NASA’s Fermi Gamma-ray Space Telescope has been observing the moon for 10 years. Even though our eyes can’t see gamma-rays, the space telescope shows us what it is like to “watch” the moon from a high-energy radiation perspective. In new Fermi images, the moon glows brighter than the sun and it is a fiery sight.
Gamma-ray observations are not sensitive enough to clearly spot lunar surface features or the moon’s disk shape, however, Fermi’s Large Area Telescope (LAT) detects a strong glow centered on the moon’s position in the sky, said a NASA press release. By studying Fermi’s images, NASA can help protect astronauts from dangerous conditions, including high-energy gamma radiation, when they visit the moon.
Francesco Loparco and Mario Nicola Mazziotta, who are both at Italy’s National Institute of Nuclear Physics in Bari, have been studying 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’re strongly impacted by magnetic fields, which the moon doesn’t have. Low-energy cosmic rays can reach the moon’s surface and turn the moon into a “space-based particle detector,” according to NASA. When cosmic rays hit the surface, they interact with the regolith (powdery surface of the moon), to generate gamma-ray emission. The moon absorbs most of these gamma rays, however, some of them escape in 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 above 31 million electron volts, more than 10 million times greater than the energy of visible light, and organized them in a timely sequence, showing how longer exposures help improve the perspective.
These images show Fermi’s improving view of the moon’s intense gamma-ray glow. (Photo Credit: NASA /DOE / Fermi LAT Collaboration)
The moon’s gamma-ray glow is impressive, however, the sun shines brighter in gamma rays with energies higher than one billion electron volts. Lower energy cosmic rays do not reach the sun because its strong magnetic field acts as a shield against them. Energetic cosmic rays can move through this magnetic screen though and hit the sun’s atmosphere, which produces gamma rays that can reach the Fermi Gamma-ray Space Telescope.
Images from our @NASAFermi space telescope are a reminder that astronauts on the Moon will need to withstand gamma radiation on the lunar surface. See how these observations are helping us prepare for a sustainable lunar presence w/ our #Artemis missions: https://t.co/wZUgxJ1iSV pic.twitter.com/GoqP5VRWl7
The gamma-ray moon doesn’t show phases in a monthly cycle, but its brightness changes over time. According to Fermi LAT data, the moon’s brightness varies by roughly 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 alter the rate of cosmic rays that reach the moon and change the production of gamma rays.
While NASA prepares to send humans to the moon by 2024 through the Artemis program, it is important to understand how the lunar environment might impact future missions. These gamma-ray observations demonstrate that astronauts on the moon will need protection from the same cosmic rays that generate this high-energy gamma radiation. With these observations, NASA can improve spacesuit designs and educate future astronauts on the dangers of gamma radiation in coming years.