2023-08-07 10:40:39
On October 28, 2021, a gigantic solar flare swept across the Earth, the Moon and Mars with full force. This is the first time that an event of this type has been simultaneously detected at three separate planetary bodies. Analysis of the phenomenon provides better insight into the levels of space radiation to which astronauts will be exposed during future missions to the Moon and Mars — an essential step in the design of protective devices.
The solar flare (or coronal mass ejection), dating from 2021, was detected by a fleet of international space devices such as the European Space Agency’s (ESA) ExoMars Trace Gas Orbiter (TGO), the Curiosity rover on Mars, NASA’s Lunar Reconnaissance Orbiter (LRO), the Chinese space agency’s Chang’e-4 lunar probe and the German low-Earth orbit satellite Eu:CROPIS.
Reaching a speed of 1300 kilometers per second, the phenomenon is class X1 on the intensity scale of solar flares (class X corresponds to flares with an intensity of 10−4 W/m2). The resulting flux of solar energetic particles (SEPs) spread over such a wide region that it swept across Earth and Mars, when they were at opposite points relative to the Sun — 250 million kilometers away. one from the other.
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The SEP was so intense that it caused what is called “ground level enhancement”. During these phenomena, the solar particles are sufficiently energetic (up to several gigaelectronvolts) to cross the Earth’s magnetosphere and be detected by the neutron detectors on the ground. This is the 73rd ground-level enhancement detected since February 1942 and the first of the 25th cycle of solar activity (one cycle lasts about 11 years). The eruptions will increase (in quantity and intensity) during the months and years to come, as the Sun approaches its peak of cyclic activity.
The October 2021 solar flare, captured by the SOHO satellite, orbiting the Sun. © ESA
Since the Moon and Mars will be the focus of future space exploration, studying such events provides insight into what astronauts will face once there, in order to develop the best possible protection systems. ” Space radiation poses a real danger to our exploration of the solar system. Measurements of high-level radiation events by robotic missions are essential to prepare for long-duration crewed missions “, explains in a communiqué Colin Wilson, researcher affiliated with the ExoMars TGO project.
A danger for astronauts
Space radiation is a real danger for astronauts. An exposure above 700 milligrays leads to the destruction of the bone marrow, causing a cascade of potentially fatal reactions throughout the body (failure of the immune system, cancer, etc.). An acute exposure of 10 grays is fatal after two weeks. Such a radiation dose was noted on the surface of the Moon in August 1972, but fortunately it took place between the Apollo 16 and 17 missions.
Illustration showing the radiation levels emitted by the October 2021 solar flare. © ESA
Indeed, faced with space radiation, Mars and the Moon do not benefit from the same protections as the Earth. First, the risks of harmful exposure are particularly high on the Moon, because it does not have an atmosphere. And although Mars has one, it is not dense enough to prevent energetic particles from reaching its surface. Not to mention that the two planetary bodies have lost their magnetic fields. Energetic particles can therefore more easily reach their surface and interact with the ground to generate secondary radiation.
In the case of the 2021 solar flare, the analysis published in the journal Geophysical Research Letters offers a simultaneous comparison of these effects at the level of the 3 planetary bodies. On Earth, the barrier effects have made it possible to have only negligible levels of energetic particles on the surface and a few tens of milligrays in orbit.
On the Moon, on the other hand, the detectors recorded a radiation level of 31 milligrays in orbit and 17 milligrays on the surface. Comparative calculations including previous ground-level enhancement events have shown that on average, one event every 5.5 years can exceed the harmful exposure level. According to Jingnan Guo, corresponding author of the study and a researcher at the University of Science and Technology of China, “understanding these events is crucial for future crewed missions to the surface of the Moon”.
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As for Mars, the detectors recorded exposure levels of 9 milligrays in orbit and 0.3 milligrays on the surface – nearly thirty times lower. This significant reduction is due to the barrier effect conferred by the Martian atmosphere. The researchers’ modeling has shown that extreme MS can induce radiation doses 100 times lower than on the Moon.
Design the best protection protocols
This study is part of a series of data collections to establish prevention and protection protocols in anticipation of future manned space missions. For the time being, that in force on board the International Space Station (ISS) consists of withdrawing into the dormitories or into the kitchen, at the level of which the walls are thick enough to protect against radiation.
In addition, the Artemis program will include a space station in lunar orbit (the Lunar Gateway) equipped with an array of internal and external sensors. Two dummies were also flown aboard the Artemis 1 mission, flying over the Moon between November and December 2022. Modeled on the basis of the female body, one of the dummies was sent unprotected while the other was fitted with a prototype radiation protection vest. The data collected by the sensors attached to the dummies is being analyzed and will make it possible to develop better protective suits for the astronauts.
Source : Geophysical Research
Letters
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