Rings n Things Rings are swarms of orbiting particles Orbits have to be very circular Elliptical orbits will result in collisions destroying the ring Rings Have to be Very Flat Inclined orbits will result in collisions and destruction of the ring ID: 279231
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Slide1
General Astronomy
Rings ‘n’ ThingsSlide2
Rings are swarms of orbiting particles
Orbits have to be very circular
Elliptical orbits will result in collisions, destroying the ringSlide3
Rings Have to be Very Flat
Inclined orbits will result in collisions and destruction of the ring
Slide4
Rings have to be Equatorial
Tilted orbits
precess
; the plane of the orbit rotates due to the planet’s equatorial bulge, other satellites, and the Sun’s gravitySlide5
A tilted ring won’t stay flat very long
Particle orbits will precess at different rates
Collisions will soon destroy the ringSlide6
Rings, Gaps, and Resonances
When two objects return to the same relative positions regularly, they are said to be in
resonance
Some resonances are stable. Mercury’s 3:2 resonance between its rotation and its orbit is an example.
Pluto’s period is 3/2 that of Neptune’s. This resonance keeps the two planets from ever colliding even though their orbits cross.Slide7
Rings, Gaps, and Resonances
Some resonances create gaps. There are no asteroids with one-half Jupiter’s period because repeated pulls by Jupiter eventually would change the asteroid’s orbit.
Gaps in Saturn’s rings are due to resonances with Saturn’s satellites.Slide8
Jupiter's Ring System
Jupiter's ring was discovered by Voyager 1 in a single image that was targeted specifically to search for a faint ring system.
The ring is now known to be composed of three major components. The
main ring
is about 7000 km wide and has an abrupt outer boundary 129,130 km from the center of the planet.
The main ring encompasses the orbits of two small moons, Adrastea and Metis, which may act as the source for the dust that makes up most of the ring.
At its inner edge the main ring merges gradually into the
halo
. The halo is a broad, faint torus of material about 20,000 km thick and extending halfway from the main ring down to the planet's cloud tops.
Just outside the main ring is a pair of broad and exceedingly faint
gossamer rings
, one bounded by the moon Amalthea and the other bounded by the moon Thebe. Slide9
Jupiter's Ring SystemSlide10
Saturn, Lord of the Rings
Saturn's rings make the planet the most spectacular object in the solar system.
Slide11
The Saturnian Rings
The rings are split into a number of different parts, which include the bright A and B rings and a fainter C ring.
The ring system has various gaps. The most notable gap is the Cassini Division, which separates the A and B rings. The Encke Division splits the A Ring.
Space probes have shown that the main rings are really made up of a large number of narrow ringlets. Slide12
Close up and Personal
Possible variations in chemical composition from one part of Saturn's ring system to another are visible in this Voyager 2 picture. Obtained Aug. 17 from a distance of 8.9 million kilometers (5.5 million miles).
The Voyager project is managed for NASA by the Jet Propulsion Laboratory, Pasadena, Calif.
Slide13
Saturn’s Rings
The origin of the rings is obscure.
One thought is that the rings may have been formed from larger moons that were shattered by impacts of comets and meteoroids.
Another possibility is a moon/comet which was pulled apart by tidal action
The ring composition is not known for certain, but the rings do show a significant amount of water.
They may be composed of icebergs and/or snowballs from a few centimeters to a few meters in size. Slide14
Shepherd Moons
Much of the elaborate structure of some of the rings is due to the gravitational effects of nearby satellites. This phenomenon is demonstrated by the relationship between the F-ring and two small moons that
shepherd
the ring material.
Shepherd Moons help maintain the sharp edges of rings
A Shepherd Moon Outside a Ring Tends to Drag Stray Particles Back, Causing Them to Fall Back Into the Ring
A Shepherd Moon Inside a Ring Tends to Speed Stray Particles Up, Causing Them to Rise Back Into the RingSlide15
Outer Shepherd MoonSlide16
Inner Shepherd MoonSlide17
Spokes
Radial, spoke-like features in the broad B-ring were also found by the Voyagers. The features are believed to be composed of fine, dust-size particles. The spokes were observed to form and dissipate in the time-lapse images taken by the Voyagers. While electrostatic charging may create spokes by levitating dust particles above the ring, the exact cause of the formation of the spokes is not well understood.
Spoke MovieSlide18
Particle Size in the Rings
Purple > 5 cm
Green < 1 cm
White: too denseSlide19
Can you find Rhea?
No, That’s Mimas
Here is RheaSlide20
Saturn’s New Ring
Recently discovered, this giant ring is visible in infrared and may be the cause of
Iapetus
’ colorationSlide21
The Uranian Ring System
The Uranian ring system was discovered in 1977 during observations of a stellar occultation by the planet.
The star was observed to blink out briefly five times before the planet and again five times afterward, indicating that the planet was encircled by five narrow rings.
Subsequent Earth-based observations indicated that there were actually nine major rings.
Working outward from the planet, they are named 6, 5, 4, Alpha, Beta, Eta, Gamma, Delta, and Epsilon.
In 1986 the Voyager spacecraft acquired additional occultations and also our best images of the ring system.
The Voyager cameras detected a few additional rings and also showed that the nine major rings are surrounded by belts of fine dust. Slide22
The Uranian Ring SystemSlide23
IR Image of Uranus’ RingsSlide24
Another IR image (colorized)Slide25
Neptune's Ring System
Evidence for incomplete arcs around Neptune first arose in the mid-1980's, when stellar occultation experiments were found to occasionally show an extra "blink" just before or after the planet occulted the star.
Images by Voyager 2 in 1989 settled the issue, when the ring system was found to contain several faint rings, the outermost of which, Adams, contains three prominent arcs now named Liberty, Equality and Fraternity.
The existence of arcs is very difficult to understand because the laws of motion would predict that arcs spread out into a uniform ring over very short timescales.
The gravitational effects of Galatea, a moon just inward from the ring, are now believed to confine the arcs.
Several other rings were detected by the Voyager cameras.
Adams Ring 63,000 km from the center of Neptune
Leverrier Ring is at 53,000 km and the broader
Galle Ring is at 42,000 km.
A faint outward extension to the Leverrier Ring has been named Lassell; it is bounded at its outer edge by the Arago Ring at 57,000 km. Slide26
Neptune's Ring SystemSlide27
Rings Are Probably Short-Lived
Gravity of the Sun and planet’s satellites constantly disturbs orbits of particles
Collisions probably happen frequently
Particles should drift out of the ring
Rings around outer planets have probably come and gone repeatedly during history of Solar System