Saturn

1. Saturn The Ringed planet Roman name for father of Jupiter Roman god of agriculture (Greek - Cronos/Zeus) Some satellites are named for the titans in mythology

2. Saturn • Sixth planet from the Sun • Second largest planet in the Solar System • Another “gas bag” or “gas giant” • Radiates more energy into space than it receives from the Sun • 35 “named” satellites • More discovered but size range is enormous • Atlas, Prometheus and Pandora are essential to keeping ring system intact • Largest ring system in our SS • Thought to be unique until 1977 • Galileo first observed w/telescope in 1610 • Initially confused by changing appearance • 1659 Christian Huygens correctly identified planet and ring geometry

3. Saturn • Orbit = 59.54 AU from the Sun • Year = 29.46yrs • Day = 10.23hrs • Axis tilt = 25.33 degrees • Diameter = 120,536km (12,756) • 9.45 X the Earth’s • Surface gravity = 9.05m/sec2 (9.78m/sec2) • 80lbs on Earth = 91lbs on Saturn • Atmosphere • 75% H • 25% He • Traces of methane, water, ammonia and “rock” • Again like Jupiter, close to primordial solar nebula comp.

4. Saturn Stats (cont’d) • Albedo = .47 (.37) • Mean cloud temperature = -125C (-190F) • Least dense of the planets • Specific gravity of 0.7 is less than water • Thick gaseous material in latitudinal zones of diff comp and velocities • Less dramatic than Jupiters • Wider at equator • Three rings (A, B, and C) can be discriminated from Earth based observations • Large gap between A and B is known as the Cassini division • Voyager images an additional 4 fainter rings • Although appear continuous from Earth actually innumerable small particles each in an independent orbit

5. Saturn’s Interior • The outer layer is primarily composed of molecular H • Deeper where the pressure reaches 100,000 bars, the gas starts to resemble a hot liquid • At 1,000,000 bar, hydrogen changes into a new state of metallic hydrogen • This metallic hydrogen state occurs at about half of Saturn's radius • Next is a layer dominated by ice where "ice" denotes a soupy liquid mixture of water, methane, and ammonia under high temperatures and pressures • The center is a rocky or rocky-ice core

6. Saturn • Visibly flattened at poles • Equatorial diameter is 10% (13,000km) greater than its polar diameter • Due to fast rate of rotation • Low density • Fluid state

7. Saturn • Images from HST 1996-2000 • Axial tilt causes seasons much like Earths • Lower image is near autumnal equinox (northern hemisphere) • Upper is near winter solstice (northern hemisphere) • Variations in seasonal storm strength • Latitudinal variations cause wind shear turbulence w/speeds approaching 500m/sec (1100mph)

8. Saturn’s Magnetosphere • Known to have a strong magnetic field • Caused by convection in metallic H zone • Measured out to twenty Saturn radii • HST observations reveal aurorae near both poles • Auroral curtain can be seen to rise as far as 1,200 mi (2,000 kms) above the cloud tops in the upper image

9. Saturn’s Storms NASA Hubble Space Telescope image of Saturn shows a rare storm near the planet's equator The storm is generated by an upwelling of warmer air, similar to a terrestrial thunderhead The east-west extent of this storm is equal to the diameter of the Earth (~12,000km)

10. Hexagonal Polar Vortex • Image acquired by Cassini above the cloud tops of Saturn shows a 'hexagon-like' atmospheric vortex • This bizarre six-sided feature encircles the north pole of Saturn near 78 degrees north latitude • Originally discovered by Voyager flybys of the early 1980’s, the new views of this polar hexagon taken in late 2006 prove that this is an unusually long-lived feature on Saturn • This image is the first polar view using Saturn’s thermal glow at 5 microns (seven times the wavelength visible to the human eye) as the light source

11. Saturn’s “Little Red Spot” Unique red oval cloud feature in Saturn's southern hemisphere The difference in color between the red oval and surrounding bluish clouds indicates that material within the oval contains a substance that absorbs more blue and violet light than the bluish clouds The oval feature did not change in appearance for several months

12. Saturn’s Ring System • Discovered almost 400 ya • 7 major divisions • Labeled in order of their discovery • From inside out D,C,B, Cassini Division, A, F,G and E • Mainly water ice • Particles vary in color from white (pure water ice) to reddish, tan or brownish (dust) • Span 74,000km across • Main rings no more than a few hundred m’s thick

