Ejecta
Written by Jerry Coffey
Ejecta is a term used for the debris that is ejected during the formation of an impact crater, material expelled in a stellar explosion or any one of a few other references. Since we are interested in astronomy here, I thought I would give the two most relevant definitions. It can contain shocked quartz, parts of the impactor, dust, or any debris that is ejected into the air and falls back to the ground or into the water.
Ejecta forms a covering in the area of the impact called the ejecta blanket. The ejecta blanket can be defined as "a generally symmetrical apron of ejecta that surrounds a crater; it is layered thickly at the crater’s rim and thin to discontinuous at the blanket’s outer edge. The falling debris forms an ejecta blanket surrounding the crater. Approximately half the volume of ejecta falls within 1 crater radius of the rim, or 2 radii from the center of the crater. The ejecta blanket becomes thinner with distance and increasingly discontinuous. Over 90% of the debris falls within approximately 5 radii of the center of the crater. Ejecta which falls within that area is considered proximal ejecta. Beyond 5 radii, the discontinuous debris is considered distal ejecta.
Ejecta behaves differently from place to place. On the Mars it apparently flowed across the ground, which may indicate that it had a mud-like consistency. On Mercury, it shot high into the air and blanketed the ground around the impact crater. Still, on Venus the ejecta is unusual in that its outer border commonly shows a lobed or flower-petal pattern, which suggests that much of it poured outward in a ground-hugging flow rather than arcing high above.
Ejecta may act differently from planet to planet and moon to moon, but it is all caused by one of two things. An asteroid impact or volcanic action. Cool stuff either way.
There is a little more research on ejecta here and here and an interesting related story here on Universe Today.
Filed under: Astronomy
Related stories on Universe Today
- 1000 Year-Old Supernova Remnant
- LCROSS Team Changes Target Crater for Impact
- Another "Where In The Universe" Challenge
- SMART-1 Ends in a Flash and Puff of Dust
- Central Peaks of Zucchius Crater
