Caliban and Sycorax Orbit With Respectively Low and High Eccentricity

Summary: Uranian irregular moons Caliban and Sycorax orbit with respectively low and high eccentricity.

Animation shows orbits of five Uranian irregular moons around their primary body, Uranus; Sycorax=magenta, Caliban=yellow, Francisco=aqua, Stephano=orange/red, Trinculo=green; data source NASA JPL HORIZONS System (https://ssd.jpl.nasa.gov/horizons/): Phoenix7777, CC BY SA 4.0 International, via Wikimedia Commons

Caliban and Sycorax orbit with respectively low and high eccentricity in their distant placement as irregular satellites in the Uranian system.

Brian G. (Geoffrey) Marsden, director of the Central Bureau for Astronomical Telegrams (CBAT), announced the discoveries in IAUC (International Astronomical Union Circular) no. 6764, dated Oct. 31, 1997. The two newly discovered satellites were assigned temporary designations of S/1997 U 1 and S/1997 U 2.

Marsden noted that the discoveries of S/1997 U 1 (Caliban) and S/1997 U 2 (Sycorax) on Sept. 6, 1997, eliminated a significant difference between Uranus and the solar system’s three other giant planets of Jupiter, Saturn and Neptune. Prior to their detection, Uranus was the only solar system giant apparently lacking irregular satellites. Occurrence in the outer reaches of its primary body’s gravitational sphere of influence and an inclined, often eccentric orbit characterize an irregular satellite.

In IAUC 6765, dated Oct. 31, 1997, Marsden indicated that computations made by him in collaboration with Gareth Vaughan Williams of the International Astronomical Union’s (IAU) Minor Planet Center (MPC) suggested S/1997 U 2 as orbiting in retrograde, that is, directionally opposite from the spin of its primary body. An arbitrary assignment of a retrograde orbit to S/1997 U 1 ensued from the “poorer distribution” of its observations.

IAUC 6780, dated Nov. 29, 1997, confirmed the status of both objects as Uranian irregular satellites. Marsden also affirmed both orbits as “indeed retrograde.”

IAUC 6833, dated March 7, 1998, noted that, per discoverer P.D. (Philip David) Nicholson’s report, co-discoverers B.J. (Brett James) Gladman and J.A. (Joseph Arthur) Burns had located images of S/1997 U 2, the brighter irregular Uranian satellite, on plates obtained in 1984 by the Canada-France-Hawaii Telescope (CFHT). The CFHT is located near the summit of Mauna Kea, in north-central Hawaii Island.

Gladman, as measurer, with D.P. (Dale Paul) Cruikshank as observer, provided semiaccurate measurements for the 1984 images of S/1997 U 2. The measurements, calculated for epoch 2000, had an uncertainty of plus / minus 3 arcseconds. For June 1.5556, S/1997 U 2 was found at right ascension 16 hours 40 minuts 44.2 seconds and declination minus 22 degrees 07 arcminutes 02 arcseconds. For June 2.5410, the irregular satellite was positioned at right ascension 16 hours 40 minutes 34.0 seconds and declination minus 22 degrees 06 arcminutes 40 arcseconds.

In IAUC 6870, dated April 7, 1998, Marsden shared 1984 precovery data, also with an uncertainty of plus / minus 3 arcseconds, for S/1997 U 1, the dimmer of the two Uranian irregular moons. Gladman as measurer and Cruikshank as observer placed the dim satellite’s right ascension at 16 hours 40 minutes 58.4 seconds and declination at minus 22 degrees 03 arcminutes 56 arcseconds on June 1.5556. For June 2.5410, it was located at right ascension 16 hours 40 minutes 48.5 seconds and declination minus 22 degrees 03 arcminutes 36 arcseconds.

