Oral Presentation

Chemical composition of nucleus in Comet C/2019 Y4 (ATLAS) inferred by means of polarimetry prior and after its disintegration in 2020

Author(s): Evgenij Zubko (Kyung Hee University, South Korea) Maxim Zheltobryukhov (Institute of Applied Astronomy of RAS, Russia) Ekaterina Chornaya (Far Eastern Federal University, Russia) Anton Kochergin (Far Eastern Federal University, Russia) et al.

Presenter: Evgenij Zubko (Humanitas College, Kyung Hee University, South Korea)

We observe Comet C/2019 Y4 (ATLAS) before and after its disintegration while making polarimetric measurements over a wide range of phase angles. The disintegration event was marked with a dramatic growth of the positive polarization branch that is consistent with a large relative abundance of absorbing material of up to (96.5 ± 3.4)%. This polarization spike relaxed as the carbonaceous particles are preferentially swept from the coma due to solar radiation pressure. The observations suggest that the primordial material stored within comets are extremely rich in carbonaceous material. The pristine cometary material is processed by subsequent solar interactions, forming a refractory crust on the nucleus surface. Polarimetry provides a means of measuring the volume ratio of carbonaceous material, and hence the weathering that has occurred on the comet due to these interactions. The polarimetric response of Comet C/2019 Y4 (ATLAS) appears similar to that of Comet C/1995 O1 (Hale-Bopp), except on few epochs that are similar to that of Comet C/1996 B2 (Hyakutake).