The Life of Super-Earths

Starred review from November 15, 2011
Since astronomers discovered the first planet circling another star in 1995, they've found hundreds; predictably, this has energized the debate on whether life exists beyond Earth. Sasselov (Astronomy/Harvard Univ.) reviews the hard evidence in favor (not much) before proceeding to explain discoveries and simulations that suggest we are not alone. No telescope has directly observed an extra-solar planet, but the author delivers a clear explanation of how instruments and, since 2009, a satellite are detecting subtle changes in a star's light or movement that reveal not only the presence of planets (600 so far) but their size, orbits and a hint of their composition. Sasselov maintains that the minority of "super-earths" possess conditions favorable to life: proper temperature, protective atmosphere, volcanism and tectonic movements. These are rocky, watery planets from one to 10 times the mass of Earth, which barely makes the cut. The author reminds readers that life is not fussy. Microbes thrive inside Antarctic ice sheets and in hot rock miles beneath us. Near boiling vents at the sea bottom, far beyond the reach of sunlight, they feed on hydrogen sulfide or other toxic chemicals that spew out and support a dense ecosystem of higher life forms. Life has existed for four billion years, a time comparable to the age of the universe (13 billion), so it may be a normal cosmic process along with planet formation. As short, cogent and stimulating as John Gribbin's Alone in the Universe (2011), but far more optimistic. Readers should check out both.

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February 15, 2012

As the codiscoverer of several extrasolar planets, Sasselov (astronomy, Harvard Univ.) provides an insider's view on planet hunting. He argues that Earth barely meets conditions favoring the formation and maintenance of life, being just large enough to hang onto an atmosphere and having just enough tectonic activity to support a chemical cycle that stabilizes the surface temperature and helps maintain liquid water on the planet's surface. It's actually the "super-Earths" of the universe--rocky, higher-mass planets--that are most likely to harbor life of some kind. The author believes that scientists will eventually discover one or more candidates. (In fact, NASA's Kepler Mission recently identified a super-Earth warm enough for liquid water to exist.) VERDICT An interesting read, but Sasselov overuses technical jargon and underemploys supporting illustrations while explaining complex astronomical research techniques. Consequently, the potential audience is limited to readers who already possess a broad background in the physical sciences. Biology buffs be warned: there's little about life itself (whether terrestrial, synthetic, or alien) in this book.--Nancy Curtis, Univ. of Maine Lib., Orono

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