  (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.