Marsden noted that recovery observations of S/1997 U 1 were conducted March 27, 1998, with the 4-meter reflector and charged-couple detector (CCD) camera at the Anglo-Australian Observatory in New South Wales, southeastern Australia, by R.M. Smith, J.B. Jones and D. (David) Windridge, with discoverer Gladman as measurer. On March 31, 1998, with co-discoverer J.J. (John J. “JJ”) Kavelaars as measurer, P. Hall and D. Graham made successful recovery observations with the 4-meter reflector and CCD camera at Cerro Tololo Interamerican Observatory. The 1998 recovery observations and orbital data computed by Marsden in collaboration with G.V. (Gareth Vaughan) Williams of the International Astronomical Union’s (IAU) Minor Planet Center (MPC) and K. (Kaare) Aksnes of the IAU Working Group for Planetary System Nomenclature (WGPSN) validated the satellite’s 1984 candidacy.

The 1998 recovery observations and orbital computations for S/1997 U 1 by Marsden et alia also confirmed the satellite’s low-e (low eccentricity; more circular than elliptical). Marsden had described previously, in IAUC no. 6780, dated Nov. 29, 1997, the fainter satellite’s orbit as “significantly less eccentric than that of the brighter.”

Marsden reported the 1998 recovery of S/1997 U 2 via IAUC no. 6869, dated April 7, 1998. The team of Smith, Jones and Windridge, with discoverer Gladman as measurer, successfully recovered the brighter of the two irregular satellites March 27 with the 4-meter reflector and CCD camera at the Anglo-Australian Observatory. Hall and Graham, with discoverer “JJ” Kavelaars as measurer, succeeded in recovering S/1997 U 2 with the 4-meter reflector and CCD camera at Cerro Tololo Interamerican Observatory.

The recovery positions varied by “fully 30”” from the prediction discussed March 7, 1998, via IAUC no. 6834. Marsden explained that computations by William, Aksnes and himself presented “another orbital solution from the 1984-1997 observations.” Their computations revealed the brighter irregular satellite’s orbit as “much more strongly perturbed by the sun.” The 1998 recovery observations clearly demonstrated the correctness of “this high-e solution” (high eccentricity) for S/1997 U 2’s orbit.

The takeaways from the determination that Caliban and Sycorax orbit with respectively low and high eccentricity are that the first irregular satellite discoveries in the Uranian system trace orbits in retrograde, i.e., in the opposite direction of Uranus’ spin, and that perturbations by the sun account for the highly eccentric orbit of the brighter satellite, S/1997 U 2 (Sycorax).

discovery images, taken one hour apart, for S/1997 U 2 (Uranus XVII; Sycorax); NASA- and Cornell University-funded study; Brett Gladman, postdoctoral associate, Canadian Institute for Theoretical Astrophysics; Sunday, Sep. 7, 1997: Public Domain, via Wikimedia Commons

Acknowledgment

My special thanks to talented artists and photographers/concerned organizations who make their fine images available on the internet.

Image credits:

Animation shows orbits of five Uranian irregular moons around their primary body, Uranus; Sycorax=magenta, Caliban=yellow, Francisco=aqua, Stephano=orange/red, Trinculo=green; data source NASA JPL HORIZONS System (https://ssd.jpl.nasa.gov/horizons/): Phoenix7777, CC BY SA 4.0 International, via Wikimedia Commons @ https://commons.wikimedia.org/wiki/File:Animation_of_Sycorax_orbit_around_Uranus.gif

discovery images, taken one hour apart, for S/1997 U 2 (Uranus XVII; Sycorax); NASA- and Cornell University-funded study; Brett Gladman, postdoctoral associate, Canadian Institute for Theoretical Astrophysics; Sunday, Sep. 7, 1997: Public Domain, via Wikimedia Commons @ https://commons.wikimedia.org/wiki/File:Sycorax.jpg

For further information:

Burns, Joseph A. “1. Some Background About Satellites.” Pages 1-38. In Joseph A. Burns and Mildred Shapley Matthews, eds. Satellites. Space Science Series. Tucson AZ: University of Arizona Press, Nov. 1, 1986.

Burns, Joseph A.; and Mildred Shapley Matthews, eds. Satellites. Space Science Series. Tucson AZ: University of Arizona Press, Nov. 1, 1986.

