TY - JOUR A1 - Baibolatov, Yernur A1 - Spahn, Frank T1 - The role of adhesion for ensembles of mesoscopic particles JF - Granular matter N2 - We present a toy-model for an ensemble of adhering mesoscopic constituents in order to estimate the effect of the granular temperature on the sizes of embedded aggregates. The major goal is to illustrate the relation between the mean aggregate size and the granular temperature in dense planetary rings. For sake of simplicity we describe the collective behavior of the ensemble by means of equilibrium statistical mechanics, motivated by the stationary temperature established by the balance between a Kepler-shear driven viscous heating and inelastic cooling in these cosmic granular disks. The ensemble consists of N' equal constituents which can form cluster(s) or move like a gas-or both phases may coexist-depending on the (granular) temperature of the system. We assume the binding energy levels of a cluster E-c = -N-c gamma a to be determined by a certain contact number N-c, given by the configuration of N constituents of the aggregate (energy per contact: -gamma a). By applying canonical and grand-canonical ensembles, we show that the granular temperature T of a gas of constituents (their mean kinetic energy) controls the size distribution of the aggregates. They are the smaller the higher the granular temperature T is. A mere gas of single constituents is sustained for T >> gamma a. In the case of large clusters (low temperatures T << gamma a) the size distribution becomes a Poissonian. KW - Adhesion KW - Statistical mechanics KW - Planetary rings Y1 - 2012 U6 - https://doi.org/10.1007/s10035-012-0325-4 SN - 1434-5021 VL - 14 IS - 2 SP - 197 EP - 202 PB - Springer CY - New York ER - TY - JOUR A1 - Bodrova, Anna A1 - Schmidt, Jürgen A1 - Spahn, Frank A1 - Brilliantov, Nikolai V. T1 - Adhesion and collisional release of particles in dense planetary rings JF - Icarus : international journal of solar system studies N2 - We propose a simple theoretical model for aggregative and fragmentative collisions in Saturn's dense rings. In this model the ring matter consists of a bimodal size distribution: large (meter sized) boulders and a population of smaller particles (tens of centimeters down to dust). The small particles can adhesively stick to the boulders and can be released as debris in binary collisions of their carriers. To quantify the adhesion force we use the JKR theory (Johnson, K., Kendall, K., Roberts, A. [1971]. Proc. R. Soc. Lond. A 324, 301-313). The rates of release and adsorption of particles are calculated, depending on material parameters, sizes, and plausible velocity dispersions of carriers and debris particles. In steady state we obtain an expression for the amount of free debris relative to the fraction still attached to the carriers. In terms of this conceptually simple model a paucity of subcentimeter particles in Saturn's rings (French, R.G., Nicholson, P.D. [2000]. Icarus 145, 502-523; Marouf, E. et al. [2008]. Abstracts for "Saturn after Cassini-Huygens" Symposium, Imperial College London, UK, July 28 to August 1, p. 113) can be understood as a consequence of the increasing strength of adhesion (relative to inertial forces) for decreasing particle size. In this case particles smaller than a certain critical radius remain tightly attached to the surfaces of larger boulders, even when the boulders collide at their typical speed. Furthermore, we find that already a mildly increased velocity dispersion of the carrier-particles may significantly enhance the fraction of free debris particles, in this way increasing the optical depth of the system. KW - Planetary rings KW - Saturn, Rings KW - Collisional physics Y1 - 2012 U6 - https://doi.org/10.1016/j.icarus.2011.11.011 SN - 0019-1035 SN - 1090-2643 VL - 218 IS - 1 SP - 60 EP - 68 PB - Elsevier CY - San Diego 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 - TY - JOUR A1 - Kempf, Sascha A1 - Srama, Ralf A1 - Grün, Eberhard A1 - Mocker, Anna A1 - Postberg, Frank A1 - Hillier, Jon K. A1 - Horanyi, Mihaly A1 - Sternovsky, Zoltan A1 - Abel, Bernd A1 - Beinsen, Alexander A1 - Thissen, Roland A1 - Schmidt, Jürgen A1 - Spahn, Frank A1 - Altobelli, Nicolas T1 - Linear high resolution dust mass spectrometer for a mission to the Galilean satellites JF - Planetary and space science N2 - The discovery of volcanic activity on Enceladus stands out amongst the long list of findings by the Cassini mission to Saturn. In particular the compositional analysis of Enceladus ice particles by Cassini's Cosmic Dust Analyser (CDA) (Srama et al., 2004) has proven to be a powerful technique for obtaining information about processes below the moon's ice crust. Small amounts of sodium salts embedded in the particles' ice matrices provide direct evidence for a subsurface liquid water reservoir, which is, or has been, in contact with the moon's rocky core (Postberg et al., 2009, 2011b). Jupiter's Galilean satellites Ganymede, Europa, and Callisto are also believed to have subsurface oceans and are