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) per cent. 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 is 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).

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分解彗星C / 2019 Y4（ATLAS）的极化

我们观察彗星C / 2019 Y4（ATLAS）的解体前后，同时在很宽的相角范围内进行极化测量。崩解事件的标志是正极化分支急剧增长，这与吸收材料的相对大丰度高达（96.5±3.4）％相一致。当碳质颗粒由于太阳辐射压力而优先从昏迷中扫除时，这种极化尖峰放松了。这些观察结果表明，储存在彗星中的原始物质中碳质物质非常丰富。原始的彗星材料通过随后的太阳相互作用进行加工，在核表面形成难熔的硬皮。旋光法提供了一种测量碳质材料体积比的方法，因此，由于这些相互作用，在彗星上发生了风化。C / 2019 Y4彗星（ATLAS）的极化响应似乎与C / 1995 O1彗星（Hale-Bopp）相似，只是在几个与C / 1996 B2彗星（Hyakutake）相似的时期外。