Planetary Geology: An Introduction (3rd ed), by Dominic Fortes and Claudio Vita-Finzi

Jon Trevelyan (UK)

Planetary geology occupies an awkward but fascinating position between disciplines. It draws its physical framework from physics and astronomy, its observational tools from remote sensing and space missions, and its interpretative instincts from terrestrial geology. Planetary Geology: An Introduction by Dominic Fortes and Claudio Vita-Finzi has, since its first appearance, sought to bring these strands together into a coherent teaching text. The newly published third edition does not attempt to reinvent that ambition, but instead updates and extends it in the light of the rapidly expanding planetary dataset of the past decade.

I reviewed the second edition of this book previously in Deposits, and that earlier assessment inevitably forms a reference point here. Many of the book’s core strengths – and a few of its structural tensions – remain recognisable. What has changed is the context in which the book now sits, and the richness of examples available to illustrate its central ideas.

Who is this book for?

Although this review is written primarily with Deposits readers in mind, it is worth being clear at the outset that this is not a book aimed principally at informed amateurs. Its core audience remains upper-level undergraduates and postgraduate students studying planetary science or geology, particularly those approaching planetary geology from an Earth-science background. For them, this is a course text – something to be read selectively, chapter by chapter, alongside lectures and tutorials, rather than a book to be read straight through.

A secondary audience includes students and researchers crossing disciplinary boundaries – geologists seeking planetary context, or physicists and astronomers looking for geological grounding. For these readers, the book functions as a structured reference rather than a narrative work.

That said, Deposits readers should not be discouraged. While few will wish to engage deeply with every mathematically intensive section, large parts of the book are not only accessible but actively rewarding for anyone with a solid grounding in Earth geology.

How the book is meant to be read

One reason this distinction matters is that the book is not designed for linear reading. Its structure is modular and process-led. Early chapters introduce planetary formation, internal structure and surface processes, establishing a conceptual toolkit that is reused throughout the book. Later chapters focus on specific geological processes – volcanism, tectonics, impact cratering, surface modification – before turning to individual planetary bodies and environments.

This architecture encourages selective reading, cross-referencing and comparison. Reading the book cover to cover, as I did for this review, is perfectly possible, but it is not the intended mode of engagement. When read continuously, some repetition and a flattening of emphasis inevitably become apparent. Used as designed – as a resource to be entered at multiple points – the structure makes much more sense.

Where the book is strongest for Deposits readers

From the perspective of an informed amateur geologist, the book is at its strongest where planetary geology can be directly compared with Earth geology. These sections allow familiar geological intuition to be carried outward into the Solar System, and they are where the authors’ approach is most effective.

Comparative discussions of volcanic styles under different gravitational and thermal regimes, the morphology and evolution of impact craters, and the influence of atmospheres on surface processes are particularly successful. In these chapters, the reader is not required to master the underlying mathematics to gain insight; geological reasoning does much of the interpretative work.

This is not to dismiss the more quantitative sections, which are essential for students and specialists. Rather, it is to acknowledge that many Deposits readers will choose to skim these parts without losing the core geological narrative. The book accommodates this selective engagement remarkably well.

Alien worlds, familiar processes

Some of the most engaging material in the third edition concerns environments where other liquids and gases take the place of water, ice and air (as on Earth and Mars), for example on Saturn’s moon, Titan. Here, methane and ethane substitute for water, hydrocarbon rain replaces rainfall, and organic sands replace quartz grains – yet the resulting landscapes remain immediately recognisable.

Drainage networks, lakes, sediment transport and basin filling on Titan are described in ways that resonate strongly with Earth-trained geologists. The boundary conditions are different, but the process logic is familiar. This kind of “process substitution” is one of the great conceptual pleasures of planetary geology, and Fortes and Vita-Finzi handle it particularly well.

One minor limitation is that these discussions are not always accompanied by the full range of spectacular imagery now being returned by planetary missions. This is almost certainly a practical decision, reflecting image licensing and production costs rather than any lack of awareness on the part of the authors, and it does not detract from the clarity of the geological argument. Nevertheless, readers familiar with recent mission imagery may occasionally find themselves mentally supplying illustrations that the text itself does not include.

For Deposits readers, these sections are especially rewarding. They demonstrate that geological insight does not end at Earth’s surface, but adapts – and that many alien landscapes remain legible once their working fluids and atmospheres are understood.

What’s new in the third edition?

The third edition reflects the steady accumulation of new planetary data rather than a radical shift in perspective. Updated mission results, revised interpretations and expanded discussion of certain bodies give the book a more contemporary feel. There is also a stronger sense of planetary diversity, with greater attention paid to environments that challenge Earth-centric assumptions.

Readers familiar with the second edition will, however, recognise much of the book’s structure and tone. This is an evolution rather than a transformation. The value of the new edition lies in synthesis and integration, not in novelty for its own sake.

A balance that won’t suit everyone

As with earlier editions, the book occupies an uneasy middle ground. It is more readable than a pure reference work, yet less narrative-driven than popular science syntheses. Some readers may find this frustrating; others will see it as a strength. For teaching and comparative use, the balance largely works.

For Deposits readers in particular, the key is to approach the book as a resource rather than a story: to dip into it, follow geological interests, and allow selective reading. The book is robust enough to support that approach without losing coherence.

Conclusion

Planetary Geology: An Introduction (3rd edition) remains what it has always been – a carefully structured bridge between Earth geology and planetary science. Its greatest strength lies in its comparative approach, which allows familiar geological processes to be reimagined under alien conditions.

For students and specialists, it provides a solid and up-to-date framework for understanding planetary surfaces and processes. For informed amateurs, including Deposits readers, it offers something slightly different but equally valuable: the chance to extend terrestrial geological intuition far beyond Earth, into landscapes shaped by unfamiliar fluids, atmospheres and histories.

Read selectively, and with curiosity, it repays the effort.

About the authors

Dominic Fortes was a former Research Fellow and Lecturer in Planetary Geology at University College London and Birkbeck, University of London, before joining the Crystallography group at the ISIS Facility as an instrument scientist. Claudio Vita-Finzi was a former Professor of Neotectonics at University College London before moving to the Earth Sciences Department at the Natural History Museum as Scientific Associate, where he works on solar history.

Planetary Geology: An Introduction (3rd ed), by Dominic Fortes and Claudio Vita-Finzi, Liverpool University Press (April 2025), paperback (336 pages), ISBN: 978-1780461045