Astronomy Picture of the Day

   [1]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.

                              2025 September 1
    [2]A dark spherical body is shown that has many light craters. Please
             see the explanation for more detailed information.

                      Callisto: Dirty Battered Iceball
      Image Credit: [3]NASA, [4]JPL-Caltech, [5]Voyager 2; Processing &
                        [6]License: [7]Kevin M. Gill;

   Explanation: Its surface is the most densely cratered in the Solar
   System -- but what's inside? [8]Jupiter's moon [9]Callisto is a
   battered ball of dirty ice that is larger than the planet [10]Mercury.
   It was visited by NASA's [11]Galileo spacecraft in the 1990s and 2000s,
   but the recently reprocessed [12]featured image is from a flyby of
   NASA's [13]Voyager 2 in 1979. The moon would appear darker if it
   weren't for the tapestry of light-colored [14]fractured surface ice
   created by eons of impacts. The [15]interior of Callisto is potentially
   even more interesting because therein might lie an internal layer of
   liquid water. This potential [16]underground sea is a candidate to
   [17]harbor life -- similar with sister moons [18]Europa and
   [19]Ganymede. Callisto is slightly larger than [20]Luna, [21]Earth's
   Moon, but because of its high ice content is slightly less massive.
   ESA's [22]JUICE and NASA's [23]Europa Clipper missions are now headed
   [24]out to Jupiter to better investigate its [25]largest moons.

                    Tomorrow's picture: flaming sky horse
     __________________________________________________________________

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    Authors & editors: [37]Robert Nemiroff ([38]MTU) & [39]Jerry Bonnell
                                 ([40]UMCP)
          NASA Official: Amber Straughn [41]Specific rights apply.
            [42]NASA Web Privacy, [43]Accessibility, [44]Notices;
                A service of: [45]ASD at [46]NASA / [47]GSFC,
                         [48]NASA Science Activation
                           & [49]Michigan Tech. U.

References

   1. https://apod.nasa.gov/apod/archivepix.html
   2. https://apod.nasa.gov/apod/image/2509/Callisto_Voyager2Gill_1602.jpg
   3. https://www.nasa.gov/
   4. https://www.jpl.nasa.gov/
   5. https://science.nasa.gov/mission/voyager/voyager-2/
   6. https://creativecommons.org/licenses/by/2.0/deed.en/
   7. https://www.flickr.com/people/kevinmgill/
   8. https://science.nasa.gov/jupiter/
   9. https://science.nasa.gov/jupiter/jupiter-moons/callisto/
  10. https://science.nasa.gov/mercury/
  11. https://science.nasa.gov/mission/galileo/
  12. https://commons.wikimedia.org/wiki/File:Callisto_-_July_8_1979_(38926064465).jpg
  13. https://science.nasa.gov/mission/voyager/voyager-2/
  14. https://thumbs.dreamstime.com/b/black-cat-pawing-broken-glass-window-s-paw-reaches-its-sharp-claws-visible-shards-scattered-around-creating-334701018.jpg
  15. https://apod.nasa.gov/apod/ap981106.html
  16. https://www.jpl.nasa.gov/news/ocean-inside-jupiters-moon-callisto-may-have-cushioned-big-impact/
  17. https://www.numberanalytics.com/blog/astrobiological-potential-of-callisto
  18. https://apod.nasa.gov/apod/ap240329.html
  19. https://apod.nasa.gov/apod/ap231128.html
  20. https://en.wikipedia.org/wiki/Luna_(name)
  21. https://science.nasa.gov/moon/
  22. https://www.esa.int/Science_Exploration/Space_Science/Juice
  23. https://science.nasa.gov/mission/europa-clipper/
  24. https://apod.nasa.gov/apod/ap170523.html
  25. https://www.jpl.nasa.gov/images/pia01299-the-galilean-satellites/
  26. https://apod.nasa.gov/apod/ap250831.html
  27. https://apod.nasa.gov/apod/archivepix.html
  28. https://apod.nasa.gov/apod/lib/apsubmit2015.html
  29. https://apod.nasa.gov/apod/lib/aptree.html
  30. https://antwrp.gsfc.nasa.gov/cgi-bin/apod/apod_search
  31. https://apod.nasa.gov/apod/calendar/allyears.html
  32. https://apod.com/feed.rss
  33. https://apod.nasa.gov/apod/lib/edlinks.html
  34. https://apod.nasa.gov/apod/lib/about_apod.html
  35. https://asterisk.apod.com/discuss_apod.php?date=250901
  36. https://apod.nasa.gov/apod/ap250902.html
  37. http://www.phy.mtu.edu/faculty/Nemiroff.html
  38. http://www.phy.mtu.edu/
  39. https://antwrp.gsfc.nasa.gov/htmltest/jbonnell/www/bonnell.html
  40. http://www.astro.umd.edu/
  41. https://apod.nasa.gov/apod/lib/about_apod.html#srapply
  42. https://www.nasa.gov/about/highlights/HP_Privacy.html
  43. https://www.nasa.gov/general/accessibility/
  44. https://www.nasa.gov/privacy/
  45. https://astrophysics.gsfc.nasa.gov/
  46. https://www.nasa.gov/
  47. https://www.nasa.gov/centers/goddard/
  48. https://science.nasa.gov/learners
  49. http://www.mtu.edu/