Spitzer observations of spacecraft target 162173 (1999 JU3)
Spitzer observations of spacecraft target 162173 (1999 JU3)
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DOI：
10.1051/0004-6361/200912374
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发表时间：
2009-08-01
影响因子：
6.5
通讯作者：
Dotto, E.
中科院分区：
文献类型：
--
作者：
Campins, H.;Emery, J. P.;Dotto, E.
上下文近地小行星162173（1999 JU 3）是日本宇宙航空研究开发机构（JAXA）隼鸟2号取样返回使命的主要目标，也是欧洲航天局（欧空局）马可波罗取样返回使命的潜在目标之一。在地球上对这一物体的研究是这些任务的基础。我们的目的是提供新的限制这个小行星的表面性质。我们提出了一个中红外光谱（5 - 38 μ m）与美国宇航局的斯皮策太空望远镜在2008年5月获得的热模型的应用结果。这些观测结果对这颗小行星的表面特性提出了新的限制。为了拟合我们的光谱，我们使用了近地小行星热模型（NEATM）和更复杂的热物理模型（TPM）。然而，自旋磁极的位置，这是不确定的，是一个关键的输入参数，用于约束与TPM的热惯性，因此，我们考虑两个磁极取向。第一种是赤道逆行几何的极端情况，由此我们导出了150 Jm（-2）s（-0.5）K-1的严格的热惯量下限。其次，当我们采用Abe等人（2008年a，第37届空间研委会科学大会）的极取向时，我们的最佳拟合热模型得出的热惯性值为700 +/-200 Jm（-2）s（-0.5）K-1，由于绝对通量校准导致的光谱形状的不确定性，甚至允许更高的值。我们对小行星162173的直径（0.90 +/-0.14公里）和几何半径（0.07 +/-0.01）的最佳估计与以前的中红外观测值一致。我们建立了一个严格的下限的热惯性，这是不太可能的，但可能的，并会与一个良好的风化类似的wthat是为小行星433爱神星。然而，热惯性预计会更高，可能类似于或大于小行星25143 Itokawa。准确确定小行星162173的自旋极将缩小其热惯性的可能值范围。
Context. Near-Earth asteroid 162173 (1999 JU3) is the primary target of the Japanese Aerospace Exploration Agency (JAXA) Hayabusa-2 sample return mission, and is also on the list of potential targets for the European Space Agency (ESA) Marco Polo sample return mission. Earth-based studies of this object are fundamental to these missions.Aims. Our aim is to provide new constraints on the surface properties of this asteroid.Methods. We present a mid-infrared spectrum (5-38 mu m) obtained with NASA's Spitzer Space Telescope in May 2008 and results from the application of thermal models.Results. These observations place new constraints on the surface properties of this asteroid. To fit our spectrum we used the near-Earth asteroid thermal model (NEATM) and the more complex thermophysical model (TPM). However, the position of the spin-pole, which is uncertain, is a crucial input parameter for constraining the thermal inertia with the TPM; hence, we consider two pole orientations. First is the extreme case of an equatorial retrograde geometry from which we derive a rigorous lower limit to the thermal inertia of 150 Jm(-2) s(-0.5) K-1. Second, when we adopt the pole orientation of Abe et al. (2008a, 37(th) COSPAR Scientific Assembly) our best-fit thermal model yields a value for the thermal inertia of 700 +/- 200 Jm(-2) s(-0.5) K-1 and even higher values are allowed by the uncertainty in the spectral shape due to the absolute flux calibration. Our best estimates of the diameter (0.90 +/- 0.14 km) and geometric albedo (0.07 +/- 0.01) of asteroid 162173 are consistent with values based on previous mid-infrared observations.Conclusions. We establish a rigorous lower limit to the thermal inertia, which is unlikely but possible, and would be consistent with a fine regolith similar to wthat is found for asteroid 433 Eros. However, the thermal inertia is expected to be higher, possibly similar to or greater than that on asteroid 25143 Itokawa. An Accurately determining the spin-pole of asteroid 162173 will narrow the range of possible values for its thermal inertia.