Olivine-rich asteroids in the near-Earth space

TL;DR

This study conducted a spectroscopic survey of near-Earth asteroids, identifying a higher-than-expected abundance of olivine-rich A-type objects, suggesting mantle fragments are more common at small sizes than previously thought.

Contribution

It provides the first large-scale estimate of olivine-rich asteroid abundance at small sizes, indicating these objects are more common than prior data suggested.

Findings

A-type NEAs constitute about 5.4% of observed small NEAs.

The abundance of olivine-rich objects is at least five times higher than previously known.

Results support the 'battered-to-bits' scenario for small asteroid populations.

Abstract

In the framework of a 30-night spectroscopic survey of small near-Earth asteroids (NEAs) we present new results regarding the identification of olivine-rich objects. The following NEAs were classified as A-type using visible spectra obtained with 3.6 m NTT telescope: (293726) 2007 RQ17, (444584) 2006 UK, 2012 NP, 2014 YS34, 2015 HB117, 2015 LH, 2015 TB179, 2015 TW144. We determined a relative abundance of $5.4\% $ (8 out of 147 observed targets) A-types at hundred meter size range of NEAs population. The ratio is at least five times larger compared with the previously known A-types, which represent less than $\sim1\%$ of NEAs taxonomically classified. By taking into account that part of our targets may not be confirmed as olivine-rich asteroids by their near-infrared spectra, or they can have a nebular origin, our result provides an upper-limit estimation of mantle fragments at size ranges bellow 300m. Our findings are compared with the "battered-to-bits" scenario, claiming that at small sizes the olivine-rich objects should be more abundant when compared with basaltic and iron ones.