Observations of "fresh" and weathered surfaces on asteroid pairs and their implications on the rotational-fission mechanism
Abstract
The rotational-fission of a "rubble-pile" structured asteroid can result in an "asteroid pair" - two unbound asteroids sharing nearly identical heliocentric orbits. Models suggest that this mechanism exposes material from below the progenitor surface that previously had never have been exposed to the weathering conditions of space.
Therefore, the surfaces of asteroid pairs offer the opportunity to observe non-weathered "fresh" spectra. Here we report near-infrared spectroscopic observations of 31 asteroids in pairs.
In order to search for spectral indications of fresh surfaces we analyze their spectral slopes, parameters of their 1 μm absorption band and taxonomic classification. Additionally, through backward dynamical integration we estimate the time elapsed since the disintegration of the pairs' progenitors.
Analyzing the 19 ordinary chondrite-like (S-complex) objects in our sample, we find two Q-type Asteroids (19289 and 54827) that are the first of their kind to be observed in the main-belt of asteroids over the full visible and near-infrared range. This solidly demonstrates that the Q-type taxonomy is not limited to the NEA population.
The pairs in our sample present a range of fresh and weathered surfaces with no clear evidence for a correlation with the ages of the pairs. However, our sample includes "old" pairs (2 x 106 > age >- 1 x 106 years) that present relatively low, meteoritic-like spectral slopes (<0.2% per μm).
This illustrates a timescale of at least TILDE OPERATOR+D912 myr before an object develops high spectral slope that is typical for S-type asteroids.