Dynamic sources of contemporary hazard from meteoroids and small asteroids

Ground-based observations of meteors and fireballs increase our data and statistics on meter-sized events entering the Earth’s atmosphere. Impacts by larger bodies are less frequent and telescopic surveys to find potentially hazardous objects are still crucial to infer the flux of these over long timescales. Telescopic surveys provide significant data on Near Earth Asteroids of few tens or hundreds of meters in diameter that can be only detected when these bodies are close to the Earth. Statistically, bodies with a diameter from a few meters up-to about a 100 m can be considered as the most direct source of contemporary hazard. Of course, larger bodies will do more damage, but impact less frequently. The behaviour of stony bodies interacting with the atmosphere is reasonably well known, but little is known about the either the flux or the behaviour of materials from dormant comets that are often associated with meteoroid streams and small Near Earth Objects. We will introduce some examples that meter-sized meteoroids following high-inclination, and eccentric orbits are not necessarily fragile, and can trace the existence of hazardous objects: dormant comets or Damocloids being an example. From all the available data, a better understanding of the rate at which asteroids impact the Earth can be derived. If meteoroids of cometary origin are included the flux of objects into the Earth’s atmosphere will be increased (Space Sci Rev 84(3/4): 327–471, 1998). However, the typical strengths of such meteoroids are too low to survive ablation in the upper atmosphere, so that they are unlikely to impact the ground. However, events such as that over Tunguska in 1908, where an air burst caused considerable damage over a large area, indicates that we should not underestimate fragile bodies as potentially hazardous sources. New missions aimed at returning samples of Near Earth Asteroids to Earth for analysis (Osiris-REx and Hayabusa 2) are very important because they will deliver to our laboratories materials probably non-sampled in meteorite collections. A better understanding of the composition of Near Earth Objects will allow the most efficient deflection techniques to be developed so that they present no hazard to human beings.