This is the second of a two-part dive into the story of oceans on Earth and elsewhere, following my review of Ocean Worlds. That book gave a deep history of how our oceans shaped Earth and life on it and briefly dipped its toes into the topic of oceans beyond Earth. Alien Oceans is the logical follow-up. How did we figure out that there are oceans elsewhere? And would such worlds be hospitable to life? Those are the two big questions at the heart of this book. If there is one person fit to answer them, it is Kevin Peter Hand, a scientist at NASA’s Jet Propulsion Laboratory and their deputy chief for solar system exploration.
Alien Oceans: The Search for Life in the Depths of Space, written by Kevin Peter Hand, published by Princeton University Press in March 2020 (hardback, 248 pages)
A major question in astrobiology is whether the evolution of life on Earth is a fluke, or whether life is bound to pop up wherever conditions are favourable. Hand very neatly frames this in the bigger history of science. Over the centuries, we figured out that the laws of physics, chemistry, and geology work beyond Earth. But “when it comes to biology, we have yet to make that leap. Does biology work beyond Earth?” (p. 15). What we have learned is that life as we know it needs water. And though there is no shortage of theories on the origins of life, oceans are very likely where it started, and thus a logical first place to start looking for answers.
If you have any interest in astrobiology, you will probably have heard of the concept of a habitable zone or Goldilocks zone where, based on the distance to a star, conditions for life are just right. Not so close as to be too hot, nor so far as to be too cold. Earth obviously falls in that zone. Next to many minor insights, Alien Oceans had three major eye-openers for me. This was the first one:
There are other Goldilocks zones.
Depending on the details of their orbit, moons can experience such strong tidal tugs from their parent planet that the constant squeezing and stretching of the rock creates enough heat through internal friction to sustain liquid water. The physics of water helps, as it has a seemingly mundane but rather unusual property. Ice floats. When water solidifies, its density decreases slightly. What this means for moons is that the liquid water exposed to the cold of deep space freezes and forms a protective icy shell. Most liquids do not have this useful property. When they freeze, they sink to the bottom exposing more liquid until all of it is frozen solid. To top it off, ice is also a good thermal insulator, helping such ocean worlds retain heat. Maybe I have been hiding under a rock, but this was revelatory for me. Suddenly, the amount of cosmic real estate suitable for life has increased quite dramatically. And we have some of it right here on our doorstep.
“Over the centuries, we figured out that the laws of physics, chemistry, and geology work beyond Earth. But “when it comes to biology, we have yet to make that leap. Does biology work beyond Earth?“”
The existence of oceans in our solar system and how we gathered the evidence is one of the two major threads running through this book. Hand examines this in detail for Jupiter’s moon Europa, which has been studied in the most detail. Three types of data are typically gathered: spectroscopic, gravimetric, and magnetometric. This is where Hand gets fairly technical, though, fortunately, he extensively uses comparisons with everyday concepts and technologies to help you understand the underlying (astro)physics. Without retreading his careful explanations, in Europa’s case, these different strands of data all converge on a moon with an icy shell and a substantial subsurface ocean some 80–170 km thick as the best explanation. Mixed in with this narrative are the details and many technical setbacks of the Galileo mission that are nail-bitingly tense in places.
Similar missions and measurements have been done for Saturn’s moons Enceladus and Titan, Jupiter’s moons Ganymede and Callisto, Neptune’s moon Triton, and Pluto. The evidence for oceans gathered so far gets less robust in this order, but there are some notable variations on the theme. Enceladus ejects spectacular plumes of water and carbon compounds that were photographed and sampled by the Cassini–Huygens mission. Ganymede, meanwhile, is so large that the bottom of its ocean might consist of an exotic form of dense ice, ice III, formed at very high pressures not seen on Earth, meaning its ocean is sandwiched between two layers of ice.
So you have found exo-oceans. Now what? Can we expect to find life here? That is the second major thread. Hand identifies five conditions for life to emerge: a solvent such as water, chemical building blocks, an energy source, catalytic surfaces, and time. Interestingly, there is a gap between two schools of thought. The top-down explanation deconstructs life backwards in time until we arrive at an RNA world, but how did that get started? The bottom-up explanation has shown that life’s basic building blocks such as amino acids exist in space, but how do we go from there to larger functional molecules?
“There are other Goldilocks zones. Moons can experience such strong tidal tugs that the heat released by internal friction can sustain liquid water.”
