Lecture 29. Jupiter and the Galilean Moons;
Tides and Friction.
reading: Chapter 8
The Galilean Moons
First observed by Galileo in 1610 with a homemade telescope.
First saw 3 “stars” near Jupiter.
Next day, saw that they moved the “wrong” way.
A few days later, a 4th “star” appeared.
After a week, saw they moved with Jupiter, and changed position.
Provided support for the Copernican model of the solar system.
Not everything revolved around the Earth.
The largest of Jupiter’s
16 moons.
Earth: 12,700 km
Mars: 6,800 km
Moon: 3476 km
Properties
Surface
Crosssection
Diameter (km)
Average
density
Orbit (Earth
days)
Io
3643
highest
(rocky)
1.77 (x)
Europa
3122
3.55 (2x)
Ganymede
5262
7.16 (4x)
Callisto
4821
lowest (icy)
16.69 (9.5x)
Orbits
Density decreases with distance from Jupiter.
All orbit in a plane around Jupiter.
Io orbits every 1.7 Earth days.
IEG in orbital resonance (1:2:4)
Nearly all the Moons are in synchronous rotation the same face always turned towards Jupiter
What does this imply
about the formation
of the Galilean
Moons?
a simulation
In this location, have more ices than rocky
elements, so bodies tend to be more icy
Average density of Jovian Moons lower than Earth’s density
Jupiter’s Moons: largely water-ice
Uranus’ Moons: larger amounts of methane and ammonia ice
Jupiter’s Other 12 Moons
-are smaller
-have irregular shapes
-orbits are highly elliptical
-orbits not in the plane of the Galilean Moons
-some are rocky and some are icy
What does this imply
about the formation
of Jupiter’s small
Moons?
Io
Rocky moon - composed of molten silicate rock
Has a core of Fe
Big surprise to Voyager scientists - geologically active.
Few if any impact craters.
Hundreds of calderas - huge volcanic craters
Voyager showed active plumes erupting 300 km high
Plumes are constant eruptions - like geysers.
Gravity is 1/6g.
Erupting material: some form of sulfur (SO2?)
Turns to sulfur snowflakes when it hits the cold of space.
Eruptions change rapidly.
4 months between V1 and V2: some volcanoes started, others
stopped, deposits surrounding the vents changed
Most of the plumes were stable
Volcanoes on Io
Io’s hot spots: 125 trillion watts!
Volcanic activity was predicted in a research paper published one
week before V1 flyby of Jupiter.
Little or no water on Io. Why is that?
Lakes of molten sulfur
Extensive flows of sulfur (?) -> colors
S2 gas erupted from vents, turns into S3 & S4 (red) then S8 (yellow)
Volcanoes have T’s of 1500˚C - basalt lavas
Europa
Similar in bulk composition to Io, but has a thin layer of ice.
Layered internal structure.
Ice layer, few km thick?
Liquid water layer, 50 km thick?
Only 3 craters > 5 km across.
Age of the surface unknown.
Little topography: few features > few hundred meters high
Images resemble sea ice on Earth.
Has an extremely thin atmosphere of O2 (10-11 bars)
Bands
Surface fractured creating dark linear, curved, wedge-shaped bands
Breaks ice into plates of 30 km across.
Areas between plates filled with icy slush and rock (?)
Ice Rafts/Chaos Regions
Plates ~13 km across.
Broken apart, floated
into new position,
refroze.
Ice must have been
watery or soft.
Looks like pack ice
in the Earth’s
polar regions.
False-color image.
Reds & browns:
contaminants in
the ice
Ridges
Cross-cutting
Faults
Form by compression
Are 8km wide
Forces change direction
Generations of Ridges
Tides
Gravity of the Moon attracts matter on
the Earth
Matter closest to the Moon feels more
gravitational interaction
Causes distortion.
Force not enough to affect rock.
But it does affect water.
Two tidal bulges on the Earth
A. water pulled toward the Moon
B. Earth pulled toward the Moon
(away from the water)
Tides, cont.
Tides move because Earth rotates.
animation.
As the tidal bulge rotates, the Moon’s
gravity pulls at the bulge.
This causes drag/tidal friction.
This slows down the Earth’s rotation
by 1 sec/50,000 years.
image copyright: Nick Strobel’s
Astronomy Notes
www.astronomynotes.com
Earth and Moon losing rotational
energy, are slowly moving apart.
Tides on Moons
The Earth also raises tides on the Moon.
Drag/friction slowed down the Moon’s rotation until the
tidal bulge never moved.
Earth is now locked into synchronous orbit.
Planets have higher gravitational fields than Moons,
so Moons go into synchronous orbit.
Jupiter is so big, it Moons were likely locked into
synchronous orbit a few million years after formation.
Tidal friction generates drag and heat.
Tides on Io
Changing tidal bulge on Io causes the Moon to be
stretched and squeezed.
Io in a tug-of-war with Jupiter, Europa, and Ganymede:
Tidal bulges in the solid crust
of Io 100 meters (Earth: ~1 m)!
Flexing causes heating.
Tides on Europa
Tidal heating also of Europa.
Tidal heating melting ice and making a liquid water ocean.
QuickTime™ and a
TIFF (Uncompressed) decompressor
are needed to see this picture.
QuickTime™ and a
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Water circulating through heated mantle material - producing
hydrothermal vents.
Lecture 30. Jupiter and the Galilean Moons;
Magnetic Moments.
QuickTime™ and a
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reading: Chapter 8
Ganymede