Tuesday, January 7, 2014

X marks the spot on the floor of Stevinus

Fractured mound, approximately 3 km in width, on the northeastern floor of Stevinus crater (71.54 km; 32.490°S, 54.137°E) LROC Narrow Angle Camera observation M1131495601R, LRO orbit 18872, August 18, 2013; resolution 78 cm per pixel [NASA/GSFC/Arizona State University].
Raquel Nuno
LROC News System

Today’s Featured Image is an LROC NAC image of an elongated mound (positive relief feature) located on the floor of Stevinus crater [32.49°S, 54.14°E]. The mound has a central fracture along its length, which intersects another perpendicular fracture, forming an "X".

Many mounds of various shapes and sizes are found on the floor of Stevinus crater, but most of them do not have fractures. How did the cracks form on this mound? Perhaps the mound was caused by the upwelling of impact melt beneath a thin solidified crust, as a hardened crust was pushed up it fractured forming the X. Similar morphologies are commonly observed on pahoehoe lava surfaces on the Earth and are known as tumuli.

Context for the 3 km fractured mound on the northeastern interior of Stevinus, and near center of this full-resolution crop from medium resolution Lunar Orbiter frame 5040, processed by the United State Geological Service. Lunar Orbiter V, from 163.74 km; 73.37° incidence angle [NASA/JPL/USGS/LPI].
Detail northeastern interior Stevinus, centered on the 3 km fractured mound, from LROC Wide Angle Camera (WAC) observation M177278416CE (604 nm), LRO orbit 11261, November 11, 2011; 69.71° incidence, resolution 67.7 meters from 49.6 km [NASA/GSFC/Arizona State University].
Tumuli form when a slow moving lava beneath a brittle crust flows upward, due to an obstruction or a topographical discontinuity, causing the crust to fracture. In our FI, instead of lava, the molten material was impact melt.  Another difference between these lunar mounds and terrestrial tumuli is their size.  On Earth, tumuli are from 2 to 10 meters high; this lunar mound reaches a height of over 160 meters. This is probably due to the lower gravity on the Moon.

Stevinus and vicinity, arrow marks the fractured mound. LROC WAC observation M177278416CE (604 nm) in mosaic with three subsequent WAC observations from orbits 11262 and 11263, November 11, 2011. View the full-resolution mosaic HERE [NASA/GSFC/Arizona State University].
The rest of this spectacular processed LROC NAC observation can be seen HERE. Can you think of another formation mechanism?

Related LROC Posts:
Pancakes in a melt pond
The Domes of Stevinus Crater
Impact melt channel

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