Time history of the Martian dynamo from crater magnetic field analysis
Time history of the Martian dynamo from crater magnetic field analysis
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通过陨石坑磁场分析了解火星发电机的时间历史
DOI：
10.1002/jgre.20105
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发表时间：
2013
期刊：
影响因子：
--
通讯作者：
H. Frey
中科院分区：
文献类型：
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作者：
R. Lillis;S. Robbins;M. Manga;J. Halekas;H. Frey
大型撞击同时重置了与撞击坑最终大小相当的区域的地壳整个深度的表面年龄和磁化强度。这些特性使得大型撞击坑（直径>300公里）成为限制火星核心发电机历史的理想“磁性标记”。然而，地壳磁化和轨道上测量的磁场之间的关系是不唯一的，使得测量到的撞击坑的磁场特征只能代表下面的磁化（或缺乏磁化）。使用蒙特卡罗傅立叶域模拟地下磁化，我们计算部分和完全退磁陨石坑的磁场签名的概率分布。我们将这些分布与41个直径大于300公里的火星旧撞击坑的磁场测量特征进行比较，并计算其磁化状态的概率。我们将这些概率与陨石坑密度和绝对模型年龄进行比较，并以这种方式得出火星大陨石坑磁化的强大时间历史，从而得出火星发电机的时间历史。我们的结论是，最有可能的情况是火星发电机活跃时，最古老的可检测的盆地形成，停止之前的希腊和乌托邦的影响，4.0和4.1 Ga（模型年龄），而不是此后重新启动。此后，火星大气层直接受到太阳风的侵蚀，显着改变了气候演变的路径。要进一步改善火星发电机的历史，需要更好的陨石坑年龄估计和低海拔磁场数据。
Large impacts simultaneously reset both the surface age and the magnetization of the entire depth of crust over areas comparable to the final size of the resulting craters. These properties make large impact craters (>300 km in diameter) ideal “magnetic markers” for constraining the history of the Martian core dynamo. However, the relationship between crustal magnetization and magnetic field measured in orbit is nonunique, making the measured magnetic field signature of an impact crater only a proxy for the magnetization (or lack thereof) below. Using Monte Carlo Fourier domain modeling of subsurface magnetization, we calculate probability distributions of the magnetic field signatures of partially and completely demagnetized craters. We compare these distributions to measured magnetic field signatures of 41 old impact craters on Mars larger than 300 km in diameter and calculate probabilities of their magnetization state. We compare these probabilities to cratering densities and absolute model ages and in this manner arrive at a robust time history of Martian large‐crater magnetization and hence of the Martian dynamo. We conclude that the most likely scenario was a Mars dynamo active when the oldest detectable basins formed, ceasing before the Hellas and Utopia impacts, between 4.0 and 4.1 Ga (in model age) and not thereafter restarting. The Mars atmosphere was thereafter exposed directly to erosion by the solar wind, significantly altering the path of climate evolution. Further improvements to the history of the Martian dynamo will require better crater age estimates and lower altitude magnetic field data.