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Francisco (moon)

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Francisco
Francisco imaged by the Very Large Telescope on 3 September 2002
Discovery[1][2][3]
Discovered by
Discovery siteCerro Tololo Obs.
Discovery date13 August 2001
Designations
Designation
Uranus XXII
Pronunciation/frænˈsɪskoʊ/[4]
Named after
Francisco (The Tempest character)
S/2001 U 3
Orbital characteristics[5]
Epoch 1 January 2020 (JD 2458849.5)
Satellite ofUranus
Proper orbital elements
4,275,700 km (0.028581 AU) AU
0.144
146.8° (to ecliptic)
492.47191 deg / yr
0.73101 yr
(267 d)
Precession of perihelion
103.904434 arcsec / yr
Precession of the ascending node
89.8814065 arcsec / yr
Physical characteristics
11–17 km[a]
22 km[7]
25.0 (average)[7]
12.9[8]

Francisco, also known as Uranus XXII and previously as S/2001 U 3, is the innermost irregular satellite or moon of Uranus, orbiting in the retrograde direction. It was discovered on 13 August 2001 by John J. Kavelaars, Matthew J. Holman, Dan Milisavljevic, and Tommy Grav using the 4.0-meter Víctor M. Blanco Telescope at Cerro Tololo Observatory, Chile. It was named after Francisco, a lord in William Shakespeare's play The Tempest. Francisco orbits Uranus at an average distance of 4.3 million km (2.7 million mi) and takes about 267 Earth days (0.73 Earth years) to complete one orbit. Francisco is estimated to be up to 22 km (14 mi) in diameter, though many of its physical properties are unknown.

Discovery

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Because Francisco is extremely faint, it is better seen by shifting-and-adding multiple images of its location. The result is Francisco appearing as a single dot against trailed background stars.

Francisco was discovered on 13 August 2001 by a group of astronomers consisting of John J. Kavelaars, Matthew J. Holman, Dan Milisavljevic, and Tommy Grav, who at the time were searching for distant moons of Uranus.[9][10] The discovery observations were made at Cerro Tololo Observatory, Chile,[1] using the 4.0-m Víctor M. Blanco Telescope equipped with a wide-field camera.[10]: 475  The group discovered Francisco and three other Uranian irregular moons (Trinculo, Ferdinand, and Margaret[b]) in the telescope images by using a computer algorithm that followed the motion of Uranus and then combined the images to enhance the faint moons—a technique known as shift-and-adding.[10]: 477 

To determine the orbit of Francisco, the group continued observing the moon from different observatories, including the 200-inch Hale Telescope at Palomar Observatory and 8.2-m Very Large Telescope at Paranal Observatory.[1][10]: 477  These follow-up observations lasted until 5 September 2002.[1][11] The Minor Planet Center announced the discovery of Francisco on 6 October 2003.[1]

Name

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When the discovery of Francisco was announced, it was given the temporary provisional designation S/2001 U 3 by the Minor Planet Center.[1] It was later named and given the Roman numeral designation Uranus XXII by the International Astronomical Union's Working Group for Planetary System Nomenclature on 29 December 2005.[12] The moon was named after the character Francisco from William Shakespeare's play, The Tempest. In the play, Francisco is a lord who is shipwrecked with King Alonso and others.[13][3]

Orbit

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Francisco is an irregular moon of Uranus, which have very wide, elliptical, and inclined orbits in contrast to the regular moons of Uranus.[14]: 1  Irregular moons like Francisco are thought to be former asteroids that were captured by their planet during the Solar System's formation.[10]: 474  The Uranian irregular moons are loosely bound by Uranus's gravity because of their great distance from the planet, so their orbits are frequently perturbed by the gravity of the Sun and other planets.[14]: 2  This results in significant changes in the orbits of irregular moons over short periods of time, so a simple Keplerian elliptical orbit cannot accurately describe the long-term orbital motions of irregular moons. 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 a long period of time.[14]: 4 

