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Mark R. Showalter

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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]

Mark R. Showalter
Mark Robert Showalter

(1957-12-05) December 5, 1957 (age 62)
ResidenceCalifornia, U.S.
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


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 lifeEdit

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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