Comet 361P/2017 S4 = 361P/2006 UR₁₁₁ (Spacewatch)

Discovery

E. Lilly, R. J. Wainscoat, and R. Weryk (Institute for Astronomy, University of Hawaii) reported the discovery of another apparent comet on four w-band CCD exposures taken with the 1.8-m Pan-STARRS1 telescope at Haleakala on 2017 Sept. 24.4 UT, together with earlier Pan-STARRS1 observations found subsequently back to Sept. 11. In each image, the object appeared slightly extended compared to nearby stars, and in a stacked image, there is possible evidence for a broad, low-surface-brightness tail extending towards position angle approximately 250 degrees.

Already on Sept. 24, Weryk suggested that the comet may be identical to an apparently asteroidal object of mag 19.7-20.3 discovered on 2006 Oct. 19 on Spacewatch images taken by J. V. Scotti with the Steward Observatory 0.9-m telescope at Kitt Peak; there had been other Spacewatch observations also that same month, back to Oct. 11, and the object was then given the minor-planet designation 2006 UR₁₁₁ (cf. MPS 184334). Gareth Williams (Minor Planet Center) confirmed the linkage, and it was announced with both designations and then quickly numbered 361P.

The discovery details were announced on CBET 4433.