Friday, September 2, 2011

Pattern of dark deposits

A portion on the central peak of Vitello crater. LROC Narrow Angle Camera (NAC) observation M135433752L; LRO orbit 5092, August 3, 2010; resolution is 0.5 meter/pixel, field of view is only 600 meters with an Incidence angle of 61° with illumination from west-northwest. View the spectacular original close-up HERE  [NASA/GSFC/Arizona State University].
Hiroyuki Sato
LROC News System

Crater Vitello, located at the southern edge of Mare Humorum, is a floor fractured crater.

The slopes, including the fractures and central peaks are already degraded, and are almost completely covered by low-reflectance, fine-grained materials. Boulders are discernible on the slopes, but not fresh outcrops.

For context, the full 2100 meter width of LROC NAC frame M135433752L and it's north-south sweep over one promontory of the complex Vitello central peak complex. The 600 meter field of view shown in detail in the LROC Featured Image is just west of center [NASA/GSFC/Arizona State University].

Today's Featured Image is a portion of the Vitello central peak summit, displaying low-reflectance deposits between the relatively higher-reflectance portions covered by boulders. These low-reflectance deposits are found in many places on the crater floor and fill the topographic lows, except for the boulder-rich slopes. What is the origin of these low-reflectance deposits? Are they very mature regolith? If so, why are they mature only at topographic lows? Are these low-reflectance deposits examples of pyroclastic materials? If so, where is the source?
Most fully illuminated orbital views of Mare Humorum present such a jumble of albedo features that little relief can be readily perceived. Fortunately, among a large catalog of LROC Wide Angle Camera (WAC) observations is this 604 nm band mosaic from two sweeps of south central Mare Humorum (above) including Vitello (lower right - LRO orbits 4571- 4572, June 23, 2010). The view reveals some of the deeper elevation relationships between the heights of the south rim of Humorum and the nearside basin's floor, The LROC NAC frame sweeps over the taller of the three promontories of the Vitello central peak cluster. See a larger version HERE [NASA/GSFC/Arizona State University].
In the case of the pyroclastic deposits, fissure eruptions could be the source. However, in general, localized dark mantle deposits on the Moon are variable and tend to be thicker near the source fissure or vent. But in this case, the low-reflectance deposits on Vitello's floor are fairly uniformly distributed, and the exposed blocky, high-reflectance areas occur primarily on slopes. Consequently, these dark deposits might be a maturity effect, with mass wasting processes having exposed the higher-reflectance, brighter materials on slopes. More observations and analysis of other LRO NAC images in this crater, combined with analyses of the multispectral LRO Wide Angle Camera data, will shed additional light on the possible origin of these dark materials.
LROC WAC 71 meter/pixel monochrome (605 nm) mosaic around Vitello, centered near 30.38°S, 322.45°E. Blue frame and yellow box indicate the range of NAC frame M135433752L and the the LROC Featured Image, September 1, 2011. The original image above was stitched from four WAC orbital viewing opportunities, LRO orbits 4221-4224, May 26, 2010. See the full-size composition HERE [NASA/GSFC/Arizona State University].
Explore the low-reflectance deposits in Vitello crater in the full NAC frame!

Related posts:
Alphonsus crater mantled floor fracture
Rimae Posidonius
Gassendi's Fractures
The fractured floor of Compton

No comments: