Cosmic Mirrors: Analogy and the Changing Concept of Habitability

Abstract

What does life need—really need—to survive? What are the boundaries of the concept of “life” in the first place? These are questions for biology, but through the lens of astrobiology, we have the chance to apply them to a wider field and explore a more universal definition for life and “habitability”—where life can live. Astrobiology seeks, among other things, to extend the reach of traditional biology. It has the potential to transform the field into a more universal science, just as physics can be applied on a universal scale. This goal relies heavily on analogy with terrestrial life, unless and until we find another example of life in the universe. Our theories and explorations to date have mostly been limited to our Solar System. Our nearest neighbors—the Moon, Mars, and Venus—as well as, more recently, the Jovian satellite Europa and Saturn’s Enceladus and Titan, have been of particular interest. Even without another example, concepts of habitability have changed over the years, pulling back and forth between an inhabited and a barren universe. We are constantly reassessing the types of life and environments we expect to find. A simplistic, linear view of habitability over the years might lead to the assumption that the size of the living universe has shrunk drastically, and that the prospects for life (particularly intelligent life) have shriveled away almost entirely. But a more careful look at the way these theories have changed, particularly with reference to the aforementioned members of our Solar System, reveals that there has rarely, if ever, been consensus regarding life in the universe. This thesis will explore the way the modern concept of habitability has emerged, solidified, and changed over the years in the context of the dialogue surrounding extraterrestrial life. We will track the evolution of the concept with the aim of understanding how the use of analogy, as well as religious and scientific reasoning, has prompted the development of often contradictory views. From a more holistic historical view, prospects for life and habitability, or at least our detection of them, have in fact increased in many ways. Our firmer understanding of the physical and biological laws guiding life in our Solar System has both created and destroyed imagined worlds, thus leaving the possibility of an inhabited universe firmly within the realm of the possible, perhaps even the probable.