The conductive cooling of planetesimals with temperature-dependent properties
The conductive cooling of planetesimals with temperature-dependent properties
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具有温度依赖性特性的星子的传导冷却
DOI：
10.1002/essoar.10504913.1
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发表时间：
2020
期刊：
影响因子：
--
通讯作者：
Murphy Quinlan M
中科院分区：
文献类型：
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作者：
Murphy Quinlan M
模拟太阳系早期小天体的行星热输运使我们能够了解陨石样品的地质背景。行星体中的传导冷却由导热系数、热容和密度控制，它们是温度(T)的函数。我们研究了热物性的T依赖关系和在热方程中引入非线性项是否会导致对不同类别陨石起源的不同解释。我们已经开发了一个有限差分程序来执行具有T依赖性质的导电冷却行星小行星的数值模型，发现包括T依赖会在热历史中产生相当大的差异，进而估计陨石形成的时间和深度。我们考察了改变输入参数对该模型的影响，并用简单的线性函数探讨了电导率的非线性T依赖关系。然后，我们应用非单调函数对电导率、热容和密度进行拟合，以符合已发表的实验数据。对于半径为250公里的闪锌矿母体的典型计算，与T有关的性质将核心结晶和发电机活动的开始延迟约40Myr，大约相当于将行星半径增加10%，并将核心结晶延长约3Myr。这影响了与古地磁证据相容的淡水母体的行星小半径和核心大小的范围。这种方法也可以用来模拟其他分化的小行星和原始陨石母体的T演化，并限制相关陨石样品的形成。
Modelling the planetary heat transport of small bodies in the early Solar System allows us to understand the geological context of meteorite samples. Conductive cooling in planetesimals is controlled by thermal conductivity, heat capacity, and density, which are functions of temperature (T). We investigate if the incorporation of the T-dependence of thermal properties and the introduction of a non-linear term to the heat equation could result in different interpretations of the origin of different classes of meteorites. We have developed a finite difference code to perform numerical models of a conductively cooling planetesimal with T-dependent properties and find that including T-dependence produces considerable differences in thermal history, and in turn the estimated timing and depth of meteorite genesis. We interrogate the effects of varying the input parameters to this model and explore the non-linear T-dependence of conductivity with simple linear functions. Then we apply non-monotonic functions for conductivity, heat capacity and density fitted to published experimental data. For a representative calculation of a 250 km radius pallasite parent body, T-dependent properties delay the onset of core crystallisation and dynamo activity by ~40 Myr, approximately equivalent to increasing the planetary radius by 10 %, and extend core crystallisation by ~3 Myr. This affects the range of planetesimal radii and core sizes for the pallasite parent body that are compatible with paleomagnetic evidence. This approach can also be used to model the T-evolution of other differentiated minor planets and primitive meteorite parent bodies and constrain the formation of associated meteorite samples.