Are humans able to survive beyond our planet’s atmosphere? For years, NASA has been grappling with this very question. Finally, in 2015, they embarked on a groundbreaking mission to study the effects of long-term space travel on human beings. But, they didn’t choose just any astronauts for this mission–they picked a pair of identical twin brothers.

It was February 21, 1964, in Orange, New Jersey, when a pair of identical twins entered the world. Little did Scott and Mark Kelly know that they would blaze a trail that no other siblings had ever done before–they both journeyed into the great unknown of space.

During the 1980s, the Kelly brothers were flying high–literally. Mark racked up an impressive 50,000 hours of flight time in 50 planes, while Scott logged an equally impressive 40,000 miles in 40 different planes. Despite the twins’ success in the world of military aviation, they decided to embark on a new challenge. 

As NASA astronauts, Scott and Mark Kelly couldn’t help but wonder if their unique bond as identical twins might hold the key to unlocking discoveries about the mysteries of space travel. As the years went by, the brothers became convinced they were ideal candidates for scientific study.

Scott was eager to take part in the experiment. He even brought up the subject to NASA shortly after he was hired as an astronaut. His passion and enthusiasm for the study were contagious. Not everyone was convinced, though. Some researchers believed that using only two brothers as test subjects was too small of a study to produce anything noteworthy. 

Why did NASA wait until 2013 to start the experiment? While the 1990s were a time of progress and technological advancement, Mars remained out of reach. But now, NASA’s goal is to send humans to the red planet by the 2030s. There is still much we don’t know about how the human body will react to the rigors of space travel and life on another planet.

Scott Kelly made history in 2013 when he boldly signed up to live in space for a year. As the crew captain (that included Russian cosmonaut Mikhail Kornienko), Scott knew that he was embarking on a journey, unlike anything that had ever been attempted.

On March 27, 2015, the world watched as two brave astronauts–Scott Kelly and Mikhail Kornienko–embarked on a journey that would make history. Their destination was The International Space Station–a marvel of engineering that orbits the Earth and acts as a hub for scientific research and exploration.

During his record-breaking year in space, Scott was more than just an astronaut–he was also a living laboratory. He conducted tests and experiments on himself to better understand how outer space affects the human body. He took his urine samples, recorded his blood tests, and took cognitive quizzes, saliva samples, and even fecal matter samples.

When Scott Kelly journeyed into space for his historic year-long mission, his twin brother Mark was right there with him–but not in the way you might think. Instead, Mark remained firmly grounded on Earth. He tracked his diet and work schedule while collecting urine and blood samples. Mark’s life was closely monitored in every detail, providing a valuable comparison to Scott’s experiences in space.

When Scott Kelly returned to Earth on March 1, 2016, he breathed a sigh of relief. But for scientists, the work was only beginning. Over the next six months, a team of researchers continued to analyze Scott’s blood, urine, cognitive function, and overall health. They wanted to know how the human body responds to prolonged exposure to weightlessness and if returning to Earth would set things right again.

Analysis of the data collected from the Twin Study required the expertise of 84 researchers from 12 different universities. Finally, on April 11, 2019, the results of the Twin Study were published in the prestigious journal Science, marking a major milestone in the history of space research.

According to geneticist Christopher Mason, over 1,000 of Scott’s genes changed. The most startling thing was the changes to Scott’s chromosomes which underwent a remarkable transformation. Parts of them were inverted, others flipped, leading to profound shifts in his biology that would take years to understand fully. 

Remarkably, Scott and Mark experienced significant changes in their DNA during the mission. While Scott’s genes went through a six-fold increase in mutation rate during the second half of his trip, Mark’s genetics also changed even more than Scott’s!

Scott Kelly’s time in space had a surprising effect on his chromosomes–the telomeres at the end of his chromosomes, which typically shorten as we age, actually lengthened. This unexpected result left scientists scratching their heads.

If humans live on Mars, will they experience longer lifespans thanks to their time in space? Andrew Feinberg, one of the study’s authors, says it’s unlikely. Despite the changes in Scott Kelly’s telomeres during his time in space, they returned to their normal length within 48 hours of his return to Earth. 

