To rocket engineers, the idea of transporting humans to Mars is a one colossal headache. Compared to inert satellites and probes, humans are highly unpredictable, needy and fragile. Radiation is our body's kryptonite; microgravity renders the bones thin and weak and if you broke a leg, it could take months to fix. These are just a few of the hundreds of problems scientists are grappling with when considering how they might send people to the rocky red planet. We'll be taking a closer look at some of those obstacles this week and asking if it's actually possible to get people to Mars. Plus, news that scientists have grown the first kidney from scratch in a petri-dish, how vitamin pills can make cancer spread, and what a 4500-year-old skeleton is revealing about our origins...