Researchers here suggest that some of the detrimental effects of prolonged space missions are mediated by an increased burden of senescent cells resulting from cosmic radiation exposure. Senescent cell accumulation is a feature of aging and cancer treatments such as chemotherapy, and contributes to the progression of age-related dysfunction and disease. Senescent cells secrete an inflammatory mix of signal molecules that disrupt nearby tissue structure, alter cell behavior, and rouse the immune system into a state of chronic inflammation. Even a small number of senescent cells can have outsized effects on tissue function due to this signaling.

The increasing duration of space missions involves a progressively higher exposure of astronauts to cosmic rays, whose most hazardous component is made up of High-Atomic number and High-Energy (HZE) ions. HZE ions interact along their tracks with biological molecules inducing changes on living material qualitatively different from that observed after irradiation for therapeutic purposes or following nuclear accidents. HZE ions trigger in cells different responses initialized by DNA damage and mitochondria dysregulation, which cause a prolonged state of sterile inflammation in the tissues. These cellular phenomena may explain why spending time in space was found to cause the onset of a series of diseases normally related to aging.

Despite their concentration in the cosmic rays being around 1%, HZE ions due to their high penetration and strong oxidizing power have been proven to induce permanent damage. The direct or indirect damage through radiolysis of mitochondria has as a consequence not only failure of its metabolic role but also establishment of a persistent oxidative imbalance. Once damaged, mitochondrial DNA may insert in nuclear chromosomes perpetuating genomic instability. The cells bearing DNA damage that cannot be quickly repaired with the DNA damage response system enter into apoptosis or the quiescent state typical of senescence. The final result is a decrease in the tissue functionality as is occurring in aging. Therefore, cosmic rays would mimic the effect of aging, inducing a persistent state of sterile inflammation damaging DNA, proteins, and lipids the consequences of which are aging-related disease such as cardiovascular diseases, neurocognitive impairment, and increase of cancer occurrence.