The sphere of plasma around Earth is affected by tides caused by the Moon, according to a new study published in Nature Physics. The discovery could have implications for space missions and studies of other planets.
High above Earth’s atmosphere is a donut-shaped ocean of plasma formed by charged particles from the solar wind trapped in our ionosphere and by Earth’s own magnetic field.
Known as the plasmasphere, this bubble of electrically charged particles has an outer boundary (plasmapause) located between 20,000 and 38,000 km from the center of the Earth at the magnetic equator. This location varies with seasons, solar activity, and other factors.
Now, a team of scientists has discovered that the plasmasphere oscillates according to the Moon’s orbit, just as the oceans do. Lunar tides occur thanks to the gravity of our natural satellite, which affects terrestrial matter in solid, liquid and gaseous states, but no one had verified whether the same also occurred with plasma.
With data from more than 50,000 plasmapause crossings, observed by various scientific instruments, the team found tides with oscillations showing a 3% difference in the “smoothness” of the plasmapause in its “normal” position.
The strangest fact of the discovery is that, unlike ocean tides, which are highest and lowest around New Moon and Full Moon, plasma tides are offset from the Moon’s position in the sky by 90°. In the plasmasphere, high tide occurs in the first quarter of the Moon, while low tide occurs in the last quarter.
There are, so far, no explanations for this displacement of the plasma tides in relation to the ocean tides. Scientists think this could mean that these tides are caused not only by gravity, but also by electromagnetic forces.
The findings could help scientists better understand the distribution of energetic particles from radiation belts, “which are a well-known danger to space infrastructure and human activities in space,” the authors said.
Source: Nature Physics; Eos
