3D numerical modeling of high-velocity impacts: cratering rates on Venus, interaction between the ejecta and atmosphere, obliquity of the K-T impact.

我们正在申请资金，请一位俄罗斯科学家（Natalia Artemieva）来帮助我们更多地了解陨石撞击。她编写了一个计算机建模程序（称为SOVA），可以准确地模拟陨石在大气层中运动时发生的情况，当它撞击行星或月球表面时会发生什么，然后物质（气体，融化的岩石和固体颗粒）如何从撞击地点喷出并穿过大气层。阿特米耶娃的计算机编程技能补充了摩根、柯林斯和布兰德在影响方面的专长。参观的主要原因是：1)确定金星上的陨石坑率在我们太阳系的整个历史中，陨石经常与我们的行星和卫星相撞。我们大概知道这种情况发生的频率，例如，一颗直径10公里的陨石大约每1亿年撞击地球一次。我们可以利用撞击坑的密度来告诉我们行星表面的年龄，当我们这样做时，我们发现金星表面只有大约6亿年的历史（即比月球或火星年轻得多），这表明金星当时发生了一次行星范围的火山事件。然而，这些计算只是近似值，因为到目前为止，还没有人确定金星非常稠密的大气对流星进入的影响。Artemieva和Bland将使用SOVA正确地模拟陨石穿过金星大气层的进入，获得金星的适当约束陨石坑率，并计算金星表面的年龄。当我们观察地球上的中型到大型陨石坑时，它们周围都是由火山口喷出的物质，这些物质是以快速湍流的方式喷射出来的。这些喷出物沉积物类似于火星上火山和一些陨石坑周围所谓的“火山碎屑流”。前者已知会导致气候变化，而后者被认为只有在火星表面下有冰的情况下才有可能发生。以前从撞击地点喷出物的模型以一种简单的方式处理喷出物。Collins和Artemieva将使用SOVA适当地模拟喷出物和大气之间的相互作用，以及这些物质在撞击地点周围的沉积。他们将用他们的模型来测试：陨石撞击是否会导致气候变冷（就像火山碎屑流一样），以及火星表面下是否有冰。如果陨石以较低的角度撞击行星表面，陨石对环境的破坏会更大，因为这样它们可以从近地表的岩石中释放出更大体积的气体。因此，低角度或许可以解释为什么6500万年前发生在墨西哥希克苏鲁伯的撞击如此具有破坏性，并导致了包括恐龙在内的大规模灭绝。摩根从世界各地收集了喷出物的样本，并确定了每个地点的颗粒大小。Morgan和Artemieva将使用SOVA来模拟粒子如何在不同的撞击角度下从撞击地点喷射出来。然后，他们将比较观测到的数据和模拟的数据，以确定这颗陨石撞击地球的角度。由此，我们将能够更好地计算出这次撞击释放到大气中的气候活性气体的体积。

We are applying for funds to bring a Russian Scientist (Natalia Artemieva) to help us learn more about meteorite impacts. She has written a computer modelling programme (called SOVA) that can accurately model what happens to a meteorite as it travels through an atmosphere, what happens when it hits the surface of a planet or moon, and then how material (gas, melted rocks and solid particles) is ejected away from the site of impact and through the atmosphere. Artemieva's computer programming skills complement Morgan, Collins and Bland's expertise in impacts. The main reasons for the visits are to: 1) Determine the cratering rate on Venus Throughout the history of our solar system, meteorites have regularly collided with our planets and moons. We know approximately how often this happens, for example a 10-km diameter meteorite will hit Earth about once every 100 million years. We can use the density of impact craters to tell us how old planetary surfaces are, and when we do this we find that Venus's surface is only about 600 million years old (i.e. much younger than the Moon or Mars), suggesting a planet-wide volcanic event on Venus at this time. However these calculations are only approximate because, until now, no one has determined the affect of Venus's very dense atmosphere on meteor entry. Artemieva and Bland will use SOVA to correctly model the entry of meteorites through the Venusian atmosphere, obtain a properly constrained cratering rate for Venus, and calculate the age of Venus's surface. 2) Model the interaction between the ejecta and atmosphere When we look at middle- to large-sized craters on Earth they are surrounded by material that has been ejected from the crater in rapid, turbulent flows. These ejecta deposits are similar to so-called 'pyroclastic flows' around volcanoes and some craters on Mars. The former are known to cause climate change, and the latter are thought to be possible only if there is ice beneath the surface of Mars. Previous models of ejecta travelling from an impact site have treated the ejected material in a simplistic manner. Collins and Artemieva will use SOVA to properly simulate the interaction between ejecta and atmosphere, and the deposition of this material around the impact site. They will use their model to test: whether meteorite impacts can cause climate cooling (as happens with pyroclastic flows), and whether there is ice beneath the Martian surface. 3) Determine the angle of the K-T impact 65 Ma Meteorites can be more environmentally damaging if they hit a planet at a low angle to the surface because then they can release a larger volume of gasses from the near-surface rocks. A low angle might therefore explain why the impact 65 million years ago at Chicxulub in Mexico was so devastating and caused a mass extinction including that of the dinosaurs. Morgan has collected samples of the ejecta from around the world, and determined the size of particles at each site. Morgan and Artemieva will use SOVA to model how particles are ejected from an impact site for different impact angles. They will then compare the observed and modelled data to determine the angle at which this meteorite hit Earth. From this we will be able to calculate better the volumes of climatically active gasses released into the atmosphere by this impact.