This was the second major eye-opener for me: “Our environment is full of chemical disequilibrium […] there are reactions just waiting to happen. […] The metabolisms that drive life accelerate reactions in the environment, releasing energy faster than would have occurred without life” (p. 144). Hand takes a leaf out of Nick Lane’s book The Vital Question (which, shame on me, I still have not read) when he enthusiastically concludes that “the why of life is metabolism” (p. 146), offering the universe a pathway to increase entropy faster. These are remarkable ideas that give a whole new meaning to philosophical questions on the meaning of life.
The third and final eye-opener concerns the need for a catalytic surface, which is where Hand circles back to oceanographic exploration here on Earth, a recurrent theme in this book. When the submarine Alvin discovered hydrothermal vents in 1977 and found them teeming with life, these quickly became a popular alternative explanation to warm tidal pools as a place where life could have started. These so-called black smokers are powered by magma rising to the surface at mid-ocean ridges, jetting out superheated water of over 400 °C. Though volcanism and tectonics are, or sometimes were, common processes on many solar system bodies, there is another option. Alkaline vents, first discovered in 2000 at the Lost City hydrothermal field, are powered by exothermic (energy-releasing) reactions between water and mineral-rich rock, heating water to a more gentle 70–100 °C. All these need are the right rocks with cracks in them so water can percolate down.
“In addition to hydrothermal vents, alkaline vents are another place where life might have started. All these need are the right type of rock with cracks in them so water can percolate down, no plate tectonics needed.”
Hand raises many other interesting questions towards the end of the book, of which I will mention just three. One, life’s metabolic reactions require so-called oxidants, oxygen being “the most glorious of oxidant” (p. 162), but how would these get down into subsurface oceans? Two, how contingent or convergent is the evolution of life’s biochemistry? Carbon is a suitable building material for life as it is “hands down the best team player on the periodic table” (p. 212). But does physics restrict us to these options, or can we sketch a periodic table of life with other, weirder possibilities? And three, how should we seek for signs of life? What makes a good biosignature? This is discussed far more in-depth in Life in the Cosmos, but Hand considers three types of evidence.
Alien Oceans limits itself to oceans in our solar system, not touching on the topic of exoplanetary oceans. Given this is not Hand’s expertise, that is reasonable. He also glosses over the question of what aliens might look like, though he speculates on the likelihood of intelligent life in ice-covered subsurface oceans. Even without these topics, Alien Oceans is information-dense, requiring me to make a summary, and then a summary of that summary while preparing this review. Nevertheless, it is an intellectually very rewarding book and the many analogies make it accessible. I enjoyed it as a follow-up to Ocean Worlds but it is a fine standalone book. Terribly fascinating, Alien Oceans makes a convincing case for exploring the moons in our solar system in the search for extraterrestrial life.
Disclosure: The publisher provided a review copy of this book. The opinion expressed here is my own, however.
Other recommended books mentioned in this review:
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Life most likely originated in the oceans, and it is to oceans that astronomers are looking to find life elsewhere in the universe. With the publication last year of Kevin Peter Hand’s Alien Oceans, I decided this was the right time to finally review Ocean Worlds, a book that I have been very keen to read ever since buying it some years ago. This, then, is the first of a two-part dive into the story of oceans on Earth and elsewhere.
Ocean Worlds: The Story of Seas on Earth and other Planets, written by Jan Zalasiewicz and Mark Williams, published by Oxford Press in December 2017 (paperback, 302 pages)
Palaeobiologists Jan Zalasiewicz and Mark Williams have previously collaborated on The Goldilocks Planet. Here, they provide a deep history of our oceans. As soon as I tucked in, it became clear that they go deeper than Eelco Rohling did in the previously reviewed The Oceans: A Deep History, a book that focused heavily on palaeoclimatology. Even though most of the action in Ocean Worlds takes place on Earth, and the wider universe is only considered in the opening and closing two chapters, the book is characterised by an almost cosmic perspective on the subject. The writing of Zalasiewicz and Williams is such that I felt as if was surveying major developments in the history of our universe from an elevated, slightly detached, almost omniscient position. The result is thrilling and at times awe-inspiring. What follows are some of the big questions and outrageously fascinating topics they consider.
To have an ocean we first need water. Hydrogen was an immediate byproduct of the Big Bang. Oxygen, however, did not appear until after the universe had gone through its first cycle of stars being born and dying, as its creation required nuclear fusion. Likely, the formation of water had to wait for a few hundred million years, though some have argued it could have started much sooner. As is usual when dealing with processes that took place in such a distant past, opinions are divided and there are several reasonable scenarios.
“the book is characterised by an almost cosmic perspective on the subject […] The result is thrilling and at times awe-inspiring.”
