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Orals: Fri, 23 Sep | Room Andalucia 3
We present the results of the implantation of sulfur ions in ice samples (H2O:C3H8) in conditions relevant to Europa and other jovian satellites. The samples were prepared and irradiated at 80 K, and were thick enough to ensure the projectiles were implanted in the ice, allowing the sulfur projectiles to become part of the ensuing chemistry. The evolution of the samples was followed with Fourier Transform Infra-Red (FT-IR) spectroscopy, and the organic residues were analyzed off-site through Ultra High Resolution Mass Spectrometry (UHRMS). The UHRMS shows formation of a complex, diverse refractory organic matter, however no evidence of organosulfur formation has been found.
Introduction:
Energetic particles from Jupiter’s magnetosphere (electrons, protons, oxygen and sulfur ions) are likely to be a key driver of the chemical evolution of the icy satellite’s surface, especially Europa; they can alter organic matter deposited on the surface from the internal ocean. In the case of impinging ions, in addition to the stopping power and total energy of the projectile [1], their reactivity is a possible factor in the chemistry. Sulfur is abundant in Jupiter’s magnetosphere [3] due to Io’s volcanic activity, and highly reactive. Experiments with sulfur projectiles have been performed and have shown the efficient creation of sulfuric acid in water ice [4, 5]; previous experiments by our group with interstellar analogs showed it can become part of the organic chemistry triggered by irradiation and form organosulfurs [6]. Here, in temperature conditions relevant to Europa (80K), we investigate the composition of the organic residue generated by the irradiation of a water:propane ice by sulfur ions.
Experiments
We performed the experiments at the ARIBE low-energy line at the Grand Accélérateur National d’Ions Lourds (GANIL) in Caen, France. The projectiles were 105 keV S6+ and 105 keV Ar7+ (the latter to produce a reference sample with a non-reactive projectile). The samples were prepared at 80K on a ZnSe window from a 2:1 H2O:C3H8 gas mixture and irradiated at a fluence of approximately 1014 ions. To ensure the products would be abundant enough to be detected, cycles of deposition-irradiation were repeated up to 15 times. The finally obtained samples were slowly warmed up to 300K to sublimate the volatiles and leave the refractory organic residue. This residue was analyzed off-site using Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS). This FT-ICR-MS technique represents the highest mass resolving power (R > 106) and highest mass accuracy (<200 ppb) among all mass spectrometric instruments [7]. This technique allows for detection and identification of species well beyond what is accessible with FT-IR. Two ionization techniques were used: Laser Desorption Ionization and Electro-Spray Ionization.
Results
Infrared spectroscopy shows little difference to previous work on irradiation with electrons of similar ices [8], except for the early production of CO2 and modest abundance of CH4. No qualitative difference was seen between Ar-irradiated and S-irradiated samples in the IR.
The results from the ESI or LDI FT-ICR-MS analysis show a very diverse, (3000 + annotations) refractory (average Double Bond Equivalent=14) organic matter (Figure 1). The residue features an insoluble phase. Heavy molecules (m/z>200) are common, showing that a fairly low dose is enough to form large molecules. No organosulfur could be identified, in stark contrast with our previous experiments [6]. Analysis of the soluble phase by ESI-FT-ICR shows that the oxygen-bearing products tend to be lighter. We discuss how our results compare to experiments using electrons ([8], and our own work).
Figure 1: Annotations (spot size is a function of intensity) obtained with the LDI-FT-ICR analysis, showing number of carbon atoms vs double bond equivalent (DBE) and number of oxygen atoms. A large amount of the residue is oxygen poor and highly aromatic.
Acknowledgements
A.B. and G.D. acknowledge the CNRS program "Programme National de Planétologie" (P.N.P, INSU), G.D. acknowledges the “Programme de Physique et Chimie du Milieu Interstellaire” (P.C.M.I, INSU) and the “Centre National d’Etudes Spatiales” (C.N.E.S) (exobiology program). H.R., P.B. and C.P.dC. acknowledge funding from Région Normandie through RIN EMERGENT SCHINOBI.
