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             Mercury, 
              January/February 2006 Table of Contents  
              
            
               
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                Image 
                    of SN 1987A courtesy of NASA, P. Challis and R. Kirshner (Harvard-Smithsonian 
                    Center for Astrophysics) and B. Sugerman (STScI).  | 
               
             
            by 
              Jennifer Birriel and Ignacio Birriel 
            Over the past 
              decade or so, we humans have become nervous about the safety of 
              our planet. In the 1980s we were informed that a collision between 
              Earth and a massive asteroid may well have resulted in the mass 
              extinctions of life that occurred 65 million years ago. By the late 
              1990s, more and more near-earth objects (NEOs) were found—many 
              passing uncomfortably close, in the astronomical sense anyway.  
            Hollywood 
              capitalized on these fears and produced two blockbuster doomsday 
              movies, Deep Impact and Armageddon, with Earth-striking 
              objects as the movies' villans. These days, most everyone seems 
              to take notice of newly discovered objects that wander "too 
              close" and pose such impact threats to us. 
            Surprisingly, 
              fewer people are aware of the dangers of cosmic radiation. Most 
              everyone has heard about the increased danger to us from solar ultraviolet 
              radiation as we have inadvertently altered the ozone concentrations 
              of our planet's atmosphere. (We're all slathering on more sun block 
              these days!) But astronomers and other scientists are now discovering 
              that even more deadly threats may come from outer space. In fact, 
              the radiation from outside the Solar System may even have resulted 
              in one or more mass extinctions in Earth's past. 
            If 
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