Therefore, it is uncertain what causes Uranus' magnetic fields. Furthermore, "Uranus' magnetic field is odd in that it is not centered on the center of the planet and is tilted almost 60 degrees with respect to the axis of rotation. It is probably generated by motion at relatively shallow depths within Uranus." (Arnett, 2004).
Like the other gas planets, Uranus has rings." (Arnett, 2004). Nine of Uranus' rings were discovered in 1977. However, Uranus' rings differ from those found surrounding both Jupiter and Saturn. "The outermost epsilon ring is composed mostly of ice boulders several feet across. A very tenuous distribution of fine dust also seems to be spread throughout the ring system." (Hamilton, 2003). In addition, there are several narrow or incomplete rings that surround Uranus. Uranus' rings "are composed of fairly large particles ranging up to 10 meters in diameter in addition to fine dust. Uranus' rings were discovered after Saturn's. The discovery of Uranus' rings "was of considerable importance since we now know that rings are a common feature of planets, not a peculiarity of Saturn alone." (Arnett, 2004).
There are 11 known rings, all very faint; the brightest is known as the Epsilon ring." (Arnett, 2004). By far the largest ring is 1986U2R, which is 2,500 kilometers wide, and approximately 38,000 kilometers from Uranus' center. Ring 6 is 1-3 kilometers wide and approximately 41,840 kilometers from the center of Uranus. Ring 5 is 2-3 kilometers wide and is approximately 42,230 kilometers from the center. Ring 4 is also 2-3 kilometers wide, and is located just past ring 5. Alpha is 7-12 kilometers wide and is 44,720 kilometers from the center. Beta is 7-12 kilometers wide and is 45,670 kilometers from the center. Eta is 0-2 kilometers wide and is 47,190 kilometers from the center. Gamma is 1-4 kilometers wide and is 47,630 kilometers from the center. Delta is 1-4 kilometers wide and is located 48,290 kilometers from the center. 1986U1R is 1-2 kilometers wide and is located 48,290 kilometers from the center. Epsilon, the most visible of the rings from the surface of the Earth, is 20-100 kilometers wide and is located approximately 51,140 kilometers from the center of Uranus. Epsilon is the probably the most visible because it is the outer ring and is much larger than most of the other rings.
Uranus also has shepherd satellites for some of its rings. The moons Cordelia and Ophelia are on either side of Uranus' epsilon ring. In fact, Uranus has a very high number of moons and other satellites. In fact, Uranus has 27 moons, 21 that have been named and six unnamed ones. Unlike the moons of other planets, which have been named after figures in classical mythology, "Uranus' moons take their names from the writings of Shakespeare and Pope." (Arnett, 2004). Most of the moons have circular orbits, although the outer moons have more elliptical orbits.
The moons can also be classified into three groups. The first group is composed of the 5 large moons that were visible from Earth. Two of these large moons, Titania and Oberon, were discovered by Herschel in 1787. In 1851, Lassell discovered two more large moons, Ariel and Umbriel. The most recently discovered large moon was Miranda, which was discovered by Kuiper in 1948.
The next group is composed of 11 small dark inner moons, which were discovered by Voyager 2. These moons were discovered in 1986. These moons are Cordelia, Ophelia, Bianca, Cressida, Desdemona, Juliet, Portia, Rosalind, Belinda, 1986U10, and Puck. These moons probably would not have been discovered without the aid of Voyager 2.
The final group consists of the more recently discovered distant moons. Showalter discovered 2003U2 and 2003U1 in 2003. Sheppard discovered 2001U3 in 2001, 2003U3 in 2003, and 2002U2 in 2002. In 1999, Gladman discovered Stephano, after discovering Caliban in 1997. Nicholson discovered Sycorax in 1997. Holman discovered Prospero in 1999. Kavelaars discovered Setebos in 1999. In addition, there is the moon Trinculo. The fact that many of these distant moons have been discovered within the last decade should make it clear that it is possible that future astronomers may discover even more moons.
An examination of Uranus' internal structure is more difficult. However, scientists have been able to infer some information about it by observing Uranus' radius, mass, period of rotation, and the shape of its gravitational field. (Hamilton, 2003). From these studies, scientists have concluded that Uranus and Neptune have similar interior structures. However, Uranus has less active atmospheric dynamics and interior heat flow. (Hamilton, 2003). To understand Uranus' composition, one must step away from the view of a planet like Earth, which, at least on the surface, has a solid composition. Uranus' outer envelope is composed of molecular hydrogen, helium, and methane. (Hamilton, 2003). Below the outer envelope, Uranus "appears to be composed of a mantle rich in water, methane, ammonia and other elements. These elements are under high temperatures and pressures deep within the planet... Uranus' core is composed of rock and ice." (Hamilton, 2003). Therefore, scientists have come to the conclusion that "Uranus does not have a rocky core like Jupiter and Saturn but rather that is material is more or less uniformly distributed." (Arnett, 2004).
While much is known about Uranus, scientists still have several important questions about the planet:
Why doesn't Uranus radiate more heat than it receives from the Sun as the other gas planets do? Is its interior cold? Why is its axis so unusually tilted? Was it due to a massive collision? Why do Uranus and Neptune have so much less hydrogen and helium than Jupiter and Saturn? Is it simply because they are smaller? Or because they're farther from the Sun? What will happen to Uranus's weather as it progresses through its seasons? (Arnett, 2004).
Hopefully, future space exploration will provide the answers to these fascinating questions.
Arnett, B. (2004). "Uranus," Nineplanets.org, [Online], Retrieved June 6, 2006 Available at http://www.nineplanets.org/uranus.html
Bell, E. (2005). "Voyager 2," Nasa.gov, [Online], Retrieved June 6, 2006 Available at http://nssdc.gsfc.nasa.gov/database/MasterCatalog?sc=1977-076A
Enchanted Learning. (2006). "Uranus," EnchantedLearning.com, [Online], Retrieved June 6, Available…