The nucleus of Comet 67P/Churyumov-Gerasimenko. A new shape model and thermophysical analysis
The nucleus of Comet 67P/Churyumov-Gerasimenko. A new shape model and thermophysical analysis
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DOI：
10.1051/0004-6361/201220116
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发表时间：
2012-12
影响因子：
6.5
通讯作者：
S. Lowry;S. Duddy;B. Rozitis;S. Green;A. Fitzsimmons;C. Snodgrass;H. Hsieh;O. Hainaut
中科院分区：
文献类型：
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作者：
S. Lowry;S. Duddy;B. Rozitis;S. Green;A. Fitzsimmons;C. Snodgrass;H. Hsieh;O. Hainaut
上下文彗星67 P/Churyumov-Gerasimenko是欧洲航天局罗塞塔航天器renewal-vous使命的目标。在彗星到达之前，详细的物理特征对使命规划以及为地面观测和数据分析方法提供试验平台都很重要。目标。进行一项长期观测方案，通过地面光学测光确定彗星核的物理特性，并将我们的新数据与文献中所有现有的彗星核数据联合收割机结合起来。方法.我们应用孔径测光技术对我们的成像数据，并结合提取的旋转光变曲线与文献中的数据。光学光变曲线反演技术被应用于约束核的自旋状态和它的宽形状。我们进行了详细的表面热分析的形状模型和光学光度法，将两者纳入新的先进热物理模型（ATPM），沿着所有可用的斯皮策8-24 μm热红外通量测量的文献。结果确定了凸三角形小平面形状模型，其中轴比B/a = 1.239和c/a = 0.819。这些值在每个轴上的变化可能高达7%，并且仍然导致与观测数据的统计学显着拟合。我们的最佳自旋态解为Psid = 12.76137 ± 0.00006 h，转动极取向在直角坐标λ = 78 π（±10 π），β = +58 π（±10 π）。核相暗化行为的测量和最好的特点是使用IAU HG系统。最佳拟合参数为：G = 0.11 ± 0.12和HR（1，1，0）= 15.31 ± 0.07。我们的形状模型与ATPM相结合，可以令人满意地协调所有的光学和热红外数据，与2004年2月拍摄的斯皮策24 μm数据的拟合非常好。我们推导出一系列相互一致的物理参数，每个热红外数据集，包括有效半径，几何半径，表面热惯性和粗糙度分数。结论.整个彗核的尺寸受到很好的限制，强烈暗示着一个更类似于9 P/坦普尔1号彗星的宽阔的彗核形状，而不是103 P/哈特利2号彗星或8 P/塔特尔彗星的高度拉长或“双叶”的彗核。得出的小于15 J m−2 K−1 s−1/2的低热惯量与其他以类似日心距离定标的彗星的测量结果相当，并且意味着表面的风化层比月球表面的物质更细。
Context. Comet 67P/Churyumov-Gerasimenko is the target of the European Space Agency Rosetta spacecraft rendez-vous mission. Detailed physical characteristation of the comet before arrival is important for mission planning as well as providing a test bed for ground-based observing and data-analysis methods. Aims. To conduct a long-term observational programme to characterize the physical properties of the nucleus of the comet, via ground-based optical photometry, and to combine our new data with all available nucleus data from the literature. Methods. We applied aperture photometry techniques on our imaging data and combined the extracted rotational lightcurves with data from the literature. Optical lightcurve inversion techniques were applied to constrain the spin state of the nucleus and its broad shape. We performed a detailed surface thermal analysis with the shape model and optical photometry by incorporating both into the new Advanced Thermophysical Model (ATPM), along with all available Spitzer 8–24 μm thermal-IR flux measurements from the literature. Results. A convex triangular-facet shape model was determined with axial ratios b/a = 1.239 and c/a = 0.819. These values can vary by as much as 7% in each axis and still result in a statistically significant fit to the observational data. Our best spin state solution has Psid = 12.76137 ± 0.00006 h, and a rotational pole orientated at Ecliptic coordinates λ = 78◦(±10◦), β = +58◦(±10◦). The nucleus phase darkening behaviour was measured and best characterized using the IAU HG system. Best fit parameters are: G = 0.11 ± 0.12 and HR(1,1,0) = 15.31 ± 0.07. Our shape model combined with the ATPM can satisfactorily reconcile all optical and thermal-IR data, with the fit to the Spitzer 24 μm data taken in February 2004 being exceptionally good. We derive a range of mutually-consistent physical parameters for each thermal-IR data set, including effective radius, geometric albedo, surface thermal inertia and roughness fraction. Conclusions. The overall nucleus dimensions are well constrained and strongly imply a broad nucleus shape more akin to comet 9P/Tempel 1, rather than the highly elongated or “bi-lobed” nuclei seen for comets 103P/Hartley 2 or 8P/Tuttle. The derived low thermal inertia of <15 J m−2 K−1 s−1/2 is comparable with that measured for other comets scaled to similar heliocentric distances, and implies a surface regolith finer than lunar surface material.