Margaret (moon)

Margaret
Blurry black-and-white image showing Margaret as a faint white spot among other white spots of other celestial objects
Margaret (circled) photographed by the Gemini North telescope on 28 September 2003
Discovery[1][2]
Discovered by
Discovery siteMauna Kea Obs.
Discovery date29 August 2003
Designations
Designation
Uranus XXIII
Pronunciation/ˈmɑːrɡərət/[3]
Named after
Margaret (Much Ado About Nothing character)
S/2003 U 3
AdjectivesMargaretian /ˌmɑːrɡəˈrɛtiən/ (trad.)[4]
Orbital characteristics (range)[a]
Observation arc20.32 years (7,421 d)[6]
Earliest precovery date13 August 2001[6]
14,318,500 to 14,538,500 km (0.095713 to 0.097184 AU)
Eccentricity0.41 to 0.89
4.48 to 4.59 years (1,637 to 1,675 d)
Inclination46° to 69° (to ecliptic)
Satellite ofUranus
GroupNone known
Proper orbital elements (average)[7][b]
14,425,000 km (0.09643 AU)
0.642
60.5° (to ecliptic)
4.53 years (1,655 d)
Precession of asc. node
1293.41317365 arcsec / yr
Physical characteristics
20 km[9][10]
25.2 (R-band)[11][9]
12.67[12]

Margaret, also known as Uranus XXIII and previously as S/2003 U 3, is an irregular moon of Uranus. It is the only known irregular moon of Uranus that follows a prograde orbit, meaning it orbits in the same direction as the planet's orbit around the Sun. It was discovered by Scott S. Sheppard and David C. Jewitt at Mauna Kea Observatory on 29 August 2003, although it had been briefly observed earlier by Matthew J. Holman and JJ Kavelaars on 13 August 2001. The moon is formally named after Margaret, the servant of Hero in William Shakespeare's play Much Ado About Nothing, while also alluding to the discoverers' family members.

Margaret follows a distant, highly inclined, and eccentric orbit around Uranus, revolving at an average distance of 14.4 million km (8.9 million mi) with an orbital period of 4.53 years (1,655 days). It has one of the most eccentric orbits of any known moon in the Solar System. The Sun's gravitational influence places the moon in the Kozai resonance, which causes large, synchronized variations in its orbital eccentricity and inclination over a 500-year period. Margaret is estimated to have a diameter of 20 km (12 mi), though most of its physical properties are unknown.

Discovery

Margaret was initially spotted on 13 August 2001 by astronomers Matthew J. Holman and JJ Kavelaars, during their search for distant moons of Uranus at Cerro Tololo Inter-American Observatory.[13] The group had planned to reobserve Margaret by September,[c] but poor observational circumstances prevented them from doing so.[d][14]: 477  With only one night of observations, the moon's orbit could not be determined and it became lost.[15][14]: 477–478 

Margaret was not spotted again until 29 August 2003, when Scott S. Sheppard and David C. Jewitt began searching for Uranian moons using the 8.3-meter (27 ft) Subaru Telescope at Mauna Kea Observatory.[15][9]: 519  After they reobserved Margaret with Mauna Kea's Gemini North telescope on 20 September, the head of the Minor Planet Center, Brian G. Marsden, recognized that it was the same moon observed by Holman and Kavelaars in 2001.[13][15] Kavelaars confirmed Marsden's suspicion after he identified a single Canada–France–Hawaii Telescope image of Margaret from 25 August 2001.[13] Once follow-up observations ended on 30 September 2003, the Minor Planet Center announced the discovery of Margaret on 7 October.[13][16] NASA and the International Astronomical Union consider Sheppard and Jewitt as the official discoverers of Margaret.[1][2][17]

For several years after its discovery, Margaret remained poorly observed and still had an uncertain orbit, which put it at risk of being lost again.[8]: 12  To improve the understanding of its orbit, a team led by Robert A. Jacobson and Marina Brozović conducted a campaign to reobserve Margaret and several other poorly observed moons from 2009 to 2011.[18] Despite these observations, Margaret's orbital uncertainty persisted[18]: 7 [8]: 12  and remained unobserved until 8 September 2021,[6] when Sheppard began another search for Uranian moons with the Subaru Telescope.[5] As of 2026, Margaret's observation arc spans 20.32 years (7,421 days) with its last recorded observation on 7 December 2021.[6]

