Disintegration of Long-period Comet C/2019 Y4 (ATLAS). II. Postperihelion Remnant Recovery

Abstract We present an investigation into the fate of disrupting near-Sun comet C/2019 Y4 (ATLAS). Imaging observations with the Lowell Discovery Telescope, obtained 3–5 months after the reported disruption and the last sighting, constrained the primary component C/2019 Y4-B to an absolute magnitude of H > 20.5 or a diameter of D < 0.5 km (assuming a geometric albedo of 0.04) at an outbound heliocentric distance of 2.71 au. A search of shallower data obtained from the Zwicky Transient Facility survey, conducted when components A and B receded from 2.5 to 2.9 au from the Sun, yielded no detections, suggesting that the fragments had either ceased to exist or were not substantially active during this period. The uncertain fate of C/2019 Y4 highlights the challenge in understanding the state of presumably disrupted comets. Our review of six other presumably disrupted long-period comets reveals that negative confirmations were not reported for half of them, leaving their disruption presumptions inconclusive.