Tuesday, August 20, 2013

Karpinskiy, superpositioned on the farside north

Karpinskiy WACGLD 100m
LROC Wide Angle Camera (WAC) mosaic overlaid with WAC and NAC-derived GLD100 color-coded digital elevation model. Karpinskiy crater is approximately 90 kilometers across and nested within the remains of an even larger and more ancient crater [NASA/GSFC/Arizona State University].
Raquel Nuno
LROC News System

Karpinskiy crater, at 72.609°N, 166.801°E and (officially 91.403 km) in diameter, rests within a larger and far older unnamed crater. How do we know which crater is older? Stratigraphic studies, or the study of superposition of rock layers (or in this case, craters), will help determine the relative ages of craters here. Geologists derive relative ages between geological features by observing how they overlap - young formations will always overlie older formations, and on airless bodies, such as the Moon and Mercury, this method becomes particularly useful. Without wind to erode its surface, only four factors affect the lunar surface: space weathering, impacts, tectonism, and volcanic resurfacing. With respect to today’s Featured Image, the Moon accumulates impact craters over time. From the cratering record we can investigate not only stratigraphic relationships (which crater formed first), but we can also derive a quantifiable measure, or crater density, to determine relative ages on the Moon.

Karpinskiy passes under Kaguya
The HDTV camera onboard Japan's lunar orbiter Kaguya (SELENE-1) anticipates a rising Earth in 2007, looking north toward the Moon's north pole as it passes ancient craters of the Farside Highlands Terrain, including Karpinskiy, nested in a much older crater, passing out of view at left, followed by Milankovic and Plaskett. View the full-size image HERE [JAXA/NHK/SELENE].
Today’s Featured Image is a great example for stratigraphic studies. The LROC WAC mosaic of Karpinskiy crater overlaid with the GLD100 color topography presents a clearer outline of the older crater (WAC mosaic below). The top portion of the image is black because the GLD100 product does not have coverage at that latitude (>79°N). Karpinskiy crater is located inside a much older, degraded crater that does not have a well-defined rim and is somewhat difficult to see in the WAC mosaic. Karpinskiy is younger because it superposes, or formed on top, of the unnamed older crater. There are younger craters superposed on the floor of Karpinskiy, that must have formed later and are therefore younger based on the relative age relationships. Thus, using stratigraphic relations we are able to derive a relative age for Karpinskiy, but what if we want to determine the absolute age? The number of craters that formed on Karpinskiy can be used to estimate its absolute age, however with such a small area the crater size frequency distribution absolute age estimate has a large uncertainty. To accurately determine the absolute age of Karpinskiy crater we have to go there and acquire samples of impact melt rock that we can radiometrically date!

Karpinskiy WAC superposition context
LROC WAC context image. Karpinskiy crater outlined in yellow, with the two neighboring craters to the north and east are Ricco, Milankovic and Milankovic E[NASA/GSFC/Arizona State University].
Explore the full image, HERE.

Related Posts:
Absolute Time
Copernicus Crater and The Lunar Timescale
Dating an Impact

1 comment:

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