In 1992, NASA studied C. elegans worms exposed to space radiation on IML-1; the experiment reported higher mutation rates than in ground controls

In January of 1992, the space shuttle Discovery made an unprecedented trip through space with the delivery of about seven million micro worms for a NASA experiment that sought to solve a question with a critical effect on future space travel. Would the radiation from outer space, not filtered through Earth's atmosphere, have the capacity to mutate DNA sufficiently to endanger astronauts on a long-duration mission? Indeed, according to NASA’s 1994 paper titled “Radiation effects in nematodes: Results from IML-1 experiments,” published in Advances in Space Research, it would.

The worms, a species scientifically called Caenorhabditis elegans, returned from the International Microgravity Laboratory-1 (IML-1) mission with a roughly eight-fold greater mutation rate than ground-based control groups, a figure describing the overall frequency of mutation events relative to background rates. Among the specific mutations recovered were 13 mutations in unc-22, a gene responsible for muscle function, and 53 additional lethal mutations scattered across the genome. It offered some of the first direct evidence. Space radiation not only passes through the living body; it mutates it. Over three decades since then, as NASA prepares for prolonged space travel to the Moon under the Artemis program and to Mars, this discovery does not appear to have been consigned to history.

Why would anyone pick a worm for this job?


C. elegans is possibly one of the favorite model organisms for biological research, and that is because it has a fully sequenced genome, an accelerated life cycle, and, most importantly, because about 60-80% of its genes have human homologs. A mutation that occurs in the worms' DNA could be extrapolated to our own with high likelihood.

In the case of the IML-1 experiment, biologists dried out the worms to place them in a hibernating state together with radiation sensors inside ESA's Biorack facility. This made it possible to trace every impact of cosmic rays on the worms' genes and the specific damage that was done to the DNA.

Why this still matters

Astronauts cannot enter a dormant state. Beyond low orbit, Earth's magnetic field offers far less protection from deep-space radiation. A voyage to Mars will result in about three years of continuous exposure to galactic cosmic rays, with practically zero protection. As stated by a 2021 consensus report issued by the National Academies of Sciences, Engineering, and Medicine, NASA still struggles with determining safe radiation thresholds for missions to the Moon and Mars.

In addition, it has been recommended that NASA should reconsider its methods of communication about the risks associated with cancer caused by deep space radiation with the very people it sends into space. In other words, 30 years after the discovery made with the help of the worm in 1992, the organization responsible for actual human lives is only now getting down to dealing with the problem. Modern worm research has only enriched the image of the phenomenon in question. According to a 2021 paper titled “Review of Biological Effects of Acute and Chronic Radiation Exposure on Caenorhabditis elegans,” in the journal Cells, subsequent experiments have reported increased mutation frequency related to radiation dose, reinforcing that this isn't a one-off fluke from a single 1992 flight.

What this actually means

The technology behind radiation shielding has advanced considerably, yet it fails to address the underlying physics: current shielding materials reduce but do not eliminate radiation exposure. All of this is not to suggest that manned missions to Mars are in trouble, or that NASA is engaging in anything but rational activity. This suggests that NASA has been aware of the radiation risk for more than 30 years, while the challenge of protecting astronauts on long missions remains unresolved