NASA's Fermi Gamma-ray Space Telescope has observed the moon for 10 years. Although our eyes cannot see gamma rays, the space telescope shows us what it's like to "see" the moon from a high-energy radiation perspective. In new Fermi images, the moon glows brighter than the sun, which is a fiery sight.
Gamma-ray observations are not sensitive enough to clearly see the lunar surface features or lunar disk shape, but Fermi's large area telescope (LAT) detects a strong glow centered on the lunar position in the sky, it said in a NASA press release. By studying Fermi's images, NASA can help protect astronauts from dangerous conditions, including high-energy gamma radiation when visiting the moon.
Francesco Loparco and Mario Nicola Mazziotta, who are both at Italy's National Institute of Nuclear Physics in Bari, have studied the moon's gamma ray glow to better understand cosmic rays, fast moving particles that are another type of radiation from space.
Since these particles are electrically charged, they are strongly affected by magnetic fields that the moon does not have. Low-energy cosmic rays can reach the lunar surface and transform the moon into a "space-based particle detector" according to NASA. When cosmic rays hit the surface, they interact with the regolith (lunar powdery surface) to generate gamma ray emission. The moon absorbs most of these gamma rays, but some of them escape during the process.
Loparco and Mazziotta analyzed Fermi LAT lunar observations to demonstrate how this view has improved during the mission. The duo collected data for gamma rays with energies over 31 million electron volts, more than 10 million times greater than the energy from visible light, and organized them in a timely order, showing how longer exposures help improve perspective.
The moon's gamma ray glow is impressive, but the sun shines brighter in gamma rays with energies over a billion electron volts. Cosmic rays with lower energy do not reach the sun because its strong magnetic field acts as a shield against them. However, energetic cosmic rays can move through this magnetic screen and hit the atmosphere of the sun, producing gamma rays that can reach the Fermi Gamma-ray Space Telescope.
Pictures from ours @NASAFermi Space Telescope is a reminder that astronauts on the Moon need to withstand gamma radiation on the moon's surface. See how these observations help us prepare for a sustainable lunar occurrence w / ours #Artemis missions: https://t.co/wZUgxJ1iSV pic.twitter.com/GoqP5VRWl7
– NASA (@NASA) August 16, 2019
The gamma-ray moon does not show phases in a monthly cycle, but its brightness changes over time. According to Fermi LAT data, the luminance of the moon varies by approx. 20 percent over the Sun's 11-year cycle. NASA says variations in the intensity of the sun's magnetic field during the cycle can change the speed of cosmic rays reaching the moon and change the production of gamma rays.
While NASA is preparing to send humans to the moon in 2024 through the Artemis program, it is important to understand how the lunar environment can impact future missions. These gamma ray observations indicate that astronauts on the moon need protection from the same cosmic rays that generate this high-energy gamma radiation. With these observations, NASA can improve space suit design and educate future astronauts about the dangers of gamma radiation in the coming years.
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