TY  - JOUR
A1  - Buratti, Bonnie J.
A1  - Thomas, P. C.
A1  - Roussos, E.
A1  - Howett, Carly
A1  - Seiss, Martin
A1  - Hendrix, A. R.
A1  - Helfenstein, Paul
A1  - Brown, R. H.
A1  - Clark, R. N.
A1  - Denk, Tilmann
A1  - Filacchione, Gianrico
A1  - Hoffmann, Holger
A1  - Jones, Geraint H.
A1  - Khawaja, N.
A1  - Kollmann, Peter
A1  - Krupp, Norbert
A1  - Lunine, Jonathan
A1  - Momary, T. W.
A1  - Paranicas, Christopher
A1  - Postberg, Frank
A1  - Sachse, Manuel
A1  - Spahn, Frank
A1  - Spencer, John
A1  - Srama, Ralf
A1  - Albin, T.
A1  - Baines, K. H.
A1  - Ciarniello, Mauro
A1  - Economou, Thanasis
A1  - Hsu, Hsiang-Wen
A1  - Kempf, Sascha
A1  - Krimigis, Stamatios M.
A1  - Mitchell, Donald
A1  - Moragas-Klostermeyer, Georg
A1  - Nicholson, Philip D.
A1  - Porco, C. C.
A1  - Rosenberg, Heike
A1  - Simolka, Jonas
A1  - Soderblom, Laurence A.
T1  - Close Cassini flybys of Saturn’s ring moons Pan, Daphnis, Atlas, Pandora, and Epimetheus
JF  - Science
N2  - Saturn’s main ring system is associated with a set of small moons that either are embedded within it or interact with the rings to alter their shape and composition. Five close flybys of the moons Pan, Daphnis, Atlas, Pandora, and Epimetheus were performed between December 2016 and April 2017 during the ring-grazing orbits of the Cassini mission. Data on the moons’ morphology, structure, particle environment, and composition were returned, along with images in the ultraviolet and thermal infrared. We find that the optical properties of the moons’ surfaces are determined by two competing processes: contamination by a red material formed in Saturn’s main ring system and accretion of bright icy particles or water vapor from volcanic plumes originating on the moon Enceladus.
Y1  - 2019
U6  - https://doi.org/10.1126/science.aat2349
SN  - 0036-8075
SN  - 1095-9203
VL  - 364
IS  - 6445
SP  - 1053
PB  - American Assoc. for the Advancement of Science
CY  - Washington
ER  - 
TY  - JOUR
A1  - Spahn, Frank
A1  - Sachse, Manuel
A1  - Seiss, Martin
A1  - Hsu, Hsiang-Wen
A1  - Kempf, Sascha
A1  - Horanyi, Mihaly
T1  - Circumplanetary Dust Populations
JF  - Space science reviews
N2  - We summarize the current state of observations of circumplanetary dust populations, including both dilute and dense rings and tori around the giant planets, ejecta clouds engulfing airless moons, and rings around smaller planetary bodies throughout the Solar System. We also discuss the theoretical models that enable these observations to be understood in terms of the sources, sinks and transport of various dust populations. The dynamics and resulting transport of the particles can be quite complex, due to the fact that their motion is influenced by neutral and plasma drag, radiation pressure, and electromagnetic forcesall in addition to gravity. The relative importance of these forces depends on the environment, as well as the makeup and size of the particles. Possible dust sources include the generation of ejecta particles by impacts, active volcanoes and geysers, and the capture of exogenous particles. Possible dust sinks include collisions with moons, rings, or the central planet, erosion due to sublimation and sputtering, even ejection and escape from the circumplanetary environment.
KW  - Circumplanetary dust
KW  - Planetary rings and tori
KW  - Dust sources and sinks
KW  - Dust dynamics
Y1  - 2019
U6  - https://doi.org/10.1007/s11214-018-0577-3
SN  - 0038-6308
SN  - 1572-9672
VL  - 215
IS  - 1
PB  - Springer
CY  - Dordrecht
ER  - 
TY  - JOUR
A1  - Hsu, Hsiang-Wen
A1  - Schmidt, Jürgen
A1  - Kempf, Sascha
A1  - Postberg, Frank
A1  - Moragas-Klostermeyer, Georg
A1  - Seiss, Martin
A1  - Hoffmann, Holger
A1  - Burton, Marcia
A1  - Ye, ShengYi
A1  - Kurth, William S.
A1  - Horanyi, Mihaly
A1  - Khawaja, Nozair
A1  - Spahn, Frank
A1  - Schirdewahn, Daniel
A1  - Moore, Luke
A1  - Cuzzi, Jeff
A1  - Jones, Geraint H.
A1  - Srama, Ralf
T1  - In situ collection of dust grains falling from Saturn’s rings into its atmosphere
JF  - Science
N2  - Saturn’s main rings are composed of >95% water ice, and the nature of the remaining few percent has remained unclear. The Cassini spacecraft’s traversals between Saturn and its innermost D ring allowed its cosmic dust analyzer (CDA) to collect material released from the main rings and to characterize the ring material infall into Saturn. We report the direct in situ detection of material from Saturn’s dense rings by the CDA impact mass spectrometer. Most detected grains are a few tens of nanometers in size and dynamically associated with the previously inferred “ring rain.” Silicate and water-ice grains were identified, in proportions that vary with latitude. Silicate grains constitute up to 30% of infalling grains, a higher percentage than the bulk silicate content of the rings.
