Molaro J L, Choukroun M, Phillips C B, Phelps E S, Hodyss R, Mitchell K L, Lora J M, Meirion-Griffith G
Planetary Science Institute, 1700 East Fort Lowell, Suite 106, Tucson, AZ 85719, USA.
Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA 91109, USA.
J Geophys Res Planets. 2019 Feb;124(2):243-277. doi: 10.1029/2018je005773. Epub 2018 Dec 26.
Ice sintering is a form of metamorphism that drives the microstructural evolution of an aggregate of grains through surface and volume diffusion. This leads to an increase in the grain-to-grain contact area ("neck") and density of the aggregate over time, resulting in the evolution of its strength, porosity, thermal conductivity, and other properties. This process plays an important role in the evolution of icy planetary surfaces, though its rate and nature are not well constrained. In this study, we explore the model of Swinkels and Ashby (1981), and assess the extent to which it can be used to quantify sintering timescales for water ice. We compare predicted neck growth rates to new and historical observations of ice sintering, and find agreement to some studies at the order of magnitude level. First-order estimates of neck growth timescales on planetary surfaces show that ice may undergo significant modification over geologic timescales, even in the outer solar system. Densification occurs over much longer timescales, suggesting some surfaces may develop cohesive, but porous, crusts. Sintering rates are extremely sensitive to temperature and grain size, occurring faster in warmer aggregates of smaller grains. This suggests that the microstructural evolution of ices may vary not only throughout the solar system, but also spatially across the surface and in the near-surface of a given body. Our experimental observations of complex grain growth and mass redistribution in ice aggregates point to components of the model that may benefit from improvement, and areas where additional laboratory studies are needed.
冰烧结是一种变质作用形式，它通过表面扩散和体扩散驱动颗粒聚集体的微观结构演化。随着时间的推移，这会导致颗粒间接触面积（“颈”）增加以及聚集体密度增大，从而使其强度、孔隙率、热导率和其他性质发生演变。尽管该过程的速率和性质尚未得到很好的限定，但它在冰行星表面的演化中起着重要作用。在本研究中，我们探讨了斯温克尔斯和阿什比（1981年）的模型，并评估了它可用于量化水冰烧结时间尺度的程度。我们将预测的颈生长速率与冰烧结的新观测结果和历史观测结果进行比较，发现在数量级水平上与一些研究结果相符。对行星表面颈生长时间尺度的一阶估计表明，即使在外太阳系，冰在地质时间尺度上也可能经历显著变化。致密化发生在长得多的时间尺度上，这表明一些表面可能会形成有粘性但多孔的外壳。烧结速率对温度和晶粒尺寸极其敏感，在温度较高的较小晶粒聚集体中发生得更快。这表明冰的微观结构演化不仅可能在整个太阳系中有所不同，而且在给定天体的表面和近表面在空间上也会有所不同。我们对冰聚集体中复杂晶粒生长和质量重新分布的实验观测指出了该模型可能需要改进的部分以及需要进行更多实验室研究的领域。
