Airburst Surface Damage and Risk Assessment: Sensitivity to Assumptions
Abstract
Chyba et al. (1993) estimated the surface effects of the 1908 Tunguska airburst using the altitude of maximum energy deposition from a pancake model as their proxy for the equivalent static height of a static burst. After the 1994 impact of Comet Shoemaker-Levy 9, different modeling groups came to different conclusions about the maximum depth achieved by fragments. The Sandia group argued for deeper penetration due in part to continued downward flow of vaporized comet after energy deposition was complete. Boslough & Crawford (2008) made a similar case for Tunguska, arguing that the "effective height of burst" can be significantly lower than the altitude of maximum energy deposition. They concluded that the observed damage can be attributed to downward-directed airburst with a lower total kinetic yield (3-5 Mt as opposed to 10- 20 Mt). Alternatively, Wheeler & Mathias (2019) take the point of maximum energy deposition as their static burst altitude, and conclude (in part on that basis) that the most probable Tunguska-scale yield is 20-30 Mt.
A Tunguska-like airburst is by far the most likely NEO disaster to take place in our lifetimes, so risk assessments rely on estimates of airburst damage as a function of size and frequency. Reducing risk uncertainty will require convergence on a consensus about the size of the Tunguska event, which in turn requires agreement on the difference (if any) between "effective height of burst" and peak energy deposition altitude, and how energy is coupled to the air and propagated to the surface. New simulations isolate that effect as a function of mass, entry angle, and velocity, suggesting that "effective height of burst" is a useful but oversimplified concept. In reality, there is no single effective height of burst, and a superposition of multiple heights of burst based on full energy deposition curve might provide a better way of estimating surface damage without a full physics simulation. An approximation that uses static burst at altitude at the point of peak energy deposition (or 50% energy loss) overestimates areas of some damage levels in some cases and underestimates them in others. Probabilistic asteroid impact risk models should be recalculated to account for this effect to determine if it makes a significant difference in airburst risk assessment.- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFMNH51C0781B
- Keywords:
-
- 4301 Atmospheric;
- NATURAL HAZARDS;
- 4314 Mathematical and computer modeling;
- NATURAL HAZARDS;
- 6008 Composition;
- PLANETARY SCIENCES: COMETS AND SMALL BODIES;
- 6022 Impact phenomena;
- PLANETARY SCIENCES: COMETS AND SMALL BODIES