The Final Cassini Science Symposium

Is Titan's hemispheric surface-liquid dichotomy anequilibrium state?Integrated laboratory, modeling and observationalinvestigations of the condensation of benzene onTitan’s stratospheric aerosolsAdjourn6:00Jonathan Mitchell (W27)BANQUETHotel Boulderado7:30-9:00Ella Sciamma-O’Brien (W28)—Invited talks 30 minutes, contributed talks 15 minutes (unless noted otherwise) includes time for discussion—Thursday, August 16—Magnetospheres & SaturnPrior to session8:30-9:00MAPS 19:00 AM(Chairs: Tamas Gombosi, Norbert Krupp)An overview of Cassini's major findings regardingSaturn's magnetosphere (INVITED)Saturn’s magnetic field observations from the CassiniGrand FinaleThe legacy of Cassini RPWS: Radio and plasma wavesat SaturnNew insights into Saturn’s inner magnetosphere duringCassini’s Grand Finale: MIMIBreak10:15 – 10:30MAPS 210:30(Chairs: Norbert Krupp , Tamas Gombosi)Saturn’s internal magnetic field revealed by CassiniGrand FinaleGlobal maps of energetic charged particles at Saturn andtheir relation to the magnetic fieldEvidence for a ring-driven current systemRelative fractions of water-group ions in Saturn’sinner magnetosphereSaturn’s ionosphere: Electron density altitude profilesand ring shadowing effects from the CassiniGrand FinaleA large seasonal variation of energetic C and CO abundances in Saturn’s magnetosphere probablyresulting from changing ring illuminationLunch12:00 – 1:15pmSATURN 11:15(Chairs: Valery Lainey, Christopher Mankovich)7Load presentationsXianzhe JiaMichele DoughertyWilliam KurthNorbert KruppLoad presentationsHao CaoJames CarbaryWillliam FarrellMark PerryLina HadidDouglas HamiltonOn your own

Constraints on Saturn’s deep interior from seismicinversionsSaturn’s deep atmosphere revealed by the Cassini GrandFinale gravity measurementsDetermination of tidal parameters at multiple frequencieswithin Saturn from ground and space dataRing seismology as a probe of Saturn’s rotationSaturn density profiles from gravity data with minimalassumptionsA refined measurement of Saturn’s gravity environmentBreak2:45 – 3:00SATURN 23:00(Chairs: Zarah Brown, Scott Edgington)Saturn: Cassini explores the giant planet (INVITED)Polar temperature profiles of Saturn from Grand FinaleUVIS stellar occultationsSaturn's stratospheric dynamics and chemistry revealedby CIRS limb observationsPOSTER SESSION – MAPS & SATURN4:00The induced magnetosphere of Titan: characterizing itsouter edgePlanetary Exploration, Horizon 2061: Some proposednext steps for Giant Planets Systems explorationA statistical picture of interchange injections at Saturnthrough energetic H flux intensificationsThe meridional magnetic field of Saturn: a newanalytical modelRe-examining the ordering of injection events withinSaturnian SLS5 longitudeA diffusive equilibrium model for the plasma densityfrom 2.4 to 10 RSAuroral hiss emissions during Cassini’s Grand Finale:Diverse electrodynamic coupling between Saturn,its rings, and EnceladusDust observation by the Radio and Plasma WaveScience instrument during the Cassini MissionThe Enceladus auroral footprint – and lack thereofTEXES Saturn's observations in support of the CassinimissionSaturn Ring Seismology: Saturn’s Normal Modes andForcing of the Slowest Density Waves in the C RingA Concept for a Future Entry Probe Mission to Saturn –The Saturn PRobe Interior and aTmosphereExplorer (SPRITE)Adjourn6:008Ethan DederickEli GalantiValery LaineyChristopher MankovichNaor MovshovitzLuciano IessLoad presentationsAndrew IngersollZarah BrownSandrine GuerletCesar Bertucci (TH29)Michel Blanc (TH30)Abigail Azari (TH31)James Carbary (TH32)George Hospodarsky (TH33)Ann Persoon (TH34)Ali Sulaiman (TH35)Shengyi Ye (TH36)Abigail Rymer (TH37)Thierry Fouchet (TH38)Jim Friedson (withdrawn)Amy Simon (TH40)

