The unusual Kuiper belt object 2003 SQ317

Abstract

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