Transcript Rings and Moons of the Giant Planets Lecture 16: The Planets Homework • Read Chapter 11: Giant Planet Systems • Homework: Ch.11 MasteringAstronomy due Friday at 6pm.

Rings and Moons
of the Giant Planets
Lecture 16:
The Planets
Homework
• Read Chapter 11:
Giant Planet Systems
• Homework: Ch.11
MasteringAstronomy
due Friday at 6pm.
Midterm #2
• Next Tuesday, Nov. 4:
• Covers Chapters: 9, 10, 11, 14
• 30 Multiple choice questions
• Study Approach:
•
- Review Lectures (PDFs, webcast.berkeley.edu)
•
- For each topic, ask, “Do I really understand this?”
•
If not, read the book, or go to Off. Hours or Disc Session.
•
- Review all homework problems
•
- Go to Discussion Sections or Office Hours
•
for review and help.
Lecture Outline
1. Saturn’s rings: Made of icy particles
2. “Four Galilean Moons” of Jupiter
Io: Volcanic
Europa: Ice crust; Ocean below
Ganymede: Icy, craters
Callisto: More ice, craters
3. Moons of Saturn:
Titan: Methane atmosphere, lakes
Enceladus: Water Geysers!
Rings: All Four Giant Planets Have Them
Jupiter
Saturn’s
rings
labeled
A-F
Neptune
Saturn
Uranus
Saturn’s Rings: Names
Saturn’s Rings: Names
Saturn’s Rings: Faint Ones
Saturn’s Rings:
What are they made of ?
Clue: View the Rings from the back side.
Observe the scattering of sun light off the back-lit rings..
Saturn’s Rings:
View from Back Side: Not Lit by Sun
The Rings scatter light forward:
Like the silver-lining (edges) of clouds.
(Big rocks would be dark on the dark side.)
The rings must be composed of tiny particles.
Saturn’s
rings
labeled
A-F
Saturn’s Rings: Viewed Edge-On
Ring Thickness: Much smaller than tiny moons.
Saturn’s
rings
labeled
A-F
Saturn’s Rings:
What are they made of ?
Spectroscopy of Rings: Water Ice and Rock !.
Saturn’s Rings:
What are they made of ?
• Small, Dirty icy particles
• Ring particles orbit around Saturn
• Flat ring (few meters thick)
• Stray orbits cause collisions between particles:
Saturn’s Rings:
Artist’s Conception
Saturn’s Rings:
Artist’s Conception
• Small, Dirty icy particles
• Ring particles orbit around Saturn
• Flat ring (few meters thick)
Saturn’s Rings:
Artist’s Conception
Rings of Saturn: Made of Icy Rocks
Artist’s Conception
Saturn’s Rings
10 sec delay to start.
Saturn’s B-Ring and A-Ring
The ring’s outside edge is influenced by meddling moon Mimas, which orbits the planet once for every two circuits the icy ring particles complete.These
periodic gravity perturbations are thought to compress the ring particles into clumps, while maintaining the ring’s well-defined outer edge.Beyond
the B-ring lies the Huygens gap, the widest dark void visible in this image, punctuated only by the bright Huygens ringlet.
The 4800 km-wide Cassini Division separates the B-ring
from the outermost A-ring, but itself is marked out with faint, concentric strands of ring material.
Encke gap
The Moon “Pan”
orbits in the middle.
Image of a gap moon that creates
ripples ahead of itself.
Where do gaps
in the rings
come from?
Gap moons
The motion of moon Pan through the A ring's Encke Gap.
Shepherd moons
gravitationally sculpt the rings
The moons Prometheus
and Pandora shepherd
the F ring of Saturn.
Shepherding moons
Gravitationally Sculpt the Rings
The moons Prometheus
and Pandora shepherd
the F ring of Saturn.
Moons of Jupiter and Saturn:
Satellites of Ice and Rock
•
•
•
•
What kinds of moons orbit Jupiter and Saturn?
What makes Jupiter’s 4 large moons remarkable?
What makes Saturn’s moons extraordinary?
Why are small icy moons more geologically active
than small rocky planets?
Many moons …
• Jupiter has over 60 moons
• Saturn has over 30 moons
Medium &
Large Moons
• Enough self-gravity
to be spherical
• They are (or were)
geologically active
• Have substantial
amounts of ice
Medium &
Large Moons
• Circular, equatorial orbits
in same direction as
planet rotation
•  Formed in orbit
around jovian planets
Small moons
• Far more numerous than the medium and large moons
• Not enough gravity to be spherical: “potato-shaped”
Small moons
• Orbits are tilted,
elliptical, and even
going backwards!
