Wavelike Structure in Saturn

1
Wavelike Structure in Saturns Rings

• Benjamin Pollard
• 2/09/06

2
Overview

• Ring System
• History
• Description
• Satellites
• Types of Structure
• Voyager Occultation Experiments
• Data and Analysis Method
• Observed Ring Structure
• Density waves
• Wakes
• Irregular Structure

3
History

• Galileo 1610
• Christian Huygens - 1655
• Jean Chapelain 1660
• Jean-Dominique Cassini 1660s
• James Clerk Maxwell - 1857

4
Ring Particle Models
5
Saturns Ring System

• Approximately 340,000 km from edge to edge
• 100 meters thick
• 7 major rings
• Less than 10 million years old?

6
Saturns Ring System
Cassini ISS
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Satellites

• 39 known satellites
• Diameter of 7 km to 5150 km
• Responsible for some ring structure
• Produce waves in the rings
• Spiral density waves
• Bending waves
• Wakes
• Shepherd F ring
• Gaps and Ringlets

8
Wavelike Structure

• Density Waves
• Bending Waves
• Wakes
• Irregular Structure

Cassini ISS
Cassini ISS
Cassini UVIS
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Voyager Occultation Experiments

• Voyager 1
• November 13, 1980
• Radio Science Experiment (RSS)
• Spacecraft occulted from earth
• Maximum resolution of 0.2 km (RSS)
• Voyager 2
• August 25, 1981
• Photopolarimeter Experiment (PPS)
• Ultraviolet Spectrometer Experiment (UVS)
• The star d Scorpii occulted
• Maximum resolution of 0.1 km (PPS) and 3.5 km
  (UVS)

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Methods
20 km
11
Spiral Density Waves
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Density Waves in the A ring
Log S (s cm4/s2)
PPS
PPS
0
0
0
1
Optical Depth
1
2
2
0
0
F (cy/km)
0
0
1
RSS X
0
0
1
Optical Depth
1
2
2
0
0
F (cy/km)
0
0
1
RSS S
0
0
1
Optical Depth
1
2
2
0
0
F (cy/km)
0
0
1
13
Calculated Surface Mass Densities From Spiral
Density Waves
10
8
6
Surface Mass Density (g/cm2)
4
2
120
RANGE (km)
14
Feature Search

• Searched C ring and Cassini Division for possible
  wave formations
• Two promising features appeared in the Cassini
  Division

Optical Depth
Frequency (cycles/km)
Frequency (cycles/km)
15
Possible Density Wave

• Prometheus 54 located in the Cassini Division at
  120,302 km
• Surface mass density measured in all three data
  sets
• Surface mass density of 30 g/cm2
• Very high value for Cassini Division

1.
1.
Frequency (cycles/km)
.
-.
Range (km)
16
Prometheus 54 Surface Mass Density Results
RSS X Band
.
.
.
Frequency (cycles/km)
.
.
12
17
Mimas 41

• Located in the C ring at 74892 km
• 16 km long wavetrain
• Previously calculated surface mass density 1.0 -
  0.1 g/cm2 and 1.1 - 0.1 g/cm2
• Our calculated surface mass density
• 5 g/cm2

.
.
.
Optical Depth
.
.
7
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The Gap
1.
1.
Frequency (cycles/km)
.
-.
Range (km)
19
Wakes

• Caused by moonlets embedded in rings
• Similar to boat traveling through water
• Wake features can be modeled based upon position
  of moon

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Pan

• Located in the Encke Gap in Saturns A ring
• Approximately 10 km in diameter
• Discovered in 1990 using Voyager occultation data

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Possible Wakes near 119950 km

• Satellite located somewhere near 119950 km
• Gap is about half the size of Encke Gap
• Possible wakes visible in both RSS and PPS data

2.
.
1.
Optical Depth
.
- .
11
22
Possible Wake?
23
Wake Fits
RSS inner fit ? 295º
RSS outer fit ? 65º
PPS inner fit ? 247º
PPS outer fit ? 113º
24
Irregular Structure
25
Sources of Irregular Structure

• Ballistic Transport from meteoritic collisions
• 100 km wavelengths
• C Ring and Inner B Ring
• Durisen, R.H. An Instability in Planetary Rings
  Due to Ballistic Transport. Icarus 115, 66-85
  (1995).
• Ring Particle Assemblies
• Up to 50 - 100 km wavelengths
• B Ring
• Tremaine, S. On the Origin of Irregular
  Structure in Saturns Rings. The Astronomical
  Journal 125, 894 901 (2003).

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Inner B Ring Large Structure
PPS

• Irregular structure visible from 92500 104500
  km
• Wavelengths between 100 and 500 km
• Appears very similar to structure studies
  previously using an image derived ring profile

100 - 500 km wavelength 350 km window size
UVS
100 - 500 km wavelength 350 km window size
Image derived ring profile
350 km window size
Horn and Cuzzi
27
Inner B Ring Finer Irregular Structure
PPS
50-100 km wavelength 105 km window
100 km wavelength 210 km window
UVS
50 100 km wavelength 105 km window
100 km wavelength 210 km window
28
C Ring 1000 km waves
RSS - Peaks removed
RSS -Original
1000 km wavelength 1500 km window
1000 km wavelength 1500 km window
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Ringlets in the C Ring

• 6 Ringlets searched
• 1 found to contain similar wavelike structure in
  both pps and rss datasets
• 89190 89300 km

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Observations

• A Ring
• Measured the surface mass density over 30 density
  waves
• B Ring
• Large and fine irregular structure
• C Ring
• Large structure
• 3-7 km wavelength in one ringlet
• Cassini Division
• Two unexplained features

32
Acknowledgements

• Linda Spilker
• Stuart Pilorz
• Idaho Space Grant Consortium
• David Atkinson
• Mark Showalter

Cassini ISS