Post-impact thermal structure and cooling timescales of Occator crater on asteroid 1 Ceres
Post-impact thermal structure and cooling timescales of Occator crater on asteroid 1 Ceres
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DOI：
10.1016/j.icarus.2018.08.028
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发表时间：
2019-03-01
期刊：
影响因子：
3.2
通讯作者：
Johnson, Brandon C.
中科院分区：
文献类型：
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作者：
Bowling, Timothy J.;Ciesla, Fred J.;Johnson, Brandon C.
奥卡托陨石坑可能是美国宇航局黎明号航天器在塞瑞安表面观察到的最明显的表面特征。陨石坑内包含地球上反照率最高的特征：Cerealia Facula 和 Vinalia Faculae，以及相对光滑的叶状流沉积物。我们提出了 Occator 陨石坑形成的水电模拟，改变了撞击前的 Cerean 表面的水与岩石的比例。我们发现，当水与岩石的质量比高达 0.3 时，Occator 撞击后地下的足够体积将高于水的熔点，从而允许通过撞击热驱动的盐水热液流出来沉积光斑状沉积物。陨石坑下方的热液活性物质储层由撞击物材料和从撞击前表面下方数十公里处升起的物质的混合物组成，可以对深层地下挥发性储层（如果存在）进行采样。使用传导冷却模型，我们估计此类系统内热液活动的寿命（取决于材料常数的选择）在 0.4 到 4 Myr 之间。我们的结果表明，来自奥卡托形成撞击的撞击加热为观察到的光斑的产生提供了一种可行的机制，前提是光斑是在陨石坑本身形成后相对较短的时间窗口内形成的。
Occator crater is perhaps the most distinct surface feature observed by NASA's Dawn spacecraft on the Cerean surface. Contained within the crater are the highest albedo features on the planet, Cerealia Facula and Vinalia Faculae, and relatively smooth lobate flow deposits. We present hydrocode simulations of the formation of Occator crater, varying the water to rock ratio of our pre-impact Cerean surface. We find that at water to rock mass ratios up to 0.3, sufficient volumes of Occator's post-impact subsurface would be above the melting point of water to allow for the deposition of faculae-like deposits via impact-heat driven hydrothermal effusion of brines. This reservoir of hydrothermally viable material beneath the crater is composed of a mixture of impactor material and material uplifted from 10's of kilometers beneath the pre-impact surface, which could sample a deep subsurface volatile reservoir, if present. Using a conductive cooling model, we estimate that the lifetime of hydrothermal activity within such a system, depending on choice of material constants, is between 0.4 and 4 Myr. Our results suggest that impact heating from the Occator forming impact provides a viable mechanism for the creation of the observed faculae, with the proviso that the faculae formed within a relatively short time window after the crater itself formed.