9th IAA PLANETARY DEFENSE CONFERENCE 2025

HYPERVELOCITY CRATRING AND DISRUPTION OF THREE L-TYPE ORDINARY CHONDRITES

George J. Flynn(1), Melissa Strait(2), Daniel Durda(3) and Robert Macke(4)
1Dept. of Physics, SUNY-Plattsburgh, 101 Broad St., Plattsburgh, NY 12901 USA (01-518-564-3163, flynngj@plattsburgh.edu),
2Dept. of Chemistry, Alma College, Alma, MI 48801 USA (straitm@alma.edu),
3SwRI, 1050 Walnut St., S-300, Boulder CO 80302 USA (durda@boulder.swri.edu).
4Vatican Observatory, V-00120 Vatican City-State (rmacke@specola.va),

Keywords: Asteroid Deflection, Momentum Enhancement Factor, Disruption Energy

The response of asteroids to hypervelocity impact influences momentum transfer in cratering and fragmentation in disruptive collisions, which together limit the maximum change in velocity (VMAX) that can be imparted by a single kinetic impact. For Qc, the energy per unit target mass for onset of fragmentation,, the ratio of impactor momentum to momentum acquired by the target, and vi, the impactor mass:
VMAX = 2Qc/vi [1].
Hydrocode modeling indicates decreases with increasing target porosity, and, QD, the energy for the onset of catastrophic disruption, increases with increasing target porosity or decreasing target strength. To test this, we performed hypervelocity cratering and disruption experiments on three asteroid samples of similar compositions but different porosities (P): the low porosity L3 Ordinary Chondrite (OC) meteorite Aba Panu (P ~3%), intermediate porosity L3-6 OC Northwest Africa 869 (NWA 869) (P ~8%), and high porosity L4 OC Saratov (P ~14%).  followed the expected pattern:  = 3.5 for Aba Panu, 2.7 for NWA 869, and 2.5 for Saratov. However, the decrease in  is not as strong as suggested by modeling, which indicates that  should be <1.2 for targets with a porosity as high as Saratov. Although modeling indicated the energy required for catastrophic disruption should increase with porosity, our results deviated from this, with the highest porosity target Saratov having QD = 1,079 J/kg, comparable to the low-porosity OC Aba Panu (QD = 1,148 J/kg) but much lower than the 1,795 J/kg for the intermediate porosity OC NWA 869. Saratov’s low QD may result from the unusual structure of OC meteorites, consisting of strong, spherical chondrules embedded in porous, weaker matrix. As the amount of matrix is reduced, the porosity of OCs increases, and strength decreases. Love et al. [2] proposed a formula for disruptive events, where QD ∝ S0.45. Using this approach, we found a power law behavior (Figure 1) between QD/S0.45 and (1 – porosity), indicating that, for these three L-type OCs, the dependence of QD on strength can be separated from the dependence on porosity. Further, we determined Qc, the energy per unit target mass for the onset of fragmentation, from a plot of the impactor kinetic energy vs the mass of the largest fragment to the target mass, and calculated VMAX for an ~5 km/s impactor speed: 0.81 m/s for Aba Panu, 1.72 m/s for NWA 869, and 0.84 m/s for Saratov. The small difference between these VMAX values, compared to the factor-of-seven difference we reported between NWA 869 and the anhydrous carbonaceous chondrite NWA 4502 [1], suggests remote sensing showing an asteroid is similar to L-type OCs may be sufficient for selecting the impactor mass and speed for kinetic impact deflection that avoids significant fragmentation.

Figure 1: Log-log plot of Q*D/S0.45 vs. (1 - porosity) for three L-type OCs shows a linear behavior, indicating the effects of strength and porosity can be separated.

References: [1] G. J. Flynn et al., (2023) Proceedings of HVIS 2022, V001T06A002. doi.org/10.1115/HVIS2022-16. [2] S. G. Love et al. (1993) Icarus, 105, 216-224.