The population of small near-Earth objects: composition, source regions and rotational properties

TL;DR

This study provides a detailed survey of small near-Earth objects, analyzing their composition, source regions, and rotational properties, revealing dominant spectral types and new subclasses, with implications for impact risk assessment.

Contribution

It presents the first comprehensive photometric and spectroscopic survey of small NEOs, identifying a new Sx spectral subclass and analyzing their source regions and rotational characteristics.

Findings

S-complex asteroids are ~66% of the sample.

Most NEOs have compositions consistent with LL-chondrites.

Identified a new Sx spectral subclass within the S-complex.

Abstract

The study of small ($<$300 m) near-Earth objects (NEOs) is important because they are more closely related than larger objects to the precursors of meteorites that fall on Earth. Collisions of these bodies with Earth are also more frequent. Although such collisions cannot produce massive extinction events, they can still produce significant local damage. Here we present the results of a photometric and spectroscopic survey of small NEOs, which include near-infrared (NIR) spectra of 84 objects with a mean diameter of 126 m and photometric data of 59 objects with a mean diameter of 87 m. We found that S-complex asteroids are the most abundant among the NEOs, comprising $\sim$66\% of the sample. Most asteroids in the S-complex were found to have compositions consistent with LL-chondrites. Our study revealed the existence of NEOs with spectral characteristics similar to those in the S-complex, but that could be hidden within the C- or X-complex due to their weak absorption bands. We suggest that the presence of metal or shock-darkening could be responsible for the attenuation of the absorption bands. These objects have been grouped into a new subclass within the S-complex called Sx-types. The dynamical modeling showed that 83\% of the NEOs escaped from the $\nu_{6}$ resonance, 16\% from the 3:1 and just 1\% from the 5:2 resonance. Lightcurves and rotational periods were derived from the photometric data. No clear trend between the axis ratio and the absolute magnitude or rotational period of the NEOs was found.