On October 28, 2021, an immense surge of plasma and magnetized particles erupted from the sun, causing a substantial solar outburst that engulfed Earth, the moon, and Mars, immersing them in radiation. Remarkably, instruments on all three celestial bodies recorded this event nearly simultaneously.

Both the European Space Agency’s ExoMars Trace Gas Orbiter (TGO) and NASA’s Curiosity rover on Mars detected the influx of energized particles.

Similarly, the Chinese National Space Administration’s Chang’e-4 and NASA’s Lunar Reconnaissance Orbiter (LRO) on the moon picked up these particles.

Closer to home, the German Aerospace Center’s Eu: CROPIS satellite observed the radiation from low Earth orbit. The findings of this solar phenomenon were published on August 8 in the journal Geophysical Research Letters.

Understanding such occurrences, known as coronal mass ejections (CMEs), holds paramount importance for future space exploration, particularly concerning planned missions to send astronauts to Mars and establish a scientific outpost on the moon.

Earth benefits from its magnetic field, which acts as a shield against the most perilous solar outbursts. However, the moon and Mars lack this protective magnetosphere, allowing a significant amount of radiation to reach their surfaces.

This excessive radiation can have adverse effects on astronauts. Exposure to high doses of radiation may lead to skin irritation, nausea, blood disorders, weakened immunity, and even cancer, as reported in a 2014 study published in the journal Life. In severe cases, it can cause burns and neurological degeneration.

A dangerous dose is considered to be around 700 milligrays (1 gray being one unit of radiation). Fortunately, the CME on October 28 was relatively weak, measuring only about 31 milligrays.

Nonetheless, CMEs tend to become more frequent and intense as the sun approaches the peak of its 11-year solar activity cycle, which could occur by the end of 2023.

A recent study showed that Earth’s magnetosphere and atmosphere rendered the radiation from the CME insignificant by the time it reached the planet’s surface.

Mars’s atmosphere provided some buffer, resulting in the surface receiving only about one-30th of the initial dose. In contrast, the moon’s surface absorbed over half of the initial radiation dose from the CME.

While this particular CME event was not potent enough to pose a threat to human health, half of the radiation from a more substantial outburst could be deadly. Analyzing the impact of CMEs on celestial bodies beyond Earth can aid scientists in developing the necessary shielding to protect future astronauts.

“Space radiation can pose a genuine danger to our exploration throughout the Solar System,” stated Colin Wilson, a project scientist on ExoMars TGO. “Thanks to data from missions like ExoMars, we can prepare for how best to protect our human explorers.”