Читать книгу Astrobiology - Charles S. Cockell - Страница 93

Astrobiologists are very interested in looking for habitable conditions on other planets, a theme that crops up throughout this book. Habitability can simply be explained as conditions suitable for life (or at least one known organism, since our concept of habitability is necessarily hemmed in by the biology that we know). This explains why the discussions in this chapter are so important, because the minimum conditions required by life ultimately determine what we define to be habitable conditions and the assessment we make of the habitability of other worlds. We need to be clear about what we think is the plausible minimum set of chemical elements and compounds as well as physical and chemical conditions required to make life.

So far, the discussions in this chapter permit us to list at least two requirements for an environment to be habitable. We need to have: (i) an environment that provides the basic elements for life (CHNOPS) and (ii) an environment where physical and chemical conditions support the existence of a suitable solvent, which at the current time we assume is liquid water. We see in Chapter 6 that we also require an energy supply. In Chapter 7, we discuss in more detail the physical and chemical limits to life on Earth, which also define the limits of habitable conditions.