When astronauts first travel to Mars, or anywhere else in deep space, they will have to contend with two problems that our planet itself protects us from on its surface - radiation and weightlessness. Scientists already know both can have a profound impact on the human body, but just how much of one, and how long that impact can last, remain a mystery. A new paper by researchers at the Medical College of Wisconsin, and published in PLoS One, tackles those questions, and unfortunately comes up with some less than ideal answers in terms of the long term implications of deep space exposure.