Name

When the discovery of Margaret was announced, it was given the temporary provisional designation "S/2003 U 3" by the Minor Planet Center.[16] It was later named and given the Roman numeral designation Uranus XXIII by the International Astronomical Union's Working Group for Planetary System Nomenclature on 29 December 2005.[19] The moon was named after the servant of Hero from William Shakespeare's play, Much Ado About Nothing.[17][2]

In a 2014 interview with the Folger Shakespeare Library, Sheppard disclosed that he chose the name "Margaret" because it matched his mother's name.[20] He got the idea of naming a moon after his mother when he searched up her name on the Web in 2002.[20] Kavelaars, who initially spotted Margaret in 2001, supported Sheppard's name choice because it matched the middle name of his elder daughter, Ruth Ann Margaret Kavelaars.[20]

Orbit

Margaret is one of Uranus's irregular moons, which follow wide, eccentric, and inclined orbits in contrast to the regular moons of Uranus.[8]: 1  It is the only known prograde irregular moon of Uranus, orbiting in the same direction as the planet's orbit around the Sun.[8]: 1  Irregular moons like Margaret are thought to have been captured by their planet during the Solar System's formation, although the exact process for this is uncertain.[5] Simulations by Matija Ćuk and Brett Gladman in 2006 showed that prograde irregular moons like Margaret could have been directly captured by Uranus if their orbits became stabilized by a 1:2 orbital resonance between Saturn and Uranus.[21]

The Uranian irregular moons are loosely bound by Uranus's gravity due to their great distance from the planet, which makes their orbits susceptible to gravitational perturbations by the Sun and other planets.[8]: 2  This results in significant changes to their orbits over short periods of time, so a simple Keplerian elliptical orbit cannot accurately describe their long-term orbital motions.[8]: 4  Instead, proper or mean orbital elements are used to describe the long-term orbits of irregular moons more accurately, since these are calculated by averaging out the perturbed orbit over an extended period of time.[8]: 4 

Over a 10,000-year time span, Margaret's semi-major axis from Uranus averages at about 14.4 million km (8.9 million mi; 0.096 AU), with an average orbital period of 4.53 years (1,655 days).[5]: 11  Its orbit is markedly more eccentric and inclined compared to other Uranian irregular moons,[22] having an average eccentricity of 0.64 and an average inclination of 61° with respect to the ecliptic.[7] Compared to other known moons of the Solar System as of 2026, Margaret has the fifth-highest average orbital eccentricity.[23]

A graphic showing the orbits of Margaret (displayed as blue), retrograde irregular moons of Uranus (displayed as red), and regular moons of Uranus (displayed as magenta), as seen from three different views. Margaret's orbit is distinctly elongated compared to other Uranian moons. The data was taken in 2026.
The orbits Uranus's irregular moons as seen from three different views. Margaret's orbit is colored blue, retrograde irregular moon orbits are colored red, and regular moon orbits are colored magenta.

Kozai resonance

Three plots showing periodic oscillations in Margaret's orbital eccentricity (e), inclination (i), and argument of pericenter (ω) over 5,000 years.
Plots showing periodic oscillations in Margaret's orbital eccentricity (e), inclination (i), and argument of pericenter (ω) over 5,000 years

Margaret's high inclination subjects it to the Kozai resonance, a dynamical phenomenon in which its orbit periodically exchanges inclination and eccentricity due to perturbations by the Sun.[9]: 525 [22]: 3841  The moon's Kozai-resonant orbit was first recognized by Kavelaars and colleagues in 2004.[14][22]: 3834  N-body simulations show that over a period of about 520 years,[e] Margaret's eccentricity oscillates from 0.41 to 0.89, while its inclination oscillates from 69° to 46°.[8]: 7  Due to the Kozai resonance, Margaret reaches minimum inclination at maximum eccentricity and vice versa.[8]: 8 [f] When near maximum eccentricity, Margaret can come within 1.7 million km (1.1 million mi; 0.011 AU) of Uranus at periapsis[g] and can stray as far as 27 million km (17 million mi; 0.18 AU) at apoapsis.[24]

Despite its large variations in eccentricity and inclination, Margaret's current orbit is considered stable under the Kozai resonance.[25]: 507 [26]: 6  However, its high inclination puts it near the edge of stability; if it had an average inclination greater than 60°, the Kozai resonance would cause Margaret's eccentricity to grow so large that it would end up getting ejected or colliding with Uranus.[9]: 525  Jet Propulsion Laboratory astrophysicists Marina Brozović and Robert A. Jacobson speculated in 2009 that Margaret may become ejected from the Uranus system in the far future.[22]