With water present in the universe, how did Earth acquire its oceans? After all, “There is a wild card here, which surely had an impact” (p. 18). We have good evidence that our proto-Earth, called Tellus by some, was hit by a small planetoid, Theia, with the resulting debris forming our current Earth–Moon system. This event would likely have obliterated what early oceans we had, if any. Various authors have proposed that certain meteorites (carbonaceous chondrites) or comets might have subsequently been water’s cosmic delivery vehicle.
However it got here, the first major effect it had was kick-starting plate tectonics. The early Earth was hot, but without the lubrication provided by water, the heat-venting mechanism of plate tectonics was not in place. How did molten rock make its way to the surface? Some scientists argue that it was through simple vertical conduits, so-called heat pipes, which would have made for a radically different surface topography: “the fundamental proportions of land area and ocean area […] would have been utterly different to today’s familiar patterns” (p. 34). Though, again, this idea is contested by others. The puzzle of when plate tectonics started, possibly 3 billion years ago, relies on truly ancient rocks, 3.5 to 3.8 billion years old, of which we have precious few remaining in places such as Australia and Greenland.
Beyond those earliest days, Ocean Worlds has much interesting material about later episodes. Life likely started in the oceans, this much I knew, but these were iron seas. Water without oxygen can hold large amounts of dissolved iron, and early organisms used this in their biochemistry to generate energy. This was the realm of the Archaea: the salt-tolerant, heat-loving, chemoautotrophic microbes for whom oxygen was poison and the Great Oxygenation Event murder. It was also a time when banded iron formations (BIFs) were built up, relevant to us today as they formed the ore deposits providing most of our iron and steel. Though, as clarified here, their formation was anything but straightforward. Other fascinating episodes are the Messinian Salinity Crisis, some 5.6 million years ago, when the Mediterranean repeatedly dried up, leaving behind kilometre-thick salt layers that reduced global ocean salinity.
“However it got here, the first major effect [water] had was kick-starting plate tectonics.”
Of course, a book about oceans has to consider current human impacts. With due diligence, the authors tackle the problems of overfishing, shifting baselines, trawling, litter, ocean warming, oxygen loss, and acidification, and conclude that: “there currently seems not the faintest chance of stopping carbon emissions over many decades, let alone overnight” (p. 191). Does this sound gloomy? I prefer the word “sobering”. Consider, they write, that the “more-than-tripling of human population” (p. 183) was enabled by the invention of the Haber–Bosch process and the plentiful artificial fertiliser it made available. To this, they add geologist Peter Haff’s argument of the technosphere that resonated with me. “The 7 billion humans on Earth today are kept alive only through the continuous action of an enormous, globally interlinked system of transport and communication, metabolized by the use of vast amounts of energy […] Without it, most of us would not be alive—and therefore we are forced to keep it going” (p. 197).
If that was not sobering enough, what really made me feel small was when they pulled back from our timescale and the current “brief ecological wrecking spree” (p. 195), to the long-term future. Our oceans are not forever. As the Sun grows hotter they will evaporate, though the “end of the oceans is not likely to be simple” (p. 207). Whether through a moist greenhouse phase where water is gently siphoned off into space by solar winds, or a runaway greenhouse hot enough to melt rock, a dry future awaits, and plate tectonics will once again grind to a halt. As this process “is unlikely to simply just stop, smoothly and without fuss” (p. 211), expect some extraordinary landscapes.
“Our oceans are not forever. […] Whether through a moist greenhouse phase where water is gently siphoned off into space by solar winds, or a runaway greenhouse hot enough to melt rock, a dry future awaits.”
Amidst these grand, cosmic scenes, the authors highlight the human stories behind this research. Such as the pioneering contributions to oceanography by the people on board the HMS Challenger expedition, the mapping of the seafloor by Marie Tharp, or the work of Wally Broecker who established a link between ocean currents and rapid climatic changes. And while Svante Arrhenius is better remembered for linking historical changes in carbon dioxide concentrations to past ice ages, both he and Fritz Haber tried to extract gold from sea water. Unsuccessfully, I might add.
In the last two chapters, the authors turn their gaze to the skies once more, discussing past and present oceans inside and outside of our solar system. With the many exoplanets discovered by the Kepler space telescope, “We are on the verge of not just a new chapter in oceanography—or exo-oceanography, if you like—but of setting up an entirely new library of oceans, for the diversity and complexity of cosmic oceans will be beyond anything that we can dream of” (p. 264).
I explore this topic more in-depth in my review of Alien Oceans. But, as a warming-up exercise and a proper deep history of oceans, Ocean Worlds is a fantastic book that strikes the right balance. Zalasiewicz and Williams present fascinating science with enviable ease, without smoothing over the fact that science is rarely a straightforward affair, proceeding by means of conflicting scenarios and competing hypotheses. The deep-time perspective and big questions asked make this one awe-inspiring book.