—Invited talks 30 minutes, contributed talks 15 minutes (unless noted otherwise) includes time for discussion—Friday, August 17—SaturnPrior to session8:30-9:00SATURN 39:00 AM(Chairs: Kevin Baines, Scott Edgington)Potential vorticity of Saturn’s polar regionsThe eye of Saturn's north polar vortex: Surprisingdiversity of cloud structures observed at high spatialresolution by Cassini/VIMS during the Grand FinaleSaturn photochemistry and ring shadowA survey of slowly moving thermal waves in Saturnfrom Cassini CIRS and ground-based thermalobservations from 2003 to 2017Saturn’s south polar cloud structure inferred from2006 Cassini VIMS spectraBreak10:15 – 10:30SATURN 410:30(Chairs: Tommi Koskinen, Robert West)Saturn in Lyman a: A comparison of Cassini and VoyagerobservationsMonitoring Saturn's upper atmosphere densityvariations and determination of the Saturnian Hemixing ratio using helium 584 Å airglowCharacteristics of the neutral influx from Saturn’s ringsThe composition of Saturn’s upper atmosphere fromCassini/INMS measurementsExploring low-latitude electrodynamics in Saturn’sthermosphereCassini UV reflection spectra of Saturn: Acetyleneand hazeAdjourn12:00pm9Load presentationsArrate Antuñano MartinKevin BainesScott EdgingtonGlenn OrtonLawrence SromovskyLoad presentationsTommi KoskinenChristopher ParkinsonMark PerryJoseph SeriganoJess VriesemaRobert West

AbstractsAlphabetical within each discipline: Icy Satellites, Magnetospheres, Rings, Saturn, TitanIcy SatellitesIcy satelites in the era of CassiniB. J. Buratti1 and the Cassini Science Teams.1Jet Propulsion Laboratory, California Institute of Technology (4800 Oak Grove Dr. Pasadena, CA 91109(bonnie.buratti@jpl.nasa.gov);Introduction: The Cassini spacecraft performed the first in-depth study of the moons of Saturn. The discovery andcharacterization of ongoing activity on Enceladus and a liquid global ocean sustaining it was one of the crowning achievements of themission. We will present the most important discoveries of the mission and discuss the main open questions. Emphasis will be put onthe final year of the mission.Main Results: Among Cassini’s prime discoveries was a heavily cratered surface on Phoebe; the unique equatorial ridge onIapetus; a possible subsurface ocean on Dione; a Rhea not in hydrostatic equilibrium; strange red streaks of unknown origin onTethys; equatorial bulges of accreted ring material on the ring moons; the existence of one or more low-albedo reddish chromopheresthat color the moons and rings; the importance of plasma-surface interactions, and ring-surface interactions, on determining the albedoand color patterns of the moons’ surfaces; unresolved evidence for activity on moons other than Enceladus; evidence for thermalmigration of volatiles on Iapetus; the discovery of CO2 and organic molecules in the system; the characterization of craters founduniquely on the surface of Hyperion, which are believed to be similar to terrestrial “suncups”; “blue pearls” on Rhea of unknownorigin; and the discovery of new small moons.Remaining questions: Even though the mission fulfilled all the science goals for icy moons, a number of questions remainoutstanding. Among them are: 1. What is the identity of the red chromophore(s) in the system? 2. Do the surfaces of any of the moonscontain ammonia or ammonia hydrate? 3. What causes the red streaks on Tethys and the “blue pearls” on Rhea? 4. What is the totalheat production on Enceladus and what are its long-term variations? Does the plume vary with the seasons of Saturn? 5. Are any of theother moons active, particularly Dione or Tethys? 6. Why are some of the moons not in hydrostatic equilibrium? 7. Is the ridge onIapetus evidence for a past ring? 8. How old are the moons? Could they possibly have had a relatively recent origin? 9. Why does theorigin of the moons of Jupiter and Saturn seem to diverge, with the jovian moons being formed relative to their position from Jupiter,and the Saturnian moons being formed by stochastic events? All these unknowns will serve as a guide for future explorations ofSaturn, when a new generation will continue where this great mission left off.Acknowledgments: This work was funded by the Cassini Project. Part of this research was carried out at the Jet PropulsionLaboratory, California Institute of Technology, under contract to the National Aeronautics and Space Administration. 2018California Institue of TechnologyOrbital history of Mimas and EnceladusM. Ćuk1, M. El Moutamid2 and M. S. Tiscareno1.1SETI Institute, 189 N Bernardo Ave, Mountain View, CA 94032, 2Cornell University, Space Sciences Building, Ithaca, NY 14853,(mcuk@seti.org).10