Margaret's orbit exhibits nodal precession over a 1,002-year period,[7] but does not exhibit apsidal precession due to the Kozai resonance.[8]: 7  Instead of circulating from 0° to 360°, Margaret's argument of pericenter librates around 90° with a 520-year period.[8]: 7  This means the moon always comes to periapsis above the ecliptic.[8]: 7–8 [h]

Physical characteristics

In red light (R band), Margaret appears very faint with an apparent magnitude of 25.2.[9] It can only be observed through long-exposure imaging by large-aperture telescopes.[14] Little is definitively known about Margaret's physical properties other than its absolute magnitude of 12.7, which can be used to estimate the moon's diameter.[27][9] Assuming Margaret has a low geometric albedo of 0.04 like other Uranian irregular moons, its diameter has been estimated to be 20 km (12 mi).[9][10] Like these moons, Margaret is expected to have a dark surface[17] composed of water ice, hydrated silicates, and organic compounds.[10]: 6 

Exploration

Margaret has not been imaged at close range by a space probe. When NASA's Voyager 2 space probe flew by Uranus in 1986, it coincidentally passed within 15 million km (9.3 million mi) of Margaret.[28] The Uranian irregular moons, including Margaret, are planned to be distant observation targets for the proposed Uranus Orbiter and Probe (UOP), which would measure the Uranian irregular moons' rotation periods and shapes by monitoring their brightness change over time.[28][27] However, the UOP may not be able to perform a close flyby of Margaret because the moon does not orbit near the ecliptic plane.[27]

See also

  • Ferdinand – another moon of Uranus lost in 2001 and recovered in 2003
  • Other Uranian moons discovered in 2003:
  • Carpo – a Kozai-resonant moon of Jupiter with a highly inclined and eccentric prograde orbit, similar to Margaret

Notes

  1. ↑ Sheppard et al. (2024) give the mean, minimum, and maximum values for Margaret's osculating orbital elements in Table 5: semi-major axis 14425000+113500
    −106500     km    , eccentricity 0.64+0.25
    −0.23    , inclination 61°+8°
    −15°     with respect to the ecliptic, and orbital period 1655+20
    −18    .[5]: 11  The error bars represent the difference between the minimum/maximum value and the average value over a 10,000-year period.[5]: 11 
  2. ↑ The proper orbital elements of Margaret listed in the infobox are average (mean) values over a 10,000-year period, as shown in Table 5 of Sheppard et al. (2024) and Jet Propulsion Laboratory's Planetary Satellite Mean Elements table.[7][8]: 7 
  3. ↑ Follow-up observations of Holman and Kavelaars's Uranian moon discoveries took place in September 2001, beginning with the Hale Telescope at Palomar Observatory.[14]: 477–478 
  4. ↑ According to Kavelaars and colleagues, "Uranus set before images deep enough to recover S/2003 U3 [Margaret] could be made."[14]: 477 
  5. ↑ Although Brozović and Jacobson (2022) do not explicitly give the oscillation period for Margaret's eccentricity and inclination, they do mention that they are correlated with Margaret's argument of pericenter libration, which has a period of ~520 years.[8]: 4, 7  This can be seen in Figure 5 of their paper.[8]: 8 
  6. ↑ In other words, the inclination and eccentricity of Margaret are out of phase.[8]: 8 
  7. ↑ For comparison, Uranus's outermost regular moon Oberon orbits with a semi-major axis of 583,511 km (362,577 mi),[23] about 3 times closer to Uranus than Margaret's minimum periapsis distance.
  8. ↑ Figures 10 and 11 of Sheppard et al. (2024) demonstrate that the vertical position of a moon's periapsis (e sin(ω), the vertical component of the eccentricity vector pointing from apoapsis to periapsis) is always positive (above the ecliptic) when its argument of pericenter (ω) librates around 90°.[5]: 13–14  For an explanation of e sin(ω), see Brozović and Jacobson (2022).[8]: 4 

