The Origin of (90) Antiope From Component-Resolved Near-Infrared Spectroscopy

TL;DR

This study used component-resolved near-infrared spectroscopy to analyze the surfaces of the binary asteroid (90) Antiope, revealing similar surface compositions and suggesting a common origin, possibly from a rubble-pile breakup.

Contribution

First spectroscopic analysis of both components of (90) Antiope showing similar surface properties and constraining its possible formation scenarios.

Findings

Both components are likely C- or Cb-type asteroids.

Spectra show no significant absorption features for minerals, ices, or organics.

Surface reflectances of both components are very similar.

Abstract

The origin of the similary-sized binary asteroid (90) Antiope remains an unsolved puzzle. To constrain the origin of this unique double system, we recorded individual spectra of the components using SPIFFI, a near-infrared integral field spectrograph fed by SINFONI, an adaptive optics module available on VLT-UT4. Using our previously published orbital model, we requested telescope time when the separation of the components of (90) Antiope was larger than 0.087", to minimize the contamination between components, during the February 2009 opposition. Several multi-spectral data-cubes in J band (SNR=40) and H+K band (SNR=100) were recorded in three epochs and revealed the two components of (90) Antiope. After developing a specific photometric extraction method and running an error analysis by Monte-Carlo simulations, we successfully extracted reliable spectra of both components from 1.1 to 2.4 um taken on the night of February 21, 2009. These spectra do not display any significant absorption features due to mafic mineral, ices, or organics, and their slopes are in agreement with both components being C- or Cb- type asteroids. Their constant flux ratio indicates that both components' surface reflectances are quite similar, with a 1-sigma variation of 7%. By comparison with 2MASS J, H, K color distribution of observed Themis family members, we conclude that both bodies were most likely formed at the same time and from the same material. The similarly-sized system could indeed be the result of the breakup of a rubble-pile proto-Antiope into two equal-sized bodies, but other scenarios of formation implying a common origin should also be considered.