13. Saturn’s Ring System • Possible variations in chemical composition from one part of Saturn's ring system to another are visible as subtle color variations (Voyager 2) • Highly enhanced false-color image assembled from clear, orange and ultraviolet frames • In addition to the previously known blue color of the C-ring and the Cassini Division, additional color differences between the inner B-ring and outer region (where the spokes form) and between these and the A-ring can be discriminated

14. From left to right, the outer portion of the C ring and inner portion of the B ring • The B ring begins a little more than halfway across the image • The general pattern is from "dirty" particles indicated by red to cleaner ice particles shown in turquoise in the outer parts of the rings

15. Recent discoveries suggest rings are the rule rather than the exception • Three major hypotheses • Tidal disruption of a satellite or comet • Roche Limit • The smallest distance at which a planetary object that has no internal strength can orbit another body without being torn apart by the larger body's gravitational force • Too close an encounter • 10-100 possible comets over Saturn’s geologic life-span • Large impact on a satellite • Destruction of moon • Debris cloud formed into disk over time • Continued collisions created smaller particles • Halted accretion • Formed from primordial circumplanetary nebula • Halt due to gravitational effects of orbital resonances with nearby satellites

16. Braided F-Ring • Saturn's narrow F ring, just outside the main ring system, is a very complex structure • Made up of two narrow bright rings and a fainter ring inside them • Bright rings contain bends, kinks, and bright clumps that give the illusion that these strands are braided • Clumps may contain mini moons

17. Mimas(The Death Star Moon) • Nicknamed the Death Star after it’s similarity to the Star Wars spacecraft • The large crater on the right limb is named Herschel • 128km wide • one-third the diameter of Mimas • 9.6km deep, with a central mountain almost as high as Mount Everest on Earth • This impact probably came close to disintegrating the moon • Appears to be responsible for lack of ring material in the Cassini Division • Pan is located in the Enke Division

18. Iapetus • Bi-albedo surface • Dark material covers the leading side • So dark that no details within this terrain were visible • Likened to tar or asphalt • Organic substances, probably including poisonous compounds such as frozen hydrogen cyanide polymers • Two theories • (1) dark material may be organic dust knocked off the small neighboring satellite Phoebe and "painted" onto the leading side • (2) the dark material may be made of icy-cold carbonaceous "cryovolcanic" lavas that were erupted from interior and then blackened by solar radiation

19. Iapetus • Ancient, 400km wide impact basin (center of disc) • Heavily overprinted by more recent, smaller craters • Steep scarps descend to basin floor • Many scarps, as well as walls of nearby craters, appear bright, probably exposed outcrops of relatively clean ice • Most unique feature is a topographic ridge that coincides almost exactly with the geographic equator • On left horizon, the ridge reaches at least 12.8km above the surrounding terrain • Along the roughly 1280km length over which it can be traced (in this image) it remains almost exactly parallel to the equator • Origin not yet explained

20. Iapetus Landslide • A landslide within the low-brightness region (image from Cassini) • Unconsolidated rubble from the landslide extends halfway across a conspicuous, 120km flat-floored impact crater that lies just inside the basin scarp • Fact that landslide traveled many kms from basin scarp could indicate that the surface material is very fine-grained

21. Enceladus • Brightest object in SS • .90 albedo • Significant atmosphere • Constantly regenerated by volcanic outgassing • Not enough mass to hold for very long • Cryo-volcanically active • Tectonics?

22. Enceladus • Ice jets send particles streaming into space hundreds of kms above the south pole • Some particles escape to form the diffuse E ring • The bright strip is the E ring, in which this body resides • The small round object at far left is a background star • Jetted material appears to retard the rotation of Saturns magnetic field relative to the spin of the planet itself • This means that the rotation of Saturn as measured is probably in error

23. Enceladus Polar Ridge Complex“Tiger Stripes” • Plumes of water and other ice vapors jet from long linear fractures near the south pole • New topographic maps show the stripes do not have a lot of relief • Flanking ridges are typically 75 to 200m high while the grooves in between the ridges are 150 to 300m deep • Intensely deformed ridges along the edge of the south polar terrains (lower right) have relief of up to 1km or so • Vert relief exaggerated by a factor of 20

