# Mark R. Showalter

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American research scientist (born 1957)

Mark R. Showalter Born Mark Robert Showalter (1957-12-05) December 5, 1957 (age 68) Abington, Pennsylvania, U.S. Alma mater Oberlin College (B.A.); Cornell University (M.Sc.), (Ph.D.) Known for Discoverer 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 Frank Yellin Scientific career Fields Astronomy, astrophysics, space science, planetary science Institutions SETI Institute

**Mark Robert Showalter** (born December 5, 1957) is an American senior research scientist at the [SETI Institute](/source/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](/source/Planetary_Data_System) Rings Node, a co-investigator on the [Cassini–Huygens](/source/Cassini%E2%80%93Huygens) mission to [Saturn](/source/Saturn), and works closely with the [New Horizons](/source/New_Horizons) mission to [Pluto](/source/Pluto).[2]

## Biography

Showalter was born in [Abington, Pennsylvania](/source/Abington_Township%2C_Montgomery_County%2C_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](/source/Telescope) in high school. He received a [Bachelor of Arts](/source/Bachelor_of_Arts) in [physics](/source/Physics) and [mathematics](/source/Mathematics) from [Oberlin College](/source/Oberlin_College) in 1979. He was initially undecided about pursuing a career in [astronomy](/source/Astronomy) after his undergraduate education, but made up his mind after seeing the images of Jupiter sent back to Earth by [Voyager 2](/source/Voyager_2).[3]

Showalter received his [MS](/source/Master_of_Science) in [astronomy](/source/Astronomy) from [Cornell University](/source/Cornell_University) in 1982, and his [PhD](/source/Doctor_of_Philosophy) from Cornell in 1985.[3][4] His thesis was on [Jupiter](/source/Jupiter)'s [ring system](/source/Planetary_ring), in which he discovered [the gossamer ring of Jupiter](/source/Rings_of_Jupiter).[a][5]

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

In 2003, Showalter and [Jack J. Lissauer](/source/Jack_J._Lissauer) discovered two new moons of [Uranus](/source/Uranus) ([Mab](/source/Mab_(moon)) and [Cupid](/source/Cupid_(moon))) in [Hubble Space Telescope](/source/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](/source/Comet_Shoemaker%E2%80%93Levy_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](/source/Kerberos_(moon)).[7][15] Working with the New Horizons team, Showalter found the fifth moon [Styx](/source/Styx_(moon)) in July 2012.[16][17]

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

Showalter was the 2021 recipient of the [Harold Masursky Award for Meritorious Service to Planetary Science](/source/Masursky_Award).[19]

The [Mars-crossing](/source/List_of_Mars-crossing_minor_planets) asteroid [18499 Showalter](/source/18499_Showalter) is named after Dr. Showalter.

## Personal life

Showalter is an avid [scuba diver](/source/Scuba_diving) and [photographer](/source/Photography). He is married to Frank Yellin; they live in California.[2][20]

## Notes

1. **[^](#cite_ref-5)** 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.

## References

1. **[^](#cite_ref-1)** Boyle, Alan (2012-07-11). ["Pluto's fifth moon discovered"](https://web.archive.org/web/20120715042657/http://cosmiclog.msnbc.msn.com/_news/2012/07/11/12683467-plutos-fifth-moon-discovered). [MSNBC.com](/source/MSNBC.com). Archived from [the original](https://cosmiclog.msnbc.msn.com/_news/2012/07/11/12683467-plutos-fifth-moon-discovered) on 2012-07-15. Retrieved 2012-07-16.

1. ^ [***a***](#cite_ref-Bio_2-0) [***b***](#cite_ref-Bio_2-1) ["Mark Showalter's Home Page"](https://web.archive.org/web/20080917215555/http://pds-rings.seti.org/showalter/). *Rings Node, NASA Planetary Data System*. July 2012. Archived from [the original](http://pds-rings.seti.org/showalter/) on 2008-09-17. Retrieved 2012-07-16.

1. ^ [***a***](#cite_ref-Bio2_3-0) [***b***](#cite_ref-Bio2_3-1) Tanner, Steve (2007-01-07). ["SETI Institute's Ring Leader"](http://www.bizjournals.com/sanjose/stories/2007/01/08/smallb1.html). *San Jose Business Journal*. Retrieved 2012-07-16.

1. **[^](#cite_ref-4)** ["Cornell University Department of Astronomy Ph.D. recipients"](https://web.archive.org/web/20120710183313/http://astro.cornell.edu/people/phds.php). Archived from [the original](https://astro.cornell.edu/people/phds.php) on 2012-07-10.