Y1  - 2018
U6  - https://doi.org/10.1126/science.aat3185
SN  - 0036-8075
SN  - 1095-9203
VL  - 362
IS  - 6410
SP  - 49
EP  - +
PB  - American Assoc. for the Advancement of Science
CY  - Washington
ER  - 
TY  - JOUR
A1  - Ye, S. -Y.
A1  - Kurth, William S.
A1  - Hospodarsky, George B.
A1  - Persoon, Ann M.
A1  - Gurnett, Don A.
A1  - Morooka, Michiko
A1  - Wahlund, Jan-Erik
A1  - Hsu, Hsiang-Wen
A1  - Seiss, Martin
A1  - Srama, Ralf
T1  - Cassini RPWS dust observation near the Janus/Epimetheus orbit
JF  - Journal of geophysical research : Space physics
N2  - During the Ring Grazing orbits near the end of Cassini mission, the spacecraft crossed the equatorial plane near the orbit of Janus/Epimetheus (similar to 2.5 Rs). This region is populated with dust particles that can be detected by the Radio and Plasma Wave Science (RPWS) instrument via an electric field antenna signal. Analysis of the voltage waveforms recorded on the RPWS antennas provides estimations of the density and size distribution of the dust particles. Measured RPWS profiles, fitted with Lorentzian functions, are shown to be mostly consistent with the Cosmic Dust Analyzer, the dedicated dust instrument on board Cassini. The thickness of the dusty ring varies between 600 and 1,000 km. The peak location shifts north and south within 100 km of the ring plane, likely a function of the precession phase of Janus orbit.
KW  - Saturn
KW  - dust
KW  - ring
Y1  - 2018
U6  - https://doi.org/10.1029/2017JA025112
SN  - 2169-9380
SN  - 2169-9402
VL  - 123
IS  - 6
SP  - 4952
EP  - 4960
PB  - American Geophysical Union
CY  - Washington
ER  - 
TY  - JOUR
A1  - Grätz, Fabio M.
A1  - Seiss, Martin
A1  - Spahn, Frank
T1  - Formation of moon-induced gaps in dense planetary rings
BT  - application to the rings of saturn
JF  - The astrophysical journal : an international review of spectroscopy and astronomical physics
N2  - We develop an axisymmetric diffusion model to describe radial density profiles in the vicinity of tiny moons embedded in planetary rings. Our diffusion model accounts for the gravitational scattering of the ring particles by an embedded moon and for the viscous diffusion of the ring matter back into the gap. With test particle simulations, we show that the scattering of the ring particles passing the moon is larger for small impact parameters than estimated by Goldreich & Tremaine and Namouni. This is significant for modeling the Keeler gap. We apply our model to the gaps of the moons Pan and Daphnis embedded in the outer A ring of Saturn with the aim to estimate the shear viscosity of the ring in the vicinity of the Encke and Keeler gap. In addition, we analyze whether tiny icy moons whose dimensions lie below Cassini's resolution capabilities would be able to explain the gap structure of the C ring and the Cassini division.
KW  - diffusion
KW  - planets and satellites: rings
KW  - scattering
Y1  - 2018
U6  - https://doi.org/10.3847/1538-4357/aace00
SN  - 0004-637X
SN  - 1538-4357
VL  - 862
IS  - 2
PB  - IOP Publ. Ltd.
CY  - Bristol
ER  - 
TY  - JOUR
A1  - Ye, Shengyi
A1  - Kurth, William S.
A1  - Hospodarsky, George B.
A1  - Persoon, Ann M.
A1  - Sulaiman, Ali H.
A1  - Gurnett, Don A.
A1  - Morooka, Michiko
A1  - Wahlund, Jan-Erik
A1  - Hsu, Hsiang-Wen
A1  - Sternovsky, Zoltan
A1  - Wang, Xu
A1  - Horanyi, M.
A1  - Seiss, Martin
A1  - Srama, Ralf
T1  - Dust Observations by the Radio and Plasma Wave Science Instrument During
JF  - Geophysical research letters
N2  - Plain Language Summary Cassini flew through the gap between Saturn and its rings for 22 times before plunging into the atmosphere of Saturn, ending its 20-year mission. The radio and plasma waves instrument on board Cassini helped quantify the dust hazard in this previously unexplored region. The measured density of large dust particles was much lower than expected, allowing high-value science observations during the subsequent Grand Finale orbits.
