The thermal evolution of planetesimals during accretion and differentiation: consequences for dynamo generation by thermally-driven convection.
The thermal evolution of planetesimals during accretion and differentiation: consequences for dynamo generation by thermally-driven convection.
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吸积和分化过程中星子的热演化：热驱动对流发电机发电的后果。
DOI：
10.1002/essoar.10504425.1
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发表时间：
2020
期刊：
影响因子：
--
通讯作者：
Dodds K
中科院分区：
文献类型：
--
作者：
Dodds K
陨石古地磁记录表明，分化（和潜在的，部分分化）星子产生发电机领域的第一个6-20万年后，形成的钙铝丰富的包裹体（CAIs）。这个早期的发电机活动已被归因于热对流在这些星子的液体核心在早期的岩浆海洋对流。为了更好地了解在星子的热发电机生成的控制，我们已经开发了一个一维模型的星子的热演化从吸积通过关闭对流在其硅酸盐岩浆海洋的各种吸积方案。这些天体的热源是短寿命的放射性同位素26 Al。在分异过程中，26 Al分配到这些天体的硅酸盐部分，导致它们的岩浆海洋升温，并在它们的核心顶部引入稳定的热分层，这抑制了发电机的产生。在“瞬时”吸积体中，这种效应导致整个核心对流和发电机产生的延迟超过1000万年，而这种分层被侵蚀。然而，在> 0.1百万年的增生体中逐渐形成核心可以最大限度地减少这种分层的发展，允许CAI形成后约4百万年的发电机产生。我们的模型还预测了部分分化的微行星，其核心和地幔覆盖着吸积时间尺度> 120万年的南极地壳，尽管这些天体都没有产生热发电机场。我们将数千次模型运行的结果与陨石古地磁记录进行比较，以限制其母体的物理特性。
The meteorite paleomagnetic record indicates that differentiated (and potentially, partially differentiated) planetesimals generated dynamo fields in the first 6-20 Myr after the formation of calcium-aluminium-rich inclusions (CAIs). This early period of dynamo activity has been attributed to thermal convection in the liquid cores of these planetesimals during an early period of magma ocean convection. To better understand the controls on thermal dynamo generation in planetesimals, we have developed a 1D model of the thermal evolution of planetesimals from accretion through to the shutoff of convection in their silicate magma oceans for a variety of accretionary scenarios. The heat source of these bodies is the short-lived radiogenic isotope, 26Al. During differentiation, 26Al partitions into the silicate portion of these bodies, causing their magmas ocean to heat up and introducing stable thermal stratifications to the tops of their cores, which inhibits dynamo generation. In'instantaneously'accreting bodies, this effect causes a delay on the order of> 10 Myr to whole core convection and dynamo generation while this stratification is eroded. However, gradual core formation in bodies that accrete over> 0.1 Myr can minimise the development of this stratification, allowing dynamo generation from~ 4 Myr after CAI formation. Our model also predicts partially differentiated planetesimals with a core and mantle overlain by a chondritic crust for accretion timescales> 1.2 Myr, although none of these bodies generate a thermal dynamo field. We compare our results from thousands of model runs to the meteorite paleomagnetic record to constrain the physical properties of their parent bodies.