Planetary and exoplanetary Astronomy Lunch Seminar (PALS) for 2020-10-19

Series: Planetary and exoplanetary Astronomy Lunch Seminar (PALS)
Date: Monday 19-Oct-2020
Time: 11:15-12:15
Location: Online via Zoom (link sent out to the PALS distribution list prior to the talk)
Speaker: Joe DeMartini (UMD)
Title: The Motion of Surface Grains in Low Gravity Environments: Applications to Apophis, The Lunar Brazil-nut Effect, and Low-G Seismic Wave Propagation

The recent OSIRIS-REx and Hayabusa2 missions have shown the surfaces of rubble piles to be complex assemblies of grains ranging from sub-mm to meters in size. One of the best ways at understanding the physics occurring on these surfaces is using simulations. Our group is using the parallel N-body gravity tree code PKDGRAV to simulate granular dynamics in low-gravity on the surfaces of planetary and asteroidal bodies. In this talk, I will highlight three of our projects that focus on the motion of grains at or near the surface of bodies with overlying regolith layers. First, I will discuss our simulations (still in progress) to confirm laboratory experiments measuring the propagation speed of a seismic wave through a granular medium under different confining pressures. Then I will go over our recent project investigating the effects of particle shape on the vertical rise time of a large subsurface intruder in response to seismic influences by the Brazil-nut Effect -- a phenomenon which has mostly been investigated using spherical grains in both laboratory and simulated experiments. Finally, I will show the results of our simulations of the 2029 Apophis close encounter, with a focus on the expected dilation and spin change of the body during the close approach and what expected results one may see from a potential mission (in-situ or otherwise) focusing on Apophis during its upcoming perigee passage.

For further information contact PALS coordinator Dr. Lori Feaga at or (301)-405-1383.


Special accommodations for individuals with disabilities can be made by calling (301) 405-3001. It would be appreciated if we are notified at least one week in advance.


Directions and information about parking can be found here.

This page was automatically generated on: 15-Oct-2020.