Early impact chronology of the icy regular satellites of the outer solar system
Early impact chronology of the icy regular satellites of the outer solar system
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DOI：
10.1016/j.icarus.2020.114184
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发表时间：
2020-11
期刊：
影响因子：
3.2
通讯作者：
E. W. Wong;R. Brasser;S. Werner
中科院分区：
文献类型：
--
作者：
E. W. Wong;R. Brasser;S. Werner
巨行星常规卫星表面的年代测定受到两个问题的阻碍。首先是缺乏可以测量放射性年龄的已知样本。第二个是，由于撞击物数量和行星系统结构的差异，与月球和火星相比，陨石坑年表可能不同，这使得直接比较和绝对年龄推导变得困难。这使得建模成为获得接近绝对表面年龄的唯一方法。在这里，我们应用并报告了一个改进的年代学模型的外太阳系在一个插曲的动力学不稳定造成的巨行星迁移。我们结合了一系列的动力学和蒙特卡洛模拟与各种陨石坑的比例尺的法律，撞击物的大小，频率分布和观测陨石坑密度计算预期的陨石坑密度的表面上的常规卫星的木星，土星和天王星。由此，我们得出了它们最古老的表面年龄。我们的撞击物来自于日心星子，它们来自于巨行星轨道外部的小天体盘，以及不规则卫星，它们可能是由巨行星之间的相互碰撞捕获的。根据陨石坑比例定律和假设巨行星在4.5 Ga开始迁移，除了土卫一、土卫二、土卫三和米兰达等内卫星和小卫星外，大多数卫星的表面年龄都超过4.3 Ga。其表面年龄估计为。虽然这些天体的质量预计已被严重侵蚀，如果它们在巨行星迁移之前就存在，它们很可能会被摧毁。我们对土星中型卫星旧表面年龄的预测对它们的形成、潮汐演化、土星内部和环的年龄都有影响。
The dating of the surfaces of the giant planets' regular satellites is hampered by two issues. The first is the lack of known samples from which radiometric ages can be measured. The second is a potentially different cratering chronology compared to those of the Moon and Mars, due to a difference in the impactor population and planetary system architecture, making a direct comparison and absolute ages derivation difficult. That leaves modelling as the only way to obtain something close to absolute surface ages. Here we applied and reported an improved chronological model of the outer solar system during an episode of dynamical instability caused by giant planet migration. We have combined a series of dynamical and Monte Carlo simulations with various crater scaling laws, impactor size-frequency distributions and observational crater densities to compute the expected crater densities on the surfaces of the regular satellites of Jupiter, Saturn and Uranus. From this, we derived their oldest surface ages. Our impactors are sourced from heliocentric planetesimals that originated from the disk of small bodies exterior to the orbit of the giant planets, and the irregular satellites, which were likely captured by the mutual encounters between the giant planets. With both crater scaling laws and the assumption that the giant planets began their migration at 4.5 Ga, most satellites' surfaces were dated to be older than 4.3 Ga, apart from the inner and small satellites, i.e. Mimas, Enceladus, Hyperion and Miranda. Their estimated surface ages are ca. 4 Ga, although these bodies' masses are expected to have been heavily eroded and if they existed prior to giant planet migration they were likely to be destroyed. Our prediction of old surface ages for the mid-sized Saturnian satellites has implications for their formation, their tidal evolution, the interior of Saturn and the ages of the rings.