From the time the human species developed eyes, we have stared up at the skies and speculated about the stars and the heavens. Yet as recently as 1835, Auguste Comte wrote that it would be impossible for us ever to understand the composition of stars. He wrote: ‘While we can conceive of the possibility of determining their shapes, their sizes, and their motions, we shall never be able by any means to study their chemical composition or their mineralogical structure.’ Presumably he would have been even more incredulous at the suggestion that we could detect planets orbiting other stars.
Indeed, even twenty years ago we had no evidence that any planet existed outside our own solar system. In 2011, by contrast, we not only know about the composition and behaviour of a whole range of star types, we have discovered hundreds of exoplanets (planets outside the Solar System) and can even begin to determine the kind of weather that exists on them.
The purpose of Strange New Worlds is to record the history of the search for exoplanets. It charts the progress of exploration from early speculation and observations, through to the latest discoveries made possible by the Kepler space mission and highly sophisticated ground-based facilities.
The ultimate prize is the discovery of rocky Earth-like planets, because these are the ones that are most likely to harbour recognisable life. Jayawardhana is good at explaining just how difficult a problem this is: ‘In visible light, an Earth twin would be nearly 10 billion [his italics] times fainter than its star and separated from it by less than one-tenth of an arcsecond, an angle that is 20,000 times smaller than the apparent diameter of the Moon in the sky’ (p166). Yet the precision of scientific instrumentation has increased to the point that, within the last year, scientists have at last begun to identify candidates for the kind of planets they seek. The final stage, the search for signs of life, now beckons. As Stephane Udry of the Geneva Observatory puts it: ‘The golden age is still ahead of us’ (p15).
Two aspects of the book stand out. One is the sheer excitement of the search, the traditional longing of mankind to know more and to discover more, although Jayawardhana has to record the failures as often as the successes. The other is the way that planet-searching has become a huge aspect of astronomic research in the last two decades. Jayawardhana names project after project, most of them using existing ground-based telescopes and facilities. High-profile space missions like Hubble and Kepler are only part of the inventory available, because sophisticated techniques have enabled conventional telescopes to compensate for the disadvantage of being trapped within the Earth’s atmosphere. Microlensing (the way gravity bends light rays round objects in space), measuring Doppler shifts and direct imaging are all techniques that are helping to identify and chart exoplanets.
This is emphatically an astronomy book, not a SETI book. Although SETI (Search for Extra-Terrestrial Intelligence) is mentioned in the last two pages, the book is concerned with the historical search for extra-solar planets. Once Earth-like planets have been discovered, the search for signs of life (biosignatures) on them can begin, but Jayawardhana is concerned with the astronomers’ techniques for this, not the SETI researchers’ hopes of detecting communications from advanced alien races. Anybody interested in that side of planet hunting should turn to Paul Davies’ excellent The Eerie Silence.
The virtues of Jayawardhana’s book are its simplicity and clarity. It’s a short text, easily read in a couple of days, and by the end of it the reader will have a very clear understanding of the history and current state of the search for alien planets. The style is that of popular science journalism, designed for the general reader with little or no technical knowledge of astronomy. This is unsurprising, as Ray Jayawardhana is an award-winning science writer as well as Professor in Observational Astrophysics at the University of Toronto, and he has emphatically pitched this book for the non-specialist. The irreducible amount of necessary technical detail is mainly conveyed through lucid and informative diagrams, graphically explaining concepts such as star birth and how radial velocity (Doppler) curves can be used to detect the presence of multiple planets round distant stars. There is also an excellent glossary which covers everything from galaxy and wavelength to microlensing and tidal locking.
The defects of the book, such as they are, are mainly the same as its virtues. Any readers with more than a perfunctory knowledge of astronomy may find that there is little that they do not already know, and wish for more advanced detail. There are no footnotes, although each chapter has a bibliography for those who wish to explore further. Just occasionally, the journalistic style grates or threatens to undermine the reader’s confidence. Jayawardhana’s story is told through the achievements of scientists both past and present, and these figures are often introduced with a degree of personal detail. This is fair enough, but can become distracting when the author permits himself to become lazily anecdotal: ‘Wedged uncomfortably in a middle seat at the back of the plane, Debra Fischer…’ (p82). The reader’s attention can be unhelpfully diverted. Was Debra Fischer ‘wedged’ because she is a particularly large lady, or because that airline has very poor seating standards? Similarly, describing difficulties with the siting of a telescope as ‘a pesky little problem’ (p96) seems cheap. The imprecision of language is trivial here, but can become more of an issue. Very early on (p6) Jayawardhana writes: ‘The stars are so distant that there is little chance of measuring their composition in situ or bringing back samples for laboratory studies.’ Well, no. There is no chance of studying distant stars in situ or bringing back samples. The imprecision, as has been said, risks losing the reader’s trust, which for a science book is fatal.
There is additionally the inevitable problem that this book has a short shelf life, because discoveries are happening at such a rate that a revised version will be needed in a very few years’ time. Overall, however, Jayawardhana succeeds admirably in his mission to explain where we stand in 2011, and what lies just ahead. Any reader who has ever looked wonderingly at the heavens will benefit from pausing long enough to read it, because the rate of change in our understanding of the universe beyond our own local solar system is breathtaking. We know a lot more about the stars than we did two centuries ago, and are beginning to discover the riches and wonder of the other worlds that inhabit our extensive universe. Auguste Comte would be impressed, and thrilled.
Richard Swan will be speaking at a panel session on Life off Earth: are the aliens out there? at the Battle of Ideas in London on Sunday 30 October.