VLT spectropolarimetry of comet 67P: dust environment around the end of its intense southern summer
VLT spectropolarimetry of comet 67P: dust environment around the end of its intense southern summer
复制标题
彗星 67P 的 VLT 分光偏振测量：强烈的南方夏季末期的尘埃环境
DOI：
10.1051/0004-6361/202141865
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发表时间：
2021
影响因子：
6.5
通讯作者：
Kwon Y
中科院分区：
文献类型：
--
作者：
Kwon Y
通过Rosetta和地面观测数据的结合，揭示了67P/Churyumov-Gerasimenko(以下简称67P)彗星尘埃粒子特征随季节的演变，揭示了彗星表面源区不同的尘埃环境。目的研究67P尘埃粒子的性质，并据此诊断其彗发和近地表尘埃环境。方法2016年1-3月，我们利用欧洲天文台/甚大望远镜(相位角26°-5°)对4000-9000Å的67P尘埃进行了光谱偏振观测。我们研究了尘埃的光学行为，与Rosetta颜色数据一起，用来搜索尘埃随彗心距离的演化。结果67P尘埃的偏振度与观测几何相似的其他动力学彗星群的偏振度的光谱相关性更平坦。它的负极化分支的深度似乎比长周期彗星要浅一些，而且随着67P的重复出现，它的深度可能会变得更浅。它的尘埃颜色在波长约5500Å、(17.3±1.4)和(10.9±0.6)%(1000Å)-1附近呈现斜率变化，略偏红，但与木星彗星的平均值基本一致。结论本研究中观测到的67P尘埃可以归因于2016年初Rosetta探测到的~100μm的尘埃团。孔隙率为60%与我们的偏振测量结果最匹配，产生的尘埃密度约为770公斤m-3。Rosetta和我们的数据的汇编表明，尘埃随着原子核距离的增加而变红，这可能是由于尘埃移出原子核时的水冰升华所驱动的。我们估计最初喷出的尘埃中可能的水冰体积分数为~6%(即耐火与冰的体积比为~14)。
ContextA cornucopia of Rosetta and ground-based observational data sheds light on the evolution of the characteristics of dust particles from comet 67P/Churyumov-Gerasimenko (hereafter 67P) with seasons, implying the different dust environments in the source regions on the surface of the comet.AimsWe aim to constrain the properties of the dust particles of 67P and therefrom diagnose the dust environment of its coma and near-surface layer at around the end of the southern summer of the comet.MethodsWe performed spectropolarimetric observations for 67P dust over 4000–9000 Å using the ESO/Very Large Telescope from January–March 2016 (phase angle ranging from ~26° –5°). We examined the optical behaviours of the dust, which, together with Rosetta colour data, were used to search for dust evolution with cometocentric distance. Modelling was also conducted to identify the dust attributes compatible with the results.ResultsThe spectral dependence of the polarisation degree of 67P dust is flatter than that found in other dynamical groups of comets in similar observing geometry. The depth of its negative polarisation branch appears to be a bit shallower than in long-period comets and might be getting shallower as 67P repeats its apparitions. Its dust colour shows a change in slope around 5500 Å, (17.3 ± 1.4) and (10.9 ± 0.6)% (1000 Å)-1, shortward and longward of the wavelength, respectively, which are slightly redder but broadly consistent with the average of Jupiter-family comets.ConclusionsObservations of 67P dust in this study can be attributed to dust agglomerates of ~100 μm in size detected by Rosetta in early 2016. A porosity of 60% shows the best match with our polarimetric results, yielding a dust density of ~770 kg m-3. The compilation of Rosetta and our data indicates the dust’s reddening with increasing nucleus distance, which may be driven by water-ice sublimation as the dust moves out of the nucleus. We estimate the possible volume fraction of water ice in the initially ejected dust as ~6% (i.e. the refractory-to-ice volume ratio of ~14).