Geophysical Research Letters: 2021 solar flare affects Earth and Mars
A giant coronal mass ejection that occurred on the Sun on October 28, 2021, simultaneously affected the Earth and Mars, which were located on opposite sides of the Sun at a distance of about 250 million kilometers from each other. This conclusion was reached by an international group of scientists who published article in Geophysical Research Letters.
The 2021 solar flare ejecta is an example of a rare phenomenon called ground level enhancements (GLE). During this event, the solar particles have enough energy to pass through the magnetic field that surrounds the Earth and shields from the effects of less strong coronal ejections. Since 1940, only 73 ground elevations have been recorded.
The 2021 GLE event is the first of its kind to take measurements simultaneously on the surfaces of the Earth, Moon and Mars. The energetic particles were captured by 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 DLR Eu :CROPIS Earth.
Since the Moon and Mars do not generate their own magnetic fields, solar particles can easily reach their surface and even interact with the soil, creating secondary radiation. But Mars still has a thin atmosphere that stops most of the lower-energy solar particles and slows down the high-energy ones.
As scientists have shown, the GLE event, which occurs on average once every 5.5 years, leads to an excess of a safe level of radiation on the moon. This may pose a risk to future manned missions. During the 2021 GLE, the dose was 31 milligrays, although the 1972 outburst could have potentially delivered 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.
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