Innumerable Globes Like This One?

books & arts Innumerable globes like this one?

How to Find a formation of the solar system and the observation. Early chapters describe Habitable Planet distribution and redistribution of volatile current methods of observation, which materials provided the Earth with its have predominantly identified large by James Kasting current inventory of water. Tectonic activity worlds orbiting close to their stars. cycles water between the lithosphere and Subsequent chapters discuss the future PRINCETON UNIV. the surface environment, and maintains the of exoplanet research: direct imaging PRESS: 2010. 360PP. carbonate–silicate cycle — a key feedback and spectroscopy could yield evidence £20.95 on greenhouse warming. Solar radiation of habitable conditions and even life. provides energy to warm the planet’s These final chapters bring the book full surface. And the atmosphere — with a circle, linking the information accessible composition continually influenced by through astronomy to the basic stellar, geology, biology and photochemistry — orbital, planetary and atmospheric factors here is a single general space, provides sufficient surface pressure and that determine habitability. “ a single vast immensity which greenhouse warming to keep water in Twe may freely call Void; in it are its liquid form. Kasting explains these innumerable globes like this one on which processes in detail, individually and in Venus (too hot) and Mars we live and grow.” their complex interactions, as he tracks (too cold) are cautionary So wrote the Dominican friar and them across the evolution of the Sun– philosopher Giordano Bruno in De Earth system. tales for worlds aspiring L’infinito Universo et Mondi, in 1584. A If Earth is ‘just right’, Venus (too hot) to habitability. quarter of a century later — ten years after and Mars (too cold) are cautionary tales Bruno was burned at the stake for this and for worlds aspiring to habitability. In other heresies — Galileo made the first the second section, ‘Limits to Planetary The book should appeal to professional telescopic observations of other planets Habitability’, the climate histories of these and armchair scientists alike. Material in our solar system. Today, more than 450 worlds are used to exemplify the processes is presented as if to a class of non- planets have been detected around other that define the inner and outer reaches of specialist undergraduate scientists. A stars. Although these globes are decidedly the ‘continuously habitable zone’. Venus’s modest familiarity with maths, physics unlike the one on which we live and grow, proximity to the sun induced a runaway and chemistry will suffice to unlock most exoplanet astronomers are setting their greenhouse effect that led to the loss of the of the book’s content, and consistent sights on the detection of habitable, and planet’s water, and the development of the attention is paid to explaining more possibly inhabited, worlds. hellish conditions that prevail at its surface challenging concepts in simple terms. In How to Find a Habitable Planet, today. Mars may have begun its history But the book also frequently touches geoscientist and astrobiologist with liquid water at the surface, but the loss on the primary literature — including James Kasting explores the science of its atmosphere over time eliminated the Kasting’s own seminal contributions to behind this emerging phase of exoplanet potential for a strong greenhouse effect; modelling planetary atmospheres — and discovery. A blend of biogeochemistry, essential for keeping the planet warm thereby provides detail for those interested planetary science and astronomy, the book owing to the lower levels of solar radiation in a deeper account of the subject matter. examines the factors and processes that it receives. Given the broad-ranging subject matter yield habitable conditions, and the methods In a prelude to the book’s final section and up-to-date account of the state of that astronomers will use to search for we learn that early searches for inhabited exoplanet science, all but those closest habitable and inhabited worlds beyond our exoplanets will probably focus on stars to the field — and perhaps even many solar system. Kasting’s wealth of first-hand of similar mass to the Sun. Planets in it — will find it difficult not to learn experience — as a researcher focused on around low mass (dim) stars would have something new. the evolution of planetary atmospheres to maintain close orbits to intercept Written in a clear and often and as the chair of NASA’s Exoplanet sufficient radiation to keep warm. As conversational style — and infused Exploration Program Analysis Group — a result, they would become tidally throughout with Kasting’s personal makes for authoritative writing across the locked — like our moon — potentially optimism regarding the existence of, full range of topics covered. causing any volatiles to freeze out on the and our ability to detect, habitable and Following a brief foray into the history permanently dark side of the planet. At inhabited worlds beyond our own — this of thought concerning life on other planets, the opposite end of the spectrum, massive is an informative and worthwhile read for Kasting explores the science of habitability stars emit high-energy radiation that may anyone who looks to the stars and wonders and the methodology of exoplanet be difficult for life to handle. They also if there is anybody out there. ❐ astronomy in three well-integrated sections. burn out quickly, leaving little time for life The interacting factors and processes that to develop. REVIEWED BY TORI M. HOEHLER have endowed the Earth with liquid water The final section, ‘How to Find Another Tori M. Hoehler is in the Exobiology Branch, NASA at the surface — the book’s key metric of Earth’, combines lessons learned in Ames Research Center, Mail Stop 239-4, Moffett habitability — are discussed in the first habitability with the basics of astronomy Field, California 94035, USA. section: ‘Our Habitable Planet Earth’. The to explore the methodology of exoplanet e-mail: tori.m.hoehler@nasa.gov

nature geoscience | VOL 3 | JULY 2010 | www.nature.com/naturegeoscience 447