References
[1] Teolis et al. JGR: Planets 122.10 (2017): 1996-2012.
[2] von Steiger, R., Schwadron, N., Fisk, L., et al. 2000, JGR: Space Physics, 105, 27217
[3] Paranicas, C., Cooper, J., Garrett, H., Johnson, R., & Sturner, S. 2009, Europa. University of Arizona Press, Tucson, 529
[4] Ding et al. Icarus 226.1 (2013): 860-864.
[5] Strazzulla, et al. Icarus 192.2 (2007): 623-628.
[6] Ruf, et al. ApJL, 885(2), L40 (2019).
[7] Ruf et al.(2017) PNAS 114(11), 2819-2824.
[8] Hand, K. P., & Carlson, R. W. JGR: Planets, 117(E3). (2012)
How to cite: Bouquet, A., Danger, G., Tenelanda-osorio, L., Boduch, P., Rothard, H., Maillard, J., Schmitz-Afonso, I., Afonso, C., Schmitt-Kopplin, P., Duvernay, F., Pires da Costa, C., and Honold, L.: Organic chemistry on the surface of jovian icy satellites: formation of complex refractory organic matter by implantation of sulfur ions into water-alkanes ices, Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-812, https://doi.org/10.5194/epsc2022-812, 2022.
1. PEP objectives
The PEP suite explores the particle populations in the Jovian system to answer three overarching science questions:
(1) How does the corotating magnetosphere of Jupiter interact with Ganymede, Callisto, Europa, and Io?
(2) How do internal and solar wind drivers cause such energetic, time variable and multi-scale phenomena in the steadily rotating giant magnetosphere of Jupiter?
(3) What are the structure and composition of the icy moons exospheres and how do they response to the external conditions?
2. PEP suite
PEP measures positive and negative ions, electrons, exospheric neutral gas, thermal plasma and energetic neutral atoms present in all domains of the Jupiter system over nine decades of energy from < 0.001 eV to > 1 MeV with full angular coverage. The six PEP sensors are:
- Jovian plasma Dynamics and Composition analyzer (JDC);
- Jovian Electrons and Ions analyzer (JEI);
- Jovian Energetic Electrons (JoEE);
- Jovian Energetic Neutrals and Ions sensors (JENI);
- Jovian Neutrals Analyzer (JNA);
- Neutral gas and Ion Mass spectrometer (NIM).
For the first time at Jupiter PEP combines global imaging via remote sensing using ENAs with in-situ measurements and performs global imaging of Europa/Io tori and magnetosphere combined with energetic ion measurements. Using low energy ENAs originating from the particle – surface interaction PEP investigate space weathering of the icy moons by precipitation particles. PEP will first-ever directly sample the exospheres of Europa, Ganymede, and Callisto with high mass resolution.
Figure 1: PEP suite and PEP sensors
3. PEP ready to go
All flight models of the PEP sensors and electronics as well as central processing unit and common power supply system have been tested, qualified, and calibrated. The complete model was delivered to ESA and ready for launch in April 2023. All sensors performance fulfilles the mission requirements. PEP will provide the most comprehensive simultaneous measurements of the plasma and neutral gas environment in the Jovian system and at the Galilean moon.
How to cite: Barabash, S., Brandt, P., and Wurz, P. and the PEP Team: The Particle Environment Package (PEP) for the JUICE mission: Ready to go!, Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-681, https://doi.org/10.5194/epsc2022-681, 2022.
