LROC: Layered basalt on the wall of Marius A

Layered basalt on the wall of Marius A crater partially covered by debris flow. The crater rim is to the right and the crater floor is to the left. LROC Narrow Angle Camera (NAC) observation M137848463R, LRO orbit 5448, August 30, 2010; field of view of the original LROC Featured Image (HERE) 460 meters, at an illumination incidence angle of 33° from an altitude of 44.37 kilometers [NASA/GSFC/Arizona State University].

Sarah Braden
LROC News System

Marius A (12.58°N, 46.05°W) is an approximately 15 kilometer crater located in Mare Insularum. The Featured Image shows basalt layering partially covered by streaks of granular material that slid down from higher up on the wall. Craters with visible basalt layers like Marius A are windows to the history of basalt deposition. 

Each thin layer seen in the wall of Marius A is probably a single flow or flow lobe, each spreading out across the lunar surface due to the low viscosity of mare basalt (basalt has a viscosity similar to that of ketchup). How much time passed between each layer is still an unanswered question. By studying many craters with visible basalt flows, however, scientists may be able to piece together a more detailed, local history for the various mare on the lunar surface. Not all craters in the mare have visible mare basalt layering, though. Additionally, over time post-impact processes like the debris in today's Featured Image and slumping of the crater walls reduce the visibility of basalt layers.

Marius A at 62 meters resolution from LROC Wide Angle Camera (WAC) observation M135493956C, orbit 5101, August 3, 2010 in a field of view roughly 42 km across; incidence angle 57.09° from 44.1 km above. The much small field of view shown in detail in the Featured Image released November 29, 2011 is located at just shy of "3 o'clock" on the east crater rim wall [NASA/GSFC/Arizona State University].

LROC WAC context image of Marius A crater. The image is 59 km across and the rectangle indicates the area of the whole NAC frame from which the Featured Image is taken. View the full size and original LROC WAC context image HERE [NASA/GSFC/Arizona State University].

There are many craters with visible basalt layers and LROC has given us our first look at these incredible details of the lunar surface. Check out the NAC frame of Marius A and then explore the rest of the lunar maria!

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Marius A in a wider oblique context view from a virtual point 254 kilometers over the bright landmark crater Kepler, showing some of the more famous landmarks also nearby. One of the wispy rays of material and reflective secondary craters, superimposed upon Marius A by the Kepler impact event crosses directly upon Marius A and beyond, a distance of 280 kilometers from crater center to crater center [NASA/LMMP/GSFC/ARC/ASU].

Dark surface materials surrounding Rima Marius

Dark surface materials on the plateau surrounding Rima Marius (17.63°N, 309.02°E). LROC Narrow Angle Camera (NAC) observation M137882287R, LRO orbit 5453, August 31, 2010; solar illumination incidence 35°, image field of view is 660 meters. View the spectacular full-resolution LROC Featured Image HERE [NASA/GSFC/Arizona State University].

Hiroyuki Sato
LROC News System

The Moon's surface is thought to be covered almost everywhere by a layer of regolith. Regolith is a term meaning soil produced by weathering of local rock. On the Moon weathering is mostly caused by impacts, both large and small. In fact the smaller impacts, micrometeorite impacts, produce most of the upper portion of the regolith. An abundance of super fine and unconsolidated grains are produced by the astounding number of micro-impacts that have occurred over the past 4 billion years. In addition to rocks breaking apart into finer and finer fractions, over time space weathering makes rocks darker and redder. This effect is especially noticeable around steep surfaces where unweathered material slides down and stands in high contrast with its surroundings.

Medium resolution view of the full field of view (2.2 kilometers) showing Rima Marius as seen in LROC NAC observation M137882287R [NASA/GSFC/Arizona State University].

Today's Featured Image focuses on a portion of southern bank of Rima Marius. Dark material, likely mature regolith, shows forked shapes at the edge of the mare. How were these irregular patterns formed? They could be remnants of collapsing plateau edges, which exposes fresh and bright slope surface in between the dark remnants. Or it might be flow marks of darker materials. If these dark fingers are flows how did they form? Perhaps small moonquakes destablized mature regolith, which then slid a bit down the slopes of the rille?

LROC Wide Angle Camera (WAC) 100 meter-per-pixel monochrome mosaic of the vicinity of Rima Marius. The blue box and while arrow indicate locations of full NAC frame and the LROC Featured Image released May 17, 2011. View full-sized WAC context frame HERE [NASA/GSFC/Arizona State University].

Explore the walls of this fascinating rille by viewing the full NAC frame!

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