The Old and the Young in Tsiolkovskiy

A recent impact narrowly missed an ancient extensional crack in the mare-filled floor, the northeast interior of Tsiolkovskiy crater (18.97°S, 130.34°E). That recent impact's crater is at lower left. An 800 meter-wide field of view from LROC Narrow Angle Camera (NAC) frame M161455429R, spacecraft orbit 8927, May 31, 2011; illumination from the east by northeast at 67.26° incidence at 61 cm per pixel resolution (in the original) from an altitude of 59 kilometers [NASA/GSFC/Arizona State University].

James Ashley

LROC News System

A common question from people examining the Moon through a small telescope for the first time is 'Why isn't the Earth covered with large craters like the Moon?' The first answer is that the Earth does have a number (more than 200) of known impact craters, but clearly nothing like the profusion of craters we see on the Moon. The more complete answer is that the Earth, during the first 600 million or so years of Solar System history, was indeed subject to the same relentless pounding that resulted in the Moon's population of large basins. However, early basins were subsequently obliterated by plate tectonics and surface weathering on the Earth. The Moon's features have been preserved because without wind, water, or plate tectonics, it takes a much, much longer time for the lunar surface to be reworked.

Today's Featured Image provides an example of this difference. We examine a length of shrinkage crack along the northern shore of Tsiolkovskiy's mare basalt volcanic deposits. Visible also in the WAC mosaic below, these features appear to result from contraction of the molten basaltic deposits during cooling. Also present (immediately adjacent to this portion of crack) is a relatively young impact crater. The two formation events are separated in time by several billion years, yet both present bouldery surfaces, and relatively sharp topographic expressions. Because of the slow rate of "space weathering," Lunar scientists must use more subtle indicators of freshness, or stratigraphic and other cross-cutting relationships, to determine the relative ages of landforms. The Apollo and Luna samples allow us to anchor portions of the lunar geologic time scale to radiometric age dates.

A12,922 line by 8,734 sample from a mosaic of both the left and right frames from LROC NAC observation M161455429, resampled to allow a medium resolution context for the field of view seen at higher resolution further above (white square). Again, that square represents approximately 800 meters and this re-sampling is about 4 kilometers across [NASA/GSFC/Arizona State University].

Compare the shadows within the linear feature to those of the recent impact in the southwest corner of the opening image. Because the crater is known to be an excavation, and the eastern walls of both features are in shadow, it is clear that the linear feature also shows negative relief. Contrast these shadows to those of this feature from within the same basin, which shows a similar outline, but represents a topographic high. Clearly several processes have been at work within these deposits. The crater is another example of a special type of impact feature called a bench crater (see October 17, 2012 LROC Featured Image).

LROC Wide Angle Camera (WAC) mosaic of the northeast quadrant of Tsiolkovskiy, field of view about 115 km across [NASA/GSFC/Arizona State University].

The full NAC image can be explored HERE. Other LROC Featured Images highlighting landforms related to mare tectonics include Tectonics in Mare Frigoris, and Not Your Average Scarp.

Since the very first grainy, misunderstood images of the Moon's far side were returned to Earth by the Soviet Union in 1959, Tsiolkovskiy immediately stood out, strongly underscoring the remarkable differences between the tidally locked hemispheres .

Weaving Boulder Trails on the Moon (July 12, 2012)
Bulging wrinkles at Tsiolkovskiy (January 11, 2012)