12 weird things space travel does to the human body

This month NASA astronaut Scott Kelly hit an incredible milestone: He has spent more time in space than any other American in history.

Oct. 16, 2015, marked his 383rd total day spent zooming 250 miles above Earth aboard the International Space Station (ISS), beating astronaut Mike Fincke's previous record of 382 days, according to NASA. And on Oct. 29, he'll have spent 216 consecutive days in space, beating Michael López-Alegría's previous record of 215 days.

Astronauts are normally limited to six-month trips in space — but this is just the beginning for Kelly. He's spending a full, uninterrupted year aboard the ISS while his identical twin brother stays here on Earth. Scientists are studying both brothers to measure how the human body changes during long-term spaceflight. The brothers are routinely giving cheek swabs, blood samples, and fecal samples to researchers for analysis and comparison.

This year-long experiment could pave the way for a long-duration trip to Mars, but it is not for the faint of heart. Scientists already know a few things about what space and microgravity does to the human body over time, some of which are downright disturbing.

Keep scrolling to see some of the bizarre things that happen to the body in space.

1. It stretches out your spine

Astronauts can grow up to 3% taller in space. That means that a 6-foot-tall astronaut could tack on an extra two inches. 

The growth spurt happens because microgravity allows the squishy spinal discs between vertebra freedom to relax and expand — almost like relieving pressure on a spring. It takes a few months to return to normal height after they get back to Earth.

It's possible Kelly could grow more than the average astronaut, since he's spending more time in space.

2. It turns your muscles into jelly

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You don't need muscles to support you in a weightless environment, so astronauts' muscles almost immediately start shrinking and absorbing that extra, now worthless tissue.

That's why there's a gym of sorts on the ISS. Strenuous exercise can help astronauts can maintain the muscle mass they need when they return to Earth and have to stand up and walk around again.

They usually budget about two hours a day for exercise, according to NASA. That includes "weight lifting" using a special resistance machine, since a free-weight weighs, well, nothing in zero gravity.

3. It makes your face puffy

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Our bodies are mostly liquid. The gravity on Earth pulls that liquid down and some of it pools in our lower extremities. In near zero-g the liquid is spread out more evenly around the body, so astronauts' faces look puffier than normal while their legs look skinnier than normal.

After a few weeks the body adjusts to the gravity change and some of the puffiness goes down.

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