PS7.3

Jupiter still has some unanswered questions regarding its formation history and atmospheric processes (Taylor et al., Cambridge Planetary Science, 2006). With this work, we hope to contribute to the progress of unravelling some of these questions.

We used the observations of Jupiter from the ESA mission Infrared Space Observatory (ISO) (Kessler et al., A&A 315, L27, 1996) in the 793.65-3125 cm^-1 (3.2-12.6 µm) region using the Short-Wave Spectrometer (SWS) (de Graauw et al, A&A 315, L49-L54, 1996). Our work is focused on the 793.65-1492.54 cm^-1 (6.7-12.6 µm) region of the spectrum. We argue that it warrants a revisit and reanalysis since it was an important step in the study of Jupiter’s atmosphere and there have been advancements in atmospheric models and line data, despite the age of this dataset.

Firstly, as a way to verify the validity of our method, we used the NEMESIS radiative transfer suite (Irwin et al., Journal of Quantitative Spectroscopy & Radiative Transfer 109, 1136–1150, 2008) to reproduce the results from Encrenaz et al., Planetary and Space Science 47, 1225-1242, 1999. This study is done using the CIRS NEMESIS template as a base adapted to the ISO-SWS data.  We use correlated k-tables compiled from line data from Fletcher et al., Nature communications 9.1, 1-14, 2018 for a NH₃, PH₃, ¹²CH₃D, ¹²CH₄, ¹³CH₄, C₂H₂, C₂H₆, He, H₂, C₂H₄ and C₄H₂ model atmosphere, with our results showing good agreement.

Having verified our method, we present here our preliminary results of the study of abundances of ¹²CH₃D, ¹²CH₄, ¹³CH₄, C₂H₂ and C₂H₆ of Jupiter’s atmosphere as well as our initial study of the pressure-temperature profile of Jupiter. We use the NEMESIS suite to determine the abundances as a function of altitude and retrieve the pressure-temperature profile. We compare our results with the profiles and abundances from Neimann et al., Journal of Geophysical Research Atmospheres 103(E10):22831-45, 1998 and Fletcher et al., Icarus 278, 128–161, 2016 with the aim to constrain the number of possible best fit profiles.

We also present our initial study the H/D and ¹²C/¹³C isotopic ratio of the Jovian atmosphere from the abundances of ¹²CH₃D, ¹³CH₄ and ¹²CH₄ following the methodology from Fouchet et al., Icarus 143, 223–243, 2000.

With this preliminary work we hope to further advance the knowledge about the chemical processes that happen in Jupiter, as well as the chemical and temperature vertical distribution. As future work, we expect to extend our frequency domain to the full range of ISO/SWS observations and study the ¹⁵N/¹⁴N ratio.

Acknowledgements

We thank Thérèse Encrenaz, from LESIA, Observatoire de Paris, for providing the data for this work and Patrick Irwin, from the University of Oxford (UK), for the help with the NEMESIS radiative transfer suite.

We acknowledge support from the Portuguese Fundação para a Ciência e a Tecnologia (FCT)/MCTES through the research grants UIDB/04434/2020, UIDP/04434/2020, (ref. PTDC/FIS-AST/29942/2017) through national funds and by FEDER through COMPETE 2020 (ref. POCI-01-0145 FEDER-007672) and through a grant of reference 2021.04584.BD.

How to cite: Ribeiro, J., Machado, P., Pérez-Hoyos, S., and Dias, J.: A reanalysis of ISO-SWS Jupiter observations: preliminary results, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4626, https://doi.org/10.5194/egusphere-egu22-4626, 2022.

Being mostly connected via closed magnetic field lines, the aurorae at the two poles display two broadly similar signatures of the same magnetospheric processes. However, differences are sometimes observed, indicative of asymmetries either in the polar regions (e.g. different solar illumination, magnetic anomalies, etc.) or in the magnetosphere (e.g. twisting of the magnetotail), thus showing two complementary sides of the magnetosphere-ionosphere coupling.

Whatever the planet, seeing the aurorae on both poles at the same time is challenging. Either both polar regions can be seen at once, but then only from the side, with poor spatial coverage (especially close and beyond the limb), or we need (at least) two observatories. Here we use the latter option to observe the two faces of the UV aurorae on Jupiter. In the last years, several Hubble Space Telescope observations with the Space Telescope Imaging Spectrograph (STIS) have been planned during close-up perijove observations of the poles with the UV spectrograph (UVS) on board the Juno spacecraft. The aurorae at Jupiter can be divided into three main components, with the Main Emissions, a quasi-continuous, but sometimes irregular, ribbon of auroral emissions, delimitating the outer emissions outside of it and the polar emissions inside of it. We compare the global morphology and the relative power emitted by the different auroral features in these three regions. Former studies also indicated that synchronized quasi-periodic flares could be observed in both hemispheres and we will look after similar events in this new dataset. Finally, even if the observations are delayed by approximately one hour, we can still compare the mean emitted power before (north) and after (south) each Juno perijove to look for a global trend.

