A variety of geologic processes form boulders on the Moon. Some boulders are thrown out as ejecta during the impact process. Other boulders are found at the top of wrinkle ridges; members of the LROC Science Team have identified boulder populations atop lava flows and other lunar volcanic landforms; still other boulder fields are found on the floors of craters after eroding out of outcrops on the walls or central peak. Of course, when we say “erosion” in the context of lunar geology, we don't mean erosion the way one would use it for terrestrial geology. The Moon has no atmosphere, no rain, and no weather, so the main processes that would cause this sort of erosion on the Moon are the constant flux of bolide impacts, and to a lesser extent, seismic activity. So which of these processes produced the boulders in today's Featured Image? Looking at a context image helps.
The Featured Image shows an area near base of Tsiolkovskiy crater's central peak. Tsiolkovskiy crater, located at -20.38°S, 128.97°E, is filled with mare basalts and has a prominent central peak. The boulders have rolled downhill from outcrops of rock at higher elevations, closer to the summit of the central peak. Central peaks are thought to be made up of the deepest materials exposed during an impact. So, these boulders present an excellent opportunity to enable future astronauts to sample materials from the deep lunar crust. But Tsiolkovskiy crater is not just interesting because of its large central peak. Tsiolkovskiy is also partially filled with mare basalt material, a relatively rare occurrence on the farside of the Moon. The combination of accessible deep crustal materials and mare basalts within traverse distance of each other make Tsiolkovskiy crater a high-priority target for future human and robotic lunar exploration.
Explore more of Tsiolkovskiy's central peak and find the source of the boulders in the full LROC NAC!
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Posted by Drew Enns on July 11, 2012 13:21.