C/2019 Y4 (ATLAS)


Type: Periodic Perihelion date: 31 May 2020 Perihelion distance (q): 0.25 Aphelion distance (Q) : 661 Period (years): 6,011 Eccentricity (e): 1.00 Inclination (i): 45.4 JPL orbit diagram COBS lightcurve A 19th magnitude object was discovered in images taken with the 0.5m Schmidt at Mauna Loa on 28 December 2019 by the ATLAS (Asteroid Terrestrial-impact Last Alert System) team. Confirmations came from several amateur observers including Michael Jaeger and Eric Bryssinck. It had been posted on the PCCP as A10j7UG. Maik Meyer noted that its orbit is very similar to that of the Great Comet 1844 Y1. Michael Jaeger reported it at 14th magnitude on 15 February 2020. It brightened rapidly and became a binocular object by mid March. During the second half of March the rate of brightening appeared to slow for many observers, however those using the smallest aperture that showed the comet clearly reported the comet as brighter than those using larger apertures. It was clear by early April that the comet had faded. Astrometric observations appeared to show large non-gravitational effects and the coma had became elongated. Separate condensations then began to appear in the coma, with one offset from the coma and placed where expected from the original orbit. This strongly suggested that the comet had undergone a major disruption event. Zdenek Sekanina suggests that a major fragmentation event occurred on or before mid March at about 1.8 au from the Sun, with the rapid brightening terminating around March 17. The component produced in this event itself fragmented in late March or early April. The detached coma began to fade. HST images suggested that this scenario was not viable and Sekanina suggested that the comet was in the process of stochastic fragmentation, which began when the comet was a long way from perihelion. Overall the comet remained at around 9th magnitude during April. The comet suddenly brightened to 8th magnitude around 8/9 May, suggesting another phase in the break-up. This appears to have been the final event in the complete disintegration of the comet. A possible alternative view to the mid March break-up is that the disruption event began in mid February when the rapid brightening commenced. Observations (VEMag = visual equivalent magnitude) Date 10x10 mag Error VEmag Coma ' 15-Mar-20 13.34 0.02 10.7 7.0 19-Mar-20 13.18 0.04 10.0 7.2 24-Mar-20 12.85 0.03 8.5 9.0