Chapter 9 Planetary : Agenda and the Other Terrestrial Worlds • Announce: – Part 2 of Projects due – Read Ch. 11 for Tuesday • Ad hoc, ex post facto • Rover Update • Ch. 9—Planetary Geology • Lab: Parallax or Waves on a String

Rover Update Ad Hoc • More than 1000 Martian days

• From Wikipedia: – Ad hoc is a Latin phrase which means "for this [purpose]." It generally signifies a solution that has been designed for a specific problem, is non-generalizable and can not be adapted to other purposes. – Ex post facto : from the Latin for "from something done afterward"

1 9.1 Connecting Planetary Interiors and What are terrestrial like Surfaces on the inside? • Our goals for learning • What are terrestrial planets like on the inside? • What causes geological activity? • Why do some planetary interiors create magnetic fields?

Seismic Waves Earth’s Interior

• Vibrations • Core: Highest that travel density; nickel through and iron Earth’s • Mantle: Moderate interior tell us density; silicon, what Earth is oxygen, etc. like on the • Crust: Lowest inside density; granite, basalt, etc.

Terrestrial Interiors Differentiation • Gravity pulls high-density material to center • Lower-density material rises to surface • Material ends up • Applying what we have learned about Earth’s separated by interior to other planets tells us what their interiors density are probably like

2 Lithosphere Strength of • A planet’s outer • Rock stretches when layer of cool, rigid pulled slowly but rock is called the breaks when pulled lithosphere rapidly • It “floats” on the • The gravity of a large warmer, softer world pulls slowly on rock that lies its rocky content, beneath shaping the world into a sphere

Special Topic: Special Topic: How do we know what’s inside a planet? How do we know what’s inside a planet?

• P waves push • P waves go matter back through Earth’s core but S and forth waves do not

• We conclude • S waves that Earth’s core shake matter must have a liquid outer side to side layer

Thought Question Thought Question

What is necessary for differentiation to occur in a What is necessary for differentiation to occur in a planet? planet?

a) It must have metal and rock in it a) It must have metal and rock in it b) It must be a mix of materials of different density b) It must be a mix of materials of different density c) Material inside must be able to flow c) Material inside must be able to flow d) All of the above d) All of the above e) b and c e) b and c

3 What causes geological activity? Heating of Interior • and differentiation when planets were young

• Radioactive decay is most important heat source today

Cooling of Interior Role of Size

• Convection transports heat as hot material rises and cool material falls • Conduction transfers heat from hot material to cool material • Smaller worlds cool off faster and harden earlier • Radiation sends energy into space • and Mercury are now geologically “dead”

Why do some planetary interiors Surface Area to Volume Ratio create magnetic fields? • Heat content depends on volume • Loss of heat through radiation depends on surface area • Time to cool depends on surface area divided by volume

4πr2 3 surface area to volume ratio = = 4 πr3 r 3 • Larger objects have smaller ratio and cool more slowly

4 Sources of Magnetic Fields Sources of Magnetic Fields • A world can have a magnetic field if • Motions of charged particles charged particles are moving inside are what create • 3 requirements: magnetic fields – Molten interior – Convection – Moderately rapid rotation

What have we learned?

• What are terrestrial planets like on the inside? – Core, mantle, crust structure – Denser material is found deeper inside • What causes geological activity? – Interior heat drives geological activity – Radioactive decay is currently main heat source • Why do some planetary interiors create magnetic fields? – Requires motion of charged particles inside planet

What processes shape planetary 9.2 Shaping Planetary Surfaces surfaces?

• Our goals for learning • What processes shape planetary surfaces? • Why do the terrestrial planets have different geological histories? • How does a planet’s surface reveal its geological age?