Io, the world with the greatest tidal flexing, volcanic and tectonic activity, and mass-loss in our solar system, begs for dedicated exploration. Missions such as Juno and JUICE, along with Earth-based telescopes such as JWST and ALMA, will acquire important Io observations over the next 15 years, as could Europa Clipper. However, a mission designed for Io science is necessary to accomplish key science goals that have been consistently prioritized in the National Academy of Sciences Decadal Surveys and the ESA Voyage 2050 (Thomas, 2021, Experimental Astronomy online), including understanding the early evolution of terrestrial planets, tidally heated exoplanets and ocean worlds, and magnetospheric physics across the galaxy. The NASA Discovery-class Io Volcano Observer (IVO; McEwen et al., 2021, LPSC 1352) completed Phase A in 2021 and was deemed selectable, but was not chosen for programmatic (i.e., non-science/engineering) reasons. The IVO concept study demonstrated how a total of ten carefully designed, close Io flybys could determine the melt distribution in Io’s interior to confirm or refute the presence of a magma ocean, constrain Io’s global average lithospheric structure, identify where and how Io is losing heat, and determine processes and rates for Io’s volatile loss. Such encounters would also measure Io’s rate of orbital migration, key to determining the stability of the LaPlace resonance that heats Europa and Ganymede, as well as Io. The ambitious (for Discovery) science payload included a magnetometer, plasma instrument, narrow-angle camera, thermal mapper, neutral mass spectrometer, plus a telecom system for gravity science and options for a student-collaboration wide-angle camera (WAC), and a technology demonstration UV spectrometer.
The next Discovery mission proposal opportunity is expected in 2025 or later, but an opportunity to propose an Io mission in NASA’s New Frontiers (NF) program is anticipated in 2023. How might that differ from a Discovery-class mission? An Io orbiter to provide better geophysical measurements has been suggested in the past, but would be very challenging deep inside Jupiter’s gravity well and high radiation zone. An orbiter might be feasible if new, more capable launch vehicles become available. On the other hand, the IVO Discovery concept would accomplish all of the science objectives of NF, and could be augmented in several key ways using the additional resources available in NF. A radiation design to support more than 10 encounters is a relatively straightforward enhancement. Ka-band would improve the data downlink capability and gravity science. With twice as many Io encounters, it would be possible to more completely map Io’s surface at multiple wavelengths; encounter Io over additional values of orbital true anomaly for improved gravity science, magnetic induction, and measuring Io’s libration; and sample more longitudes and times of day to understand Io’s atmosphere, plumes, magnetospheric interactions, and mass loss. The WAC, which is especially important for mapping Io’s topography, could be a required Baseline experiment. There are many science instruments that would be valuable additions, including altimetry, ultraviolet and near-IR spectroscopy, a dust mass spectrometer, passive radar sounding (using Jupiter radiation), active radar sounding, and additional fields and particle instruments. Greater emphasis may be placed on tracing the mass and energy flows in the Io-Jupiter system, especially because the new US Planetary Science and Astrobiology Decadal Survey places much emphasis on understanding planetary systems relevant to exoplanets. Interferometric synthetic aperture radar (InSAR) would be challenging but could transform our understanding of active processes on Io. An even more daring idea is to deliver a penetrator that could measure Io’s seismicity and conducted heat flow, perhaps also with a laser retroreflector or radio transponder to measure Io’s rotational and tidal deformation. However, getting substantial data back to the main spacecraft for transmittal to Earth is challenging in the very fast flybys that are preferred to keep the total ionizing radiation dose low. In terms of international collaboration, we expect a thermal mapper from DLR and a neutral mass spectrometer from UBE, plus science co-investigators; additional contributions are possible. In summary, a highly capable mission to one of the most exciting objects in the Solar System is overdue.
Figure: Io is a spectacular target to observe both in daytime and at night (simulated hot spots).
How to cite: McEwen, A., Carter, L., DellaGiustina, D., Kestay, L., Denevi, B., Haapala, A., Westlake, J., Park, R., Khurana, K., Thomas, N., Wurz, P., and Helbert, J.: A NASA New Frontiers Mission Concept to Io, Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-37, https://doi.org/10.5194/epsc2022-37, 2022.
