Stanford University has indicated that spending two years in a Mars mission can significantly impact an astronaut's skeletal health. The research raises concerns about the potential fragility of bones when astronauts return to Earth’s gravity after such an extended period in space. This leads to questions about the risks associated with bone health for astronauts completing long-duration missions, especially regarding their ability to safely adapt to Earth's gravitational forces.

Mary Roach's book, "Packing for Mars: The Curious Science of Life in the Void," explores these challenges faced by astronauts. With the risk of bones becoming weaker during the mission, there is a legitimate concern that an astronaut could suffer a bone fracture upon returning to Earth's gravity. This highlights the importance of understanding the physiological effects of space travel on the human body, particularly for future long-term interplanetary missions.