Mark R. Showalter

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Mark R. Showalter
Mark Robert Showalter

(1957-12-05) December 5, 1957 (age 62)
Alma materOberlin College (B.A.); Cornell University (M.Sc.), (Ph.D.)
Known forDiscoverer or co-discoverer of Jovian gossamer ring, Saturnian moon Pan, Uranian moons Mab and Cupid, Uranian rings μ and ν, Neptunian moon Hippocamp, Plutonian moons Kerberos and Styx
Spouse(s)Frank Yellin
Scientific career
FieldsAstronomy, astrophysics, space science, planetary science
InstitutionsSETI Institute

Mark Robert Showalter (born December 5, 1957) is a Senior Research Scientist at the SETI Institute.[1] He is the discoverer of six moons and three planetary rings. He is the Principal Investigator of NASA's Planetary Data System Rings Node, a co-investigator on the Cassini–Huygens mission to Saturn, and works closely with the New Horizons mission to Pluto.[2]


Showalter was born in Abington, Pennsylvania. He enjoyed playing with science-themed toys while a child, and later mowed lawns as a teenager so that he might purchase a telescope in high school. He received a Bachelor of Arts in physics and mathematics from Oberlin College in 1979. He was initially undecided about pursuing a career in astronomy after his undergraduate education, but made up his mind after seeing the images of Jupiter sent back to Earth by Voyager 2.[3]

Showalter received his MS in astronomy from Cornell University in 1982, and his PhD from Cornell in 1985.[3][4] His thesis was on Jupiter's ring system, in which he discovered the gossamer ring of Jupiter.[a][5]

In 1990, using ten-year-old Voyager data, Showalter discovered Pan, the eighteenth and innermost moon of Saturn. It orbits within and keeps open the Encke Gap in Saturn's rings via shepherding.[6][7]

In 2003, Showalter and Jack J. Lissauer discovered two new moons of Uranus (Mab and Cupid) in Hubble Space Telescope images.[7][8] In 2006, they announced the discovery of two very faint rings, the μ and ν rings, within the same data.[9][10]

In 2010, Showalter discovered that spiral vertical corrugations in Jupiter's rings were caused by the impact of Comet Shoemaker–Levy 9 in July 1994. A second smaller set of corrugations appear to be consistent with an unknown impact in early 1990. He and co-researchers also found similar spiral patterns in Saturn's D Ring.[11][12][13][14]

Showalter has assisted the New Horizons team in determining what hazards the spacecraft would encounter as it flew close to Pluto. A search for faint dust rings of Pluto using the Hubble Space Telescope in 2011 led to the discovery of the fourth moon Kerberos.[7][15] Working with the New Horizons team, Showalter found the fifth moon Styx in July 2012.[16][17]

On July 15, 2013, a team of astronomers led by Showalter discovered a previously unknown fourteenth moon in images taken by the Hubble Space Telescope from 2004 to 2009. Unnamed at that time, Hippocamp is thought to measure around 34.8 km in diameter.[18]

The Mars-crossing asteroid 18499 Showalter is named after Dr. Showalter.

Personal life[edit]

Showalter is an avid scuba diver and photographer. He is married to Frank Yellin; they live in California.[2][19]


  1. ^ At the time of discovery, the gossamer ring was thought to be a single ring. Later observations have resolved the gossamer ring into two separate, overlapping rings: the Thebe gossamer ring and the Amalthea gossamer ring.


  1. ^ Boyle, Alan (2012-07-11). "Pluto's fifth moon discovered". Archived from the original on 2012-07-15. Retrieved 2012-07-16.
  2. ^ a b "Mark Showalter's Home Page". Rings Node, NASA Planetary Data System. July 2012. Archived from the original on 2008-09-17. Retrieved 2012-07-16.
  3. ^ a b Tanner, Steve (2007-01-07). "SETI Institute's Ring Leader". San Jose Business Journal. Retrieved 2012-07-16.
  4. ^ "Cornell University Department of Astronomy Ph.D. recipients". Archived from the original on 2012-07-10.
  5. ^ Showalter, Mark; Burns; Cuzzi; Pollack (August 8, 1985). "Discovery of Jupiter's 'gossamer' ring". Nature. 316 (6028): 526–528. Bibcode:1985Natur.316..526S. doi:10.1038/316526a0. PMID 11536560.
  6. ^ Showalter, Mark R (27 June 1991). "Visual detection of 1981S13". Nature. 351 (6329): 709–73. Bibcode:1991Natur.351..709S. doi:10.1038/351709a0.
  7. ^ a b c "Gazetteer of Planetary Nomenclature". International Astronomical Union Working Group for Planetary System Nomenclature. Astrogeology Science Center, United States Geological Survey. 2006-07-21. Retrieved 2012-07-16.
  8. ^ Blunck, Jürgen (2010). Solar System Moons: Discovery and Mythology. Dordrecht. p. 95. ISBN 9783540688525.
  9. ^ Showalter, Mark R; Lissauer (17 February 2006). "The second ring-moon system of Uranus: discovery and dynamics". Science. 311 (5763): 973–977. Bibcode:2006Sci...311..973S. doi:10.1126/science.1122882. PMID 16373533.
  10. ^ Grün, Eberhard (2001). Interplanetary Dust. Springer. p. 668. ISBN 3540420673.
  11. ^ Mason, J.; Cook, J.-R. C. (2011-03-31). "Forensic sleuthing ties ring ripples to impacts". CICLOPS press release. Cassini Imaging Central Laboratory for Operations. Retrieved 2011-04-04.
  12. ^ NASA (2011-03-31). "Subtle Ripples in Jupiter's Ring". PIA 13893 caption. NASA / Jet Propulsion Laboratory-Caltech / SETI. Retrieved 2011-04-04.
  13. ^ Showalter, M. R.; Hedman, M. M.; Burns, J. A. (2011). "The impact of comet Shoemaker-Levy 9 sends ripples through the rings of Jupiter". Science. 332 (6030): 711–3. Bibcode:2011Sci...332..711S. doi:10.1126/science.1202241. PMID 21454755.
  14. ^ Matson, John (2011-03-31). "A New Wrinkle: Comet Strikes in the 1980s and 1990s Left Ripples in Jupiter's and Saturn's Rings". Scientific American. Retrieved 2012-07-16.
  15. ^ Showalter, M. R.; Hamilton, D. P. (2011-07-20). "New Satellite of (134340) Pluto: S/2011 (134340) 1". Central Bureau for Astronomical Telegrams. International Astronomical Union. Retrieved 2011-07-20.
  16. ^ Sanders, Ray (11 July 2012). "Hubble Space Telescope detects fifth moon of Pluto". Retrieved 11 July 2012.
  17. ^ Overbye, Dennis (20 July 2012). "Despite Downgrade, Pluto Adds to Entourage". New York Times. Retrieved 2012-07-16.
  18. ^ Beatty, Kelly. "Neptune's Newest Moon." Sky and Telescope. July 15, 2013. Accessed 2013-07-17. Archived July 16, 2013, at
  19. ^ "Harvard-Radcliffe Class of 1980 - Class Notes". Archived from the original on 25 December 2008.

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