How to cite: Bonfond, B., Grodent, D., Palmaerts, B., Gladstone, R., Badman, S., Clarke, J., Gérard, J.-C., Giles, R., Greathouse, T., Haewsantati, K., Hue, V., Kammer, J., Nichols, J., Sicorello, G., Wannawichian, S., and Yao, Z.: The two faces of the Jovian UV aurorae, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5947, https://doi.org/10.5194/egusphere-egu22-5947, 2022.

We present a preliminary study of the H₃⁺ auroral emission at Jupiter, which uses data taken with the long-slit Echelle spectrometer, iSHELL, available at the NASA Infrared Telescope Facility (IRTF). Since first light in 2016, iSHELL has been used to provide ground-based support for the NASA-Juno mission, observing Jupiter’s aurora while Juno takes in-situ measurements of the magnetosphere as well as observing the aurora. These ground-based iSHELL measurements are critical as Juno-JIRAM lacks the spectral resolution to measure the Doppler shift of the H₃⁺ spectra, from which the line-of-sight velocity can be derived, and the ionospheric flows inferred.

Previous ground-based H₃⁺ studies have identified several significant ionospheric flows in Jupiter’s auroral region. Sub-rotating flows have been recorded in the dusk-side of the main auroral emission, which is in agreement with our current understanding of the generation of the aurora. However, super-rotating flows were also identified in the dawn-side of the main auroral emission, the origin for which remain uncertain but could lie either in driving from a dynamically changing thermosphere following a solar wind compression or the increase in angular velocity of magnetic field lines past corotation as they rotate into the dawn sector of the magnetosphere and are compressed. Furthermore, previous studies have identified a region of stationary H₃⁺ ions (relative to the magnetic pole) in the polar aurora. This stationary region was originally located coincident to the UV swirl region, however, a more recent study, using a dataset with higher spatial resolution, located the stationary region coincident with the UV dark region, which is also dark in the IR. It is thought that the stationary region is due to coupling to the solar wind either through a Dungey-like process where a single convection cell is confined by the Vasyliunas cycle or through solar wind viscous flow interaction. Therefore, the mechanisms which couple Jupiter’s aurora to the solar wind are yet to be determined.

Here we discuss the longevity and variability of the above flows using the preliminary results from the iSHELL dataset. We consider how, moving forwards, these preliminary results can be compared to Juno data to advance our understanding of the generation of Jupiter’s aurora and how it is coupled to the solar wind. 

How to cite: Johnson, R., Stallard, T., and Melin, H.: Preliminary results from IRTF–iSHELL of Jupiter’s aurora during the NASA-Juno mission, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8147, https://doi.org/10.5194/egusphere-egu22-8147, 2022.

The JUpiter ICy moons Explorer (JUICE) of the European Space Agency will investigate Jupiter and its icy moons Europa, Ganymede, and Callisto, with the aim to better understand the origin and evolution of our Solar System and the emergence of habitable worlds around gas giants. The Particle Environment Package (PEP) on JUICE is designed to measure neutrals and ions and electrons at thermal, suprathermal, and radiation belt energies (eV to MeV). 

In the vicinity of Callisto, PEP will characterize the plasma environment, the outer parts of Callisto's atmosphere and ionosphere and their interaction with Jupiter's dynamic magnetosphere. About 20 Callisto flybys with closest approaches between 200 km and 5000 km altitude are
planned over the course of the JUICE mission. In this presentation, we review the state of knowledge regarding Callisto's ambient environment and magnetospheric interaction with recent modeling efforts for Callisto's atmosphere and ionosphere to identify science opportunities for the PEP observations and to optimize scientific insight gained from the foreseen JUICE flybys. These considerations inform science operation planning of PEP and JUICE and they will guide future model development for the atmosphere and ionosphere of Callisto and their interactions with the plasma environment.

How to cite: Galli, A., Vorburger, A., Carberry Mogan, S. R., Roussos, E., Stenberg Wieser, G., Wurz, P., Föhn, M., Krupp, N., Fränz, M., Barabash, S., Futaana, Y., Brandt, P. C., Kollmann, P., Haggerty, D., Jones, G. H., Johnson, R. E., Tucker, O. J., Simon, S., Tippens, T., and Liuzzo, L.: Callisto's atmosphere and its space environment: prospects for the Particle Environment Package on board JUICE, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1348, https://doi.org/10.5194/egusphere-egu22-1348, 2022.

