标题： 土星D环中于2011年底形成的新图案 显示英文标题

标题： A new pattern in Saturn's D ring created in late 2011

摘要： 2012年至2015年间卡西尼号航天器获得的图像显示，土星D环的一个区域出现了周期性的亮度变化，该区域之前看起来相当平坦。此外，自首次观察以来，这种图案的强度和径向波数一直在稳步下降。基于D环其他类似结构的类比，我们认为这个结构是由某种事件引起的，该事件扰乱了环粒子的轨道运动，使它们具有有限的轨道偏心率，并且初始时近日点对齐。然后，轨道进动的差异将这一结构转化为环光学深度中的螺旋图案，并随着时间的推移变得越来越紧密。该图案径向波数的观测趋势大致符合这一基本模型，还表明扰动环的事件发生在2011年12月初。1979年的类似事件可能由旅行者号航天器在此同一区域观察到的周期性图案产生。2011年的事件可能是由碎片撞击环引起的，或者是行星电磁环境的扰动引起的。在短短几年内亮度变化强度迅速减少表明，该区域可能存在某种过程，要么是阻尼轨道偏心率，要么是导致具有相同半长轴的粒子的轨道近日点变得不对齐。 显示英文摘要

摘要： Images obtained by the Cassini spacecraft between 2012 and 2015 reveal a periodic brightness variation in a region of Saturn's D ring that previously appeared to be rather featureless. Furthermore, the intensity and radial wavenumber of this pattern have decreased steadily with time since it was first observed. Based on analogies with similar structures elsewhere in the D ring, we propose that this structure was created by some event that disturbed the orbital motions of the ring particles, giving them finite orbital eccentricities and initially aligned pericenters. Differential orbital precession then transformed this structure into a spiral pattern in the ring's optical depth that became increasingly tightly wound over time. The observed trends in the pattern's radial wavenumber are roughly consistent with this basic model, and also indicate that the ring-disturbing event occurred in early December 2011. Similar events in 1979 may have generated the periodic patterns seen in this same region by the Voyager spacecraft. The 2011 event could have been caused by debris striking the rings, or by a disturbance in the planet's electromagnetic environment. The rapid reduction in the intensity of the brightness variations over the course of just a few years indicates that some process is either damping orbital eccentricities in this region or causing the orbital pericenters of particles with the same semi-major axis to become misaligned.