New research highlights the risks space radiation poses to lunar and Mars exploration, focusing on recent solar energetic particle events. The study highlights the varying degrees of natural protection from this radiation on Earth, the Moon and Mars, and highlights the importance of developing effective shielding for the safety of astronauts on future space missions.
Space radiation poses a major challenge to human space exploration ambitions, particularly in missions to the Moon and Mars. This radiation mainly comes from solar energetic particles (SEPs) produced by solar flares, which can significantly increase radiation levels and pose a threat to astronauts' health.
In addition, intense solar high-energy particle events can trigger ground radiation enhancements (GLEs), further increasing radiation levels on the surface of celestial bodies.
The research team led by Professor Guo Jingnan of the University of Science and Technology of China, Chinese Academy of Sciences, collaborated with researchers from Germany, Bulgaria, and the United States to focus on analyzing a SEP event that occurred on October 28, 2021, which was energetic enough to trigger a GLE event on the Earth's surface.
In addition, this high-energy particle event was detected by the Chang'e-4 lunar mission on the lunar surface and the Curiosity rover on the Martian surface.
This is the first GLE event detected on the surface of three planetary bodies. By combining measurement and modeling methods, the team examined the potential radiation risks posed by SEPs that humans might face in the future on the moon and Mars. The findings were recently published in the journal Geophysical Research Letter.
Earth’s protection of SEP
Earth's magnetic field and atmosphere protect against lower-energy space charged particles. The GLE the team studied, called GLE73, is the most recent GLE event ever detected. While Earth's shielding mitigates the risk, the Moon and Mars lack similar protection.
The Moon lacks a global magnetic field and atmosphere, making it vulnerable to SEP particles. China's Chang'e 4 lunar mission and NASA's Lunar Reconnaissance Orbiter (LRO) observed the GLE73 event, but the measured radiation doses were within safe limits.
However, simulation results indicate that without adequate shielding, future lunar missions may face radiation risks from approximately one in every five SEP events, which would further pose a serious threat to astronaut lives.
Radiation Challenge on Mars
Mars, located between the moon and Earth, lacks a global magnetic field but has a thin atmosphere that absorbs high-energy particles. Instruments aboard ESA's ExoMars TGO and NASA's MSL observed the recent GLE73 event, showing radiation levels in Mars' orbit about 30 times higher than on the surface.
This indicates that the Martian atmosphere has a strong ability to absorb radiation caused by SEP. However, its shielding effect on background galactic cosmic rays (GCR) is limited. Simulations show that past GLE events on the Martian surface remain below the acute radiation syndrome (ARS) threshold.
However, extreme high-energy solar radiation events that occur en route to Mars or in orbit around Mars pose significant radiation risks to future deep space missions.
In summary, when energetic particles from the Sun reach the Earth, Moon, and Mars, their fates and radiation effects are not the same. Recent detections of SEP events on the surface of the Moon and Mars highlight the need to address these challenges. Therefore, further research and effective shielding measures are crucial for astronaut safety.