Japanese astronaut Norishige Kanai, on a mission to the International Space Station, apologized on Wednesday for saying he had grown 9 cm (3.5 inches) while in space and expressing concern about whether he’d be safe on his return to Earth.
Norishige Kanai, an astronaut with the Japan Aerospace Exploration Agency, tweeted from the International Space Station (ISS) — where he has been stationed since Dec. 19 as part of Expedition 54 — on Monday he had grown by an incredible 9 centimeters (more than 3.5 inches) in the three weeks he had been in space. And as everyone down on Earth began talking about it and his tweet appeared in several news reports, Kanai put out two more tweets Tuesday, apologizing for the “fake news.”
How there was a “measurement error” of 7 centimeters during his physical that prompted his Monday tweet is not clear, but Kanai clarified he had grown only 2 centimeters, according to a measurement he took himself after the expedition leader Alexander Misurkin of Russia’s Roscosmos raised suspicions about the earlier measurement.
On Monday, Kanai had also expressed concern over whether he would be able to fit inside the Russia-built Soyuz capsule that would bring him back to Earth once his time aboard the space station came to an end. After he apologized for the misinformation, he also expressed relief at the fact that his increased height wouldn’t come in the way of his ride back home.
The cramped space of the Soyuz spacecraft that brings back astronauts from the ISS could be a real concern if an astronaut who is already taller than usual actually gained more than a couple of inches while in space, but some height increase is inevitable when spending time in zero-gravity environment. This happens because gravity keeps the vertebrae — pieces of the backbone — pushed together, but when that force is taken away, the backbone stretches out.
According to NASA, “the spine elongates by up to three percent while humans travel in space. There is less gravity pushing down on the vertebrae, so they can stretch out — up to 7.6 centimeters (3 inches).”
Space suits are designed keeping this in mind, especially since most of the elongation of the body happens as soon as the spacecraft goes into orbit. Astronauts keep growing in height a lot more gradually for some time afterward too, but that “gradual relaxation of the spine” is not infinite. So, even if someone were to spend an eternity in space, it wouldn’t mean becoming infinitely tall.
Also, this stretching is not permanent, and astronauts return to their normal height once they come back to Earth, where the familiar force of gravity does its familiar thing on their bones. In the same way they gain height, the reversal to their normal height is also a two-step procedure. The normal curvature of the spine reappears as soon as astronauts hit normal gravity. Complete normality is restored in about 10 days.
If you want to try this out for yourself, you don’t really need to go to space or even a specially designed laboratory with micro-gravity. Gravity affects the vertebrae differently when you are lying down, and you are a centimeter or two taller right after you wake up from a night’s sleep than you are during the day.