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| A gradational distribution of boulders inside a crater. LROC Narrow Angle Camera (NAC) observation M176224625L, LRO orbit 11105, November 18, 2011; field of view 500 meters across at 0.51 meters resolution from 47.61 kilometers, incidence angle 55.29° [NASA/GSFC/Arizona State University]. |
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A distribution of boulders within the floor of an unnamed crater demonstrates physics at work. In the Featured Image (located in the lunar highlands at 6.275°N, 214.770°E) you can see that smaller boulders are (on average) closer to the boundary where the wall of the crater meets the floor. As distance increases from this boundary, the size of the individual boulders increases.
Why is this happening?
The larger boulders have more kinetic energy at the bottom of the slope due to their greater mass. Kinetic energy is 1/2 the mass times the velocity squared. So at the bottom of the crater wall, the more massive boulders will have more kinetic energy than the small boulders, even though they are all subject to the same acceleration due to the Moon's gravity. The crater floor is relatively flat, so the larger boulders will travel further than the small boulders before coming to a halt. An alternative explanation is that larger boulders originate preferentially from the rim of the crater and thus fall from a greater height on average compared to small boulders. Either way, the larger boulders have more kinetic energy when the reach the bottom of the crater.
During the Apollo 15 mission, Commander David Scott performed a related physics experiment live for the TV cameras! You can watch the video here: Apollo 15 Hammer and Feather Drop. He dropped a rock hammer and a feather from the same height at the same time. The point of the experiment was to show that in an environment with no atmospheric drag (a vacuum) the feather and the hammer will fall at the same speed (and hit the ground at the same time) regardless of the difference in mass. This basic idea is attributed to Galileo. Read more about the Apollo 15 experiment HERE.
Physics is fun, especially on the Moon!
Explore the entire NAC frame, HERE.
Related LROC Featured Images:
Crater Covered With Boulders
Ray of Boulders
Sampling a Central Peak
Why is this happening?
The larger boulders have more kinetic energy at the bottom of the slope due to their greater mass. Kinetic energy is 1/2 the mass times the velocity squared. So at the bottom of the crater wall, the more massive boulders will have more kinetic energy than the small boulders, even though they are all subject to the same acceleration due to the Moon's gravity. The crater floor is relatively flat, so the larger boulders will travel further than the small boulders before coming to a halt. An alternative explanation is that larger boulders originate preferentially from the rim of the crater and thus fall from a greater height on average compared to small boulders. Either way, the larger boulders have more kinetic energy when the reach the bottom of the crater.
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| Full width, 4000 lines in a mosaic of both left and right frames of LROC NAC M176224625 shows the tumbled mix of impact melt typical of craters with larger floors. The field of view at shown at full resolution in the Featured Image is the upper most contact between the crater floor and north wall [NASA/GSFC/Arizona State University]. |
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| August 2, 1971, Hadley Rille Delta Apollo 15 commander Dave Scott demonstrates the basic physics of falling objects on the surface of an airless body. In tribute to Galileo, Scott simultaneously drops a 1.32-kg aluminum geological hammer and a 0.03 kg falcon feather and both objects, falling at identical acceleration, reach the surface at the same time [NASA]. |
Physics is fun, especially on the Moon!
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| LROC Wide Angle Camera (WAC) context image, photographed as the LROC NAC (and LROC Featured Image) captured a much higher resolution field of view (asterisk) of the boulder distribution deep within this unnamed, young 12 km crater in the farside lunar highlands. LROC WAC observation M176217257C (643nm) LRO orbit 11105, November 18, 2011; resolution 62 meters per pixel [NASA/GSFC/Arizona State University] |
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| The crater is shown in greater, smaller-scale context, within a roughly 82 km-wide field of view; from a mosaic of LROC WAC observations captured in orbits 11104 and 11105, November 18, 2011. The wider region, northwest of Vavilov crater and northeast of the ancient South Pole-Aitken impact basin, is characterized by some of the highest elevations (and thickest crust) on the Moon. The nearest named crater, Artem'ev L, at upper right, received its official designation in 2006 [NASA/GSFC/Arizona State University]. |
Explore the entire NAC frame, HERE.
Related LROC Featured Images:
Crater Covered With Boulders
Ray of Boulders
Sampling a Central Peak
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