Transcript Planets and their Moons

Planets and their Moons
Nebular* Hypothesis for Formation of
Solar System
• Formed almost 5 billion years ago from the
remains of an exploding star
• Central portion contracted due to its own
gravity
• Compressed to the point of nuclear fusion
(energy source of the sun)
• Outlying part of nebula coalesced to form
the planets
*Nebula - rotating cloud of gas and dust
p.584a
Figure 1.12
The solar system
– Solar wind – a stream of positive ions and
electrons from the sun, radiating at high
speed. This blew most gases away from the
inner solar system
– This left four inner, rocky, terrestrial planets
and four outer, gaseous, Jovian planets
The Solar System
Mercury
• Closest to the sun
• Hottest – 427oC on the sunny side, -175oC
on the other
• Slow rotation – 3 days every 2year
• Appears to have icy poles
• Lack of atmosphere prevents erosion of
cratered surface
Mercury
Spring 1974, Mariner 10 sent images of the
surface to Earth
– Heavily cratered – moon-like
– No evidence of tectonics
– Has a magnetic field – but curious as the planet
has no molten core
Fig. 23-1, p.553
Venus
• closest to Earth in size and mass
• Closer to sun, so initially hotter
• No liquid water – no seas for CO2 to
dissolve
• Water vapor and CO2 combined to make a
runaway greenhouse effect
• Lack of craters indicates significant
erosion of surface since formation
Venus
• Opaque atmosphere (radar has been used
to survey this planet)
• Very few craters; most landforms probably
300-500 million years old
• “Blob tectonics” – lifted crust and lack of
spreading suggest that “blobs” of plastic
crust drive surface features
Fig. 23-2, p.553
Fig. 23-3, p.554
Fig. 23-4, p.554
Mars
• About ½ Earth’s size
• (-56oC on average and almost never above
freezing anywhere) & very dry
• Polar ice contains frozen CO2
• Atmosphere comparable to Earth’s at 43km
high
• Contains water – as ice – at poles, and in
subsurface soils
Mars
• Evidence of prior liquid water evident
– Stream channels, eroded areas, lake beds
– Probably as recent as 1 million years ago
• Valles Marineris – 10x longer and 6x wider than the
Grand Canyon
• Spirit & Opportunity – two mobile robots landed in
Jan 2004 to explore Mars.
– Discovered mineral composition of martian rocks
– Sulfates, ripple marks, indicating presence of water at one
time on Mars
Mars
• a mix of old-cratered terrain and younger,
tectonically altered regions
• Olympus Mons – largest volcano in the solar system
• Blob tectonics?
– Parallel cracks along Tharsis
• Earth-like tectonics?
– Possible strike-slip faults
– Evidence of recent (few mya) lava flows
Fig. 23-9, p.558
Fig. 23-10, p.558
Fig. 23-11, p.559
p.560
Fig. 23-12, p.560
p.561
The Jovian planets: size,
composition, and atmosphere
• Jupiter – 71,000km in radius
– Mostly Hydrogen and helium
– Sea of liquid molecular H2 & He 12,000km deep
– At the bottom, 30,000oC under 100 trillion times
Earth normal pressure
• H2 dissociates into 2H and atoms compress
• Electrons become free to flow like metals on Earth
– Liquid metallic hydrogen
– Generates Jupiter’s massive magnetic field
The Jovian planets: size,
composition, and atmosphere
• Jupiter (cont)
– Rocky core 10-20x Earth size
– Atmosphere is verified H2, He, with NH4, H2O,
CH4
– Great Red Spot – Earth would fit into it!
• Spot and bands have existed for centuries
• Galileo’s probe stopped transmitting at 130km in at
150oC (300oF) with 650km/hr winds at 22 bars
• Winds likely driven by heat from below
Fig. 23.16, p.595
Fig. 23-15, p.563
Fig. 23-14, p.563
23.4 The Jovian planets: size,
composition, and atmosphere
• Saturn – the 2nd largest planet
– Lowest density – would float
– Much like Jupiter regarding bands, clouds,
storms, magnetic field strength
– Rings!
Fig. 23.25, p.600
Fig. 23.26, p.600
23.4 The Jovian planets: size,
composition, and atmosphere
• Uranus & Neptune
– Atmosphere of H2 & He with C, N2, O2
– Molecular hydrogen, no LMH
– Neptune has a Great Dark Spot
• Methane may decompose into Carbon, and under
pressure into diamond
• Crystallization causes heat that drives the winds
– Uranus magnetic field is tilted 58o from its axis
(and its axis is nearly horizontal)
– Neptune’s magnetic field is 50o from its axis