1. **[^](#cite_ref-6)** Showalter, Mark; Burns; Cuzzi; Pollack (August 8, 1985). ["Discovery of Jupiter's 'gossamer' ring"](https://zenodo.org/record/1233033). *Nature*. **316** (6028): 526–528. [Bibcode](/source/Bibcode_(identifier)):[1985Natur.316..526S](https://ui.adsabs.harvard.edu/abs/1985Natur.316..526S). [doi](/source/Doi_(identifier)):[10.1038/316526a0](https://doi.org/10.1038%2F316526a0). [PMID](/source/PMID_(identifier)) [11536560](https://pubmed.ncbi.nlm.nih.gov/11536560). [S2CID](/source/S2CID_(identifier)) [4281782](https://api.semanticscholar.org/CorpusID:4281782).

1. **[^](#cite_ref-7)** Showalter, Mark R (27 June 1991). "Visual detection of 1981S13". *Nature*. **351** (6329): 709–73. [Bibcode](/source/Bibcode_(identifier)):[1991Natur.351..709S](https://ui.adsabs.harvard.edu/abs/1991Natur.351..709S). [doi](/source/Doi_(identifier)):[10.1038/351709a0](https://doi.org/10.1038%2F351709a0). [S2CID](/source/S2CID_(identifier)) [4317496](https://api.semanticscholar.org/CorpusID:4317496).

1. ^ [***a***](#cite_ref-Gazeteer_8-0) [***b***](#cite_ref-Gazeteer_8-1) [***c***](#cite_ref-Gazeteer_8-2) ["Gazetteer of Planetary Nomenclature"](https://planetarynames.wr.usgs.gov/Page/Planets). *International Astronomical Union Working Group for Planetary System Nomenclature*. Astrogeology Science Center, [United States Geological Survey](/source/United_States_Geological_Survey). 2006-07-21. Retrieved 2012-07-16.

1. **[^](#cite_ref-9)** Blunck, Jürgen (2010). *Solar System Moons: Discovery and Mythology*. Dordrecht. p. 95. [ISBN](/source/ISBN_(identifier)) [9783540688525](https://en.wikipedia.org/wiki/Special:BookSources/9783540688525).

1. **[^](#cite_ref-10)** Showalter, Mark R; Lissauer (17 February 2006). ["The second ring-moon system of Uranus: discovery and dynamics"](https://doi.org/10.1126%2Fscience.1122882). *Science*. **311** (5763): 973–977. [Bibcode](/source/Bibcode_(identifier)):[2006Sci...311..973S](https://ui.adsabs.harvard.edu/abs/2006Sci...311..973S). [doi](/source/Doi_(identifier)):[10.1126/science.1122882](https://doi.org/10.1126%2Fscience.1122882). [PMID](/source/PMID_(identifier)) [16373533](https://pubmed.ncbi.nlm.nih.gov/16373533). [S2CID](/source/S2CID_(identifier)) [13240973](https://api.semanticscholar.org/CorpusID:13240973).

1. **[^](#cite_ref-11)** Grün, Eberhard (2001). [*Interplanetary Dust*](https://archive.org/details/interplanetarydu00fech). Springer. pp. [668](https://archive.org/details/interplanetarydu00fech/page/n688). [ISBN](/source/ISBN_(identifier)) [3540420673](https://en.wikipedia.org/wiki/Special:BookSources/3540420673).

1. **[^](#cite_ref-12)** Mason, J.; Cook, J.-R. C. (2011-03-31). ["Forensic sleuthing ties ring ripples to impacts"](https://web.archive.org/web/20110530095933/http://www.ciclops.org/view.php?id=6762). *[CICLOPS](/source/Space_Science_Institute) press release*. Cassini Imaging Central Laboratory for Operations. Archived from [the original](http://www.ciclops.org/view.php?id=6762) on 2011-05-30. Retrieved 2011-04-04.

1. **[^](#cite_ref-13)** [NASA](/source/NASA) (2011-03-31). ["Subtle Ripples in Jupiter's Ring"](https://web.archive.org/web/20140419221526/http://www.ciclops.org/view/6760/Subtle_Ripples_in_Jupiters_Ring). *PIA 13893 caption*. NASA / Jet Propulsion Laboratory-Caltech / SETI. Archived from [the original](http://www.ciclops.org/view/6760/Subtle_Ripples_in_Jupiters_Ring) on 2014-04-19. Retrieved 2011-04-04.

1. **[^](#cite_ref-14)** 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](/source/Science_(journal))*. **332** (6030): 711–3. [Bibcode](/source/Bibcode_(identifier)):[2011Sci...332..711S](https://ui.adsabs.harvard.edu/abs/2011Sci...332..711S). [doi](/source/Doi_(identifier)):[10.1126/science.1202241](https://doi.org/10.1126%2Fscience.1202241). [PMID](/source/PMID_(identifier)) [21454755](https://pubmed.ncbi.nlm.nih.gov/21454755). [S2CID](/source/S2CID_(identifier)) [27371440](https://api.semanticscholar.org/CorpusID:27371440).

