土星的快速自转由其引力场和扁率决定
Saturn's fast spin determined from its gravitational field and oblateness
摘要：
土星的磁极与自转轴对齐，排除了使用磁场测量来确定其自转周期。之前旅行者号宇宙飞船通过无线电测量确定的周期为10 h 39 m 22.4 s。当卡西尼号探测器测量到10 h 47 m 6 s的周期时，发现它在连续测量之间也会发生变化，很明显射电周期不能用来确定大部分行星的自转周期。基于土星测得的风场的估计增加了更多的不确定性，给出的数字小于旅行者号的自转周期，目前土星的自转周期被认为是在10小时32米和10小时47米之间，这对这样一个基本属性是不满意的。在这里，我们报告了一个10小时32分45秒+-46秒的周期，基于优化方法，使用土星的测量引力场和限制观察到的形状和可能的内部密度分布。此外，即使仅使用来自其引力场的约束，也可以以几分钟的精度推断旋转周期。为了验证我们的方法，我们将相同的程序应用于木星，并正确地恢复了其众所周知的旋转周期。
英文摘要：
The alignment of Saturn's magnetic pole with its rotation axis precludes the use of magnetic field measurements to determine its rotation period. The period was previously determined from radio measurements by the Voyager spacecraft to be 10h 39m 22.4s. When the Cassini spacecraft measured a period of 10h 47m 6s, which was additionally found to change between sequential measurements, it became clear that the radio period could not be used to determine the bulk planetary rotation period. Estimates based upon Saturn's measured wind fields have increased the uncertainty even more, giving numbers smaller than the Voyager rotation period, and at present Saturn's rotation period is thought to be between 10h 32m and 10h 47m, which is unsatisfactory for such a fundamental property. Here we report a period of 10h 32m 45s +- 46s, based upon an optimization approach using Saturn's measured gravitational field and limits on the observed shape and possible internal density profiles. Moreover, even when solely using the constraints from its gravitational field, the rotation period can be inferred with a precision of several minutes. To validate our method, we applied the same procedure to Jupiter and correctly recovered its well-known rotation period.
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