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Wavelike Structure in Saturn’s Rings. Benjamin Pollard 2/09/06. Overview. Ring System History Description Satellites Types of Structure Voyager Occultation Experiments Data and Analysis Method Observed Ring Structure Density waves Wakes Irregular Structure. History.

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Wavelike structure in saturn s rings

Wavelike Structure in Saturn’s Rings

Benjamin Pollard

2/09/06


Overview
Overview

  • Ring System

    • History

    • Description

    • Satellites

    • Types of Structure

  • Voyager Occultation Experiments

  • Data and Analysis Method

  • Observed Ring Structure

    • Density waves

    • Wakes

    • Irregular Structure


History
History

  • Galileo – 1610

  • Christian Huygens - 1655

  • Jean Chapelain – 1660

  • Jean-Dominique Cassini – 1660’s

  • James Clerk Maxwell - 1857



Saturn s ring system
Saturn’s Ring System

  • Approximately 340,000 km from edge to edge

  • 100 meters thick

  • 7 major rings

  • Less than 10 million years old?


Cassini Division

Encke Gap

C

B

A

Saturn’s Ring System

Cassini ISS


Satellites
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


  • Wavelike structure
    Wavelike Structure

    • Density Waves

    • Bending Waves

    • Wakes

    • Irregular Structure

    Cassini ISS

    Cassini ISS

    Cassini UVIS


    Voyager occultation experiments
    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 δ Scorpii occulted

    • Maximum resolution of 0.1 km (PPS) and 3.5 km (UVS)


  • Methods

    20 km



    Density Waves in the A ring

    Log S

    (σ 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


    Calculated Surface Mass Densities From Spiral Density Waves

    10

    8

    6

    Surface Mass Density (g/cm2)

    4

    2

    120

    RANGE (km)


    Feature search
    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)


    Possible density wave
    Possible Density Wave

    • Prometheus 5:4 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)


    Prometheus 5 4 surface mass density results
    Prometheus 5:4 Surface Mass Density Results

    .

    RSS X Band

    .

    .

    Frequency (cycles/km)

    .

    .

    12


    Mimas 4 1
    Mimas 4:1

    • 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


    The gap
    The Gap

    1.

    1.

    Frequency (cycles/km)

    .

    -.

    Range (km)


    Wakes
    Wakes

    • Caused by moonlets embedded in rings

    • Similar to boat traveling through water

    • Wake features can be modeled based upon position of moon


    Pan

    • Located in the Encke Gap in Saturn’s A ring

    • Approximately 10 km in diameter

    • Discovered in 1990 using Voyager occultation data


    Possible wakes near 119950 km
    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



    Wake fits
    Wake Fits

    RSS inner fit θ = 295º

    RSS outer fit θ = 65º

    PPS inner fit θ = 247º

    PPS outer fit θ = 113º



    Sources of irregular structure
    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 Saturn’s Rings. The Astronomical Journal 125, 894 – 901 (2003).


    Inner b ring large structure
    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


    Inner b ring finer irregular structure
    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


    C ring 1000 km waves

    ~800-1200 km wavelength

    2500 km window

    C Ring 1000 km waves

    RSS - Peaks removed

    RSS -Original

    ~1000 km wavelength

    1500 km window

    ~1000 km wavelength

    1500 km window


    Ringlets in the c ring
    Ringlets in the C Ring

    • 6 Ringlets searched

    • 1 found to contain similar wavelike structure in both pps and rss datasets

    • 89190 – 89300 km


    Ringlet between 89190 – 83000 km

    RSS

    ~5-10 km wavelength

    18km window

    ~5-7 km wavelength

    12 km window

    PPS

    ~3-5 km wavelength

    21 km window

    ~3-5 km wavelength

    27 km window


    Observations
    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


    Acknowledgements
    Acknowledgements

    • Linda Spilker

    • Stuart Pilorz

    • Idaho Space Grant Consortium

    • David Atkinson

    • Mark Showalter

    Cassini ISS


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