Space Topics: Uranus
Uranus' Rings
Saturn’s rings were thought to be unique for three centuries. Then,
in 1977, a stellar occultation experiment accidentally yielded the discovery
of Uranus’ ring system. Nine narrow rings were discovered from
Earth; Voyager 2 found two more; and two more were first spotted in Hubble
images in 2005.
The rings are unusual in that they are not perfectly circular, they vary
in width, and they are slightly inclined to Uranus’ equator. Voyager
2 discovered that at least one of the rings -- the brightest, “Epsilon” ring
-- is herded into shape by two tiny satellites Cordelia and Ophelia. Uranus'
outermost ring, R/2003 U1, is probably replenished by dust kicked off of
Uranus' moon Mab by small impacts.
Since the advent of powerful telescopes, the Uranian ring system has been “open” to
view from Earth. As Uranus approaches its equinox, the ring system
is closing. The rings will completely close to view from Earth on May
2, 2007.
| Feature |
Boundary (km) |
Eccentricity |
Inclination
(deg) |
Optical
Depth |
| Middle |
Width |
| Six |
41,837 |
1.5 |
0.00101 |
0.062 |
~ 0.3 |
| Five |
42,234 |
~ 2 |
0.00190 |
0.054 |
~ 0.5 |
| Four |
42,571 |
~ 2 |
0.001065 |
0.032 |
~ 0.3 |
| Alpha |
44,718 |
4 to 10 |
0.00076 |
0.015 |
~ 0.4 |
| Beta |
45,661 |
5 to 11 |
0.00044 |
0.005 |
~ 0.3 |
| Eta |
47,176 |
1.6 |
-- |
-- |
≤ 0.4 |
| Gamma |
47,627 |
1 to 4 |
0.00109 |
0.000 |
≥ 0.3 |
| Delta |
48,300 |
3 to 7 |
0.00004 |
0.001 |
~ 0.5 |
| Lambda |
50,024 |
~ 2 |
0. |
0. |
~ 0.1 |
| Epsilon |
51,149 |
20 to 96 |
0.00794 |
0.000 |
0.5 to 2.3 |
| R/2003 U1 |
|
|
|
|
|
| R/2003 U2 |
97,700 |
|
|
|
|
| Data from the PDS
Rings Node |
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Orbits of Uranus' rings and moons
Uranus' rings and moons form a bullseye of orbital paths around the tilted
planets. Credit: NASA
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Uranus' rings silhouetted
Uranus's nine most prominent rings are seen in silhouette against the
smooth globe of the planet in this Voyager 2 view from January 24,
1986, just 24 minutes before its closest approach. Epsilon is the darkest
ring at right. Credit: NASA/JPL |
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Uranus rings and shepherds
Voyager 2 discovered that Uranus' brightest Epsilon ring is shepherded
by two satellites, Cordelia (1986U7) and Ophelia (1986U8), each only
about 40 kilometers in diameter. Credit: NASA/JPL |
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Keck's Changing View of Uranus
From 2001 to 2004, Uranus's motion around the Sun has changed its orientation as seen from Earth in these images taken through Keck II's K prime filter. The four images show how the Adaptive Optics system has improved over time. Color: Greyscale.
Credit: Imke de Pater, Seran Gibbard, Heidi Hammel / W. M. Keck Observatory
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Faint dust in Uranus' rings
As Voyager 2 exited the Uranian system it looked back and caught the
rings at a very high phase angle. The lighting makes lanes of fine
dust visible that are not seen from any other point of view. The image
is smeared because it is a 96-second exposure. Faint streaks are background
stars.Credit: NASA/JPL |
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Newly discovered rings and moons of Uranus
This pair of composite images from the Hubble Space Telescope shows newly discovered rings around Uranus. The outermost of the two rings (R/2003 U1) is thought to be replenished by dust tossed off of a newly discovered moon, named Mab, which shares an orbit with the ring. Mab is visible as a bright streak at the top of the outer ring. Source
Credit: NASA, ESA, and M. Showalter (SETI Institute)
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