Solar flare hits Earth, Moon and Mars

On October 28, 2021, a giant coronal mass ejection occurred on the Sun, which affected the Earth and Mars at the same time. These two planets were on opposite sides of the Sun at a distance of about 250 million kilometers from each other. An international group of scientists who published an article in the journal Geophysical Research Letters, came to this conclusion.

The mass ejection associated with a solar flare is a rare phenomenon known as ground level enhancements (GLE). During this event, the solar particles have enough energy to overcome the magnetic field that surrounds the Earth and protects it from the effects of less strong coronal ejections. Since 1940, only 73 cases of ground elevation have been recorded.

The 2021 GLE event is unique in that measurements were taken simultaneously on Earth, the Moon, and Mars. An international fleet of spacecraft, including the ESA ExoMars Trace Gas Orbiter (TGO), NASA’s Curiosity rover, CNSA’s Chang’e-4 lunar lander, NASA’s Lunar Reconnaissance Orbiter (LRO), and the DLR Eu:CROPIS Earth orbiter, recorded energy particles.

Since the Moon and Mars do not have their own magnetic fields, solar particles easily reach their surface and can even interact with the soil, creating secondary radiation. However, Mars still has a thin atmosphere that keeps most low-energy solar particles at bay and slows down the high-energy ones.

Studies have shown that the GLE event, which occurs on average once every 5.5 years, leads to an excess of safe levels of radiation on the Moon. This may pose a risk to future manned missions. During the 2021 GLE, the radiation dose was 31 milligrays, although the potential release in 1972 could have produced a dose of 10 grays if it had reached the moon. The researchers also compared measurements taken by the ExoMars TGO spacecraft and the Curiosity rover and found that the atmosphere on Mars reduces the radiative forcing from a coronal mass ejection by a factor of 30 to 0.3 milligray.