Analysis: new research has found that the genetic changes caused by space radiation are potentially dangerous and could lead to cancer

A new report from the U.S. National Academies of Sciences, Engineering, and Medicine has highlighted the hazard of radiation for long space missions. It also proposes changes to assessing the radiation risks in individual astronauts over their careers.

The ionizing radiation that consists of highly energetic galactic cosmic rays and solar particles is of particular concern to space travellers. This can damage the DNA that makes up our genetic material, but can also cause harmful chemical changes in the cells.

Exposure to high doses of radiation leads to acute radiation sickness, which arises from the loss of key stem cell populations in the blood, with cells in the skin, eye, intestine and lungs also being very sensitive to irradiation. Causes of fatal radiation sickness include failure in blood production, infection, haemorrhage, pneumonia and organ failure.

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From RTÉ Radio 1's Drivetime, Guillaume Weerts from the European Space Agency on the 270 Irish people who want to become astronauts

The severity of this sickness depends on the dose received. The radiation dose is measured in Grays (Gy). However, as different types of radiation cause different types of physical or chemical damage to cells and can penetrate the body (or other material) to varying depths, the equivalent dose is derived by correcting for the biological effect of the particular radiation and is measured in Sieverts (Sv). 5 Sv (5 Gy) of ionizing radiation, which equates to 500 computerised tomography scans of the whole spine, or 35,000 chest X-rays, would kill half the people exposed within weeks.

A dose that is lethal to 50% of the population is called the LD50. Specialised hospitalisation is required to allow people to survive such doses, although more than 10 Sv is invariably lethal. Radiation protection is needed in case of incidents that might expose astronauts to high levels of irradiation.

The longer-term effects of much lower, non-lethal radiation doses over extended exposure periods are difficult to assess. In 2019, a NASA study compared a number of physiological and genetic changes between identical twins, one of whom spent 340 days on the International Space Station, while the other remained on Earth. The twins were 50 year-old males who both had previous spaceflight experience. Notably, extended time in space caused increased chromosomal abnormalities and persistent changes in gene expression, while several other changes seen during spaceflight returned to initial levels.

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From NASA, what happens to our bodies when we leave the surface of Earth to travel in space or visit the International Space Station?

The genetic changes caused by space radiation are potentially dangerous because of the risk that such changes can lead to cancer. How much cancer risk is caused by ionizing radiation exposure has been assessed by examining atomic bomb survivors and radiation workers. This data indicates that there are age- and sex-related differences in radiation-dependent cancer risk, so NASA currently set different exposure limits between male and female astronauts: 180 mSv for a 30-year old female and 700 mSv for a 60-year old male.

The new report suggests that a career exposure limit of 600 mSv be applied, irrespective of sex or age. This limit aims to ensure all astronauts remain below 3% mean risk of cancer mortality above the non-exposed baseline population, although the report notes that the hazardous nature of spaceflight itself makes this risk assessment more challenging.

Altering the allowable exposure limits may allow greater opportunity for female participation in spaceflight, albeit with some increased risk of radiation-induced cancer mortality over an astronaut's entire lifespan. Currently, the Russian, European and Canadian Space Agencies set a limit of 1000 mSv, independent of age and sex. A mission to Mars would entail an exposure of around 1000 mSv.

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From TEDxAntwerp, Head of Radiobiology at SCK-CEN Sarah Baatout on how to better protect astronauts from space radiation

Ultimately, humans are unlikely to be the only species travelling in space. Compared to other types of organism, mammals are particularly sensitive to ionizing radiation, with LD50's of 3-10 Gy in a range of species. LD50’s range from 10-100 Gy for fish, then from 20-1,000 Gy for various invertebrate species. More dramatic radioresistance exists in the tardigrades (LD50 of 5,000 Gy) and the bacterium Deinococcus radiodurans (LD50 of 5,000-30,000 Gy).

Specialised DNA repair mechanisms and some protein-protective adaptations are believed to facilitate the striking capacity of Deinococcus to survive irradiation, which may have evolved as a means to survive desiccation in its natural environment; similar evolutionary pressure exists for tardigrades, so that they may also have had to develop the means to preserve their genetic material. Recent papers reported that dehydrated Deinococcus cells survived three years in low Earth orbit outside the International Space Station, although with lower survival rates than dehydrated controls kept on Earth.

Compared to other types of organism, mammals are particularly sensitive to ionizing radiation

How different multicellular organisms have such widely varying abilities to survive radiation is unknown. While DNA repair mechanisms are highly conserved throughout evolution, specific types of cell respond differently to DNA damaging treatment- for example, human blood precursors are particularly sensitive to irradiation and undergo programmed cell death after radiation exposure.

Cell types with less stringent programmed cell death responses can survive long enough to repair their DNA damage, so that DNA repair processes are not the only determinant of radioresistance. As the LD50 measures short-term survival, it is a relatively crude indicator of how well a species might fare in space. Other factors, like reproductive capacity and cancer propensity, may need to be considered in filling the next ark.


The views expressed here are those of the author and do not represent or reflect the views of RTÉ