Current rotations on the International Space Station put astronauts in zero gravity for six months, a comparable length of time to a one-way trip to Mars. This gives researchers the ability to better understand the physical state that astronauts going to Mars will arrive in. Once on Mars, surface gravity is only 38% of that on Earth.[43] Upon return to Earth, recovery from bone loss and atrophy is a long process and the effects of microgravity may never fully reverse.