Floating in microgravity may look effortless, but for bones, it’s anything but. Anew NASA study on mice reveals that the bones most critical for bearing weight on Earth are especially vulnerable to deterioration in space — and the effects may be irreversible.

Floating about in microgravity might seem like a blissful reprieve for the human body's weight-bearing skeleton, but when astronauts spend months in space, their bone density takes a serious hit that they may never fully recover from.

Suni Williams and Butch Wilmore spent 286 days on the International Space Station after their week-long mission was met with technical issues.