Other recommended books mentioned in this review:
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Volcanoes are some of the most awe-inspiring natural spectacles on our planet. There is much more to them, though, than the stereotypical image of a conical fire-spitting mountain, and I have been keen to learn more. As I searched for serious introductory books on volcanology, this was one title that kept coming up. But wait, why is a biologist reviewing geology textbooks?
Volcanoes, written by the late Peter Francis and Clive Oppenheimer, published by Oxford University Press in December 2003 (paperback, 521 pages)
A short preamble seems in place. My choice to study biology went at the expense of geology, although the latter topic continued to fascinate me. Two decades later, my job exposes me to many fascinating-sounding but advanced-level earth science books. I have since started to make inroads into this field for the sheer joy of expanding my knowledge. And thus I found myself eyeing up the new book Volcanotectonics. Yet, as I recently rediscovered, there is still a gap between having covered the essentials of geology and diving headlong into an advanced topic. Hoping to bridge that gap, I turned to Francis & Oppenheimer’s Volcanoes.
The first edition of this book was published in 1993 and authored by volcanology professor Peter Francis. When he passed away in 1999, his former PhD student Clive Oppenheimer, now a professor of volcanology in his own right, took it upon him to revise the text and bring it up to date for this second edition, published in 2003. Francis’s desire was to write a book to be read rather than consulted. Volcanoes is thus less of a textbook than you might think: there are no chapter summaries or student exercises. What you will find is a logical flow of chapters detailing the inner workings of volcanoes, glued together by the fascinating stories of past eruptions and, occasionally, Francis’s trademark humour, lampooning the field of volcanology.
“Volcanoes is […] less of a textbook than you might think: there are no chapter summaries or student exercises. What you will find is a logical flow of chapters detailing the inner workings of volcanoes, glued together by the fascinating stories of past eruptions […]”
Volcanoes starts with very primordial questions. Where do the heat and the rocks that drive volcanism come from? This introduces you to planetary formation and the radioactive decay of isotopes. In case you were expecting to start with plate tectonics, that is the next subject to be tackled. This explains the difference between volcanoes at plate margins where the oceanic crust is either formed or destroyed, and the minority occurring far from margins, such as the volcanic islands of Hawai’i.
Chapters four to twelve form, to my mind, the nuts-and-bolts section of this book, going into all the glorious and gory details of an eruption from beginning to end. This covers everything from formation and movement of magma; different eruption styles; types of lava; eruption columns and the deposits of ash and pyroclastic rocks they leave behind; pyroclastic density currents, debris avalanches, and mudflows or lahars—and their deposits; the different landscape forms left after eruptions, including types of volcanoes and how they erode, and the landscape depressions known as calderas; super-eruptions; and, finally, the common but hard-to-observe phenomenon of underwater volcanism.
The last four chapters cover closely allied topics: volcanoes in the solar system; the effects of recent eruptions on climate and the palaeoclimatological evidence of older ones; and, new to this edition, two chapters on monitoring of volcanoes, and assessing and managing the risks they pose.
“I was fascinated by some of the technicalities. For example by […] the physics behind eruption columns and the interplay with the wind, and how to deduce eruption intensity from them […]”
Two aspects, I thought, make this book very enjoyable to read. First, it broaches subjects without overwhelming you. When it talks of magma, it mentions the physics of gas bubble formation and growth (vesiculation), and the flow of liquid rock (rheology) without smothering you in detail. It will list different eruption styles (Hawaiian, Strombolian, Vulcanian, Plinian, etc.) and lavas (andesitic, dacitic, rhyolitic, etc.) while highlighting the arbitrary nature of such classifications, as these things exist on a continuum. And where formulas are given, for instance in the chapter on eruption columns, it is to demonstrate principles rather than go deep into the mathematics. If you are so inclined, each chapter comes with recommended sources and literature references for further research.
The authors explain terminology as they go, supported by many photos and diagrams. I would have liked a glossary—lacking that, I occasionally had to grab my dictionary to jog my mind. Even so, I was fascinated by some of the technicalities. For example by the distinction between central vent and large-scale fissure eruptions. By the underground movement of magma and intrusion of dikes. By the physics behind eruption columns and the interplay with the wind, and how to deduce eruption intensity from them. By the detective work that uses palaeoenvironmental records such as tree rings, and the extent and thickness of deposits to reconstruct eruptions for which there is no eyewitness testimony. Or by what makes pyroclastic density currents so terrifyingly destructive.