Over a 30,000-year time period, Francisco's average semi-major axis or orbital distance from Uranus is 4.28 million km (2.66 million mi; 0.0286 AU), with an average orbital period of 0.73 years (267 d).[14]: 7  Francisco is the innermost irregular moon of Uranus.[13] Francisco has an average orbital eccentricity of 0.14 and an average inclination of 147° with respect to the ecliptic, or the plane of Earth's orbit.[5][14]: 7  Since Francisco's orbital inclination is greater than 90°, the moon has a retrograde orbit, meaning it orbits in the opposite direction of Uranus' orbit around the Sun.[13] Francisco's orbital elements fluctuate over time due to perturbations: its semi-major axis varies by ±700 km (430 mi), eccentricity varies by ±0.05, and inclination varies by ±2°.[14]: 7 [15]: 11  Compared to other Uranian irregular moons, Francisco's eccentricity variations are significant, although they occur over relatively slow periods of several thousand years.[14]: 4  Francisco's orbit exhibits nodal and apsidal precession with average periods over 10,000 Earth years.[c]

Francisco is not known to be part of a collisional family or group; its orbit is apparently unique among the known Uranian irregular moons.[16]: 2537 [15]: 2  If there is a collisional family associated with Francisco, then any Uranian irregular moons related to it are likely undiscovered because they are presumably small and faint.[15]: 15 

  • Animation of Francisco's orbit (cyan) around Uranus.    Uranus  ·   Sycorax ·   Francisco ·    Caliban  ·    Stephano  ·    Trinculo
    Animation of Francisco's orbit (cyan) around Uranus.
       Uranus  ·   Sycorax ·   Francisco ·    Caliban  ·    Stephano  ·    Trinculo
  • Irregular satellites of all four giant planets, plotted by average distance from their planet (semi-major axis in Hill radii) and orbital inclination (in degrees wrt ecliptic). Data as of February 2024.
    Irregular satellites of all four giant planets, plotted by average distance from their planet (semi-major axis in Hill radii) and orbital inclination (in degrees wrt ecliptic). Data as of February 2024.

Physical characteristics

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Francisco is very faint with an average apparent magnitude of 25.0,[7] so it could only be observed with long-exposure imaging by large-aperture telescopes.[9][10] Nothing is known about Francisco's physical properties other than its absolute magnitude of 12.9, which can be used to estimate the moon's diameter.[8] Francisco is expected to have a dark surface[13] composed of water ice, hydrated silicates, and organic compounds, similar to other irregular moons.[17]: 6  Assuming a geometric albedo range of 0.04–0.10 that is typical for most irregular moons,[18] Francisco should have a diameter between 11–17 km (7–11 mi).[a] Scott Sheppard, who has discovered many irregular moons around other giant planets, estimates Francisco's diameter to be 22 km (14 mi).[7]

Exploration

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Francisco has not been imaged up close by a space probe, although Voyager 2 did pass within 2.4 million km (1.5 million mi) of Francisco during its flyby of Uranus in 1986.[19] All Uranian irregular moons including Francisco are planned to be distant observation targets for the upcoming Uranus Orbiter and Probe (UOP), which will measure the Uranian irregular moons' rotation periods and shapes by watching their brightness change over time.[19][20] The UOP may not be able to do a close flyby of Francisco because the moon does not orbit near the ecliptic plane.[20]

See also

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Notes

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  1. ^ a b The diameter (in km) is calculated from absolute magnitude (H) and geometric albedo (p) according to the formula .[6] Given H = 12.9, and assuming an albedo range of 0.04–0.10, the diameter range is 11–17 km.
  2. ^ Margaret ended up lost in 2001, but was rediscovered by Scott Sheppard and David Jewitt in 2003.[10]: 477 
  3. ^ Brozovic et al. (2022) gives 18,000 and 14,000 years for Francisco's apsidal and nodal precession periods, respectively.[14]: 7  On the other hand, JPL (2024) gives 12,473 and 14,419 years for Francisco's apsidal and nodal precession periods, respectively.[5]

