Water ice clouds form in the mesospheres of terrestrial planets in the solar system (and most likely elsewhere) by vapor deposition at low pressures and temperatures. Under these conditions a range of crystalline and amorphous phases of ice might form. The phase is important because it influences nucleation kinetics, density, vapor pressure over the solid, growth rates and particle shape. In the past, the temperature range over which these different phases exist has been defined on the basis of depositing ice at low temperature and warming it while observing phase changes. However, the direct deposition of ice at a range of temperatures relevant for the terrestrial planets has not been systematically investigated. Here we present X‐ray Diffraction (XRD) measurements of water ice deposited at temperature intervals between 88 and 145 K in a vacuum chamber. XRD patterns showed that low density amorphous ice was formed at ≤120 K, stacking disordered ice I formed from 121 to 135 K and hexagonal ice I formed at 140 and 145 K. Direct deposition results in the stable hexagonal phase at much lower temperatures than when warming stacking disordered ice. All three phases of water ice observed here are possible in clouds in the mesospheres of Earth and Mars, while on Venus only amorphous ice is likely to form.

中文翻译：

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在火星，金星和地球的中层冷云中形成的水​​冰阶段

在低压和高温下，水汽云通过在水汽沉积过程中在太阳系（以及最可能在其他地方）的地行星中层形成。在这些条件下，可能会形成一定范围的冰晶和非晶相。该相很重要，因为它会影响成核动力学，密度，固体上的蒸气压，生长速率和颗粒形状。过去，已经基于在低温下沉积冰并在观察相变的同时对其进行加热的基础上定义了这些不同相存在的温度范围。然而，尚未系统地研究在与陆地行星有关的温度范围内冰的直接沉积。在这里，我们介绍在真空室中以88至145 K的温度间隔沉积的水冰的X射线衍射（XRD）测量。XRD图谱表明，在≤120K时形成低密度无定形冰，在121至135 K时形成无序冰I，在140和145 K时形成六方冰I。直接沉积可在比温度低得多的温度下形成稳定的六方相。气候变暖，堆积无序的冰块。在这里观测到的水冰的所有三个阶段都可能在地球和火星的中层云中，而在金星上只有非晶冰可能形成。与加热无序堆冰时相比，直接沉积可在更低的温度下产生稳定的六方相。在这里观察到的水冰的所有三个阶段都可能在地球和火星的中层云中出现，而在金星上只有非晶冰可能形成。与加热无序堆冰时相比，直接沉积可在更低的温度下产生稳定的六方相。在这里观察到的水冰的所有三个阶段都可能在地球和火星的中层云中出现，而在金星上只有非晶冰可能形成。