The Mars Society wants to send a group of mice to space where it can breed and then come back. Since many astronauts lose bone density on trips to space, the idea is to simulate gravity in the spacecraft to see if that can help with the ordeal.
Thus, we might have a better understanding of how humans would cope with a long term trip on Mars. The Univeristy of Washington, the University of Quensland and MIT are behind this project.
To simulate the gravity conditions of Mars while the mice fly through space, researchers are thinking of using a rotating spacecraft. The mice would leave for a 2 month journey in 2005.