Ancient and primordial collisional families as the main sources of X-type asteroids of the inner main belt
Ancient and primordial collisional families as the main sources of X-type asteroids of the inner main belt
复制标题
古代和原始碰撞族是内主带X型小行星的主要来源
DOI：
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发表时间：
2019
影响因子：
6.5
通讯作者：
A. Morbidelli
中科院分区：
文献类型：
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作者：
M. Delbo’;C. Avdellidou;A. Morbidelli
目标。近地小行星的数量表明，存在一个内部主要的小行星带来源，属于光谱X复合体，具有中等反照率。到目前为止，还没有确定这样一个来源。我们认为，最有可能的来源是到目前为止逃脱发现的一个或多个碰撞小行星家族。
方法：研究方法。我们应用一种新的方法在属于中等反照率的X复合体的小行星的内主带种群中寻找小行星家族。我们的方法不是在轨道元素空间中搜索小行星星团，而是寻找轨道半长轴和小行星大小相反的相关性。当轨道元素空间超过数十亿年时，小行星可能会严重分散。这种相关性是在雅可夫斯基热效应的影响下从一个共同中心漂移而来的碰撞家族成员的特征。
结果。在中等反照率的X复合体小行星中，我们在内主带中发现了两个以前不为人知的家族。其中一颗小行星编号最小的小行星是(161)Athor，年龄约为3 Gyr，而第二颗小行星编号最小的天体是(689)Zita，其年龄可能与太阳系一样古老。后者家族的成员有轨道偏心率和倾斜度，它们分布在整个内主带，这表明这个家族可能是原始的，也就是说，它是在巨行星轨道不稳定之前形成的。
结论。内主带的绝大多数中等反照率X复合体小行星都与基因有关，因为它们可以归入几个小行星家族。只有9颗内部主带具有中等反照率的X复合体小行星不能被归入小行星家族。我们认为，这些天体是由原行星盘中的固体直接吸积而成，因此是幸存下来的行星体。
Aims. The near-Earth asteroid population suggests the existence of an inner main belt source of asteroids that belongs to the spectroscopic X complex and has moderate albedos. The identification of such a source has been lacking so far. We argue that the most probable source is one or more collisional asteroid families that have escaped discovery up to now.
Methods. We apply a novel method to search for asteroid families in the inner main-belt population of asteroids belonging to the X complex with moderate albedo. Instead of searching for asteroid clusters in orbital element space, which could be severely dispersed when older than some billions of years, our method looks for correlations between the orbital semimajor axis and the inverse size of asteroids. This correlation is the signature of members of collisional families that have drifted from a common centre under the effect of the Yarkovsky thermal effect.
Results. We identify two previously unknown families in the inner main belt among the moderate-albedo X-complex asteroids. One of them, whose lowest numbered asteroid is (161) Athor, is ~3 Gyr old, whereas the second one, whose lowest numbered object is (689) Zita, could be as old as the solar system. Members of this latter family have orbital eccentricities and inclinations that spread them over the entire inner main belt, which is an indication that this family could be primordial, that is, it formed before the giant planet orbital instability.
Conclusions. The vast majority of moderate-albedo X-complex asteroids of the inner main belt are genetically related, as they can be included into a few asteroid families. Only nine X-complex asteroids with moderate albedo of the inner main belt cannot be included in asteroid families. We suggest that these bodies formed by direct accretion of the solids in the protoplanetary disc, and are thus surviving planetesimals.