1. **[^](#cite_ref-15)** Matson, John (2011-03-31). ["A New Wrinkle: Comet Strikes in the 1980s and 1990s Left Ripples in Jupiter's and Saturn's Rings"](https://www.scientificamerican.com/article.cfm?id=ring-ripples). *Scientific American*. Retrieved 2012-07-16.

1. **[^](#cite_ref-16)** Showalter, M. R.; Hamilton, D. P. (2011-07-20). ["New Satellite of (134340) Pluto: S/2011 (134340) 1"](http://www.cbat.eps.harvard.edu/cbet/cbet002769.txt). *Central Bureau for Astronomical Telegrams*. [International Astronomical Union](/source/International_Astronomical_Union). Retrieved 2011-07-20.

1. **[^](#cite_ref-Sanders_2012-07-11_17-0)** Sanders, Ray (11 July 2012). ["Hubble Space Telescope detects fifth moon of Pluto"](http://phys.org/news/2012-07-hubble-space-telescope-moon-pluto.html). [Phys.org](/source/Phys.org). Retrieved 11 July 2012.

1. **[^](#cite_ref-18)** Overbye, Dennis (20 July 2012). ["Despite Downgrade, Pluto Adds to Entourage"](https://www.nytimes.com/2011/07/21/science/space/21pluto.html). *[New York Times](/source/New_York_Times)*. Retrieved 2012-07-16.

1. **[^](#cite_ref-19)** [Beatty, Kelly. "Neptune's Newest Moon." *Sky and Telescope.* July 15, 2013.](http://www.skyandtelescope.com/news/Neptunes-Newest-Moon-215535121.html) Accessed 2013-07-17. [Deprecated link](https://en.wikipedia.org/wiki/Wikipedia:Archive.today_guidance) archived July 16, 2013, at [archive.today](/source/Archive.today)

1. **[^](#cite_ref-20)** ["Harold Masursky Award for Meritorious Service to Planetary Science"](https://dps.aas.org/prizes/masursky). *American Astronomical Society*. Retrieved 10 August 2021.

1. **[^](#cite_ref-21)** ["Harvard-Radcliffe Class of 1980 - Class Notes"](https://web.archive.org/web/20081225025702/http://classes.harvard.edu/olc/pub/HAA/college/notes.jsp?chapter=61). Archived from [the original](http://classes.harvard.edu/olc/pub/HAA/college/notes.jsp?chapter=61) on 25 December 2008.

## External links

- [Mark Showalter's SETI Institute home page](https://www.seti.org/our-scientists/mark-showalter)

- [Planetary Data System rings node home page](http://pds-rings.seti.org/)

- [Silicon Valley Astronomy Lectures, November 12, 2008](https://www.youtube.com/watch?v=X5zcrEze8L4) on [YouTube](/source/YouTube_video_(identifier)) Saturn's Restless Rings: Results from the Cassini Mission

- [Silicon Valley Astronomy Lectures, Jan. 28, 2015](https://www.youtube.com/watch?v=KfODJpfS0fo) on [YouTube](/source/YouTube_video_(identifier)) Pluto on the Horizon: Anticipating our First Encounter with the Double Planet

v t e New Horizons Timeline Exploration of Pluto List of New Horizons topics New Frontiers program Targets Flybys 132524 APL Jupiter Pluto 486958 Arrokoth Observations Neptune and Triton 2011 JY31 2011 KW48 15810 Arawn 28978 Ixion Quaoar Haumea Eris Makemake 307261 Máni (516977) 2012 HZ84 (556416) 2014 OE394 2012 HE85 Rejected 2011 HM102 2014 MT69 2014 OS393 2014 PN70 Spacecraft Instruments Alice Long Range Reconnaissance Imager PEPSSI Ralph REX Venetia Burney Student Dust Counter SWAP Subsystems GPHS-RTG Personnel Institutions Applied Physics Laboratory Ball Aerospace Goddard Space Flight Center Jet Propulsion Laboratory KinetX Southwest Research Institute Stanford University University of Colorado People Frances Bagenal Richard Binzel Alice Bowman Marc Buie Lisa Hardaway Brian May Cathy Olkin Daniel Sarokon Mark Showalter Alan Stern Hal Weaver Logistics Atlas V (launch vehicle) Centaur (upper stage) Star 48B (3rd stage) Cape Canaveral Air Force Station Space Launch Complex 41 (launch site) Deep Space Network Related Hubble Space Telescope Kuiper belt New Horizons 2 Pluto Kuiper Express Category

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Adapted from the Wikipedia article [Mark R. Showalter](https://en.wikipedia.org/wiki/Mark_R._Showalter) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/Mark_R._Showalter?action=history)). Available under [Creative Commons Attribution-ShareAlike 4.0 International](https://creativecommons.org/licenses/by-sa/4.0/). Changes may have been made.