From: henry@spsystems.net   
      
   In article <427eb4c7$0$61918$892e7fe2@authen.white.readfreenews.net>,   
   Orilly   wrote:   
   >If at some future time evidence of biological presence on Mars is ever   
   >discovered (e.g. bacteria), how will scientists be sure it's not just   
   >contamination from previous Earthcraft that landed there?   
      
   Given the harshness of the Martian surface environment, it's grossly   
   unlikely that any bacterial hitchhikers on past spacecraft have grown and   
   spread.  Any contamination will almost certainly be in the immediate   
   vicinity of recognizable debris.   
      
   Martian life, if there is any, is far more likely to be found underground,   
   in places like hydrothermal vents.  No spacecraft have been there.   
      
   >Surely NASA doesn't claim that it's probes etc are guaranteed sterile when   
   >they land... or do they?   
      
   The Viking landers were indeed sterilized -- necessarily, since they were   
   carrying life-detection instruments.  More recent landers are not, but   
   efforts are made to reduce the level of bacterial contamination, precisely   
   to minimize the chances of confusing later life-detection efforts.   
   --   
   "Think outside the box -- the box isn't our friend."    |   Henry Spencer   
                                   -- George Herbert       | henry@spsystems.net   
      
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