57P/du Toit-Neujmin-Delporte



Type: Periodic Perihelion date: 17 October 2021 Perihelion distance (q): 1.7 Aphelion distance (Q) : 5.2 Period (years): 6.4 Eccentricity (e): 0.50 Inclination (i): 2.9 JPL orbit diagram COBS lightcurve Daniel du Toit (Harvard College Observatory, Boyden station, Bloemfontein, South Africa) discovered this comet on 18 July 1941. He described it as magnitude 10. Wartime conditions prevented the cabled information from reaching Harvard College Observatory (Massachusetts, USA) until 27 July. At that time, the information was held pending confirmation. Unbeknownst to astronomers in Massachusetts, Paul Ahnert (Sonneberg, Germany) confirmed the discovery on 22 July, but this message would not arrive until the first days of September. Meanwhile, Grigory N. Neujmin (Simeis Observatory, Russia) was routinely examining photographic plates exposed for asteroids. On a plate exposed on 25 July he made an independent discovery of the same comet. He estimated the magnitude as 9. Neujmin confirmed his observation on 29 July, and radiogrammed the news from Moscow to Harvard, but the same wartime conditions caused this message to take nearly 20 days to arrive, thus, keeping the official announcement from being widely published until 22 August. A few days later, word came that Eugéne Joseph Delporte (Royal Observatory, Uccle, Belgium) had independently found this comet on 19 August. He had estimated the magnitude as 9, and said the comet was diffuse, with a central condensation. Beginning with the orbit computed for the 1941 apparition by Grosch, W. E. Beart and W. P. Henderson applied perturbations by Jupiter and Saturn and predicted the comet would next arrive at perihelion on 14 January 1947. They said the comet would remain close to the sun from October 1946 to May 1947, and then would venture out to an elongation of about 30 degrees. They added that the comet's faintness would prevent it from being seen. The comet was not seen at its expected 1952 return, despite a likely maximum brightness of 13. A. S. Sotchilina pointed out that the comet passed 0.656 AU from Jupiter in 1954, which caused "considerable changes" to the comet's orbit. The 1958 apparition was expected to be rather favourable, with an expected maximum brightness near 12, but the comet was not found. The comet was also missed at its next return in the 1960s. The comet was finally recovered in 1970. B. G. Marsden redetermined the 1941 orbit and found an uncertainty of ±10 days. He also computed two variation orbits. All three orbits were then integrated forward. Marsden found the comet to have passed close to Jupiter in 1954 and 1966. The former passage acted to increase the orbital period of this comet from 5.5 years to 5.9 years, while the second passage increased it to 6.6 years. Under normal circumstances, the expected error for the upcoming 1970 apparition would be assumed to be ±50 days, since five revolutions had taken place since 1941, but Marsden noted that the effects of the two Jupiter approaches acted as a mirror in that the shorter the period before 1954, the longer it would become after 1966, and vice versa. Thus, Marsden determined the perihelion date as 8 October 1970, and the expected error amounted to only ±5 days. Marsden added that differential perturbations in the other orbital elements would confine the comet to an even smaller area of the sky at this apparition, especially during August, when the comet would be at its brightest with an expected magnitude of 18. The comet was recovered by Charles T. Kowal (Palomar Observatory, California, USA) on 6 July 1970. His precisely measured position indicated Marsden's prediction required a correction of only -0.1 day. The comet was too poorly placed for recovery in 1977, but it was observed as a faint object during the 1983 and 1989 apparitions. The comet surprised astronomers during the 1996 return. During a late July outburst in brightness, the total magnitude reached about 12, making this the brightest observed apparition since 1941. Numerous observers reported the comet had become fainter than 13 by mid-August, but by late August reports again showed the comet near magnitude 12. The comet was recovered in May 2002 at magnitude 17 and steadily brightened during the next two months as it headed toward a 31 July perihelion date. On 12 July a report was received at the Central Bureau for Astronomical Telegrams that said NEAT had found a possible NEO (Near Earth Object). It was described as cometary. The Minor Planet Center quickly noted the object had the same motion as comet 57P, but with a perihelion date 0.19 day later. It was located about 0.2 degrees from the main comet. Confirmation was requested and the cometary nature was confirmed. On July 13, G. Masi (Campo Catino, Italy) described it as a well-defined coma 12 arcsec across, with a slight northeast-southwest elongation. Interestingly, astronomers using the University of Hawaii 2.2-m reflector on July 17 and 18 found an additional 18 fragments. The comet and its 19 companions were spread across a roughly straight line, with the object furthest from the main comet, labelled "T", having a perihelion date 0.354 day later than the main comet (see image at top of page). The magnitudes of these 18 objects ranged from 20.0 to 23.5. Although most were centrally condensed, six were completely devoid of condensation. Observations (VEMag = visual equivalent magnitude) Date 10x10 mag Error VEmag Coma ' 22-Jul-15 16.67 0.04 15.9 0.2 08-Aug-15 16.66 0.05 14.8 0.2 15-Aug-15 16.90 0.01 14.2 0.4 22-Aug-15 16.79 0.01 14.9 0.4 07-Sep-15 16.68 0.01 14.5 0.4 14-Sep-15 16.64 0.02 14.8 0.5 21-Sep-15 16.70 0.01 13.5 0.3 19-Oct-15 17.38 0.02 14.5 0.3 30-Oct-15 17.73 0.05 15.7 0.2 07-Nov-15 17.98 0.03 15.9 0.2 16-Nov-15 18.08 0.06 15.1 0.2 03-Dec-15 18.93 0.14 16.9 0.2 06-May-21 18.9 0.4 01-Jun-21 18.0 0.4 13-Jun-21 17.6 0.4 09-Sep-21 17.2 0.4