We present 3D Monte-Carlo simulation results for the surface-sputtered and sublimated H₂O molecules in Ganymede's atmosphere. To calculate particle fluxes onto Ganymede's surface, we use test particle model results for electrons, thermal H⁺ and O⁺, energetic H⁺, O⁺⁺, and S⁺⁺⁺, with unprecedented energy resolution. In addition, besides a thermal model based on Galileo measurements, we use recently published surface water content maps and recently measured water sputter yields.

Our simulations show that for the sputtered atmosphere, it is mainly the impinging O⁺, O⁺⁺, and S⁺⁺ ions that deliver H₂O to the atmosphere, while electrons and protons only play a minor role in comparison. With Ganymede's surface temperature ranging from 80 K to 150 K (the latter being an upper bound), most returning H₂O molecules stick to the surface. As a consequence of this, the morphology of Ganymede's magnetosphere, and the resulting patterns in the precipitation maps, are well preserved in the exosphere up to altitudes of a few thousand kilometers.

In the sub-solar region, it is the sublimated H₂O that dominates the atmosphere by up to four orders of magnitude. The sublimated atmosphere quickly decreases with altitude, though, and sputtering becomes the dominant release process for H₂O molecules reaching beyond a few hundred kilometers altitude. The sublimated H₂O atmosphere is thus quite substantial but highly limited in spatial extent.

In addition to our most important modeling results concerning Ganymede's H₂O atmosphere, we will also discuss their implications for spacecraft observability. Using the recently updated JUICE trajectories (CREMA 5), we will show which atmospheric populations (sublimated and/or sputtered H₂O) will be encountered during the different Ganymede orbit phases (elliptical, high polar, and low polar). Finally, we will present expected measurement results for the Neutral and Ion Mass spectrometer (NIM), part of the Particle and Environment Package (PEP) onboard JUICE / ESA.

How to cite: Vorburger, A., Shahab, F., Galli, A., Liuzzo, L., Poppe, A., and Wurz, P.: 3D Monte-Carlo Simulations of Ganymede's Water Atmosphere - Predictions for JUICE/PEP/NIM, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7590, https://doi.org/10.5194/egusphere-egu22-7590, 2022.

The Juno Waves instrument measured plasma waves associated with Ganymede's magnetosphere during its flyby on 7 June, day 158, 2021.  Three distinct regions were identified including a magnetotail/wake, and nightside and dayside regions in the main magnetosphere distinguished by their electron densities and associated variability. The main magnetosphere includes electron cyclotron harmonic emissions including a band at the upper hybrid frequency, as well as whistler-mode chorus and hiss. These waves likely interact with energetic electrons in Ganymede’s magnetosphere by pitch angle scattering and/or accelerating the electrons.  The magnetotail/wake is accentuated by low-frequency turbulence and electrostatic solitary waves.   Radio emissions observed before and after the flyby likely have their source in Ganymede’s magnetosphere. 

How to cite: Kurth, W., Sulaiman, A. H., Hospodarsky, G. B., Menietti, J. D., Mauk, B. H., Clark, G., Allegrini, F., Valek, P., Connerney, J. E. P., Waite, J. H., Bolton, S. J., Imai, M., Santolik, O., Li, W., Duling, S., Saur, J., and Louis, C.: Juno Plasma Wave Observations at Ganymede, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10441, https://doi.org/10.5194/egusphere-egu22-10441, 2022.

ESA’s JUICE and NASA’s Europa Clipper (EC) are the next two missions to the Jupiter system, focusing on three of the Galilean moons: Europa, Ganymede, and Callisto.

JUICE will spend four years in the Jovian system and after tens of flybys of Europa, Ganymede, and Callisto will enter into orbit around Ganymede where it will nominally remain for nine months, until its end of mission. EC will also spend about four years in orbit around Jupiter, performing more than 50 flybys of Europa, the main mission target, but it will also fly by Ganymede and Callisto several times. Combining the data of the two missions will enable a better global estimation of the moons’ gravity fields and ephemerides.

During the Jupiter tours of both missions and JUICE’s Ganymede orbital phase, radiometric tracking data will be acquired at Earth ground stations, enabling precise spacecraft orbit determination, and joint estimation of the main dynamical parameters of the Jupiter system. The two missions rely on different radio links: JUICE is endowed with a triple two-way radio link configuration in two frequency bands (X/X, X/Ka and Ka/Ka) which will allow for a full calibration of dispersive noise sources. EC is capable of X/X and X/Ka links, with X/X being the nominal configuration during Europa flybys.  

