Joshua Colwell - The Ringed Planet: Cassini’s Voyage of Discovery at Saturn

The Ringed Planet (Second Edition)

Cassinis voyage of discovery at Saturn

Joshua Colwell

University of Central Florida, Florida, USA

Morgan & Claypool Publishers

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Media content for this book is available from https://iopscience.iop.org/book/978-1-64327-714-1.

ISBN 978-1-64327-714-1 (ebook)

ISBN 978-1-64327-711-0 (print)

ISBN 978-1-64327-712-7 (mobi)

DOI 10.1088/2053-2571/ab3783

Version: 20191101

IOP Concise Physics

ISSN 2053-2571 (online)

ISSN 2054-7307 (print)

A Morgan & Claypool publication as part of IOP Concise Physics

Published by Morgan & Claypool Publishers, 1210 Fifth Avenue, Suite 250, San Rafael, CA, 94901, USA

IOP Publishing, Temple Circus, Temple Way, Bristol BS1 6HG, UK

To my mother, my wife, and my daughter, who see me through.

One of the wonderful things about the Saturn system is that there is so much happening in it that it can almost be used as a review of planetary sciences in general. And that is also the challenge in writing a book about the system. Like the Cassini mission itself, this book explores Saturn, its rings, moons, and magnetosphere. Thats a lot of material to cover in a limited space. I emphasize the physical processes that have shaped the Saturn system, using some of the most dramatic and intriguing discoveries made by Cassini at Saturn as case studies to illustrate these processes. The book is written for a general audience, and it is also appropriate as an introduction to planetary sciences for students.

Cassinis observations of Saturn, spanning more than 13 years, have revolutionized our understanding of the planet, its complex ring system, and many of its moons, especially Enceladus and Titan. I have always been interested in why things are the way they are, and there are many astounding observations made by Cassini that demand an answer to the question why is that?. We have answers to that question for many of Cassinis discoveries, and this book covers a diverse set, from the origins of dusty ring particles to the heart of the giant planet itself. At the same time, there are new questions revealed by Cassini that will require more research and future missions. I emphasize links between the phenomena at Saturn and planetary systems in general. And still this only scratches the surface. There are many more intriguing phenomena and discoveries that I could not include without having the book expand to several times its current length. I hope the reader is inspired to learn more about this fascinating planet and its family of rings and moons. The images in this book are also just a sampling of those returned by Cassini to illustrate the physics described in the book and to whet the appetite of the reader to discover more at the public repositories of all Cassini data.

Cassinis mission at Saturn ended with two daring sequences of orbits, known as the Ring Grazing Orbits, in early 2017 and the final set of orbits, known as the Proximal Orbits, that threaded the gap between the planet and the rings. This Grand Finale concluded with the spacecraft entering the atmosphere of the planet on 15 September 2017, exactly one month shy of the 20th anniversary of its launch. These unique orbits provided new views of the planet and its rings. In the time since Cassinis dramatic end, scientists have assembled the jigsaw puzzle-pieces of data collected over the course of more than a decade from virtually every instrument on the spacecraft to try to answer one of the biggest questions about Saturn: how old are its rings? While they appear to be relative newcomers to the solar system at under 100 million years, there are still some intriguing puzzles that may upend this conclusion. More surprises were in store for Cassini scientists when they analyzed the same data to understand Saturns interior and magnetic field. These are some of the many revelations from Cassinis Grand Finale that have been added to this expanded second edition of The Ringed Planet.

Each chapter has been revised and updated based on the last dramatic year of Cassinis mission, and a new chapter devoted to the origin of the rings has been added. In addition to providing new data and information on what we have learned from Cassinis final year, every chapter has been revised to include more background, context, and improved and simpler descriptions and explanations.

The data from Cassini will be analyzed for many years, and our understanding of the planet will certainly deepen and evolve. But we are now at a point where the broad strokes of the tapestry of Saturn have been revealed by Cassini. The goal of this expanded second edition is to illuminate that tapestry and to provide a guide for the reader for further exploration and investigation of this jewel of the solar system.

I am one of the lucky few who has worked on the Cassini mission continuously for almost three decades, and I owe that opportunity to Larry Esposito, my dissertation advisor and Principal Investigator of the Cassini Ultraviolet Imaging Spectrograph. I thank my colleagues on the Cassini UVIS team and the project in general for making the mission not only a scientific success but a wonderful working environment all these years. I was privileged to work with and learn from Joe Burns, Sebastien Charnoz, Jeff Cuzzi, Ccile Ferrari, Dick French, Matt Hedman, Essam Marouf, Carl Murray, Phil Nicholson, Stu Pilorz, Carolyn Porco, Mark Showalter, Frank Spahn, Linda Spilker, Matt Tiscareno, and the rest of the Cassini Rings Working Group. I thank all those scientists whose work has provided the substance for this book. Several more books could be filled with stories of discoveries that time and space did not permit me to include here.

I am grateful to my Cassini colleagues, who number in the hundreds, but especially my UVIS colleagues. In particular I thank Nicole Albers, Michael Aye, Laura Bloom, Todd Bradley, Shawn Brooks, Scott Edgington, Candy Hansen, Amanda Hendrix, Greg Holsclaw, Uwe Keller, Bill McClintock, Wayne Pryor, Trina Ray, Ralf Reulke, Don Shemansky, Miodrag Sremcevic, Glen Stewart, Ian Stewart, and Bob West for their assistance, insights, and camaraderie over the years. I owe a special debt to the many hard-working Cassini Science Planning Engineers who designed observation sequences, including my own observations, especially Brad Wallis and Kelly Perry. I have learned much from work with my own students: Kevin Bailli, Tracy Becker, Richard Jerousek, and Akbar Whizin who have embarked on their own voyages of discovery, and current students Stephanie Eckert and Melody Rachael Green.

Thanks to Mark Lewis for his beautiful simulations of the rings, Joe Spitale for providing a mosaic of the A ring edge, and Richard Jerousek for his figure of self-gravity wakes in stellar occultation data.

I received invaluable feedback from my mother, Ann Colwell, who let me see the material through the eyes of a non-scientist.