Probabilistic Assessment of Tunguska-scale Asteroid Impacts and Frequencies

Asteroids exhibit very diverse properties, with densities, strengths, and structural compositions ranging from monolithic iron bodies to loosely bound rubble piles. These varied properties, along with different impact velocities and entry angles, could greatly affect the amount of damage an asteroid of a given size could cause if it strikes the Earth. The 1908 Tunguska event provides a rare source of evidence for characterizing these effects, and many studies have attempted to infer the object's size, properties, or impact characteristics. However, most such studies only consider small subset of cases, employing selective assumptions of representative properties. In this study, we used our Probabilistic Asteroid Impact Risk (PAIR) model to more broadly characterize the range and relative likelihood of asteroid properties that could yield Tunguska-scale impacts. We modeled the entry, airburst, and ground damage from 50 million Tunguska-scale asteroid impacts, which were sampled from probabilistic distributions that represent current knowledge of asteroid properties and size frequencies. Results demonstrate that a broad range of asteroid characteristics can produce Tunguska-like airburst events and emphasize the relative probabilities among them. A key result is that Tunguska-scale ground damage is more likely to be caused by asteroids around 70 m in diameter or 25 Mt of initial impact energy, which is on the larger end of estimated size and energy ranges. Even when relative size frequencies are accounted for, the greater damage potential of larger objects outweighs their rarity, while the low damage potential of small objects counteracts their frequency. The study also evaluates impact frequencies as a function of size, mass, energy, and blast damage, and demonstrates that accounting for realistic distributions of asteroid properties can significantly reduce expected impact intervals and increase risk compared to estimates based on mean albedo, density, and velocity assumptions.