Tuesday, June 18, 2013

"Ka Pow!" on Joliot's central peaks

High-reflectance ejecta and low-reflectance impact melt streamers surround this fresh impact crater on the slopes of the central peak formation of Joliot crater. LROC Narrow Angle Camera (NAC) mosaic M189994606R, LRO orbit 13048, April 25, 2012; field of view 2.25 km, 43.12° angle of incidence at 1.11 meters per pixel resolution, from 147.53 km [NASA/GSFC/Arizona State University].
Lillian Ostrach
LROC News System

High-reflectance ejecta blankets the terrain surrounding a 650 meter diameter crater (26.525°N, 93.518°E).

From samples collected during the Apollo missions we know that high-reflectance ejecta represents recently exposed material that has not yet been affected by space weathering processes (maturity rays) or material exposed that is a different composition than the surrounding area (compositional rays).

The impact crater in the opening image formed near the base of the central peak of Joliot crater (172.79 km in diameter, 25.79°N, 93.39°E), the floor of which was partially flooded with volcanic material. What type of ejecta rays are observed in today's Featured Image - compositional or maturity?

LROC WAC monochrome mosaic of the central interior of Joliot crater, with a fresh impact (arrow) at the base of the central peak complex [NASA/GSFC/Arizona State University].
The crater formed on the base of the central peak which is likely highlands material. The rays extend outward more than two crater diameters onto the mare material. Thus we have an example that is both a maturity ray and compositional ray. Over time as the ejecta matures, the portion on the highlands material will be indistinguishable, while the portion on the mare will still be visible. The much larger crater Tycho (93 km diameter) shows the same combination maturity-compositional rays.

Explore the full LROC NAC image for yourself; HERE. Do you see evidence for impact melt and if so, what do you see (ponds, streamers, flows)?

Related Posts:
Polka-dot Ejecta
Ejecta Starburst
Symmetric Ejecta
Ejecta Sweeps The Surface
Minty Fresh

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