Displays

Neptune’s atmosphere is covered by tropospheric clouds and elevated hazes that are highly contrasted in hydrogen and methane absorption bands that dominate the red and near-infrared spectrum of the planet. The major cloud systems observed in these wavelengths evolve in time-scales of days, months and years. However, the differential rotation of the atmosphere, and the vertical wind shear implied by the motion of some of these systems, result in challenges in identifying common cloud systems observed in images obtained with a time difference of only a few weeks. Given the small apparent size of Neptune’s disk (2.3 arc sec at best) there are outstanding difficulties in obtaining sufficient high-resolution data to trace Neptune’s atmospheric dynamics and study the variability in the atmosphere.

In 2019 Neptune has been observed by a battery of different large telescopes and techniques including: Adaptive Optics observations from the Keck, Lick and other telescopes, observations from Hubble Space Telescope in two different dates, and lucky-imaging observations with the GranTeCan 10.4m, Calar Alto 2.2m and the 1.05m Pic du Midi telescope. In addition, some ground-based observers using small telescopes of 30-40 cm have been successful to image Neptune’s major clouds completing a dense time-line of observations. We will present comparative results of Neptune’s major cloud systems observed with these facilities at a variety of spatial resolutions and long-term drift rates of some of these cloud systems. These will be compared with similar multi-telescope results obtained in the past with several of these telescopes since 2015. Future punctual observations achievable with new observational facilities such as the JWST will benefit from ground-based coordinated campaigns and will require a combination of several telescopes to understand drift rates and evolutionary time-lines of major cloud systems in Neptune.

How to cite: Hueso, R., de Pater, I., Simon, A., Wong, M., Sromovsky, L., Redwing, E., Chavez, E., Sánchez-Lavega, A., Dhillon, V., Fry, P., Littlefair, S., Tollefson, J., Delcroix, M., Ordonez-Etxeberria, I., Iñurrigarro, P., Hernández-Bernal, J., Pérez-Hoyos, S., Rojas, J. F., and Marsh, T.: Monitoring Neptune's atmosphere with a combination of small and large telescopes, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10443, https://doi.org/10.5194/egusphere-egu2020-10443, 2020.

The ice giants Uranus and Neptune are the least understood class of planets in our solar system but the most frequently observed type of exoplanets. Unfortunately, no designated mission to either of the two ice giants exists so far. Almost all of our gathered information on these planets comes from remote sensing. Whereas information provided by remote sensing is undoubtedly highly valuable, remote sensing of a planet's atmosphere also has limitations. In recent years, NASA and ESA have started planing for future missions to Uranus and Neptune, with both agencies focusing their attention on orbiters and atmospheric probes. A mass spectrometer experiment is a favored science instrument for an atmospheric probe for in situ composition measurements in most of these studies. Mass spectrometric measurements can provide unique scientific data, i.e., sensitive and quantitative measurements of the chemical composition of the atmosphere, including isotopic, elemental, and molecular abundances. Of major interest for the formation and evolution process of our Solar System are the species including the major volatiles CH₄, CO, NH₃, N₂; the noble gases He, Ne, Ar, Kr, Xe; and the isotopic ratios D/H,¹³C/¹²C, ¹⁵N/¹⁴N, ³He/⁴He, ²⁰Ne/²²Ne, ³⁸Ar/³⁶Ar, ³⁶Ar/⁴⁰Ar, as well as those of Kr and Xe. We will review the state-of-the-art mass spectrometry with respect to an application on such an atmospheric probe.  

How to cite: Wurz, P., Vorburger, A., Waite, H., and Mousis, O.: Chemical and Isotopic Composition Measurements on Atmospheric Probes for Giant Planets, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4492, https://doi.org/10.5194/egusphere-egu2020-4492, 2020.

To date a variety of different types of Mass Spectrometers has been utilized on missions to study the composition of atmospheres of many solar system bodies including Venus, Mars, Jupiter, Titan, the moon and several comets. For in-situ exploration of ice giant atmospheres, the highest priority composition measurements are helium and the other noble gases, noble gas isotopes, and other key isotopes including ³He/⁴He and D/H. Other important but lower priority composition measurements include abundances of volatiles C, N, S, and P, isotopes ¹³C/¹²C, ¹⁵N/¹⁴N, ¹⁸O/¹⁷O/¹⁶O and disequilibrium species PH₃, CO, AsH₃, GeH₄, and SiH₄. Required measurement accuracies are largely defined by the accuracies achieved by the Galileo (Jupiter) probe Neutral Mass Spectrometer and Helium Abundance Detectors, and current measurement accuracies of solar abundances^[1].

The Jet Propulsion Laboratory’s Quadrupole Ion Trap Mass Spectrometer (QITMS)^[2] is a compact, wireless instrument with a mass of only 7.5 kg, designed to meet these requirements and challenges specific to the planetary probe missions. It is currently the smallest flight MS available, capable of making measurements of all required constituents in the mass range 1-600Da, with a sensitivity of up to 10¹³ counts/mbar/sec and resolution of m/∆m=12000 at 40Da.

During a fly-by or a descent mission, the time available to perform an in-situ measurement is usually short. This makes it challenging to measure the abundances of minor constituents for which long integration times are needed. Mass spectrometers largely employ a non-discriminatory electron impact ionization of sampled gas mixtures for creating ions, which means the probability to create and trap ion fragments of trace species is very low and further destabilized by space charge effects due to an excessive number of ions from dominant species. A selective resonant ejection technique was employed to lower the amount of major constituent species, while keeping the minor constituents intact, which resulted in higher accuracy measurements of minor species.

Another inherent challenge of planetary entry probe mass spectrometers is the introduction of material to be sampled into the instrument interior, which operates at vacuum. Atmospheric entry probe mass spectrometers typically require a specially designed sample inlet system, which ideally provides highly choked, nearly constant mass-flow intake over a large range of ambient pressures. An ice giant descent probe would have to operate over a range of atmospheric pressures covering 2 or more orders of magnitude, 100 mb to 10+ bars, in an atmospheric layer of ~120 km at Neptune to ~150 km at Uranus. The QITMS features a novel MEMS based inlet system driven by a piezo-electric actuator that continuously regulates gas flow at inlet pressures of up to 100 bar.

