Habitability: A Process Variable Framework with Implications and Tests

Is habitability something that characterizes a planet or is it something that flows through a planet? That is, is habitability a state or a process variable. That question relates to issues that have been central to thinking about life: the balance between chance and necessity, contingency and determinism, order and irreversibility. It also relates to debates about wether habitability is binary or continuous. We present arguments for a process variable view together with observational tests. The tests will need to be statistical but we argue that the number of needed observations is not prohibitive in terms of time and cost commitments. In addition we explore the implications of a process variable view for the modeling of planetary habitability over time, with a focus on issues of habitability initiation and long time maintenance. From the modeling perspective, we argue for the development of minimal complexity level models and more dedicated efforts toward uncertainty quantification.