After a year of being apart, Mark finally saw his twin brother. While Scott appeared largely unchanged, there was a noticeable difference. His eyeballs had undergone some alterations, causing his vision to be less sharp. Researchers suggest that the cause of this change could be linked to exposure to carbon dioxide in space.

In space, the lack of gravity changes the way blood flows in the body. On Earth, gravity pulls most of the blood down to the legs. Without it, the brain and chest receive more blood. This caused Scott Kelly to experience more fluid flow into his head than his Earthbound twin brother, Mark.

Scott Kelly’s trip to space not only affected his DNA and immune system but also impacted his circulatory system. A team of researchers from the University of California, San Diego, delved into how Scott’s proteins changed during his time in space. They discovered that the increased blood flow near his head caused his arteries and blood vessels to harden. 

According to the San Diego research team, Scott’s body created more collagen, a protein responsible for building hair and fingernails. Additionally, he had higher levels of aquaporin 2, a marker of dehydration, and this suggests that he might have had to drink more water in space to stay hydrated. 

After Scott Kelly returned from his year-long space trip, scientists were curious to see how his genome had been impacted. As stressful situations and radiation exposure can lead to gene alterations, researchers were particularly interested in the state of Scott’s genes. Fortunately, medical researcher Andrew Feinberg reported that the genomic changes observed in Scott were not a cause for concern.

While 90% of his genes returned to normal, around 800 genes, roughly 10%, remained active. These genes controlled immune response and DNA repair and worked hard to help Scott’s body repair itself after his long stint in space.

The unusual changes in Scott’s telomeres due to his time in space might have unintended outcomes. Susan Bailey, a radiation professor, speculates that this could have placed excessive stress on his body, potentially increasing his likelihood of age-related illnesses such as cardiovascular diseases and cancer.

Scott Kelly’s brain faced a unique challenge during his space mission. From puzzles to computerized tests, Scott took a variety of cognitive assessments throughout his trip. However, his performance declined rapidly in the second half of the flight. His scores continued to drop even after he landed. 

According to Mathias Basner, a psychiatry professor, Scott Kelly’s cognitive decline may have resulted from the stress of being in space. Basner’s team at the University of Pennsylvania stated that space is a very hostile environment.

As the researchers delved into Scott’s physiology, another team at Northwestern University was investigating the astronaut’s gut microbiome. They discovered that certain bacterial types proliferate in space while others decrease. Still, the diversity of gut bacteria remained stable, indicating that the intestines remain healthy even in a microgravity environment.

While the long-term effects of space travel are still uncertain, researchers have some predictions for what may happen. One concern is that Scott’s arteries may have hardened due to increased blood flow. His heart may have also weakened. Both are potential signs of heart disease.

Scott is no stranger to space travel, having flown on several missions of varying durations. He told Space.com, “[I had] flown flights of increasing duration throughout my career: seven days; 13; 159 and 340.” However, with every mission, he found that the recovery time increased after returning to Earth. 

Though the Twins Study has been a valuable source of information, it’s still too early to make sweeping generalizations about the effects of space travel on all astronauts. Scientists at the University of California, San Diego, point out that the sample size used in the study is too small to draw definitive conclusions.

Though Scott Kelly’s experience of being in space for a year had some physical and psychological impacts, he still believes humans can go to Mars. Scott told Space.com that despite experiencing significant recovery time, he has faith in the ability of astronauts to handle a three-year trip to Mars.

NASA is taking the Twins Study success to the next level. As per the Colorado State University press release, NASA has set up an ambitious plan to send ten astronauts on one-year missions, another ten on six-month missions, and the rest on two to three months trips at a time.

In a fascinating interview with Scientific American, Scott Kelly shared his thoughts on the future of space travel. He believes that if humans want to explore beyond Mars, NASA needs to experiment with artificial gravity. This technology is crucial for training astronauts to endure extreme space conditions. 

After an illustrious career at NASA, Scott Kelly retired in 2016 and was appointed a United Nations Champion for Space. Kelly then wrote a fascinating novel chronicling his time in space titled Endurance: A Year in Space, a Lifetime of Discovery.