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                           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.   
      
                                 2024 September 16   
        The cratered surface of a large body is shown: Mercury. The largest   
      feature visible is a large impact crater with two rings, near the image   
       center. Arms from the BepiColumbo spacecraft that took the image are   
       seen extending into the image from the top and the right. Please see   
                  the explanation for more detailed information.   
      
                     Mercury's Vivaldi Crater from BepiColombo   
                     Image Credit: ESA, JAXA, BepiColombo, MTM   
      
      Explanation: Why does this large crater on Mercury have two rings and a   
      smooth floor? No one is sure. The unusual feature called Vivaldi Crater   
      spans 215 kilometers and was imaged again in great detail by ESA's and   
      JAXA's robotic BepiColombo spacecraft on a flyby earlier this month. A   
      large circular feature on a rocky planet or moon is usually caused by   
      either an impact by a small asteroid or a comet fragment, or a volcanic   
      eruption. In the case of Vivaldi, it is possible that both occurred --   
      a heavy strike that caused a smooth internal lava flow. Double-ringed   
      craters are rare, and the cause of the inner rings remains a topic of   
      research. The speed-slowing gravity-assisted flyby of Mercury by   
      BepiColombo was in preparation for the spacecraft entering orbit around   
      the Solar System's innermost planet in 2026.   
      
                          Tomorrow's picture: dusty heart   
        __________________________________________________________________   
      
          Authors & editors: Robert Nemiroff (MTU) & Jerry Bonnell (UMCP)   
               NASA Official: Amber Straughn Specific rights apply.   
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                         A service of: ASD at NASA / GSFC,   
                              NASA Science Activation   
                                & Michigan Tech. U.   
      
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