A solar eruption detected simultaneously at Earth, the Moon, and A coronal mass ejection erupted from the Sun on October 28, 2021, and its impact was so widespread that both Mars and Earth, despite being on opposite sides of the Sun and about 250 million kilometers (160 million miles) apart, received an influx of energetic particles.
A Rare and Significant Event
This marks the first time that a solar event was measured simultaneously on the surfaces of Earth, the Moon, and Mars, as reported on August 2 in a Geographical Research Letters paper. The outburst was detected by an international fleet of spacecraft including ESA’s 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.
These simultaneous measurements on different worlds help improve our knowledge of the impact of solar outbursts and how a planet’s magnetic field and atmosphere can help protect astronauts against them.
Comparing Different Worlds
The event that took place on October 28, 2021, is an example of a rare ‘ground level enhancement’. During these events, particles from the Sun are energetic enough to pass through the magnetic bubble that surrounds Earth and protects us from less energetic solar outbursts. This was only the 73rd ground level enhancement since records began in the 1940s, and none have been recorded since.
As the Moon and Mars do not generate their own magnetic fields, particles from the Sun can easily reach their surfaces, and even interact with the soil to generate secondary radiation. But Mars does have a thin atmosphere that stops most of the lower energy solar particles and slows down the highly energetic ones.
The Importance of Understanding Solar Events
With the Moon and Mars as the focus of future human exploration, it is extremely important to understand these solar events and their potential impact on the human body. Astronauts face the risk of radiation sickness. A radiation dose above 700 milligray – the unit for the absorption of radiation – may induce radiation sickness via destruction of the bone marrow, resulting in symptoms such as infection and internal bleeding.
If an astronaut receives more than 10 gray, they are extremely unlikely to survive more than two weeks. One solar outburst in August 1972 would have given such a high radiation dose to an astronaut on the lunar surface, but it, fortunately, fell between the crewed Apollo 16 and 17 missions.
Recent Findings and Protection Measures
By comparison, during the event on October 28, 2021, the dose in lunar orbit, measured by
“Currently, we live in a golden age of Solar System physics. Radiation detectors aboard planetary missions such as BepiColombo, on its way to Mercury, and Juice, cruising to
Lunar Gateway
The Artemis program that is sending astronauts to the Moon includes a space station in lunar orbit, called the Gateway. On the Gateway three suites of instruments will monitor the radiation environment around the Moon: ESA’s European Radiation Sensors Array (ERSA), NASA’s Heliophysics Environmental and Radiation Measurement Experiment Suite (HERMES), and the ESA/
Luna Twins and Future Research
Space agencies are also looking into protective attire to minimize the impact of space radiation on the body. Two identical mannequins, developed by the German Aerospace Center (DLR), were passengers on the Artemis I test flight, which flew by the Moon during November and December 2022. The mannequins, nicknamed Helga and Zohar, were modeled based on the female body and were equipped with radiation sensors provided by DLR and NASA. Helga flew unprotected, but Zohar wore a newly developed radiation protection vest covering her torso. Researchers at DLR are currently comparing the two datasets measured by Helga and Zohar.
Colin Wilson, ExoMars TGO project scientist, concludes: “Space radiation can create a real danger to our exploration throughout the Solar System. Measurements of high-level radiation events by robotic missions is critical to prepare for long-duration crewed missions. Thanks to data from missions like ExoMars TGO we can prepare for how best to protect our human explorers.”
Reference: “The First Ground Level Enhancement Seen on Three Planetary Surfaces: Earth, Moon, and Mars” by Jingnan Guo, Xiaolei Li, Jian Zhang, Mikhail I. Dobynde, Yuming Wang, Zigong Xu, Thomas Berger, Jordanka Semkova, Robert F. Wimmer-Schweingruber, Donald M. Hassler, Cary Zeitlin, Bent Ehresmann, Daniel Matthiä and Bin Zhuang, 2 August 2023, Geographical Research Letters.
DOI: 10.1029/2023GL103069