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TITLE: Impacts on Other Worlds


[Photo: Meteorite Impact]

This meteorite, Paragould, is the product of a collision, or number of collisions, on an asteroid. It is heavily fragmented and preserves evidence of a long history of battering on its parent asteroid. In this rock and in other meteorites like it, we see the same fragmented textures and evidence for melting that are so obvious in rocks that have been transformed by impacts here on Earth. From features like these we are able to reconstruct long histories of bombardment on other worlds.




Ground Zero
Collisions heat and melt rocks near the surface at the point of impact. Along fractures in the bedrock, the heat from intense friction produces thin, dark veins of melt that then solidify to form shock veins. More extensive melting creates the rocks known as impact melts.

See caption at left.

 

At the Surface – Pulverized
Eons of bombardment pounded the rocks of asteroids into layers of soil called regolith. Later impacts sometimes welded these mixtures of powder and fragments into new rocks called regolith breccias. These rocks contain particles emitted by the Sun—solar wind—which is trapped only in the uppermost layers of the regolith.

See caption at left.

 

Beneath the Surface – Battered and Broken
Impacts transformed the rocks beneath the regolith, too. Under intense hammering, they were fractured and, in places, even melted. The constant battering welded the hot fragments together, creating fragmental breccias. These rocks were buried too deeply to be affected by the solar wind. Both fragmental breccias and regolith breccias have fragmented and broken textures. But the absence of trapped solar wind in meteorites like Cumberland Falls indicates that they are deeply buried fragmental breccias.


See caption at left.

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Smithsonian National Museum of Natural History Department of Mineral Sciences website Credits