Cornell Chronicle. “’Irregular’ Satellites S/1997 U1 and S/1997 U2 Discovered With Palomar Mountain’s 5-Meter Hale Telescope.” Cornell University > Stories. Oct. 31, 1997.
Available @ http://news.cornell.edu/stories/1997/10/planet-uranus-has-two-more-moons-cornell-and-canadian-astronomers-find

Gladman, Brett J.; Philip D. Nicholson; Joseph A. Burns; JJ Kavelaars; Brian J. Marsden; Gareth V. Williams; and Warren B. Offutt. “Discovery of Two Distant Irregular Moons of Uranus.” Nature, vol. 392 (April 30, 1998): 897-899.
Available via Nature @ https://www.nature.com/articles/31890

Grav, Tommy; and Matthew J. Holman. “Photometry of Irregular Satellites of Uranus and Neptune.” The Astrophysical Journal, vol. 613 (Sept. 20, 2004): L77-L80. Available @ https://iopscience.iop.org/article/10.1086/424997/pdf

International Astronomical Union (IAU) / U.S. Geological Survey (USGS) Gazetteer of Planetary Nomenclature. ““Uranian System.” USGS Astrogeology Science Center > Gazetteer of Planetary Nomenclature > Nomenclature > Planet and Satellite Names and Discoverers.
Available @ https://planetarynames.wr.usgs.gov/Page/Planets

Johnston, William Robert. “List of IAU Preliminary Designations of Natural Satellites.” Johnston’s Archive > Astronomy and Space.
Available @ http://www.johnstonsarchive.net/astro/moonlist.html

Levy, David H. Skywatching. Revised and updated. San Francisco CA: Fog City Press, 1994.

Maris, Michele; Giovanni Carraro; Gabriele Cremonese; and Marco Fulle. “Multicolor Photometry of the Uranus Irregular Satellites Sycorax and Caliban.” The Astronomical Journal, vol. 121, no. 5 (May 2001): 2800-2803.
Available via IOPscience @ https://iopscience.iop.org/article/10.1086/320378

Marriner, Derdriu. “Nine Irregular Uranian Moons Were Discovered Between 1997 and 2003.” Earth and Space News. Wednesday, July 6, 2011.
Available @ https://earth-and-space-news.blogspot.com/2011/07/nine-irregular-uranian-moons-were.html

Marriner, Derdriu. “Uranian Irregular Moons Caliban and Sycorax Were Discovered Sept. 6, 1997.” Earth and Space News. Wednesday, July 13, 2011.
Available @ https://earth-and-space-news.blogspot.com/2011/07/uranian-irregular-moons-caliban-and.html

Marriner, Derdriu. “William Herschel Discovered First Two Uranian Moons on Jan. 11, 1787.” Earth and Space News. Wednesday, Jan. 12, 2011.
Available @ https://earth-and-space-news.blogspot.com/2011/01/william-herschel-discovered-first-two.html

Marsden, Brian G. “S/1997 U 1.” Central Bureau for Astronomical Telegrams > IAU Circular No. 6833. March 7, 1998.
Available @ http://www.cbat.eps.harvard.edu/iauc/06800/06833.html

Marsden, Brian G. “S/1997 U 1.” Central Bureau for Astronomical Telegrams > IAU Circular No. 6870. April 7, 1998.
Available @ http://www.cbat.eps.harvard.edu/iauc/06800/06870.html

Marsden, Brian G. “S/1997 U 2.” Central Bureau for Astronomical Telegrams > IAU Circular No. 6833. March 7, 1998.
Available @ http://www.cbat.eps.harvard.edu/iauc/06800/06833.html

Marsden, Brian G. “S/1997 U 2.” Central Bureau for Astronomical Telegrams > IAU Circular No. 6834. March 7, 1998.
Available @ http://www.cbat.eps.harvard.edu/iauc/06800/06834.html

Marsden, Brian G. “S/1997 U 2.” Central Bureau for Astronomical Telegrams > IAU Circular No. 6869. April 7, 1998.
Available @ http://www.cbat.eps.harvard.edu/iauc/06800/06869.html