In this paper, we present an overview of the QITMS capabilities including instrument design and characteristics of the inlet system, as well as the most recent results from laboratory measurements in different modes of operation.

[1] Mousis, O., et al., Pl. Sp. Sci., 155 12–40, 2018.

[2] Madzunkov, S.M., Nikolic, D., J. Am. Soc. Mass Spectrom. 25(11), 2014.

How to cite: Simcic, J., Nikolic, D., Belousov, A., Atkinson, D., and Madzunkov, S.: Quadrupole Ion Trap Mass Spectrometer for ice giant atmospheres exploration, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2024, https://doi.org/10.5194/egusphere-egu2020-2024, 2020.

            Liquid and solid particles are present in the atmosphere of many Solar System objects. Measuring aerosol properties can provide major constraints about both atmospheric composition and dynamics. While some bulk aerosol properties can be estimated using remote measurements, the size distributions and the typologies of the aerosols, which are related to their formation process, their origin and their evolution, are often poorly known. We propose a new concept of optical instrument dedicated to in situ measurements of aerosols as part of the science payload of an atmospheric entry probe or of a surface module. It relies the Earth atmospheric light aerosol counter LOAC used since 2013 under various types of balloons. This instrument measures the aerosol concentrations in 19 size classes between 0.2 and 50 micrometers, and estimates their typology

            The LONSCAPE (Light Optical Nephelometer Counter Sizer and Counter for Aerosols in Planetary Environments) concept combines counter measurements and nephelometric measurements at several phase angles, particle by particle, to retrieve for all size classes the concentrations and the scattering functions. This approach is the novelty of the instrument concept. The scattering functions can be compared to results of theoretical calculations but also to laboratory databases obtained for levitating particles and from the microwave analogy technics, to retrieve the refractive indices of the liquid and solid particles to better identify their nature and origin. Up to 10 angles measurements for the scattering function and one angle measurement for the counting provide an optimal configuration to distinguish between liquid, icy and possibly solid particles in the Uranus or Neptune atmosphere. Such an instrument must be able to detect up to tens of particles greater than 0.1 micrometer within 1 cm³.

            For ice giants, the instrument must work for pressures up to 10 bars. No pumping system should be needed since the aerosols will be injected in the optical chamber by an inlet parallel to the descent motion of the probe under parachutes. Considering the relative velocity between the atmosphere and the probe, the electronics must be able to detect particles crossing the laser beam up to several tens of m/s, which can be done by “conventional” electronics. Preliminary studies show that the instrument could have a total mass of about 2 kg and an electric consumption of about 2W.

How to cite: Renard, J.-B., Mousis, O., Berthet, G., Geffrin, J.-M., Levasseur-Regourd, A.-C., Rannou, P., and Verdier, N.: The LONSCAPE instrument, a Light Optical Nephelometer Sizer and Counter for Aerosols in Planetary Environments, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3495, https://doi.org/10.5194/egusphere-egu2020-3495, 2020.

In-situ probe measurements of planetary atmospheres add an immense value to remote sensing observations from orbiting spacecraft or telescopes, as highlighted and justified in numerous publications [1,2,3]. Certain key measurements such as the determination of noble gas abundances and isotope ratios can only be made in situ by atmospheric entry probes, but represent essential knowledge for investigating the formation history of the solar system as well as the formation and evolutionary processes of planetary atmospheres. Following the above rationale, a planetary entry mission to one of the outer planets (Saturn, Uranus and Neptune) has been identified as a mission of high priority by international space agencies. In particular, an entry probe mission proposal to Neptune has been selected as a flagship mission study in the next NASA decadal survey.

Within the scientific frame of atmospheric planetary sciences, a two- to three-year research study called IPED (Impact of the Probe Entry Zone on the Trajectory and Probe Design) investigates the impact of the interplanetary and approach trajectories on the feasible range of atmospheric entry sites as well as the probe design, considering Saturn, Uranus and Neptune as target bodies. The objective is to provide a decision matrix for entry site selection by comparing several mission scenarios for different science cases.

In this presentation, the focus is on approach circumstances of the planetary entry probe upon arrival at a normalized, spherical planet. Science objectives are organised in four (planetocentric) latitude ranges: (1) low latitudes < 15°, (2) mid latitudes between 15° and 45°, (3) high latitudes between 45° and 75° and (4) polar latitudes of > 75°. The latitude ranges are considered as potential entry zones for the implementation. The implementation strategy will be explained and discussed. Astrodynamically accessible latitudes are presented as a function of the approach velocity  vector v_∞ (both declination of the approach asymptote and magnitude). A roadmap is shown that explains the next implementation step to include the physical characteristics of the destination planet such as the planet’s size, rotation period, shape, ring geometries and obliquity.

The presented research was supported by an appointment to the NASA Postdoctoral Program (NPP) at the Jet Propulsion Laboratory (JPL), California Institute of Technology, administered by Universities Space Research Association (USRA) under contract with National Aeronautics and Space Association (NASA). © 2020 All rights reserved.

[1] Mousis, O. et al., Scientific Rationale for Saturn’s in situ exploration, Planetary and Space Science 104 (2014) 29-47.

[2] Mousis, O. et al., Scientific Rationale for Uranus and Neptune in situ explorations, Planetary and Space Science 155 (2018) 12-40.

[3] Hofstadter, M. et al., Uranus and Neptune missions: A study in advance of the next planetary science decadal survey, Planetary and Space Science 177 (2019) 104680.

How to cite: Probst, A., Spilker, L., Spilker, T., Atkinson, D., Mousis, O., Hofstadter, M., and Simon, A.: Accessible Latitudes for Planetary Entry Probe Missions to Saturn, Uranus or Neptune, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11891, https://doi.org/10.5194/egusphere-egu2020-11891, 2020.

