In situ collection of dust grains falling from Saturn's rings into its atmosphere

• Published in: Science (American Association for the Advancement of Science) 2018-10, Vol.362 (6410)
• Main Authors: Hsu, Hsiang-Wen, Schmidt, Jürgen, Kempf, Sascha, Postberg, Frank, Moragas-Klostermeyer, Georg, Seiß, Martin, Hoffmann, Holger, Burton, Marcia, Ye, ShengYi, Kurth, William S, Horányi, Mihály, Khawaja, Nozair, Spahn, Frank, Schirdewahn, Daniel, O'Donoghue, James, Moore, Luke, Cuzzi, Jeff, Jones, Geraint H, Srama, Ralf
• Format: Article
• Language: English
• Subjects: Atmosphere; Atmospheric entry; Atmospheric sciences; Auroras; Cassini mission; Charged particles; Composition; Cosmic dust; Deposition; Dominance; Dust; Dust control; Ejecta; Ejection; Emission analysis; Erosion; Exploration; Falling; Fluctuations; Grains; Ice; Ice formation; Latitude; Magnetic fields; Measuring instruments; Neutrons; Orbits; Radiation; Radioactive decay; Rain; Saturn; Saturn atmosphere; Scientific Concepts; Silica; Silicates; Southern Hemisphere; Spacecraft; Upper atmosphere; Water
• ISSN: 0036-8075; 1095-9203
• DOI: 10.1126/science.aat3185

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.