The Human Body in Zero Gravity: Lessons from Scott Kelly’s Year in Space

In 2015, astronaut Scott Kelly embarked on a historic mission, spending an entire year aboard the International Space Station (ISS). While previous cosmonauts like Valery Polyakov had spent longer durations in space, Kelly’s mission provided a unique scientific opportunity. Because Kelly is an identical twin, scientists had the perfect control group: his brother, Mark Kelly. This study allowed researchers to analyze the physiological and genetic impact of space travel by comparing the twins before, during, and after Scott’s year-long journey.

The Physical Challenges of a Microgravity Environment

Space is a hostile environment for the human body, which has evolved for Earth’s gravity. Upon entering the ISS, the absence of gravity immediately affected Scott Kelly’s physiology. Without the constant downward force of gravity on his spine, Kelly grew about three centimetres taller.

Furthermore, the lack of resistance meant that Kelly did not need to use his muscles to navigate the station, as he could move by simply "lightly kicking a wall." While this sounds effortless, it poses a significant risk of "muscles atrophy" and a loss of power. To combat this, astronauts must engage in rigorous exercise to maintain muscle tone and bone density. Daily life also presents practical challenges; in space, water does not stay in a cup, so astronauts must consume liquids from a "pouch" or straw, and waste management systems are essential to prevent the environment from becoming contaminated.

Genetic Adaptation and Gene Expression

One of the most groundbreaking aspects of the study involved "gene expression." Professor Christopher Mason noted that upon entering space, there was a "huge change in over 1000 genes." This suggests that the human body and its cells were actively "adapting to this new environment." While the body showed remarkable resilience—with some changes even strengthening Kelly’s immune system—there were clear negative consequences.

The Toll on Human Health

Long-term exposure to space flight resulted in several concerning health issues. Kelly experienced a change in the shape of his eyes, leading to worsened vision. Furthermore, his blood vessels became "swollen," and he faced an increased risk of heart disease. Perhaps most critically, the exposure to cosmic radiation significantly increased his risk for cancer. Even after returning to Earth, Kelly faced lingering effects, including DNA damage and cognitive difficulties, though he eventually reported feeling "normal again" after several months.

Preparing for Future Interplanetary Travel

The findings from the Kelly study are vital for the next generation of space exploration. As humanity looks toward "distant planets or other solar systems," understanding these biological risks is essential. Space affects every individual differently, and the data gathered from Kelly will help scientists "predict things that might go wrong" and develop preventative measures for future explorers.

Despite the physical toll, the allure of the cosmos remains powerful. Scott Kelly described space as "the most joyous and magical place," a sentiment shared by many in the space community. As historian John Logsdon suggests, the inherent danger of space travel is unlikely to deter future pioneers. The mystery and scientific interest of the universe continue to drive humanity to reach further, ensuring that the lessons learned from one year in space will pave the way for the future of human discovery.