The REASON ground penetrating radar (GPR) on Europa Clipper and the RIME GPR on JUICE will produce radargrams for Europa to determine the nature and depth of the ice overlying a putative ocean. The REASON radar is dual frequency, 9 MHz and 60 MHz, and the RIME frequency is 9 MHz. The surface temperature of Europa is between 50 and 100 Kelvin. At 9 MHz, the REASON GPR could map relative permittivity to about 30 km with a resolution of 150 m. These two GPRs may be able to spot pockets of water within the ice shell that could serve as a passageway for chemicals between the surface and the ocean below. The upper ice crust is expected to contain magnesium and sodium sulfates, and perhaps calcium sulfate [J. Moore, 1999].

To fill this gap in knowledge about the properties of the ice crust on Europa, we will make laboratory measurements of the relative permittivity (complex dielectric coefficient using impedance spectroscopy) and thermal properties (thermal conductivity and specific heat) of ice-salt mixtures at 9 and 60 MHz, over the temperature range 50 to 100 Kelvin, for the ice-salt mixtures given in Table X. This Table was provided by Kevin Collins (UCF). We do not plan to include any dust content in these ice-salt mixtures. These laboratory data may assist in the interpretation of future radargrams from RESSON and RIME

   TABLE 1, Europan ice-salt specimens for electrical and thermal property measurements.

We are planning also to make similar measurements of the electrical and thermal properties of ice on Titania (moon of Uramus), over temperature range of 60 to 90 Kelvin, and at 9 MHz. The surface of Titania is mainly water ice, with some frozen carbon dioxide and possibly salts. We will devise a table of salt-ice mixtures that is appropriate for Titania, based on available information on surface content.

How to cite: Frampton, R.: Icy Moon Ice-Salt Measurements for Dielectric and Thermal Properties, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12460, https://doi.org/10.5194/egusphere-egu2020-12460, 2020.

In June 2017, NASA published the Ice Giants Pre-Decadal Survey Mission Study Report which took a fresh look at science priorities and mission concepts for missions to the Uranus and Neptune systems. In addition to science objectives, the team explored the state of required technologies for remote and in-situ science exploration. Notably, three of the four mission architectures considered in the study included an atmospheric probe. More recently, interest has grown within ESA for outer planet exploration. In support of this objective, ESA has performed two CFD studies (January & July 2019) which analyzed the feasibility of stand-alone elements (orbiter and probes) provided by ESA as a part of a NASA led mission to the Uranus or Neptune systems. The first study was carried out by ESA experts with active participation of NASA/JPL. ESA highlighted the necessity to deepen the knowledge characterizing the aerothermal environment of the probes.

Entry environments for the NASA study were estimated using an aeroheating correlation that was calibrated to data returned from the Galileo probe entry to Jupiter. For the ESA concept study, aeroheating estimates were made using correlations employed during the design of the Galileo probe. Importantly, these correlations show large discrepancies in predicted total aeroheating (in some cases more than 100%), largely due to differences in the predicted radiative heat load. The magnitude of the disagreement is disconcerting in and of itself, but the problem is made worse by the fact that both correlations are being extrapolated from the extreme Galileo entry conditions to the (relatively) more benign Uranus and Neptune entry. It is likely that neither correlation is providing an accurate assessment of the true aeroheating loads at this time. Given that current NASA predictions are near the limits of existing TPS test capability, and that ESA predictions are more severe, improving the accuracy and associated margins of the prediction is critical to better assess mission feasibility.

Recent work in NASA by Cruden (AIAA Paper No. 2015-0380) and Erb (AIAA Paper No. 2019-3360) have substantially improved our fundamental understanding of aerothermodynamics in Hydrogen-Helium atmospheres. Similar work is planned in ESA as well. However, these recent data have not been incorporated into updated design models for Outer Planet probes. In addition, this work does not address the problem of trace atmospheric constituents (such as Methane) that are known to be present in Ice Giant atmospheres and may substantially alter the resulting shock layer radiation signal by providing a ready source of free electrons to initiate excitation processes. The proposed presentation will review the current status of aerothermal modeling for Ice Giant entries and propose a path forward to reduce key uncertainties and enable optimized thermal protection system designs.

How to cite: Wright, M., Walpot, L., Cruden, B., Brandis, A., and Johnston, C.: Aerothermal Modeling Challenges for Ice Giant Entry Probes, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11828, https://doi.org/10.5194/egusphere-egu2020-11828, 2020.

Saturn’s icy moon Enceladus is with its roughly 500 km diameter a differentiated geological active body that harbours a liquid ocean between its rocky core and icy mantle. This ocean is among the most promising places to host extraterrestrial life in our solar system.

At Enceladus’ south pole terrain, active geysers form a passage from the ocean to the surface; erupting ice, dust and gas particles. Most of those particles escape the moon’s gravity, but some portion falls back to the surface. Considering the current output, about 10 m of snow gets sedimented at a distance of about 100 m away from the geyseres within 10⁵-10⁶ years. Hence, depending on the timescale the geysers are active at the same location, the snow layer would have a thickness of some km already, assuming no densification.

A first model of the density profile of the snow layer as a function of the ice/vacuum ratio will be provided at the conference. To investigate the density at the surface, mainly the distribution of the ice grain shapes and the grain sizes have to be considered and put into a state equation. For modelling the density change in respect to the depth, also the pressure from the overlying weight has to be accounted for. As temperatures at Enceladus’ surface are too low, neither sintering nor processes such as melting and re-freezing can thereby contribute to densification. These processes however are acting in terrestrial glaciers. We propose therefore, because the temperatures on Enceladus are far below the melting point of ice, to consider the ice grains on Enceladus rather as sand than as snow in respect to these materials on Earth, when modelling the density within the snow layer.