References

  1. 1 2 "Planetary Satellite Discovery Circumstances". JPL Solar System Dynamics. NASA. Archived from the original on 27 September 2021. Retrieved 18 June 2026.
  2. 1 2 3 "Planet and Satellite Names and Discoverers". Gazetteer of Planetary Nomenclature. USGS Astrogeology Science Center. Archived from the original on 18 June 2026. Retrieved 18 June 2026.
  3. ↑ Benjamin Smith (1903) The Century Dictionary and Cyclopedia
  4. ↑ Cathcart (1971) The Duchess of Kent
  5. 1 2 3 4 5 6 Sheppard, Scott S.; Tholen, David J.; Brozović, Marina; Jacobson, Robert A.; Trujillo, Chadwick A.; Lykawka, Patryk Sofia (December 2024). "New Moons of Uranus and Neptune from Ultradeep Pencil-beam Surveys". The Astronomical Journal. 168 (6): 258. arXiv:2410.00108. Bibcode:2024AJ....168..258S. doi:10.3847/1538-3881/ad7fed. S2CID 273022766.
  6. 1 2 3 4 "MPC Explorer - Uranus 23". Minor Planet Center. Archived from the original on 18 June 2026. Retrieved 18 June 2026.
  7. 1 2 3 4 "Planetary Satellite Mean Elements". JPL Solar System Dynamics. NASA. Archived from the original on 6 June 2026. Retrieved 21 June 2026.
  8. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 Brozović, Marina; Jacobson, Robert A. (May 2022). "Orbits of the Irregular Satellites of Uranus and Neptune". The Astronomical Journal. 163 (5): 241. Bibcode:2022AJ....163..241B. doi:10.3847/1538-3881/ac617f. S2CID 248458067.
  9. 1 2 3 4 5 6 7 8 Sheppard, Scott S.; Jewitt, David; Kleyna, Jan (January 2005). "An Ultradeep Survey for Irregular Satellites of Uranus: Limits to Completeness". The Astronomical Journal. 129 (1): 518–525. arXiv:astro-ph/0410059. Bibcode:2005AJ....129..518S. doi:10.1086/426329.
  10. 1 2 3 Cartwright, Richard J.; Beddingfield, Chloe B.; Nordheim, Tom A.; Elder, Catherine M.; Castillo-Rogez, Julie C.; Neveu, Marc; et al. (June 2021). "The Science Case for Spacecraft Exploration of the Uranian Satellites: Candidate Ocean Worlds in an Ice Giant System". The Planetary Science Journal. 2 (3): 120. arXiv:2105.01164. Bibcode:2021PSJ.....2..120C. doi:10.3847/PSJ/abfe12. S2CID 220525809.
  11. ↑ Sheppard, Scott S. "Moons of Uranus". Earth & Planets Laboratory. Carnegie Institution for Science. Archived from the original on 18 February 2024. Retrieved 18 June 2026.
  12. ↑ "Natural Satellites Ephemeris Service". Minor Planet Center. Archived from the original on 4 October 2022. Retrieved 18 June 2026. Check "Just the following Uranian outer irregular satellites", then check "Uranus 23 (Margaret)", then go to "Output Format(s) Required" and check "I require Orbital Elements", and then click the gray "Get Information" button.
  13. 1 2 3 4 Sheppard, S. S.; Jewitt, D. C.; Marsden, B. G.; Holman, M.; Kavelaars, J. (8 October 2003). Green, Daniel W. E. (ed.). "IAUC 8217: S/2003 U 3; 157P; AG Dra". IAU Circular (8217). Central Bureau of Astronomical Telegrams: 1. Bibcode:2003IAUC.8217....1S. Archived from the original on 7 December 2025. Retrieved 18 June 2026.
  14. 1 2 3 4 5 6 Kavelaars, J. J.; Holman, M. J.; Grav, T.; Milisavljevic, D.; Fraser, W.; Gladman, B. J.; et al. (June 2004). "The discovery of faint irregular satellites of Uranus". Icarus. 169 (2): 474–481. Bibcode:2004Icar..169..474K. doi:10.1016/j.icarus.2004.01.009. S2CID 248458067.
  15. 1 2 3 Sheppard, Scott S. "New Satellites of Uranus Discovered in 2003". Institute for Astronomy at the University of Hawaii. Archived from the original on 5 May 2008. Retrieved 19 December 2008.
  16. 1 2 Marsden, Brian G. (9 October 2003). "MPEC 2003-T58 : S/2003 U 3". Minor Planet Electronic Circulars. Minor Planet Center. Archived from the original on 8 March 2026. Retrieved 18 June 2026.
  17. 1 2 3 "Margaret". NASA. 3 November 2024. Archived from the original on 2 April 2026. Retrieved 18 June 2026.
