In deciding whether to come out with a revised version of a previously published work, authors always have to ask themselves: Is there enough new information to warrant a rewrite? In the case of Louis Irwin’s and my new book, Life in the Universe: Expectations and Constraints, that was easy. The field of astrobiology has advanced by leaps and bounds since our last edition came out 10 years ago.
This new, third edition, for example, highlights the current intense discussion over where life on Earth originated. Did it occur at an oceanic hydrothermal vent? In volcanic hydrothermal pools on land, or tidal flats, or even in sea ice?
In the last few years, the discovery of thousands of exoplanets has sparked a revolution in our thinking about possible life outside our own Solar System. We have even started to detect the first exomoons. That prompted Irwin and I to add a new chapter on exoplanets, and to lay out the future observations and technologies that will allow us to conclude whether an exoplanet is habitable or not. These methods can be applied to studying Proxima Centauri b, Kepler 452b, and Kapetyn b, just to name three of the most exciting candidates.
The question of whether we have already discovered extraterrestrial life also took some exciting turns over the last decade. Previous assessments and interpretations of results from the Viking life detection experiments and analyses of the Martian meteorite ALH84001 may have to be revised based on new discoveries, such as the confirmed existence of indigenous organic compounds on Mars.
Even SETI—the search for signs of extraterrestrial intelligence—has seen new developments, including renewed discussions of the famous Wow! Signal and the question of whether Fast Radio Bursts are of natural or artificial origin. We’ve also seen heated debates over METI, or the attempt to initiate contact with extraterrestrial civilizations.
We’ve even included in this new edition ideas that were once considered outlandish, such as the notion of life based on a shadow biosphere on Earth, crystalline life, and Clement Vidal’s suggestion of stellivores.
As in the previous versions, the goal in this third edition of our book was to avoid as much as possible being Earth-centric, and to think as broadly as possible about the phenomenon of “life” and where we might find it in the Universe.