The term habitable is used to describe planets that can harbour life. Debate exists as to specific conditions that allow for habitability but the use of the term as a planetary variable has become ubiquitous. This paper poses a meta-level question: What type of variable is habitability? Is it akin to temperature, in that it is something that characterizes a planet, or is something that flows through a planet, akin to heat? That is, is habitability a state or a process variable? Forth coming observations can be used to discriminate between these end-member hypotheses. Each has different implications for the factors that lead to differences between planets (e.g. the differences between Earth and Venus). Observational tests can proceed independent of any new modelling of planetary habitability. However, the viability of habitability as a process can influence future modelling. We discuss a specific modelling framework based on anticipating observations that can discriminate between different views of habitability.

中文翻译：

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宜居性：具有观察测试和理论意义的过程与状态变量框架

宜居一词用于描述可以孕育生命的行星。关于允许可居住性的特定条件存在争议，但将该术语用作行星变量已变得无处不在。本文提出了一个元层次的问题：宜居性是什么类型的变量？它类似于温度，因为它是行星的特征，还是流经行星的东西，类似于热？也就是说，宜居性是一个状态变量还是一个过程变量？即将到来的观察可用于区分这些最终成员假设。对于导致行星之间差异的因素（例如地球和金星之间的差异），每个因素都有不同的含义。观测测试可以独立于任何新的行星可居住性模型进行。然而，可居住性作为一个过程的可行性会影响未来的建模。我们讨论了一个基于预期观察的特定建模框架，该框架可以区分不同的宜居性观点。