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arXiv 1301.7433astro-ph.EP
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柯伊伯带小天体的初始大小和大小分布

Initial Planetesimal Sizes and the Size Distribution of Small Kuiper Belt Objects

Hilke E. Schlichting, Cesar I. Fuentes, David E. Trilling

摘要:

我们表明,通过比较观测与理论模型,观测到的柯伊伯带的大小分布是很好地匹配的凝聚模型,从一个初始的小行星人口半径约为1公里,随后的碰撞演化。我们发现,在太阳系年龄段内,观测到的R > 30 km的尺度分布没有受到碰撞演化的影响,而R ~ 30 km以下的尺度分布受到了碰撞的影响,其斜率与使用已发表的强度定律的碰撞演化模型很好地匹配。我们详细地研究了从0.01公里到30公里的天体的尺寸分布,发现其斜率在接近R <0.1公里的物质强度主导的天体的平衡碰撞级联的预期值之前作为半径的函数变化了几次。与0.01 ~ 30 km范围内的单一幂律尺度分布相比,我们发现R ~ 10 km范围内的天体数量严重不足,而2km范围内的天体数量严重过剩。这种赤字和过剩是由在公里大小范围内的小微行星的过剩质量造成的,这是从失控的增长阶段遗留下来的,在4.5 Gyrs的碰撞演化后,在尺寸分布中留下了一个签名。因此,对小KBO尺寸分布的观测可以测试大KBO是否是由于失控生长而生长的,并限制初始的星子尺寸。我们发现,从最近的KBO掩星调查的结果和所观察到的KBO的大小分布可以最好地匹配的初始星子人口,包含约相等的质量,每个对数质量箱的机构,从0.4公里到4公里的半径。此外,我们发现,我们不能匹配所观察到的KBO的大小分布,如果大部分的星子质量包含在半径为10公里或更大的机构。

英文摘要:

We show, by comparing observations with theoretical models, that the observed Kuiper Belt size distribution is well matched by coagulation models, which start from an initial planetesimal population with radii of about 1km, and subsequent collisional evolution. We find that the observed size distribution for R > 30km has not been modified by collisional evolution over the age of the solar system, and that the size distribution below R ~ 30km has been modified by collisions and that its slope is well matched by collisional evolution models that use published strength laws. We investigate in detail the resulting size distribution of bodies ranging from 0.01km to 30km and find that its slope changes several times as a function of radius before approaching the expected value for an equilibrium collisional cascade of material strength dominated bodies for R < 0.1km. Compared to a single power law size distribution that would span the whole range from 0.01km to 30km, we find a strong deficit of bodies around R ~10km and a strong excess of bodies around 2km. This deficit and excess are caused by an excess mass in small planetesimals in the km size range that was left over from the runaway growth phase and that leaves a signature in the size distribution that is not erased after 4.5 Gyrs of collisional evolution. Observations of the small KBO size distribution can therefore test if large KBOs grew as a result of runaway growth and constrain the initial planetesimal sizes. We find that results from recent KBO occultation surveys and the observed KBO size distribution can be best matched by an initial planetesimal population that contained about equal mass per logarithmic mass bin in bodies ranging from 0.4km to 4km in radius. In addition, we find that we cannot match the observed KBO size distribution if most of the planetesimal mass was contained in bodies that were 10km in radius or larger.

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