Transcript 20gasgiantmoons2s

The Moons of the Gas Giants
Astronomy 311
Professor Lee Carkner
Lecture 20
The Group of Seven
There are seven large (diameter >2000 km)
satellites in the solar system







Each is a distinct world of its own
Jupiter’s Lovers
Io, Europa and
Callisto were
Jupiter’s lovers in
Greek mythology

Saturn was the king
of the Titans

The Galilean Moons
Discovered by Galileo in 1610

Studied by Voyager 1 and 2, HST and
Galileo (the spacecraft)

Orbits of the Galilean Moons
All are tidally locked to Jupiter in a 1to-1 ratio
1
The periods of the orbits of the 3 inner
moons are in a 1:2:4 ratio


Formation of the Galilean
Moons
The inner parts of the nebula were hotter than
the outer


The inner 3 satellites experienced tidal
heating and differentiated into a rocky core
and an icy crust

The Interiors of the Galilean Moons
Galileo Visits the Galilean Moons
The Galileo spacecraft arrived at Jupiter
in 1995 and has been studying the
moons from Jupiter orbit ever since




Galileo at Io
Surfaces of the Galilean Moons
Io
Io is the most volcanically active world in the solar
system

These changing forces squeeze and flex Io producing
heat

The interior heat has also produced a differentiated
interior

Volcanism on Io
Io has no impact craters

Volcanoes produce plumes of material
that extend up to 280 km above the
surface

Volcanoes can be very long lived

Io’s Plasma Torus
Io’s volcanoes put lots of ions into its
orbit

The ions are effected by Jupiter’s
magnetic field producing a plasma
torus

Europa
Europa’s surface is covered with a layer
of ice

Water flows up to the top continually
resurfacing Europa


Tidal flex may also crack the surface
Evidence for Warm Oceans on
Europa
Europa has ice rafts where the surface has been
broken up and reassembled

Europa also has smooth areas where water has
flowed up and re-frozen
Galileo magnetometer measurements indicate that
Europa has a variable magnetic field



Models for the Interior of Europa
Ganymede
Ganymede is the largest moon in the solar system


Ganymede should have little tidal heating due to its
distance from Jupiter

Ganymede must have had more geological activity
in the past

The Surface of Ganymede
Ganymede shows 2 types of surface features
Old dark terrain


New bright terrain


Callisto
Callisto is the most distant Galilean moon
from Jupiter
It has experienced the least tidal heating

Callisto shows few signs of interior or surface
activity

Large impact basin Valhalla


Titan
The second largest moon in the solar
system

Only moon with an atmosphere

Why does Titan have an atmosphere?


Titan’s Atmosphere
Titan has a thicker atmosphere than the Earth

Titan’s atmosphere may have originally been
composed of ammonia (NH3) and methane
(CH4)

90% of the atmosphere is N2

Chemicals in Titan’s Atmosphere
Titan’s atmosphere also contains hydrocarbons
(composed of H and C) and polymers (long chains of
H, N and C)


Titan may have the necessary organic material to form
the building blocks of life

Triton
Triton is in a decaying, highly inclined (23
degrees), retrograde orbit

Triton shows evidence of geologic activity




When Triton was first captured it was probably in
a highly eccentric orbit which resulted in tidal
heating
Triton’s Atmosphere
Triton has a very thin nitrogen atmosphere
(1.6 X 10-5 atmospheres of pressure)

A little bit of nitrogen evaporates to
produce the atmosphere

Summary
The six large moons of the gas giants
resemble the terrestrial planets of the
inner solar system
They can have volcanoes, atmospheres,
and evidence of resurfacing
In general they are cold and have rocky
interiors and icy exteriors
Some produce internal energy through
tidal heating
Europa and Titan may possibly have
the conditions for life to exist
Summary: Io and Europa
Io
Strong tidal heating produces massive volcanism
Volcanism produces powerful outgassed plumes,
sulfurous surface and plasma torus of ions
Europa
Icy surface shows evidence for water flowing up
from interior
May have a warm subsurface ocean due to tidal
heating
Summary: Ganymede and
Callisto
Ganymede
Shows both old dark terrain and bright new
terrain
Must have had more internal heat to drive
geologic activity in the past
Callisto
No tidal heating results in no differentiation
Fairly uniform mixture of icy and rock with many
craters
Summary: Titan and Triton
Titan
Large size and low temperatures results in an
thick atmosphere
Atmosphere composed of nitrogen, methane,
hydrocarbons and polymers
Triton
Has a decaying, inclined retrograde orbit
Thin atmosphere and surface activity