3:30 PM - 3:45 PM
[SCG62-11] Shape relaxation of quasi-2D crater by vibration
Keywords:Crater, Vibration, Experiment of geographical relaxation
There are numerous craters on the surface of celestial bodies, including the Moon, other planets, and asteroids. Of cource, each crater was formed at a different time, and there are some differences in shape between relatively young craters and old ones that have experienced various degradation events for a long time. For instance, younger craters have sharp rims, whereas older ones have low and vague rims. One of the main factors contributing to this type of crater relaxation is thought to be vibration caused by meteorite impacts. However, there are few quantitative studies based on laboratory experiments regarding this relaxation process and its timescale.
In this study, we focused on the crater-shape relaxation caused by vibrations and conducted quasi-two-dimensional experiments. Since the acceleration of vibrations varies depending on various factors like the size of the impacting meteorite, the vibration acceleration is considered the most crucial parameter in this study. We aimed to experimentally clarify the effect of vibration acceleration on the timescale of crater relaxation. To observe the crater shape degradation, we constructed an acrylic container with a width of 150 mm, a height of 100 mm, and a thickness of 10 mm. In this container, we created an initial crater shape by pressing a triangular wooden mold into a bed of 0.4 mm glass beads. The wooden mold had a base width of 100 mm and a height of 20 mm. This size was determined based on the tendency of fresh lunar craters to have a diameter-to-depth ratio close to 10:2. Besides, this ratio is more or less close to the repose angle of the glass beads used in the experiment. After preparing the initial crater, we applied vertical vibrations and recorded the variation in crater shape using a camera. The applied vibration was a 100 Hz sinusoidal wave, and its maximum acceleration amplitude was varied in eight steps of 0.5 G from 0.5 G to 4 G. Here, G=9.8 m/s2 is gravitational acceleration. We binarized the images obtained by the experiment. The boundary shape was identified, and its shape was linearly fitted. Then, the standard deviation of the residuals from this linear fit was used to characterize the degree of freshness of the crater shape. This residuals-from-linear-fit method was chosen because the final shape did not always achieve the completely horizontal final shape. In some cases, the surface with a linear slope is stabilized. The method allowed us to track variations in crater shape even under such conditions. We examined the temporal variation of the absolute mean of the residuals at each acceleration and discussed the relationship between vibration acceleration and its relaxation timescale.
The specific data obtained through this experiment will be introduced in this presentation. The obtained results indicate that acceleration of vibrations clearly influence crater relaxation. We observed a tendency for crater relaxation to progress more rapidly as acceleration of vibrations increased. On the other hand, at around 1 G or lower accelerations, crater relaxation progressed very slowly or hardly occurred at all, indicating different behaviors.
In this study, we focused on the crater-shape relaxation caused by vibrations and conducted quasi-two-dimensional experiments. Since the acceleration of vibrations varies depending on various factors like the size of the impacting meteorite, the vibration acceleration is considered the most crucial parameter in this study. We aimed to experimentally clarify the effect of vibration acceleration on the timescale of crater relaxation. To observe the crater shape degradation, we constructed an acrylic container with a width of 150 mm, a height of 100 mm, and a thickness of 10 mm. In this container, we created an initial crater shape by pressing a triangular wooden mold into a bed of 0.4 mm glass beads. The wooden mold had a base width of 100 mm and a height of 20 mm. This size was determined based on the tendency of fresh lunar craters to have a diameter-to-depth ratio close to 10:2. Besides, this ratio is more or less close to the repose angle of the glass beads used in the experiment. After preparing the initial crater, we applied vertical vibrations and recorded the variation in crater shape using a camera. The applied vibration was a 100 Hz sinusoidal wave, and its maximum acceleration amplitude was varied in eight steps of 0.5 G from 0.5 G to 4 G. Here, G=9.8 m/s2 is gravitational acceleration. We binarized the images obtained by the experiment. The boundary shape was identified, and its shape was linearly fitted. Then, the standard deviation of the residuals from this linear fit was used to characterize the degree of freshness of the crater shape. This residuals-from-linear-fit method was chosen because the final shape did not always achieve the completely horizontal final shape. In some cases, the surface with a linear slope is stabilized. The method allowed us to track variations in crater shape even under such conditions. We examined the temporal variation of the absolute mean of the residuals at each acceleration and discussed the relationship between vibration acceleration and its relaxation timescale.
The specific data obtained through this experiment will be introduced in this presentation. The obtained results indicate that acceleration of vibrations clearly influence crater relaxation. We observed a tendency for crater relaxation to progress more rapidly as acceleration of vibrations increased. On the other hand, at around 1 G or lower accelerations, crater relaxation progressed very slowly or hardly occurred at all, indicating different behaviors.