                        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.

                                 2023 July 8

                               Stickney Crater
              Image Credit: HiRISE, MRO, LPL (U. Arizona), NASA

   Explanation: Stickney Crater, the largest crater on the martian moon
   Phobos, is named for Chloe Angeline Stickney Hall, mathematician and
   wife of astronomer Asaph Hall. Asaph Hall discovered both the Red
   Planet's moons in 1877. Over 9 kilometers across, Stickney is nearly
   half the diameter of Phobos itself, so large that the impact that
   blasted out the crater likely came close to shattering the tiny moon.
   This enhanced-color image of Stickney and surroundings was recorded by
   the HiRISE camera onboard the Mars Reconnaissance Orbiter as it passed
   within some six thousand kilometers of Phobos in March of 2008. Even
   though the surface gravity of asteroid-like Phobos is less than
   1/1000th Earth's gravity, streaks suggest loose material slid down
   inside the crater walls over time. Light bluish regions near the
   crater's rim could indicate a relatively freshly exposed surface. The
   origin of the curious grooves along the surface is mysterious but may
   be related to tidal stresses experienced by close-orbiting Phobos or
   the crater-forming impact itself.

                       Tomorrow's picture: doomed star
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       Authors & editors: Robert Nemiroff (MTU) & Jerry Bonnell (UMCP)
            NASA Official: Phillip Newman Specific rights apply.
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                             & Michigan Tech. U.

