139P/Vaisala-Oterma (0139P)

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Type: Periodic Perihelion date: 9 December 2017 Perihelion distance (q): 3.4 Aphelion distance (Q) : 5.6 Period (years): 9.6 Eccentricity (e): 0.25 Inclination (i): 2.3 JPL orbit diagram COBS lightcurve During a routine asteroid search program at Turku, Yrjö Väisälä found this object on 7 October 1939 in Aries. The object was classed as an asteroid and designated 1939 TN. The magnitude was determined as 15.8. The object was further photographed on 18 and 20 October. The fourth and final observation came on 11 November. Precise positions were not published until 1979 and an orbit calculation by Liisi Oterma suggested the object was a comet. In addition, she communicated to the Central Bureau for Astronomical Telegrams in 1981 that a reexamination of the plates suggested the object was somewhat diffuse. The LINEAR program discovered an apparent asteroidal object on 18 November 1998. Additional positions were obtained on 18 and 21 November. The object was given the asteroidal designation 1998 WG22. S. Nakano subsequently noted the orbit was similar to that of 1939 TN and he successfully linked the two apparitions. D. Balam (Dominion Astrophysical Observatory) observed the object on 6 December using a 1.8-m reflector and noted a coma 8 arc seconds across and a tail extending 18 arc seconds toward PA 260 degrees. Observations (VEMag = visual equivalent magnitude) Date 10x10 mag Error VEmag Coma ' 25-Aug-17 19.68 0.03 18.5 0.2 27-Sep-17 19.29 0.21 18.9 0.2 18-Oct-17 19.01 0.07 18.7 0.2 29-Oct-17 18.72 0.07 18.0 0.2 19-Nov-17 18.67 0.10 18.1 0.2 04-Jan-18 19.06 0.08 18.4 0.2 13-Feb-18 19.67 0.18 19.1 0.2