On the formation and evolution of asteroid belts and their potential significance for life

Abstract

Suggestions have been made that asteroid belts may be important both for the existence of life and perhaps even for the evolution of complex life on a planet. Using numerical models for protoplanetary discs we calculate the location of the snow line, and we propose that asteroid belts are most likely to form in its vicinity. We then show that observations of warm dust in exo-solar systems, thought to be produced by collisions between asteroids in a belt, indicate that asteroid belts (when they exist), indeed coincide with the radial location and the temperature of the snow line. Giant planets form outside the snow line and prevent planet formation just inside of their orbit creating an asteroid belt there. However, the migration of giant planets through the asteroid belt likely disperses the compact formation. We examine existing observations of giant exo-planets and find that less than 4% are at radial locations outside of the snow line. This definitely may be the consequence of observational selection effects. However, with this caveat in mind, we point out that the dearth of giant planets outside the snow line may also suggest that compact asteroid belts are not common, and more speculatively that complex life may not expected in most of the currently observed systems.

What Sets the Radial Locations of Warm Debris Disks?

“…The actual location of the primordial snow line is less certain than its predicted relation with stellar mass, considering the uncertainty on the values of all the factors in Equation (1) and the fact that the primordial snow line location likely evolves with time. Nevertheless, Martin & Livio (2013b) did find that the absolute stellocentric distances of warm debris disks reported in the literature were roughly consistent with the location of the primordial snow line.…”

On the current distribution of main belt objects: Constraints for evolutionary models

“…The origin of these objects is most probably associated with the earlier stages of the solar system, during the accretion phase of the planetesimals and of the Sun itself. Further observational data will allow us to better understand the mixing processes of material and the structure of the early solar system in the presence of shifted snow line (Martin & Livio 2013). For the present, our limited understanding of disk structure, formation, and early evolution of planetary systems makes it difficult to obtain solid conclusions about this phase of the MB evolution.…”

“…Considering the evolution of the MB, the most meaningful distinction that can be obtained from taxonomy is whether an object is volatile-poor or volatile-rich, since this classification would indicate that they originally formed closer to or farther away from the Sun than the snow line (Martin & Livio 2013). In this regard, the most fundamental distinction would be between objects of classes belonging to the S-complex (Bus & Binzel 2002) and those classified in the C-or X-complexes (Bus & Binzel 2002), which also have low geometric albedos.…”

“…The peculiar position of the snow line, just in the middle of the MB at 2.7 AU (Martin & Livio 2013), would be the most obvious reason for the distinct compositions. However, as noted since the first surveys of compositions in the MB (e.g., Gradie & Tedesco 1982), the observational data show significant overlap and our analysis in Sect.…”

“…It is currently accepted that the MB consists of solid debris that remains after the clearing of the protoplanetary solar disk, which occurred during the latest stage of the giant planet formation (O'Brien & Sykes 2011;Martin & Livio 2013). The estimation of the initial mass of the MB as ∼0.15 M ⊕ was found in Weidenschilling (1977), where the surface of density of the solar nebula was reconstructed by spreading the masses of the solar system planets through zones surrounding their orbits.…”