A second development is the arrival of gorgeously detailed photographs of astronomical objects – which most people will associate with NASA’s Hubble telescope, but can actually be traced back to a book that came out in 1979 called Catalogue of the Universe, which contained the very first true-colour astronomical photograph the general public ever saw. One of that book’s authors was Paul Murdin – co-discoverer of the first black hole, and now a prolific writer whose latest offering is reviewed here. It deals with another of the recent developments that transformed astronomy from a dry academic subject into an exciting one for everyone.
Exoplanets are planets that orbit other stars beyond the solar system. In real-life astronomy, they only form a small fraction of the whole subject, but in science fiction they’re the only thing in outer space that really matters. The reason is obvious – planets are the place we’re likely to find ‘new life and new civilisations’, to quote from Star Trek (as Murdin does in the first chapter of this book). The real-world study of exoplanets, which is only around 30 years old, comes with one potentially disappointing caveat – there are no photographs. Astronomers can only image surface features on a tiny handful of nearby giant stars, so doing the same for any exoplanet is out of the question. So, apart from a couple of solar-system-sized protoplanetary discs, the only pictures in this book are artist’s renderings.
Even so, there’s more to the study of exoplanets than just a list of detections. As Murdin says, ‘astronomers have been able to infer the conditions on some of them – their temperatures, the composition of their surfaces, the strength of their winds, whether their skies are cloudy’. There are several ways to find exoplanets, but the most productive is the ‘transit method’ – in effect, watching what happens when a planet passes in front of its host star. This can tell us the mass, size and density of the planet, and even give us an idea of its chemical composition and atmosphere. Two NASA spacecraft – Kepler and TESS (Transiting Exoplanet Survey Satellite) – have found and analysed thousands of new exoplanets in this way.
Before any exoplanets were discovered, it was naively assumed they would all be close counterparts of the planets of our own solar system: Earth-like, Jupiter-like, Neptune-like and so forth. As it turns out, however, far more types have been discovered – including hot Jupiters (Jupiter-sized planets whose orbits hug closely round their host star), super-Earths, sub-Neptunes and even ‘super-puffs’ – low-density planets with a large radius but a low mass. There are water-worlds with planet-spanning oceans, planets that always keep one face to their parent star (like Mercury was thought to in 1950s-era science fiction) and planets with two suns, like Tatooine in Star Wars. Readers suffering from climate anxiety should be particularly wary of HD189733b, where wind speeds can reach 8,700 kilometres per hour, or WASP-76b, where it rains molten iron.
This book provides what might be called a ‘second generation’ view of exoplanets. I read three or four books on the subject circa 2016 to 2020, when it was approaching its first maturity, but a lot has changed since then – most of it for the good, although there’s been one bit of unpleasantness. Astronomy, fortunately, doesn’t tend to suffer from academic cancellation as much as some other fields, but there’s one notable exception in the world of exoplanets. A prominent ‘hero’ in a couple of those earlier books was Geoff Marcy – without whom it’s arguable the subject would have been much slower to take off. But Marcy’s career came to a sudden and ignominious end with revelations about inappropriate behaviour towards some of his colleagues.
In a humanities subject, a person in this position could simply be deleted from history, but that really isn’t an option in this book, because Marcy’s role was so pivotal. So Murdin has something of a tightrope to walk, concluding rather poetically that: ‘It was a story both of triumphant human endeavour and unacceptable human failing, set against the backgrounds of human justice, public judgement and the impassive cosmos. The fault, however, was not in his stars but in himself.’
On the positive side, there’s been no shortage of exciting new discoveries – from sources like TESS and the James Webb Space Telescope (JWST) – that make this book a hugely welcome update on its predecessors of less than a decade ago. There is, for example, JWST’s discovery of dimethyl sulphide, a chemical closely associated with marine life here on Earth, in the atmosphere of the watery exoplanet K2-18b, or TESS’s discovery of a Jupiter-sized planet orbiting around a super-dense white dwarf star that is only a tenth as big (though far more massive). So if you want a concise and up-to-date overview of the current state of exoplanet science, you really can’t do better than this book.
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Review by Andrew May - See all our online articles or subscribe to a weekly email free here
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