Scientists have identified a region of reduced cosmic radiation near Earth's moon, which could significantly decrease astronauts' exposure to harmful radiation during future lunar missions by scheduling surface operations for local morning hours.
This discovery, based on data from China's Chang'e-4 lunar lander, suggests Earth's magnetic field extends its influence in space further than previously understood. This challenges the earlier assumption that galactic cosmic rays are largely uniform in the space between Earth and the moon outside the planet's protective magnetic field.
Study Details
The study, published in Science Advances, analyzed measurements from the Lunar Lander Neutron and Dosimetry experiment aboard Chang'e-4. Researchers reported a region of reduced galactic cosmic rays during the moon's local morning, which is a few hours after lunar sunrise.
Implications for Astronaut Safety
Cosmic rays pose significant radiation hazards to astronauts beyond low Earth orbit. These high-energy particles can damage DNA and elevate cancer risks. With more crewed missions planned for the moon, including NASA's Artemis II, a detailed map of radiation intensity could assist mission planners in minimizing astronauts' radiation exposure during surface explorations.
Robert Wimmer-Schweingruber, a professor at Kiel University and a corresponding author of the study, stated that lunar morning appears to be the optimal time for excursions, potentially reducing radiation on astronauts' skin by approximately 20% compared to average lunar levels.
Methodology and Findings
The researchers analyzed data spanning 31 lunar cycles from January 2019 to January 2022. They focused on periods of low solar activity when galactic cosmic rays were the predominant source of space radiation.
They observed consistent changes in measured proton counts from these rays as the moon orbited Earth. Specifically, lower-energy protons (in the 9.18 to 34.14 mega-electron-volt range) decreased by about 20% during the moon's local morning, particularly during its waxing gibbous phase.
The recurring nature of this decrease led the team to conclude that the moon was passing through a genuine region of reduced cosmic ray radiation. They believe this is caused by Earth's magnetic field blocking some high-energy protons. Simulations confirmed the existence of this cavity.
Earth's Magnetic Field Influence
The findings suggest an updated understanding of cosmic radiation behavior between Earth and the moon. While it was generally thought that galactic cosmic rays were evenly distributed beyond Earth's magnetosphere, this study indicates Earth's magnetic field influences space beyond its previously expected extension. This affects regions both ahead of the magnetosphere on the sunward side and within the magnetotail.
Future studies with expanded datasets are expected to further define the size and characteristics of this cavity, contributing to safer lunar exploration.