Chinese scientists first to detect lunar tidal signals in the Earth's plasmasphere


Using data from multiple spacecraft, Chinese scientists have become the first to observe lunar tidal signals in the Earth's plasmasphere, according to an article published in the academic journal Nature Physics on Thursday.

As the sole natural satellite of the Earth, the moon's most direct effect on the Earth is the tidal effect caused by gravity, found in the latter's crust, oceans, atmosphere and ionosphere. Whether a lunar tide effect exists in the Earth's magnetosphere was unexplored before.

By analyzing "variations in the plasmasphere's boundary location over the past four decades from multi-satellite observations," researchers led by Xiao Chao, a postdoctoral fellow of Shandong University, and He Fei from the Institute of Geology and Geophysics under Chinese Academy of Sciences, found evidence of "a lunar tide-induced signal in the plasmasphere," the inner region of the magnetosphere filled with cold plasma.

"The signal possesses distinct diurnal (and monthly) periodicities, which are different from the semidiurnal (and semimonthly) variations dominant in the previously observed lunar tide effects in other regions," said the researchers in the article entitled "Evidence for lunar tide effects in Earth's plasmasphere." 

The study further discussed how the lunar tide formed in the plasmasphere and summarized three fundamental elements for the plasma tidal signal, namely the existence of a two-body celestial system, plasma and a magnetic field.

As planetary environments that meet all three conditions are so common in stellar systems, the plasma tide may be observed throughout the universe, said the authors.

"Therefore, the finding of this lunar tidal effect in the plasmasphere not only extends our knowledge of the Earth-Moon system but also opens new perspectives for further studies of tidal interactions in other planetary and larger-scale systems," they said.

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