2004 TT₃₅₇: A Potential Contact Binary in the Trans-Neptunian Belt

We report photometric observations of the trans-Neptunian object 2004 TT357 obtained in 2015 and 2017 using the 4.3 m Lowell's Discovery Channel Telescope. We derive a rotational period of 7.79 +/- 0.01. hr and a peak-to-peak lightcurve amplitude of 0.76 +/- 0.03. mag. 2004 TT357 displays a large variability that can be explained by a very elongated single object or can be due to a contact/close binary. The most likely scenario is that 2004 TT357 is a contact binary. If it is in hydrostatic equilibrium, we find that the lightcurve can be explained by a system with a mass ratio q(min) = 0.45 +/- 0.05, and a density rho(min) = 2 g cm(-3), or less likely a system with q(max) = 0.8 +/- 0.05, and rho(max) = 5 g cm(-3). Considering a single triaxial ellipsoid in hydrostatic equilibrium, we derive a lower limit to the density of 0.78 g cm(-3), and an elongation (a/b) of 2.01 assuming an equatorial view. From Hubble Space Telescope data, we report no resolved companion orbiting 2004 TT357. Despite an expected high fraction of contact binaries in the trans-Neptunian belt, 2001. QG(298) is the unique confirmed contact binary in the transNeptunian belt, and 2004 TT357 is only the second candidate to this class of systems, with 2003 SQ(317).