The main belt as a source of near-Earth asteroids

Abstract

We investigate the flux of main-belt asteroid fragments into resonant orbits converting them into near-Earth asteroids (NEAs), and the variability of this flux due to chance interasteroidal collisions. A numerical model is used, based on collisional physics consistent with the results of laboratory impact experiments. The assumed main-belt asteroid size distribution is derived from that of known asteroids extrapolated down to sizes of S 40 cm, modified in such a way to yield a quasi-stationary fragment production rate over times ZZ 100 Myr. The results show that the asteroid belt can supply a few hundred km-sizedNEAs per year, well enough to sustain the current population of such bodies. On the other hand, if our collisional physics is correct, the number of existing IO-km objects implies that these objects either have very long-lived orbits, or must come from a different source (i.e., comet,s). Our model predicts that the fragments supplied from the asteroid belt have initially a power-law size distribution somewhat steeper than the observed one, suggesting preferential removal of small objects. The component of t$he NEA population with dynamical lifetimes shorter than or of the order of 1 Myr can vary by a factor reaching up to a few tens, due to single large-scale collisions in the main belt; these fluctuations are enhanced for smaller bodies and faster evolutionary time scales. As a consequence, the Earth's cratering rate can also change by about an order of ma.gnitude over the 0.1 to 1 Myr time scales. Despite these sporadic spikes, when averaged over times of 10 Myr or longer the fluctuat,ions are unlikely to exceed a factor two.

Properties of the Near-Earth object population: the ACM 2005 view

“…Many observational factors indicate the mainbelt as their predominant source: their general matching of taxonomic and mineralogic distributions -especially for differentiated assemblages, their approximate same shapes and rotation, and their overall similar optical properties and surface structure. This conclusion does not contradict the recent results of dynamic considerations, according to which the main asteroid belt can supply a few hundred km-sized NEAs per 1 Myr, well enough to sustain the current population of asteroid-like NEOs (Menichella et al 1996).…”

The Population of Mars-Crossers: Classification and Dynamical Evolution

“…The proper combination of these sources may also depend on the considered interval of diameters of the asteroids. Previous studies (Menichella et al 1996) suggest that the source of subkilometer Earth-crossers could be main belt asteroids injected into strong resonances which increase their orbital eccentricity, such that they are led to Earth-crossing orbits. For subkilometer bodies, the number and frequency of collisions between asteroids close to these resonances seems sufficient to generate the required amount of material at the appropriate rate.…”

“…Therefore, to sustain via these resonances the population of Earth-crossing asteroids (denoted hereafter ECs)-also characterized by a short dynamical lifetime (<10 Myr)-in a steady state, the number of bodies injected into the resonance per unit of time would need to be much larger than previously assumed. While this may still be plausible for small bodies (up to 1 km in size) the scenario becomes unrealistic for multikilometer asteroids (Menichella et al 1996, Gladman et al 1997 for the following reason. Ten bodies larger than 5 km are presently known to be on Earth-crossing orbits, i.e.…”

Debiased Orbital and Absolute Magnitude Distribution of the Near-Earth Objects

“…Up to now, only order-of-magnitude estimates exist on the rates at which main belt asteroids are supplied to the ν 6 and 3 : 1 resonances via collisions (Farinella et al 1993, Menichella et al 1996, Rabinowitz 1997a,b, Zappalà et al 1999) or semimajor axis mobility caused by the Yarkovsky force (Farinella and Vokrouhlický 1999). Estimates of the number of NEOs supplied by the Mars-crosser population can be found in Migliorini et al (1998), Morbidelli and Nesvorný (1999), and Michel et al (2000b).…”

“…With a model of the collisional evolution of the asteroid belt, using ejection velocities derived from asteroid family studies, Menichella et al (1996) estimated that 160 bodies larger than 1 km in diameter are injected into these resonances per million years. Similar results have been obtained by Zappalà et al (1999).…”