Abstract. Bierson and Nimmo [1] have proposed that, under certain circumstances, as Galilean-scale satellites accrete they may lose substantial (if not all) of their accreted water ice. This is not, however, a get out of jail free card for satellite accretion models or scenarios. Each satellite accretion model (of which there are many) must be evaluated against the parameters chosen in [1], and the modest ice content of Europa and the apparent anhydrous nature of Io accounted for. Here we evaluate published models in this light, and focus especially on the roles of background protojovian subnebula temperatures and pressures.
Introduction. The formation of Jupiter in the core accretion–gas capture model inevitably ends with a circumplanetary accretion and/or decretion disk (CPD) around the planet. Numerous satellite formation models have been proposed [2-11], with different parameters for disk structure (surface density, temperature, opacity, viscosity). All rely on inferences and assumptions of mass and angular momentum inflow to Jupiter. Numerical gap opening calculations [e.g., 12] provided the basis for the gas-starved model [2-4]. Later 3D radiative-hydrodynamic inflow calculations prompted consideration of heliocentric planetesimal capture as the dominant source of satellite-building solids [13]. Hypotheses for dust and small pebble deposition range from distant infall [e.g., 14] to close-in infall and formation of an outflowing, decretion disk [15]. Multiple generations of satellites may form and be lost [3], Or maybe not, if a magnetospheric cavity opens up close to Jupiter and the innermost satellite, destined to become Io, stalls there [e.g., 16,17].
The thermal environment of Io and Europa’s formation could have been hot enough to largely devolatilize any small, accreting satellitesimals, including the ablated fragments of heliocentric planetesimals that encounter the CPD [8]. Some models call for accretion of Io and Europa in the cold outer disk followed by inward type I migration [e.g., 15,18]. Ultimate removal of major amounts of ice is a non-trivial requirement in such scenarios.
Hydrodynamic Wind. We consider a water vapor atmosphere at the saturation vapor pressure (SVP) of a water ocean formed during accretion [1]. If the outflow wind speed u, which increases away from the surface, becomes transonic at the critical radius rc = GM/2c2 (where G is the gravitational constant, M the satellite mass, and c the isothermal sound speed), then the outflow can continue unimpeded [19,20]. For example, If Europa accreted with a 300 K water surface, the SVP would be 3.35 kPa, with a c = 372 m/s. The isothermal atmosphere is a favorable case for hydrodynamic escape, and because it admits simple analytic solutions for u(r), it is well-suited to this discussion. The critical distance rc = 7.4Re, where Re is Europa’s present radius. At the surface rs [20]:
For the 300 K Europa case above, us ≈ 0.04 m/s, and for steady-state (mass flux conserved) outflow, both the thermodynamic and ram pressure at rc are ≈6 mPa. Such pressures are low compared with the CPD pressures in even gas-starved models [1,2], even far from Jupiter, which suggests that CPD details as well as accretional mass, radius and surface T, determine if blowoff is possible (e.g., Fig. 1).
Figure 1. Escape of isothermal water vapor atmospheres from Io is suppressed by the back pressure of the CPD if the back pressure exceeds the wind's critical point pressure. E.g., for a nebular pressure of 1 Pa, an escaping wind begins to blow only for T>400 K. If the back pressure exceeds the critical pressure, the flow reverses sign and Io accretes nebular gas.
Discussion. Ram and thermodynamic pressures at the critical, transonic radius are strong functions of satellite radius and accretional surface temperature. Larger values imply free flow to the background CPD, whereas smaller values (if below ambient) imply the wind is inhibited (the pressure boundary condition at rc cannot be met). Because saturation is assumed at the surface, the actual atmospheric pressure should follow the saturation vapor curve, implying even lower transonic pressures and more stringent limits [19,20]. For cold CPD conditions consistent with the condensation of water ice (<200 K) or its survival in small satellitesimals, any H2O loss will depend critically on accretion timescale and surface temperatures reached [1]. For accretion of icy satellitesimals in warm to hot CPD conditions, such as resulting from inward drift or direct capture from heliocentric orbit, the satellitesimals themselves should actively sublimate prior to accretion. Such comet-style loss would not in itself contribute to isotopic shifts [cf. 1]. Most importantly, however, the hydrodynamic loss model discussed here is an idealization, and implicitly assumes a static background gas subnebula (or lack thereof). The reality of satellite accretion involves a nebular headwind, which will act to sweep any water vapor atmosphere away from the growing satellite. This process is daunting to model, but will both act to accelerate water vapor loss (the ultimate limit being free sublimation) but at the same time increase sublimation cooling.
