Wavelike Structure in Wavelike Structure in Saturn’s RingsSaturn’s Rings

Benjamin PollardBenjamin Pollard

2/09/062/09/06

OverviewOverview Ring SystemRing System

History History DescriptionDescription SatellitesSatellites Types of StructureTypes of Structure

Voyager Occultation ExperimentsVoyager Occultation Experiments Data and Analysis MethodData and Analysis Method Observed Ring StructureObserved Ring Structure

Density wavesDensity waves WakesWakes Irregular StructureIrregular Structure

HistoryHistory

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

Ring Particle Models

Saturn’s Ring SystemSaturn’s Ring System

Approximately 340,000 km from edge to edgeApproximately 340,000 km from edge to edge 100 meters thick100 meters thick 7 major rings7 major rings Less than 10 million years old?Less than 10 million years old?

Saturn’s Ring System Saturn’s Ring System

CC AABB

Encke GapCassini Division

Cassini ISS

SatellitesSatellites

39 known satellites39 known satellites Diameter of 7 km to 5150 Diameter of 7 km to 5150

kmkm

Responsible for some Responsible for some ring structurering structure Produce waves in the Produce waves in the

ringsrings Spiral density wavesSpiral density waves Bending wavesBending waves WakesWakes

Shepherd F ringShepherd F ring Gaps and RingletsGaps and Ringlets

Wavelike StructureWavelike Structure

Density WavesDensity WavesBending WavesBending WavesWakesWakes Irregular StructureIrregular Structure

Cassini UVIS

Cassini ISS

Cassini ISS

Voyager Occultation ExperimentsVoyager Occultation Experiments

Voyager 1Voyager 1 November 13, 1980November 13, 1980 Radio Science Experiment (RSS)Radio Science Experiment (RSS) Spacecraft occulted from earthSpacecraft occulted from earth Maximum resolution of 0.2 km Maximum resolution of 0.2 km

(RSS)(RSS)

Voyager 2 Voyager 2 August 25, 1981August 25, 1981 Photopolarimeter Experiment Photopolarimeter Experiment

(PPS)(PPS) Ultraviolet Spectrometer Ultraviolet Spectrometer

Experiment (UVS)Experiment (UVS) The star The star δδ Scorpii occulted Scorpii occulted Maximum resolution of 0.1 km Maximum resolution of 0.1 km

(PPS) and 3.5 km (UVS)(PPS) and 3.5 km (UVS)

MethodsMethods

20 km

Spiral Density WavesSpiral Density Waves

PPS

Density Waves in the A ring

PPS

RSS X

RSS S

0

Log

S

(σ c

m4/s

2)

001122

0000

0000

0000

0

0

0

0

1

11

122

22

Opt

ical

Dep

thO

ptic

al D

epth

Opt

ical

Dep

thF

(cy

/km

)F

(cy

/km

)F

(cy

/km

)

1

1

1

Calculated Surface Mass Densities From Spiral Density Waves

RANGE (km)

Sur

face

Mas

s D

ensi

ty (

g/cm

2 )

2

4

6

8

10

120

Feature SearchFeature Search

Searched C ring and Searched C ring and Cassini Division for Cassini Division for possible wave possible wave formations formations

Two promising Two promising features appeared in features appeared in the Cassini Divisionthe Cassini Division

Op

tica

l De

pth

Fre

qu

en

cy (

cycl

es/

km)

Fre

qu

en

cy (

cycl

es/

km)

Possible Density Wave Possible Density Wave Prometheus 5:4 Prometheus 5:4

located in the Cassini located in the Cassini Division at 120,302 km Division at 120,302 km

Surface mass density Surface mass density measured in all three measured in all three data setsdata sets

Surface mass density Surface mass density of ~30 g/cmof ~30 g/cm22

Very high value for Very high value for Cassini DivisionCassini Division

Range (km)

1.

1.

.

-.

Fre

quen

cy (

cycl

es/k

m)

Prometheus 5:4 Surface Mass Prometheus 5:4 Surface Mass Density ResultsDensity Results

RSS X Band

Fre

quen

cy (

cycl

es/k

m)

.

.

.

.

.

12

Mimas 4:1Mimas 4:1

Located in the C ring Located in the C ring at 74892 kmat 74892 km

16 km long wavetrain16 km long wavetrain Previously calculated Previously calculated

surface mass density surface mass density 1.0 +- 0.1 g/cm1.0 +- 0.1 g/cm22 and and 1.1 +- 0.1 g/cm1.1 +- 0.1 g/cm22

Our calculated Our calculated surface mass density surface mass density

~5 g/cm~5 g/cm22

7

.

