We did it, Reddit: We made it to space. Next stop: MARS!

Astronaut Scott Kelly held the first ever NASA Reddit AMA (Ask Me Anything session) this week from space! Now, Kelly is extremely important right now for scientists because he may hold the key to helping us understand how to send humans to Mars.

You're invited! 300 days of a #YearInSpace today! Ready to @Reddit? Join me Sat., Jan 23, 4pm ET to #AskMeAnything! pic.twitter.com/XRj5mPQabL — Scott Kelly (@StationCDRKelly) January 22, 2016

That’s because Kelly is the first American to spend a whole consecutive year in space. Kelly, who has been living on the International Space Station (ISS) since March of last year, has already spent more than 300 days in space—so his body has gone through several changes to adapt to zero gravity.

But Commander Kelly comes with an advantage (besides his epic Instagram account). And that’s his identical twin brother, Mark, who lives back on Earth. Scientists are studying the two to see how space changes the human body during long-term space travel. In fact, Kelly talks about the bodily changes he underwent in the AMA—and it’s not nothing short of fascinating. Check it out below:

Why do you always have your arms folded?

And this is probably what you were thinking. Wasn’t it?

Can you tell us something unusual about being in space that most people don’t think about?

What does weightlessness feel like on your body?

What’s the creepiest thing you’ve encountered on the job?

Acid? Urine? Whaaat? Don’t worry—Kelly delivers:

Is your dream world mostly in zero gravity?

What’s the Internet connectivity like up there?

Are you typing on a laptop?

What does space smell like?

What’s your favorite part of Earth to watch?

Do you wear space sunscreen?

What’s it like to sleep in zero gravity?

Have you seen any fights aboard the ISS?

Read the entire AMA with Commander Scott Kelly here.