therefore prime targets for future NASA and ESA outer Solar System missions. The Galilean moons are engulfed in tenuous dust clouds consisting of tiny pieces of the moons' surfaces (Kruger et al., 1999), released by hypervelocity impacts of micrometeoroids, which steadily bombard the surfaces of the moons. In situ chemical analysis of these grains by a high resolution dust spectrometer will provide spatially resolved mapping of the surface composition of Europa. Ganymede, and Callisto, meeting key scientific objectives of the planned missions. However, novel high-resolution reflectron-type dust mass spectrometers (Sternovsky et al., 2007; Srama et al., 2007) developed for dust astronomy missions (Gran et al., 2009) are probably not robust enough to be operated in the energetic radiation environment of the inner Jovian system. In contrast, CDA's linear spectrometer is much less affected by harsh radiation conditions because its ion detector is not directly facing out into space. The instrument has been continuously operated on Cassini for 11 years. In this paper we investigate the possibility of operating a CDA-like instrument as a high resolution impact mass spectrometer. We show that such an instrument is capable of reliably identifying traces of organic and inorganic materials in the ice matrix of ejecta expected to be generated from the surfaces of the Galilean moons. These measurements are complementary, and in some cases superior, compared to other traditional techniques such as infrared remote sensing or in situ ion or neutral mass spectrometers. KW - Europa KW - Ganymede KW - Callisto KW - Surface composition KW - Mass spectroscopy KW - Dust Y1 - 2012 U6 - https://doi.org/10.1016/j.pss.2011.12.019 SN - 0032-0633 VL - 65 IS - 1 SP - 10 EP - 20 PB - Elsevier CY - Oxford ER - TY - JOUR A1 - Srama, Ralf A1 - Krueger, H. A1 - Yamaguchi, T. A1 - Stephan, T. A1 - Burchell, M. A1 - Kearsley, A. T. A1 - Sterken, V. A1 - Postberg, F. A1 - Kempf, S. A1 - Grün, Eberhard A1 - Altobelli, Nicolas A1 - Ehrenfreund, P. A1 - Dikarev, V. A1 - Horanyi, M. A1 - Sternovsky, Zoltan A1 - Carpenter, J. D. A1 - Westphal, A. A1 - Gainsforth, Z. A1 - Krabbe, A. A1 - Agarwal, Jessica A1 - Yano, H. A1 - Blum, J. A1 - Henkel, H. A1 - Hillier, J. A1 - Hoppe, P. A1 - Trieloff, M. A1 - Hsu, S. A1 - Mocker, A. A1 - Fiege, K. A1 - Green, S. F. A1 - Bischoff, A. A1 - Esposito, F. A1 - Laufer, R. A1 - Hyde, T. W. A1 - Herdrich, G. A1 - Fasoulas, S. A1 - Jaeckel, A. A1 - Jones, G. A1 - Jenniskens, P. A1 - Khalisi, E. A1 - Moragas-Klostermeyer, Georg A1 - Spahn, Frank A1 - Keller, H. U. A1 - Frisch, P. A1 - Levasseur-Regourd, A. C. A1 - Pailer, N. A1 - Altwegg, K. A1 - Engrand, C. A1 - Auer, S. A1 - Silen, J. A1 - Sasaki, S. A1 - Kobayashi, M. A1 - Schmidt, J. A1 - Kissel, J. A1 - Marty, B. A1 - Michel, P. A1 - Palumbo, P. A1 - Vaisberg, O. A1 - Baggaley, J. A1 - Rotundi, A. A1 - Roeser, H. P. T1 - SARIM PLUS-sample return of comet 67P/CG and of interstellar matter JF - EXPERIMENTAL ASTRONOMY N2 - The Stardust mission returned cometary, interplanetary and (probably) interstellar dust in 2006 to Earth that have been analysed in Earth laboratories worldwide. Results of this mission have changed our view and knowledge on the early solar nebula. The Rosetta mission is on its way to land on comet 67P/Churyumov-Gerasimenko and will investigate for the first time in great detail the comet nucleus and its environment starting in 2014. Additional astronomy and planetary space missions will further contribute to our understanding of dust generation, evolution and destruction in interstellar and interplanetary space and provide constraints on solar system formation and processes that led to the origin of life on Earth. One of these missions, SARIM-PLUS, will provide a unique perspective by measuring interplanetary and interstellar dust with high accuracy and sensitivity in our inner solar system between 1 and 2 AU. SARIM-PLUS employs latest in-situ techniques for a full characterisation of individual micrometeoroids (flux, mass, charge, trajectory, composition()) and collects and returns these samples to Earth for a detailed analysis. The opportunity to visit again the target comet of the Rosetta mission 67P/Churyumov-Gerasimeenternko, and to investigate its dusty environment six years after Rosetta with complementary methods is unique and strongly enhances and supports the scientific exploration of this target and the entire Rosetta mission. Launch opportunities are in 2020 with a backup window starting early 2026. The comet encounter occurs in September 2021 and the reentry takes place in early 2024. An encounter speed of 6 km/s ensures comparable results to the Stardust mission. KW - Interstellar dust KW - Cometary dust KW - Churyumov Gerasimenko KW - Interplanetary dust KW - IMF KW - Cosmic vision KW - Sample return KW - Dust collector KW - Mass spectrometry Y1 - 2012 U6 - https://doi.org/10.1007/s10686-011-9285-7 SN - 0922-6435 SN - 1572-9508 VL - 33 IS - 2-3 SP - 723 EP - 751 PB - SPRINGER CY - DORDRECHT ER -