Unexpected Surprises
on
Saturn's Moons and Rings
Nicole Albers
Laboratory for Atmospheric and Space Physics
Colorado Space Science Teacher's Summit 2010
A few Previous Unexpected Finds
1. Wandering stars
2. Jovian moons
3. Saturn's rings
4. The Cassini division in Saturn's rings
5. The Uranian ring system … and many more Sending the Voyager spaceprobes gave us not only the Jovian and Neptunian rings but also the first close­up view of the extensive Saturnian ring system.
Planetary Mean Radii
Jupiter: 71,492 km
Saturn: 60,268 km
Uranus: 25,559 km
Neptune: 24,764 km
NASA and The Hubble Heritage Team
(STScI/AURA)
Launch on October 15, 1997
from KSC
7 year cruise on
Venus-Venus-Earth-Jupiter
gravity assist
Selected Highlights
Microstructure: Self­gravity wakes and overstable waves
●
A few words about stellar occultations
Cassini UVIS
Variability of the B ring edge
●
C and D ring corrugations
●
Daphnis and its wakes
●
A moonlet belt in the A ring
●
Inner and outer Saturnian satellites
●
(Stellar) Occultations = Light Time Series
Stellar Occultation by Saturn's A ring
Mimas Occultation by Saturn's F ring
Typical UVIS Occultation Profile
Colwell et al. (2007)
Multiple Cassini UVIS Stellar Occultation Profiles
with Different Viewing Geometries
Colwell et al. (2007)
N­body Simulations vs Cassini UVIS observations
Glen Stewart, LASP, CU
UVIS 2D autocorrelation
Miodrag Sremčević, LASP
Autocorrelation = Measure of Self­similarity
Heikki Salo, Oulu, Finland
Structures of this scale are currently inaccessable to real imaging.
Self­gravity wakes: A close­up view
Stellar level
transparent
gap
opaque
SG wake
Sremčević et al. (2009)
~150m
Sremčević et al. (2009)
Overstable waves time series
Overstable waves in inner A ring
Coadded
wavelet
Optical depth
Sremčević et al. (2009)
Wavelet
transform
Selected Highlights
Microstructure: Self­gravity wakes and overstable waves
A few words about stellar occultations
Cassini UVIS
Variability of the B ring edge
●
C and D ring corrugations
●
Daphnis and its wakes
●
A moonlet belt in the A ring
●
Inner and outer Saturnian satellites
●
Saturn's B Ring Edge: Structure
compression
relaxation
optical depth
A new image of Saturn's rings with a non­
stationary size distribution emerges distance from resonance location
Spitale and Porco (2009, arXiv)
early 2007
early 2008
late 2008 – early 2009
Esposito et al., Albers et al. Spectral analysis reveals sub­km size structure during relaxation phase of the ring material (seen as brighter colors on the left) with its abundance increasing in time
Saturn's C and D Ring Corrugation
Consistent with impact in 1984. Similar evidence found for Jovian rings consistent with the Shoemaker­Levy encounter in 1994 (Hedman et al., Showalter et al.)
Embedded Moons and Moonlets
Daphnis (Keeler Gap)
Moonlet Propeller: Belts and Giants
Giant Propeller in A ring
Tiscareno et al. (2006)
Shards of a catastrophic impact or are they being accreted in the rings?
What is their connection to the other inner satellites?
Sremčević et al. (2007)
The Inner Saturnian Satellites
Porco et al. (2007)
ENCELADUS
Radius: 252 km
● Distance: ~4 Saturn radii ● Orbital Period: 1.4 days
●
ENCELADUS
Radius: 252 km
● Distance: ~4 Saturn radii ● Orbital Period: 1.4 days
Plumes at the South Pole (Tiger Stripes) eject material and sustain the dusty E ring. ●
RHEA
Radius: 764 km
● Distance: 8.7 Saturn radii
● Orbital Period: 4.5 days
●
RHEA
Radius: 764 km
● Distance: 8.7 Saturn radii
● Orbital Period: 4.5 days
●
Electromagnetic drop­out signatures and a dark equatorial band are potential indicators of a satellite ring system so far unseen by remote sensing.
TITAN
Radius: 2575 km
● Distance: ~20 Saturn radii
● Orbital Period: ~16 days
●
TITAN
Radius: 2575 km
● Distance: ~20 Saturn radii
● Orbital Period: ~16 days
●
Only moon in the Solar system with an extended atmosphere. A methane world where rocks are made of ice with a chance of ethane rain.
Geologic terrain includes mountains, fluvial structures, lakes; thing very similar to terrestrial ones.
IAPETUS
Radius: 735 km
● Distance: ~59 Saturn radii
● Orbital Period: ~79 days
●
For More Information and Pretty Pictures:
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Cassini Equinox Mission: http://saturn.jpl.nasa.gov/
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Ultraviolet Imaging Spectrograph: http://lasp.colorado.edu/cassini
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PDS Rings Node: http://pds­rings.seti.org ●
NASA/JPL Photojournal: http://photojournal.jpl.nasa.gov Image Credit (unless noted otherwise): NASA/JPL/Space Science Institute