Chang'e-4 Discovers 'Cosmic Ray Cavity' in Earth-Moon Space, Providing New Insights for Deep Space Radiation Protection
Summary: A research team led by Professor Shi Quanqi from Shandong University, through analyzing over three years of continuous observational data from the Chang'e-4 lander's Lunar Surface Neutron and Dose Rate Monitoring Detector, has discovered a region of significantly reduced low-energy galactic cosmic ray flux in the Moon's orbit daylight side, known as the "cosmic ray cavity." This discovery breaks traditional understanding and provides new scientific basis for understanding the Earth-Moon space radiation environment structure and radiation avoidance strategies for future deep space exploration missions.
Credit: Unsplash / Conceptual illustration
Sources (original pages)
- Chang'e-4 Data Discovers "Cosmic Ray Cavity" in Earth-Moon Space, May Provide Optimized Path for Interstellar Navigation Radiation Avoidance - China National Space Administration Official Website
Galactic cosmic rays are high-energy charged particle streams originating from deep within the Milky Way galaxy, widely present throughout interplanetary space. For a long time, the scientific community generally believed that in the Earth-Moon space area far from planetary magnetic field influence, galactic cosmic rays should be approximately uniformly distributed. However, Professor Shi Quanqi's research team from Shandong University, through analyzing over three years of continuous observational data from China's Chang'e-4 lander's Lunar Surface Neutron and Dose Rate Monitoring Detector, discovered a region of significantly reduced low-energy galactic cosmic ray flux in the Moon's orbit daylight side, known as the "cosmic ray cavity."
The formation of this spatial structure originates from the modulation effect of Earth's magnetic field on the propagation path of galactic cosmic rays, indicating that the influence range of Earth's magnetic field on the space environment can extend to the Moon's orbit and even farther. This discovery breaks traditional understanding and provides new scientific basis for understanding the Earth-Moon space radiation environment structure and radiation avoidance strategies for future deep space exploration.
Galactic cosmic rays are generally considered high-energy charged particle streams originating from deep within the Milky Way galaxy, possessing extremely strong penetration and ionization effects that can damage spacecraft electronic devices and biological tissues. They are one of the most harmful radiation sources in the deep space environment, and currently there are no effective protective measures for deep space travel. Traditional observations and theoretical research generally believe that galactic cosmic rays are nearly isotropically uniform in interplanetary space, with natural shielding effects usually appearing only within the magnetic field range of strongly magnetized celestial bodies.
Chang'e-4 successfully landed on the far side of the Moon on January 3, 2019, opening a new era for human far side lunar exploration. Its Lunar Surface Neutron and Dose Rate Monitoring Detector can perform periodic scan observations of the Earth-Moon space radiation environment with the lunar orbital period (about 28 days) as the scale. The research team systematically analyzed over three years of continuous observational data accumulated during the mission and discovered that under stable interplanetary magnetic field and solar wind conditions, in the orbital interval before the moon phase of 12 hM (corresponding to the new moon position), the low-energy galactic cosmic ray count rate was significantly lower than other orbital areas, forming a stable low-flux spatial structure.
To further reveal the formation mechanism of this spatial structure, the research team conducted three-dimensional particle orbit numerical simulation studies including Earth's magnetic field and interplanetary magnetic field background. The simulation results show that Earth's magnetic field can significantly change the propagation trajectory of galactic cosmic ray particles, forming a stable low particle density area in specific regions of Earth-Moon space, i.e., the "cosmic ray cavity." The simulation results are highly consistent with the observational results, successfully reproducing the phenomenon of galactic cosmic ray flux reduction in specific regions of the Moon's orbit at 20 MeV and 100 MeV proton energy ranges, verifying the physical mechanism of Earth's magnetic field modulating galactic cosmic ray propagation at the Earth-Moon space scale.
This result indicates that beyond its existing range, Earth's magnetic field can still modulate and affect the distribution pattern of high-energy particles in deep space at the Earth-Moon space scale. Compared to protons, heavy ions have higher charge numbers and stronger biological damage effects. Although their relative proportion is small, they are a source of concern in deep space radiation hazards. Given that the gyroradius of heavy ions of the same energy is smaller than that of protons, they are more easily deflected by magnetic fields. Therefore, the "cosmic ray cavity" formed by Earth's magnetic field may have a more significant shielding effect on heavy ions, which is more important for reducing high-risk heavy ion radiation.
In addition, similar cosmic ray cavity phenomena may also widely exist around other planets with strong magnetic fields, and may provide new scientific basis and important inspiration for radiation avoidance strategies of deep space exploration missions and future interstellar navigation path optimization.