After obtaining the ratio between ice and vacuum, it is possible to define the dielectric properties of the snow layer. The dielectric profile in turn is the primary diagnostic property for radar based geophysical investigation. It determines the velocity of radio waves in a medium as well as their reflection and refraction at interfaces.
Because of the above mentioned possibility that primitive extraterrestrial life might exist in Enceladus’  hidden ocean, there will likely be future space missions with the aim to reach a water reservoir and probe it. A well-defined density profile could then help to radar navigate a melting probe through the ice.

How to cite: Friend, P., Kyriacou, A., and Helbing, K.: Modelling the dielectric properties of the geyser deposited snow layer on Enceladus, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1146, https://doi.org/10.5194/egusphere-egu2020-1146, 2020.

We investigate nine Titan impact craters using Visual and Infrared Mapping Spectrometer (VIMS) data and a radiative transfer code (RT) [e.g. 1] in addition to emissivity data, in order to constrain the spectral behavior and composition of the craters. Past studies have looked at the chemical composition of impact craters either by using qualitative comparisons between craters [e.g. 2;3] or by combining all craters into a single unit [4], rather than separating them by geographic location or degradation state. Here, we use a radiative transfer model to first estimate the atmospheric contribution to the data, then extract the surface albedos of the impact crater subunits, and finally constrain their composition by using a library of candidate Titan materials. Following the general characterization of the impact craters, we study two impact crater subunits, the ‘crater floor’, which refers to the bottom of a crater, and the ‘ejecta blanket’, which is the material thrown out of the crater during an impact event. The results show that Titan’s mid-latitude plain craters: Afekan, Soi, and Forseti, in addition to Sinlap and Menrva are enriched in an OH-bearing constituent (likely water-ice) in an organic based mixture, while the equatorial dune craters: Selk, Ksa, Guabonito, and Santorini, appear to be purely composed of organic material (mainly unknown dune dark material). This follows the pattern seen in [4], where midlatitude alluvial fans, undifferentiated plains, and labyrinths were found to consist of a tholin-like and water-ice mixture, while the equatorial undifferentiated plains, hummocky terrains, dunes, and variable plains were found to consist of a dark material and tholin-like mixture in their very top layers. These observations also agree with the evolution scenario proposed by [3], wherein the impact cratering process produces a mixture of organic material and water ice, which is later “cleaned” through fluvial erosion in the midlatitude plains; a cleaning process that does not appear to operate in the equatorial dunes, which seem to be quickly covered by a thin layer of sand sediment. This scenario agrees with other works that suggest that atmospheric deposition is similar in the low-latitudes and midlatitudes on Titan, but with more rain falling onto the higher latitudes causing additional processing of materials in those regions [e.g. 5]. In either case, it appears that active processes are working to shape the surface of Titan, and it remains a dynamic world in the present day.

[1] Hirtzig, M., et al. (2013). Icarus, 226, 470–486; [2] Neish, C.D., et al. (2015), Geophys. Res. Lett. 42, 3746–3754; [3] Werynski, A., et al. (2019), Icarus, 321, 508-521; [4] Solomonidou, A., et al. (2018), J. Geophys. Res, 123, 2, 489-507; [5] Neish, A.C., et al. (2016), Icarus, 270, 114–129.


How to cite: Solomonidou, A., Neish, C., Coustenis, A., Malaska, M., Le Gall, A., Lopes, R., Altobelli, N., Witasse, O., Lawrence, K., Schoenfeld, A., Matsoukas, C., Baziotis, I., Schmitt, B., and Drossart, P.: The chemical composition of impact craters on Titan, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6131, https://doi.org/10.5194/egusphere-egu2020-6131, 2020.

We assess the gravity constraints on the interior structure of Europa in anticipation of the Europa Clipper mission.

Moore and Schubert (2000) illustrated that the diurnal tide amplitude, quantified by the diurnal (tidal) Love numbers, k₂^d and h₂^d, can be used to determine the presence of a subsurface liquid ocean due to the significant increase in tidal amplitudes associated with the mechanical decoupling of the shell with a subsurface ocean.  However, they considered a limited range of possible interior parameters except the ice shell rigidity, which was assumed to be in the range of 1-10 GPa. We consider a wider range of possible interior structure parameters and a more realistic ice shell rigidity range of 1-4 GPa. Inferring the presence of a subsurface ocean is slightly easier than previously thought (Verma & Margot 2018), with required absolute precisions of 0.08 for k₂^d , and 0.44 for h₂^d .

Previous work have considered diurnal (tidal) gravity constraints alone or static gravity constraints alone using a forward modeling approach (e.g.  Anderson et al., 1998; Moore and Schubert, 2000; Wahr et al., 2006). We evaluate constraints on interior structure parameters using Bayesian inversion with the mass, static gravity, and diurnal gravity as constraints, allowing a probabilistic view of Europa's interior structure. Given the same relative uncertainties, the static Love numbers provide stronger constraints on the interior structure relative to those from the mean moment of inertia (MOI). Additionally, the static Love numbers can be inferred directly from the static gravity field whereas inferring the MOI requires the Radau-Darwin approximation.

Jointly considered with the static shape, the static gravity field can constrain the average and long-wavelength thickness of the shell. For an isostatically compensated shell, it is usual to conceptualize the crust as a series of independently floating columns of equal cross-sectional area which, by application of Archimedes' principle, should have equal mass above the depth of compensation. However, this approach is unphysical in the presence of curvature and self-gravitation. We consider alternative prescriptions of Airy isostasy: the equal-pressure prescription (Hemingway and Matsuyama, 2017), and the minimum-stress prescription (Dahlen 1982; Beuthe et al., 2016; Trinh et al., 2019).  The gravitational coefficients are more sensitive to shell thickness than would be expected from the classical (equal-mass) approach, illustrating that the equal-mass prescription can lead to large errors in the inferred average shell thickness and its lateral variations.