Range, range-rate, as well as VLBI (lateral positioning) tracking data, from both missions, will allow to retrieve the static gravity field and tidal parameters of the moons, together with their orbital position. This will also provide crucial information about Jupiter’s gravity tidal parameters, in particular the imaginary part of its Love numbers at the frequency of the Galilean moons. A better characterization of tidal interactions between Jupiter and the Galilean moons can unveil crucial information about the stability and the evolution of the Laplace resonance, governing the dynamics of the three innermost Galilean moons.

In this study, we analyze the attainable uncertainties for the parameters characterizing the ephemerides reconstruction of the Galilean moons using range, range-rate, and VLBI simulated observables. VLBI data mainly provide the spacecraft angular position with respect to reference radio sources (quasars) tied to an inertial frame (“plane of sky”), while range and range and range-rate (being computed along the line of sight) especially constrain the spacecraft state within their orbital plane. Including VLBI data is thus expected to be particularly effective in improving the uncertainty of the moon ephemerides in the out-of-plane direction. We will quantify the synergy between the different radiometric observable types, assess their respective contribution to the moons' ephemerides, the imaginary part of Jupiter’s Love number and analyze the sensitivity of the estimation solution to various parameters (observation planning, expected data quality, etc.)

How to cite: Magnanini, A., Fayolle, M., Gomez Casajus, L., Zannoni, M., Tortora, P., Lainey, V., Dirkx, D., Gurvits, L., Mazarico, E., and Park, R.: Combining JUICE and Europa Clipper range, range-rate and VLBI observables to Improve the Galilean moons ephemerides, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7836, https://doi.org/10.5194/egusphere-egu22-7836, 2022.

For the entire ion energy range observed at Europa, we calculate spatially-resolved maps of the surface sputtering rates of H₂O_, O₂, and H₂ from impacts by magnetospheric ions. We use the perturbed electromagnetic fields from a hybrid model of Europa’s plasma interaction, along with a particle-tracing tool, to calculate the trajectories of magnetospheric ions impinging onto the surface and their resultant sputtering yields. We examine how the distribution of the sputtering rates depends on the electromagnetic field perturbations, the angle between the solar radiation and the corotating plasma flow, and the thickness of the oxygen-bearing layer within Europa's surface. Our major findings are: (a) Magnetic field-line draping partially diverts the impinging ions around Europa, reducing the sputtering rates on the upstream hemisphere, but allowing for substantial sputtering from the downstream hemisphere. In contrast, zero sputtering occurs in much of the downstream hemisphere with uniform electromagnetic fields. (b) If the oxygen-bearing surface layer is thin compared to the penetration depth of magnetospheric ions, thermal ions dominate the O₂ sputtering rates, and the region of strongest sputtering is persistently located near the upstream apex. However, if the oxygen-bearing layer is thick compared to the penetration depth, energetic ions sputter the most O₂, and the location of maximum sputtering follows the sub-solar point as Europa orbits Jupiter. (c) The global production rate of O₂ from Europa’s surface varies by a factor of three depending upon the moon's orbital position, with the maximum particle release occurring when Europa's sun-lit and upstream hemispheres coincide.

How to cite: Addison, P., Liuzzo, L., and Simon, S.: Effect of the Magnetospheric Plasma Interaction and Solar Illumination on Ion Sputtering of Europa's Surface Ice, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-659, https://doi.org/10.5194/egusphere-egu22-659, 2022.

The NASA mission Europa Clipper is designed to conduct multi-disciplinary investigations of the interior, composition, and habitability of the Galilean moon Europa. The measurement of Europa’s gravity field, tides, orientation, and moment of inertia (MoI) will enable an accurate characterization of the moon’s interior by constraining internal structure models through the inversion of geophysical measurements. The refined knowledge of Europa’s interior will provide a better understanding of its thermal evolution and of the processes that formed and maintained the liquid water ocean underneath the moon’s outer icy shell. The accurate estimation of the tidal Love number k₂ is expected to provide geodetic evidence of the existence of the ocean, and its combination with the Love number h₂ will enable the estimation of the icy shell mean global thickness.

The determination of the MoI, obtained either through measurements of the degree-2 gravity field with the hydrostatic equilibrium assumption or by also measuring Europa’s orientation and obliquity, will provide information on the deep interior of the moon, possibly constraining the size and the composition of the solid interior. Numerical simulations are performed to assess the expected accuracy of the key geophysical quantities from the analysis of Europa Clipper radiometric data. These measurements are used in a Bayesian Inversion (e.g., Monte Carlo Markov chain) to explore the properties of Europa’s hydrosphere and deep interior.

How to cite: Petricca, F., Genova, A., Castillo-Rogez, J., and Mazarico, E.: Constraining the Interior Structure of Europa with Gravity Measurements, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5851, https://doi.org/10.5194/egusphere-egu22-5851, 2022.