The second aspect that makes Volcanoes very readable is that this is not a theoretical treatise with hypothetical scenarios. Explanations are given by means of real-world examples of past eruptions. Four classic ones are introduced early on (Vesuvius, Krakatau, Mount Pelée, and Mount St. Helens), but plenty of others are recounted throughout. This includes those familiar from popular accounts (e.g. Tambora, Laki, and Toba), technical books (e.g. Pinatubo and the Soufrière Hills volcano), and those only known to volcanologists and victims (e.g. El Chichón and Nevado del Ruiz). You will learn as much about these eruptions as about what we learned from them.
“Having read the book cover to cover, there remains one important question that is difficult for me to answer. Given its publication date, how up to date is it? And is it time for a new edition?”
Having read the book cover to cover, there remains one important question that is difficult for me to answer. Given its publication date, how up to date is it? And is it time for a new edition? Technological advances and new space missions have revealed much more about extraterrestrial volcanoes—this book was published before the Opportunity and Curiosity rovers started trundling over the surface of Mars, for example. But what about volcanism here on earth? Recent eruptions have probably taught us new lessons (2010 tongue-twister Eyjafjallajökull no doubt revealing more about ash clouds), but not being a student of earth sciences, this is a hard question for me to answer. The only other more recent book I could think of was The Encyclopedia of Volcanoes, published in a second edition in 2015. But at over 1400 pages this can hardly be called an introductory textbook.
I decided to contact Clive Oppenheimer who kindly replied that there have not been any paradigmatic shifts in volcanology since then, but he did mention, in addition, the 2010 Merapi eruption, and highlighted new technology such as synchrotron radiation sources for fine-scale chemical analysis of volcanic rocks. Additionally, he pointed out Volcanoes: Global Perspectives (2022) as a recent textbook. And a third edition? It is not yet in the making, though he hopes to get around to it when time allows.
So, in sum, if you are looking for a good introductory volcanology textbook, I found this one both enjoyable and accessible. I came away feeling I understood much more about volcanoes. Bring on Volcanotectonics.
Disclosure: The publisher provided a review copy of this book. The opinion expressed here is my own, however.
Other recommended books mentioned in this review:
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“Catching Stardust: Comets, Asteroids and the Birth of the Solar System”, written by Natalie Starkey, published by Bloomsbury Sigma (a Bloomsbury Publishing imprint) in March 2018 (hardback, 264 pages)
Astronomers largely agree on how our Solar System formed, and Starkey runs the reader through the basics of the nebular hypothesis: giant gas clouds condensing and contracting to form nascent stars with protoplanetary discs of dust swirling around them that start to congeal into planets. Plate tectonics on Earth has erased most traces of our planet’s very deep history and only a few places, such as Greenland, host rocks older than 3 billion years (see my review of A Wilder Time: Notes from a Geologist at the Edge of the Greenland Ice). The beauty of nearby comets is that they are effectively 4.6 billion-year-old frozen time capsules of the early nebular cloud from which our Solar System formed.
But what of asteroids? After reviewing Cosmic Impact: Understanding the Threat to Earth from Asteroids and Comets, I complained being left puzzled by what the differences are between the two. Starkey here takes a bit more space to explain it all. The classic model classified comets as fluffy, icy, fragile bodies that would have formed in the cold reaches of outer space, and asteroids as hard, dry, solid objects that would have formed closer to the Sun. But data from recent space missions shows that this neat dichotomy is not the whole story, and there is a spectrum of chemical and structural compositions possible in between these two extremes. Further complications arise from models suggesting that the early Solar System saw some dramatic rearrangements of planetary orbits, with the contents of the distant Oort Cloud possibly having formed closer to the Sun than the currently closer Kuiper Belt. As Starkey is keen to point out, there are still many, many unresolved questions here.
Catching Stardust is largely a book of the how and the why of studying space rocks and alternates between these questions. Other than Solar System formation, there is also the question of how Earth formed, where its water came from, and whether comets and asteroids seeded our planet with the chemical precursors of life. Although hydrogen and carbon are found throughout space, I was fascinated to learn that amino acids, one of life’s basic building blocks, are too. But there remain interesting questions. Why do lifeforms only use one variant of amino acids (the left-handed one)? And do comets and asteroids contain equal mixtures of both, as you might expect, or not? (There is titillating evidence they don’t.)
“The beauty of nearby comets is that they are effectively 4.6 billion-year-old frozen time capsules of the early nebular cloud from which our Solar System formed.”