Diurnal gravity data alone can only constrain the product of the shell rigidity and thickness (Moore and Schubert, 2000; Wahr et al., 2006). An additional observational constraint that is sensitive to these parameters is the libration amplitude, which can be obtained from direct imaging or from altimeter data. We show that a joint gravity and libration analysis is able to separately constrain the shell thickness and rigidity.

How to cite: Matsuyama, I. and Trinh, A.: Gravity constraints on the interior structure of Europa, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6150, https://doi.org/10.5194/egusphere-egu2020-6150, 2020.

In this study, we present the Uranus implementation of the planetWRF model [1]. For the determination of the radiative heat fluxes in our three-dimensional global circulation model, we make use of a simple analytic radiative model. This model is based on two-stream approximation and using a power-law scaling for the relationship between the optical depth and the pressure [2]. Preliminary results are compared to the zonal wind [3] and vertical temperature observations [4]. The effect of model's resolution, both vertical and horizontal, on the representation of the strong zonal transport in the Uranian atmosphere, is investigated. Moreover, we discuss the seasonal wind speed variations predicted by our model, assessing its potential to predict the changes in the zonal transport before and after the equinox in 2007. Possible implications for the Entry, Descent, and Landing applications are also presented. The devleoped GCM can also be potentially applied to the atmosphere of Neptune. 

[1] Richardson, Mark I., Anthony D. Toigo, and Claire E. Newman. "PlanetWRF: A general purpose, local to global numerical model for planetary atmospheric and climate dynamics." Journal of Geophysical Research: Planets 112.E9 (2007).
[2] Robinson, Tyler D., and David C. Catling. "An analytic radiative-convective model for planetary atmospheres." The Astrophysical Journal 757.1 (2012): 104.
[3] L.A. Sromovsky, I. de Pater, P.M. Fry, H.B. Hammel, P. Marcus, High S/N Keck and Gemini AO imaging of Uranus during 2012–2014: new cloud patterns, increasing activity, and improved wind measurements. Icarus 258, 192–223 (2015).
[4] Marley, Mark S., and Christopher P. McKay. "Thermal structure of Uranus' atmosphere." Icarus 138.2 (1999): 268-286.

How to cite: Temel, O. and Karatekin, Ö.: Development of a three-dimensional global circulation model for Uranus, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10146, https://doi.org/10.5194/egusphere-egu2020-10146, 2020.

Context: After more than thirteen years of exploration, Cassini-Huygens space mission provided a large amount of data about the atmosphere of Saturn’s largest moon, Titan. It is the only satellite in the solar system to house such a diversified chemistry triggered by the dissociation of N₂and CH₄under the action of different sources of energy (electrons, ions, solar photons, …)¹that reach the highest atmospheric layer. It results in the formation of complex carbon and nitrogen-based molecules. At lower altitudes, depending on temperature profile and saturation vapor pressures variations, these same compounds condense, thereby forming icy clouds in the stratosphere. In particular, between 2013 and 2017, two distinct benzene-containing clouds have been identified by the Cassini Composite Infrared Spectrometer for the first time during the mission, at the south pole at high stratospheric altitudes that are crossed by long-UV solar photons (λ>230nm). For the highest cloud located below 300km, the spectral signature of icy benzene is mixed with the ones of other molecules unassigned yet². The second cloud detected around 250km of altitude³, comes from a more complex process consisting in the simultaneous condensation of benzene with hydrogen cyanide. Thereafter in the mission, a significant warming-up in the stratosphere was reported, contributing to the sublimation of these same ices photo-processed.

Aim: Laboratory experiments have demonstrated that stratospheric ices evolve photo-chemically under long-UV solar photons and contribute to the formation of polymeric materials and volatile photo-products that will subsequently sediment at the surface. This work has been realized in the context of the preparation of the future Dragonfly space mission dedicated to analyze the organic layer that recovers the surface of Titan. We have chosen to simulate experimentally the photochemical aging process undergone by these benzene-containing icy clouds to characterize the chemical composition of the polymers photo-produced - to determine if their spectroscopic signature can match the one of the stratospheric aerosols layer observed by VIMS instrument - as well as the nature of the volatile photo-products released during the warming-up of the stratosphere. To do so, we irradiated pure benzene (C₆H₆) and hydrogen cyanide (HCN) ices, first isolated and then condensed simultaneously, with a high-pressure vapor mercury lamp (λ>230nm) - energetic conditions similar to Titan’s stratospheric ones - in a high vacuum chamber. This experimental set-up⁴ is designed to characterize the solid phase via in situ FT-IR spectroscopy and the volatile photo-products by a GC-MS instrument.

References :

1. Waite, J. H. et al. Science 316, 870–875 (2007).
2. Vinatier, S. et al. Icarus (2017) doi:10.1016/j.icarus.2017.12.040.
3. Anderson, C. et al. in vol. 49 304.10 (2017).
4. Abou Mrad, N., Duvernay, F., Theulé, P., Chiavassa, T. & Danger, G. Anal. Chem. 86, 8391–8399 (2014).

How to cite: Mouzay, J., Couturier-Tamburelli, I., Pietri, N., Danger, G., and Chiavassa, T.: Laboratory experiments in support of the Dragonfly space mission : Simulation of the photochemical aging process of benzene-containing clouds in Titan's stratosphere, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10500, https://doi.org/10.5194/egusphere-egu2020-10500, 2020.

We investigate the enrichment patterns of several delivery scenarios of the volatiles to the atmospheres of ice giants, having in mind that the only well constrained determination made remotely, i.e. the carbon abundance measurement, suggests that their envelopes possess highly supersolar metallicities, i.e. close to two orders of magnitude above that of the PSN. In the framework of the core accretion model, only the delivery of volatiles in solid forms (amorphous ice, clathrates, pure condensates) to these planets can account for the apparent supersolar metallicity of their envelopes. In contrast, because of the inward drift of icy particles through various snowlines, all mechanisms invoking the delivery of volatiles in vapor forms predict subsolar abundances in the envelopes of Uranus and Neptune. Alternatively, even if the gravitational instability mechanism remains questionable in our solar system, it might be consistent with the supersolar metallicities observed in Uranus and Neptune, assuming the two planets suffered subsequent erosion of their H-He envelopes. Because current technologies do not enable entry probes to reach levels deeper than a few dozens of bars in the atmospheres of giant planets, subsequent probe measurements should focus on the determination of the abundances of the noble gases since these latter never condense in the envelopes of Uranus and Neptune and are expected to be well mixed, even in the top layers at the ~1-bar level. Because these species are highly sensitive to the considered mechanism of volatiles delivery, they should be considered in the top priority of the measurements to be made by an ice giant entry probe.

