Department of Earth and Planetary Sciences, University of California Santa Cruz, Santa Cruz, California 95064, USA.
Department of Earth & Planetary Sciences and Physics & Astronomy, Johns Hopkins University, Baltimore, Maryland 21218, USA.
Nature. 2017 Nov 15;551(7680):352-355. doi: 10.1038/nature24465.
Pluto's atmosphere is cold and hazy. Recent observations have shown it to be much colder than predicted theoretically, suggesting an unknown cooling mechanism. Atmospheric gas molecules, particularly water vapour, have been proposed as a coolant; however, because Pluto's thermal structure is expected to be in radiative-conductive equilibrium, the required water vapour would need to be supersaturated by many orders of magnitude under thermodynamic equilibrium conditions. Here we report that atmospheric hazes, rather than gases, can explain Pluto's temperature profile. We find that haze particles have substantially larger solar heating and thermal cooling rates than gas molecules, dominating the atmospheric radiative balance from the ground to an altitude of 700 kilometres, above which heat conduction maintains an isothermal atmosphere. We conclude that Pluto's atmosphere is unique among Solar System planetary atmospheres, as its radiative energy equilibrium is controlled primarily by haze particles instead of gas molecules. We predict that Pluto is therefore several orders of magnitude brighter at mid-infrared wavelengths than previously thought-a brightness that could be detected by future telescopes.
冥王星的大气层寒冷且朦胧。最近的观测结果表明，其温度比理论预测的要低得多，这表明存在未知的冷却机制。大气气体分子，特别是水蒸气，被认为是一种冷却剂；然而，由于预计冥王星的热结构处于辐射-传导平衡状态，在热力学平衡条件下，所需的水蒸气需要超饱和许多数量级。在这里，我们报告说，大气中的霾而不是气体，可以解释冥王星的温度分布。我们发现，霾颗粒的太阳加热和热冷却速率比气体分子大得多，从地面到 700 公里的高度主导着大气辐射平衡，在这一高度以上，热传导维持着等温和的大气层。我们的结论是，在太阳系行星大气中，冥王星的大气是独一无二的，因为其辐射能量平衡主要由霾颗粒而不是气体分子控制。我们预测，因此，冥王星在中红外波长下比之前认为的要亮几个数量级——这种亮度可以被未来的望远镜探测到。
