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Lecture #30: Satellites and Rings I
The Main Point
• Satellites of the giant planets:
– Io, Europa, Ganymede, and Callisto.
There are 6 large, 12 mid-sized, and more than
100 small planetary satellites in the outer solar
system, and many of these have had complex
surface and even atmospheric histories.
– Titan.
Titan
– Triton.
– And many other smaller worlds...
• Reading: Chapters 11.2-11.3.
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Overview
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Major Properties
• Distinct and important
differences in density,
composition, and
orbital properties
• Io has volcanoes!
• Europa has an ocean?
• Titan has a thick
atmosphere and lakes
on surface.
• Triton has a thin
atmosphere (very
similar to Pluto?)
• Many other small icy
satellites.
• Jupiter:
– 4 large "Galilean satellites"
• Io, Europa, Ganymede, Callisto.
– dozens of other small satellites.
• Saturn:
– Titan: large moon with a thick atmosphere.
– 6 medium, dozens of small satellites.
• Uranus:
– 5 medium, dozens of small satellites.
• Neptune
– Triton: large moon with a thin atmosphere.
– 1 medium, dozen of small satellites.
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Relative sizes of the major satellites
of the outer planets and other objects.
Major Satellites
of Jupiter
Io
• New worlds discovered
by Galileo in 1610.
• A "mini solar system"
around Jupiter.
• Io:
Classification:
• Large (D>1500 km): active and ongoing
geology.
• Medium (D>300 km): evidence for some
geologic activity in the past.
• Small.
Europa
– Active volcanoes!
• Europa:
Ganymede
– Subsurface ocean?
• Ganymede:
– Large-scale tectonism.
• Callisto:
– Battered surface.
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Callisto
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Sizes (not distances) to scale
Io ("EYE-oh")
• Inner Galilean moon.
• Most volcanically-active world in the solar system!
• Interior melted by tides from Jupiter.
I ' A
Io's
Amazing
i L
Landforms!
df
!
Density:
3.57 g/cm3
• Volcanic calderas several km deep.
• Lakes of molten sulfur.
• Mountains that are NOT volcanoes.
• Lava flows hundreds of km long:
Eccentricity not
exactly 0 because
of resonance with
outer moons.
Low viscosity fluid (sulfur rich?)
Flow temperatures > 1000°C to 1500°C.
• Volcanic vents.
• Io's color caused by sulfur compounds
(white is sulfur dioxide frost).
Tidal energy heats
the interior!
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Ganymede
Europa
• Icy surface with
bright & dark areas.
• Many more craters
than Europa (older).
• But craters degraded
or “softened”.
• Extensive network
of tectonic ridges.
• Ice-covered Moon.
• flat flat flat!
• Crust broken up
into moving plates!
• "salty" deposits well
up between plates
• Subsurface ocean??
Map of salt-rich "contaminants" in Europa's crust
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Callisto
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Galilean Satellite Interiors
• Ancient, heavily
cratered surface.
• Bright icy deposits.
• Dark "powdery"
coating of unknown
composition.
co
pos o .
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HST
Infrared
Titan
Major Satellites of Saturn
•Titan:
– Larger than Mercury!
– Thick atmosphere!
•6 mid-size moons:
Voyager 2
– All icy.
i
– All heavily cratered.
– But different crater
densities, implying
unique resurfacing
histories.
• Thick, hazy atmosphere, with lots
of hydrocarbons:
- formed by sunlight breaking
up CH4 molecules.
- similar to early Earth?
• Surface pressure: 1.5 bars!
• Surface temp.: 95K (-290°F).
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Titan Images
from Cassini
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Huygens Probe Descent to Titan
Jan 14, 2005
• Sequence of images taken by the Descent
Imager/Spectral Radiometer (DISR)
instrument.
UV image of Titan’s
night side limb
reveals haze layer.
Image from
the Huygens
probe reveal
surface flow
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•The sequence starts from an altitude of 152
kilometers (about 95 miles) and initially only
shows a hazy view looking into thick cloud.
•As the probe descends, ground features can
be discerned and Huygens emerges from the
clouds at around 30 kilometers (about 19
miles) altitude.
•The ground features seem to rotate as
Huygens spins slowly under its parachute.
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First color view of Titan’s surface.
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Mid-sized icy Saturnian moons...
Mid-sized icy Saturnian moons...
Enceladus
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Tethys
Dione
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Rhea
Mimas
Iapetus
Major Satellites
of Uranus
Geyser-like “plumes” on Enceladus!
• 5 mid-size moons.
• All icy.
• All fairly dark.
• All heavily cratered:
– But: Evidence for resurfacing, tectonism, and other processes.
Miranda
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Ariel
Umbriel
Titania
Oberon
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Triton: Neptune's
only large satellite
• Nearly same size and density as Pluto:
– Triton: R = 1350 km; ρ = 2.08 g/cm3.
– Pluto: R = 1140 km; ρ = 2.07 g/cm3.
• Bizarre retrograde orbit and high tilt:
5 km cliff!
– is Triton a "captured Pluto"?
•
•
•
•
•
Miranda
• Tiny moon (< 500 km diameter).
• Yet some of the strangest and least
understood geology in the solar system!
• Recall that out here, ice acts like rock.
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Surface is bright: albedo = 0.7 to 0.8.
Surface temperature only ≈ 35K (-391°F).
Thin atmosphere! Pressure = 0.01 mbar.
Few craters: Surface is “young”.
Voyager discovered active geysers!
– “volcanoes” of ice and other volatiles.
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Triton's Active Surface
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Small Satellites
Ice "volcanoes"?
• 100+ other smaller rocky/icy worlds known.
• Could be a few hundred more to be found…
• Two major classes:
– Small inner satellites (often ring shepherds).
– Small and distant outer "irregular" satellites.
• All are irregular in shape.
• Many may be captured asteroids or comets.
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Triton geyser model
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Outer Uranian moon
Proteus (Neptune)
Cassini Views of Saturn’s Small Satellites…
Janus
Inner satellites of Jupiter
Pandora
Hyperion
Hyperion
Small satellites
of Saturn
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Telesto
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• Ring Systems
• There are 6 planet-sized moons in the outer solar
system, and each has unique and complex traits:
– Overview of rings:
Io: Active volcanism, extremely young surface.
Europa: Active "plate
plate tectonics
tectonics";; subsurface ocean?
Titan: Thick smoggy atmosphere; early Earth analog?
Triton: Active geysers; Pluto/Kuiper Belt clone?
• Jupiter,
p , Saturn,, Uranus,, Neptune.
p
– What are rings made of?
– How do they form?
• There are about a dozen mid-sized icy satellites,
with evidence for complex surface geology.
• There are more than 100 other small, irregular
moons that may be captured asteroids or comets.
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Next Lecture...
Summary
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–
–
–
Calypso
Epimetheus
• Reading: Chapters 11.2-11.3
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