How to cite: Mousis, O., Aguichine, A., Atkinson, D. H., Atreya, S. K., Cavalié, T., Lunine, J. I., Mandt, K. E., and Ronnet, T.: Key Atmospheric Signatures for Identifying the Source Reservoirs of Volatiles in Uranus and Neptune, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5263, https://doi.org/10.5194/egusphere-egu2020-5263, 2020.

The Galileo Probe was designed to measure the abundances of the heavy elements (mass >helium) and helium in Jupiter since they are key to understanding the planet’s formation and heat balance. Broadly speaking, the same formation scenarios presumably apply also to the Icy Giant Planets (IGP), Uranus and Neptune, so the determination of their heavy elements and He is equally important. We will show that the bulk of C, N, S, and O are sequestered in condensible volatiles whose well-mixed regions in the atmospheres of the IGP’s are extremely deep compared to Jupiter. That poses formidable challenges to their direct in situ measurements. On the other hand, being non-condensible and chemically inert, the noble gases − He, Ne, Ar, Kr and Xe – are expected to be uniformly mixed all over the planet, unlike the condensibles whose distribution is governed by dynamics, convection and purported deep oceans. Thus the noble gases would provide the most critical set of data for constraining the IGP formation models. Although the noble gases should be well-mixed everywhere below the homopause, measurements at and below the 1-bar level are needed considering their low mixing ratios, except for He. That depth also gets around any potential cold trapping of the heavy noble gases at the tropopause or adsorption on methane ice aerosols. Entry probes deployed to relatively shallow pressure levels of 5-10 bars would allow a robust determination of the abundances and isotopic ratios of the noble gases, amongst other things. A measurement of CO from orbit, along with other disequilibrium species has the potential of estimating the O/H ratio. Microwave radiometry from orbiter and the Earth have the potential of measuring the depth profiles of NH₃ and H₂O, which would be important for understanding the atmospheric dynamics and weather in the deep atmosphere. Combined with the above data and the data on the interior and the magnetic field, the probe results on the noble gases would provide essential constraints to the formation, migration and evolution models of the Icy Giant Planets. 

How to cite: Atreya, S. K., Mousis, O., and Reh, K. R.: Synergistic Probe-Orbiter Science and Measurements for Understanding the Formation and Evolution of the Icy Giant Planets, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2232, https://doi.org/10.5194/egusphere-egu2020-2232, 2020.

To discern the origin and evolution of the solar system including the formation of the terrestrial planets, an understanding of giant planet formation and evolution is needed. Among the most important measurements are the atmospheric composition, structure, and processes of the ice giant. Noble gas abundances in particular are diagnostic of the conditions under which the giant planets formed, and the abundances of cloud-forming (condensable) species are indicators of both the characteristics of the protosolar nebula at the time and location of planetary formation as well as the mechanisms by which additional heavy elements might have been delivered to the planets. Although many key properties of ice giant systems can be accessed by remote observations from flyby and orbiting spacecraft, measurements of the abundances of the noble gas and key isotopes as well as deeper thermal structure, dynamics, clouds, and other atmospheric processes require direct in situ exploration by an atmospheric entry probe.

Entry probe measurements can be classified as either Tier 1 or Tier 2. Tier 1 represents the minimum, threshold science required to justify the probe mission. Tier 2 is high value science that would complement and enhance the Tier 1 measurements, but alone are not enough to justify the entry probe mission.

Tier 1 measurements include atmospheric abundances of noble gases (including helium), key noble gas isotope ratios ²²Ne/²⁰Ne, ³⁶Ar/³⁸Ar, ¹²⁹Xe/total Xe, ¹³¹Xe/total Xe, and ¹³²Xe/total Xe, additional key isotopic ratios D/H, ³He/⁴He, and ¹⁵N/¹⁴N, and the atmospheric thermal structure along the probe descent trajectory. To achieve the Tier 1 measurements, the probe payload must include a mass spectrometer, a helium abundance detector, and an atmospheric structure instrument including pressure and temperature sensors and an atmospheric acoustic properties sensor for speed of sound measurements from which the ratio of ortho- to para- molecular hydrogen can be determined. Depending on mission architecture and probe-carrier telecom design, Tier 1 science can be achieved with a relatively shallow probe descending to several bars.

Tier 2 science includes additional key isotopic ratios such as ¹³C/¹²C and ¹⁸O/¹⁷O/¹⁶O, abundance of condensables, and additional atmospheric structure and processes including the dynamics of the atmosphere (winds and waves), the net balance of upwelling thermal infrared and downwelling solar visible radiative fluxes, and the location, structure, composition and properties of the clouds. The presence of the disequilibrium species such as PH₃, CO, AsH₃, GeH₄, and SiH₄ is primarily due to atmospheric convective upwelling, and abundance measurements would help constrain both the composition of the very deep atmosphere and deep atmosphere chemistries. Additional instrumentation necessary to fully achieve the Tier 2 objectives includes a net flux radiometer, a Nephelometer, and an ultrastable oscillator (USO) as part of the telecommunications system to enable probe Doppler tracking for measurements of atmospheric dynamics.

To address all the Tier 1 and Tier 2 science objectives, a deep probe to 10 bars and beyond would provide measurements of atmospheric thermal structure, dynamics, and processes at levels beyond the direct influence of sunlight that are out of reach of remote sensing.