5 Processes that Shape Surfaces Impact Cratering • Impact cratering • Most cratering – Impacts by or happened soon after • formed – Eruption of molten rock onto surface • Craters are about 10 • Tectonics times wider than object that made them – Disruption of a planet’s surface by internal stresses • Small craters greatly • outnumber large ones – Surface changes made by wind, water, or ice

Impact Craters Impact Craters on Mars

Meteor Crater () Tycho (Moon) “standard” crater impact into icy ground eroded crater

Volcanism Lava and Volcanoes • Volcanism happens when molten rock (magma) finds a path through lithosphere to the surface • Molten rock is called lava after it reaches the Runny lava makes flat Slightly thicker lava Thickest lava makes surface lava plains makes broad shield steep stratovolcanoes volcanoes

6 Outgassing Tectonics

• Convection of the mantle creates stresses in the crust called tectonic forces • Volcanism also releases gases from Earth’s interior • Compression forces make mountain ranges into atmosphere • Valley can form where crust is pulled apart

Plate Tectonics on Earth Erosion • Earth’s continents • Erosion is a blanket term for weather-driven slide around on processes that break down or transport rock separate plates of • Processes that cause erosion include crust – Glaciers – Rivers – Wind

Erosion by Water Erosion by Ice

• Colorado River • Glaciers carved continues to the Yosemite carve Grand Valley Canyon

7 Erosion by Wind Erosional Debris

• Wind wears • Erosion can away rock and create new builds up sand features by dunes depositing debris

Why do the terrestrial planets have Role of Planetary Size different geological histories?

• Smaller worlds cool off faster and harden earlier • Larger worlds remain warm inside, promoting volcanism and tectonics • Larger worlds also have more erosion because their gravity retains an atmosphere

Role of Distance from Role of Rotation

• Planets close to Sun are too hot for rain, snow, ice and so have less erosion • Planets with slower rotation have less weather and • More difficult for hot planet to retain atmosphere less erosion and a weak magnetic field • Planets far from Sun are too cold for rain, limiting • Planets with faster rotation have more weather and erosion more erosion and a stronger magnetic field • Planets with liquid water have most erosion

8 Thought Question Thought Question

How does the cooling of planets and potatoes vary How does the cooling of planets and potatoes vary with size? with size?

a) Larger makes it harder for heat from inside to a) Larger makes it harder for heat from inside to escape escape b) Larger has a bigger ratio of volume (which needs b) Larger has a bigger ratio of volume (which needs to cool) to surface area (the surface is where cooling to cool) to surface area (the surface is where cooling happens) happens) c) Larger takes longer to cool c) Larger takes longer to cool d) All of the above d) All of the above

How does a planet’s surface reveal History of Cratering its geological age? • Most cratering happened in first billion years

• A surface with many craters has not changed much in 3 billion years

Cratering of Moon Cratering of Moon • Some areas of Moon are more heavily cratered than others

• Younger regions were flooded by lava after most cratering

Cratering map of Moon’s entire surface

9 What have we learned? 9.3 and Mercury • What processes shape planetary surfaces? – Cratering, volcanism, tectonics, erosion • Our goals for learning • Why do the terrestrial planets have different geological histories? • What geological processes shaped our – Differences arise because of planetary size, Moon? distance from Sun, and rotation rate • What geological processes shaped • How does a planet’s surface reveal its Mercury? geological age? – Amount of cratering tells us how long ago a surface formed

What geological processes shaped Lunar Maria our Moon? • Smooth, dark lunar maria are less heavily cratered than lunar highlands

• Maria were made by flood of runny lava

Formation of Lunar Maria Tectonic Features • Wrinkles arise from cooling and contraction of lava flood Early surface Large impact Heat build - Cooled lava covered with crater up allows is smoother craters weakens lava to well and darker crust up to surface than surroundings

10 What geological processes shaped Geologically Dead Mercury? • Moon is considered geologically “dead” because geological processes have virtually stopped

Cratering of Mercury Cratering of Mercury

Caloris basin is Region opposite • A mixture of heavily cratered and smooth regions largest Caloris Basin is like the Moon on Mercury jumbled from • Smooth regions are likely ancient lava flows seismic energy of impact

What have we learned? Tectonics on Mercury • What geological processes shaped our Moon? – Early cratering still present – Maria resulted from volcanism • What geological processes shaped Mercury? – Cratering and volcanism similar to Moon • Long cliffs indicate that Mercury shrank early in its – Tectonic features indicate early shrinkage history

11 How did Martians invade popular 9.4 culture?

• Our goals for learning • How did Martians invade popular culture? • What are the major geological features of Mars? • What geological evidence tells us that water once flowed on Mars?

