Why can solar flares endanger astronauts outside Earth’s magnetic field?

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Sun Joshua trees at sunset, Joshua Tree National Park, southern California, U.S.

Solar flares endanger astronauts outside Earth’s magnetic field because they produce an intense flux of high-energy particles, primarily protons. While Earth’s magnetosphere typically deflects these charged particles, astronauts traveling in interplanetary space lack this protective shield.12

Exposure to this ionizing radiation poses severe health risks, as it can damage DNA and cells, potentially leading to radiation sickness, the development of fatal tumors, or even death. Because these solar energetic particles are difficult to predict or shield against, they represent a critical hazard for long-duration human spaceflight missions, such as those to the Moon or Mars.342