Download Jovian Planets

Jovian Planets
Fall, 205
Astronomy 110
1
Jovian Planets
•
•
•
•
Bigger & more massive
Lower density, different composition
Rings
Numerous moons
Fall, 205
Astronomy 110
2
Jovian Planet Formation
• Formed beyond the frost line, planetesimals could
accumulate ice.
• Hydrogen compounds are more abundant than
rock/metal.
• Jovian planets got bigger and acquired H/He
atmospheres.
• The jovian cores are very similar: ~10x Earth masses
• Differences are in the amount of H/He gas accumulated.
Fall, 205
Astronomy 110
3
Jovian Planet Formation:
How Differences Arise
• TIMING: the planet that forms earliest
captures the most hydrogen & helium gas.
Capture ceases after the first solar wind
blew the leftover gas away.
• LOCATION: the planet that forms in a
denser part of the nebula forms its core first.
Fall, 205
Astronomy 110
4
Jovian Planets - Composition
Fall, 205
2
Density (g/cc)
1.5
1
0.5
0
Ju
pi
te
Sa r
tu
U rn
ra
N nu
ep s
tu
ne
• Jupiter & Saturn: almost
all H & He, very little
metal & rock (less dense)
• Uranus & Neptune: <50%
H & He, the rest hydrogen
compounds (water,
methane, ammonia), with
some metal & rock (more
dense)
Astronomy 110
5
More massive planets
could even be smaller!
• Jupiter and Saturn are nearly the same size
• But Jupiter is 3x more massive than Saturn
Fall, 205
Astronomy 110
6
Jovian planets: Internal Structure
• No solid surface.
• Layers under high pressure and
temperatures.
• Cores (~10 Earth masses) made of hydrogen
compounds, metals & rock
• The layers are different for the different
planets.
Fall, 205
Astronomy 110
7
Layers Differ in Phase
Density of water is ~1g/cm3
Metallic hydrogen conducts
electricity; it is not solid.
Core is hydrogen compounds,
metals, rocks. But 10 x the mass
of Earth inside a volume the size
of Eath.
Jupiter
Fall, 205
Astronomy 110
8
Why different?
• Less mass → less gravity → less compression.
• Boundaries of the layers are deeper in less massive
jovian planets.
• The physical states of the cores of the less massive jovian
planets are less extreme - could be liquid.
Fall, 205
Astronomy 110
9
Magnetic Fields
• Jupiter has a powerful magnetic field generated by its
rotating, convecting layer of metallic hydrogen.
Fall, 205
Astronomy 110
10
The Jovian Planets: Appearance
Colorful surface features:
Bands and Clouds of differing
compositions
Complex Weather Systems
High Wind speeds
Storms, some long-lived
Fall, 205
Astronomy 110
11
Planet colors
Jupiter’s
colors
• Ammonium sulfide clouds reflect red/brown.
• Ammonia, the highest coldest layer, reflects white.
Fall, 205
Astronomy 110
12
Planet colors
Saturn’s
Colors
Saturn’s layers are the same, but deeper in and
farther from the Sun --- more subdued.
Fall, 205
Astronomy 110
13
Uranus and Neptune’s upper layers are colder still,
allowing methane to condense.
Methane gas absorbs red light and transmits blue
light reflected by clouds
Fall, 205
Astronomy 110
14
Jupiter winds and storms
• Earth’s rotation makes storms ‘spin’.
• Jupiter’s fast rotation stretches storms in to
bands that surround the planet.
• High east/west winds (up to 400 km/hr)
Fall, 205
Astronomy 110
15
The
Great
Red
Spot
• twice as wide as the Earth
• Has existed for at least 3 centuries
Fall, 205
Astronomy 110
16
Storms Other Jovian Planets
• Saturn: even faster winds
• Neptune: can see storms, but not as long
lived.
• Uranus: dull when Voyager 2 flew by, but
HST captured major storms.
– Extreme tilt means that Uranus’ southern
hemisphere may just now be getting sunshine
for the first time in decades.
Fall, 205
Astronomy 110
17
Jovian Planets: Satellites
• More than 100 Jovian moons and counting
• 60+ moons of Jupiter alone.
• Medium and large moons mostly formed at the
same time as their planets.
• Small moons are mostly captured asteroids and
comets.
Fall, 205
Astronomy 110
18
Medium & large
moons
• Enough self-gravity to be
spherical
• Are or were geologically active.
• Have substantial amounts of ice.
• Formed in orbit around jovian
planets.
• Circular, equatorial orbits in
same direction as planet rotation
Fall, 205
Astronomy 110
19
Small moons
• Far more numerous than the medium and large
moons.
• Not enough gravity to be spherical: “potato-shaped”
• Captured asteroids, so orbits do not follow patterns.
• Orbits can be tilted, elliptical, and even backwards!
Fall, 205
Astronomy 110
20
Jupiter’s Galilean Satellites
Io,
Europa,
Ganymede,
Callisto
Io has volcanoes.
Europa may have an ocean under its ice.
Ganymede & Callisto may also have sub-surface oceans
Fall, 205
Astronomy 110
21
Io’s Volcanoes
Io is the most volcanically active world in the solar system.
