Discovery and physical characterization of a large scattered disk object at 92 au

We report the observation and physical characterization of the possible dwarf planet 2014 UZ224 ("DeeDee"), a dynamically detached trans-Neptunian object discovered at 92 au. This object is currently the second-most distant known trans-Neptunian object with reported orbital elements, surpassed in distance only by the dwarf planet Eris. The object was discovered with an r-band magnitude of 23.0 in data collected by the Dark Energy Survey between 2014 and 2016. Its 1140 year orbit has (a,e,i)=(109 au,0.65,26.8. It will reach its perihelion distance of 38 au in the year 2142. Integrations of its orbit show it to be dynamically stable on Gyr timescales, with only weak interactions with Neptune. We have performed follow-up observations with ALMA, using 3 hr of on-source integration time to measure the object's thermal emission in the Rayleigh–Jeans tail. The signal is detected at 7s significance, from which we determine a V-band albedo of 13.1 -2.4+3.3(stat) -1.4+2.0(sys) percent and a diameter of 635 -61+57(stat) -39+32(sys) km, assuming a spherical body with uniform surface properties.