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        Summary 
        
         
          
           | Description | 
           When Galileo first turned his telescope toward Jupiter four centuries ago, he saw that the giant planet had four large satellites, or moons. These, the largest of dozens of moons that orbit Jupiter, later became known as the Galilean satellites. The larger two, Callisto and Ganymede, are roughly the size of the planet Mercury; the smallest, Io and Europa, are approximately the size of Earth's Moon. This MGS MOC image, obtained from Mars orbit on 8 May 2003, shows Jupiter and three of the four Galilean satellites (from left): Callisto, Ganymede, and Europa. At the time, Io was behind Jupiter as seen from Mars, and Jupiter's giant red spot had rotated out of view. This image has been specially processed to show both Jupiter and its satellites, since Jupiter, at an apparent magnitude of -1.8, was much brighter than the three satellites. | 
          
          
           | Date | 
           Released by NASA 22 May 2003 | 
          
          
           | Source | 
            http://photojournal.jpl.nasa.gov/catalog/PIA04532 | 
          
          
           | Author | 
           NASA/JPL/Malin Space Science Systems | 
          
         
         
         Licensing 
        
         
          
           | Public domainPublic domainfalsefalse | 
          
         
         
          
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           This file is in the  public domain because it was solely created by  NASA. NASA copyright policy states that "NASA material is not protected by copyright unless noted". (See  Template:PD-USGov,  NASA copyright policy page or  JPL Image Use Policy.) | 
           
            
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