The Material Properties of Asteroids and Comets - Implications for Planetary Defence Strategies

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M.J. Genge (1999), JBIS, 52, 95-110

Refcode: 1999.52.95

The impact of bodies which are too small to cause global mass extinctions pose a hazard to humankind due to the relatively high frequency of such collisions. The material properties of small asteroids and comets significantly affect the outcome of both impact and planetary defence strategies that might be employed. The material properties of Earth-crossing objects are discussed in the current paper by comparison with those of meteorites and micrometeorites in order to identify a hazard scale for sub-critical impactors based on both their material and orbital properties. Simulations of atmospheric entry of small asteroids and comets which consider their fragmentation were conducted and suggest a maximum hazard of ~140 average fatalities per year which is dominated by extinct Halley family comets. The results also suggest that abundant asteroid types present a greater hazard than certain groups of comets with increasing size. The implications of the material properties of small asteroids and comets for planetary defence techniques were also considered to evaluate whether object specific strategies need to be adopted for the mitigation of impact threats. Simple approximations to the fragmentation behaviour of small asteroids and comets suggest there are minimum interception times for the deflection of hazardous objects below which disruption will occur. It may not be possible to deflect even small comets without significant disruption at interception times less than a few months. These results emphasise the need for early detection and interception of hazardous objects and the need for taxonomic characterisation to be incorporated into follow up detection operations.

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