Bierson C J, Nimmo F
Department of Earth and Planetary Sciences, UC Santa Cruz, Santa Cruz, CA 95064, USA.
Icarus. 2019 Jul;326:10-17. doi: 10.1016/j.icarus.2019.01.027.
Telescopic observations of Kuiper Belt objects have enabled bulk density determinations for 17 objects. These densities vary systematically with size, perhaps suggesting systematic variations in bulk composition. We find this trend can be explained instead by variations in porosity arising from the higher pressures and warmer temperatures in larger objects. We are able to match the density of 14 of 17 KBOs within their 2 errors with a constant rock mass fraction of 70%, suggesting a compositionally homogeneous, rock-rich reservoir. Because early Al would have removed too much porosity in small (~100 km) KBOs we find the minimum formation time to be 4 Myr after solar system formation. This suggests that coagulation, and not gravitational collapse, was the dominant mechanism for KBO formation. We also use this model to make predictions for the density of Makemake, 2007 OR, and MU.
对柯伊伯带天体的望远镜观测已能够确定17个天体的整体密度。这些密度随大小呈系统性变化，这或许暗示了整体成分的系统性变化。相反，我们发现这种趋势可以用较大天体中较高压力和较高温度导致的孔隙率变化来解释。我们能够以70%的恒定岩石质量分数在其2倍误差范围内匹配17个柯伊伯带天体中14个的密度，这表明存在一个成分均匀、富含岩石的物质库。由于早期的铝会消除小尺寸（约100千米）柯伊伯带天体中过多的孔隙率，我们发现其最小形成时间为太阳系形成后400万年。这表明凝聚作用而非引力坍缩是柯伊伯带天体形成的主导机制。我们还使用这个模型对阋神星、2007 OR和MU的密度进行预测。
