Ian Randall reviews What’s Hidden Inside Planets? by Sabine Stanley
Humanity has a remarkable drive for exploration. We have sent astronauts 384,400 kilometres out into space to walk on the Moon; delivered rovers and helicopters roughly 225 million kilometres away to survey Mars; and sent probes a whopping 24.3 billion kilometres out to the furthest reaches of our solar system. It is remarkable, then, that when it comes to our own home, we have literally only scratched the surface – the deepest hole ever dug reached less than 1% of the distance to the centre of the Earth.
The question of how we get to grips with the other 99% of what lies under our feet – not to mention beneath the surface of other worlds – is the subject of this sparkling new book, “What’s Hidden Inside Planets?” by Sabine Stanley, a physicist at Johns Hopkins University
Starting with an imagined journey down to the centre of the Earth in a hi-tech travel capsule, Stanley explains how, even though we have only ever drilled about a third of the way through the crust, phenomena on the surface can be used to infer the structure of the rest of the planet. The seismic waves that follow an earthquake change speed and direction as they pass through the Earth, which tells us that the interior has distinct layers – the mantle, the liquid outer core and the solid inner core. In addition, diamonds found on the Earth’s surface can tell us about the hot, high-pressure conditions below the surface where they were formed.
Stanley’s focus soon sweeps out to explore the rest of the solar system. Though we can’t send probes to the centres of other planets, clues to their interior composition sometimes fall at our feet in the form of meteorites. These are remnants of the early solar system that tell us about the conditions in which the planets formed.
The book also explains why Venus is at least one planetary scientist’s bête noire given that it resists all the techniques used to investigate planetary interiors. The planet has an atmosphere that is opaque to remote optical observations and the extreme conditions on the surface make it incredibly challenging to operate seismometers.
Stanley also includes a spin through upcoming planetary science missions and what they might tell us – from the Mars Sample Return Mission, which could shine more light on the red planet’s geology, to the Jupiter Icy Moons Explorer, to various missions to study the surface and interior of Venus. She finishes with a reflection on the importance of looking after the Earth as our home.
The chapter I most enjoyed was “Curious planetary elements”, which explores the weird-and-wacky phenomena believed to occur on and within other worlds, from helium rain and metal volcanoes to exotic phases of water and diamond icebergs.
I was intrigued to encounter for the first time the term “precovery”, which is when fresh information on astronomical objects is found in archive data and images that predates the actual discovery. As Stanley notes, for example, “Pluto was officially discovered in 1930, but astronomers digging through archives since then have found evidence of its discovery going farther back, at least to 1914, and possibly to 1909.”
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Stanley also takes the reader through one of my favourite episodes in the history of science, and the reason we have reached that aforementioned 1% down into the Earth. This was the space race’s geological counterpart, the contest to drill the deepest possible hole into the Earth. The US broke ground (both literally and metaphorically) in 1961 with “Project Mohole”, which aimed to collect samples from the Mohorovičić (Moho) discontinuity, the boundary between the crust and mantle identified some 50 years previously via its impact on the velocity of seismic waves. Beset by mismanagement, the endeavour was abandoned after its first phase, reaching just 183 metres beneath the ocean floor. In 1979 the Soviet Union picked up the gauntlet to bore, within a decade, to a depth of more than 12.2 kilometres; this is about a third of the way through the crust at the site on north-west Russia’s Kola Peninsula.
The strength of Stanley’s work lies in her engaging, conversational, almost conspiratorial writing style
The strength of Stanley’s work lies in her engaging, conversational, almost conspiratorial writing style, which – amid a slew of running jokes, anecdotes and charming food-based metaphors – makes light work of considerable scientific ground that, in less deft hands, could easily have become a painful slog.
However, I feel the preface has far too much of the author’s personality and life history. Some of the introduction sets up later preoccupations – a family background in restauranteering, for example, fits the conceit of comparing planets to soup, cake, pudding and fruit. However, other details venture too far into “Dear Diary” territory. Details of childhood friends, teachers, fictional idols and university mentors, for example, do little to advance the book’s theme and might have been better gently edited into the acknowledgements section instead.
My only other real criticism is that while the journey is engaging, the destination of the book isn’t entirely clear. The final chapter touches on how our home is unique, how there is no Earth 2.0 to retreat to amid the growing chaos of anthropogenic climate change. This is an important take-home message, but not one that the rest of the book feels like it was working towards. I cannot help but feel that a stronger through-line could have set up this conclusion to a more satisfying effect.
- 2023 Johns Hopkins University Press 272pp £14/$16.95 pb
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- Source: https://physicsworld.com/a/what-lies-beneath-unearthing-the-secret-interior-lives-of-planets/
