Unraveling the role of gravity in shaping intruder dynamics within vibrated granular media

Our experiments aboard the Chinese Space Station reveal a gravity-driven transition in intruder dynamics within vibrated granular media. While vibrations typically enable an intruder to ascend in a granular bed, low-gravity conditions induce it to descend under similar vibrations. Using a Hall-sensor array tracking method, we monitor the intruder’s movement throughout each vibration cycle and identified two competing mechanisms: inertia and gravity-dependent penetration. As gravity decreases, we observe a significant reduction in the scaled damping coefficient and hydrostatic pressure coefficient indicating that bed particles disperse more readily upon intruder impact, facilitating deeper penetration. Our findings highlight a critical transition from downward to upward motion of the intruder as vibration acceleration exceeds a threshold, which increases as gravity decreases. These insights into intruder dynamics in low-gravity environments have significant implications for asteroid exploration and lunar base construction, enhancing our understanding of the Brazil nut effect and the formation of planetesimal. Granular segregation may play a role in shaping the surface features of small celestial bodies such as asteroids that can be explained with the Brazil-nut effect. The authors study intruder dynamics in granular media on board the Chinese Space Station, finding that contrary to what occurs on Earth intruders tend to descend in microgravity conditions under specific vibration parameters