What are the major geological “Canals” on Mars features of Mars?

• Percival Lowell misinterpreted surface features seen in telescopic images of Mars

Cratering on Mars Volcanism on Mars • Mars has many large shield volcanoes

• Olympus Mons is largest volcano in solar system

• Amount of cratering differs greatly across surface • Many early craters have been erased

12 What geological evidence tells us Tectonics on Mars that water once flowed on Mars?

• System of valleys known as thought to originate from tectonics

Dry Riverbeds? Erosion of Craters • Close-up • Details of some photos of Mars craters suggest show what they were once appear to be filled with dried-up water riverbeds

Martian Rocks Martian Rocks

• Mars rovers have found rocks that appear to have • Exploration of impact craters has revealed that formed in water Mars’ deeper layers were affected by water

13 Hydrogen Content Crater Walls • Gullies on crater walls suggest occasional liquid water flows have happened less than a million years ago

• Map of hydrogen content (blue) shows that low- lying areas contain more water ice

What have we learned? What have we learned?

• How did Martians invade popular culture? • What geological evidence tells us that – Surface features of Mars in early telescopic water once flowed on Mars? photos were misinterpreted as “canals” – Features that look like dry riverbeds • What are the major geological features of – Some craters appear to be eroded Mars? – Rovers have found rocks that appear to have formed in water – Differences in cratering across surface – Gullies in crater walls may indicate recent – Giant shield volcanoes water flows – Evidence of tectonic activity

What are the major geological 9.5 Geology of features of Venus?

• Our goals for learning • What are the major geological features of Venus? • Does Venus have ?

14 Radar Mapping Cratering on Venus

• Impact craters, but fewer than Moon, Mercury, Mars

• Thick atmosphere forces us to explore Venus’ surface through radar mapping

Volcanoes on Venus Tectonics on Venus

• Many volcanoes, • Fractured and including both shield contorted surface volcanoes and indicates tectonic stratovolcanoes stresses

Erosion on Venus Does Venus have plate tectonics?

• Photos of rocks • Most of Earth’s major geological features taken by lander can be attributed to plate tectonics, which show little gradually remakes Earth’s surface erosion • Venus does not appear to have plate tectonics, but entire surface seems to have been “repaved” 750 million years ago

15 What have we learned? 9.6 The Unique Geology of Earth • Our goals for learning • What are the major geological features of • Our goals for learning Venus? • How do we know Earth’s surface is in – Venus has cratering, volcanism, and tectonics motion? but not much erosion • How is Earth’s surface shaped by plate • Does Venus have plate tectonics? tectonics? – The lack of plate tectonics on Venus is a mystery • Was Earth’s geology destined from birth?

How do we know Earth’s surface Continental Motion is in motion?

• Motion of continents can be measured with GPS

Continental Motion Seafloor Crust • Idea of • Thin seafloor continental drift crust differs from was inspired by thick continental puzzle-like fit of crust continents • Dating of seafloor • Mantle material shows it is erupts where usually quite seafloor spreads young

16 How is Earth’s surface shaped by Seafloor Recycling plate tectonics?

• Seafloor is recycled through a process known as subduction

Surface Features Surface Features • Major geological • Himalayas are features of North forming from a America record collision history of plate between plates tectonics

Surface Features Rifts, Faults, Earthquakes • Red Sea is • San Andreas forming where fault in plates are pulling California is a apart plate boundary

• Motion of plates causes earthquakes

17 Plate Motions Hot Spots • Measurements of plate motions tell us past and future layout of continents

• Hawaiian islands have formed where plate is moving over volcanic hot spot

Was Earth’s geology destined Earth’s Destiny from birth? • Many of Earth’s features determined by size, rotation, and distance from Sun

• Reason for plate tectonics not yet clear

What have we learned? What have we learned?

• How do we know that Earth’s surface is in • Was Earth’s geology destined from birth? motion? – Many of Earth’s features determined by size, distance from Sun, and rotation rate – Measurements of plate motion confirm idea of continental drift – Reason for plate tectonics still a mystery • How is Earth’s surface shaped by plate tectonics? – Plate tectonics responsible for subduction, seafloor spreading, mountains, rifts, and earthquakes

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