• Captured asteroids, so
orbits have randomly
oriented orbits.
Jupiter’s 4 “Galilean” moons
Io
Europa
Ganymede
Earth’s Moon for scale
Callisto
Jupiter’s 4 “Galilean” moons
• Io has volcanoes
• Europa has an ocean under its ice
• Ganymede & Callisto may also have
sub-surface oceans
…but they’re so small???
Shouldn’t they be cold and geologically dead?
(like our moon and Mercury)
Jupiter’s moon Io:
Volcanos !
Prometheus Plume: ~75 km
Pillan Patera Plume: 140 km
Jupiter’s moon Io:
Volcanoes !
Jupiter’s Moon, Io
Are there any impact craters? No!
Io is the most volcanically active world in the solar system.
The surface is paved over by lava every century.
Jupiter's moon Io
Galileo spacecraft caught this volcanic eruption
Why is Io Volcanic?
Tidal Heating of Io
Io is squished and
stretched as it orbits
Jupiter
But why is its
orbit so elliptical?
Orbital Resonances
The grav. tugs add
up over time,
making all 3 orbits
elliptical.
Every 7 days, these 3
moons line up.
Which moon has the strongest
tidal heating?
(A) Io
(B) Europa
(C) Ganymede
(D) Callisto
Europa – A Water World
with a Sub-Surface Ocean?
Europ
a
Density: 3 g/cm3 (same as rock + ice); High reflectivity
(60%); Spectrum: absorption lines of water ice
Internal structure: metal-rich core, rocky mantle,
100 – 150 km thick crust composed of water/ice
Few Crater Impacts on Europa
Few large impact craters: Suggests 60 Myr surface age.
A couple of multi-ringed impacts: Penetrated 20 km thick ice!
Ridges and Cracks
in the ice surface of Europa
Ridges and Cracks
in the ice surface of Europa
Europa:
Is there life in its ocean?
Ganymede
• Largest moon in solar system (2x size of Earth moon)
• Very old geological activity
• Tidal heating expected - less than Io, Europa
Ganymede: tectonic features, but lots of craters
Bright grooved terrain and old, heavily cratered areas
Evidence of shear motion
G
a
n
y
m
e
d
e
Enki Catena Crater Chain On Ganymede Galileo Image
Callisto
• “Classic” cratered
iceball
• No tidal heating - no
orbital resonance
• Furthest from Jupiter
among all four
Galilean moons
Io: Fe/FeS core,
rocky mantle
Europa: Fe/FeS core, rocky
mantle, ~100 km water/ice
crust
Ganymede: Fe/FeS
core, rocky mantle, ice
crust
Callisto: ice/rock
mixture, icy crust.
Jupiter’s big
Moons
• Like a mini solar system
• Decreasing geological activity from
innermost to outmost satellite
(decreasing importance of tidal heating)
• Increasing amount of ice with increasing
distance from Jupiter
• Europa and Io are geological active now
Largest Moon of Saturn:
Titan
Atmosphere!
TITAN:
Atmosphere: very thick
90% Nitrogen
few% Methane, Argon
Surface Pressure: 1.5 Earth’s atm
Surface Temp: -180C cold!
Bulk Density: 1.9 g/cm3
(rock+ lots of ice)
Gravity << Earth’s
Voyager images
of Titan
Titan up close
Landed July 2004
Art by Craig Attebery
Saturn’s Moon: Titan
Lakes (radar-smooth regions)
Saturn’s Moon: Titan
Lakes (radar-smooth regions)
Saturn’s Moon: Titan
Lakes (radar-smooth regions)
Saturn’s Moon Titan: Mountains and rivers
Titan:
Fluid transported
cobbles of ice
15 cm
Saturn’s Moon:
Enceladus
Enceladus
Water Geisers on Enceladus
John Whatmough (extrasolar.net)
Water Geisers on Enceladus
John Whatmough (extrasolar.net)
Water Geisers on Enceladus
Water Geisers on Enceladus
John Whatmough (extrasolar.net)
Geisers on Enceladus
John Whatmough (extrasolar.net)
Why are small icy moons
more geologically active
than small rocky planets?
Why are small icy moons more geologically
active than small rocky planets?
• Hot interiors are necessary for geological
activity
• Ice deforms more easily than solid rock,
so less internal heat is required, and
smaller objects can be geologically active
• Tidal heating is not important for rocky
planets (except Io)