数以百计的外太阳系行星的最近发现使得有关类地行星和宇宙生命的探索得到关注。在未来，大型空间观测可直接探测岩态行星的散射光，但仍无法对行星表面进行空间解析。运用反射模型和源自卫星观测的实时云数据，我们在此表明，尽管地球具有动态天气模式， 遥距假定观察者所观察到的地球散射光作为时间函数仍包含了能精确测量地球自转周期的足量信息。这是因为洋流和大陆导致了相对稳定的平均全球云层模式。这些测量的精度会因视域几何和其他观测限制因素而有所不同。假如旋转周期可以被准确测量，那么我们就可以对持续数月的数据进行相干合并从而来获得有关行星表面单个区域的光谱信息。此外，周期信号偏差还可用于推断大气层中比如云层这类相对短时生灭结构的表现。这可以为那些拥有相较于旋转周期随时变化的活跃天气系统的系外行星提供有效识别技术。 这种可变性可能与临近相变的大气温度和压力有关且可能证实星球表面具有液态水存在。
With the recent discoveries of hundreds of extrasolar planets, the search for planets like Earth and life in the universe is quickly gaining momentum. In the future, large space observatories could directly detect the light scattered from rocky planets, but they would not be able to spatially resolve a planet’s surface. Using reflectance models and real cloud data from satellite observations, here we show that, despite Earth’s dynamic weather patterns, the light scattered by the Earth to a hypothetical distant observer as a function of time contains sufficient information to accurately measure Earth’s rotation period. This is because ocean currents and continents result in relatively stable averaged global cloud patterns. The accuracy of these measurements will vary with the viewing geometry and other observational constraints. If the rotation period can be measured with accuracy, data spanning several months could be coherently combined to obtain spectroscopic information about individual regions of the planetary surface. Moreover, deviations from a periodic signal can be used to infer the presence of relatively short-lived structures in its atmosphere (i.e., clouds). This could provide a useful technique for recognizing exoplanets that have active weather systems, changing on a timescale comparable to their rotation. Such variability is likely to be related to the atmospheric temperature and pressure being near a phase transition and could support the possibility of liquid water on the planet’s surface.