The Unusual Kuiper Belt Object 2003 SQ317

TL;DR

This study presents photometric observations of Kuiper belt object 2013 SQ317, revealing an extremely elongated shape or binary nature, with implications for its density, composition, and relation to the Haumea family.

Contribution

First detailed photometric analysis of 2013 SQ317 indicating its possible binary structure and estimating its density and shape.

Findings

Large lightcurve amplitude suggests an elongated shape or binary structure.

Estimated density varies significantly depending on the model (binary vs. single object).

Potential identification as the second close binary in the Kuiper belt.

Abstract

We report photometric observations of Kuiper belt object 2013 SQ317 obtained between 2011 August 21 and 2011 November 1 at the 3.58 m New Technology Telescope, La Silla. We obtained a rotational lightcurve for 2013 SQ317 with a large peak-to-peak photometric range 0.85+/-0.05 mag, and a periodicity, P=7.210+/-0.001 hr. We also measure a nearly neutral broadband colour B-R=1.05+/-0.18 mag and a phase function with slope beta=0.95+/-0.41 mag/deg. The large lightcurve range implies an extremely elongated shape for 2013 SQ317, possibly as a single elongated object but most simply explained as a compact binary. If modelled as a compact binary near hydrostatic equilibrium, the bulk density of 2013 SQ317 is near 2670 kg m^(-3). If 2003 SQ317 is instead a single, elongated object, then its equilibrium density is about 860 kg m^(-3). These density estimates become uncertain at the 30% level if we relax the hydrostatic assumption and account for solid, "rubble pile"-type configurations. 2013 SQ317 has been associated with the Haumea family based on its orbital parameters and near-infrared colour; we discuss our findings in this context. If confirmed as a close binary, 2013 SQ317 will be the second object of its kind identified in the Kuiper belt.