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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.
                  NASA Web Privacy, Accessibility, Notices;
                      A service of: ASD at NASA / GSFC,
                           NASA Science Activation
                             & Michigan Tech. U.

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