Book Reviewed: Life in the Universe by Jeffrey O. Bennett and Seth Shostak

Looking for life elsewhere

This book is an introduction to astrobiology, and it is designed to convey some of the major conceptual foundations in astrobiology that cut across traditional fields such as chemistry, biology, geology, physics and astronomy. The study of astrobiology received a great impetus in 2019 when astronomers Michel Mayor and Didier Queloz were awarded the 2019 Nobel Prize in Physics for the discovery of extrasolar planet 51 Pegasi b orbiting a Sun-like star. It is a gas giant, a type that astronomers had expected would orbit the outer reaches of a solar system. But it was orbiting much closer to its star than Mercury is to the Sun. This was an early sign that other planetary systems might not be like our own. Since then more than 4,000 exoplanets have been known to exist and most of them are gas giants like Jupiter. The 2016 revised edition of this book includes several new discoveries of extrasolar planets, since then there have been new and exciting detection of habitable extrasolar planets. Methods and tools used to detect these planets uses biosignatures such as planetary temperatures, evidence for water, carbon-based compounds and other indications of atmospheric systems.

The exoplanet K2-18b, which is 124 light-years away, is 2.6 times the radius of Earth, and orbits its star within the habitable zone. Two teams of scientists announced recently that they've found water vapor in this world's atmosphere, which is a big milestone in the search for alien life. Outer planets in the TRAPPIST-1 star system is also conducive to life. It is relatively close to our solar system and hosts seven planets that are potentially Earth-like. Their cores are stretched by its star’s gravity, which generates heat. And the two furthest away from their star could be warm, wet and perhaps even have living systems.

In solar system life is known to exist in deep underground on Mars, and in the sub-surface oceans of moons of Jupiter and Saturn. Jovian moons like Europa, Ganymede, and Callisto are known to have oceans beneath the surface. The moons of Saturn such as Enceladus, Titan and possibly Dione are also known to have liquid water oceans. Enceladus is among NASA’s top targets in the search for life beyond Earth because it appears to have three of life’s most important ingredients: the right chemical ingredients (such as carbon or hydrogen), available energy and liquid water. Plume of water erupting from Enceladus contain molecular hydrogen. This helped strengthen the case for habitability on Enceladus, because hydrogen is an important food source to critters that thrive near hydrothermal vents on Earth. Titan, which is half the size of Earth, is intriguing not only for its internal ocean, but also for its dense, nitrogen-rich atmosphere and complex carbon chemistry. Whether it's inhabited or not, Titan is a fantastic natural laboratory for the chemistry of life.

This is a college textbook for astrobiology courses. I like the depth and the level of discussion. The authors themselves are leading astronomers in the detection of alien-planets. Seth Shostak is a senior astronomer at the SETI Institute, a not-for-profit research organization whose mission is to explore, understand, and explain the origin and nature of life in the universe.