Lost in space: Astronauts struggle to regain bone density
Astronauts lose decades' worth of bone mass in space that many do not recover even after a year back on Earth, researchers said Thursday, warning that it could be a "big concern" for future missions to Mars.. "The longer you spend in space, the more bone you lose," Boyd told AFP. Boyd said it is a "big concern" for planned for future missions to Mars, which could see astronauts spend years in space.