Thursday, May 16, 2013

Dynamic Textures in the Farside Highland Terrain

Northeastern portion of unnamed crater ejecta, above 77°N latitude, in the farside north. LROC Narrow Angle Camera (NAC) M138600267R, LRO orbit 5559, September 8, 2010; sunlight angle of incidence 80.3° over a field of view 1080 meters across, resolution 1.08 meters per pixel, from 51.96 km. Image center 77.086°N, 200.336°E, incidence angle is 80.3° [NASA/GSFC/Arizona State University].
Hiroyuki Sato
LROC News System

This far side high latitude (just above 77°N) fresh crater (roughly 1.1 kilometers in diameter) presents striking linear patterns in its ejecta.

Due to the high latitudes, the incidence angle is always very high in this area (including in this image), which enhances subtle topographic features.

The ejecta source crater is toward bottom left (outside the image field of view), thus the ejecta landed with the velocity component in upper right (northeast) direction, consistent with linear stripes dominating this whole area of this Featured Image.

LROC Wide Angle Camera (WAC) observation shows the whole crater of interest, at the center of this 46.2 km-wide field of view captured at 79.7 meters per pixel. North a smaller fresh crater almost immediately to the south-southeast. Both these crater's fresh, bright and optically immature ejecta fields are visible in the HDTV stills from Japan's SELENE-1 orbiter Kaguya, below. LROC WAC M173944659C (643 nm), spacecraft orbit 10768, October 22, 2011 [NASA/GSFC/Arizona State University].
Context for the LROC NAC frame outlined in this crop from LROC WAC monochrome mosaic (100 meters per pixel) of the unnamed crater and surrounding vicinity, centered near 77.46°N, 200.83°E, image width is about 142 km. NAC footprint (blue box) and the location of today's Featured Image (white arrow) are indicated here [NASA/GSFC/Arizona State University].
Interestingly, the lower left (closest to the rim) and upper left corners of this image show a craggy, rough surface, while the right portion shows only the striped pattern. What causes such texture differences within the same ejecta blanket?

Demonstration of just how far north the crater of interest resides in this three-HDTV frame animation, showing an Earthrise over Plaskett crater in the Moon's far north as captured from Japan's lunar orbiter SELENE-1 ('Kaguya') in 2007. The crater later photographed from overhead from LRO is designated with an arrow in the final frame. A large reproduction of the final still can be viewed HERE [JAXA/NHK/SELENE].
One possibility is the impact melt content was enriched near the rim, increasing the cohesion among the rock fragments and decelerating the flow inducing multiple pressure ridges perpendicular to the flow direction. Perhaps variations in roughness of the pre-existing surface controlled the final look of the ejecta. What else?

Explore this fascinating ejecta morphology in full NAC frame (HERE), and find your own hypothesis and answers!

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Swept Surface
Ejecta Patterns

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