Throughout these chapters, Starkey gently introduces the reader to the more complicated underlying scientific concepts. Whether isotopes, why isotope ratios of hydrogen and deuterium (a slightly heavier variant of hydrogen) matter and what they reveal about the origin of water, or the chirality of amino acids (the left- or right-handedness I mentioned just now) – she is an enthusiastic communicator with a knack for keeping the reader both informed and entertained.
Equally fascinating is the how. The easiest way to study asteroids and comets is to start right here on Earth with meteorites. But scientists are also studying much smaller interplanetary dust particles gathered from our planet’s stratosphere. What is really pushing the envelope technically is to study comets and asteroids in situ, in space. The Rosetta mission to the comet 67P/Churyumov–Gerasimenko, which had a very unexpected shape, captured the public imagination, and was well publicised by the European Space Agency. Starkey takes the reader through the trials and tribulations of this mission, but is equally infectious about NASA’s Stardust mission. And she shortly details other missions, less well known outside of the circles of astronomy-aficionados.
What I really appreciated here was that Starkey gave very clear-cut reasons for why we mount such expensive and high-risk missions where much can go wrong. We cannot really send sensitive scientific instruments that need careful calibration and constant human attention into space unattended, so there is a really good reason to try and develop missions that can return samples to Earth, as has been done a few times now. But it also forces us to develop new technologies so that the instruments we do send out can operate remotely in the harsh conditions of outer space. There have been some real boons and bonuses as a consequence of developing new technology detailed here. Who would have thought there could be a link between spacecraft technology, bedbugs and perfume?
“Who would have thought there could be a link between spacecraft technology, bedbugs and perfume?”
The final two topics Starkey tackles are space mining and, of course, the threat of impact and countermeasures. I always thought of the former as sci-fi, but Starkey takes this topic very seriously, giving a clear overview of how it could be done and what the hurdles are. With rare earth elements being uneconomical to extract and humanity’s high-tech society being very dependent on them, I am starting to see why there is such interest in this. Starkey describes how it could even be the stepping stone for expanding out into space.
The danger of impact was recently discussed in my review of Cosmic Impact and is not the focus of this book. Starkey nevertheless does not ignore the topic altogether and gives a very good overview of the inevitability of impact in the long run, the consequences for life, recent examples such as the Tunguska Event and the Chelyabinsk meteor, and the various strategies we could employ to counter this threat.
The highlight of Catching Stardust for me was how Starkey champions the relevance of scientific research, and the wider, real-world benefits “astronomers-having-fun” brings. Since she is a host on Neil deGrasse Tyson’s StarTalk Radio podcast, you might have already guessed Starkey is a good science communicator. And she brings this flair to what is, unbelievably, only her first book. Another excellent addition to the Bloomsbury Sigma imprint and a great example of well-written popular science.
Disclosure: The publisher provided a review copy of this book. The opinion expressed here is my own, however.
Other recommended books mentioned in this review:
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“Cosmic Impact: Understanding the Threat to Earth from Asteroids and Comets”, written by Andrew May, published by Icon Books in February 2019 (paperback, 167 pages)
The story of the extinction of the dinosaurs and its link to the Chixculub impactor has featured repeatedly on this blog. Walter Alvarez told the story in his own words in T. rex and the Crater of Doom, and it featured as one of the big five mass extinctions in Brannen’s The Ends of the World: Volcanic Apocalypses, Lethal Oceans and Our Quest to Understand Earth’s Past Mass Extinctions, while any dinosaur book worth its salt features the topic (see e.g. my reviews of The Rise and Fall of the Dinosaurs: The Untold Story of a Lost World and The Dinosaurs Rediscovered: How a Scientific Revolution is Rewriting History). Now, if someone could please show the dinosaurs the door, because there is far more to the topic than them, or the bad science shown in disaster movies such as Deep Impact and Armageddon.
May starts off with a short history of comets and asteroids. It obviously took a while before shooting stars were recognised for what they were: not bad omens, but hunks of space junk. Even so, the possibility of cosmic impacts was long dismissed. Although May doesn’t mention him by name, it was Scottish geologist Charles Lyell’s doctrine of uniformitarianism (May instead calls it gradualism in this book) that long held sway and pretty much ruled out (cosmic) catastrophes. The pseudoscience espoused in the 1950s by psychologist Immanuel Velikovsky (see The Pseudoscience Wars: Immanuel Velikovsky and the Birth of the Modern Fringe) also did not help its credibility. But, as documented at length elsewhere, it eventually became an accepted idea (see my reviews of Four Revolutions in the Earth Sciences: From Heresy to Truth and Cataclysms: A New Geology for the Twenty-First Century).