Acknowledgement. WBM thanks NASA’s Europa Clipper project.
References
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[2] Canup. R.M. and W.R. Ward. 2002. AJ, 124, 3404-3423.
[3] Canup, R.M. and W.R. Ward. 2006. Nature, 441, 834-839.
[4] Canup, R. M. and W. R. Ward. 2009. In Europa, 59-83.
[5] Mosqueira, I., and P.R. Estrada. 2003. Icarus, 163, 198-231.
[6] Mosqueira, I. and P.R. Estrada. 2003. Icarus, 163, 232-255.
[7] Estrada, P. R., et al.. 2009. In Europa, 27-58.
[8] Ronnet, T., et al. 2017. ApJ, 845, 92.
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[10] Ronnet, T. and A. Johansen. 2020. A&A, 633, 93.
[11] Estrada, P.R., and I. Mosqueira. 2006. Icarus, 181, 486-509.
[12] Lubow S. H., M. Seibert, and P. Artymowicz P. 1999. ApJ, 526, 1001-1012.
[13] Schulik, M., et al. 2020. A&A, 642, A187.
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[15] Batygin, K. and A. Morbidelli. 2020. ApJ, 894, 143.
[16] Sasaki, T., et al.. 2010. ApJ, 714, 1052-1064.
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How to cite: McKinnon, W. B. and Zahnle, K. J.: On the Potential Hydrodynamic Loss of Water Vapor During Accretion of the Galilean Satellites, Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-1015, https://doi.org/10.5194/epsc2022-1015, 2022.
- 1. Introduction
Tethys is unusual among icy moons for its low bulk mean density of 0.985 g/cm3, suggesting a low rock mass fraction and/or high porosity. Like other mid-sized icy satellites Tethys has an intense fracture history [1], including Ithaca Chasma as well as several hundred arcuate andlinear troughs, grooves, and cracks. Unique to Tethys, however, are dark reddish linear features visible to Cassini under high solar illumination conditions (a lower albedo and flatter spectral signature in the green–IR range; Figs. 1, 2). Our CDAP-funded research is focused on mapping these features and testing hypotheses for their formation and implications for Tethys’ evolution
Figure 1: Color view of Tethys showing IR lineations (reddish arcs). Cassini IR3, green, UV3 image composite.
Figure 2: Preliminary spectral plot showing IR lineaments (red) and adjacent cratered plains (green) from ISS images.
Figure 3: Global map of fractures, ridges, and lineations on Tethys. IR lineations are shown in red. Odysseus is large circle at upper center.
1.1 IR-Lineations
There are at least three prominent sets in the northern anti-Saturn hemisphere, centered on the anti-Saturn meridian (Fig. 3). Each setconsists of ~5–10 parallel lineations a few kilometers across and 50–250 km long. The lineations are remarkably curvilinear (i.e., non-sinuous), do not follow great circles, and are not deflected by major impact structures: they cross the floor of the 400-km-diameter, 9-km-deep Odysseus impact basin as if it were not there.
Although more poorly observed, sub-Saturn hemispheric color imaging at low-phase angle clearly shows a similar set of arcuate, reddishlineations on that hemisphere, despite deposition of E-ring dust particles from Enceladus [2] indicating that these features are being renewed on some time-scale.