EccentricitySemimajor axis (RS)Background: Saturn's moon Enceladus is currently in the 2:1 meanmotion resonance (MMR) with a larger moon Dione. This resonance4.02excites the eccentricity of Enceladus and apparently plays an integral role4 2:3 MMR with Mimasin Enceladus's intense internal heating. While older estimates of tidalEnceladus3.98 2:1 MMR with Dioneheating, based on lower tidal evolution rates, could not account for the3.96observable heat flux (assuming equilibrium, Meyer and Wisdom 2007),the recently proposed lower tidal Q of Saturn would naturally resolve this3.94discrepancy (Lainey et al 2012, 2017). The most important remaining3.92problem concerning Enceladus's resonance is that the current e-Enceladus3.9sub-resonance is the last of the six sub-resonances that Enceladus wouldencounter as its orbit was converging with that of Dione. Prior0.04 Mimascalculations have shown that capture into the e-Dione resonance would be0.035Enceladusvery robust and hard to avoid (Meyer and Wisdom 2008), and our own0.03Dionenumerical tests have confirmed that result. The very low inclination of0.025Enceladus (0.003 deg) also makes it likely to be captured in the0.02inclination-type sub-resonances (most notably the pure i-Enceladus one).0.015However, these inclination-type resonant captures certainly did not0.01happen, or the inclinations of either Enceladus or Dione would be higher0.005than we observe them to be.0Our work: We propose to test a hypothesis that there was a0100 200 300 400 500 600 700“handoff” between the Mimas-Enceladus and Enceladus-DioneTime in kyrresonances. The Mimas-Enceladus 3:2 MMR would be established first,after which the pair would encounter the MMR with Dione (3:1 forMimas, 2:1 for Enceladus). During the handoff, the presence of Mimas affects the dynamics of capture into the Enceladus-DioneMMR in two ways. First, the presence of Mimas creates resonance overlap and chaos. Second, Mimas “pushes” Enceladus outwardmuch faster than it otherwise would evolve. The figure below shows a preliminary accelerated simulation of such a scenario, whereMimas first captures Enceladus into 3:2 e-Enceladus resonance, then the pair captures Dione into a e-Dione resonance. A chaoticresonance overlap ensues, during which the eccentricity of Mimas is excited to just above its current value. Eventually Mimas breaksfrom the triple resonance, moving on to encounter the MMR with Tethys. Enceladus and Dione remain in the 2:1 e-Enceladus MMRobserved today. This scenario is very promising for explaining the capture into the current Enceladus-Dione MMR, as well as thecurrently unexplained eccentricity of Mimas. Additionally, the “handoff” explains how Enceladus and Dione were captured into theirMMR in less than 100 Myr, despite their slow orbital convergence.H2O ice phase measurements and mapping of the Saturn icy satellitesC.M. Dalle Ore1,2, F. Scipioni1, K. Stephan3, and D.P. Cruikshank1. [Presented by Michelle Kirchoff, Southwest Research Institute,kirchoff@boulder.swri.edu]1NASA Ames, MS 245-6, Moffett Field, CA 94035, (Dale.P.Cruikshank@nasa.gov), (francesca.scipioni@nasa.gov) 2SETIInstitute,183 Bernardo Ave, Mountain View, CA 94043, (cmdalleore@gmail.com), 3Institute of Planetary Research, DLR, 12489Berlin, Germany (Katrin.Stephan@dlr.de)Introduction: In spite of having been the focus of many thorough studies since the arrival of the Cassini spacecraft at Saturn, thesurfaces of the icy satellites continue to intrigue. Temperature maps of the satellites show anomalous and unexpected distributions ontwo of the satellites (Howett et al 2011, 2012, 2013 and references therein) attributed to changes in thermal inertia due to the highenergy electron bombardment affecting the surfaces. Color maps of Mimas and Tethys also show patterns (Schenk et al. 2011) that areindicative of interaction between the ice and the very high-energy electrons. Dione shows patterns, the Wispy Terrains, that arereminiscent of the fractures, the ‘Tiger Stripes’ that distinguish EnceladusAt the typical average temperature, 80 K, amorphous ice is stable against thermal recrystallization for long timescales (Mastrapaet al. 2013). Nevertheless, surfaces are generally observed to be crystalline.The phase of the ice records information on the localphysical conditions, such as temperature, irradiation, and bombardment changes. Crystalline ice is usually associated with iceformation in warmer temperatures (above 135 K) (Mastrapa & Brown 2006). Amorphous H2O ice, on the other hand, implies coldertemperatures (below 135 K) and can result from irradiation from sufficiently energetic photons or charged particle bombardment ofthe crystalline phase (Baragiola et al. 2003). Amorphous H2O ice will convert back to the crystalline phase at 135 K (Mastrapa &Brown 2006). Because both phases are stable at Saturn’s icy satellites, then the presence of one phase versus the other can trace thehistory of the ice on the surface.11

