“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 scientist Jingnan Guo, researcher of the 28 October event.

The coronal mass ejection, erupting from the Sun, spread across such a vast area that it reached both Mars and Earth, even though they were around 250 million kilometers apart and on opposite sides of the Sun. This remarkable event was recorded for the first time, as reported in a Geographical Research Letters paper yesterday. The outburst was observed by an international fleet of spacecraft, including European Space Agency’s (ESA) ExoMars Trace Gas Orbiter (TGO), NASA’s Curiosity Mars rover, the CNSA Chang’e-4 Moon lander, NASA’s Lunar Reconnaissance Orbiter (LRO), and DLR’s Eu:CROPIS Earth orbiter.

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The event on 28 October 2021 is a rare example of a ‘ground level enhancement,’ during which solar particles are energetic enough to penetrate Earth’s magnetic bubble that normally protects us from less energetic solar outbursts. This marked only the 73rd ground level enhancement since records began in the 1940s, and none have been recorded since as reported by Geophysical Research Letters.

Space radiation poses a genuine threat: Expert

Space radiation poses a genuine threat to our exploration of the Solar System, and measurements from robotic missions, like ExoMars TGO, are crucial in preparing for the safety of future human explorers, according to Colin Wilson, ExoMars TGO project scientist. Simultaneous measurements on different celestial bodies explain how a planet’s magnetic field and atmosphere can shield astronauts from their effects and offer valuable insights into the impact of solar outbursts. 

While the Moon and Mars lack their own magnetic fields, solar particles can easily reach their surfaces and interact with the soil, generating secondary radiation. However, Mars does have a thin atmosphere that blocks most of the lower-energy solar particles and slows down the highly energetic ones.

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With future human exploration missions targeting the Moon and Mars, understanding these solar events and their potential impact on the human body is of utmost importance. Astronauts face the risk of radiation sickness, and a radiation dose above 700 milligray could lead to bone marrow destruction, resulting in infection and internal bleeding. An astronaut is unlikely to survive more than two weeks if he/she receives more than 10 gray.

The event on 28 October 2021 in lunar orbit measured by NASA’s Lunar Reconnaissance Orbiter was only 31 milligray, a much lower dose compared to a solar outburst in August 1972, which would have been lethal to an astronaut on the lunar surface. Understanding these events is vital for the safety of future crewed missions to the Moon. 

Comparing measurements made by ExoMars TGO and the Curiosity rover highlights the protection offered by Mars’s atmosphere. TGO measured 9 milligray, while the surface registered only 0.3 milligray. ESA’s inner Solar System missions Solar Orbiter, SOHO, and BepiColombo were also affected by the solar outburst.

Protecting astronauts during space ventures is a crucial task for ESA, and understanding and predicting intense radiation events is a vital part of this effort. By monitoring the radiation environment in space and providing timely warnings, astronauts can take necessary precautions, such as wearing protective gear or seeking shelter in case of solar events. Such precautions are already in place on the International Space Station, where astronauts retreat to shielded areas when necessary.

The Artemis program, which aims to send astronauts to the Moon, includes a space station called the Gateway in lunar orbit. The Gateway will host three suites of instruments to monitor the radiation environment around the Moon.

Space agencies are also exploring protective attire to minimise the impact of space radiation on the human body. Two identical mannequins, Helga and Zohar, modeled based on the female body developed by the German Aerospace Center (DLR), were part of the Artemis I test flight. Helga flew unprotected, while Zohar wore a newly developed radiation protection vest covering her torso. Comparing the data from these mannequins will aid in the development of effective radiation protection measures.

Updated: 03 Aug 2023, 12:18 PM IST