• Identical twin astronauts Mark and Scott Kelly (NASA)Source: NASA
With the only sibling astronauts ever to go to space, NASA has been performing a twin study that's most certainly unique.
Signe Dean

18 Mar 2016 - 2:04 PM  UPDATED 18 Mar 2016 - 4:14 PM

You’ve probably heard of Scott Kelly, the NASA astronaut who recently returned from one of the longest-ever stints a human has spent in space.

During NASA’s special One-Year Mission he was one of two astronauts who spent 340 consecutive days aboard the International Space Station (ISS) performing various research experiments, trying to stay sane, and, in Kelly’s case, posting countless photos on social media.

11 cool things Scott Kelly did during his year in space
Astronaut Scott Kelly is returning from his longest stay in space - and we look back at #YearInSpace.

It makes perfect sense that Kelly in particular was picked for this special mission with the overarching goal of studying long-term space travel effects on the human body. According to NASA, only two siblings have ever both travelled into space, and they happen to be Scott and his identical twin brother, retired astronaut Mark Kelly.

From a scientific perspective, that’s just terrific - not only can you send one body up into space for a prolonged period of time, but here back on Earth you get another person who is just as fit, has a similar lifestyle, and, most importantly, carries identical genes. Compare the two and you have a twins study like no other.

Being able to continuously compare samples from both Kelly brothers means NASA can get unique insights into some of the health effects of weightlessness, and the general stress that living in a space environment can extol on the human body.

Collection of samples started before Scott’s departure to ISS over a year ago, and the data from both astronauts is actually being used for ten separate investigations, conducted as one integrated research project.

Coming back taller

The scientists are focusing on four major aspects - human physiology, behavioural health, microbiology, and studies of bodily changes at a molecular level.

This goes well beyond the quirky fact that Scott came back to Earth two inches taller than his brother - a well-known temporary effect of weightlessness is the lack of pressure on the spinal vertebrae, causing them to be less squished together.

During his year in space, Scott Kelly had to draw his own blood and send these samples down along with stool, urine, and saliva swabs, which could then be studied in careful comparison with the samples his brother provided back on the planet.

Both of them also underwent a series of cognitive and psychological tests to gather insights into the emotional toll prolonged space-faring could leave on us.

Another of the research projects involves the microbiome - our internal ecocystem of microbes that is made up in no small part by the contents of the foods we eat, especially fresh fruit and vegetables.

You're surrounded by a microbe cloud - and here's what's in it
All around you is a wafting cloud of billions of airborne bacteria, detached from various parts of your body... including the gut.

The ISS is a perfectly controlled environment, and comparison of how Scott Kelly’s prolonged space food diet impacted his gut flora can yield insights into the interplay between our genes and the microbiome. (He did grow and eat a salad lettuce once, though).

Of course, studying twins still makes for a small test group of only two people, and even though they’re identical, they’re not the same person.

“If something happens after Scott departs, increases during his trip, and then goes back to normal after he comes back to Earth - if we don't see that kind of sequential change in his twin, well, it's not proof of anything, but it certainly suggests something interesting is going on," Andrew Feinberg of Johns Hopkins Medical School told the Washington Post last year before the launch.

Even if you don’t get definitive answers, that’s still okay and is part and parcel of the scientific process. For researchers working on the space twins study, it’s an excellent chance to reveal some clues on how one day we might be able to tolerate the long, long trek to Mars.

“This is a unique opportunity for the agency,” NASA’s Human Research Program chief Craig Kundrot said back in 2014 when the study was announced.

“The investigations are a pathfinder for the agency with regard to the study of astronaut physiology.”

Mirror Twins: the siblings that go beyond identical
It can be hard to tell twins apart at the best of times, but when asymmetrical mirror twins visually reflect on another, it makes it far more confusing.

For more twins, check out SBS Insight: Part two of Insight’s special on twins airs Tuesday 22 March, 8:30pm SBS.