  18. 1 2 Jacobson, R.; Brozović, M.; Gladman, B.; Alexandersen, M.; Nicholson, P. D.; Veillet, C. (November 2012). "Irregular Satellites of the Outer Planets: Orbital Uncertainties and Astrometric Recoveries in 2009-2011". The Astronomical Journal. 144 (5): 132. Bibcode:2012AJ....144..132J. doi:10.1088/0004-6256/144/5/132.
  19. ↑ Green, D. W. E. (29 December 2005). Green, Daniel W. E. (ed.). "IAUC 8648: Sats of Uranus; 2005mf, 2005mg; C/2005 U7, C/2005 U8, C/2005 Y1". IAU Circular (8648). Central Bureau of Astronomical Telegrams: 1. Bibcode:2005IAUC.8648....1G. Archived from the original on 16 January 2016. Retrieved 18 June 2026.
  20. 1 2 3 Paul, Richard (19 November 2014). "The Shakespearean Moons of Uranus". folger.edu. Folger Shakespeare Library. Archived from the original on 25 February 2024. Retrieved 25 February 2024.
    • Sheppard: So, I just simply did a search for "Margaret," which was my Mom's name, on the Web, and "Shakespeare." And it came up with Much Ado about Nothing. And I said that's it, that's what I'll name it.
    • Kavelaars: My other daughter's name is Ruth Ann Margaret Kevelaars. And I said "Scott, this is perfect, because now I can go to my other daughter who, right now, you know, is really angry with me because she didn't get a satellite of the planets. And I can tell her, 'No, you do.'"
  21. ↑ Ćuk, Matija; Gladman, Brett J. (August 2006). "Irregular satellite capture during planetary resonance passage". Icarus. 183 (2): 362–372. Bibcode:2006Icar..183..362C. doi:10.1016/j.icarus.2006.03.005.
  22. 1 2 3 4 Brozović, M.; Jacobson, R. A. (March 2009). "The Orbits of the Outer Uranian Satellites". The Astronomical Journal. 137 (4): 3834–3842. Bibcode:2009AJ....137.3834B. doi:10.1088/0004-6256/137/4/3834.
  23. 1 2 "Planetary Satellite Mean Elements (Sortable)". JPL Solar System Dynamics. NASA. Archived from the original on 19 May 2026. Retrieved 18 June 2026.
  24. ↑ "JPL Horizons Orbital Elements of Margaret from 1800-Jan-01 to 2200-Jan-01". JPL Horizons On-Line Ephemeris System. Jet Propulsion Laboratory. Retrieved 19 June 2026. Ephemeris Type: Osculating Elements, Center: 500@7 (Uranus Barycenter), Timestep: 1 year, Units: km and days.
    Key: EC = eccentricity, QR = periapsis distance (km), AD = apoapsis distance (km)
  25. ↑ Grishin, Evgeni (August 2024). "Irregular fixation – II. The orbits of irregular satellites". Monthly Notices of the Royal Astronomical Society. 533 (1): 497–509. arXiv:2407.05123. Bibcode:2024MNRAS.533..497G. doi:10.1093/mnras/stae1752. S2CID 271051291.
  26. ↑ Lei, Hanlun; Leng, Xiaoyan; Grishin, Evgeni (May 2026). "Extensions of Brown Hamiltonian–III. Applications to irregular satellites of giant planets". Monthly Notices of the Royal Astronomical Society. 549 (2) stag921. arXiv:2605.12864. Bibcode:2026MNRAS.549ag921L. doi:10.1093/mnras/stag921.
  27. 1 2 3 Denk, Tilmann; Verbiscer, Anne J.; Mottola, Stefano; Porter, Simon B. (July 2023). Observing the Irregular Moons of Uranus by the Uranus Orbiter Probe Mission, Part 2: Observation Campaigns (PDF). Uranus Flagship: Investigations and Instruments for Cross-Discipline Science Workshop (poster). Bibcode:2023LPICo2808.8169D. 8169. Archived (PDF) from the original on 5 July 2025. Retrieved 5 July 2025.
  28. 1 2 Verbiscer, Anne J.; Denk, Tilmann; Mottola, Stefano; Porter, Simon B. (July 2023). Observing the Irregular Moons of Uranus by a Uranus Flagship Mission (PDF). Uranus Flagship: Investigations and Instruments for Cross-Discipline Science Workshop (poster). Bibcode:2023LPICo2808.8187V. 8187. Archived from the original (PDF) on 29 February 2024.
Wikimedia Commons logo
Wikimedia Commons has media related to Margaret (moon).
This page is issued from Wikipedia. The text is available under Creative Commons Attribution-Share Alike 4.0 unless otherwise noted. Additional terms may apply for the media files.