Ongoing and future space missions aim to identify potentially habitable planets in our Solar System and beyond. Planetary habitability is determined not only by a planet’s current stellar insolation and atmospheric properties, but also by the evolutionary history of its climate. It has been suggested that icy planets and moons become habitable after their initial ice shield melts as their host stars brighten. Here we show from global climate model simulations that a habitable state is not achieved in the climatic evolution of those icy planets and moons that possess an inactive carbonate–silicate cycle and low concentrations of greenhouse gases. Examples for such planetary bodies are the icy moons Europa and Enceladus, and certain icy exoplanets orbiting G and F stars. We find that the stellar fluxes that are required to overcome a planet’s initial snowball state are so large that they lead to significant water loss and preclude a habitable planet. Specifically, they exceed the moist greenhouse limit, at which water vapour accumulates at high altitudes where it can readily escape, or the runaway greenhouse limit, at which the strength of the greenhouse increases until the oceans boil away. We suggest that some icy planetary bodies may transition directly to a moist or runaway greenhouse without passing through a habitable Earth-like state.

中文翻译：

---

冰雪世界的突然气候变化，从雪球到潮湿或失控的温室

正在进行的和未来的太空任务旨在确定我们太阳系内外的潜在宜居行星。行星的宜居性不仅取决于行星当前的恒星日照和大气特性，还取决于其气候的演化历史。有人建议，当它们的初始恒星变亮时，冰冷的行星和卫星在其最初的冰盾融化之后变得可居住。在这里，我们从全球气候模型模拟中发现，那些碳酸盐-硅酸盐循环不活跃且温室气体浓度低的冰冷行星和卫星的气候演化过程中，并未达到宜居状态。这种行星体的例子有冰冷的欧罗巴和土卫二卫星，以及某些绕G和F恒星运转的冰外系行星。我们发现，克服行星初始雪球状态所需的恒星通量太大，以至于导致大量水份流失，无法居住。具体来说，它们超过了潮湿的温室极限（在该高度处水蒸气易于在高处积聚，在该高度处水蒸气可以轻易逸出），或者超过了失控的温室极限（在该极限处，温室的强度不断增加，直到海洋沸腾为止）。我们建议某些冰冷的行星体可能会直接过渡到潮湿或失控的温室，而不会经过像地球一样宜居的状态。温室的强度不断增加，直到海洋沸腾为止。我们建议某些冰冷的行星体可能会直接过渡到潮湿或失控的温室，而不会经过像地球一样宜居的状态。温室的强度不断增加，直到海洋沸腾为止。我们建议某些冰冷的行星体可能会直接过渡到潮湿或失控的温室，而不会经过像地球一样宜居的状态。