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Eight years after the first edition of this book was published, I am delighted to introduce a second edition. Although the structure of the book has not changed, the contents have been considerably revised and updated to reflect the flood of new information sent back by our robotic explorers.

The list of landmark events that have taken place since 2012 is impressive.

An entirely new book could be devoted to the discoveries Cassini made during its 13 years in orbit around beautiful Saturn. The completion of the Cassini mission in 2017 saw the first exploration of the gap between the inner ring and the planet. Other remarkable discoveries were made at cloud‐shrouded Titan and on the icy geyser world of Enceladus, as well as the giant planet and its ever‐changing rings.

The nuclear‐powered New Horizons spacecraft revealed sheets of nitrogen ice, mountains, and deep valleys on distant Pluto and Charon, worlds that were previously believed to be inactive balls of ice. This success was followed by the first rendezvous with an even more remote Kuiper Belt object. Double‐lobed 2014 MU69, a leftover remnant from the birth of the Solar System, seems to have been assembled during a low‐speed collision.

More than 40 years after they left Earth, two more nuclear‐powered craft, Voyagers 1 and 2, have left the Sun's realm and made the first crossings into interplanetary space.

The Juno orbiter is probing the invisible depths of Jupiter, providing new insights into the colorful cloud layers and deep interior of the gas giant.

Meanwhile, the MESSENGER spacecraft completed the first detailed reconnaissance of iron‐hearted Mercury, whilst Japan's Akatsuki entered orbit around Venus and began imaging the super‐rotating clouds.

Numerous robot explorers continue to study Mars from orbit and the surface, confirming the long‐held beliefs that the Red Planet once supported rivers and large bodies of surface water – possible habitats for hardy, primitive organisms.

The smaller denizens of the Solar System have also attracted considerable attention. China achieved the first landing on the far side of the Moon, touching down on the unexplored South Pole‐Aitken Basin.

Europe's Rosetta spacecraft made history when it flew alongside a comet for two years and released a lander onto its icy surface. Spacecraft from the U.S. and Japan have rendezvoused with small asteroids, revealing rocky rubble piles, and, following the success of Hayabusa 1, they are in the process of grabbing surface samples for analysis in labs back on Earth.

Following the release of huge amounts of new data from the armada of pioneering space missions, the scientific literature has expanded dramatically with the publication of new models and hypotheses – some contradictory, some revolutionary. Although planetary (and solar) science is in a continuous state of flux, I have tried to include many of these ground‐breaking results and theories in this book, in an effort to showcase the latest research.

One of the most exciting research fields is the study of exoplanets, where space‐based observatories, such as Kepler, and new ground‐based instruments are opening new windows on an astonishing variety of alien worlds, many unlike anything that exists in our Solar System.

Only by studying distant worlds, whether in the Solar System or much further afield, can we hope to understand how our planetary system came about and how it may evolve in the future. There can be few more exciting areas of research, and I hope that the readers of this volume will be enthused by the evolving story of exploration described within these pages.

Peter Bond, September 2019