Life Among the Stars

Cabrol writes, “Today, we still do not know what exact environmental conditions led to life, but here is what we know for certain: the building blocks of life are everywhere.” (p. 42). She explores various theories of life’s origin(s), and also acknowledges that scientists need to expect the unexpected, and perhaps we may find conditions leading to life in places that we thought would not yield life, including the “edge of the habitable zone of our solar system.” (p. 46).

She takes the reader to various planets, as mentioned previously, exploring planetary and environmental aspects that might encourage the development of life. Following that, she turns her attention to exoplanets and exomoons, noting that while the numbers change almost daily, there have been over 5,000 exoplanets and 3,677 planetary systems confirmed in just a small area of our galaxy; nearly 8,500 other exoplanets have yet to be confirmed, and there could also be an estimated 20 to 80 trillion moons in our galaxy alone. Not to mention that deep field images, like those from the Hubble Space Telescope, hint at 125 billion galaxies in the observable universe. She cheekily writes, “…if life is an accident, the universe has to be the mother of all pileups.” (p. 158).

To think that Earth alone has life, then, would be an incredible act of hubris, no?

Cabrol’s writing is descriptive and accessible, and her enthusiasm for the topics shines through in her prose: “Exoplanets give us a new gallery of alien worlds to think about. As an astrobiologist, this is what I find the most exciting about them because they open up countless unexplored probabilities of the coevolution of life and planetary environments.” (p. 174). She freely admits to how much we actually know, which conversely makes her a much more trustworthy guide to the galaxy, and endears her to the reader. At times, the material becomes quite dense, but for the astrophysics/astrobiology/astronomy reader, this isn’t a problem. While Cabrol covers a huge amount of information in the book, she manages to maintain her focus and tie the information together.

At the beginning of the book, in the section where Cabrol explores the question of life’s origin(s) and what she refers to as the “grammar of life” and the terminology used in astrobiology, she introduces the reader to a philosophical question about the definition of life. She explains that up until now, the framework supporting life and what life does — and by this, she explains that she means how it assembles, how it functions, and any evidence of its existence that it leaves behind — is pretty much “what life does defines what life is.” (p. 239). However, as she points out, “…new scientific paradigms have been proposed in the past two decades, which do not consider the ‘plumbing of life’ as what defines it. In other words, explaining the origin of life might not be enough to define it.” (p. 239). Defining life, then, may not be as easy as we had originally thought, or even hoped.