Disk-resolved photometry of Asteroid (2867) Steins
Disk-resolved photometry of Asteroid (2867) Steins
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小行星 (2867) Steins 的圆盘分辨光度测量
DOI：
10.1016/j.icarus.2012.06.021
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发表时间：
2012
期刊：
影响因子：
3.2
通讯作者：
Jian
中科院分区：
文献类型：
--
作者：
S. Spjuth;L. Jorda;P. Lamy;H. Keller;Jian
本文提出了一种新的方法来进行盘分辨测光，以研究太阳系小天体表面的本征光度学性质。我们采用标准的方法，形状模型与光度形式主义相结合-在实践中的Hapke形式主义-去除地形的影响，并恢复的光度（Hapke）参数的全球表面或，在其最详细的形式，这些参数的空间变化在整个表面。我们的方法在表示身体的三维形状的小平面的空间中操作，而所有过去的分析总是在图像像素的空间中执行，尽管它们不是身体表面所固有的。这具有自动跟踪一系列图像上的相同局部表面元素的优点。我们首先将我们的方法应用于由深度撞击航天器上的高分辨率成像仪（HRI）仪器获得的彗星9 P/Tempel 1的核图像，并且我们导出的Hapke参数与Li等人（Li，J.- Y.等人[2007]。Icarus 187，41-55）在各自的不确定性。我们证实了在核的南半球存在一个更高粗糙度的扩展区域，以及Sunshine等人确定的冰丰富区域的更高粗糙度（Sunshine，J.M.等人[2006]。科学311，1453-1455）赤道附近。然后，从2008年9月5日罗塞塔号航天器上的OSIRIS广角相机（WAC）在其飞越期间获得的多光谱图像中研究了小行星（2867）Steins的光度特性。我们的分析表明，该表面是高度多孔的（约84%），它既表现出阴影隐藏的反对效果（SHOE），并可能，相干后向散射反对效果（CBOE）。单次散射的散射系数是航天器访问过的小天体中观测到的最高的（SSA=0.57）。我们的建模粗糙度参数是一个高的微尺度粗糙度的指示。Steins的表面实际上可能表现出具有高粗糙度的分形表面，其存在于从微米到厘米的大范围尺度上。用Hapke参数计算几何和键矢，得到Ap=0.39±0.02和AB=0.24±0.01。这一高丰度与贫铁的表面成分相一致，类似于被怀疑来自E型小行星的奥布莱特陨石。我们发现没有光度变化的表面上的（有限的）空间分辨率的WAC图像。
We present a new method to perform disk-resolved photometry in order to investigate the intrinsic photometric properties of the surface of small Solar System bodies. We adopt the standard approach where a shape model is combined with a photometric formalism – in practise the Hapke formalism – to remove the effects of topography and recover the photometric (Hapke) parameters of either the global surface or, in its most elaborated form, the spatial variations of these parameters across the surface. Our method operates in the space of the facets representing the three-dimensional shape of the body, whereas all past analysis have always been performed in the space of the image pixels although they are not intrinsic to the surface of the body. This has the advantage of automatically tracking the same local surface element on a series of images. We first apply our method to images of the nucleus of Comet 9P/Tempel 1 obtained by the High-Resolution Imager (HRI) instrument on board the Deep Impact spacecraft and our derived Hapke parameters are in good agreement with those published by Li et al. (Li, J.-Y. et al. [2007]. Icarus 187, 41–55) within their respective uncertainties. We confirm the presence of an extended region of higher roughness in the southern hemisphere of the nucleus and the higher albedo of the ice-rich regions identified by Sunshine et al. (Sunshine, J.M. et al. [2006]. Science 311, 1453–1455) near the equator. The photometric properties of Asteroid (2867) Steins are then studied from multi-spectral images obtained with the OSIRIS Wide Angle Camera (WAC) on board the Rosetta spacecraft during its flyby on 5 September 2008. Our analysis indicates that the surface is highly porous (∼84%) and that it exhibits both a shadow-hiding opposition effect (SHOE) and probably, a coherent-backscatter opposition effect (CBOE). The single scattering albedo is the highest (SSA=0.57) ever observed among small bodies visited by spacecrafts. Our modelled roughness parameter is indicative of a high microscale roughness. The surface of Steins may in fact exhibit a fractal surface with high roughness present on a large range of scales, from micrometers to centimeters. The geometric and Bond albedos are calculated with the Hapke parameters yielding Ap=0.39±0.02 and AB=0.24±0.01. This high albedo is consistent with an iron-poor surface composition similar to aubrite meteorites which are suspected to originate from the E-type asteroids. We find no photometric variations on the surface at the (limited) spatial resolution of the WAC images.