Rosetta任务的小行星目标21 Lutetia表面的不均匀性
Inhomogeneities on the surface of 21 Lutetia, the asteroid target of the Rosetta mission
摘要：
背景：2010年7月，欧空局的罗塞塔号航天器将飞越主带小行星21 Lutetia。到目前为止，已经对这颗小行星进行了几次观测，但它的表面组成和性质仍然是一个有争议的问题。很长一段时间以来，Lutetia被认为具有金属性质，因为它具有高的IRAS反射率。后来有人提出它的表面成分类似于原始的碳质球粒陨石，而进一步的观察则提出它可能与更进化的顽火辉石球粒陨石有遗传联系。目标：为了在解决Lutetia性质的难题方面做出重要贡献，我们于2008年11月在Telescopio Nazionale Galileo（TNG，La Palma，西班牙）对这颗小行星进行了可见光谱观测。方法：在不同旋转相位下获得13个可见光谱。研究结果：我们证实了Lazzarin等人（2009年）在Lutetia光谱中发现的约0.47-0.48微米处的窄光谱特征的存在。我们还发现了Lazzarin等人（2004年）在Lutetia光谱中发现的约0.6微米的光谱特征。更重要的是，我们的光谱在0.6和0.75微米之间表现出不同的光谱斜率，特别是，我们发现高达20%的Lutetia表面可以具有更平坦的光谱。结论：我们在不同的旋转阶段检测到光谱斜率的变化，这可以解释为可能是由于化学/矿物成分的差异，以及Lutetia表面结构的不均匀性（例如，在南半球的陨石坑或火山点的存在）。
英文摘要：
CONTEXT: In July 2010 the ESA spacecraft Rosetta will fly-by the main belt asteroid 21 Lutetia. Several observations of this asteroid have been so far performed, but its surface composition and nature are still a matter of debate. For long time Lutetia was supposed to have a metallic nature due to its high IRAS albedo. Later on it has been suggested to have a surface composition similar to primitive carbonaceous chondrite meteorites, while further observations proposed a possible genetic link with more evolved enstatite chondrite meteorites. AIMS: In order to give an important contribution in solving the conundrum of the nature of Lutetia, in November 2008 we performed visible spectroscopic observations of this asteroid at the Telescopio Nazionale Galileo (TNG, La Palma, Spain). METHODS: Thirteen visible spectra have been acquired at different rotational phases. RESULTS: We confirm the presence of a narrow spectral feature at about 0.47-0.48 micron already found by Lazzarin et al. (2009) on the spectra of Lutetia. We also find a spectral feature at about 0.6 micron, detected by Lazzarin et al. (2004) on one of their Lutetia's spectra. More importantly, our spectra exhibit different spectral slopes between 0.6 and 0.75 micron and, in particular, we found that up to 20% of the Lutetia surface could have flatter spectra. CONCLUSIONS: We detected a variation of the spectral slopes at different rotational phases that could be interpreted as possibly due to differences in the chemical/mineralogical composition, as well as to inhomogeneities of the structure of the Lutetia's surface (e.g., the presence of craters or albedo spots) in the southern hemisphere.
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