1
|
Abstract
The Cassini-Huygens mission to Saturn provided a close-up study of the gas giant planet, as well as its rings, moons, and magnetosphere. The Cassini spacecraft arrived at Saturn in 2004, dropped the Huygens probe to study the atmosphere and surface of Saturn's planet-sized moon Titan, and orbited Saturn for the next 13 years. In 2017, when it was running low on fuel, Cassini was intentionally vaporized in Saturn's atmosphere to protect the ocean moons, Enceladus and Titan, where it had discovered habitats potentially suitable for life. Mission findings include Enceladus' south polar geysers, the source of Saturn's E ring; Titan's methane cycle, including rain that creates hydrocarbon lakes; dynamic rings containing ice, silicates, and organics; and Saturn's differential rotation. This Review discusses highlights of Cassini's investigations, including the mission's final year.
Collapse
Affiliation(s)
- Linda Spilker
- Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA 91109, USA
| |
Collapse
|
2
|
Tiscareno MS, Nicholson PD, Cuzzi JN, Spilker LJ, Murray CD, Hedman MM, Colwell JE, Burns JA, Brooks SM, Clark RN, Cooper NJ, Deau E, Ferrari C, Filacchione G, Jerousek RG, Le Mouélic S, Morishima R, Pilorz S, Rodriguez S, Showalter MR, Badman SV, Baker EJ, Buratti BJ, Baines KH, Sotin C. Close-range remote sensing of Saturn's rings during Cassini's ring-grazing orbits and Grand Finale. Science 2019; 364:364/6445/eaau1017. [PMID: 31196983 DOI: 10.1126/science.aau1017] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/07/2018] [Accepted: 05/07/2019] [Indexed: 11/02/2022]
Abstract
Saturn's rings are an accessible exemplar of an astrophysical disk, tracing the Saturn system's dynamical processes and history. We present close-range remote-sensing observations of the main rings from the Cassini spacecraft. We find detailed sculpting of the rings by embedded masses, and banded texture belts throughout the rings. Saturn-orbiting streams of material impact the F ring. There are fine-scaled correlations among optical depth, spectral properties, and temperature in the B ring, but anticorrelations within strong density waves in the A ring. There is no spectral distinction between plateaux and the rest of the C ring, whereas the region outward of the Keeler gap is spectrally distinct from nearby regions. These results likely indicate that radial stratification of particle physical properties, rather than compositional differences, is responsible for producing these ring structures.
Collapse
Affiliation(s)
- Matthew S Tiscareno
- Carl Sagan Center for the Study of Life in the Universe, SETI Institute, Mountain View, CA 94043, USA.
| | | | | | - Linda J Spilker
- NASA Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109, USA
| | - Carl D Murray
- Astronomy Unit, Queen Mary University of London, London E1 4NS, UK
| | - Matthew M Hedman
- Department of Physics, University of Idaho, Moscow, ID 83844, USA
| | - Joshua E Colwell
- Department of Physics, University of Central Florida, Orlando, FL 32816, USA
| | - Joseph A Burns
- Department of Astronomy, Cornell University, Ithaca, NY 14853, USA.,College of Engineering, Cornell University, Ithaca, NY 14853, USA
| | - Shawn M Brooks
- NASA Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109, USA
| | | | | | - Estelle Deau
- NASA Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109, USA.,Department of Earth, Planetary, and Space Sciences, University of California at Los Angeles, Los Angeles, CA 90095, USA
| | - Cecile Ferrari
- Institut de Physique du Globe de Paris, Centre National de la Recherche Scientifique (CNRS)-Unité Mixte de Recherche (UMR) 7154, Université Paris-Diderot, Université Sorbonne-Paris-Cité (USPC), Paris, France
| | - Gianrico Filacchione
- INAF-IAPS (Istituto Nazionale di AstroFisica-Istituto di Astrofisica e Planetologia Spaziali), Rome, Italy
| | - Richard G Jerousek
- Department of Physics, University of Central Florida, Orlando, FL 32816, USA
| | - Stéphane Le Mouélic
- Laboratoire de Planetologie et Geodynamique, CNRS-UMR 6112, Université de Nantes, 44322 Nantes, France
| | - Ryuji Morishima
- NASA Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109, USA.,Department of Earth, Planetary, and Space Sciences, University of California at Los Angeles, Los Angeles, CA 90095, USA
| | - Stu Pilorz
- Carl Sagan Center for the Study of Life in the Universe, SETI Institute, Mountain View, CA 94043, USA
| | - Sébastien Rodriguez
- Institut de Physique du Globe de Paris, Centre National de la Recherche Scientifique (CNRS)-Unité Mixte de Recherche (UMR) 7154, Université Paris-Diderot, Université Sorbonne-Paris-Cité (USPC), Paris, France
| | - Mark R Showalter
- Carl Sagan Center for the Study of Life in the Universe, SETI Institute, Mountain View, CA 94043, USA
| | - Sarah V Badman
- Physics Department, Lancaster University, Lancaster LA1 4YB, UK
| | | | - Bonnie J Buratti
- NASA Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109, USA
| | - Kevin H Baines
- NASA Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109, USA
| | - Christophe Sotin
- NASA Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109, USA
| |
Collapse
|
3
|
Hsu HW, Schmidt J, Kempf S, Postberg F, Moragas-Klostermeyer G, Seiß M, Hoffmann H, Burton M, Ye S, Kurth WS, Horányi M, Khawaja N, Spahn F, Schirdewahn D, O'Donoghue J, Moore L, Cuzzi J, Jones GH, Srama R. In situ collection of dust grains falling from Saturn's rings into its atmosphere. Science 2019; 362:362/6410/eaat3185. [PMID: 30287635 DOI: 10.1126/science.aat3185] [Citation(s) in RCA: 31] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/14/2018] [Accepted: 09/07/2018] [Indexed: 11/02/2022]
Abstract
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.
