小行星出生时很大
Asteroids Were Born Big
摘要：
第一个星子有多大？我们试图回答这个问题，通过进行凝聚模拟，其中微行星通过相互碰撞生长，形成更大的机构和行星胚胎。初始星子的大小频率分布（SFD）被认为是一个自由参数在这些模拟中，我们搜索的一个产生在结束时的对象与SFD是一致的小行星带的约束。我们发现，如果最初的星子是小的（例如公里大小），最终的SFD无法满足这些约束。特别是，要重现目前小行星SFD中直径D~ 100 km处观测到的撞击，需要初始微行星的最小尺寸也是~ 100 km。这支持了星子形成大的想法，也就是说，原行星盘中固体的大小从亚米尺度“跳跃”到数公里尺度，而没有通过中间值。此外，我们发现证据表明，最初的微行星必须有100到几百公里的大小，甚至可能是1,000公里，而且它们的SFD必须在这个区间上有一个斜率，与当前相同大小范围内的小行星的特征相似。这一结果对星子形成模型提出了新的约束，为研究小行星和柯伊伯带的碰撞演化以及巨行星核的吸积开辟了新的视角。
英文摘要：
How big were the first planetesimals? We attempt to answer this question by conducting coagulation simulations in which the planetesimals grow by mutual collisions and form larger bodies and planetary embryos. The size frequency distribution (SFD) of the initial planetesimals is considered a free parameter in these simulations, and we search for the one that produces at the end objects with a SFD that is consistent with asteroid belt constraints. We find that, if the initial planetesimals were small (e.g. km-sized), the final SFD fails to fulfill these constraints. In particular, reproducing the bump observed at diameter D~100km in the current SFD of the asteroids requires that the minimal size of the initial planetesimals was also ~100km. This supports the idea that planetesimals formed big, namely that the size of solids in the proto-planetary disk ``jumped'' from sub-meter scale to multi-kilometer scale, without passing through intermediate values. Moreover, we find evidence that the initial planetesimals had to have sizes ranging from 100 to several 100km, probably even 1,000km, and that their SFD had to have a slope over this interval that was similar to the one characterizing the current asteroids in the same size-range. This result sets a new constraint on planetesimal formation models and opens new perspectives for the investigation of the collisional evolution in the asteroid and Kuiper belts as well as of the accretion of the cores of the giant planets.
机构、总结、中文摘要均由AI分析而来，可能存在错误，请以论文正文为准。
