Kinematik planetarer Ringe
Final Report Abstract
Within the framework of this project, different experimental approaches were conducted to gain information about the collisional properties of Saturnian ring particles. Three different experimental setups were developed to allow for the study of binary collisions, many-body collisions, and the inter-particle forces of water ice at cryogenic temperatures. The coefficients of restitution obtained from two parabolic flight campaigns show a significant scatter that has not been observed by previous experimental studies. On the one hand this can arise from the distributed impact parameters in these free particle collisions, while on the other hand the presence of thin frost layers on the surfaces of our samples is evident from the image sequences and may also contribute. In collision experiments with ∼ 5-millimeter-sized samples we observed an upper limit of the coefficient of restitution, which is (with one exception) at about εmax = 0.65. In comparison to collisions of larger samples, the assumption that the size alters the coefficient of restitution can be regarded as justified, since in this case the identical setup was used under similar conditions. A similar size effect is apparent when considering the mean coefficients of restitution of ε5 mm = 0.37 and ε15 mm = 0.45 obtained in the free particle collisions. This trend confirms the findings of Higa et al. (1998) and is in agreement with our recent collision model. An influence of small fractions of pollution to the ice was not apparent in the parabolic flight experiments. The analysis of free binary collisions of ice spheres in many-particle systems enabled us to apply the model of Krijt et al. to the data set of the rebounding particles, while the influence of a regolith layer on the surfaces of the samples could not be pinpointed within this study. The synopsis of the bouncing collisions of plain water-ice spheres and the sticking incidents yield clear constraints on the specific surface energy γ = 0.23 J m^−2 and the viscous timescale Tv = 2.85·10^7 s. Hence, for 1-centimeter-sized ice spheres the critical sticking velocity threshold is expected to be at vstick = 0.015 m s^−1 . Under the assumption of the validity of the same input parameters, the model can also be applied to the collisions of ice spheres of different sizes. Utilizing the derived sticking velocity threshold, the formation of larger clumps and aggregates in the undisturbed regions of Saturn’s main rings – such as the C ring and the Cassini Division – can be investigated to constrain size limits of the growth of Dynamical Ephemeral Bodies to sizes of 60 . . . 100 m. The independent measurements of the thermal behavior of the specific surface energy of macroscopic water-ice samples provides similar results to the value obtained from Krijt et al.’s model. Furthermore, it was found to be in good agreement with the findings made for microscopic ice samples (Gundlach et al., 2011). The data set shows a trend of decreasing specific surface energy towards low temperatures. However, the exact functional dependence could not be revealed and should be adressed in a more extensive study.
Publications
- (2010). Microgravity experiments on the collisional behavior of Saturnian ring particles. Icarus , 206:424-430
Heißelmann, D., Blum, J., Fraser, H. J., Wolling, K.
(See online at https://dx.doi.org/10.1016/j.icarus.2009.08.009) - (2012). Normal Collisions of Spheres: A Literature Survey on Available Experiments
Güttler, C., Heißelmann, D., Blum, J., Krijt, S.
- (2013). Energy dissipation in head-on collisions of spheres. Journal of Physics D: Applied Physics, 46(43):435303
Krijt, S., Güttler, C., Heißelmann, D., Dominik, C., Tielens, A. G. G. M.
(See online at https://doi.org/10.1088/0022-3727/46/43/435303) - (2014). Laboratory Drop Towers for the Experimental Simulation of Dust-aggregate Collisions in the Early Solar System. Journal of Visualized Experiments, 88, e51541
Blum, J., Beitz, E., Bukhari, M., Gundlach, B., Hagemann, J.-H., Heißelmann, D., Kothe, S., Schräpler, R., von Borstel, I., Weidling, R.
(See online at https://doi.org/10.3791/51541) - (2015). Collisional properties of Saturnian ring particles. [Berlin] : Uni-Ed., Zugl.: Braunschweig, Techn. Univ., Diss., 2015
Heißelmann, D.
- (2015). Collisions of small ice particles under microgravity conditions. Astronomy & Astrophysics, 573:A49
Hill, C. R., Heißelmann, D., Blum, J., Fraser, H. J.
(See online at https://doi.org/10.1051/0004-6361/201424069) - (2015). Collisions of small ice particles under microgravity conditions. II. Does the chemical composition of the ice change the collisional properties? Astronomy & Astrophysics, 575:A6
Hill, C. R., Heißelmann, D., Blum, J., Fraser, H. J.
(See online at https://doi.org/10.1051/0004-6361/201425336)