Fall, 205
Astronomy 110
22
Tidal Heating
Io is compressed and stretched as
it orbits Jupiter
Fall, 205
Astronomy 110
23
Europa’s Ocean: Waterworld?
Fall, 205
Astronomy 110
24
Tidal stresses crack Europa’s surface ice.
Fall, 205
Astronomy 110
25
Europa’s interior also warmed by tidal heating
Fall, 205
Astronomy 110
26
Ganymede
• Largest moon in the solar system
• Clear evidence of geological activity
• Tidal heating expected - but is it enough?
Fall, 205
Astronomy 110
27
Callisto
• “Classic” cratered
iceball.
• No tidal heating no orbital
resonances.
• But it has
magnetic field
Fall, 205
Astronomy 110
28
Saturn: Titan
Titan is the only moon with a
thick atmosphere.
Titan may also have surface
lakes of methane and ethane.
Fall, 205
Astronomy 110
29
Titan’s Atmosphere
• 90% nitrogen, the rest argon, methane, ethane,
other hydrogen compounds.
• Methane & ethane are greenhouse gases.
• Still cold: 93 K (-180 degrees C)
• Chemical reactions on Titan could produce
organic chemicals.
• Titan could have liquid methane and ethane lakes.
• The Huygens probe from Cassini landed on Titan
in January.
Fall, 205
Astronomy 110
30
Saturn’s Medium-Sized Moons
Fall, 205
Astronomy 110
31
Uranus’
Miranda
shows
huge cliffs
& tectonic
activity
and few
craters.
Fall, 205
Astronomy 110
32
Neptune’s Moon Triton
• Probably a captured
Kuiper belt object:
orbiting Neptune
opposite Neptune’s
direction of rotation.
• Smaller than Earth’s
Moon, yet has recent
geological activity.
Fall, 205
Astronomy 110
33
Jovian Planets: Rings
Fall, 205
Astronomy 110
34
Saturn’s Rings
• Made up of numerous, tiny
individual particles of ice and
dust
• Orbit over Saturn’s equator
• Many particle collisions
cause rings to be very thin
(tens of meters!)
• Gap moons and orbital
resonances create the effect
of rings and gaps.
Fall, 205
Astronomy 110
35
Earth-based view
Fall, 205
Astronomy 110
36
Spacecraft view
Fall, 205
Astronomy 110
37
Jovian Planets: Rings
• Formed from dust created in impacts on
orbiting moons.
• Not left over from planet formation-- the
particles are too small to have survived this
long.
• Tiny particles are constantly ejected and
must be continuously replaced.
Fall, 205
Astronomy 110
38
Implications
• Jovian planets all have rings because they
possess many small moons close-in
• Impacts on these moons are random
• Saturn’s incredible rings may be an ‘accident’
of our time
Fall, 205
Astronomy 110
39
Mass Extinctions
• Large dips in total species diversity in the
fossil record.
• The most recent was 65 million years ago,
ending the reign of the dinosaurs.
Was it caused by an impact?
How would it have happened?
Fall, 205
Astronomy 110
40
No dinosaur fossils
in these rock layers
Thin layer containing
iridium from impactor
Dinosaur fossils in
lower rock layers
Fall, 205
Astronomy 110
41
Iridium - evidence of an impact
• Iridium is very rare in Earth surface rocks
but often found in meteorites.
• Luis and Walter Alvarez found a worldwide
layer containing iridium, laid down 65
million years ago.
Fall, 205
Astronomy 110
42
Comet or
asteroid about
10km in
diameter
approaches
Earth
Fall, 205
Astronomy 110
43
Fall, 205
Astronomy 110
44
Fall, 205
Astronomy 110
45
Fall, 205
Astronomy 110
46
Fall, 205
Astronomy 110
47
An iridium-rich
sediment layer and
an impact crater on
the Mexican coast
show that a large
impact occurred
at the time the
dinosaurs died out,
65 million years
ago.
Fall, 205
Astronomy 110
48
Facts
• Asteroids and comets have hit the Earth.
• A major impact is only a matter of time: not IF but
WHEN.
• Major impact are very rare.
• Extinction level events ~ millions of years.
• Major damage ~ tens-hundreds of years.
Fall, 205
Astronomy 110
49
Tunguska, Siberia: June 30, 1908
The ~40 meter object disintegrated and exploded in the
atmosphere
Fall, 205
Astronomy 110
50
Meteor Crater, Arizona: 50,000 years ago (50 meter object)
Fall, 205
Astronomy 110
51
Impacts will certainly occur in the future, and while the chance of
a major impact in our lifetimes is small, the effects could be
devastating.
Fall, 205
Astronomy 110
52
Hydrostatic Equilibrium:
Gravity is Balanced by Pressure
Fall, 205
Astronomy 110
53
Hydrostatic Equilibrium:
Gravity is Balanced by Pressure
Applications:
•Gravity from planet
• Jovian Planets
Gravity External
• Planetary Atmospheres
•Gravity from Core + Atm
•All “atmosphere”
Fall, 205
Self Gravitating
• Stars
Astronomy 110
54