24. Left panel map of the south pole • Four prominent fractures, (informally called "tiger stripes“) cut diagonally across the south polar region • Right-hand panel map of the south polar heat radiation • A prominent warm region, appearing yellow and orange in this view, coincides with the locations of the tiger stripes • Some scattered close-up snapshots by the Composite Infrared Spectrometer showed that the heat radiation was concentrated along the tiger stripe fractures, but those snapshots covered only a small fraction of the south polar region

25. Tectonic Spreading Center? • Two side-by-side images compare a "twisted" sea-floor spreading feature on Earth, (an Offset Spreading Center (OSC)), to a very similar looking axial discontinuity, in the Damascus Sulcus "tiger stripe" • Left is a shaded relief map of bathymetry data along a spreading ridge on the East Pacific Rise • OSC's occur only along fast-spreading ridges (>4 in/yr) • The axial discontinuity on Enceladus’ Damascus Sulcus (right) twists in the same helical way that the OSC does on Earth • However, the morphological resemblance is no guarantee that both features are caused by fast spreadingCredit: NASA/JPL/Space Science Institute

26. Titan • In Greek mythology the Titans were a family of giants, the children of Uranus and Gaia, who sought to rule the heavens but were overthrown and supplanted by the family of Zeus • Discovered by Christiaan Huygens in 1655 • Fifteenth of Saturn’s satellites • 5150km diam • Long thought Titan was the largest satellite in SS but recent observations have shown it's atmosphere is so thick that its solid surface is slightly smaller than Ganymede's • Titan is nevertheless larger in diameter than Mercury and larger and more massive than Pluto

27. Similar in bulk composition to Ganymede, Callisto, Triton and (probably) Pluto • ~ half water ice and half rocky material • Probably differentiated into several layers • 3400 km rocky center surrounded by several layers composed of different crystal forms of ice • Interior may still be hot • Alone of all the satellites in the solar system, Titan has a significant atmosphere • Pressure is more than 1.5 bar (50% higher than Earth's) • Primarily molecular nitrogen (as is Earth's) with no more than 6% argon and a few % methane • Trace amounts of at least a dozen other organic compounds (i.e. ethane, hydrogen cyanide, carbon dioxide) and water • Organics form as methane (which dominates in Titan's upper atmosphere) is destroyed by sunlight • Result is similar to the smog found over large cities, but much thicker • In many ways, this is similar to the conditions on Earth early in its history when life was first getting started • This thick hazy atmosphere that makes it so hard to see Titan's surface Titan

28. This image shows two thin haze layers • The outer haze layer is detached and appears to float high in the atmosphere • Because of its thinness, the high haze layer is best seen at the moon's limb • Images like this one show key steps in the formation and evolution of Titan's haze • Process is thought to begin at altitudes above 250 mi, where ultraviolet light breaks down methane and nitrogen molecules • The products are believed to react to form more complex organic molecules containing carbon, hydrogen and nitrogen that can combine to form the very small particles seen as haze Titan

29. Huygens at Titan • Mosaic of three frames from the Huygens Descent Imager/ Spectral Radiometer (DISR) instrument provides detail of the high ridge area including the flow down into a major river channel from different sources • Note dendritic drainage pattern, a clear indication of surface, fluvial flow

30. Titans Seas and Dunes • Titan features dunes and lakes, one of which is larger than any lake on Earth and could be legitimately called a sea • Titan’s lakes are thought to consist of liquid methane and ethane • In places, the lakes reside in what appear to be nested, near-circular depressions, reminiscent of nested calderas • Dune fields interspersed with exposed bright mounds • In places, the dunes wrap around the bright mounds, which suggests the mounds are raised

31. Hyperion • View shows a low density body blasted by impacts • Scientists now think Unusually low density for such a large object • weak surface gravity • high porosity • Characteristics help preserve the original shapes of Hyperion’s craters by limiting the amount of impact ejecta coating the moon’s surface • Weak gravity, and low escape velocity • what little ejecta is produced has a good chance of escaping the moon • At 280km across, Hyperion’s impact-shaped morphology makes it the largest of Saturn's irregularly-shaped moons • Captured comet?

32. Hyperion