Caves in space

Abstract

The definition of a cave has centered on its accessibility to humans, an understandable, but arbitrary, approach. Caves without humanly accessible entrances are still caves. As we reach out to the moons and planets of our solar system, and eventually the stars, we need to evaluate caves as possible reservoirs of extraterrestrial life and as potential human habitats. If humanly passable caves are a subset of all caves, then caves can exist from the tiny, subatomic dimension up to and including the entire universe. They can form and exist for only milliseconds or for billions of years. What’s more, they can form in almost any solid material, and perhaps even in liquids, and contain within them vacuum, gases, liquids or solids. Caves can be initially classified as natural and artificial. Natural caves form either by constructive processes that build a boundary, which contains the void, or by destructional processes that remove or shift material to create a void, where none existed before. Caves are defined by answering five questions: 1. How did the void form? 2. How big is it? 3. How long has it lasted? 4. What does it contain? 5. How does it connect to exterior space? As humans move from a geocentric view of natural features to a more universal view, we need to see caves across a broader continuum of possibilities.