Simulated deep-space radiation left rats with heart scarring that doubled in 270 days
Medical College of Wisconsin researchers report that 1.5 gray of simulated deep-space radiation doubled coronary scar tissue in rats by day 270. The rats were tracked about a year, which phys.org equates to 25 human years, so the damage shows up late.
The Scientist · Science desk
Three figures: 83% of rats had heart scarring a year after a lower dose akin to a three-year Mars mission, not visible right away; about a year of monitoring equals around 25 human years; at 1.5 gray, rats developed coronary scar tissue.
| Figure | Value | Note | Claim |
|---|---|---|---|
| Rats scarred a year after a dose akin to a Mars mission | 83% of rats | 10 | |
| Monitoring, in human years | 25 years, around | 6 | |
| Dose with coronary scars | 1.5 gray | 7 |
What happened
- The rats were middle-aged, chosen to mimic career astronauts, and had their hind legs lifted at a 30-degree angle by tail harnesses for 30 days to simulate weightlessness.
- Radiation came from the NASA Space Radiation Laboratory at Brookhaven, whose five-ion, six-beam simulator fires protons and heavy ions such as silicon and iron.
- At a lower dose akin to a three-year Mars mission, scarring was not visible right away, but 83% of the rats had it a year after exposure.
- Months after exposure, the rats' spleens were still missing two-thirds of their natural killer cells.
Why it matters
- exposure If the rat pattern carries over, a health check soon after a mission could miss the heart damage, because it was absent at first in this model.
- decision Countermeasure studies will need to apply radiation and unloading together, since microgravity alone did not leave a lasting immune deficit.
- constraint Long-term deep-space exposure cannot be tested on people, so estimates of astronaut risk will keep resting on animal models like this one.
The design lets the paper separate the two stressors, and the two organ systems answered differently. In the heart, weightlessness had essentially no effect, and the scarring appeared to be entirely caused by radiation [9]. The immune system needed both. Rats exposed only to microgravity eventually recovered to normal cellular levels, while rats also hit with radiation had a muted recovery [13]. According to phys.org's account, the cosmic rays appeared to stunt the bone marrow's ability to respond to physiological stress [14].
Natural killer cells wipe out virus-infected and cancerous cells [12]. The spleens kept only a third of them [19].
The heart was the researchers' original focus [15]. At 1.5 gray, the rats developed perivascular fibrosis, a scar tissue that wrapped around the coronary vessels [7]. By 270 days after exposure it had doubled in size, squeezing the vessels to the point where a heart attack became much more likely [8]. Applying the one-year-to-25-years conversion in a straight line puts 270 days at about 18 human years [21]. The straight line is our assumption, and the conversion was stated for the whole monitoring period [6].
The lower-dose group is the closer match to a mission, since its dose was akin to what astronauts would absorb over three years [10]. A year out, 17% of those rats showed no scarring [18]. phys.org concludes that radiation's effects might take decades of a human lifespan to present themselves [20]. The coverage does not give the number of rats per group or the lower dose in gray, so the 83% has no denominator attached.
The exposure schedule is the main condition on all of this. The rats were unloaded for five days, bombarded for a few minutes at extremely high levels meant to mimic months of exposure, then suspended for another 25 days [5]. The thing this doesn't tell you is whether the same total dose spread over months would scar the vessels as fast.
The PLOS ONE paper from the Medical College of Wisconsin has three primary findings [16]. The third, on mutations linked to cancer and cardiovascular risk, is not covered here [17].
What to watch
- Whether the full paper reports group sizes and the lower dose in gray, which would give the 83% figure a denominator.
- Whether a follow-up delivers the same total dose over months instead of minutes and still produces the coronary scarring.
- How the paper's third finding, on mutations linked to cancer and cardiovascular risk, ties to disease outcomes in the rats.
Clarity's read
What the record supports and how the coverage leans. The claims behind it follow.
Reality
- Evidence40
- Adoption
- Insufficient
- Hype gap+25
- Incentives
- Insufficient
- Confidence45
Claim ledger
Ranked by verification strength, evidence, and original report placement.
- [1]
Researchers at the Medical College of Wisconsin published a paper in PLOS ONE on the long-term implications of deep-space exposure to radiation and weightlessness.
- [2]
Running long-term exposure experiments on humans is impractical and unethical, so the researchers turned to rats.
- [3]
Middle-aged rats, chosen to mimic the typical age of career astronauts, had their back legs lifted off the ground at a 30-degree angle by harnesses connected to their tails for 30 days (NASA's hindlimb unloading protocol).
- [4]
The NASA Space Radiation Laboratory at Brookhaven National Laboratory used a five-ion, six-beam cosmic ray simulator called simGCRsim, which fires high-speed protons and heavy ions like silicon and iron.
- [5]
Under the protocol, rats were unloaded for five days, bombarded for a few minutes at extremely high radiation levels meant to mimic months of exposure, and then kept with hind legs suspended for another 25 days.
- [6]
After the exposure the rats lived out the rest of their lives, with a monitoring period of about a year equivalent to around 25 years of human life.
- [7]
With a dose of 1.5 gray, the rats developed perivascular fibrosis, scar tissue wrapped around the coronary vessels that feed the heart.
- [8]
By 270 days after the radiation exposure, the scar tissue had doubled in size, squeezing the blood vessels to a point where a heart attack became much more likely.
- [9]
The weightlessness simulation had essentially no effect on the heart scarring outcome, which appeared to be entirely caused by radiation.
- [10]
At a lower dose akin to the total radiation astronauts would receive over a three-year Mars mission, heart scarring was not visible right away, but a year after exposure 83% of rats had developed it.
- [11]
Months after their exposure, the rats' spleens were still missing two-thirds of their natural killer (NK) cells.
- [12]
NK cells wipe out virus-infected cells and cancerous cells.
- [13]
Rats exposed only to microgravity eventually recovered to normal cellular levels, but if they were also hit with radiation, the recovery was muted.
- [14]
It appeared that the cosmic rays stunted the bone marrow's ability to respond to physiological stress.
- [15]
The heart finding was originally the researchers' focal point.
- [16]
The paper describes three primary findings.
- [17]
One section of the phys.org article, headed 'Mutations linked to cancer and cardiovascular risk', concerns a further finding on mutations.
- [18]
In the lower-dose group, 17% of rats showed no heart scarring a year after exposure.
- [19]
If two-thirds of NK cells were missing, about one-third remained in the spleens.
- [20]
phys.org concludes that the effects of radiation might take decades of a human lifespan to present themselves.
- [21]
Scaling the one-year-to-25-human-years conversion linearly, 270 days corresponds to about 18 human years.
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Sources
1 independent publisher whose own reporting we read for this story.
- phys.orgA trip to Mars could come at a heartbreaking cost
1 article · October 14, 2026
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