Friday, July 18, 2014

Dorsum Nicol

This tectonic feature was formed as stresses built up in the lunar surface until it gave way. The energy released was immense, and the displaced rock is the north-south trending wrinkle ridge seen today in southeast Mare Serenitatis. LROC NAC-derived digital terrain model, slope angle and recent imagery. Field of view is 4765 meters across [NASA/GSFC/Arizona State University].
Aaron Boyd
LROC News System

Dorsum Nicol is a wrinkle ridge found in southern Mare Serenitatis.

The opening Featured Image is a LROC NAC image, juxtaposed with a slope map, NAC-derived DTM and recent LROC NAC observation of area.

Slope maps are useful to planetary scientists because topographic features like craters and small ridges really stand out. At the  location in the LROC Featured Image field of view, the mare on the west side of the ridge is about 100 meters higher in elevation than the mare on east side of the wrinkle ridge, and the peak elevation is around 50 meters above that (see profile below).

Elevation profile across Dorsum Nicol, at field of view for LROC  Featured Image released July 17, 2014. (Points A and B correspond to A and B in LROC WAC context image, below [NASA/GSFC/Arizona State University].
The difference in elevation between the eastern and western flanks of the ridge could be due to the lunar surface buckling and folding beneath the surface, or it could be from mare fill after the wrinkle ridge was formed.  Dorsum Nicol has a width of 10 km at its widest and 5 km at its narrowest. Take a look at the full feature in the context image below.

LROC WAC context image of Dorsum Nicol in Mare Serenitatis. The yellow box is the approximate location of today's Featured Image, the red box is the location of the full NAC DTM. A profile taken along the white line from A to B and is shown above. Context image spliced from LROC Wide Angle Camera (WAC) monochrome (604 nm) mosaic of three observations swept up over three sequential orbital passes (LRO orbits 9031-9033) June 8, 2011; incidence 75.86° resolution 58 meters from 42 km [NASA/GSFC/Arizona State University]. [NASA/GSFC/Arizona State University].
Wrinkle ridges are are surface expressions of compressional forces being released; they are seen in all large maria on the Moon. The loading from the massive flood basalts during mare volcanism could have caused the lithosphere to flex because the density of the flood basalts is higher than the anothositic highlands material. Buoyancy forces were at work here, causing viscoelastic relaxation and inducing forces in the mare rock.

Full-sized LROC WAC mosaic, from three sequential passes June 8, 2011. See full size mosaic HERE [NASA/GSFC/Arizona State University].
Southwestern Mare Serenitatis in HDTV. Dorsum Nichol (next to the ghost crater Brackett, butted up against Rimae Plinius, together with Dorsa Lister, and in the foreground, the belt of darker basalts encircling the entire impact basin, Rimae Plinius and Promontorium Archerusia are at lower left, a view Harrison Schmitt describes as close to what Apollo expeditions saw in orbit. From a HDTV still, captured from Japan's lunar orbiter Kaguya (SELENE-1) in 2008. See the original release image HERE [JAXA/NHK/SELENE].
These forces caused the once convex surface of the maria to become more planar as time went on. This is a problem because a plane has less area than a curved surface when they are bounded by the same radius. Where was the rock going to go? Well, the maria resisted this change in topology until something broke! Wrinkle ridges are the expression of that thrust fault behavior.

Locating Dorsum Nicol in southeast Mare Serenitatis is easier than actually seeing these features, through a modest telescope. The stacked photograph above, assembled by Astronominsk in Minsk, Belarus, was captured at the best illumination incidence for such a purpose, on June 28, 2009, right after local sunrise, before First Quarter (in an early evening sky, here on Earth). Locating Taurus Littrow valley, the landing site of Apollo 17, and Promontorium Archerusia, along with other features in the contact area between Mare Serenitatis and Mare Tranquillitatis are relatively easy, however, throughout the lunar day [Astronominsk].
Check out the full NAC frame on the the LROC DTM product page, HERE.

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