well just a skimming of the atmosphere of mars and trust us we will take care of it and sterilized any possible alien viruses, before we bring them back to earth http://www.scientificamerican.com/article/mars-mission-could-return-samples-to-earth-by-2020/ http://www.scientificamerican.com/article/mars-mission-could-return-samples-to-earth-by-2020/