Icy moons of Jupiter and Saturn are privileged targets in currently developed space missions by several space agencies and in particular ESA, NASA and their partners. One of these missions is ESA’s first large mission in the Cosmic Vision Programme, JUICE [1], which is being developed to address questions regarding the Jupiter system and its satellites, with a focus on the largest moon, Ganymede. The overarching theme for JUICE is the emergence of habitable worlds around gas giants taking into account the requirements involving the presence of organic compounds, trace elements, water, energy sources and a relative stability of the environment over time.

Among other, JUICE will determine the characteristics (composition and dynamics) of the exospheres of the icy moons [2], in particular Ganymede and Europa, with for instance coordinated observations among sets of instruments like UVS, PEP, RPWI, MAJIS, 3GM, J-MAG, JANUS and SWI. The JUICE mission is scheduled to be launched in spring 2023 and arrive at Jupiter in mid-2031 and is foreseen to last nominally for 3 and a half years. JUICE investigations will benefit from current observations by JUNO and will be synergistic to NASA’s Europa Clipper mission. I will describe the foreseen investigations of the tenuous atmospheres of the icy moons around Jupiter.

Cassini explored the dense and organic-laden atmosphere of Titan during several flybys over 13 years [2,3] and also determined the characteristics of the Enceladus plumes. However, new questions have risen and several cold cases [4] remain that will constitute major science objectives for future space missions to the satellites around Saturn, like Dragonfly [5] or an orbiter in the Saturn system or a dedicated Enceladus mission…

In particular, Titan’s atmosphere has not yet revealed all its secrets, in particular for the chemical composition, which should be much more complex than what was detected by Cassini-Huygens. Future in situ measurements will be extremely useful in unveiling this unique complex world. In the meantime, ground-based observations with large telescopes like ALMA, elsewhere in Chile or the ones in Hawaii can help complement the past discoveries.

References:

[1] Coustenis, A., Witasse, O., Erd, C., 2021. The JUICE mission: expectations and challenges. Fall issue of The Bridge on space exploration, Sept. 2021, Vol. 51, issue #3, pp. 41-50.

[2] Coustenis, A., Tokano, T., Burger, M. H., Cassidy, T. A., Lopes, R. M., Lorenz, R. D., Retherford, K. D., Schubert G., 2010. Atmospheres/exospheres characteristics of icy satellites. Space Sci. Rev., 153, 155-184. https://www.nae.edu/260902/The-JUICE-Mission-Challenges-and-Expectations

[3] Coustenis, A., 2021. “The Atmosphere of Titan”. In Read, P. (Ed.), Oxford Research Encyclopedia of Planetary Science. Oxford University Press (August 31). doi: https://doi.org/10.1093/acrefore/9780190647926.013.120

[4] Nixon, C. A., Lorenz, R. D., Achterberg, R. K., et al. (2018). Titan's cold case files - Outstanding questions after Cassini-Huygens. Planetary and Space Science, 155, 50-72.

[5] Barnes, J. et al. (2021). Science Goals and Objectives for the Dragonfly Titan Rotorcraft Relocatable Lander. The Plan. Sci. J., VoL. 2, Issue 4, id.130, 18 pp.

How to cite: Coustenis, A., Nixon, C., Encrenaz, T., Lavvas, P., and Witasse, O.: Future atmospheric research objectives of missions to the Jovian and the Kronian systems, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4379, https://doi.org/10.5194/egusphere-egu22-4379, 2022.

The Cassini Langmuir Probe (LP) data acquired in the ionosphere of Titan are re-analysed to finely study the electron behaviour in the birthplace of Titan’s aerosols (900-1200 km) [Waite et al 2007].

The detailed analysis of the complete Cassini LP dataset below 1200 km (57 flybys) shows the systematic detection of 2 to 4 electron populations (further named P₁, P₂, P₃, P₄), with reproducible characteristics depending on altitude and solar illumination. Populations P₁ and P₂ are always present, contrarily to P₃ and P₄. Due to their low density and low potential, P₁ electrons are suspected to be photo-electrons [Wahlund et al 2009] or secondary electrons emitted on the probe stick.

The electron populations densities and temperatures are deduced from the Orbital Motion Limited theory and the Sheath Limited theory [Wahlund et al 2009, Whipple 1965]. We observe that electron temperatures do not vary much with altitude between 1200 and 950 km, except for P₄. Statistical correlations with other quantities measured by Cassini are investigated. In particular, we observe that P₃ and P₄ densities are correlated with the extreme UV flux.

