Radar Observations of Asteroid 1620 Geographos
Radar Observations of Asteroid 1620 Geographos
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DOI：
10.1006/icar.1996.0071
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发表时间：
1996-05
期刊：
影响因子：
3.2
通讯作者：
S. Ostro;R. Jurgens;K. Rosema;R. Hudson;J. Giorgini;R. Winkler;D. Yeomans;D. Choate;R. Rose;M. Slade;S. Howard;D. Scheeres;D. Mitchell
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文献类型：
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作者：
S. Ostro;R. Jurgens;K. Rosema;R. Hudson;J. Giorgini;R. Winkler;D. Yeomans;D. Choate;R. Rose;M. Slade;S. Howard;D. Scheeres;D. Mitchell
1994年8月28日至9月2日，Goldstone雷达对Geographos的观测产生了400多幅延迟多普勒图像，其线性空间分辨率范围从1075到151米，以及138对双偏振（OC，SC）光谱，一维分辨率为103米。每种数据类型都提供全面的旋转覆盖。这些图像包含内在的南北模糊性，但赤道视图允许准确确定小行星在任何旋转阶段的极侧轮廓的雷达面对部分的形状。覆盖几乎完整旋转的共同配准图像的总和定义了该轮廓的极度细长形状（S。J. Ostro，K. D.罗斯马河S.哈德逊河F. J. D.尤尔根斯乔治尼河Winkler，D. K.约曼斯，D.乔特河罗斯，M。A. Slade，S. D.霍华德和D. L. Mitchell 1995，Nature 375，474-477）。在这里，我们提出了超过30°的旋转相位的单独图像和共同注册的总和，以更精细的细节显示了轮廓的结构特征，并揭示了轮廓“内部”的许多对比度特征。这些特征包括几个候选陨石坑以及其他类型的大规模地形起伏的迹象，包括一个突出的中央凹陷。小行星两端的突起可能与小行星重力场造成的喷出物移除和沉积模式有关。小行星的表面是均匀的，在厘米到米的尺度上只有适度的粗糙度。我们对雷达散射截面的估计和目前对小行星尺寸的限制与近表面体积密度在2和3 g cm − 3之间是一致的。Geographos质心的延迟多普勒轨迹在8月28日被确定为约200米，在8月31日被确定为约100米，比观测前的星历表提高了两个数量级。
Abstract Goldstone radar observations of Geographos from August 28 through September 2, 1994 yield over 400 delay-Doppler images whose linear spatial resolutions range from ∼75 to ∼151 m, and 138 pairs of dual-polarization (OC, SC) spectra with one-dimensional resolution of 103 m. Each data type provides thorough rotational coverage. The images contain an intrinsic north/south ambiguity, but the equatorial view allows accurate determination of the shape of the radar-facing part of the asteroid's pole-on silhouette at any rotation phase. Sums of co-registered images that cover nearly a full rotation have defined the extremely elongated shape of that silhouette (S. J. Ostro, K. D. Rosema, R. S. Hudson, R. F. Jurgens, J. D. Giorgini, R. Winkler, D. K. Yeomans, D. Choate, R. Rose, M. A. Slade, S. D. Howard, and D. L. Mitchell 1995, Nature 375, 474–477). Here we present individual images and co-registered sums over ∼30° of rotation phase that show the silhouette's structural characteristics in finer detail and also reveal numerous contrast features “inside” the silhouette. Those features include several candidate craters as well as indications of other sorts of large-scale topographic relief, including a prominent central indentation. Protuberances at the asteroid's ends may be related to the pattern of ejecta removal and deposition caused by the asteroid's gravity field. The asteroid's surface is homogeneous and displays only modest roughness at centimeter-to-meter scales. Our estimates of radar cross section and the currently available constraints on the asteroid's dimensions are consistent with a near-surface bulk density between 2 and 3 g cm − 3 . The delay-Doppler trajectory of Geographos' center of mass has been determined to about 200 m on August 28 and to about 100 m on August 31, an improvement of two orders of magnitude over pre-observation ephemerides.