Über die Autorin bzw. den Autor

Ralph Lorenz is a planetary scientist at the Johns Hopkins University Applied Physics Laboratory. Jacqueline Mitton is a writer, editor, and media consultant in astronomy. They are the coauthors of Lifting Titan's Veil: Exploring the Giant Moon of Saturn.

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"A great book for anyone wanting to know what it's like to be on the front lines of a mission to perhaps the most fascinating planetary body in the solar system. Lorenz and Mitton bring home the fact that planetary exploration is not a faceless enterprise done by anonymous men in white coats, but a personal adventure carried along by real people with real charisma, real quirks, and real lives."--Mike Brown, California Institute of Technology

"This book could hardly be more timely. Titan is inarguably one of the most intriguing objects in the solar system, and the wealth of new information revealed by the successful Cassini-Huygens mission is revolutionizing our knowledge of this mysterious moon. Lorenz and Mitton are well qualified for the project, and have written a very compelling book."--Edwin L. Turner, Princeton University

"This is the first trade book that looks at the mission results in a comprehensive way. It gives a summary of our knowledge of Titan prior to the probe, describes the history of the probe project, and discusses the results from the mission. I am not aware of any books like this one."--Christopher P. McKay, NASA Ames Research Center

"Titan Unveiled is an authentic and lively insider's account of one of the grand enterprises in modern space exploration. The authors present a compelling human story of interplanetary exploration, rich in detail and strong on science. Readers get an authoritative description of many of the latest results from Cassini."--Richard G. French, Wellesley College and Cassini Radio Science Team

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Titan Unveiled

Princeton University Press

Contents

List of Illustrations and Tables.....................................viiPreface..............................................................xi1. The Lure of Titan.................................................12. Waiting for Cassini...............................................213. Cassini Arrives...................................................674. Cassini's First Taste of Titan....................................1015. Landing on Titan..................................................1326. The Mission Goes On...............................................1747. Where We Are and Where We Are Going...............................211Afterword to the Paperback Edition...................................233Appendix: Summary of Dynamical and Physical Data.....................255Further Reading......................................................257Index................................................................261

Chapter One

On July 1, 2004, the Cassini spacecraft arrived at Saturn after a journey from Earth lasting almost seven years. At 6.8 m in length, this monstrous robotic explorer was the largest western spacecraft ever to be dispatched on an interplanetary mission. Its battery of scientific instruments was designed to return images and data not only from the giant planet itself and its spectacular ring system, but also from members of Saturn's family of over fifty moons. Foremost in interest among the diverse collection of icy worlds in orbit around Saturn was Titan, a body so special, so intriguing in its own right that Cassini carried with it a detachable package of instruments—named the Huygens probe—that would parachute through Titan's atmosphere to observe its surface.

By any reckoning, Titan is an unusual moon. It is 5,150 km across—nearly 50 percent bigger than our own Moon and 6 percent larger than Mercury. If it happened to orbit around the Sun, its size and character would easily make it as much a planet as Mercury, Venus, Earth, and Mars. But the landscape of this extraordinary world remained hidden to us throughout the first decades of the space age, partially because of Titan's remote location and partially because it is swathed in a thick and visually impenetrable blanket of haze. Thanks to Cassini–Huygens and the technological advances that have vastly extended the reach of ground-based telescopes, the situation has now changed dramatically. Titan is undergoing an all-out scientific assault both by the most powerful telescopes on Earth and from the cameras and radar aboard Cassini, the flagship international space mission. This observational barrage, topped off by the Huygens probe's daring drop down to the surface of Titan, is serving to unveil this enigmatic moon, revealing more of its intriguing features than we have ever seen before.

THE IMPERATIVE TO EXPLORE

When the two Voyager craft sped past Jupiter and Saturn between 1979 and 1981, they returned a wealth of new information about the two giant planets and their moons. But the images and data received from these missions were essentially snapshots—fleeting opportunistic glances at worlds demanding more serious and systematic attention. And as far as Titan was concerned, the results of these flybys were especially disappointing.

Observing Titan was a high priority for the planners of the Voyager missions, and in November 1980, Voyager 1 passed Titan at a distance of 4,394 km. The encounter sent the spacecraft hurtling out of the plane of the solar system and prevented it from exploring any more moons or planets. However, curiosity about Titan was so great that the sacrifice was considered worth making.

A principal reason for the great interest in Titan was the fact that it possesses a significant atmosphere. Astronomers had been aware of Titan's atmosphere since 1944, when Gerard Kuiper announced that spectra he had taken of Titan revealed the presence of methane gas. Therefore, planetary scientists were not going to be surprised to find haze or clouds in the atmosphere, but at the very least, they hoped that parts of Titan's surface would be visible when Voyager arrived.

Unfortunately, those hopes were completely dashed. The whole of Titan proved to be shrouded from pole to pole in opaque orange haze. Voyager's camera was sensitive only to visible light, and the spacecraft carried no instruments (such as an infrared camera or imaging radar) capable of probing below the haze. Voyager was able to return some important new data about the atmosphere but virtually nothing about the surface.

The exploration of the Jupiter and Saturn systems continued to beckon, however, and the next logical step was to send orbiters to make close and detailed observations over a sustained period of time.

Between the two of them, Jupiter and Saturn possess five of the seven largest moons of the solar system, and they both have far more known moons than any of the other major planets. With such a variety of planetary bodies to observe from close quarters, not to mention Saturn's iconic ring system, the urge to send orbiters was very compelling. As the nearer of the two, Jupiter was the first to be targeted. The Galileo spacecraft was launched on its six-year journey to Jupiter from the space shuttle in 1989. It operated successfully between 1995 and 2003 and was deliberately crashed into Jupiter at the end of its useful life.

An orbiter for Saturn was scheduled to follow, and Titan was firmly in the sights of the Saturn mission planners. The Voyager experience generated an overwhelming incentive to design a mission to the Saturnian system capable of discovering what lay below Titan's haze. Both the National Aeronautics and Space Administration (NASA) and the European Space Agency (ESA) were involved from early on with the conception and development of the mission; the idea from the beginning was to send an orbiter carrying a Titan probe. In what turned out to be a highly successful international collaboration, NASA provided the orbiter and ESA built the probe. The orbiter was named in honor of Giovanni Domenico Cassini, the French-Italian astronomer who discovered four of Saturn's moons and the gap separating the two main rings. The probe was named after Christiaan Huygens, the Dutch astronomer who discovered Titan. Cassini would be equipped with radar and infrared imaging capabilities for penetrating the haze; the independent probe was to parachute through the haze and radio back via Cassini the data collected by its instruments and camera.

No mission as complex as Cassini–Huygens had ever before been undertaken at such an immense distance from Earth. Even when Earth and Saturn are at their closest, the gulf between them is around 1.3 billion km. By the time Cassini was launched in 1997, Galileo had been performing well at Jupiter for nearly two years, even though its main communications dish had failed to unfurl correctly. But Saturn is roughly twice as far away as Jupiter. Light and radio signals take over an hour to make the one-way trip between Saturn and Earth, and even getting to Saturn at all would be less than straightforward.

Cassini's route was...