Meteorites and Snow Carrots
On February 15, 2013, a meteor lit up the sky over western Russia. Parts of the meteoroid survived the descent through the atmosphere and broke apart into smaller pieces. The fragments landed in snow 70cm thick and were subsequently collected by geologists.
We know that meteorites create craters when they impact rock or soil, but what happens when they hit a thick layer of snow? It turns out they sometimes create something called “snow carrots” – dense formations of snow so compacted that scientists were able to dig them out and turn them over without them falling apart; they even still held tight to their meteorite (pictured).
The meteorite fragments were mostly found in funnel-shaped holes in the snow with unusually coarse-grained walls. The largest pieces went through all 70cm to reach the frozen ground. The smaller fragments were trapped in snow carrots.
The Chelyabinsk meteorite snow carrots formed at the bottom 15 – 25cm of depth within the holes, as defined by where the funnel narrowed into a cone shape. The meteorites were at the tip of the carrots surrounded by a dense shell of coarse-grained snow similar to the grain of the wall.
Scientists were not sure how the carrots formed, but suspected either melting or compaction as the mechanism. They set up computer models to test both possibilities. The models showed that most of the fragments cooled so much before reaching the ground that melting could not be responsible for the carrots. However, when the projectiles hit, they pushed snow out of the way forming a funnel, and compressed the snow enough to increase the density 13-18% and creating funnel walls approximately 3.4cm thick. In other words, it formed a snow carrot.
The research may help explain what happens during any high-velocity impact into a porous, compressible material. The researchers noted something similar to snow carrots was seen in NASA’s Stardust mission where comet particles were captured in aerogel on a spacecraft.
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Photo Credit: C. Lorenz
References: http://www.hou.usra.edu/meetings/lpsc2015/pdf/1724.pdf
http://bit.ly/1MRedH1
