Origin of Asteroid (101955) Bennu and its Connection to the New Polana Family

TL;DR

This study investigates the connection between asteroid Bennu and the New Polana family by analyzing their spectral features, revealing differences in hydration that suggest a more complex origin or internal structure for Bennu.

Contribution

It provides new spectral analysis data of asteroid Polana and discusses implications for Bennu's origin and aqueous alteration history.

Findings

Polana lacks discernable 3-micron hydrated mineral absorption.

Bennu shows a significant 3-micron absorption feature.

Results suggest Bennu may not originate from the New Polana family or has a heterogeneous interior.

Abstract

The asteroid (142) Polana is classified as a B-type asteroid located in the inner Main Belt. This asteroid is the parent of the New Polana family, which has been proposed to be the likely source of primitive near-Earth asteroids such as the B-type asteroid (101955) Bennu. To investigate the compositional correlation between Polana and Bennu at the 3-micron band and their aqueous alteration histories, we analyzed the spectra of Polana in the ~2.0-4.0-micron spectral range using the NASA Infrared Telescope Facility in Hawaii. Our findings indicate that Polana does not exhibit discernable 3-micron hydrated mineral absorption (within 2 sigma), which is in contrast to asteroid Bennu. Bennu displayed a significant 3-micron absorption feature similar to CM- and CI-type carbonaceous chondrites. This suggests two possibilities: either Bennu did not originate from the New Polana family parented by asteroid Polana or the interior of Bennu's parent body was not homogenous, with diverse levels of aqueous alteration. Several explanations support the latter possibility, including heating due to shock waves and pressure, which could have caused the current dehydrated state of Bennu's parent body.