Enceladus
Cassini
Titan
Cassini
Moons of Jupiter and Saturn
PTYS/ASTR 206
Io
New Horizons
Moons of Jupiter and Saturn
4/12/07
Europa
Galileo
Announcements
• Reading Assignment
– Chapter 17
• 5th homework due now.
– The 6th (and final!) homework is now posted on the
website (due Tuesday, April 24th)
• Reminder about term paper – due April 17.
– Details of turnitin.com
• Go to www.turnitin.com
• Click on “new users”
• Class ID: 1868418
PTYS/ASTR 206
usertype  student
Password: Section2
Moons of Jupiter and Saturn
4/12/07
Announcements (cont.)
• Mission Updates?
• Next study-group session is Monday, April 16, from
10:30AM-12:00Noon – in room 330.
• Movie Night
– Monday April 23rd 6:30PM, this room
– Which Movie?
• “Deep Impact” or “The Day After Tomorrow”
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Moons of Jupiter and Saturn
4/12/07
• The innermost
Galilean satellite
Io
• Looks like a pizza
• The most geologically
active body in the solar
system.
• Its surface is the
youngest in the solar
system
– no impact craters
are known.
• Io has so many active
volcanoes that its
surface is repaved
completely (to a dept
of 1m) every 100 years
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Moons of Jupiter and Saturn
4/12/07
Tidal Flexing of Io
• Io suffers extreme tidal flexing because of the competing pulls of its giant
planet and its three neighboring moons.
– When Io moves inward (toward Jupiter), the tidal deformation
produced by Jupiter increases;
– Has ~2.5W/m2 of internal energy (Earth only has 0.06 W/m2)
• In one 41-hour orbit,
parts of Io's surface can
rise and fall more than
300 feet, the equivalent
of a 30-story building.
– During these
repeated
deformations friction
in the interior of the
moon generates
tremendous
amounts of heat.
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Moons of Jupiter and Saturn
4/12/07
Io’s active eruptions and lava flows
• Galileo has imaged an active or recent lava
flow, still hot as suggested by its orange
color. This is the first time a "living" flow has
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of Jupiter and
Saturn
been seen
on any other Moons
planetary
body:
4/12/07
Io’s plasma torus
• Jupiter’s charged particles
bombard Io and Io’s volcanic
plume ejecting particles into
space
• This creates a huge donutshaped ring of charged particles
(mostly sulfur) around Jupiter the
size of Io’s orbit
• This can be seen from Earth with
special filters
Aurora on Jupiter linked to Io
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Moons of Jupiter and Saturn
4/12/07
Europa
• Smallest of the Galilean satellites
• One of the brightest objects in
the solar system
– Albedo = 0.64
• Very smooth
– No mountains (>1 km)
• Few craters
• The spectrum of reflected
sunlight off of its surface closely
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Moons of Jupiter and Saturn
resembles water ice
4/12/07
• Europa is crisscrossed by
numerous fractures and ridges.
Europa
• There are also features
reminiscent of ice flows
• It is believed that the surface of
Europa consists of 10-30km of ice,
which lies over a very deep (100200km) water ocean
– Maintained as a liquid because
of energy arising from tidal
forces from Jupiter, and other
moons
• Europa’s mean density is about
3000 kg/m3. This is considerably
higher than water
• Thus, it is mostly made up of
rocky silicates. The water and ice
make up the outer layers of the
moon.
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Moons of Jupiter and Saturn
4/12/07
Cycloidal Features on Europa
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Moons of Jupiter and Saturn
4/12/07
Liquid water under
Europa’s surface
• The cycloidal geologial features were
explained by Randy Tufts and Gregg
Hoppa of LPL
– They are caused by tidal stresses
arising from Jupiter’s moons Io and
Ganymede
• Indicates the presence of large liquid
ocean underneath a layer of ice
• More direct evidence came from
Galileo measurements of an induced
magnetic field that is caused by a
conducting layer of salty water (brine)
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Moons of Jupiter and Saturn
4/12/07
Europa Ridges
• Often made of
multiple ridges
• Some aren’t straight
• Not all the same age
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Moons of Jupiter and Saturn
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Formation of Ridges on Europa
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Moons of Jupiter and Saturn
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Ice Floes on Europa (and Earth)
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Moons of Jupiter and Saturn
4/12/07
Lenticulae
• Local dark regions are
probably due to ruddy,
warmer ice rising from
below
• This indicates a
convection process.
• The energy for this is
likely due to tidal forces
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Moons of Jupiter and Saturn
4/12/07
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Moons of Jupiter and Saturn
4/12/07
• It has a larger diameter than Mercury,
but only about half its density
– Ganymede density ~1.9 g/cm3
Ganymede: The
Largest Satellite in
the Solar System
• Many surface craters
• The surface is mostly water ice and is
characterized by large bright and dark
regions (similar to the moon)
– Dark areas are more heavily
cratered
• OLDER
– Bright areas are less cratered
• YOUNGER
(Note that his is opposite to the case
of our Moon !)
