Thursday, July 12, 2012

LROC: Simpelius Scarp

A lobate scarp formed in the far south nearside lunar highlands. Lunar scientists keep finding more of these tectonic features as LROC Narrow Angle Camera (NAC) high-resolution image coverage of the lunar surface continues to grow. An image from the Commissioning phase of the LRO mission, LROC NAC observation M106807247L, orbit 886, September 5, 2009; field of view is approximately 1000 meters wide, a 74.06° illumination incidence angle at 1 meter resolution from 42.59 km [NASA/GSFC/Arizona State University].
Drew Enns
LROC News System

Lobate scarps are, along with wrinkle ridges, one of the major contractional features found on the Moon. Though unlike wrinkle ridges, lunar lobate scarps form (almost) exclusively in the lunar highlands. This lobate scarp, designated Simpelius scarp, is located far to the south at 73.609°S, 8.764°E.

Unlike lobate scarps on other planets, the lunar scarps are fairly small with <100 meters maximum relief.

So how do such small features survive the onslaught of small impactors over time?

LROC QuickMap 64 meter resolution context for the Simpelius Scarp, located above the business end of the yellow arrow. At this scale and smaller the scarp is difficult to spot because it's small. [NASA/GSFC/Arizona State University].

The sharp features, lack of larger superposed craters, and cross-cutting relationship with small craters all imply that Simpelius scarp is young. The most compelling evidence that it is very young is simply that it exists at all. After about 100 million years the Moon's surface is saturated (every square inch of the surface has been reset with a crater of this size) with 100 meter diameter craters.

And the scarp is invisible altogether in this LROC QuickMap 1000 meter field of view covering the central meridian lunar surface south from 60°S to just beyond the ancient rim of South Pole-Aitken basin to Shackleton, host to the Moon's South Pole [NASA/GSFC/Arizona State University].
Since we can find only a very few craters of this size, the scarp must be significantly younger than that saturation age. If so, the Moon must have undergone compression recently, since lobate scarps are found everywhere on the Moon, and scientists are fairly certain that the Moon is still shrinking as its molten core continues to solidify and shrink. The crust is rigid and suffers brittle fracture, due to the shrinkage, that results in lobate scarp formation. Yes, the Moon is an active place just waiting for a network of seismometers to probe its interior!

Explore more of the lobate scarp in the full LROC NAC, HERE.

Related Posts:
Not Your Average Scarp
Tectonics in Mare Frigoris
Lobate Scarp or Fluidized Ejecta

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