In the pursuit of unraveling the mysteries of the cosmos, we are continually pushing the boundaries of human exploration. However, one significant obstacle remains - space radiation. This invisible threat poses a considerable risk to the health of astronauts, especially during long-term missions to future lunar or Martian stations. This concern was highlighted in a recent study conducted by scientists at the University of Science and Technology of China.
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Space radiation, particularly sporadic solar energetic particles (SEPs) generated by extreme solar eruptions, can elevate lunar or Martian surface radiation levels to potentially hazardous values. This was brought to light during a solar storm detected on October 28, 2021. The findings of this event were recently published, shedding new light on the challenges of space exploration.
A Rare Solar Storm
The solar storm was captured by an international fleet of spacecraft, including the European Space Agency's (ESA) ExoMars Trace Gas Orbiter (TGO), NASA's Curiosity Mars rover, the China National Space Administration (CNSA) Moon lander, NASA's Lunar Reconnaissance Orbiter (LRO), and the German Aerospace Center's (DLR) Eu:CROPIS Earth orbiter.
The event was a rare 'ground-level enhancement,' meaning the particles released in the explosion were energetic enough to penetrate Earth's protective magnetic bubble, which usually shields us from less active solar outbursts. This was only the 73rd ground-level enhancement recorded since the 1940s and the first time a solar storm has simultaneously hit three planetary surfaces.
The Impact on Moon and Mars
Unlike Earth, the Moon and Mars lack a protective 'bubble,' allowing solar particles to interact with the soil and create secondary radiation. However, Mars' thin atmosphere does stop most lower-energy solar particles and slows down the highly energetic ones.
ESA stated that a radiation dose above 700 milligray could induce radiation sickness, leading to symptoms such as infection and internal bleeding. A dose exceeding 10 gray could be fatal within two weeks. Fortunately, the 2021 solar storm did not release enough radiation to harm astronauts in lunar orbit, with NASA's Lunar Reconnaissance Orbiter registering just 31 milligray.
The Need for Further Research
Scientist Jingnan Guo, who researched the solar event, emphasized the importance of understanding these events for future crewed missions to the Moon's surface. Guo's calculations of past ground-level enhancement events indicate that on average, one event every 5.5 years may have exceeded the safe dose level on the Moon if no radiation protection had been provided.
The study also revealed that the ExoMars measured 9 milligray, 30 times more than the 0.3 milligray detected on the surface by the Curiosity rover. ESA's inner Solar System missions, Solar Orbiter, SOHO, and BepiColombo, were also caught in the blast, providing additional vantage points to study this solar event.
Marco Pinto, an ESA research fellow working on radiation detectors, expressed his excitement, stating, "We live in a golden age of Solar System physics." The radiation detectors aboard planetary missions such as BepiColombo, en route to Mercury, and Juice, heading to Jupiter, provide much-needed coverage to study the acceleration and propagation of solar energetic particles.
As we continue to explore the cosmos, understanding and mitigating the risks of space radiation will be crucial in ensuring the safety and success of future missions.
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