A1 12 Rings

Rings of the Gas GiantsLACC §11.1, 11.4

• Understand what conditions and processes shaped the gas giant planets’ ring systems: Roche limit, shepherding moons

• Know the following ring systems in some detail: Jupiter (dust from moons?), Saturn (recent break up of icy object?), Uranus (break up of a moon?), Neptune (unknown)

• Bright = icy and young, Dark = dusty and old

An attempt to answer the “big questions”: what is out there? Are we alone?

1Monday, October 19, 2009

Ring Systems

http://www.jb.man.ac.uk/distance/strobel/solarsys/solsysb.htm




Ring Systems





Ring Systems

http://www.astro.rug.nl/%7Eetolstoy/ACTUEELONDERZOEK/JAAR2000/moons/aoz.html

Moons of Saturn: 1.Atlas 2.1980S27 3.1980S26 4.Janus 5.Epimetheus 6.Mimas 7.Enceladus 8.Telesto 9.Tethys 10.Calypso 11.Dione 12.1980S6 13.Rhea 14.Titan 15.Hyperion 16.Iapetus 17.Phoebe

Moons of Jupiter: 1.Metis 2.Adrastea 3.Amalthea 4.Thebe 5.Io 6.Europa 7.Ganymede 8.Callisto 9.Leda 10.Himalia 11.Lysithea 12.Elara 13.Ananke 14.Carme 15.Pasiphae 16.Sinope




Jupiter’s Ring

http://pds.jpl.nasa.gov/planets/captions/jupiter/jupring.htm

Jupiter's intricate, swirling ring system is formed by dust kicked up as interplanetary meteoroids smash into the giant planet's four small inner moons, according to... NASA's Galileo spacecraft.

http://www2.jpl.nasa.gov/galileo/status980915.html








Saturn’s Rings

http://pds.jpl.nasa.gov/planets/captions/saturn/2moons.htm

Most of the rings are only a few tens of meters thick with a total mass equivalent to a medium sized moon. The rings are made out of particles ranging from microscopic dust to barnyard sized boulders with perhaps a few kilometer-sized objects as well. ...the rings are composed mostly of ice crystals with some impurities.

Scientists once thought that the rings were formed at the same time, as the planets when they coalescing out of swirling clouds of interstellar gas 4.8 billion years ago. Under this model, remnants of material within the Roche limit could not condense and would become rings. However, in recent years this idea seems to be flawed. The rings appear to be young, perhaps only hundreds of millions of years old. One of the clues to this theory is that the rings are bright. As Saturn travels though space, the rings accumulate dust particles that have been darkened from solar radiation. If the rings were old, they should appear dark. Another theory suggests that perhaps a comet few too close to Saturn and tidal forces broke it into pieces.... Perhaps one of Saturn's moons was struck by an asteroid smashing it into the bits and pieces that form the rings.

http://www.solarviews.com/eng/saturnrings.htm








Saturn’s Rings

http://science.nasa.gov/headlines/y2002/12feb_rings.htm




Saturn’s Rings

http://www.dailymail.co.uk/sciencetech/article-1172205/Saturn-close-Sensational-cosmic-images-bring-ringed-planet-life.html

This image shows Saturn's rings and the shadow of nearby Mimas. They are now nearly edge-on toward the Sun, and long moon

shadows drape across them. Scientists are now studying the clumpy, disturbed ring material, stretching up to two miles above

the ring plane - contrasted with an estimated normal ring thickness of only six feet






Saturn’s Rings: Shepherd Moons


This composite of two images shows Pan, left, and Prometheus, right, in nearby rings. Pan is trailed by a series of edge waves in the outer boundary of the gap. Prometheus just touches the inner edge of Saturn's F ring, and is followed by a series of dark channels






Saturn’s Rings: New Ring Discovered in Infrared

http://gallery.spitzer.caltech.edu/Imagegallery/image.php?image_name=ssc2009-19a

This diagram highlights a slice of Saturn's largest ring. The ring (red band in inset photo)

was discovered by NASA's Spitzer Space Telescope, which detected infrared light, or heat, from the dusty ring material. Spitzer

viewed the ring edge-on from its Earth-trailing orbit around the sun.

