31P/Schwassmann-Wachmann

(0031P)

TRY AGAIN 2026

Type: Periodic Perihelion date: 18 March 2028 Perihelion distance (q): 3.4 Aphelion distance (Q) : 5.0 Period (years): 8.7 Eccentricity (e): 0.19 Inclination (i): 4.5 JPL orbit diagram COBS lightcurve Atlas A. Schwassmann and A. A. Wachmann (Hamburg Observatory, Bergedorf, Germany) discovered this comet in southern Auriga on photographs exposed on 17 January 1929. It was described as magnitude 11. Shortly after the discovery was announced, prediscovery images were found on plates exposed at Yerkes Observatory, Harvard Observatory and Tokyo Observatory. The first predicted return was that of 1935 and astronomers realised the comet would be unfavourably placed. Nevertheless, early attempts were made to find the comet and on 11 December 1934 it was found by van Biesbroeck at magnitude 16.5. The indicated correction to the predicted perihelion date was -2.6 days. The comet has been seen at every apparition, with the comet frequently reaching magnitude 13 and sometimes becoming brighter than 12, as in 1942 and 1981. In 1973 L. Kresak suggested the comet could probably be seen throughout its orbit and therefore be classed as an annual comet. An attempt was made to find the comet as it passed through aphelion during December 1977, but these failed and the comet was not found until 14 December 1979. This marked the earliest the comet had ever been recovered, but further attempts were made to find the comet near aphelion. Although the comet has still not been seen at aphelion, astronomers came closer than ever before in 1991 when a Kitt Peak telescope found the comet on 12 September, nearly a year after aphelion and 865 days before perihelion. The comet experienced two close approaches to Jupiter during the 20th century and makes one more approach during the 21st century: • 0.18 AU from Jupiter on 22 March 1926 (decreased perihelion distance from 3.56 AU to 2.09 AU, decreased orbital period from 9.29 to 6.42 years) • 0.25 AU from Jupiter on 18 March 1997 (increased perihelion distance from 2.07 AU to 3.41 AU and increased orbital period from 6.39 to 8.72 years) • 0.84 AU from Jupiter on 28 November 2033 (will decrease perihelion distance from 3.41 AU to 2.90 AU and decrease orbital period from 8.70 to 7.76 years) Observations (VEMag = visual equivalent magnitude) Date 10x10 mag Error VEmag Coma ' 06-Oct-18 19.32 0.27 19.0 0.2 02-Dec-18 19.38 0.19 19.2 0.2 28-Dec-18 18.38 0.08 18.2 0.2 08-Jan-19 18.47 0.06 18.1 0.2 15-Jan-19 18.51 0.06 17.9 0.2 27-Dec-19 19.53 0.07 19.3 0.2 04-Jan-20 19.60 0.14 19.3 0.2 03-Feb-20 19.17 0.11 18.8 0.2 18-Feb-20 19.21 0.13 19.0 0.2 21-Mar-20 18.83 0.06 18.5 0.3 28-Mar-20 18.84 0.05 18.5 0.3 24-May-20 19.74 0.05 19.5 0.2