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

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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 – 427 o C on the sunny side, -175 o C 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 CO 2 to dissolve Water vapor and CO 2 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 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 (-56 o C on average and almost never above freezing anywhere) & very dry Polar ice contains frozen CO 2 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

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The Jovian planets: size, composition, and atmosphere Jupiter – 71,000km in radius –Mostly Hydrogen and helium –Sea of liquid molecular H 2 & He 12,000km deep –At the bottom, 30,000 o C under 100 trillion times Earth normal pressure H 2 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 H 2, He, with NH 4, H 2 O, CH 4 –Great Red Spot – Earth would fit into it! Spot and bands have existed for centuries Galileo’s probe stopped transmitting at 130km in at 150 o C (300 o F) with 650km/hr winds at 22 bars Winds likely driven by heat from below

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23.4 The Jovian planets: size, composition, and atmosphere Saturn – the 2 nd largest planet –Lowest density – would float –Much like Jupiter regarding bands, clouds, storms, magnetic field strength –Rings!

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23.4 The Jovian planets: size, composition, and atmosphere Uranus & Neptune –Atmosphere of H 2 & He with C, N 2, O 2 –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 58 o from its axis (and its axis is nearly horizontal) –Neptune’s magnetic field is 50 o from its axis