Collapse
Affiliation(s)
- Hsiang-Wen Hsu
- Laboratory for Atmospheric and Space Physics, University of Colorado-Boulder, Boulder, CO, USA.
| | - Jürgen Schmidt
- Astronomy Research Unit, University of Oulu, Oulu, Finland
| | - Sascha Kempf
- Laboratory for Atmospheric and Space Physics, University of Colorado-Boulder, Boulder, CO, USA
| | - Frank Postberg
- Institut für Geowissenschaften, Universität Heidelberg, Heidelberg, Germany.,Institut für Geologische Wissenschaften, Freie Universität Berlin, Berlin, Germany
| | | | - Martin Seiß
- Institut für Physik und Astronomie, Universität Potsdam, Potsdam, Germany
| | - Holger Hoffmann
- Institut für Physik und Astronomie, Universität Potsdam, Potsdam, Germany
| | | | - ShengYi Ye
- Department of Physics and Astronomy, University of Iowa, Iowa City, IA, USA
| | - William S Kurth
- Department of Physics and Astronomy, University of Iowa, Iowa City, IA, USA
| | - Mihály Horányi
- Laboratory for Atmospheric and Space Physics, University of Colorado-Boulder, Boulder, CO, USA
| | - Nozair Khawaja
- Institut für Geowissenschaften, Universität Heidelberg, Heidelberg, Germany.,Institut für Geologische Wissenschaften, Freie Universität Berlin, Berlin, Germany
| | - Frank Spahn
- Institut für Physik und Astronomie, Universität Potsdam, Potsdam, Germany
| | - Daniel Schirdewahn
- Institut für Physik und Astronomie, Universität Potsdam, Potsdam, Germany
| | | | - Luke Moore
- Center for Space Physics, Boston University, Boston, MA, USA
| | - Jeff Cuzzi
- NASA Ames Research Center, Moffett Field, CA, USA
| | - Geraint H Jones
- Mullard Space Science Laboratory, University College London, Holmbury St. Mary, Dorking, UK.,The Centre for Planetary Sciences at University College London/Birkbeck, London, UK
| | - Ralf Srama
- Institut für Raumfahrtsysteme, Universität Stuttgart, Stuttgart, Germany.,Center for Astrophysics, Space Physics, and Engineering Research, Baylor University, Waco, TX, USA
| |
Collapse
|
4
|
Size distribution of particles in Saturn's rings from aggregation and fragmentation. Proc Natl Acad Sci U S A 2015; 112:9536-41. [PMID: 26183228 DOI: 10.1073/pnas.1503957112] [Citation(s) in RCA: 81] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Saturn's rings consist of a huge number of water ice particles, with a tiny addition of rocky material. They form a flat disk, as the result of an interplay of angular momentum conservation and the steady loss of energy in dissipative interparticle collisions. For particles in the size range from a few centimeters to a few meters, a power-law distribution of radii, ~r(-q) with q ≈ 3, has been inferred; for larger sizes, the distribution has a steep cutoff. It has been suggested that this size distribution may arise from a balance between aggregation and fragmentation of ring particles, yet neither the power-law dependence nor the upper size cutoff have been established on theoretical grounds. Here we propose a model for the particle size distribution that quantitatively explains the observations. In accordance with data, our model predicts the exponent q to be constrained to the interval 2.75 ≤ q ≤ 3.5. Also an exponential cutoff for larger particle sizes establishes naturally with the cutoff radius being set by the relative frequency of aggregating and disruptive collisions. This cutoff is much smaller than the typical scale of microstructures seen in Saturn's rings.
Collapse
|