Just 20 years ago, we knew of only one planetary system in the entire cosmos: our own family of eight planets. In the week I wrote this review, we discovered our 5th planet orbiting a distant star and another sun in our galaxy - and this tally will probably be out of date by the time you read these words.
The discovery of new extrasolar planets is proceeding at a blistering pace: in February 2011, Nasa's Kepler space telescope released its first major batch of results - well over 1,000 new planetary candidates. These are only candidates, and to be confirmed they will need to be checked by other telescopes, but the expectation is that the vast majority of these are genuine planets.
We are in the midst of a veritable golden age of discovery, finding not just a new world or continent over our own horizon, but multitudes of new worlds orbiting other suns in the heavens.
Ray Jayawardhana provides here a dramatic account of how this story has unfolded over the years - and you won't find a more able guide for the journey. He is an eminent astrophysicist and planet hunter himself; he holds a professorship at the University of Toronto and is an award-winning science writer. This combination of the insider's expert perspective and storyteller's skill really shines through in Strange New Worlds.
Jayawardhana does an admirable job of describing the long road from the development of crucial techniques, such as the spectroscopic analysis of distant stars in the late 1800s, to the very first extrasolar planets discovered in the 1990s. He explains the different planet-hunting techniques now proving so successful in revealing the bounty of worlds, and the theories on how planetary systems are formed. Many of these extrasolar planets have been detected indirectly by their effects on the light of their star, but a handful have been directly photographed. Astronomers have even released the first weather report for a planet around another star, a temperature map of a gas giant scorchingly close to its sun.
Of course, the holy grail in this field would be to find a twin of our own homeworld: an Earth-sized planet in a habitable orbit around a sun-like star, and a rocky world that is potentially warm and wet and offers the best chances for extraterrestrial life to emerge.
The Kepler space telescope may offer our best hope for spotting just such a world. In fact, over its three-year mission, Kepler is expected to discover dozens of candidate Earth-like planets. But as Jayawardhana notes, the challenge will lie in actually confirming such a discovery. Although Kepler will be able to deliver revolutionary statistics on the likely prevalence of Earth-like worlds, many of the stars that it is monitoring are too far away and thus too faint for even our largest current telescopes to be able to capture a usable spectrum and confirm the planet's existence. But if we're lucky, Kepler, or ground-based observatories, may spot a few habitable planets on our own galactic doorstep.
Two advanced space observatories, the Terrestrial Planet Finder and Darwin, are still on the drawing boards awaiting funding approval. If they come to fruition, they will be capable of analysing the chemical make-up of planetary atmospheres, and could detect signs of life around even relatively distant stars. There is a real buzz in the community that the discovery of extraterrestrial life is finally within our technological grasp.
"That dramatic moment," says Jayawardhana, "is no longer a remote possibility: it may well occur in our own lifetime, if not during the next decade." I hope he is right.
Strange New Worlds: The Search for Alien Planets and Life Beyond Our Solar System
By Ray Jayawardhana. Princeton University Press. 288pp, £16.95. ISBN 9780691142548. Published 30 March 2011