Earth’s magnetic field may be more powerful than we thought
A major defense against everything space throws at us, Earth’s magnetic field may even protect the moon from damaging galactic cosmic rays
Far from the Earth’s magnetic core, the moon feels even more of its effects than scientists previously thought.
Barreling through the universe with incredible power and speed, galactic cosmic rays are a major source of radiation in space. But thanks to Earth’s strong magnetic field, these charged particles don’t usually make it directly to our planet, so we are protected from the radiation’s damaging effects. This field may be doing much more: new data collected by China’s Chang’e 4 lunar lander shows that our magnetic field’s influence is so powerful that it extends farther into space than previously believed—stretching even beyond the moon.
In a study published on Wednesday in Science Advances, researchers describe a “cavity” in space between Earth and the moon where cosmic rays are deflected by Earth’s magnetic field. This suggests that the effects of our planet’s magnetism are present much farther from us than anyone could have expected.
Gravitational cosmic rays spiral through the heliosphere, but Earth’s magnetic influence shields a large area of space from some of the particles.
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Launched in 2018, Chang’e 4 was the first spacecraft to land on the far side of the moon. Among the many scientific instruments onboard was the Lunar Lander Neutron and Dosimetry experiment, which was designed to measure the radiation future astronauts might experience if they were to land there. Scientists had long assumed most of the moon lay beyond the protection of Earth’s magnetic field, but in 2019 scientists began noticing something odd about the experiment’s data that suggested the moon was somewhat protected from galactic cosmic rays.
The finding came as “a surprise,” says Robert Wimmer-Schweingruber, a co-author of the study and a physicist at Kiel University in Germany. “Personally, I didn’t believe it for a long, long time. I thought it was an artifact in the data until we did a lot of statistical tests.”
Galactic cosmic rays originate from a variety of sources in space, such as stars, supernovae and black holes. These diverse origins mean that by the time the rays get near Earth, they don’t all carry the same level of energy. The highest-energy particles move quickly through the solar system, while some of the weaker particles linger—and their radiation could affect astronauts, Wimmer-Schweingruber says.
“These low-energy particles weren’t that interesting to us until we saw this effect, and then we realized this is actually important for the skin dose of astronauts,” he says.
Shielding astronauts from the dangers of radiation is critical to ensuring a human presence in space. This means creating materials that are light enough to bring into space but protective enough to keep radiation at bay, says Philip Metzger, a professor of planetary science and space technology at the University of Central Florida, who was not involved in the new study. Knowing more about the distribution of radiation in space, and especially between the moon and Earth, could help scientists plan safer missions.
For example, if NASA’s plan to put humans on the moon in a semipermanent capacity comes to pass, then it may make sense for astronauts to schedule activities outside any sheltered habitats while the moon is within the influence of Earth’s magnetic field.
“It is brilliant research, and it just shows us that the more we study phenomena outside of our planet, the more we discover we don’t know,” Metzger says. “That’s why we need to do space missions.”
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