The red lineaments centered near ~25° N, 175°E were imaged at high resolution. Mapping at ~90–125 m/pixel (Fig. 4) (together with stereo andlower resolution color imaging) shows no discrete scarp, ridge, or other tectonic manifestation along the ~100 km portion of the feature soimaged. Only a faint discoloration of the surface has been identified (Fig. 5). Further, >20 dark spots 200–800 m in diameter lie along this setof lineaments. These spots are characterized by very low albedos, sharp boundaries, and no evidence of raised rims consistent with an impactorigin. Of these, >60% are situated at the bottom of impact craters.
Figure 4: High-resolution, 90 m/pixel mosaic of IR lineaments, merged with IR3–Gr–UV3 color mosaic.
Figure 5: Enlargement of high-resolution view in Figure 4 showing reddish lineament (red arrows) and small dark spots (blue arrows).
Red streaks centered at 45° N, 333°E were targeted for high resolution ISS and VIMS observations in late 2015 (although the VIMS cubes were partially corrupted). As at the above site no discrete faults, scarps or grooves was resolved here despite pixel scales as good as ~60 m.
- 2. Origin of IR-Lineaments
The spatial pattern of IR lineaments on Tethys shows a strong symmetry (Fig. 3), centered on the current tidal axis with Saturn. A lack ofcorrelation with local geology might suggest an exogenic origin. Conversely, there are no rayed craters at the radial centers of these features.Further, the locations of the patterns on both the sub- and anti-Saturn hemispheres, and the lineaments’ parallel orientations, argue against adisrupted comet origin (à la SL9). The lineaments have no systematic orientation relative to Odysseus, indicating that stresses arising fromthe relaxation of that basin [3] are not responsible for these features.
Global stresses might have produced the pattern we observe. The IR lineaments may match patterns of strain predicted to result from a non-synchronous rotation stress state, although this is unlikely for a cold, triaxial body like Tethys. The best-fit patterns correspond to a combination of global expansion with true polar wander or tidal axis reorientation (Fig. 6a, b). The misfit for global expansion combined recession is significantly larger (Fig. 6c). The dramatic lack of such features in the southern hemisphere (Fig. 3), where only a few short isolated red streaks are evident, is not explained by any currently considered stress regime.
Figure 6: (a-c) Observed (red) and predicted (green) tectonic patterns due to combination of global expansion with (a) true polar wander, (b) tidal axis reorientation, (c) orbit recession. Solid and open circles indicate location of initial rotation and tidal axes. (d) Relative frequency distribution of misfit between observed and predicted fault segment azimuths for processes in panels a-c. Labels show mean misfit for each model.
The lack of obvious tectonic deformation despite the strong color signature is unusual (although features may exist below the currentresolution limit). The lineaments could be reactivated ancient fractures, producing a temporal discoloration. At present there is no topographic or morphologic signature to support this. If tectonic, the lineaments might be still forming, with deformation only on a scale below that which we can resolve.
The dark and reddish coloration could be due to a particulate contaminant in the ice grains that is more spectrally visible if the grain sizes are larger along the streaks. Alternatively, a dark reddish contaminant has been deposited on the surface along the streaks. Such a contaminant could be due to precipitation of a distinct material along unresolved surface or near-surface fractures, with subsequent mixing of contaminant into the local regolith. VIMS spectral cubes are being reprocessed to verify whether organic rich materials may be involved. Low-volume but persistentoutgassing and emplacement of volatiles from the interior (possibly due to clathrate decomposition associated with fracture formation) thecolors of which are distinct from the evolved surface and/or result from alteration due to exposure to the space environment, may be responsible.
The coloration of Tethys unique red streaks, and collocated dark spots, are consistent with active alteration of the surface, given that E-ringaccumulation is expected to remove intrinsic color signatures in a geologically short time period. Differences in particle sizes of the outgassed material may add to this spectral distinctiveness.
How to cite: Schenk, P., Buratti, B., Clark, R., Byrne, P., McKinnon, W., Matsuyama, I., Nimmo, F., and Scipioni, F.: Red Streaks on Tethys: Evidence for Recent Activity, Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-732, https://doi.org/10.5194/epsc2022-732, 2022.
