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Published December 2020 | Published
Journal Article Open

Cassini Exploration of the Planet Saturn: A Comprehensive Review

Abstract

Before Cassini, scientists viewed Saturn's unique features only from Earth and from three spacecraft flying by. During more than a decade orbiting the gas giant, Cassini studied the planet from its interior to the top of the atmosphere. It observed the changing seasons, provided up-close observations of Saturn's exotic storms and jet streams, and heard Saturn's lightning, which cannot be detected from Earth. During the Grand Finale orbits, it dove through the gap between the planet and its rings and gathered valuable data on Saturn's interior structure and rotation. Key discoveries and events include: watching the eruption of a planet-encircling storm, which is a 20- or 30-year event, detection of gravity perturbations from winds 9000 km below the tops of the clouds, demonstration that eddies are supplying energy to the zonal jets, which are remarkably steady over the 25-year interval since the Voyager encounters, re-discovery of the north polar hexagon after 25 years, determination of elemental abundance ratios He/H, C/H, N/H, P/H, and As/H, which are clues to planet formation and evolution, characterization of the semiannual oscillation of the equatorial stratosphere, documentation of the mysteriously high temperatures of the thermosphere outside the auroral zone, and seeing the strange intermittency of lightning, which typically ceases to exist on the planet between outbursts every 1–2 years. These results and results from the Jupiter flyby are all discussed in this review.

Additional Information

© The Author(s) 2020. This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article's Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article's Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by/4.0/. Received 10 October 2019; Accepted 10 October 2020; Published 26 October 2020. This research was supported by Grant NAS7-03001, Cassini Project, NASA Jet Propulsion Laboratory, USA. I thank my Cassini colleagues for their many scientific contributions and their ability to work together in guiding this mission. Scott Edgington and Linda Spilker were extremely helpful as I prepared this document. It was a pleasure working on this great mission. The lesson is, if you build a well-equipped spacecraft and send it to an unexplored place, the discoveries will come. Funding: Grant NAS7-03001, Cassini Project, NASA Jet Propulsion Laboratory, USA. Conflict of interest: None.

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Created:
August 22, 2023
Modified:
October 20, 2023