Saturn’s Strangest Ring
description
Transcript of Saturn’s Strangest Ring
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Saturn’s Strangest Ring
Saturn’s Strangest Ring
Carl Murray(Cassini ISS Team Member)
with help from Kevin Beurle, Nick Cooper,Mike Evans, Gareth Williams and Carlos
Chavez
Astronomy UnitQueen Mary, University of London
Carl Murray(Cassini ISS Team Member)
with help from Kevin Beurle, Nick Cooper,Mike Evans, Gareth Williams and Carlos
Chavez
Astronomy UnitQueen Mary, University of London
CHARM TeleconMay 25th,
20101
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PIA09803
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Outline
•Pioneer 11, Voyager and HST observations of the F ring
•Cassini observations of the F ring
- Objects in the vicinity of the F ring
- The effect of Prometheus
- Evidence for embedded objects
•Conclusions
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A B C D
F
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Pioneer 11 image
Gehrels et al. (1980)
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Pioneer 11 charged particle data
Simpson et al. (1980)
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Voyager 1 image showing:
“braids”
“clumps”
“kinks”
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Voyager 1Nov 1980
Voyager 2Aug 1981
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2a
2b
3
4
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Murray, Gordon &
Giuliatti Winter (1997)
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August 1981
February 1994
Murray & Giuliatti Winter (1996)PIA07549
PIA07632
Pandora
Prometheus
differential precession
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Giuliatti Winter, Murray & Gordon (2000)
Showalter & Burns (1982)
Δa
Δh
Δk
Δθ
Gravitational effect of close satellite
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Showalter (2004)
Tracking clumps in the F ring
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(McGhee et al. 2001)
Ring Plane CrossingObservations
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S/2004 S 3 S/2004 S 6
June 2004October 2004
= S/2004 S 4?
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2005 DOY103 Detections
typically~90
detectionsof
eachobject
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2005 DOY121 Detections
typically~6
detectionsof
eachobject
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2005 DOY123,4 Detections
typically~6
detectionsof
eachobject
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Cassini VIMS and UVIS Occultationof the F Ring (Alpha Sco Egress)
“Pywacket”(479m)
Esposito et al. (2007)
Evidence for Additional Objects Near F Ring Core
13 objects detected, all within ~10km from core;mostly semi-opaque; sizes in the range 30m –9km
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WAC NAC
Prometheus
Cassini SOI images
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Production of “streamers” and “channels” by Prometheus
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2005 DOY103
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22 2005 DOY103 FMOVIE
Sheared channels in F ring
Pr
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Simulation of Prometheus interacting with the F ring
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The perturbing effect of Prometheus
Murray et al. (2005)
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Comparison of simulation with Cassini images
Murray et al. (2005)
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Prometheus perturbing the F ring
ISS_033RF_FRSTRCHAN001_PRIME
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“FMOVIE” “AZSCAN”
sequence of images at near-constant inertial longitude
sequence of images at various inertial longitudes
Two Ways To Obtain Longitudinal Coverage
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Spiral structure of F ring strands
Charnoz et al. (2005)28
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Sample Mosaic of F Ring (2005 DOY103)Co-rotating with F Ring’s mean motion
0 360
0
-750
+750
Co-rotating Longitude (deg.)
Epoch 12h UTC 1st January 2007
Radia
l O
ffse
t (k
m)
1492
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Colwell et al. (2009)
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Cassini ISS F Ring Longitudinal Coverage 2005–2007
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Major event in F ring between 2006 DOY329 and DOY357
N1545564642
PIA08863
N1545564642N1545564196
Reprojected Images
8.5°
150
0km
radial motion ~200 km/h outwards
Evidence for Larger Objects Near the F ring
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2005 DOY172 2005 DOY180
Detections of S/2004 S 6
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15432006-
329
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15452006-
357
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Radia
l O
ffse
t (k
m)
Co-rotating Longitude
2007-005
2007-041
2007-058
2006-357
Passage of S/2004 S 6
Murray et al. (2008)
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Radia
l O
ffse
t (k
m)
Co-rotating Longitude
2007-090
2007-108
2007-125
2007-076
Passage of S/2004 S 6
Murray et al. (2008)
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Comparison of mosaic with jet simulations
Murray et al. (2008)
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15552007-
108
14922005-
103Gross features of F ring are similar
to those that existed 2 years previously=> Caused by same object?
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N1538169712 N155287157 N1557039476
Evidence For Embedded Objects in Core
(examples of “fans”)40
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Effect of embedded satellite on circular orbit
horseshoe zone
chaotic zone
passing zone
Murray & Dermott (1999)
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5km satellite on circular orbit at edge of 50km-wide ring
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5km satellite on 4ε eccentric orbit at edge of 50km-wide ring
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N1537876778
Embedded object on eccentric orbit perturbs adjacent material which acts like a tracer for the gravitational effect of the object — entirely analagous to the mechanism by which Prometheus creates channels in the F ring
Comparison of image with integrationMurray et al. (2008)
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PIA09782Reprojected image showing “fans”
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PIA08290
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Embedded satellite plus Prometheus conjunction
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PIA10593
Prometheus
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Numerical simulation
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Conclusions
•There exist several hundred small (radius <1km) moonlets/clumps in the vicinity of the F ring
•Prometheus creates the “streamer-channel” structures in the F ring
•Collisions between objects (such as S/2004 S6) and the core lead to jet formation
•The “fans” suggest the presence of embedded objects which themselves get perturbed
•The complex nature of the F ring can be understood by relatively simple processes