How to cite: Atkinson, D. H., Mousis, O., and Spilker, T. R.: Science Payload for Ice Giant Entry Probes, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2410, https://doi.org/10.5194/egusphere-egu2020-2410, 2020.

Tidal dissipation is thought to power volcanism or cryovolcanism on a number of moons, most notably Io and Enceladus. The amount and distribution of tidal heating within the moon are however still misunderstood, and intricately related to surface observations like heat flow and distribution of volcanic activity. From an extensive benchmark between a set of numerical and semi-analytical models, we show that, in the presence of a subsurface (magma or water) ocean, librations (i.e. spin rate variations) along the orbit trigger additional deformation mechanisms, enhancing the amount of dissipation compared to traditional tidal dissipation (by at least 25% for Enceladus), and affecting the distribution of dissipation within the moon. We illustrate these mechanisms with numerous animations, and identify librational loading as the most relevant process.

How to cite: Trinh, A. and Matsuyama, I.: Tidal-librational dissipation within volcanic and cryovolcanic worlds, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12733, https://doi.org/10.5194/egusphere-egu2020-12733, 2020.

A set of key observations over the Cassini spacecraft's tenure has constrained Saturn's rings' age to be less than a few 100 Myr effectively ruling out currently accepted ring origin scenarios, all of which require that the rings are ancient or primordial. We propose a new scenario motivated from evidence of a comparably recent dynamical instability ~100 Myr ago which would have led to collisions between Saturn's pre-existing mid-size icy moons, opening the door to possible ring formation during that epoch. Successfully testing this scenario requires better  understanding of collisional outcomes. Toward that end, we introduce a new suite of simulations modeling impacts between Saturn's icy moons using the next generation smoothed hydrodynamical and gravity code SWIFT. The unprecedented spatial resolution achieved in these simulations (10^8.5 particles within the simulation box) allows us to depict the myriad of gravitationally bound objects formed during icy moon collisions which may afterwards evolve both thermally and dynamically to re-accrete or collide with other bodies. Our unprecedented high resolution further allows us to determine a size distribution of fragments which can be used to inform crater impact distributions on newly accreted or remaining moons.

How to cite: Teodoro, L., Estrada, P., Kegerreis, J., Cuzzi, J., Eke, V., and Cuk, M.: The Origin of Saturn’s Rings Revisited, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18372, https://doi.org/10.5194/egusphere-egu2020-18372, 2020.

Introduction: Enceladus, a satellite of Saturn, is the smallest celestial body in the Solar System where endogenic activity is observed. Since its accretion, Enceladus has lost about 20% of its mass.  This is the base of hypothesis about proto-Enceladus [1, 2]. It means that this satellite should be treated as new type of the celestial body, the body that is losing its mass as a result of internal activity.

Present activity:  Activity of Enceladus is concentrated in the South Polar Terrain (SPT). The mass of matter ejected into space by volcanic activity of Enceladus is 200 kg s^-1 [e.g. 1, 2, 3].  We have suggested that this mass loss is a main driving mechanism of the present Enceladus’ tectonics [1, 2]. Usually the loss of matter from the body’s interior (or thermal contraction) lead to global compression of the crust. Typical effects of compression are: thrust faults, folding and subduction [5]. However, such forms are not dominant on Enceladus. We proposed tectonic model that could explain this paradox [1, 2, 5].

Proto-Enceladus: Just after the accretion, Enceladus could be substantially larger. Its radius was ~300 km. We  refer here this body as proto-Enceladus [2]. Two assumptions could be used for calculation of the size of proto-Enceladus. Both approaches give similar results [2]. Note also possible biological role of proto-Enceladus [6].

Past activity: There are some traces of past activity on the surface of Enceladus [4]. The traces could be interpreted as indication that the past activity was similar to the present one (similar features like ‘tiger stripes’), but we do not know how old are these traces.   

Model of activity: We found some places where signs of the past activity are observed. However, we need a better model of this activity. The only known type of activity is the center in SPT. Are other forms of activity possible? We uses numerical model to find these other possible forms. Preliminary results indicate some possibility of smaller centers. Calculations indicate also that that the activity could be periodic.

Future activity center: We suggested that ovoid-shaped depression down to 2 km deep, of size 200×140 km with the centre at 200E, 15S is a good candidate for the future center [5]. However, our recent calculations using numerical model are presently inconclusive.

Acknowledgements: The research is partly supported by BST funds of the University of Warsaw. We are grateful also to the ICM.

References

[1] Czechowski, L. (2014)  EGU 2014, Vienna.

[2] Czechowski, L. (2014) Planet. Sp. Sc. 104, 185-199

[3] Kargel, J.S. (2006) Science 311, 1389–1391.

 [4] Spencer, J. R., et al. (2009), Enceladus: An Active Cryovolcanic Satellite, in: M.K. Dougherty et al. (eds.), Saturn from Cassini-Huygens, Springer, Sciencep. 683.

[5] L. Czechowski (2017) Presented in EPSC 2017.

[6] L. Czechowski (2018) Geological Quarterly 62, 1, 172-180.

How to cite: Czechowski, L.: Activity of Enceladus and proto-Enceladus, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18541, https://doi.org/10.5194/egusphere-egu2020-18541, 2020.

Salt-rich icy particles within Saturn’s E-Ring are relatively young (<~200 years), and originate from frozen aerosolized droplets of the salty seawater of Enceladus’ subsurface ocean, ejected into space, through fractures in the moon’s south polar region, within a plume of gas and ice particles. The salt-rich grains are therefore believed to reflect the composition of the ocean water. In situ mass spectra of the plume and E-ring icy particles, obtained by the Cosmic Dust Analyzer (CDA) impact ionization mass spectrometer onboard the Cassini spacecraft, indicate significant compositional diversity within the salt-rich population. Understanding the compositions of dissolved salts within the grains, and thus the ocean, can provide important constraints for geochemical models of Enceladus’ core/ocean environment.

