Wednesday, February 03, 2010

Impact Melt Flow at Byrgius A

Byrgius A (19 km diameter) is located west of Mare Humorum at 24.5°S, 63.7°W. Lunar geologists have known that this Copernican-aged crater is surrounded by an extensive system of bright rays, and that its ejecta blanket is rough, since the Apollo era of lunar exploration. Newly acquired LROC Narrow Angle Camera images reveal the exquisite state of preservation of many features related to to the formation of this young crater. These spectacular geologic features include impact melt pools, flows, levees, lobate margins, and delicate coatings on the crater interior. Because of the rain and wind that weather terrestrial geologic features, you cannot find ancient craters this well-preserved on Earth. However, you can find them on the moon, where billions of years of Solar System impact history are preserved. Exploring stunning features like the one you can see here will provide key insights into the geologic history of the moon, Earth and the other terrestrial planets.

Young lunar craters have deposits of lava-like material in and around the crater. Initially thought to be volcanic because of their flow-like morphology, these deposits are now known to have been formed by high shock pressures and related melting of materials at the impact site. Lunar impact melt deposits are observed as thin veneers, flows, and ponds. The state of preservation of these features tells us the crater is relatively young -- but how young? Recent age estimates from the Kaguya spacecraft put the Byrgius A impact at 48 million years old, but that age estimate will eventually need to be confirmed by collecting samples from this crater in order to be sure.

Spectacularly preserved viscous flow on the NE rim of Byrgius A (19 km diameter) crater. This flow has a form similar to lava flows on Earth, however it formed as a result of an asteroid or comet slamming into the moon at hyper-velocity (speeds exceeding 16 km/second, or 35,791 mph). So much energy was released in the impact, that solid rock was melted and thrown out of the crater where it flowed down the crater flanks. (Image width 810 meters.) Credit: NASA/Goddard/Arizona State University

The spectacular leveed flow you see above is about 3.2 km from the crater's rim crest. Distinctive lobes and surface flow features are seen 800 meters from the end of the flow. The flow averages 130 meters wide in this area, and both a primary channel (80 meters wide) and an inner channel (about 10 meters wide) are apparent. The delicate morphology of these features are enhanced by the extremely low Sun angle (75°) and the local tilt of the rim away from the Sun. The main flow terminates in a series of digitate lobes.

Related Links

› Arizona State University's Web site for the LRO Camera
› More images from Arizona State University's LROC site

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