How Astronaut Scott Kelly Got Two Inches Taller While in Space

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When identical twin brothers Scott and Mark Kelly were little, their own mom reportedly found it so tough to tell them apart that she once resorted to drawing a mustache on Mark’s face just to be sure who was who.

She wouldn’t need to do that today. The grown men – both celebrated astronauts with NASA – now have a very noticeable differentiating characteristic (beyond Mark’s voluntary mustache), at least for the next several months. That’s because, having just wrapped up a year in the weightless environment of the International Space Station (ISS), Scott is currently almost two full inches taller than he was the last time he blasted off from earth.

Click here for some strange spine facts that may surprise you.

What happens to the spine in microgravity?

While much has yet to be studied with regard to the effects of living in space on the human body, researchers know that astronauts can get up to 3 percent taller when they spend enough time in microgravity. This is because the vertebrae and disks in the spine are able to expand when not subjected to the load-bearing pressure of standing, sitting, exercising – indeed, doing just about anything -- in a gravity-laden environment. This expansion causes the spine to temporarily stretch and lengthen (as opposed to actually growing longer) so the astronaut gets taller. On earth, it’s the compression of the spinal disks due to gravity that causes most of us to get shorter as we age, and that same gravitational pull will eventually cause Scott Kelly to return to his normal height.

Here are four easy exercises to keep your spine strong as you get older.

Recently, NASA began employing a special ultrasound device onboard the International Space Station to take a close look at the anatomical changes that occur to astronauts’ spines while in space. As of 2013, ISS crews started using the device to take scans of each other’s backs at the 30-, 90- and 150-day mark of their residency on the station. Such advanced capabilities for musculoskeletal imaging and research will no doubt lead to an even greater understanding of how spinal structures “stretch” and expand during space missions.

Beyond height, what other changes might the spine experience after a year spent in space?

Astronauts today follow rigorous exercise programs while in space. This is in order to minimize the breakdown of muscles and bones that can occur in the back, legs and hips when all you have to do is float from one place to another rather than walking. But even with these precautions, the reduction in load-bearing activities typically allows for some weakening of the bones and causes them to lose calcium, which in turn makes them more brittle and prone to fractures. Veteran astronauts may also be more subject to injuries caused by falls due to an imbalance or weakening of their leg and core muscles. Going forward, researchers will certainly be looking at the strength and stability of Scott’s spine in comparison to his brother’s as they collect more clues about the effects of space travel.

For a quick overview of some of the many conditions that can affect the human spine due to overuse, injury and normal wear-and-tear during life on earth, click here.


After a year in space, Scott Kelly returns 2 inches taller (3/3/2016). Retrieved from USA Today:

Astronaut Scott Kelly is Two Inches Taller Than Twin Brother Mark After #YearinSpace (n.d.). Retrieved from Inquisitr:

NASA’s Scott Kelly Grew 2 Inches: The Body After a Year in Space (3/2/2016). Retrieved from

Strange But True: Astronauts Get Taller in Space (1/7/2013). Retrieved from

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