Astronomy Picture of the Day  
    
      Discover the cosmos! Each day a different image or photograph of our  
        fascinating universe is featured, along with a brief explanation  
                      written by a professional astronomer.  
    
                                   2026 July 5  
     An unusually colored ball is shown against a dark background. The ball  
      has numerous craters but a very large cratered near the lower center.  
      Much of the ball is light colored, but around the right and top it is  
      green-brown, with a border area that seems splattered. Please see the  
                   explanation for more detailed information.  
    
                         Saturn's Iapetus: Painted Moon  
             Image Credit: NASA, ESA, JPL, SSI, Cassini Imaging Team  
    
     Explanation: What has happened to Saturn's moon Iapetus? Vast sections  
     of this strange world are dark as coal, while others are as bright as  
     snow. To help better understand this unusually tinted moon, in 2007  
     NASA directed the robotic Cassini spacecraft then orbiting Saturn to  
     swoop within 2,000 kilometers. Pictured here, from about 75,000  
     kilometers out, is the hemisphere of Iapetus that is always trailing. A  
     large impact crater seen in the south spans 500 kilometers and appears  
     superposed on an older crater of similar size. The dark material is  
     seen increasingly coating the easternmost part of Iapetus, darkening  
     craters and highlands alike. A leading hypothesis is that the dark  
     material is mostly a form of carbon-rich soil leftover from when  
     relatively warm but dirty ice sublimates. An initial coating of this  
     dark material may have been effectively painted on by the accretion of  
     meteor-liberated debris from other moons.  
    
                    Jigsaw Moon: Astronomy Puzzle of the Day  
                     Tomorrow's picture: dueling space bands  
       __________________________________________________________________  
    
         Authors & editors: Robert Nemiroff (MTU) & Jerry Bonnell (UMCP)  
              NASA Official: Amber Straughn Specific rights apply.  
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                               & Michigan Tech. U.  
    
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