Enceladus, Dione, Rhea and Mimas orbit Saturn at different distances and sample different parts of its magnetosphereexperiencing varying degrees of exposure to high-energy electrons. We use measurements of crystallinity looking for possibleexplanations for some of the phenomena characterizing these surfaces.Method: To measure the crystalline to amorphous ratios we apply the methods from Dalle Ore et al. (2015). The first stepconsists in determining variations in the 1.5-µm band indicative of changes in grain-size/temperature/composition on the surface,which could mistakenly be interpreted as phase variations. We then model the 2-µm band shape with varying amounts of crystalline toamorphous ice to calibrate the effect on the spectral signature. The calibration is applied to the measured 2.0 µm band asymmetry togauge the phase change. The resulting ice phase ratio were mapped, compared, and contrasted among the satellites.References:Baragiola, R.A., 2003 Planet. Space Sci. 51, 953–961; Dalle Ore, C.M., Cruikshank, D.P., Mastrapa, R.M.E., Lewis, E., and White,O.L. 2015. Icarus, 261, 80-90; Filacchione, G., D'Aversa, E., Capaccioni, F., et al. 2016. Icarus, 271, 292-313; Howett, C.J.A.,Spencer, J.R., Schenk, P., et al. 2011. Icarus, 216, 221; Howett, C.J.A., Spencer, J.R., Hurford, T., Verbiscer, A., & Segura, M. 2012.Icarus, 221, 1084; Howett, C.J.A., Spencer, J.R., Paranicas, C., & Schenk, P.M. 2013. LPI Contributions, 1719, 2824; Mastrapa,R.M.E., Brown, R.H., 2006. Icarus 183, 207–214; Mastrapa, R.M.E., Grundy, W.M., and Gudipati, M.S. 2013. The Science of SolarSystem Ices, 371-408.Saturn's irregular moons: Cassini imaging observation campaignT. Denk1 and S. Mottola2.1Freie Universität Berlin, Malteserstr. 74-100, 12249 Berlin, Germany (tilmann.denk@fu-berlin.de), 2Deutsches Zentrum für Luftund Raumfahrt (DLR), Rutherfordstr. 2, 12489 Berlin, Germany (Stefano.Mottola@dlr.de).Introduction: With 38 known members, the outer or irregular moons constitute the numerically largest group of satellites in theSaturnian system. Their orbital semi-major axes range between 11.4 and 25.2·106 km. Nine objects occupy prograde, the other 29retrograde orbits.All but exceptionally big Phoebe (ø 213 km) were discovered between year 2000 and 2007 and thus after the launch of CassiniHuygens. Except Phoebe (targeted flyby on 11 June 2004 at 2070 km altitude), they were not part of the original science goals of themission.Ground-based vs. Cassini: As seen from Earth, Phoebe reaches a brightness of 16 mag. Approximately 30-40 km sized objectsAlbiorix and Siarnaq barely scratch the 20-mag mark, while the rest ( 4-25 km) does not exceed 21 to 25 mag. Therefore, obtaining

Saturn’s rings Particle size and ring structure of Saturn’s rings from Tracy Becker (M6) stellar and solar occultations in the UV The structure of Saturn’s B ring from Cassini CIRS Shawn Brooks (M7) High-resolution scans Clues to clumping Joshua Colwell (M8) Particle properties in Saturn’s rings from skewness of Melody Green (M9)