Modulation of Saturn’s radio clock by solar wind speed
Modulation of Saturn’s radio clock by solar wind speed
复制标题
太阳风速对土星无线电钟的调制
DOI：
10.1038/nature06237
复制
发表时间：
2007
期刊：
影响因子：
64.8
通讯作者：
H. Rucker
中科院分区：
文献类型：
--
作者：
P. Zarka;L. Lamy;B. Cecconi;R. Prangé;H. Rucker
巨行星的内部自转速率可以通过云的运动来估计，但这种方法并不十分精确，因为绝对风速并不是先验已知的，而是取决于纬度：无线电发射的周期性被认为与行星内部磁场有关。土星，尽管有着明显的轴对称磁场，但从极光源发射出波长为1000米的光子。这种发射被调制在一个最初确定为10 h 39 min 24 ± 7 s的周期，这被认为是土星的自转周期。然而，随后的观察显示，在几个月到几年的时间尺度上，这个时间段的变化为±6分钟。在这里，我们报告说，公里辐射周期系统地变化±1%，特征时间尺度为20-30天。在这里，我们表明这些波动与土星的太阳风速度相关，这意味着土星的无线电时钟至少部分地受到行星磁层外部条件的控制。没有发现与太阳风密度、动压或磁场的相关性;因此，太阳风速度具有特殊的功能。我们还表明，长期波动只是短期波动的平均值，因此长期变化可能也是由太阳风的变化驱动的。
The internal rotation rates of the giant planets can be estimated by cloud motions, but such an approach is not very precise because absolute wind speeds are not known a priori and depend on latitude: periodicities in the radio emissions, thought to be tied to the internal planetary magnetic field, are used instead. Saturn, despite an apparently axisymmetric magnetic field, emits kilometre-wavelength (radio) photons from auroral sources. This emission is modulated at a period initially identified as 10 h 39 min 24 ± 7 s, and this has been adopted as Saturn’s rotation period. Subsequent observations, however, revealed that this period varies by ±6 min on a timescale of several months to years. Here we report that the kilometric radiation period varies systematically by ±1% with a characteristic timescale of 20–30 days. Here we show that these fluctuations are correlated with solar wind speed at Saturn, meaning that Saturn’s radio clock is controlled, at least in part, by conditions external to the planet’s magnetosphere. No correlation is found with the solar wind density, dynamic pressure or magnetic field; the solar wind speed therefore has a special function. We also show that the long-term fluctuations are simply an average of the short-term ones, and therefore the long-term variations are probably also driven by changes in the solar wind.