“Now, if someone could please show the dinosaurs the door, because there is far more to the topic than them […]”
So, we have dealt with the dinosaurs, and we have the idea on the table as something to be taken seriously. But before May can start talking about the threat to human civilization and what, if anything, can be done to avert it, there is a whole lot of astronomy to be dealt with first.
This is where I feel the book does an excellent job introducing the basic science, although he does seem to falter right at the start in explaining the differences between meteors, asteroids, and comets. Clear-cut definitions have been formulated elsewhere, but May instead focuses on the caveats, pointing out that these names were coined before people really understood what they were talking about. Furthermore, the more we study them, the more their properties seem to overlap. That’s all fair enough, but after a few pages I still was not quite clear on the difference between asteroids and comets.
“It obviously took a while before shooting stars were recognised for what they were: not bad omens, but hunks of space junk.”
Luckily, the more complex topics of the all-important orbits (which determine whether they will cross Earth’s path), the underlying celestial mechanics, and its terminology are all lucidly explained, including helpful diagrams. May briefly covers the different sources for all these rocks (the nearby asteroid belt, the more distant Kuiper belt, and the still more distant and hypothetical Oort Cloud) and the likelihood of impact. He is quick to inject a healthy dose of realism and sobering numbers here, because even the asteroid belt is, in reality, not particularly densely packed with debris. No matter how Star Wars depicted it, the Millenium Falcon could easily coast through this with the crew snoozing and no one would be the worse for wear.
But impacts do happen. Just look at the moon, May says. Although Meteor Crater in Arizona was long recognised as the only clear crater on the face of the Earth, many others have now been found. Coverage of this topic would not be complete without mention of the 1908 Tunguska Event in Siberia (see also The Tunguska Mystery, although May thinks there little mystery left here), the 2013 Chelyabinsk meteor, or the 1994 impact of the Shoemaker-Levy 9 comet on Jupiter (see The Great Comet Crash: The Collision of Comet Shoemaker-Levy 9 and Jupiter).
“No matter how Star Wars depicted it, the Millenium Falcon could easily coast through [the asteroid belt] with the crew snoozing and no one would be the worse for wear”
Now that cosmic impact is a topic that can be brought up again in polite company, new wild ideas have been quick to follow. May gives a quick and appropriately sceptical overview of the revival of the idea of panspermia (comets seeding planets with life), epidemics-from-space, the alleged periodicity of mass extinctions and its link to cosmic phenomena (see the latter part of Cataclysms but especially Dark Matter and the Dinosaurs: The Astounding Interconnectedness of the Universe), or the idea of a dark star companion to our sun (see The Nemesis Affair: A Story of the Death of Dinosaurs and the Ways of Science).
But, to repeat, impacts do happen, and May briefs the reader on NASA’s efforts at monitoring so-called near-earth objects, and the fantastic missions that landed on asteroids. Finally, he seriously considers the various options we have to defend ourselves from incoming asteroids and comets (blow them up, deflect them, redirect their course?).
“Especially the topic of planetary defence has tickled the imagination […]”
Especially the topic of planetary defence has tickled the imagination with a host of books on it in recent years, such as Near-Earth Objects: Finding Them Before They Find Us and The Asteroid Threat: Defending Our Planet from Deadly Near-Earth Objects. And Cosmic Impact is not the final word on the topic, see also my review of Fire in the Sky: Cosmic Collisions, Killer Asteroids, and the Race to Defend Earth.
Of all these, May’s book is the least expensive. At 155 pages his coverage of topics is well-balanced, though necessarily cursory in places. Given the brief of the Hot Science series this book is part of, that is only to be expected though. What it does deliver is a fast-paced and very readable book that avoids hype and is cautiously sceptical where it needs to be. A book that is sure to whet the appetite.
Disclosure: The publisher provided a review copy of this book. The opinion expressed here is my own, however.
Other recommended books mentioned in this review:
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“Exoplanets: Hidden Worlds and the Quest for Extraterrestrial Life“, written by Donald Goldsmith, published by Harvard University Press in September 2018 (hardback, 254 pages)
I first touched on exoplanets in my review of astrobiologist Charles Cockell’s book The Equations of Life: The Hidden Rules Shaping Evolution, who provided a very brief introduction to them as a little aside. Their existence and the remote possibility of finding worlds inhabited by other lifeforms has captured the public imagination. Just in the last two years there have been at least three other popular science book on the topic (The Planet Factory: Exoplanets and the Search for a Second Earth, Exoplanets: Diamond Worlds, Super Earths, Pulsar Planets, and the New Search for Life Beyond Our Solar System, and One of Ten Billion Earths: How we Learn about our Planet’s Past and Future from Distant Exoplanets). So where do you start? Though I haven’t read these books yet, what I can tell you is that Goldsmith here provides an inclusive overview.
