Mysterious ‘snow carrots’ observed at meteorite impact sites

Cyril Lorenz

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Mysterious 'snow carrots' observed at meteorite impact sites

In February 2013, the Chelyabinsk meteorite streaked across the early morning sky over western Russia. The bulk of the body exploded high in the atmosphere, but many smaller fragments survived and rained down onto the snow-covered ground. This week, at the 46th Lunar and Planetary Science Conference, researchers report that some of the impacts carved out strange funnel-shaped “carrots” in the snow. The scientists were able to recreate the impact conditions in computer models in order to learn more about the Chelyabinsk meteorite as well as how meteorites penetrate porous targets in general. Initially, researchers had speculated that the carrot shapes may have been caused by hot fragments that melted the snow during the impact, but the simulations showed that the fragments would have had ample time to cool to atmospheric temperatures before reaching the ground. Instead, the strange funnels appear to be formed mostly by mechanical forces. In the first phase of the impact, a rounded crater is formed, and the snow beneath the rock is compressed, causing its density to increase. Over the next 10 milliseconds, the denser snow gradually slows the meteorite and the walls of the funnel narrow accordingly. The shapes seen both in the models and in reality are similar to other funnel-shaped impact craters, such as those seen on NASA’s Stardust spacecraft, which collected space dust particles in aerogel. That leads researchers to conclude that the physics of such impacts are applicable to many highly porous materials.  

(PDF data credit: Robert Luther)