.

.

.

.

Opt

ical

Dep

th

The GapThe Gap1.

1.

.

-.

Fre

qu

en

cy (

cycl

es/

km)

Range (km)

WakesWakes Caused by moonlets Caused by moonlets

embedded in ringsembedded in rings

Similar to boat traveling Similar to boat traveling through waterthrough water

Wake features can be Wake features can be modeled based upon modeled based upon position of moonposition of moon

PanPan

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

Approximately 10 km in Approximately 10 km in diameterdiameter

Discovered in 1990 using Discovered in 1990 using Voyager occultation dataVoyager occultation data

Possible Wakes near 119950 kmPossible Wakes near 119950 km Satellite located somewhere near 119950 kmSatellite located somewhere near 119950 km Gap is about half the size of Encke GapGap is about half the size of Encke Gap Possible wakes visible in both RSS and PPS dataPossible wakes visible in both RSS and PPS data

Op

tica

l De

pth 1.

.

2.

.

- .11

Possible Wake?Possible Wake?

Wake Fits Wake Fits RSS inner fit θ = 295º RSS outer fit θ = 65º

PPS inner fit θ = 247º PPS outer fit θ = 113º

Irregular StructureIrregular Structure

Sources of Irregular Structure Sources of Irregular Structure

Ballistic Transport from meteoritic collisionsBallistic Transport from meteoritic collisions 100 km wavelengths100 km wavelengths C Ring and Inner B RingC Ring and Inner B Ring Durisen, R.H. An Instability in Planetary Rings Due to Ballistic Transport. Durisen, R.H. An Instability in Planetary Rings Due to Ballistic Transport. IcarusIcarus 115, 66-85 115, 66-85

(1995).(1995).

Ring Particle AssembliesRing Particle Assemblies Up to 50 - 100 km wavelengthsUp to 50 - 100 km wavelengths B RingB Ring Tremaine, S. On the Origin of Irregular Structure in Saturn’s Rings. Tremaine, S. On the Origin of Irregular Structure in Saturn’s Rings. The Astronomical The Astronomical

JournalJournal 125, 894 – 901 (2003). 125, 894 – 901 (2003).

Inner B Ring – Large StructureInner B Ring – Large Structure Irregular Irregular

structure visible structure visible from 92500 – from 92500 – 104500 km104500 km

Wavelengths Wavelengths between 100 between 100 and 500 kmand 500 km

Appears very Appears very similar to similar to structure studies structure studies previously using previously using an image an image derived ring derived ring profileprofile

Horn and Cuzzi

Image derived ring profile

PPS

UVS

100 - 500 km wavelength350 km window size

100 - 500 km wavelength350 km window size

350 km window size

Inner B Ring Finer Irregular StructureInner B Ring Finer Irregular StructurePPS

UVS

~50-100 km wavelength105 km window

~50 – 100 km wavelength105 km window

~100 km wavelength210 km window

~100 km wavelength210 km window

C Ring 1000 km wavesC Ring 1000 km wavesRSS - Peaks removed

RSS -Original

~1000 km wavelength1500 km window

~800-1200 km wavelength2500 km window

~1000 km wavelength1500 km window

Ringlets in the C RingRinglets in the C Ring 6 Ringlets searched6 Ringlets searched

1 found to contain similar wavelike structure in both pps and rss datasets1 found to contain similar wavelike structure in both pps and rss datasets

89190 – 89300 km89190 – 89300 km

RSS

~5-10 km wavelength18km window

~5-7 km wavelength12 km window

PPS

~3-5 km wavelength27 km window

~3-5 km wavelength21 km window

Ringlet between 89190 – 83000 km

ObservationsObservationsA RingA Ring

Measured the surface mass density over 30 Measured the surface mass density over 30 density wavesdensity waves

B Ring B Ring Large and fine irregular structureLarge and fine irregular structure

C RingC RingLarge structureLarge structure3-7 km wavelength in one ringlet 3-7 km wavelength in one ringlet

Cassini DivisionCassini DivisionTwo unexplained featuresTwo unexplained features

AcknowledgementsAcknowledgements

Linda SpilkerLinda SpilkerStuart PilorzStuart Pilorz Idaho Space Grant ConsortiumIdaho Space Grant ConsortiumDavid AtkinsonDavid AtkinsonMark ShowalterMark Showalter

Cassini ISS