The Bad Astronomy website is a great place to find answers to many of your 'spacey' questions. The scientist who directs the website is Phil Plait. I met Phil once and I know you'll be impressed with what he has to say and how easy it is to understand his explanations. You will find it here.
Phil Plait also wrote a book titled "Death From The Skies" which includes more detail about what I discussed in my video.
NASA even has a website telling you about their work to protect Earth as well as other planets they explore with their space probes. The mission of the Office of Planetary Protection is to minimize the biological contamination that may result from exploring the solar system. In other words, NASA wants to make sure humans don't send any bacteria, viruses, or anything else from Earth that will affect the environment of planets we explore (like Mars). The website can be found here.
NASA wants to make sure astronauts living for several months in space will not be hurt by space radiation. They have a website that explains how this is done here.