分类： 天文学 >> 天文学 提交时间： 2023-02-19
Quanzhi Ye
David Jewitt
Man-To Hui
Qicheng Zhang
Jessica Agarwal
Michael S. P. Kelley
Yoonyoung Kim
Jing Li
Tim Lister
Max Mutchler
Harold A. Weaver
摘要： Near-Sun Comet C/2019 Y4 (ATLAS) is the first member of a long-period comet group observed to disintegrate well before perihelion. Here we present our investigation into this disintegration event using images obtained in a 3-day {\it Hubble Space Telescope} (\hst) campaign. We identify two fragment clusters produced by the initial disintegration event, corresponding to fragments C/2019 Y4-A and C/2019 Y4-B identified in ground-based data. These two clusters started with similar integrated brightness, but exhibit different evolutionary behavior. C/2019 Y4-A was much shorter-lived compared to C/2019 Y4-B, and showed signs of significant mass-loss and changes in size distribution throughout the 3-day campaign. The cause of the initial fragmentation is undetermined by the limited evidence but crudely compatible with either the spin-up disruption of the nucleus or runaway sublimation of sub-surface supervolatile ices, either of which would lead to the release of a large amount of gas as inferred from the significant bluing of the comet observed shortly before the disintegration. Gas can only be produced by the sublimation of volatile ices, which must have survived at least one perihelion passage at a perihelion distance of $q=0.25$~au. We speculate that Comet ATLAS is derived from the ice-rich interior of a non-uniform, kilometer-wide progenitor that split during its previous perihelion. This suggests that comets down to a few kilometers in diameter can still possess complex, non-uniform interiors that can protect ices against intense solar heating.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： We present imaging observations of the disintegrating long-period comet C/2021 A1 (Leonard). High resolution observations with Hubble Space Telescope show no evidence for surviving fragments, and place a 3 sigma upper limit to their possible radius about 60 m (albedo 0.1 assumed). In contrast, wide field observations from the Swan Hill Observatory, Australia, show an extensive debris cloud, the cross-section and estimated mass of which are consistent with complete disintegration of the nucleus near mid- December 2021 (at about 0.8 au). Two methods give the pre-disruption nucleus radius, r = 0.6+/-0.2 km. Tidal, collisional, sublimation and pressure-confined explosion models provide implausible explanations of the disintegration. However, rotational instability driven by outgassing torques has a very short timescale (of order 0.1 year) given the orbit and size of the C/2021 A1 nucleus, and offers the most plausible mechanism for the disruption. Initial rotational breakup is accelerated by the exposure and strong sublimation of previously buried volatiles, leading to catastrophic destruction of the nucleus.
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