# Olivine-dominated A-type asteroids in the Main Belt: Distribution, Abundance and Relation to Families

## TL;DR

This study identifies and characterizes olivine-dominated A-type asteroids in the main belt, revealing their low abundance, wide distribution, and likely external origin, which informs understanding of differentiated asteroid remnants.

## Contribution

The paper doubles the known number of A-type asteroids and provides the first comprehensive estimate of their abundance and distribution in the main belt.

## Key findings

- A-type asteroids constitute less than 0.16% of main-belt objects larger than 2 km.
- Approximately 600 A-type asteroids are estimated to exist.
- A-type asteroids are evenly distributed and not concentrated in any asteroid family.

## Abstract

Differentiated asteroids are rare in the main asteroid belt despite evidence for ~100 distinct differentiated bodies in the meteorite record. We have sought to understand why so few main-belt asteroids differentiated and where those differentiated bodies or fragments reside. Using the Sloan Digital Sky Survey (SDSS) to search for a needle in a haystack we identify spectral A-type asteroid candidates, olivine-dominated asteroids that may represent mantle material of differentiated bodies. We have performed a near-infrared spectral survey with SpeX on the NASA IRTF and FIRE on the Magellan Telescope. We report results from having doubled the number of known A-type asteroids. We deduce a new estimate for the overall abundance and distribution of this class of olivine-dominated asteroids. We find A-type asteroids account for less than 0.16% of all main-belt objects larger than 2 km and estimate there are a total of ~600 A-type asteroids above that size. They are found rather evenly distributed throughout the main belt, are even detected at the distance of the Cybele region, and have no statistically significant concentration in any asteroid family. We conclude the most likely implication is the few fragments of olivine-dominated material in the main belt did not form locally, but instead were implanted as collisional fragments of bodies that formed elsewhere.