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.

                              2023 February 26
      [2]An unusual two-toned ball is pictured. The ball, Saturn's moon
      Iapetus, has many craters and an unusual ridge running along its
    equator that makes it look like a walnut. Please see the explanation
                       for more detailed information.

                Saturn's Iapetus: Moon with a Strange Surface
   Image Credit: [3]NASA, [4]ESA, [5]JPL, [6]SSI, [7]Cassini Imaging Team

   Explanation: What would make a moon look like a walnut? A strange ridge
   that circles [8]Saturn's moon [9]Iapetus's equator, visible near the
   bottom of the [10]featured image, makes it appear similar to a popular
   [11]edible nut. The origin of [12]the ridge remains unknown, though,
   with hypotheses including ice that welled up from below, a ring that
   crashed down from above, and structure left over from its formation
   perhaps 100 million years ago. Also strange is that about half of
   [13]Iapetus is so dark that it can nearly disappear when viewed from
   Earth, while [14]the rest is, reflectively, quite bright. Observations
   [15]show that the degree of darkness of the terrain is strangely
   uniform, as if a dark coating was somehow recently applied to an
   ancient and highly cratered surface. Last, several large impact basins
   occur around [16]Iapetus, with a 400-kilometer wide crater visible near
   the image center, surrounded by [17]deep cliffs that drop sharply to
   the crater floor. The [18]featured image was taken by the
   Saturn-orbiting [19]Cassini spacecraft during a [20]flyby of Iapetus at
   the end of 2004.

                    Tomorrow's picture: dawn before dawn
     __________________________________________________________________

      [21]< | [22]Archive | [23]Submissions | [24]Index | [25]Search |
   [26]Calendar | [27]RSS | [28]Education | [29]About APOD | [30]Discuss |
                                    [31]>
     __________________________________________________________________

    Authors & editors: [32]Robert Nemiroff ([33]MTU) & [34]Jerry Bonnell
                                 ([35]UMCP)
          NASA Official: Phillip Newman [36]Specific rights apply.
              [37]NASA Web Privacy Policy and Important Notices
                A service of: [38]ASD at [39]NASA / [40]GSFC,
                         [41]NASA Science Activation
                           & [42]Michigan Tech. U.

References

   1. https://apod.nasa.gov/apod/archivepix.html
   2. https://apod.nasa.gov/apod/image/2302/iapetus_cassini_960.jpg
   3. https://www.nasa.gov/
   4. https://www.esa.int/
   5. https://www.jpl.nasa.gov/
   6. https://www.spacescience.org/
   7. https://ciclops.org/
   8. https://apod.nasa.gov/apod/ap200419.html
   9. https://solarsystem.nasa.gov/moons/saturn-moons/iapetus/in-depth/
  10. https://photojournal.jpl.nasa.gov/catalog/PIA06166
  11. https://youtu.be/QF20_XWL2Vs
  12. https://en.wikipedia.org/wiki/Equatorial_ridge_on_Iapetus
  13. https://apod.nasa.gov/apod/ap180603.html
  14. https://en.wikipedia.org/wiki/Iapetus_(moon)#Two-tone_coloration
  15. https://ui.adsabs.harvard.edu/abs/2004Icar..170..125V/abstract
  16. https://en.wikipedia.org/wiki/Iapetus_(moon)
  17. https://apod.nasa.gov/apod/ap970218.html
  18. https://photojournal.jpl.nasa.gov/catalog/PIA06166
  19. https://solarsystem.nasa.gov/missions/cassini/mission/spacecraft/cassini-orbiter/
  20. https://youtu.be/6EE2rDEUB-U
  21. https://apod.nasa.gov/apod/ap230225.html
  22. https://apod.nasa.gov/apod/archivepix.html
  23. https://apod.nasa.gov/apod/lib/apsubmit2015.html
  24. https://apod.nasa.gov/apod/lib/aptree.html
  25. https://antwrp.gsfc.nasa.gov/cgi-bin/apod/apod_search
  26. https://apod.nasa.gov/apod/calendar/allyears.html
  27. https://apod.nasa.gov/apod.rss
  28. https://apod.nasa.gov/apod/lib/edlinks.html
  29. https://apod.nasa.gov/apod/lib/about_apod.html
  30. http://asterisk.apod.com/discuss_apod.php?date=230226
  31. https://apod.nasa.gov/apod/ap230227.html
  32. http://www.phy.mtu.edu/faculty/Nemiroff.html
  33. http://www.phy.mtu.edu/
  34. https://antwrp.gsfc.nasa.gov/htmltest/jbonnell/www/bonnell.html
  35. http://www.astro.umd.edu/
  36. https://apod.nasa.gov/apod/lib/about_apod.html#srapply
  37. https://www.nasa.gov/about/highlights/HP_Privacy.html
  38. https://astrophysics.gsfc.nasa.gov/
  39. https://www.nasa.gov/
  40. https://www.nasa.gov/centers/goddard/
  41. https://science.nasa.gov/learners
  42. http://www.mtu.edu/