Ferdinand (moon)

Ferdinand
Ferdinand in a sequence of discovery images
Provisional or systematic name	S / 2001 U 2
Central body	Uranus
Properties of the orbit
Major semi-axis	20,507,100 km
Periapsis	11,663,850 km
Apoapsis	29,350,350 km
eccentricity	0.4312285
Orbit inclination	167.34637 (ecliptic) °
Orbital time	2805.51 d
Mean orbital velocity	0.54 km / s
Physical Properties
Albedo	≈ 0.04-0.07
Apparent brightness	25.1 mag
Medium diameter	≈ 21 km
Dimensions	≈ 1.3-5.4 · 10 15 kg
surface	≈ 1,300 km 2
Medium density	≈ 1.3-1.5 g / cm 3
Acceleration of gravity on the surface	≈ 0.0025 m / s 2
Surface temperature	≈ −184 to −208 ° C ≈ 89–65 K
discovery
Explorer	Matthew J. Holman , John J. Kavelaars , Dan Milisavljevic , Brett J. Gladman , Scott S. Sheppard , David C. Jewitt
Date of discovery	August 13, 2001
Remarks	Physical data relatively imprecise

Ferdinand (also Uranus XXIV ) is the outermost of the 27 known and the outermost irregular moon of the planet Uranus . It is one of the smaller natural satellites on the planet.

Discovery and naming

Ferdinand was discovered on August 13, 2001 by a team consisting of the astronomers Matthew J. Holman , John J. Kavelaars , Dan Milisavljevic and Brett J. Gladman on photographic images around the same time as the innermost known Uranus moon Francisco . The recordings were made with the 4-meter Blanco telescope at the Cerro Tololo Inter-American Observatory in Chile . Soon after the recordings, which also showed Francisco, Trinculo and actually Margaret , the astronomers unfortunately lost track of the moon again, even though it was recorded on September 21 and November 15 and even a year later on September 13. August and September 5, 2002 could be seen. As the orbit could therefore not be secured, the International Astronomical Union decided not to publish the discovery. It was Scott S. Sheppard who met Ferdinand on September 24, 2003 on recordings from August 29 to 30 with the 8.2-meter Subaru telescope and on September 20, 2003 with the 8.1-meter Gemini Reflecting telescope (both in Hawaii ) by David C. Jewitt and himself. On September 30th, Matthew Holman made confirmatory observations at the Las Campanas Observatory in Chile. The discovery was announced on October 1, 2003; the moon was initially given the provisional designation S / 2001 U 2 .

On December 29, 2005 the moon was officially named Ferdinand, like all irregular Uranus moons except Margaret after a figure in William Shakespeare's The Tempest . Ferdinand was the son of Alonso , King of Naples . Ferdinand finally marries Prospero's daughter Miranda and helps his father-in-law to regain his lost duchy of Milan .

So far, all Uranus moons have been named after characters from Shakespeare or Alexander Pope . The first four Uranus moons discovered ( Oberon , Titania , Ariel , Umbriel ) were named after suggestions by John Herschel , the son of the Uranus discoverer Wilhelm Herschel . Later the tradition of naming was retained.

The provisional designation S / 2001 U 2 corresponds to the system of the International Astronomical Union (IAU).

Track properties

Classification in the irregular moons

Ferdinand orbits Uranus in a retrograde , strongly elliptical orbit between 11,663,850 and 29,350,350 km from its center ( major orbit half-axis 20,507,100 km or 802.344 Uranus radii), i.e. around 20,481,500 km above its cloud ceiling. The orbital eccentricity is 0.4312285, the orbit is 167.34637 ° inclined to the ecliptic . Ferdinand is over 35 times as far from Uranus as the outermost regular moon Oberon .

Due to the great distance to Uranus and gravitational disturbances from the sun and other factors, the orbit parameters are possibly variable; the moon could perhaps also enter a heliocentric orbit (again). The eccentricity is therefore also given between 0.3682 and 0.3993, the orbit inclination (compared to the ecliptic) between 169.793 ° and 169.840 ° and the major orbit half-axis between 20.430 and 20.901 million km.

Ferdinand is a member of the Sycorax group , a subgroup of the irregular moons with very high eccentricity and high orbital inclinations between 140 and 170 °, to which Sycorax , Prospero and Setebos also belong. Within this group, however, Ferdinand is the only one to stand out due to the approximately 20 ° higher incline of the orbit and thus represents a separate dynamic group.

The orbit of the closest moon Setebo is on average about 3.09 million km from Ferdinand's orbit.

Ferdinand orbits Uranus in around 2805 days, 12 hours and 14 minutes, or around 7,681 earth years. The orbital period is also given as 2790.03 to 2887.21 days. So Ferdinand needs more than half the orbit time of the planet Jupiter around the sun for one orbit around Uranus .

Physical Properties

Ferdinand has an estimated diameter of 21 km (according to other information 20 km), based on the assumed reflectivity of 4%, which can, however, also be 7%. In any case, the surface is extremely dark. Its density is estimated to be between 1.3 and 1.5 g / cm ³ . The moon is therefore likely to be composed mainly of water ice and silicate rock. On its surface, the acceleration due to gravity is 0.0025 m / s ² , which corresponds to about 2 ‰ of that on earth. Ferdinand appears in the spectrum in gray color.

Emergence

Ferdinand is believed to be a trapped object of the Kuiper Belt and not arose in the accretion disk that formed the uranium system. It is conceivable that the moon first went from a Kuiper belt object to a centaur and was then captured by Uranus. The exact trapping mechanism is unknown, but trapping a moon requires dissipating energy. The hypotheses range from the entry of gas into the protoplanetary disk , interactions in the context of the multibody problem and capture by the rapidly increasing mass of Uranus.

exploration

Because of the great distance to Uranus and the weak brightness of 25.1 mag, which is 1: 69200000 compared to the central planet, Ferdinand was not found when the Voyager 2 space probe flew by in 1986. Since the discovery in 1999, Ferdinand could only be observed through earth-based telescopes and its orbital elements and its brightness could be determined.

Web links

• MPEC 2003-S105: S / 2001 U 2 September 30, 2003 (discovery)
• IAUC 8213: S / 2001 U 2 and S / 2002 N 4 October 1, 2003 (discovery)
• IAUC 8648: Satellites of Uranus December 29, 2005 (numbering and naming)
• Polish moon page: Ferdinand description and further links (English)

Individual evidence

1. ^ IAU: Natural Satellites Ephemeris Service. IAU Minor Planet Center, accessed February 11, 2011 .