Scott Kelly has been in space for 172 days. Right now, as you read these words, he’s orbiting Earth in the International Space Station, as a participant in the first international One Year Mission with cosmonaut Mikhail Kornienko — the goal of which is to study the effects of life in space on the human body in a slew of experiments.

Scott’s identical twin brother, fellow astronaut, and former NASA Commander Mark has been living comfortably on Earth during that same time. Since Mark and Scott are the same age, same fitness level, and have identical genetics, they make the perfect test subjects for studies on human physiology, behavioral health, microbiome and molecular continuity. They form the center of NASA’s Twin Study.

On Tuesday, September 15, 2015 C-SPAN2 aired a National Press Club discussion. Mark Kelly talked about the ongoing research and his brother fielded questions from the ISS via video link.

John Hughes, National Press Club President asked Scott how he was doing: “How do you feel, what effects have microgravity had on you so far during this almost six month period?”

Scott said, “As far as physically, I feel good, we have some pretty good exercise equipment up here, but there are a lot of effects of this environment that we can’t see or feel, bone loss, effects on our vision, our genetics, DNA, RNA and proteins, and that’s why we’re studying this.”

Chromosomal samples from each of the 51 year old twins were banked before Scott rocketed into space to allow researchers to track comparative changes in their telomeres and epigenomes. Telomeres are DNA that protects the tips of chromosomes. The longer we live, the shorter this protection gets, and as our chromosomes unravel we feel the effects of old age. Inquiring minds also want to know how the body decides which genes are expressed. Our environment has serious effects on epigenomes, so the time spent weightless in space could be a real eye-opener.

More physical samples are collected regularly.  Mark gets the easy side of sampling: Scott has to draw his own blood, freeze it, and send it home on ships returning from the space station. They didn’t talk about how he handles some other samples, like stool required for microbiome-focused projects.

The bacteria, yeasts, and molds (or as Scott put it, “The things in us that are not us”), which are so important to our natural body chemistry, are replenished by what we eat, and Scott gets no fresh food in space. “One of the principal investigators told me that my brother and my microbiomes are completely different.”

Later, Hughes asked, “Do you think that you or Mark got the better end of the deal on the twin study?”

Scott responded, “It’s a privilege to fly on this flight, but sometimes when he sends me pictures of his breakfast, I’m a little envious.”

One of the weird side effects of life in space we don’t hear a lot about: Baby feet. Scott explained, “We don’t use the bottom of our feet much. Over time any callouses on our feet kind of fall off. After about five months up here you have baby feet. When I got back from my last flight… I was getting a massage… and the masseuse said, ‘You have the softest feet I’ve ever felt in my whole life.’  And my response was, ‘Thank you, I’m very proud of them.’ ”

You can check out the full C-SPAN coverage here, or watch the National Press Club video at the top of the page. The twin astronaut experiment or Twin Study will continue for two years following Scott’s return March 3, 2016, to see if telomere loss slows and the brothers begin to match on the chromosomal level again.