From our results we suggest possible origins for the three populations P₂, P₃ and P₄, coming from the plasma surrounding the probe:

-P₂ is detected in all cases, at rather low density (~500 cm^-3) and temperature (~0.04 eV). These are possibly induced by particle precipitation.

-P₃ electrons are denser with stronger solar illumination and higher pressure (up to 3000 cm^-3). Therefore, they are likely to be related to photo-ionization. They are hotter than P₂ electrons (~0.06-0.07 eV).

-P₄ electrons are only observed on dayside and below 1200 km, in the place where heavy negative ions and aerosols are present. They are then plausibly linked to dusty plasma effects. We suggest two possible formation processes: (1) the photo-emission of electrons from grains could be triggered by photons of a few eV due to the negative charge born by the aerosols [Shebanits et al 2016; Tigrine et al 2018] ; (2) electrons could also be thermo-emitted from the grains, as a result of their heating by diverse processes such as heterogeneous chemistry, sticking of electrons or recombination of radicals [Woodard et al 2020].

How to cite: Chatain, A., Wahlund, J.-E., Shebanits, O., Hadid, L. Z., Morooka, M., Edberg, N. J. T., Carrasco, N., and Guaitella, O.: Re-analysis of the Cassini RPWS/LP data in Titan’s ionosphere: electron density and temperature of cold electron populations, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8878, https://doi.org/10.5194/egusphere-egu22-8878, 2022.

Titan’s ionosphere, host to a global dusty (ion-ion) plasma, provides a unique environment for studies of dusty ionospheres, featuring one of the largest dusty plasma datasets from 126 flybys of the moon over 13 years. Recent studies have shown the charged dust to have a large impact on the electric properties of plasmas, in particular planetary ionospheres. Here we use in-situ data to derive the electric conductivities and define the conductive dynamo region at Titan.

Our results show that using the full plasma content increases the Pedersen conductivities at ~1100-1200 km altitude by up to 35% compared to only using electrons. The Hall conductivities are not consistently affected but several cases indicate a reverse Hall effect at 900 km altitude (closest approach) and below. We also discuss day-night differences, solar activity impact and compare to similar environments.

How to cite: Shebanits, O., Wahlund, J.-E., Waite, H., and Dougherty, M.: Conductivities of Titan's dusty ionosphere, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8592, https://doi.org/10.5194/egusphere-egu22-8592, 2022.

The Langmuir Probe (LP) onboard Cassini was one of the three experiments that could measure the cold inner magnetospheric plasma, along with the Radio and Plasma Waves Science (RPWS) and the Cassini Plasma Spectrometer (CAPS). While the century-old LP theory looks quite straight-forward, in reality things are much more complicated.

The operation of the LP is quite simple: by applying positive bias voltages, the probe attracts the electrons and repels the ions of the surrounding plasma. From the resulting current-voltage curve characteristics of the ambient electrons can be estimated, i.e. density and temperature. When negative bias voltages are applied to the probe the characteristics of the ambient ions can be estimated, i.e. density, temperature, and mass.

Though the LP operation and interpretation are quite simple and straightforward, there are assumptions made and therefore the theoretical models may not always reflect the actual plasma conditions in Saturn’s magnetosphere. For this study we are focused on the effect of the photoelectrons, i.e. electrons generated by the incident sunlight on Cassini’s surfaces, that are difficult to calibrate for on the ground and then observe and characterise in the LP data.

We present algorithms for identifying when Cassini is in the shadow of Saturn and its rings, and when the LP is in the shadow of Saturn, its rings or Cassini itself. The LP data inside and outside the eclipses are compared using the algorithms developed. In this presentation we will first discuss the impact of the photoelectron generation from the spacecraft surfaces to the LP current-voltage curves, and understand the variations of the measured plasma density connected with the photoelectrons. Then, using that knowledge, we attempt to define the optical depth of the rings in the wavelengths the LP operates in.

How to cite: Xystouris, G., Arridge, C. S., Morooka, M., and Wahlund, J.-E.: Langmuir Probe observations during eclipses of Cassini with Saturn and the Main Rings: ring optical depths and photoelectrons, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13530, https://doi.org/10.5194/egusphere-egu22-13530, 2022.

Based on Cassini observations from 2004 to 2016, we perform a comprehensive analysis of the statistical distribution of the occurrence rate, averaged amplitude, wave normal angle (WNA), ellipticity and power spectral intensity of ion cyclotron waves in Saturn’s inner magnetosphere. Our results show that ion cyclotron waves mainly occur between the orbits of Enceladus and Dione near the equatorial region (λ<20°), with higher occurrence rates in the northern hemisphere than the southern hemisphere. The averaged wave amplitudes vary between 0.1–2 nT with a strong day-night asymmetry and a pronounced minimum at the equator. Saturnian ion cyclotron waves are predominantly left-handed polarized with small WNAs near the equator, and become linearly polarized with larger WNAs at higher latitudes. The major wave power occurs frequently at frequencies of 0.5-1.2 f_w+, where f_w+ is the equatorial gyrofrequency of H₂O⁺ ions, with the strongest intensity (>~10 nT²/Hz) at L~6.5 statistically present in the midnight sector.

