Titan Unveiled: Saturn's Mysterious Moon Explored

On 14 January 2005, many people who were in one way or another involved in the Cassini-Huygens space mission were waiting anxiously in laboratories, observatories and offices around the world. This was the day when the Huygens probe, after a decade of development followed by a seven-year journey, would at last reach Titan to investigate its atmosphere and surface in situ. The scientists most closely involved in the probe were at the European Space Operations Centre, where the long-awaited data would first arrive.

Among those team members was Ralph Lorenz. More than a decade earlier, Lorenz had worked on the design and calibration of the penetrometer - the instrument that would first contact Titan's surface. The data duly arrived: the instruments indicated a thin, hard surface with softer material beneath. The analogy summarising years of effort and waiting flashed out around the world: Crème brûlée .

With this work, planetary scientist Lorenz and astronomy writer Jacqueline Mitton have taken the opportunity of following up their earlier book, Lifting Titan's Veil, incorporating results learned from the Huygens descent and the continuing observations from the Cassini orbiter. The result is again an enjoyable mix: a very accessible summary of current knowledge about Titan is combined with a firsthand account that gives a flavour of what it has been like to be part of this grand, bold international collaboration that is the Cassini-Huygens project.

Having been involved both with the lander and with the radar instrument on the orbiter, Lorenz is ideally placed to tell an insider's story, and with Mitton has woven this into a fascinating book. Furthermore, the recent official announcement of a two-year extended mission for Cassini makes this an opportune time to admire the scientific harvest from this richly successful mission.

The scientific thread of the work starts by summarising the development of our knowledge of Titan from historical ground-based observation, through the revelations of the Voyager flyby missions and subsequently using new telescopes and techniques both from the ground and from the Hubble Space Telescope. Having established what was known, and what big questions remained unanswered, we move on to the Cassini-Huygens era. The subsequent chapters pull together a multidisciplinary account of the data that this mission has returned so far, and its interpretation in planetary science terms.

First, the information gained from the various instruments on the lander is addressed, and then the Titan encounters of the Cassini orbiter through to mid-2006 - each with its distinct "flavour" of instrumentation and target area on the surface. The opportunity is also taken to look at some of the other discoveries from the mission: notably the entirely unexpected "plumes" found on Enceladus.

Interwoven with this is the "operations" thread, which gives an insight into the meetings, teleconferences and meticulous planning that have gone into making the mission work so well despite the work being scattered throughout the US and Europe, along with the scientists and engineers involved.

There is also some discussion of the first extended mission, recently approved, which will continue until at least 2010. Now entitled the Cassini Equinox Mission, it promises to tell us much more by investigating seasonal events. A Saturn (or Titan) year is 30 Earth years: by 2010 the Sun will have crossed their equatorial planes and summer will be coming to their northern hemispheres - Titan scientists in particular are eager to see what effects this will have both on its atmospheric circulation and on its surface features. I do hope that Lorenz and Mitton will produce a subsequent volume to update us on the findings from the continuing mission.