To investigate and quantify variations in grain composition, a Laser Induced Liquid Beam Ion Desorption (LILBID) technique has been used to desorb and ionize a wide range of Enceladean ocean-like solutions containing dissolved salts. The resulting ions were then measured by a reflectron-type time of flight mass spectrometer. As the laser desorption mechanism simulates the ice grain impact process occurring on the CDA target, spectra produced in the laboratory from a large range of well-characterized salt solutions can be used to determine the CDA-applicable spectral appearances of substances within the ice grains emitted from Enceladus’ ocean.

Here we present the results of an investigation of CDA E-ring spectra, supported by laboratory analogue experiments, which show significant compositional heterogeneity within the salt-rich grains originating from Enceladus’ subsurface ocean. Two main spectral subtypes, representing endmember compositions within the salt-rich grains, are identified. These mass spectra are dominated by features from chloride-rich or carbonate-rich compounds and the laboratory detectability of other, additional, compounds within these brines is discussed.

How to cite: Zou, Z., Postberg, F., Hillier, J., Khawaja, N., Klenner, F., and Nölle, L.: Compositional heterogeneity amongst salt-rich grains emitted from Enceladus’ subsurface ocean, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18970, https://doi.org/10.5194/egusphere-egu2020-18970, 2020.

We explore the long-term evolution of Pluto’s subsurface ocean in the absence of an insulating clathrate hydrate layer. Numerical simulations of the thermal history of the interior are performed using a 1D model assuming Pluto was initially differentiated into an outer hydrosphere (H₂O shell) and an inner rocky core. We consider two endmember initial conditions: the hydrosphere was either entirely molten or frozen. We also consider different radiogenic heating rates, core sizes, ice reference viscosities, and ammonia concentrations. Our results indicate that the present-day Pluto can possess a subsurface ocean if the ice shell is purely conductive or only weakly convective. Our results also indicate that the initial state affects only little on the evolution scenario. These results strengthen previous conclusions obtained based on thermal evolution studies with limited calculation conditions. The thickness of the present-day ocean can be up to ~130 km, depending on the radiogenic heating rate and ice reference viscosity. The reference viscosity of ice required to maintain an ocean until today for the case of a CI chondritic core is approximately an order of magnitude higher than that for the case of an ordinary chondritic core. We also find that a thick subsurface ocean can be maintained until relatively recently for a dense small core case, which allows the formation of high-pressure ice at the seafloor. An inclusion of ammonia in the ocean increases the possibility of the current presence of a subsurface ocean even in the case of 1 wt% NH₃ at the initial.

How to cite: Kimura, J. and Kamata, S.: Stability of the subsurface ocean of Pluto, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21273, https://doi.org/10.5194/egusphere-egu2020-21273, 2020.

Galactic cosmic rays (GCRs) represent a major ionization source in planetary atmospheres, particularly within deeper layers that are largely unaffected by solar UV and charged particle precipitation. When GCR particles undergo inelastic collisions with atmospheric nuclei they create large numbers of secondary interactions, resulting in extensive nuclear and electromagnetic particle cascades. In thick atmospheres, such as those of the giant planets, these cascades can develop much more extensively than what is the case on Mars and Earth. Furthermore, GCRs are strongly modulated by the heliosphere, and therefore GCR fluxes are significantly higher at the Ice Giants than in the inner Solar System. Intriguingly, observations of Uranus and Neptune show brightness variations that appear to be associated with known variability in the background GCR flux (Aplin and Harrison 2016;2017).

Using a full 3D Monte Carlo particle physics code, we have carried out the first detailed study of cosmic ray ionization within the atmospheres of Uranus and Neptune. We will show preliminary results of this study and discuss the possible importance of GCR ionization to atmospheric chemistry and atmospheric electricity. We will also discuss GCR shielding by the planetary magnetic fields of Uranus and Neptune, and what effect this has on predicted GCR ionization rates at different locations. 

References

Aplin K.L. and Harrison R.G. (2016), Determining solar effects in Neptune's atmosphere, Nature Communications, 7, 11976 doi:10.1038/ncomms11976

Aplin K.L. and Harrison R.G (2017), Solar-driven variability in the atmosphere of Uranus, Geophys. Res. Letts. 44, doi: 10.1002/2017GL07374

How to cite: Aplin, K., Nordheim, T., Sinclair, J., and Jasinski, J.: Cosmic ray ionization of Ice Giant atmospheres, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6977, https://doi.org/10.5194/egusphere-egu2020-6977, 2020.

We discuss the importance to determine the structure and composition of the upper atmospheres and ionospheres of the Icy Giants (Uranus & Neptune) as well as Triton’s ionosphere in the light of numerous recently obtained Cassini results. The ionizing radiation and charging environment within the upper atmospheres of Saturn and Titan creates a very complex organic chemistry leading to charged sub-nm-sized to 100 nm-sized aerosols. The charged dust has a profound effect on the ionospheric structure and related chemistry, enhancing the ion number density well above photochemical equilibrium levels, while the electrons tend to become attached to the dust population. The organic chemistry leads to compounds reaching above 50,000 amu diffusing downward and possibly creating a pre-biotic chemistry. This process, involving nitrogen, methane and water may very well be a more general process, also applicable for the cases of Uranus, Neptune and Triton, were all have these starting species abundant in their upper atmospheres. We therefore propose that a future mission to the Ice Giants and the moon Triton has Langmuir probe, electron spectrometer, dust, ion- and neutral mass spectrometers onboard to make detailed in-situ measurements on both the orbiter and atmospheric probe in order to investigate this fundamental chemistry and aerosol formation.

How to cite: Wahlund, J.-E., Morooka, M. W., Andrews, D., André, M., Bergman, J., Edberg, N., Eriksson, A. I., Hadid, L., Khotyaintsev, Y., Vaivads, A., and Vigren, E.: The Icy Giants & Triton’s Ionospheres – lessons learned from Cassini observations within Saturn’s and Titan’s ionospheres, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-22682, https://doi.org/10.5194/egusphere-egu2020-22682, 2020.