Mission to Mars: Radiation as the Major Concern for Mars Travel
In the Pixar science-fiction animation WALL-E, the Earth is so polluted and trashed that all humans have fled for refuge in outer space, leaving only two robots to clean up. The film insinuates that being aboard a space capsule far from Earth is safer for the characters than being on our planet. But is this really true? Would we really survive better somewhere else in the universe? Perhaps, but there are also some great risks for future space-dwellers. Journeys to space stations and the moon have shown that space travel can lead to many medical issues, such as cataracts due to light from the sun, and bone loss due to decreased calcium metabolism. Most importantly, as NASA and SpaceX are gearing up to send a manned craft to Mars, the effects of radiation on genes are at the forefront of current studies.
Radiation occurs when an energy source emits waves or particles of energy which can be absorbed by the object in the path of that energy. On a molecular level, though, radiation energy is described as being “deposited” into the receiver’s cells, causing changes in the cell’s functioning and modifications of gene activation or inactivation. These effects can result in damage to the genome and death of the affected cell, causing acute ramifications, with symptoms like nausea and confusion, or delayed consequences, such as cancer. Increased fluence, or energy particles per unit area of the radiated matter, is directly associated with more tumors.
A less simplistic result of radiation is the “bystander effect”. Cells that are subjected to the heavy ions emitted by an energy source can also cause oncogenesis in unaffected nearby cells. Studies have shown that radiation can be transmitted from those irradiated cells to unirradiated ones close by. This effect is so strong that even low doses of low energy radiation can lead to oncogenesis in the unirradiated cells. Therefore, even if astronauts are mostly protected from radiation, any effects that do get through to their bodies and cells can be multiplied.
In 1997, a study following a space station mission showed that seven astronauts were noted to have greater amounts of mutated chromosomes. While these mutations in the lymphocytes can be largely attributed to radiation, a more recent study claims that zero-gravity may have been a factor. Thus, radiation can commence the process of cancerous growth, but other factors are key in promoting the growth. Lengthy exposure to a zero-gravity environment has been known to inhibit the immune system’s defense against cancerous cells. Similarly, psychological stress, from long-term confinement and other factors, has been known to exacerbate chromosomal aberrations.
Compared to the space station and other space missions, the Mars mission is much more dangerous. According to a 2013 study, the astronauts on the International Space Station, for instance, experience less radiation-induced death than those conducting near-Earth asteroid exploration, and both are projected to have less risk than astronauts travelling to Mars. A journey to the Red Planet would require at least 900 days in space, with at least one year in deep space. As the space shuttle moves away from Earth, astronauts must deal with multiple sources of radiation. Along with risk from protons and electrons trapped in the inner and outer Van Allen radiation belt, which are areas with high concentrations of charged particles, solar energy particles pose great risk to humans in space. Solar cosmic rays, or SCRs, are mostly made up of protons, with just a few helium and heavy ions involved . These rays, therefore, are low energy and of little concern until solar particle events, or SPEs, send higher energy into the solar system. This is necessary to consider for Mars travel, as just one strong flare of the high energy can kill an astronaut.
Even more significant than SCRs, though, are galactic cosmic rays, or GCRs. These rays, specifically in the form of X-rays, are emitted due to nuclear and atomic reactions outside of the solar system. This radiation contains heavy ions that can lead to carcinogenesis within just a few months. In particular, the high energy characteristic of the radiation, in addition to the ability for these particles to directly penetrate cells, can cause serious cell damage. A 1999 study shows that what makes GCRs so much worse than any SCRs or other radiation is that, for Mars explorers especially, GCRs are nearly impossible to avoid. Thicker radiation shielding will not significantly decrease the number of tumors, as radiation will still be able to penetrate the space shuttle.
No matter how much shielding, Mars astronauts will be exposed to greater amounts of radiation, due to longer time in space and specifically in deep space. A 2007 study has shown that more time in space is associated with more radiation. Nevertheless, that more time in space can make an astronaut a little more resistant to the effects of additional radiation.
Some cosmonauts, however, were found to have fewer mutations than expected . An experiment to reproduce these results used mice and concluded that T regulatory cells experienced less radiation-induced expansion if the mice were previously exposed to low-dose radiation. So too, astronauts going to Mars can have accumulation of exposure leading to cancer and other ramifications, but they can also have accumulation of exposure leading to better resistance to the outer space radiation.
Although researchers agree that thicker aluminum shielding is key in avoiding too much radiation, given the lack of completely protective radiation shielding for Mars astronauts, other solutions are necessary. One possibility is deuterium-free water. As deuterium is a stable isotope of hydrogen, with one extra neutron, water with 65% less deuterium, and thus less stability, causes the water to have “anti-cancer” properties. Brain scans showed regression of metastatic cancer after a few months of consumption of deuterium-depleted water. Less stable isotopes kept the tumor from maintaining stability, thereby shrinking the growth. With similar technologies, hopefully astronauts will be able to explore Mars and farther into space without concern for severe genotoxicity.
Radiation, as well as microgravity and stress, is a significant factor to consider for space missions in general and Mars in particular. Most people avoid detrimental activities, such as jumping off bridges; so too, astronauts should not travel to Mars until the radiation and other medical issues are no longer considered exceedingly detrimental. One day, though, perhaps WALL-E will no longer be science-fiction but rather be scientific reality.
12
