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Wavelike Structure in Saturn’s Rings

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

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  1. Wavelike Structure in Saturn’s 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 – 1660’s • James Clerk Maxwell - 1857

  4. Ring Particle Models

  5. Saturn’s Ring System • Approximately 340,000 km from edge to edge • 100 meters thick • 7 major rings • Less than 10 million years old?

  6. Cassini Division Encke Gap C B A Saturn’s Ring System Cassini ISS

  7. 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

  9. 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)

  10. Methods 20 km

  11. Spiral Density Waves

  12. 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

  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 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)

  16. Prometheus 5:4 Surface Mass Density Results . RSS X Band . . Frequency (cycles/km) . . 12

  17. 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

  18. 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

  20. Pan • Located in the Encke Gap in Saturn’s A ring • Approximately 10 km in diameter • Discovered in 1990 using Voyager occultation data

  21. 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 θ = 295º RSS outer fit θ = 65º PPS inner fit θ = 247º PPS outer fit θ = 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 Saturn’s Rings. The Astronomical Journal 125, 894 – 901 (2003).

  26. 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. ~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

  29. Ringlets in the C Ring • 6 Ringlets searched • 1 found to contain similar wavelike structure in both pps and rss datasets • 89190 – 89300 km

  30. 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

  31. 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

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