Posters: Thu, 22 Sep, 18:45–20:15 | Poster area Level 1
Electrostatic analyzers are key instruments for understanding magnetospheric plasma. Their measurements
also contribute to the determination of the surface and interior composition of moons and planets. They
measure properties in particle charge, energy and 3D velocity vectors of electrons and ions. Calibration of
these instruments is challenging. Ground facilities can not reproduce the electromagnetic and radiation
background of Jupiter. Also the particle flows and, their full energy- and 3D flow spectrum over the
complete field of view of a spherical analyzers can not be produced by our facilities. Instead beams
larger than the field of view of at least one detector channel reproduce step-vise parts of the parameter
spaces of the expected spectrum. By combining simulations, ground based calibration and in-flight
calibration, the reliability of the calibration can be increased. The calibration of the flight model of
the The Jupiter Electron and Ion Spectrometer (JEI) showed good agreement with the simulations, except
for a significant discrepancy in azimuth resolution and the geometric factor at high pole inclinations.
After a final upgrade of the test bench, we will allow for better comparison of results between
The Jupiter Icy Moons Explorer (JUICE) and the BepiColombo missions by cross-calibrating JEI and
the The Planetary Ion Camera (PICAM).
ticles helps to understand the interaction and allows to analyze the surfaces and interiors of planets and
moons as a result of their interaction with their surrounding magnetic field. Unfortunately, calibration of
these instruments is complicated because accelerators only produce a small spectrum of the target particle
streams at once. In order to improve the results, calibration measurements on the ground are combined
with simulations and later with calibrations during the mission using known plasma, like the solar wind. The
calibration for JEI agreed with the simulations, except for high polar angles(Fig. 1.)
JUICE will explore the Jovian magnetosphere and three of the four Galilean moons. After several fly-
bys of Europa and Callisto it will eventually enter orbit around Ganymede. JEI is part of The Particle Environ-
ment Package (PEP) on JUICE. JEI will measure electron and ion distributions in the range from a few eV to a few
MeV with almost full hemispheric coverage.
PICAM on BepiColombo has overlaps with JEI in its energy range from 1 eV to 3 keV. While mea-
suring ions only, PICAM has additionally a time-of-flight unit, which allows to resolve incoming particles
at a m/δm ratio of 100. There are links between Mercury and Ganymede. Besides being similar
size, they are the only known solid objects in the solar system other than Earth that have intrinsic mag-
netic fields. While the magnetic moments are similar in strength, Mercury is exposed to a supersonic plasma
2. Results
For all JEI models, including the qualification model, the polar-, energy- and azimuth resolution could be
measured in agreement with the accompanying simulations and within the specifications of the original
proposal. The resolutions and deflector response are plotted in Fig. 2. Only the azimuth resolution deviates
at higher polar inclinations from the simulations. The deviation directly affects the geometric factor, which
differs over the polar inclinations in the same range.
The deviation is suspected to be reasoned by the different exposure of the sensor in the particle flow be-
tween the simulations and the beam in the test facility. Simulations and measurements with an off-center
beam are currently conducted to confirm the cause.
A slight coaxial misalignment between the inner and outer spheres could be measured due to the deviations
of the individual energy peaks of the channels.
Currently the positing system is under replacement to allow joint measurements of JEI and PICAM.
This works is supported by DLR grants 50QW1702
and 50QJ1503.
How to cite: Bambach, P., Krupp, N., Fränz, M., Roussos, E., Heumüller, P., Fischer, H., Meyer, F., and Szemerey, I.: The Calibration results of the Flight model of the Jovian Electron and Ion spectrometer for the Jupiter Icy Moons Explorer and their link to Mercury, Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-1093, https://doi.org/10.5194/epsc2022-1093, 2022.