After familiarising the reader with the vast distances involved and the units astronomers use, including Astronomical Units, light years and parsecs (yes, the one George Lucas famously got wrong), the first half of the book dives into the how. Given that even the nearest stars are very far away, and planets emit no light, how, indeed, do you find them?
“Given that even the nearest stars are very far away, and planets emit no light, how, indeed, do you find them?”
Two indirect methods have been particularly successful and are explained here in-depth by Goldsmith: radial velocity measurements and transit observations.
The former relies on the fact that as a planet circles a star, it exerts a small gravitational tug on the star, causing both the star and the planet to turn around a shared centre of mass that is not exactly at the centre of the star, but somewhere towards its edge or even outside of it. In effect, the star wobbles, and this wobble can be observed in changes in the wavelength of the light that reaches us. Remember the Doppler effect? How a siren sounds higher in tone when an ambulance approaches you, and lower in tone when it moves away from you? It is the same for light. The differences are minute, but with sensitive enough equipment these shifts in wavelength can be measured.
The second method, pioneered by NASA’s now-retired Kepler space telescope, is perhaps easier to grasp: a planet moving in front of its star causes a temporary blip in the intensity of the star’s light. If these observed blips are regular enough you have a candidate exoplanet. Of course, this only works when a planet’s orbit passes in front of a star from our vantage point, but there are plenty of stars out there for which this is true.
“What we have discovered and catalogued so far has very much surprised everyone […] our Solar System is far from the only possible configuration. “
These two methods have led to the discovery of thousands of exoplanets. But Goldsmith would not be thorough if he did not also explain other methods, such as direct observations using the infrared radiation emitted by planets, gravitational lensing (the bending of light’s path due to the proximity of massive objects – one of those counterintuitive phenomena Einstein predicted), orbital brightness modulation (where a star’s observed brightness fluctuates ever so slightly by light reflected off nearby orbiting planets), changes in light polarization (also due to reflection off a planet), and several other obscure methods, some of which have so far been unsuccessful. I found his explanations here clear, and they gave several of those “aha” moments. For example when he explains adaptive optics, an engineering solution employed in modern telescopes to correct for image distortion caused by Earth’s atmosphere (so that is why I keep seeing photos of telescopes shooting a laser beam into the sky).
Throughout, Goldsmith is careful to point out the limitations and biases of current methodologies. Despite their success, the resolution of most methods is still so poor that we can only find planets (much) bigger than Earth. Technological improvements are continuing apace though, and new observatories, whether on Earth or in orbit, are finding smaller and smaller planets.
What we have discovered and catalogued so far has very much surprised everyone. Goldsmith takes the reader through an eye-opening tour of the weird and wonderful planetary systems; giant planets racing around stars at a fraction of the distance between our Sun and Mercury, planets around binary stars, planets young and old, big and small, dense and fluffy… our Solar System is far from the only possible configuration. Goldsmith adds a very interesting chapter on how this affects our existing theories of star and planet formation.
“For the moment, the exoplanet search is largely a cataloguing exercise and we have gathered only the most basic of [information].”
But it is not all hard facts. Goldsmith permits himself plenty of informed speculation towards the end of the book as he ponders which planets are likely to be friendly to life as we know it. For the moment, the exoplanet search is largely a cataloguing exercise and we have gathered only the most basic of estimates on sizes, masses, distances to stars, and orbital periods. Ongoing and planned projects such as ESA’s PLATO mission and NASA’s James Webb Space Telescope will hopefully change this and Goldsmith gives an informative overview of future missions and the technical challenges that need to be overcome to improve our detection methods. He happily veers into near science fiction when speculating about future missions that will send nanoprobes into interstellar space to pass by the nearest discovered exoplanets, and the hypothetical possibility of sending humans on interstellar missions.
Goldsmith lightens up his writing with the occasional wry observation on the quirks of his profession, and quotes from fellow astronomers who he has interviewed. There are places where I would have liked a few more illustrations to explain certain principles, although the ones that have been included are useful and clear, having been carefully redrawn for this book.
The strong suit of the book is its solid writing though: Goldsmith goes into plenty of technical detail but he never lost me. The book strikes the right balance between starting from first principles for readers without a background in astronomy or astrophysics in a way that is not patronising, while delivering plenty of technical details and caveats about what we know so far. Above all, he transmits the sheer awe that this fast-moving field inspires.
Disclosure: The publisher provided a review copy of this book. The opinion expressed here is my own, however.
Other recommended products mentioned in this review:
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