The B-ring's surface mass density from hidden density waves: Less than meets the eye?
The B-ring's surface mass density from hidden density waves: Less than meets the eye?
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来自隐藏密度波的 B 环表面质量密度：小于肉眼所见？
DOI：
10.1016/j.icarus.2016.01.007
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发表时间：
2016
期刊：
影响因子：
3.2
通讯作者：
P. Nicholson
中科院分区：
文献类型：
--
作者：
M. Hedman;P. Nicholson
土星的B环是我们太阳系中最不透明的环，但它的许多基本参数，包括它的总质量，都没有很好的约束。土星卫星的平均运动共振产生的螺旋密度波提供了一些对环质量密度的最佳限制，但是在B环中检测和量化这种波一直是具有挑战性的，因为这个环的高度不透明和丰富的精细尺度结构。利用Cassini航天器上可见光和红外成像光谱仪（VIMS）对十字座星星γ星17次掩星的小波分析，我们可以观测到B环中的5种密度波。其中两个波分别由距离土星中心96，427公里和101，311公里的Janus 2：1和Mimas 5：2 Inner Lindblad Resonance产生。这两种波都可以在单独的掩星剖面中检测到，但是多剖面小波分析揭示了Janus 2：1波的模式速度的意外变化，这可能是由于Janus轨道的周期性变化引起的。其他三个波特征与Janus 3：2，Enceladus 3：1和Pandora 3：2在115，959公里，115，207公里和108，546公里处的林德布拉德内共振有关。这些波在单独的剖面中是不可见的，但是具有正确模式速度的结构可以在适当相位校正的平均子波中被检测到。根据这五个波估计环的表面质量密度在40到140 g/cm 2之间，尽管环在这些区域的光深范围从1.5到几乎5。这表明B环的总质量很可能是土星卫星土卫一质量的三分之一到三分之二。
Saturn’s B ring is the most opaque ring in our Solar System, but many of its fundamental parameters, including its total mass, are not well constrained. Spiral density waves generated by mean-motion resonances with Saturn’s moons provide some of the best constraints on the rings’ mass density, but detecting and quantifying such waves in the B ring has been challenging because of this ring’s high opacity and abundant fine-scale structure. Using a wavelet-based analyses of 17 occultations of the starγCrucis observed by the Visual and Infrared Mapping Spectrometer (VIMS) onboard the Cassini spacecraft, we are able to examine five density waves in the B ring. Two of these waves are generated by the Janus 2:1 and Mimas 5:2 Inner Lindblad Resonances at 96,427 km and 101,311 km from Saturn’s center, respectively. Both of these waves can be detected in individual occultation profiles, but the multi-profile wavelet analysis reveals unexpected variations in the pattern speed of the Janus 2:1 wave that might arise from the periodic changes in Janus’ orbit. The other three wave signatures are associated with the Janus 3:2, Enceladus 3:1 and Pandora 3:2 Inner Lindblad Resonances at 115,959 km, 115,207 km and 108,546 km. These waves are not visible in individual profiles, but structures with the correct pattern speeds can be detected in appropriately phase-corrected average wavelets. Estimates of the ring’s surface mass density derived from these five waves fall between 40 and 140 g/cm2, even though the ring’s optical depth in these regions ranges from ∼1.5 to almost 5. This suggests that the total mass of the B ring is most likely between one-third and two-thirds the mass of Saturn’s moon Mimas.