How to cite: Long, M., Cao, X., Ni, B., Gu, X., Ye, S., Yao, Z., Wu, S., and Xu, Y.: Statistical distribution of ion cyclotron waves in Saturn’s inner magnetosphere: A survey of Cassini measurements between 2004 and 2016, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2110, https://doi.org/10.5194/egusphere-egu22-2110, 2022.

The Soi crater region, an extensive region covering almost 10% of Titan’s surface, has the Soi crater in its middle, which is a relatively well-preserved crater on Titan.  This region includes the boundaries between the equatorial regions of Titan and the mid-latitudes, and extends into the high northern latitudes (above 50^o). All these three Titan latitudes are dominated by different types of geomorphological units, such as dunes, mountains, and lakes, and are governed by different geological processes (such as lacustrine, aeolian and fluvial). An additional important and unique characteristic of the Soi crater region is that it includes 59 empty lakes, and the extent of these features reaches as far south as 40^oN. We mapped this region at 1:800,000 scale and produced the first detailed geomorphological map of the region using the same methodology as presented by [1;2] and Schoenfeld et al. [3]. We included non-SAR (Synthetic Aperture Radar) data such as radiometry, ISS, and VIMS data in order to analyze vast areas not observed by SAR. We performed detailed VIMS analysis of hundreds of distinct regions for all geomorphological units with a radiative transfer technique [4] and a mixing model [5], to infer constraints on the composition. In our results, we introduce new geomorphological units, which were not seen in previous mapping of large Titan regions such as the Afekan and South Belet, and report the extensive presence of the scalloped plains units and their possible origin. A total of 10 craters, including Soi, are identified in this region, which are older than the plains and dune units. The radiative transfer analysis from VIMS showed that the major constituents covering the Soi crater region are compatible with water ice and organic alkane, alkene and alkyl-like stretch materials. We discuss our results in terms of origin and evolution theories.

[1] Malaska, M., et al. (2016), Icarus 270, 130; [2] Malaska, M., et al. (2020), Icarus, 344, 113764. [3] Schoenfeld, A., et al. (2021), Icarus 366, 114516. [4] Solomonidou, A., et al. (2020a), Icarus, 344, 113338; [5] Solomonidou, A., et al. (2020b), A&A 641, A16.

How to cite: Solomonidou, A., Schoenfeld, A., Lopes, R., Malaska, M., Coustenis, A., and Schmitt, B.: The Soi crater region on Titan: Detailed geomorphological and compositional maps, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5912, https://doi.org/10.5194/egusphere-egu22-5912, 2022.

Our team is using radio observations of Uranus, collected with the Very Large Array (VLA) telescope, to track seasonal changes in the deep troposphere of Uranus between 1981 and the present. In Hofstadter, Akins, and Butler (https://doi.org/10.5194/egusphere-egu21-1374), we reviewed evidence for seasonal changes in Uranus’ atmosphere from a record of VLA observations between 1981 and 2012. We found that large scale latitude structure has remained essentially similar for the bulk of the record with the exception of the pole-equator contrast differences between mid-summer observations in 1985 and late summer observations in 1994. This record has been extended to the present (close to ½ a Uranian year) with VLA observations in 2015 (published in Molter et al. 2021 https://doi.org/10.3847/PSJ/abc48a) and in late 2021 (and early 2022). Here, we will discuss our analysis of data obtained between 2012 and the present. All observations during this period were made with the upgraded Jansky VLA receivers and thus obtain higher sensitivities than those obtained before this time. This sensitivity permits resolution of zonal banding in the deep atmosphere, with bands observed between 0 and 20 degrees with 2 K brightness temperature contrasts at depths between 1-10 bar. These variations are likely driven by small-scale circulation patterns and associated condensation effects similar to those associated with the large pole-to-equator variations. We will discuss the consistency of these datasets and inferred distribution of opacity sources (NH₃ or H₂S). As we approach winter solstice in 2030, it will be particularly important to monitor Uranus’ deep atmosphere to provide further evidence for near-solstice changes in the deep atmosphere structure or composition as a seasonal phenomenon. Confirmation would provide insight into how varying insolation due to Uranus’ obliquity drives atmospheric changes in a manner unlike other giant planets.

