2007 TY430: A Cold Classical Kuiper Belt Type Binary in the Plutino Population

TL;DR

2007 TY430 is the first wide, equal-sized binary discovered in the 3:2 Neptune resonance, with ultra-red colors and a likely origin as a primordial cold classical Kuiper Belt object that was later captured.

Contribution

This paper reports the discovery and detailed analysis of 2007 TY430, the first known wide, equal-sized binary in the 3:2 resonance, providing insights into its formation and orbital characteristics.

Findings

2007 TY430 has a mutual orbit period of ~961 days.

The binary components are ultra-red and nearly equal in size.

Simulations suggest it is a captured cold classical object.

Abstract

(Abridged) 2007 TY430 is the first wide, equal-sized, binary known in the 3:2 mean motion resonance with Neptune. The binary has a maximum separation of 1 arcsec with less than 0.1 mags difference between components with identical ultra-red colors (g-i=1.49+-0.01 mags). The orbit of the mutual components was found to have a period of 961.2+-4.6 days with a semi-major axis of 21000+-160 km and eccentricity of 0.1529+-0.0028. The inclination is 15.68+-0.22 degs and the mirror orbit rejected at high confidence. The total system mass is 7.90+-0.21 x 10^17 kg. Equal-sized, wide binaries and ultra-red colors are common in the low inclination "cold" classical part of the Kuiper Belt and likely formed through some sort of three body interactions within a much denser Kuiper Belt. To date 2007 TY430 is the only ultra-red, equal-sized binary known outside of the classical Kuiper belt. Numerical simulations suggest 2007 TY430 is moderately unstable in the outer part of the 3:2 resonance and thus 2007 TY430 is likely an escaped "cold" classical object that later got trapped in resonance. Similar to the known binaries in the cold classical population, 2007 TY430 requires a high albedo and very low density to obtain the total mass found. For a realistic minimum density of 0.5 g/cm^3 the albedo of 2007 TY430 would be greater than 0.17. The radii of either component should be less than 60 km and thus the relatively low eccentricity of the binary is interesting since no tides should be operating on the bodies. The low prograde inclination of the binary also makes it unlikely the Kozai mechanism has altered the orbit, making 2007 TY430 likely one of the few relatively unaltered primordial binary orbits known. Under some binary formation models, the low inclination prograde orbit of the 2007 TY430 binary indicates formation within a relatively high velocity regime in the Kuiper Belt.