Luspay-Kuti A, Altwegg K, Berthelier J J, Beth A, Dhooghe F, Fiethe B, Fuselier S A, Gombosi T I, Hansen K C, Hässig M, Livadiotis G, Mall U, Mandt K E, Mousis O, Petrinec S M, Rubin M, Trattner K J, Tzou C-Y, Wurz P
Johns Hopkins University Applied Physics Laboratory, 11100 Johns Hopkins Rd., Laurel, MD 20723, USA.
Physikalisches Institut, University of Bern, Sidlerstr. 5, 3012 Bern, Switzerland.
Astron Astrophys. 2019 Oct;630. doi: 10.1051/0004-6361/201833536. Epub 2019 Sep 30.
Pre-equinox measurements of comet 67P/Churyumov-Gerasimenko with the mass spectrometer ROSINA/DFMS on board the Rosetta spacecraft revealed a strongly heterogeneous coma. The abundances of major and various minor volatile species were found to depend on the latitude and longitude of the nadir point of the spacecraft. The observed time variability of coma species remained consistent for about three months up to equinox. The chemical variability could be generally interpreted in terms of surface temperature and seasonal effects superposed on some kind of chemical heterogeneity of the nucleus.
We compare here pre-equinox (inbound) ROSINA/DFMS measurements from 2014 to measurements taken after the outbound equinox in 2016, both at heliocentric distances larger than 3 AU. For a direct comparison we limit our observations to the southern hemisphere.
We report the similarities and differences in the concentrations and time variability of neutral species under similar insolation conditions (heliocentric distance and season) pre- and post-equinox, and interpret them in light of the previously published observations. In addition, we extend both the pre- and post-equinox analysis by comparing species concentrations with a mixture of CO and HO.
Our results show significant changes in the abundances of neutral species in the coma from pre- to post-equinox that are indicative of seasonally driven nucleus heterogeneity.
The observed pre- and post-equinox patterns can generally be explained by the strong erosion in the southern hemisphere that moves volatile-rich layers near the surface.
利用罗塞塔号航天器上的质谱仪ROSINA/DFMS对67P/丘留莫夫－格拉西缅科彗星进行春分前测量时，发现其彗发存在强烈的不均匀性。结果发现，主要挥发性物质和各种次要挥发性物质的丰度取决于航天器最低点的纬度和经度。在春分之前，彗发物质的观测时间变化在大约三个月内保持一致。化学变化通常可以根据表面温度和叠加在核的某种化学不均匀性上的季节效应来解释。
我们在此比较2014年春分前（向内飞行）的ROSINA/DFMS测量结果与2016年春分后向外飞行时在日心距离大于3天文单位处进行的测量结果。为了进行直接比较，我们将观测范围限制在南半球。
我们报告了春分前后在相似日照条件（日心距离和季节）下中性物质浓度和时间变化的异同，并根据先前发表的观测结果对其进行解释。此外，我们通过将物质浓度与一氧化碳和水的混合物进行比较，扩展了春分前后的分析。
我们的结果表明，从春分前到春分后，彗发中中性物质的丰度发生了显著变化，这表明存在季节性驱动的核不均匀性。
观测到的春分前后模式通常可以用南半球的强烈侵蚀来解释，这种侵蚀使富含挥发性物质的层靠近表面。