The Cassini mission explored Saturn’s system from 2004 to 2017. On its board, a RADAR operating at a wavelength of 2.2 cm (13.78 GHz), had been initially designed for the exploration of the surface of Titan but also regularly turned its antenna towards the main airless icy satellites of Saturn (Elachi et al., 2004). In addition to its active mode, the Cassini RADAR included a passive (or radiometry) mode designed to record the thermal emission from the targeted surfaces at 2.2-cm. The scientific objectives of Cassini RADAR icy satellite observations were to provide constraints on the thermal, physical and compositional properties of the first few meters below the surface of the investigated objects. Doing so, it brings insights into the degree of purity and maturity of their water-ice regolith which are both indicative of their geological activity and interaction with their environment.
The RADAR dataset acquired on icy moons has already proved to be very fruitful bringing light to notable differences among Saturn’s mid-sized satellites (Ostro et al., 2006; 2010; Le Gall et al., 2019). However, it has not been fully analyzed yet. Following the final analysis of Cassini RADAR active observations of Saturn’s icy moons described in Le Gall et al. (2019) and expanding and improving upon the work of Ostro et al. (2006; 2010), we here present the analysis of all Cassini distant passive RADAR observations of these objects. This represents a total of 63 observations collected during 4 flybys of Mimas, 10 of Enceladus, 3 of Tethys, 6 of Dione, 9 of Rhea, 3 of Iapetus, 1 of Phoebe.
Most of Cassini RADAR icy satellite observations were distant i.e., occurred at ranges where the antenna beamwidth is comparable to or greater than the apparent angular extent of the target’s disk and were thus primarily designed to provide disk-integrated quantities: hemispheric-averaged radar albedos in the RADAR active mode and disk-integrated brightness temperatures in the passive mode. We here present the reduction of all available Cassini passive radiometry data with the goal of providing a range of possible values for the disk-averaged 2.2-cm emissivity of Saturn’s main airless satellites (separating their leading and trailing sides if relevant). These latter are obtained as a function of their possible thermal and electrical properties using a combined thermal and radiative transfer model (Le Gall et al., 2012; Bonnefoy et al., 2020). As an example, Fig. 1 displays the emissivity values obtained for Mimas from 4 distant radiometry observations. These values are shown as a function the assumed thermal inertia and ratio of electrical and thermal skin depths of Mimas’s near-surface. For all sets of parameters they are very low, as low as 0.5. For comparison, the disk 2.2-cm emissivity of Iapetus (Le Gall et al., 2014), Phoebe and Titan (see Sultana et al., this conference) is close to 0.9. Mimas low emissivity is indicative of subsurface mostly made of pure water ice and where volume scattering is very efficient maybe due to a highly fractured structure. We find that Enceladus and Tethys also exhibit low emissive surfaces and that, as a general rule, moon-to-moon and hemispheric emissivity variations seems to reflect variations in the moon interaction with Saturn’s dust rings, namely the E-ring for Enceladus and its neighbours and Phoebe’s ring further away from Saturn (Iapetus and Phoebe).
The derived emissivities will be analysed in light of the (active) radar albedos measured on the same hemispheres. Both active and passive microwave observations will be compared to several combined emissivity-backscatter models thus providing further clues on the physical properties of the icy moons. Their implications in terms of surface geology and evolution will be discussed.
Fig. 1: 2.2-cm emissivity of Mimas’s surface derived from Cassini distant radiometry observations and a combined thermal and radiative transfer model as a function of Mimas subsurface thermal and electrical properties (namely its thermal inertia and the ratio of its electrical and thermal skin depths). The sub-spacecraft point of each distant observation is indicated on an ISS map of the satellite.
How to cite: Le Gall, A., Sultana, R., Bonnefoy, L., Leyrat, C., and Janssen, M. A.: Microwaving Saturn's airless icy moons Mimas, Enceladus, Tethys, Dione, Rhea, Iapetus and Phoebe, Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-607, https://doi.org/10.5194/epsc2022-607, 2022.