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