Man's ability to survive long-term space travel has been thrown into doubt after mice returned from orbit with liver damage.
Scientists at the University of Colorado examined the livers of mice that had spent 13.5 days aboard the Atlantis shuttle, finding the spaceflight had induced scarring and long-term damage.
The two-week mission represents a significant proportion of the one to two-year average lifespan of a mouse, and the study's authors believe the findings could have worrying implications for NASA's manned deep space travel, such as a mission to Mars which could take a year.