This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: When astronauts first travel to Mars or anywhere else in deep space, they will have to contend with two problems that our planet protects us from on its surface—radiation and weightlessness. Scientists already know both can have a profound impact on the human body, but the extent of that impact and how long it can last remain a mystery.
A new paper by researchers at the Medical College of Wisconsin, published in PLOS ONE, tackles those questions and unfortunately comes up with some less-than-ideal answers about the long-term implications of deep-space exposure. Humanity hasn't yet built a deep-space research lab where researchers can run experiments in the actual environment of deep space. So researchers generally have to make do with what they have on the ground.
And since running these types of long-term exposure experiments on humans is both impractical and unethical, the researchers turned to a cornerstone of biological testing—rats. To simulate weightlessness in earthbound rats, NASA developed a protocol called hindlimb unloading (HLU). In this experiment, 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 specialized harnesses connected to their tails for 30 days.
This tilt shifts much of the body's fluids to the head and takes the weight off their lower bodies at least, which is about as close as the researchers can get to mimicking what happens to astronauts when they are floating in microgravity. Recreating radiation is harder and requires specialized equipment. Luckily, NASA has developed just such equipment.
At Brookhaven National Laboratory, the NASA Space Radiation Laboratory is capable of simulating the radiation environment that constantly bombards the solar system outside the protective shell of Earth's atmosphere. For this experiment, scientists used a five-ion, six-beam cosmic ray simulator dubbed "simGCRsim." It blasts a target with high-speed protons and heavy ions like silicon and iron that could potentially make their way through the hull shielding of a ship going to Mars. Under the experimental protocol described in the paper, the 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 their hind legs suspended for another 25 days.
After that, they were allowed to live out the rest of their lives, with the monitoring period of about a year equivalent to around 25 years of human life. There were three primary findings described in the paper, but the one that was originally the researchers' focal point concerned the heart. With a dose of 1.5 gray (a measure of absorbed radiation dose), the rats began to develop perivascular fibrosis—a type of scar tissue that wrapped around the coronary vessels that feed blood to the heart.
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