Most small asteroids are defined as “rubble piles” or bodies with zero tensile strength and large bulk porosity. The cohesive forces that hold them together act at the grain scale, and their magnitude is often estimated from similar materials when used in simulations. Improving the accuracy of predictions of asteroid strengths requires suitable laboratory measurements of relevant materials, as well as increasing the availability of materials from sample return. Atomic force microscopy (AFM) is well suited for force measurements relative to particle–particle interactions. In this work, we use AFM force measurements to evaluate the cohesive forces that act between micron-sized grains. We investigate the effect of the sizes of the interacting grains of JSC-1 lunar simulant using three sample sizes (<45, 75–125, and 125–250
We present the results of a series of laboratory low-speed impacts (< 4 m s−1) of centimeter-sized spherical projectiles into simulated dry and icy regolith samples. The target material was comprised of JSC-1 (Johnson Space Center) lunar simulant grains in the size range 100–250
- NSF-PAR ID:
- 10484946
- Publisher / Repository:
- DOI PREFIX: 10.3847
- Date Published:
- Journal Name:
- The Planetary Science Journal
- Volume:
- 3
- Issue:
- 7
- ISSN:
- 2632-3338
- Format(s):
- Medium: X Size: Article No. 176
- Size(s):
- ["Article No. 176"]
- Sponsoring Org:
- National Science Foundation
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Abstract μ m) and three spherical AFM tip diameters (2μ m, 15μ m, and 45μ m). In all cases, adhesion forces were larger at ambient relative humidity (RH), where the water layer on the surface of the grains is more prominent, creating a larger meniscus between the tip and the grain upon contact. We observed weaker adhesion with larger grain/tip size, which can be attributed to the changing contact area between the samples and the tips. We expect that our approach will pave the way to a better understanding of regolith surface properties such as adhesion and cohesion and provide suitable input for models that can be used to predict the evolution of asteroids and their particle behaviors. -
Abstract The surfaces of many planetary bodies, including asteroids and small moons, are covered with dust to pebble-sized regolith held weakly to the surface by gravity and contact forces. Understanding the reaction of regolith to an external perturbation will allow for instruments, including sensors and anchoring mechanisms for use on such surfaces, to implement optimized design principles. We analyze the behavior of a flexible probe inserted into loose regolith simulant as a function of probe speed and ambient gravitational acceleration to explore the relevant dynamics. The EMPANADA experiment (Ejecta-Minimizing Protocols for Applications Needing Anchoring or Digging on Asteroids) flew on several parabolic flights. It employs a classic granular physics technique, photoelasticity, to quantify the dynamics of a flexible probe during its insertion into a system of bi-disperse, centimeter-sized model grains. We identify the force chain structure throughout the system during probe insertion at a variety of speeds and for four different levels of gravity: terrestrial, Martian, lunar, and microgravity. We identify discrete, stick-slip failure events that increase in frequency as a function of the gravitational acceleration. In microgravity environments, stick-slip behaviors are negligible, and we find that faster probe insertion can suppress stick-slip behaviors where they are present. We conclude that the mechanical response of regolith on rubble-pile asteroids is likely quite distinct from that found on larger planetary objects, and scaling terrestrial experiments to microgravity conditions may not capture the full physical dynamics.more » « less
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