Miller's Astronomy 1 lecture notes on Gas Giant Rings

1. Rings of the Gas Giants
LACC §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?
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2. Ring Systems
http://www.jb.man.ac.uk/distance/strobel/solarsys/solsysb.htm
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3. Ring Systems
http://www.jb.man.ac.uk/distance/strobel/solarsys/solsysb.htm
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4. Ring Systems
Moons of Saturn:
Moons of Jupiter:
1.Atlas
1.Metis
2.1980S27
2.Adrastea
3.1980S26
3.Amalthea
4.Janus
4.Thebe
5.Epimetheus
5.Io
6.Mimas
6.Europa
7.Enceladus
7.Ganymede
8.Telesto
8.Callisto
9.Tethys
9.Leda
10.Calypso
10.Himalia
11.Dione
11.Lysithea
12.1980S6
12.Elara
13.Rhea
13.Ananke
14.Titan
14.Carme
15.Hyperion
15.Pasiphae
16.Iapetus
16.Sinope
17.Phoebe
http://www.astro.rug.nl/%7Eetolstoy/ACTUEELONDERZOEK/JAAR2000/moons/aoz.html
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5. Jupiter’s Ring
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
http://pds.jpl.nasa.gov/planets/captions/jupiter/jupring.htm
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6. Saturn’s Rings
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/
http://pds.jpl.nasa.gov/planets/captions/saturn/2moons.htm saturnrings.htm
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7. Saturn’s Rings
http://science.nasa.gov/headlines/y2002/12feb_rings.htm
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8. Saturn’s Rings
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
http://www.dailymail.co.uk/sciencetech/article-1172205/Saturn-
close-Sensational-cosmic-images-bring-ringed-planet-life.html
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9. 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
http://www.dailymail.co.uk/sciencetech/article-1172205/Saturn-
close-Sensational-cosmic-images-bring-ringed-planet-life.html
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10. Saturn’s Rings: New
Ring Discovered in
Infrared
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=ssc2009-19a
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11. http://gallery.spitzer.caltech.edu/Imagegallery/image.php?image_name=ssc2009-19b
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12. Saturn’s Rings: New Ring
Discovered in Infrared
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.
http://gallery.spitzer.caltech.edu/Imagegallery/image.php?image_name=ssc2009-19b
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13. Uranus’s Ring(s)
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
http://pds.jpl.nasa.gov/planets/captions/neptune/neprings.htm
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14. 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://pds.jpl.nasa.gov/planets/captions/neptune/neprings.htm
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15. Neptune’s (Rings)
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.
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.
http://www.britannica.com/EBchecked/topic/409330/Neptune/54304/The-ring-system
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16. Rhea’s (Rings!? 6 March ‘08)
http://planetary.org/news/2008/0306_A_Ringed_Moon_of_Saturn_Cassini.html
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17. 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.
http://planetary.org/news/2008/0306_A_Ringed_Moon_of_Saturn_Cassini.html
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18. HW Ch 11: Franknoi, Morrison, and
Wolff, Voyages Through the Universe,
3rd ed.
• 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.
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