Story highlights NASA says Scott Kelly is 2 inches taller after spending nearly a year in space

He's about to reunite with his twin brother in Houston

Since his return to Earth, the astronaut has been sharing photos of life on the ground

(CNN) Astronaut Scott Kelly and his twin brother used to be the same height.

But it's likely that won't be true when the two stand side by side for the first time in nearly a year.

NASA's Jeff Williams told CNN that Scott Kelly grew 2 inches during his time aboard the International Space Station

It was expected, and it's temporary, Williams said.

"Astronauts get taller in space as the spine elongates," Williams said, "but they return to preflight height after a short time back on Earth."