Size of the smallest particles in Saturn's rings
Size of the smallest particles in Saturn's rings
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土星环中最小粒子的大小
DOI：
10.1016/j.icarus.2019.06.007
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发表时间：
2019
期刊：
影响因子：
3.2
通讯作者：
Hiroshi Kimura
中科院分区：
文献类型：
--
作者：
Keiji Ohtsuki;Hiroshi Kawamura;Naoyuki Hirata;Hiroshi Daisaka;Hiroshi Kimura
航天器和地面观测表明，土星主环中的粒子在厘米到10米之间具有幂律分布，但似乎缺乏亚厘米粒子。最近根据卡西尼号的观测结果进行的研究表明，最小的颗粒尺寸大约为毫米，尽管它们的丰度低于根据更大尺寸范围的幂律分布推断的预期。粒子间的凝聚力已被提出来解释亚厘米级粒子的缺乏，但它的强度取决于撞击速度。为了更好地理解最近的卡西尼观测小环粒子，我们研究的碰撞速度（v imp）之间的环粒子使用N体模拟，包括尺寸分布。我们发现大多数碰撞都发生在低速下，v imp 0.1 cm s-1;即使在粒子速度弥散因重力尾流而增强的致密环中，它们也会以如此低的速度碰撞，因为粒子往往在尾流中相干移动。这个速度太低，无法分离由于凝聚力而附着在大颗粒表面的亚厘米颗粒，这解释了它们在主环中的缺乏。另一方面，在较高速度下的碰撞偶尔会发生，或者是在稀环中高速尾部的颗粒之间的碰撞，或者是在密环中相邻尾流之间的碰撞。这种罕见的高速撞击释放出牢固附着在大颗粒表面的毫米级颗粒，这就解释了所观察到的游离毫米级颗粒丰度相对较低的原因。我们的研究结果表明，土星环中的小颗粒的研究将提供约束的冰颗粒之间的凝聚力，这不仅是重要的起源和演化的行星环，但也为其他天体物理问题，包括尘埃演化和星子形成的原行星盘。
Spacecraft and ground-based observations have shown that particles in Saturn's main rings have a power-law distribution roughly between centimeter and ten meters, but sub-centimeter particles appear to be lacking. Recent studies based on Cassini observations suggest that the minimum particle size is on the order of millimeters, although their abundance is lower than is expected from the extrapolation of the power-law distribution for the larger size range. Cohesive force between particles has been proposed to explain the paucity of sub-centimeter particles, but its strength depends on impact velocity. In order to better understand recent Cassini observations about small ring particles, we examine impact velocity (v imp) between ring particles using N-body simulation including size distribution. We find that most collisions take place at low velocities with v imp≲ 0.1 cm s− 1; even in dense rings where particles' velocity dispersion is enhanced by gravitational wakes, they collide at such low velocities because particles tend to move coherently in the wakes. This velocity is too low to detach sub-centimeter particles that are attached to the surface of large ones due to the cohesive force, explaining their paucity in the main rings. On the other hand, impacts at higher velocities occasionally occur, either as collision between particles in the high-velocity tail in dilute rings, or as collisions between adjacent wakes in the case of dense rings. Such infrequent high-velocity impacts release millimeter-sized particles strongly attached to the surface of large ones, explaining the observed free millimeter-sized particles with relatively low abundance. Our results suggest that studies of small particles in Saturn's rings would provide constraints on the cohesive force between icy particles, which is important not only for the origin and evolution of planetary rings but also for other astrophysical problems including dust evolution and planetesimal formation in protoplanetary disks.
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影响因子：
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作者：
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作者：
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DOI：
10.1086/301182
发表时间：
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期刊：
The Astronomical Journal
影响因子：
--
作者：
K. Ohtsuki;H. Emori
通讯作者：
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