We already know that low-gravity causes all kinds of bone and muscle weakness and even messes with eyesight in a dramatic manner.
The scary part is while the bones/muscles can be healed over time, the eyesight problems persist and appear to be irreversible.
They have to solve this before trips to Mars will be possible, unless they are going to simulate gravity by constantly (slowly) accelerating half-way there and then slowly decelerating. It's technically plausible but a million other little problems have to be solved too. Won't happen in the lifetime of anyone alive right now.
The scary part is while the bones/muscles can be healed over time, the eyesight problems persist and appear to be irreversible.
They have to solve this before trips to Mars will be possible, unless they are going to simulate gravity by constantly (slowly) accelerating half-way there and then slowly decelerating. It's technically plausible but a million other little problems have to be solved too. Won't happen in the lifetime of anyone alive right now.