stratified layer in the core, highlight the importance of coupling mantle evolution with that of the core. We employ interior structure models that agree with geodesy observations and make use of recent equations of state to describe the thermodynamic properties of Mercury’s Fe-S-Si core for our thermal evolution calculations. 
 A Spiral arm or a Vortex in the outer disk of PDS-70 ?
Authors: Juillard Sandrine , Christiaens Valentin , Absil Olivier , Benisty Myriam
Published: September 2022

Observing dynamical interactions between planets and disks is key to understanding their formation. Two protoplanets have recently been observed within PDS 70's transition disk, along with an extended signal towards the north-west of the star. In this contribution, I will present a temporal analysis of the PDS 70 disk morphology with the aim of assessing whether it could trace a spiral arm caused by the dynamical interaction between the planet PDS 70 c and the disk - or rather be the footprint of a vortex, which can mimic a spiral-arm in an inclined disk. I will show the PDI and ADI images obtained with SPHERE-IRDIS spanning 6 years of observations. We reduced PDI datasets through the IRDAP polarimetric data reduction pipeline (for PDI data) and a novel algorithm that we developed (MUSTARD, for ADI data). I will explain the principle of our inverse-problem based MUSTARD algorithm. I will then show the trace of the potential spiral that we inferred by identifying local radial maxima in azimuthal slices of the disc in each dataset. I will then compare the measured traces with the expected motion of a spiral launched by planet c - i.e. in rigid-body motion. I will show how the traces seem to perfectly align in all datasets, and will finally discuss the implications of our results on the nature of this extended feature.
Numerical simulations demonstrating Eddy-driven jets and meridional circulation cells on gas giants
Authors: Duer Keren , Galanti Eli , Kaspi Yohai
Published: September 2022

Jupiter's atmosphere consists of a number of dynamical regimes: the equatorial superrotation and its adjacent retrograde jets, the midlatitude, eddy-driven, alternating jet streams, and the associated meridional circulation cells and the turbulent polar region. While intensive research has been conducted in the past decades on each of these regimes, they all remain only partially understood and somewhat mysteries. Different models give a variety of possible explanations for each of these regions, and only a handful of models can even capture two areas at once. This study presents new numerical simulations, using a 3D anelastic GCM, that can reproduce the midlatitudinal pattern of the mostly barotropic, alternating eddy-driven jets and the meridional circulation cells accompanying them. As expected for a gas giant, we find that the vertical eddy momentum fluxes are just as important as the meridional eddy momentum fluxes, which drive the midlatitudinal circulation on Earth. The number of the jets/cells, their extent, strength, and location are directly related to the boundary conditions, the Ekman number, and the depth of the atmosphere. Studies have shown that the rotation rate, the forcing scheme, and the Rayleigh number are also responsible for the emergence of jets in simulations of gas giants, but we keep these constant in our simulations. Our simulations also capture the tilted convection columns in the tangent cylinder region, leading to the superrotation at the equator and the adjacent, subrotating jets. We show that tilted columns can also generate equatorial subrotation, possibly explaining the zonal wind pattern on the ice giants. We find that the location and strength of the adjacent jet can indicate the depth of the atmosphere, as they are well correlated in all the simulations and on Jupiter and Saturn, according to gravity measurements by Juno and Cassini, respectively. Our analysis provides another step towards understanding the deep atmospheres of gas giants.
From HST to JWST - New tools to analyse exoplanet spectrocopic observations from space
Authors: Tsiaras Angelos
Published: September 2022

In the last 15 years, significant progress has been made in the field of atmospheric characterisation of exoplanets, utilising the most advanced instruments both on the ground and in space. Today, we are entering an era of very exiting prospects for the field of exoplanet characterisation. The James Webb Space Telescope (JWST) has been successfully launched, deployed and aligned, while ESA’s M4 mission, Ariel, has been adopted and is planned to fly in 2029.

This era will be characterised by the large volume of data that will be delivered from the new observatories. In my talk I will discuss the challenges we have to face in order to analyse the large data volume expected in the next decade. I will discuss the lessons learnt in the past years using the Wide Field Camera 3 on HST - the most successful instrument for exoplanet characterisation - and I will present a next-generation pipeline for the analysis of exoplanet spectroscopic observations, together with the first implementation on JWST data.