Space Medicine: Why Our Bodies Aren’t Built for Mars
Written by Rathusha Nimalan
Edited by Gesi Huang
When astronaut Scott Kelly rocketed into orbit in 2015, his voyage was not about exploration in the traditional sense; it was an experiment in endurance. For 340 days, Kelly lived in microgravity aboard the International Space Station (ISS) while his identical twin brother, Mark Kelly, remained on Earth. Together, the twins became the centerpiece for NASA’s Twins Study, a project that aimed to understand how space changes the human body on a molecular level.
The paper, which was published in 2019, revealed sobering findings, especially for those who fantasized about the possibility of mankind on Mars. Though the human body is generally resilient, when the environment in which it resides is significantly changed, its systems begin to collapse. In space, gravity no longer anchors blood and bone, radiation bombards cells constantly, and the circadian rhythm is modified. Kelly’s time in space left molecular fingerprints that scientists are still decoding. From shifts in DNA expression to thickened arteries to evolved gut bacteria, it seemed that little of Kelly’s body was left untouched.
Photos by RDNE Stock project (left) and Murat Esibatir (right) via Pexels. Curated by Leticia De Almeida Smolka (lds234@cornell.edu).
Kelly’s telomeres, which are protective caps at the ends of chromosomes that protect DNA and normally shorten as we age, unexpectedly lengthened in orbit. On a cellular level, this could hint at a rejuvenating influence of time in space. However, upon returning to Earth, his telomeres shortened drastically, some even to a smaller length than they were prior to his departure.
Additionally, over 8% of Kelly’s genes showed altered activity during the flight and still have yet to revert to their original levels. Many of the affected genes were involved in DNA repair, bone formation, and inflammation, all of which are required functions for the body to adapt to a new environment. Thankfully, Kelly’s immune system did not suffer severe impact; he satisfactorily responded to a flu vaccine administered in space.
Without the tug of gravity, muscles atrophy, bones weaken and fluids drift towards the head, distorting vision and pressurizing the brain. During his mission, Scott lost 7% of his body mass despite his strict workout regimen. His bones broke down and the walls of his carotid artery thickened, normally a sign of cardiovascular aging on Earth. When Scott returned home, the necessary adjustment to Earth’s force of gravity was a challenge to be overcome.
In space, Kelly’s gut microbiome altered immensely, but changed back as he returned back to Earth. Furthermore, Kelly’s cognition remained unchanged . However, after returning to Earth, his reaction times slowed down and his accuracy dropped, symptoms that lasted for a few months.
In addition to the physical strain, space missions are a mental battle. During his trip, Kelly faced isolation and disorientation, putting his psychological strength to test.
The ISS, where Kelly was stationed, orbits only 250 miles above Earth. Mars, on the other hand, lies roughly 140 million miles away, a journey that could stretch across three years. And once astronauts make it there, they would find themselves on a planet with 38% of Earth’s gravity, a thin carbon dioxide atmosphere, and high radiation levels that would bombard DNA and brain cells.
Photo by SpaceX via Pexels. Curated by Leticia De Almeida Smolka (lds234@cornell.edu).
Journeying to Mars would mean sacrificing all the existing safety measures for space missions, including emergency rescues, resupply ships, and shields from cosmic radiation. Therefore, future space missions will be focused on improving an astronaut's endurance, with long communication delays and acceptance that there is no quick way home.
Science remains in the brainstorming stage for planning a trip to Mars. Some researchers are exploring ways to induce a hibernation-like state during the long journey. Others are focusing on testing bone-protecting drugs, one of which has already succeeded in preventing bone loss aboard the ISS.
Researchers are also investigating how microgravity alters the brain’s fluid balance. Because of the unclear nature of this endeavor, researchers are forced to dig deep. They are currently looking into sex-based physiology, examining how women more effectively use oxygen and retain body mass compared to men, to inform the design of future Mars crews. Yet despite these advances, it is undeniable that humankind was sculpted for Earth – every biological function relies on Earth's gravity, magnetism and atmosphere.
Nonetheless, what was once thought impossible – putting a man on the moon – is now a comparatively easy feat. With that same determination, it will only be years before humanity takes its next big leap.
Even if the rockets are ready, our DNA is not.
The human body remains a creation of Earth.
Yet ambition has always defined what it means to be human.
Rathusha Nimalan ’28 is in the College of Arts and Sciences. She can be reached at rn349@cornell.edu.
