Fragmentation and History of Comet Pair C/1844 Y1 and C/2019 Y4

TL;DR

This paper examines the fragmentation, history, and relationships of the long-period comet pair C/1844 Y1 and C/2019 Y4, highlighting recent observations and the disintegration process of C/2019 Y4.

Contribution

It provides a detailed analysis of the fragmentation process of C/2019 Y4 and clarifies its relationship with C/1844 Y1, including new fragment detections and orbital insights.

Findings

Fragment B was the main mass of C/2019 Y4.

Fragmentation likely began around 22 January 2020.

New fragment E was observed on three days.

Abstract

I call attention to extraordinary features displayed by the genetically related long-period comet pair of C/1844 Y1 (Great Comet) and C/2019 Y4 (ATLAS). The issue addressed most extensively is the fragmentation and disintegration of the latter object, itself a thousands-of-years-old fragment. Of the four fragments of C/2019 Y4 recognized by the Minor Planet Center -- A, B, C, and D -- I confirm that B was the principal mass, which stayed undetected until early April. The comet's 2020 fragmentation is proposed to have begun with a separation of B and A near 22 January, when the nuclear condensation suddenly started to brighten rapidly. From late January to early April, only Fragment A was observed. The remaining Fragments C and D split off most probably from A in mid-March, but they too were detected only in April. A new fragment, E, is proposed to have been observed on three days. Further addressed are the issues of the orbital period and antitail of C/1844 Y1 and the extreme position of this pair among the genetically related groups/pairs of long-period comets.