Comet ATLAS (C/2024 S1) -- Second Ground-Based Discovery of a Kreutz Sungrazer in Thirteen Years

Abstract

Comet ATLAS (C/2024 S1) is a bright dwarf sungrazer, the second Kreutz comet discovery from the ground this century, 13 years after comet Lovejoy (C/2011 W3). The Population II membership of comet ATLAS sets it apart from the overwhelming majority of other bright dwarf sungrazers, most of them classified as members of Populations I, Pe, or Pre-I in the context of the contact-binary model. The new sungrazer might be closely related to comet du Toit (C/1945 X1), but most exciting is the possibility that it is a fragment of the parent comet of the Great September Comet of 1882 (C/1882 R1) and comet Ikeya-Seki (C/1965 S1). However, this scenario requires that the original orbital period of comet ATLAS -- rather poorly known at present -- be 886 yr. If its orbital period should turn out to be decidedly shorter, another scenario involving a 13th-century sungrazer should be preferred instead. More work on the orbit needs to be done. The apparent contradiction between the discovery of comet ATLAS and previous failures to find any dwarf Kreutz sungrazers in images taken with large ground-based telescopes at moderate heliocentric distances is explained by the propensity of Population II dwarf comets for outbursts, acting in collusion with extremely rare occurrences of these objects. Also addressed are the dynamical properties of perihelion fragmentation as well as the nature and timing of the expected 21st-century cluster of Kreutz comets, swarms of dwarf sungrazers, and related issues.