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How does an ejecta blanket form around a meteorite crater?
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Meteorite crater
Four impact craters of the same size (30 km [20 miles] in diameter) imaged by spacecraft on different solid bodies of the solar system and reproduced at the same scale. They are (clockwise from upper left) Golubkhina crater on Venus, Kepler crater on the Moon, an unnamed crater on Jupiter's moon Ganymede, and an unnamed crater on Mars. The images are oriented such that the craters appear illuminated from the left; the Venusian crater is imaged in radar wavelengths, the others in visible light.
An ejecta blanket forms during the excavation stage of a meteorite crater formation. When a hypervelocity impact occurs, shock waves and subsequent pressure gradients project surface material upward and outward in an outward-slanted curtain. This excavated material is deposited around the crater, creating an elevated rim and a surrounding layer known as the ejecta blanket.1
The specific characteristics of the blanket depend on the presence of an atmosphere:
- Airless bodies: Excavated particles follow ballistic trajectories, resulting in a blanket that is thickest at the crater rim and decreases steadily in thickness with distance.2
- Planetary bodies with atmospheres: Excavated material mixes with the atmosphere to create a surface-hugging fluid flow, similar to a pyroclastic flow. This process produces a blanket of relatively constant thickness that terminates abruptly at its outer edge.2
On planets like Mars, these flows may also be influenced by the presence of near-surface water, which can contribute to the formation of mudflows.2