An image of the Earth and Moon comparing ocean tides (shown as a small blue ring) to plasmasphere tides (shown as a large orange ring) (Image credit: Chinese Academy of Sciences)
The Moon exerts a previously unknown tidal force on the “plasma ocean” that surrounds Earth’s upper atmosphere, creating fluctuations similar to tides in the oceans, a new study suggests.
In the lunar study, published Jan. 26 in the journal Nature Physics (opens in new tab), scientists used more than 40 years of data collected from satellites to study the tiny changes in the shape of the plasmasphere, the inner region of the magnetosphere the earth, which protects our planet from solar storms and other types of high-energy particles.
The plasmasphere is a roughly annular blob of cool plasma (opens in new tab) that sits on Earth’s magnetic field lines, just above the ionosphere, the electrically charged part of the upper atmosphere. The plasma or ionized gas in the plasmasphere is denser than the plasma in the outer regions of the magnetosphere, causing it to sink to the bottom of the magnetosphere. The boundary between this dense sunken plasma and the rest of the magnetosphere is known as the plasmapause.
“Because of its cold, dense plasma properties, the plasmasphere can be thought of as a ‘plasma ocean,’ and the plasmapause represents the ‘surface’ of that ocean,” the researchers write in the paper. The moon’s gravitational pull can distort this “ocean,” causing its surface to rise and fall like the ocean tides.
Related: A colossal asteroid impact changed the balance of the moon forever (opens in new tab)
It is already known that the moon exerts tidal forces on the earth’s oceans, crust, near-surface magnetic field, and gas in the earth’s lower atmosphere. However, no one had previously tested whether there is a tidal effect on the plasmasphere.
To answer this question, the researchers analyzed data from more than 50,000 satellite crossings of the plasmasphere belonging to 10 science missions, including NASA’s Time History of Events and Macroscale Interactions during Substorms (THEMIS) mission. The satellites’ sensors are able to detect minute changes in plasma concentration, allowing the team to map the precise boundary of the plasmapause in more detail than ever before.
The satellite crossings occurred between 1977 and 2015, and during that time there were four complete solar cycles. This information allowed the team to consider the role of solar activity on Earth’s magnetosphere. Once the Sun’s influence was accounted for, it became clear that fluctuations in the shape of the plasmapause followed daily and monthly patterns very similar to ocean tides, suggesting that the Moon was the most likely cause of the plasma tides.
Researchers aren’t sure exactly how the moon is causing the plasma tides, but their best guess right now is that the moon’s gravity is causing perturbations in Earth’s electromagnetic field. But more research is needed to say for sure.
Related: How was the moon formed? A supercomputer could have the answer (opens in new tab)
The team believes this previously unknown Earth-Moon interaction could help researchers better understand other parts of the magnetosphere, such as the Van Allen radiation belts, which capture high-energy particles from the solar wind and trap them in the outer magnetosphere.
“We suspect that the observed plasma tide may subtly affect the distribution of energetic radiation belt particles, which pose a known threat to space-based infrastructure and human activities in space,” the researchers wrote. A better understanding of the tides could therefore help improve work in these areas, they added.
The researchers also want to see if plasma in other planets’ magnetospheres is affected by those planets’ moons. “These results could have implications for tidal interactions in other two-body celestial systems,” they wrote.
Originally) released on LiveScience.com
Source: www.space.com
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