References

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  1. ^ a b c d e f Marsden, Brian G. (6 October 2003). "MPEC 2003-T29 : S/2001 U 3". Minor Planet Electronic Circulars. Minor Planet Center. Retrieved 5 July 2025.
  2. ^ "Planetary Satellite Discovery Circumstances". JPL Solar System Dynamics. NASA. Retrieved 5 July 2025.
  3. ^ a b "Planet and Satellite Names and Discoverers". Gazetteer of Planetary Nomenclature. USGS Astrogeology Science Center. Retrieved 5 July 2025.
  4. ^ Benjamin Smith (1903) The Century Dictionary and Cyclopedia
  5. ^ a b c "Planetary Satellite Mean Elements". JPL Solar System Dynamics. NASA. Retrieved 5 July 2025.
  6. ^ "Asteroid Size Estimator". Center for Near Earth Object Studies. NASA. Retrieved 5 July 2025.
  7. ^ a b c d Sheppard, Scott S. "Moons of Uranus". Earth & Planets Laboratory. Carnegie Institution for Science. Retrieved 5 July 2025.
  8. ^ a b "Natural Satellites Ephemeris Service". Minor Planet Center. Retrieved 5 July 2025. Check "All Uranian outer irregular satellites", go to "Output Format(s) Required" and check "I require Orbital Elements", and then click the gray "Get Information" button.
  9. ^ a b Kavelaars, J. J. (27 November 2001). "Three more minor moons for Uranus". Dominion Astrophysical Observatory. Archived from the original on 6 July 2011. Retrieved 5 July 2025.
  10. ^ a b c d e f g Kavelaars, J. J.; Holman, M. J.; Grav, T. Grav; 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.
  11. ^ Marsden, Brian G.; Holman, M.; Gladman, B.; Rousselot, P.; Mousis, O. (7 October 2003). Green, Daniel W. E. (ed.). "IAUC 8216: P/2003 T1; S/2001 U 3; (66063) 1998 RO_1". IAU Circular (8216). Central Bureau of Astronomical Telegrams: 2. Bibcode:2003IAUC.8216....2M. Retrieved 8 January 2011.
  12. ^ Green, Daniel W. E., ed. (29 December 2005). "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. Retrieved 5 July 2025.
  13. ^ a b c d "Francisco". NASA. 25 January 2024. Retrieved 5 July 2025.
  14. ^ a b c d e f g h Brozović, Marina; Jacobson, Robert A. (May 2022). "Orbits of the Irregular Satellites of Uranus and Neptune". The Astronomical Journal. 163 (5). Bibcode:2022AJ....163..241B. doi:10.3847/1538-3881/ac617f. S2CID 248458067. 241.
  15. ^ a b c 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). arXiv:2410.00108. Bibcode:2024AJ....168..258S. doi:10.3847/1538-3881/ad7fed. S2CID 273022766. 258.
  16. ^ Ćuk, Matija; Burns, Joseph A. (November 2004). "On the Secular Behavior of Irregular Satellites". The Astronomical Journal. 128 (5): 2518–2541. arXiv:astro-ph/0408119. Bibcode:2004AJ....128.2518C. doi:10.1086/424937. S2CID 18564122.
  17. ^ 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). arXiv:2105.01164. Bibcode:2021PSJ.....2..120C. doi:10.3847/PSJ/abfe12. S2CID 220525809. 120.
  18. ^ Sharkey, Benjamin N. L.; Reddy, Vishnu; Kuhn, Olga; Sanchez, Juan A.; Bottke, William F. (November 2023). "Spectroscopic Links among Giant Planet Irregular Satellites and Trojans". The Planetary Science Journal. 4 (11). arXiv:2310.19934. Bibcode:2023PSJ.....4..223S. doi:10.3847/PSJ/ad0845. S2CID 264819644. 223.
  19. ^ a b 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.
  20. ^ a b 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.
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