The ring has a diameter equivalent to 300 Saturns lined up side to side. And it's thick too -- about 20 Saturns could fit into its vertical

height. The ring is tilted about 27 degrees from Saturn's main ring plane.




http://gallery.spitzer.caltech.edu/Imagegallery/image.php?image_name=ssc2009-19b





Saturn's newest halo is tilted at about 27 degrees from the main ring plane and encompasses the orbit of the moon Phoebe. Both the ring and Phoebe orbit in the opposite direction of Saturn's other rings

and most of its moons, including Titan and Iapetus.

Why did it take so long to find something so big? The answer is that the ring is very tenuous, made up of a sparse collection of ice and

dust particles. If you could transport yourself to the ring, you wouldn't even know you were there because the particles are so far apart. There's not a lot of sunlight out at Saturn, so this small density of particles doesn't reflect much visible light. Spitzer was able to spot

the band because it sees infrared light, or heat radiation, from objects. Even though the ring material is very cold, it still gives off

heat that can Spitzer can see.

Saturn’s Rings: New Ring Discovered in Infrared




Uranus’s Ring(s)

http://pds.jpl.nasa.gov/planets/captions/neptune/neprings.htm

Radio measurements showed the outermost ring, the epsilon, to be composed mostly of ice boulders several feet across. However, a very tenuous distribution of fine dust also seems to be spread throughout the ring system.

The particles that make up the rings may be remnants of a moon that was broken by a high-velocity impact or torn up by gravitational effects.

http://www.nineplanets.org/uranus.html






Shepherd Moons


Shepherd moons work in pairs on the inner and outer edge of rings to gravitational push and pull (accelerate and de-accelerate) ring particles. The result is to confine the ring particles to within the shepherd moons orbits.




http://astro.unl.edu/classaction/jovianplanets.html



















Neptune’s (Rings)

http://www.britannica.com/EBchecked/topic/409330/Neptune/54304/The-ring-system

The present rings are narrow, and scientists have found it difficult to explain how the orbits of the known moons can effectively confine the natural radial spreading of the rings. This has led many to speculate that Neptune’s present rings may be much younger than the planet itself, perhaps substantially less than a million years. The present ring system may be markedly different from any that existed a million years ago. It is even possible that the next spacecraft to visit Neptune’s rings will find a system greatly evolved from the one Voyager 2 imaged in 1989.

None of Neptune’s rings were detected from scattering effects on Voyager’s radio signal propagating through the rings, which indicates that they are nearly devoid of particles in the centimetre size range or larger. The fact that the rings were most visible in Voyager images when backlit by sunlight implies that they are largely populated by dust-sized particles, which scatter light forward much better than back toward the Sun and Earth.Their chemical makeup is not known, but, like the rings of Uranus, the surfaces of Neptune’s ring particles (and possibly the particles in their entirety) may be composed of radiation-darkened methane ices.




http://www.britannica.com/EBchecked/topic/409330/Neptune/54304/The-ring-system#




Rhea’s (Rings!? 6 March ‘08)

http://planetary.org/news/2008/0306_A_Ringed_Moon_of_Saturn_Cassini.html




Ring Systems


They are not stable; they evolve and change over time. Unless something replenishes them or keeps them from dissipating, they will not last longer than a few 100 millions years; one of Neptune’s might not last a century.

They generally form inside a planet’s Roche limit. Object’s that come closer than this distance to a planet tend to be ripped apart by tidal forces. Since the gas giants have strong gravitational fields, they have strong tidal forces.

Shepherding moons are moons that keep a ring system nice an tidy, by not letting material drift out of a ring and/or into gaps.




• Ch 11, pp. 263-264: 9.

• Ch 13: Image Analysis Quiz accessible from: http://www.brookscole.com/cgi-brookscole/course_products_bc.pl?fid=M20b&product_isbn_issn=9780495017899&discipline_number=19

Due at the beginning of next class period.

Be working your Solar System project.

HW Ch 11: Franknoi, Morrison, and Wolff, Voyages Through the Universe,

3rd ed.


http://www.brookscole.com/cgi-brookscole/course_products_bc.pl?fid=M20b&product_isbn_issn=9780495017899&discipline_number=19




A1 12 Rings

Education

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