Marsden, Brian G. “Satellites of Uranus.” Central Bureau for Astronomical Telegrams > IAU Circular No. 6764. Oct. 31, 1997.
Available @ http://www.cbat.eps.harvard.edu/iauc/06700/06764.html

Marsden, Brian G. “Satellites of Uranus.” Central Bureau for Astronomical Telegrams > IAU Circular No. 6765. Oct. 31, 1997.
Available @ http://www.cbat.eps.harvard.edu/iauc/06700/06765.html

Marsden, Brian G. “Satellites of Uranus.” Central Bureau for Astronomical Telegrams > IAU Circular No. 6780. Nov. 29, 1997.
Available @ http://www.cbat.eps.harvard.edu/iauc/06700/06780.html

Marsden, Brian G. “Satellites of Uranus.” Central Bureau for Astronomical Telegrams > IAU Circular No. 7132. March 27, 1999.
Available @ http://www.cbat.eps.harvard.edu/iauc/07100/07132.html

Minor Planet Center. “Uranus XVI (Caliban).” Minor Planet Circular 40991. July 26, 2000.
Available @ https://www.minorplanetcenter.net/iau/ECS/MPCArchive/2000/MPC_20000726.pdf

Minor Planet Center. “Uranus XVII (Sycorax).” Minor Planet Circular 40991. July 26, 2000.
Available @ https://www.minorplanetcenter.net/iau/ECS/MPCArchive/2000/MPC_20000726.pdf

Moore, Patrick, Sir. Philip’s Atlas of the Universe. Revised edition. London UK: Philip’s, 2005.

Nemiroff, Robert; and Jerry Bonnell. “Irregular Moons Discovered Around Uranus.” NASA Astronomy Picture of the Day (APOD). Nov. 3, 1997.
Available @ https://apod.nasa.gov/apod/ap971103.html

Rabinowitz, Harold; and Suzanne Vogel, eds. The Manual of Scientific Style: A Guide for Authors, Editors, and Researchers. First edition. Burlington MA; San Diego CA; London, UK: Academic Press, 2009.

Schmude, Richard, Jr. “Captured Objects.” Pages 58-59. “Chapter 1 The Uranus System.” Uranus, Neptune, Pluto and How to Observe Them: 1-59. Astronomers’ Observing Guides. New York NY: Springer Science + Business Media LLC, 2008.
Available via ePDF @ https://epdf.pub/uranus-neptune-and-pluto-and-how-to-observe-them-astronomers-observing-guides.html
Available via Google Books @ https://books.google.com/books?id=47azIwooFqEC&pg=PA27

Segelken, Roger. “Planet Uranus Has Two More Moons.” Cornell University News Service. Oct. 31, 1997.
Available via NASA GSFC (Goddard Space Flight Center) NSSDC (NASA Space Science Data Coordinated Archive) > Solar System Exploration > Planetary Science > Uranus.
Available @ https://nssdc.gsfc.nasa.gov/planetary/text/uran_pr_971031.txt

Sheppard, Scott S.; David Jewitt; and Jan Kleyna. “An Ultradeep Survey for Irregular Satellites of Uranus: Limits to Completeness.” The Astronomical Journal, vol. 129, no. 1 (January 2005): 518-525.
Available via IOPscience @ https://iopscience.iop.org/article/10.1086/426329/pdf

Williams, David R. (Richard), Dr. “Uranus Fact Sheet.” NASA GSFC (Goddard Space Flight Center) NSSDC (NASA Space Science Data Coordinated Archive) > Solar System Exploration > Planetary Science > Uranus.
Available @ https://nssdc.gsfc.nasa.gov/planetary/factsheet/uranusfact.html

Williams David R. (Richard), Dr. “Uranian Satellite Fact Sheet.” NASA GSFC (Goddard Space Flight Center) NSSDC (NASA Space Science Data Coordinated Archive) > Solar System Exploration > Planetary Science > Uranus.
Available @ https://nssdc.gsfc.nasa.gov/planetary/factsheet/uraniansatfact.html