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arXiv 1209.3797astro-ph.EP
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土星环热红外辐射的多层模型。III：从卡西尼CIRS推断的热惯性

A multilayer model for thermal infrared emission of Saturn's rings. III: Thermal inertia inferred from Cassini CIRS

Ryuji Morishima, Linda Spilker, Keiji Ohtsuki

备注：
47 pages, 7 tables, 13 figures
发表信息：
Icarus 215, 107-127, 2011
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摘要：

土星的主要环（A，B，C环和卡西尼司）的热惯性值来自我们的热模型，方位角扫描的卡西尼复合红外光谱仪（CIRS）所采取的光谱。模型拟合表明，环粒子的热惯性分别为16，13，20和11 JmPDMATHABMM K $^{-1}$ s $^{-1/2}$的A，B和C环，和卡西尼司，分别。然而，在土星阴影中的模拟和观测温度之间存在系统偏差，这取决于太阳相位角，这些偏差表明表观热惯性随太阳相位角增加。如果大的慢旋转颗粒具有比小的快旋转颗粒更低的热惯性值，则可能解释这种依赖性，因为慢旋转体的热发射在低相位时比快旋转体的热发射相对更强，反之亦然。附加的参数拟合，假设慢和快旋转体具有不同的热惯性值，显示出慢（快）旋转体的导出的热惯性值分别为8（77），8（27），9（34），5（55）JmPDMATHABMM K $^{-1}$ s $^{-1/2}$，对于A，B和C环，以及Cassini分区。快速旋转体的数值仍然比没有孔隙的固体冰的数值小得多。因此，快速旋转器可能有表面风化层，但这些可能不像慢速旋转器那样蓬松，可能是因为快速旋转器保持风化颗粒的能力有限，因为快速旋转器表面上的强大离心力。其他额外的参数拟合，其中快速旋转体的半径是不同的，表明小于$\sim$ 1厘米的粒子不应该占据超过一半的截面的A，B和C环。

英文摘要：

The thermal inertia values of Saturn's main rings (the A, B, and C rings and the Cassini division) are derived by applying our thermal model to azimuthally scanned spectra taken by the Cassini Composite Infrared Spectrometer (CIRS). Model fits show the thermal inertia of ring particles to be 16, 13, 20, and 11 Jm$^{-2}$K$^{-1}$s$^{-1/2}$ for the A, B, and C rings, and the Cassini division, respectively. However, there are systematic deviations between modeled and observed temperatures in Saturn's shadow depending on solar phase angle, and these deviations indicate that the apparent thermal inertia increases with solar phase angle. This dependence is likely to be explained if large slowly spinning particles have lower thermal inertia values than those for small fast spinning particles because the thermal emission of slow rotators is relatively stronger than that of fast rotators at low phase and vise versa. Additional parameter fits, which assume that slow and fast rotators have different thermal inertia values, show the derived thermal inertia values of slow (fast) rotators to be 8 (77), 8 (27), 9 (34), 5 (55) Jm$^{-2}$K$^{-1}$s$^{-1/2}$ for the A, B, and C rings, and the Cassini division, respectively. The values for fast rotators are still much smaller than those for solid ice with no porosity. Thus, fast rotators are likely to have surface regolith layers, but these may not be as fluffy as those for slow rotators, probably because the capability of holding regolith particles is limited for fast rotators due to the strong centrifugal force on surfaces of fast rotators. Other additional parameter fits, in which radii of fast rotators are varied, indicate that particles less than $\sim$ 1 cm should not occupy more than a half of the cross section for the A, B, and C rings.

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