(505478) 2013 UT15

 is an extreme trans-Neptunian object from the scattered disc, located in the outermost regions of the Solar System, approximately 260 km in diameter. It was discovered on 2 August 2013, by astronomers of the Outer Solar System Origins Survey at Mauna Kea Observatory, Hawaii, United States.

Orbit
With a semi-major axis of 196 AU, orbits the Sun at a distance of 43.9–348 AU once every 2,742 years. Its orbit has an eccentricity of 0.78 and an inclination of 11° with respect to the ecliptic. It has a similar orbit to, except for a smaller inclination.

belongs to a small number of detached objects with perihelion distances of 30 AU or more, and semi-major axes of 150 AU or more. Such objects can not reach such orbits without some perturbing object, which lead to the speculation of planet nine.

Spectral type
The object is estimated to have a bluish spectra (BB).

Diameter
has been estimated to measure 243 and 340 kilometers in diameter, based on an assumed albedo of 0.09 and 0.04, respectively. A generic magnitude-to-diameter conversion gives a mean-diameter of 260 kilometers, using with a typical albedo of 0.08 and a published absolute magnitude of 6.2951.

Numbering and naming
was numbered (505478) by the Minor Planet Center on 4 November 2017 (M.P.C. 107067). As of 2017, this minor planet has not received a name.