Rotational Characterization of Hayabusa II Target Asteroid (162173) 1999 JU3

TL;DR

This study provides detailed spectral analysis of asteroid 1999 JU3, suggesting a mostly homogeneous surface or small-scale heterogeneity, which informs expectations for the Hayabusa II sample return mission.

Contribution

It offers new visible and near-infrared spectra of 1999 JU3, evaluates surface heterogeneity, and discusses implications for the asteroid's composition and surface variability.

Findings

Spectral data show no significant variability across epochs.

Thermally altered carbonaceous chondrites are plausible analogs.

Surface heterogeneity, if present, is limited to small regions.

Abstract

The Japanese Space Agency's Hayabusa II mission is scheduled to rendezvous with and return a sample from the near-Earth asteroid (162173) 1999 JU3. Previous visible-wavelength spectra of this object show significant variability across multiple epochs which could be the result of a compositionally heterogeneous surface. We present new visible and near-infrared spectra to demonstrate that thermally altered carbonaceous chondrites are plausible compositional analogs, however this is a tentative association due to a lack of any prominent absorption features in our data. We have also conducted a series of high signal-to-noise visible-wavelength observations to investigate the reported surface heterogeneity. Our time series of visible spectra do not show evidence for variability at a precision level of a few percent. This result suggests two most likely possibilities. One, that the surface of 1999 JU3 is homogenous and that unaccounted for systematic effects are causing spectral variation across epochs. Or two, that the surface of 1999 JU3 is regionally heterogenous, in which case existing shape models suggest that any heterogeneity must be limited to terrains smaller than approximately 5% of the total surface area. These new observations represent the last opportunity before both the launch and return of the Hayabusa II spacecraft to perform ground-based characterization of this asteroid. Ultimately, these predictions for composition and surface properties will be tested upon completion of the mission.