spaceSpace and Physics

No, A Japanese Astronaut Didn't Grow 9 Centimeters Taller In Space


Robin Andrews

Science & Policy Writer

JAXA astronaut Norishige Kanai prepping for launch back in December 2017. NASA/GCTC/Andrey Shelepin

As was widely reported yesterday, a Japanese spacefarer by the name of Norishige Kanai suspected he’d grown 9 centimeters (3.54 inches) taller after just three weeks aboard the International Space Station (ISS).

Astronauts do get a few centimeters taller while living in a microgravity setting – more on why in just a tad. Growing 9 centimeters in less than a month, however, was rather remarkable, and it certainly got everyone’s attention.


Unfortunately, the reality of the situation was very different, and in the end, Kanai had sprouted just 2 centimeters (0.79 inches), something that’s well within the boundaries of what’s expected. So – what exactly happened here, and why do astronauts grow taller in a microgravity environment anyway?

Tweeting from way up above, Kanai explained on January 8 that his height had been measured aboard the ISS, and was stunned to find a 9-centimeter increase. He pointed out that it was the most he’d grown since junior high school, and suggested he wouldn’t be able to fit into the Earthbound Soyuz capsule at the end of his novel tenure in orbit around our blue marble.


In space, astronauts experience a range of bizarre and barely understood medical afflictions, including a recently discovered “space fever” that can cause internal body temperature to become higher than that of humans on Earth.

They also get taller, because in the absence of a significant gravitational pull, the vertebrae in their spines loosen, and the spine itself expands. This quickly reverts back to normal upon returning to terra firma, but – along with some associated muscle atrophy – this can ultimately cause some fairly inconvenient back problems for some astronauts.


Our height is actually curiously changeable throughout the day. When standing, gravity helps to squash up our spine and joints, making us ever so slightly shorter. Laying down has the opposite effect.

In space, then, the lack of gravity makes sudden changes in height unsurprising. It was the magnitude of the height change that Kanai appeared to experience that raised some eyebrows, though. As recently revealed by the astronaut himself, it turned out to be nothing more than a simple error.

A series of additional tweets sent out over the last 24 hours by Kanai explain that his Russian cosmonaut colleague, Anton Shkaplerov, was suspicious of the 9-centimeter increase. Kanai was apparently re-measured, and it turned out to be a 2-centimeter increase after all.

“I am a bit relieved to be able to ride on the return Soyuz,” he added, after apologizing for the original error. It's a little unclear as to how the original mis-measurement was made, but at least it was ultimately spotted.


So there you have it. Everyone makes mistakes from time to time – even astronauts. Good on Kanai for quickly remedying the situation, we say.


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