Margaret Was Discovered Aug. 29, 2003, as Ninth Uranian Irregular Moon

Summary: Margaret was discovered Aug. 29, 2003, as the ninth Uranian irregular moon and as the only irregular with a prograde orbit.

Discovery images of S/2003 U 3 (permanent name Margaret; permanent designation Uranus XXIII) show the newly found Uranian irregular satellite’s motion relative to background stars and galaxies: NASA Planetary Photojournal, via NASA Science Solar System Exploration

Margaret was discovered Aug. 29, 2003, as the ninth Uranian irregular moon and as the only irregular satellite with a prograde orbit in the Uranian system.

Daniel W.E. Green, director of the Central Bureau for Astronomical Telegrams (CBAT), announced the discovery of a new Uranian outer satellite candidate in International Astronomical Union Circular (IAUC) No. 8217, dated Oct. 9, 2003. He assigned the provisional designation of S/2003 U 3 to the candidate.

The announcement credited the Aug. 29, 2003, discovery to S.S. (Scott Sander) Sheppard and D.C. (David Clifford) Jewitt of the Institute of Astronomy (IfA) at the University of Hawai’i at Mānoa (U.H. Mānoa) in Honolulu, O’ahu. The discovery images were obtained by the 8.2-meter (320-inch) Subaru Telescope at the Mauna Kea Observatories (MKO) on the summit of Mauna Kea on the Big Island of Hawai’i.

On the same date that Sheppard and Jewitt discovered S/2003 U 3, they also detected another Uranian irregular satellite candidate. This irregular candidate was determined to be S/2001 U 2, which had been discovered Aug. 13, 2001, had been observed again Sept. 21 and then had eluded detection.

IAUC 8648, dated Dec. 29, 2005, reported the approval of a permanent designation and a permanent name for Uranian irregular satellite S/2003 U 3 by the IAU Working Group for Planetary System Nomenclature (WGPSN). The permanent designation of Uranus XXIII for S/2003 U 3 reflects the satellite’s status as the 23rd discovered Uranian satellite. S/2003 U 3 received the permanent name of Margaret in conformance with the convention of namesaking Uranian satellites after characters either in plays by Elizabethan playwright William Shakespeare (bapt. April 26, 1564-April 23, 1616) or in “Rape of the Lock” by 18th-century English poet Alexander Pope (May 21, 1688-May 30, 1744).

Margaret’s discovery brought the tally of Uranian irregular satellites to nine. Until the Sept. 6, 1997, discoveries of Caliban (provisional designation S/1997 U 1; permanent designation Uranus XVI) and of Sycorax (provisional designation S/1997 U 2; Uranus XVII) as the first two Uranian irregular satellites, Uranus appeared to be the only one of the solar system’s giant planets (Jupiter, Saturn, Uranus, Neptune) lacking in irregular satellites.

Irregular satellites are also known as distant satellites, irregular moons, irregular natural satellites or outer satellites. Irregular satellites occur at great distances from their primary bodies and exhibit eccentric orbits.

The second set of Uranian irregular satellites was discovered almost one year 10 and one-half months (one year 10 months 12 days) after the Sept. 6, 1997, discoveries of the Uranian system’s first two irregular satellites. Setebos (S/1999 U 1; Uranus XIX), Stephano (S/1999 U 2; Uranus XX) and Prospero (S/1999 U 3; Uranus XVIII) were discovered July 18, 1999, as the third, fourth and fifth discovered Uranian irregular satellites.

The third set of Uranian irregular satellites was discovered almost two years one month (two years 26 days) after the detection of the second. Trinculo (S/2001 U 1; Uranus XXI), Ferdinand (S/2001 U 2; Uranus XXIV) and Francisco (S/2001 U 3; Uranus XXII) were discovered Aug. 13, 2001, as the Uranian system’s sixth, seventh and eighth discovered irregular satellites.

Margaret distinguishes itself from its fellow Uranian irregular satellites in its prograde orbit. Also known as a direct orbit, a prograde orbit moves in the same direction as that of its primary body’s spin. Margaret joins the Uranian system’s 18 regular satellites in tracing prograde orbits. Caliban, Ferdinand, Francisco, Setebos, Stephano, Sycorax and Trinculo exhibit retrograde motion, or opposite directional movement.

The takeaways from Margaret’s Aug. 29, 2003, discovery as the ninth Uranian irregular satellite are that Margaret, provisionally designated as S/2003 U 3, was detected via the 8.2-meter (320-inch) Subaru Telescope at the Mauna Kea Observatories (MKO) on the summit of Mauna Kea on the Big Island of Hawai’i and that Margaret’s permanent designation as Uranus XXIII reflects the irregular satellite’s status as the 23rd discovered satellite in the Uranian system.

Discovery of Margaret (provisional designation S/2001 U 3; permanent designation Uranus XXIII) were made via the 8.2-meter Subaru Telescope at Mauna Kea Observatories (MKO), Big Island of Hawai’i; Saturday, July 7, 2007: Hirohisat, CC BY SA 3.0 Unported, 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:

Discovery images of S/2003 U 3 (permanent name Margaret; permanent designation Uranus XXIII) show the newly found Uranian irregular satellite’s motion relative to background stars and galaxies: NASA Planetary Photojournal, via NASA Science Solar System Exploration @ https://solarsystem.nasa.gov/moons/uranus-moons/margaret/in-depth/; Public Domain, via Wikimedia Commons @ https://commons.wikimedia.org/wiki/File:Margaret_discovery.gif

Discovery of Margaret (provisional designation S/2001 U 3; permanent designation Uranus XXIII) were made via the 8.2-meter Subaru Telescope at Mauna Kea Observatories (MKO), Big Island of Hawai’i; Saturday, July 7, 2007: Hirohisat, CC BY SA 3.0 Unported, via Wikimedia Commons @ https://commons.wikimedia.org/wiki/File:Subaru_view.jpg

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