Band 8 flux density as a function of the distance from the Sun with the diameter as the parameter, in 10³ km and next to or atop the curves and arbitrarily limited to 6000 km, i.e., slightly smaller than the diameter of Mars. Both the surface temperature and radius are a priori undetermined. A few known TNOs with their names are shown with red dots (www.minorplanetcenter.org/iau/lists/Sizes.html.). In parentheses, the apparent diameter in milli-arcseconds and the estimated blackbody temperature are given. The size of the ALMA synthesized beam, θ = 120 mas, is given in the upper right corner, confirming that these objects would be point-like to ALMA. The observed Band 8 flux density of the unidentified object is indicated by the horizontal blue-shaded dashed line (± 1σ). The distance to the U source remains to be determined.