Y1  - 2018
U6  - https://doi.org/10.1029/2018GL078059
SN  - 0094-8276
SN  - 1944-8007
VL  - 45
IS  - 19
SP  - 10101
EP  - 10109
PB  - American Geophysical Union
CY  - Washington
ER  - 
TY  - JOUR
A1  - Seiler, Martin
A1  - Sremcevic, Miodrag
A1  - Seiss, Martin
A1  - Hoffmann, Holger
A1  - Spahn, Frank
T1  - A Librational Model for the Propeller Bleriot in the Saturnian Ring System
JF  - The astrophysical journal : an international review of spectroscopy and astronomical physics ; Part 2, Letters
KW  - planets and satellites: individual (Saturn)
KW  - planets and satellites: rings
Y1  - 2017
U6  - https://doi.org/10.3847/2041-8213/aa6d73
SN  - 2041-8205
SN  - 2041-8213
VL  - 840
PB  - IOP Publ. Ltd.
CY  - Bristol
ER  - 
TY  - JOUR
A1  - Hoffmann, Holger
A1  - Seiss, Martin
A1  - Salo, Heikki
A1  - Spahn, Frank
T1  - Vertical structures induced by embedded moonlets in Saturn's rings
JF  - Icarus : international journal of solar system studies
N2  - We study the vertical extent of propeller structures in Saturn's rings (i) by extending the model of Spahn and Sremcevic (Spahn, F., Sremcevic, M. [2000]. Astron. Astrophys., 358, 368-372) to include the vertical direction and (ii) by performing N-body box simulations of a perturbing moonlet embedded into the rings. We find that the gravitational interaction of ring particles with a non-inclined moonlet does not induce considerable vertical excursions of ring particles, but causes a considerable thermal motion in the ring plane. We expect ring particle collisions to partly convert the lateral induced thermal motion into vertical excursions of ring particles in the course of a quasi-thermalization. The N-body box simulations lead to maximal propeller heights of about 0.6-0.8 Hill radii of the embedded perturbing moonlet. Moonlet sizes estimated by this relation are in good agreement with size estimates from radial propeller scalings for the propellers Bleriot and Earhart. For large propellers, the extended hydrodynamical propeller model predicts an exponential propeller height relaxation, confirmed by N-body box simulations of non-self gravitating ring particles. Exponential cooling constants, calculated from the hydrodynamical propeller model agree fairly well with values from fits to the tail of the azimuthal height decay of the N-body box simulations. From exponential cooling constants, determined from shadows cast by the propeller Earhart and imaged by the Cassini spacecraft, we estimate collision frequencies of about 6 collisions per particle per orbit in the propeller gap region and about 11 collisions per particle per orbit in the propeller wake region. (C) 2015 Elsevier Inc. All rights reserved.
KW  - Planetary rings
KW  - Saturn, rings
KW  - Saturn, satellites
KW  - Disks
Y1  - 2015
U6  - https://doi.org/10.1016/j.icarus.2015.02.003
SN  - 0019-1035
SN  - 1090-2643
VL  - 252
SP  - 400
EP  - 414
PB  - Elsevier
CY  - San Diego
ER  - 
TY  - GEN
A1  - Spahn, Frank
A1  - Seiss, Martin
T1  - Charges dropped
T2  - Nature physics
Y1  - 2015
SN  - 1745-2473
SN  - 1745-2481
VL  - 11
IS  - 9
SP  - 709
EP  - 710
PB  - Nature Publ. Group
CY  - London
ER  - 
TY  - JOUR
A1  - Guimaraes, Ana H. F.
A1  - Albers, Nicole
A1  - Spahn, Frank
A1  - Seiss, Martin
A1  - Vieira-Neto, Ernesto
A1  - Brilliantov, Nikolai V.
T1  - Aggregates in the strength and gravity regime Particles sizes in Saturn's rings
JF  - Icarus : international journal of solar system studies
N2  - Particles in Saturn's main rings range in size from dust to kilometer-sized objects. Their size distribution is thought to be a result of competing accretion and fragmentation processes. While growth is naturally limited in tidal environments, frequent collisions among these objects may contribute to both accretion and fragmentation. As ring particles are primarily made of water ice attractive surface forces like adhesion could significantly influence these processes, finally determining the resulting size distribution. Here, we derive analytic expressions for the specific self-energy Q and related specific break-up energy Q(star) of aggregates. These expressions can be used for any aggregate type composed of monomeric constituents. We compare these expressions to numerical experiments where we create aggregates of various types including: regular packings like the face-centered cubic (fcc), Ballistic Particle Cluster Aggregates (BPCA), and modified BPCAs including e.g. different constituent size distributions. We show that accounting for attractive surface forces such as adhesion a simple approach is able to: (a) generally account for the size dependence of the specific break-up energy for fragmentation to occur reported in the literature, namely the division into "strength" and "gravity" regimes and (b) estimate the maximum aggregate size in a collisional ensemble to be on the order of a few tens of meters, consistent with the maximum particle size observed in Saturn's rings of about 10 m.
KW  - Collisional physics
KW  - Accretion
KW  - Planetary rings
KW  - Saturn, Rings
Y1  - 2012
U6  - https://doi.org/10.1016/j.icarus.2012.06.005
SN  - 0019-1035
SN  - 1090-2643
VL  - 220
IS  - 2
SP  - 660
EP  - 678
PB  - Elsevier
CY  - San Diego
ER  -