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

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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.