Transcript Document

The Jovian Planets - Jupiter
Diameter = 11.2 x Earth’s
Density = 1.33 x water
Rotates in 9h 50min. at equator, 9h 55min.
at poles, giving violent weather.
Atmospheric composition 82% hydrogen,
18% helium, traces of other elements;
similar to Sun’s. Atmosphere ~1000 km
thick, clouds of ammonia crystals visible,
liquid ammonia and water ice lower down.
Pressure and temperature increase inwards
so hydrogen becomes liquid then metallic becomes a good conductor of electricity so
Jupiter has a strong magnetic field.
Core may be molten rock at 40,000 K.
Still cooling, Jupiter gives out twice as much
heat as it receives from the Sun.
Has four major “Galilean” satellites, Io,
Europa, Ganymeade and Callisto, many
minor moons and a ring system.
PHYS1142
56
Jupiter’s Moons
Io
About the size of our Moon.
Very thin sulphur dioxide atmosphere.
Active volcanoes - hot interior due to tidal
heating - spew out liquid sulphur at 400 K.
Hence, young surface, no craters visible.
Europa
Surface made up of water ice, density
implies a rocky interior.
Surface is cracked and almost crater free.
Colouring of cracks suggests that dirty
water may have erupted from a hypothetical
underlying water ocean.
Varying magnetic field consistent with
liquid layer beneath surface, tidally heated.
PHYS1142
57
Jupiter’s Moons
Ganymede
Largest moon in the Solar System - bigger than
Mercury.
Cratered region and grooved region.
Craters up to 150 km wide - flat, suggesting
surface flows over time. Surface is dark from
accretion of rocks and carbon-rich materials.
Grooved region is lighter, most probably water
ice mixed with rock; cracking up under stress.
Density suggests ice crust lies over a water/ice
mantle surrounding a rocky core.
Callisto
Heavily cratered implying an old surface estimate 4000 million years old.
Craters shallow due to flow of ice/rock crust.
Density indicates ice/rock crust over water/ice
mantle and rocky core.
PHYS1142
58
Jupiter’s Moons - Life Signs?
Best bet - Europa.
Observations are consistent with a liquid
water ocean below the surface. Comparison
with Io suggests that there may be volcanic
vents on the ocean bed.
Organic cyanides (nitriles) containing CN
group found on Ganymede and Callisto.
Life exists on Earth under similar
conditions near the Mid-Atlantic Ridge in
the form of thermophylic bacteria.
PHYS1142
59
The Jovian Planets - Saturn
Diameter = 9.45 x Earth’s
Density = 0.7 x water i.e. it would float!
Atmospheric composition 96% hydrogen,
3% helium, traces of other elements. Cloud
belts, differential rotation and weather
similar to Jupiter (not as violent), but haze
above clouds makes colours less dramatic.
Interior likely to be liquid hydrogen and
metallic hydrogen.
Like Jupiter, it has a strong magnetic field.
It radiates more heat than it receives,
maybe due to falling helium rain??
Most prominent feature is the ring system.
Voyager spacecraft revealed complex
structure with small “shepherd” satellites
stabilising rings. Rings made up of water
ice and rocky particles ranging from dust
grain-sized to tens of metres.
PHYS1142
60
Saturn’s Moons
Titan
Diameter = 5120 km
Surface temp. = 94 K
Density = 1.9 x water
Atmospheric pressure = 1.5 x Earth’s
Density suggests surface crust and mantle are
ice surrounding a rocky core.
Atmosphere mostly nitrogen, 1% methane.
Also hydrocarbons such as ethane, propane,
acetylene, trace of water discovered.
Covered in orange smog - cannot see surface.
Ultraviolet light from sun converts methane
to heavier hydrocarbons, so methane should
run out in a few million years, but Titan is
4500 million years old.
So, must be a source of methane - volcanism?
Heavier hydrocarbons e.g. ethane are liquid
at 94 K, so fall as rain  oceans?
PHYS1142
61
Saturn’s Moons
Titan continued...
Evidence?
Bounce radio waves off surface - amount
reflected is too high for all liquid ocean; could
be due to ice continents.
As part of the Cassini Mission to Saturn,
launched in 1997, the Huygens probe was
dropped onto Titan at 9am on 14th January
2005 
“squelch-down”
Huygens landed on a surface with a texture
like crème brulée - water ice grains of a sandy
consistency soaked with liquid methane?
Surface at landing site shows signs of
weathering and erosion.
Turbulent atmosphere encountered during
Huygen’s descent - methane clouds.
Cassini Orbiter radar images show what look
like drainage channels, river beds and shore
lines.
PHYS1142
62
The Jovian Planets - Uranus
Twice as far from the Sun as Saturn (see
lecture 2). Getting colder  58 K.
Density = 1.27 x water
Atmosphere of hydrogen, helium, methane,
ammonia and water above a mantle of ices
and rock, with a rocky core at the centre.
Rotation axis in plane of orbit; at present
its south pole points towards the Sun.
Figs. Z11.30 & K9-36
Its moons are rocky and icy and show
cratering and grooving.
Miranda has the most complex surface
with signs of tidal heating.
Has a tenuous ring system discovered in
1977. Rings are dark - probably particles
contain carbon and are bare of ice.
PHYS1142
63
The Jovian Planets -Neptune
Warmer (60 K) than expected due to solar
heating (44 K) - must still be cooling down.
Density = 1.64 x water
Atmosphere is hydrogen, helium and a little
methane giving it a bluish colour.
Neptune has four rings similar to Uranus’.
Only moons known before Voyager’s fly-by
in 1989 were Triton and Nereid.
Triton shows volcanic activity - a cracked
crust with relatively fresh ice. It is in a
retrograde orbit (east-to-west) inclined at
23o to Neptune’s equator.
Nereid has a highly eccentric orbit.
Perhaps Triton and Nereid were not
associated with Neptune when they were
formed and have since been “captured”.
PHYS1142
64
Pluto and Charon
Pluto’s distance from the Sun varies from
30 AU to 49 AU - it was closer to the Sun
than Neptune was from 1979 - 1999.
Its maximum temperature is about 60 K.
Density = 2.1 x water - consistent with
composition being 75% rocky, 25% ices.
Surface coated with solid methane, solid
nitrogen and solid carbon monoxide. The
same molecules form a very tenuous gaseous
atmosphere.
Composition shows similarities to Neptune’s
moons.
May be an escaped moon of Neptune - could
be related to cause of Triton’s retrograde
orbit if there was a close encounter?
Charon is Pluto’s (largest) moon and is about
half its size, in fact more like a companion
dwarf planet. It may consist of ices.
PHYS1142
65