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Moons of Jupiter and Saturn
4/12/07
Geological Activity on Ganymede
• Two types of terrain are found on the icy surface of Ganymede:
– areas of dark, ancient, heavily cratered surface (covered with
a layer darker material?)
– regions of heavily grooved, lighter-colored, younger terrain
(younger,
icy, reflective
material?)
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Moons
of Jupiter and Saturn
4/12/07
Ganymede’s magnetosphere
• Surprisingly, Ganymede has
its own magnetic field (and
magnetosphere)
– It is the only Moon to have
a strong global magnetic
field
– Stronger than Mercury’s
magnetic field
• Indicates a moving
conducting liquid interior
• Possibly left over heat
from formation (odd!)
• Possibly due to
electromagnetic heating
from Jupiter
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Moons of Jupiter and Saturn
4/12/07
Callisto:
The outermost Galilean Satellite
• Most heavily cratered body in the
solar system
– Geologically dead
– Oldest surface in the solar
system
• Darkest of the Galilean satellites
– but still twice as reflective as
our moon!
• Slightly larger than Mercury, but
only 1/3 of its mass
– Callisto density ~ 1.9 g/cm3
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Moons of Jupiter and Saturn
4/12/07
• While it has many craters,
there are very few with
diameters that are smaller
than 1 km
– Unlike Ganymede
– This is puzzling since
they both should have
the same bombardment
history
– Probably eroded away
(but how?)
• Covered by layer of rustycolored material
– Not known what this is
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Moons of Jupiter and Saturn
4/12/07
Callisto
• Discovered by Christiaan
Huygens in 1655.
• 2nd largest satellite in the solar
system (only Ganymede is larger)
– Larger than Mercury
Titan
(Moon of Saturn)
• Has a thick atmosphere
– Higher pressure than Earth at
its surface (more gas) – by
about a factor of 1.5
– Only moon in the solar system
with a thick atmosphere
• Density is 1.9 g/cm3 (similar to
Ganymede and Callisto)
– Probably about ½ rock - ½ ice
• Synchronous rotation with Saturn
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Moons of Jupiter and Saturn
4/12/07
Titan has a thick, opaque atmosphere rich
in methane, nitrogen, and hydrocarbons
• Titan’s atmosphere is mostly nitrogen
– Ammonia (abundant in the outer
solar nebula) is disassociated by
solar UV
– The liberated H2 escapes (weak
gravity) leaving N2
• A variety of hydrocarbons are
produced in the atmosphere by the
interaction of sunlight with methane
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• These compounds form an aerosol
layer in Titan’s atmosphere
– Which leads to the “haze” that
shields Titan’s surface from view
– They can also exist in liquid form
Moons of Jupiteron
and Titan’s
Saturn
surface
4/12/07
Beneath the Haze:
Images from the Huygens lander
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Moons of Jupiter and Saturn
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Moons of Jupiter and Saturn
4/12/07
Titan’s surface
• Visual evidence from Cassini suggests that Titan’s surface is
quite young.
– it has few craters and possibly even some evidence of
cryovolcanic activity
• Titan’s surface has evidence of lakes of liquid methane.
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Moons of Jupiter and Saturn
4/12/07
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Moons of Jupiter and Saturn
4/12/07
• The lakes may be
filled in by
precipitation (a)
– methane rain!!
• Or they may be
filled in from below
through a “methane
table” below the
surface (b)
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Moons of Jupiter and Saturn
4/12/07
• The 6 moderate sized
moons of Saturn all
rotate in prograde orbits
close to Saturn’s equator
More of Saturn’s Moons
Closest to Saturn
• They are all in
synchronous rotation
with Saturn
– Tidally locked
• All have low densities
(smaller than the
Galilean satellites)
indicating they are made
primarily of ices with
very little rock.
– Densities < 1.4 g/cm3
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Moons of Jupiter and Saturn
4/12/07
Farthest from Saturn
Enceladus
• Discovered by William
Herschel (who also
discovered Uranus) in
1789
• Density
– 1240 kg/m3
• Its albedo is 0.99
– The highest of any
object in the solar
system
– Reflects nearly all light
incident
on it!
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Moons of Jupiter and Saturn
4/12/07
Cassini images of a “spray” emanating from Enceladus
Evidence of liquid water beneath the surface?
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Do these particles populate Saturn’s E ring?
Moons of Jupiter and Saturn
4/12/07
The “Tiger Stripes” of Enceladus: Local hot spots
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Moons of Jupiter and Saturn
4/12/07
What is the source of the
“Fountains of Enceladus” ?
• The water may be liquid lower
down and shot out like a geyser.
• How is the interior kept warm?
Enceladus is a small moon and its
interior should have died long ago.
– In fact, its surface is quite
young (less than 100 million
years old)
– Possibly heating from tidal
forces from the other moons
and Saturn (it is in 2:1 orbital
resonance with Dione).
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Moons of Jupiter and Saturn
4/12/07