Astronaut-menacing sunstorm spotted rippling across inner solar system

Rare coronal mass ejection so powerful it was observed from Earth, Moon, and Mars

Spacecraft orbiting the Earth, Moon, and Mars have all detected the same giant coronal mass ejection from the Sun – the first time vehicles in all three locations - plus one on the surface of Mars - have all observed the same event of this sort.

The solar outburst, tagged GLE73, took place on October 28, 2021, and sent a huge wave of energetic particles into space. A team of astronomers working in China, Europe, and the US described the eruption as a "ground level enhancement event" (GLE).

GLEs are relatively rare. Only 73 such events have been detected since the 1940s and none have happened since 2021. Particles ejected by GLEs are particularly energetic in comparison to solar storms and can reach vast distances across space.

Our star's GLE73 was picked up by instruments aboard the European Space Agency's ExoMars Trace Gas Orbiter (TGO), NASA's Curiosity Mars rover, the China National Space Agency's Chang'e-4 Moon lander, NASA's Lunar Reconnaissance Orbiter (LRO), and the German Aerospace Center's Eu:CROPIS experimental satellite, according to the researchers.

The spread of energy from GLE73 led astroboffins to warn about the risks of space radiation for astronauts exploring the Moon and Mars in the future. 

Ionizing radiation is measured in units called grays. Doses above 700 milligray can damage bone marrow and lead to sickness, internal bleeding, and infections. At higher doses, astronauts receiving 10 gray of radiation probably wouldn't survive in space for longer than two weeks.

Lunar explorers could have been hit by up to 10 gray worth of radiation if they were unlucky enough to be subjected to a coronal mass ejection event in August 1972. Luckily, it occurred between the Apollo 16 and 17 missions when nobody was on the moon.

Thankfully, NASA's LRO measured GLE73 at just 31 milligray.

"Our calculations of the past ground level enhancement events show that on average one event every 5.5 years may have exceeded the safe dose level on the Moon if no radiation protection had been provided," said Jingnan Guo, first author of the study published in Geophysical Research Letters, and a research professor at the University of Science and Technology of China. "Understanding these events is crucial for future crewed missions to the surface of the Moon."

The radiation impact dwindled further away on Mars, where ESA's TGO orbiter measured nine milligray – higher than Curiosity's 0.3 milligray on the red planet's surface. The researchers believe that studying these events is crucial for understanding and predicting coronal mass ejections. 

Work is already underway to build instruments on the planned lunar station, Gateway, that will monitor radiation levels around the Moon. The German Aerospace Center also sent two test mannequins aboard NASA's Artemis I in November to study the impact of radiation during the test flight. 

Colin Wilson, a project scientist working on the ExoMars TGO mission, concluded that "Space radiation can create a real danger to our exploration throughout the Solar System. Measurement of high-level radiation events by robotic missions is critical to prepare for long-duration crewed missions." ®

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