How to cite: Akins, A., Hofstadter, M., Butler, B., Molter, E., and de Pater, I.: Seasonal Change in the Deep Atmosphere of Uranus, 1981 to 2021, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6614, https://doi.org/10.5194/egusphere-egu22-6614, 2022.

Uranus and Neptune exhibit strong zonal winds reaching up to 200 m/s and 400 m/s relative to their assumed bulk rotation, respectively. Furthermore, recent studies show that planetary ices such as water and ammonia become ionically conducting under conditions present in the ice giants. With rapidly increasing electrical conductivity, zonal flows inevitably couple to the background magnetic field, inducing electrical currents and magnetic field perturbations spatially correlated with zonal flows. Induced currents generate Ohmic dissipation, which can be used to constrain the depth of the zonal winds via the energy/entropy flux throughout the planetary interior. Constraining the zonal wind decay can be used to estimate the strength of magnetic field perturbations. Flows coupled to the background magnetic field induce poloidal and toroidal field perturbations through the ω-effect. Toroidal perturbations are expected to diffuse downwards and produce poloidal fields through turbulent convection, which are comparable to those induced by the ω-effect.We present a method for calculating electrical conductivity profiles of ionically conducting H-He-H₂O mixtures using results from ab-initio simulations. We then apply this prescription on several published interior structure models of Uranus and Neptune, assuming the heavy elements are represented by water. Structure models with higher water abundances (hot models) also have larger electrical conductivity values and their zonal winds need to decay faster compared to colder models. Using our solutions for the zonal wind decay, we estimate the strength of magnetic field perturbations induced by the zonal flows. We find that colder models could potentially have poloidal field perturbations that reach up to O(0.1) of the background magnetic field in the most extreme case. The possible existence of poloidal field perturbations spatially correlated with zonal flows could be used to constrain the interior structure of Uranus and Neptune.

How to cite: Soyuer, D. and Helled, R.: The Interplay between Zonal Winds and Magnetic Fields in Uranus and Neptune, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2522, https://doi.org/10.5194/egusphere-egu22-2522, 2022.

How to cite: Saha, P., Soyuer, D., Zwick, L., and D'Orazio, D.: Ice-giant missions as gravitational-wave detectors, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5598, https://doi.org/10.5194/egusphere-egu22-5598, 2022.

Future ice giant missions could be used to constrain the dark sector. Modifications to the third Kepler-law and deviations from the inverse square law of gravity can be tested by observing the extra perihelion precession of Uranus and Neptune, which allows probing the local dark matter density, modified gravity scenarios and Yukawa-like interactions. As of now, the extraprecession measurements of ice giants are done via ephemerides measurements, which have large uncertainties and provide looser constraints with respect to constraints by other planets. Current upper bound on the local dark matter density lies around ρ_DM ~ 10^-20 g/cm³. However, Doppler tracking missions to Uranus and Neptune with radio ranging accuracy of a few meters can improve this upper bound by 2 to 3 orders of magnitude via the extraprecession technique. Moreover, estimates coming from the spacecraft cruise time energy budget could yield an even better estimate than the Doppler ephemerides measurements, potentially providing evidence for dark matter or shedding light on modified gravity scenarios. Therefore, in addition to planetary science, in situ exploration of Uranus and Neptune also carries significance for exploring the local dark sector and probing fundamental physics.

How to cite: Zwick, L., Soyuer, D., and Saha, P.: Local Constraints on the Dark Sector by Future Missions to Uranus and Neptune, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2570, https://doi.org/10.5194/egusphere-egu22-2570, 2022.

We present the primary results from our recent analyses of mid-infrared observations of Neptune and Uranus from ground-based telescopes, including VLT-VISIR, Subaru-COMICS, and Gemini-TEXES.  We discuss our recent discovery that Neptune’s stratospheric temperatures appear to be changing dramatically in just the past few years, following decades of cooling.  In contrast, we show that no evidence yet exists of long-term thermal changes in Uranus’ stratosphere, but mid-IR observations of Uranus are still extremely limited. We share new observations from VLT-VISIR, express the need for continued ground-based imaging, and discuss how the James Webb Space Telescope MIRI observations will help greatly advance our understanding of the Ice Giants in the years ahead.  

How to cite: Roman, M. T., Fletcher, L. N., Orton, G. S., Greathouse, T. K., Moses, J., Rowe-Gurney, N., Irwin, P. G. J., Kasaba, Y., Fujiyoshi, T., Hammel, H. B., de Pater, I., Sinclair, J., and Antuñano, A.: Mid-Infrared Observations of Neptune and Uranus: Recent Discoveries and Future Opportunities, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4149, https://doi.org/10.5194/egusphere-egu22-4149, 2022.