Birth of the Solar System and Terrestrial Planets

According to the nebular theory, our solar system formed from a giant cloud of interstellar gas. (nebula = cloud)

Galactic Recycling Elements that formed planets were made in stars and then recycled through interstellar space.

Conservation of Angular Momentum The rotation speed of the cloud from which our solar system formed must have increased as the cloud contracted. Rotation of a contracting cloud speeds up for the same reason a skater speeds up as she pulls in her arms.

Flattening Collisions between particles in the cloud caused it to flatten into a disk. Collisions between gas particles in a cloud gradually reduce random motions. Collisions between gas particles also reduce up and down motions. The spinning cloud flattens as it shrinks.

CollapseCollapse of the Solar Nebula

Evidence from Other Gas Clouds We can see stars forming in other interstellar gas clouds, lending support to the nebular theory.

Disks Around Other Stars Observations of disks around other stars support the nebular hypothesis.

Motion of Large Bodies All large bodies in the solar system orbit in the same direction and in nearly the same plane. Most also rotate in that direction.

Two Major Planet Types ____________ planets are rocky, relatively small, and close to the Sun. _______ planets are gaseous, larger, and farther from the Sun.

Why are there two major types of planets?

Conservation of Energy As gravity causes the cloud to contract, it heats up. Inner parts of the disk are hotter than outer parts. Rock can be solid at much higher temperatures than ice.

TemperatureTemperature Distribution of the Disk and the Frost Line

Inside the ________: Too hot for hydrogen compounds to form ices Outside the __________: Cold enough for ices to form Fig 9.5

Formation of Terrestrial Planets Small particles of rock and metal were present inside the frost line. Tiny solid particles stick to form ________________. Gravity draws planetesimals together to form planets. This process of assembly is called _________.

Accretion of Planetesimals Many smaller objects collected into just a few large ones.

SummarySummary of the Condensates in the Protoplanetary Disk

Heavy Bombardment Leftover planetesimals bombarded other objects in the late stages of solar system formation.

Why have the planets turned out so differently, even though they formed at the same time from the same materials?

Terrestrial Planet Interiors Applying what we have learned about Earth’s interior to other planets tells us what their interiors are probably like.

__________________ Gravity pulls high-density material to center Lower-density material rises to surface Material ends up separated by density

_____________ A planet’s outer layer of cool, rigid rock is called the lithosphere. It “floats” on the warmer, softer rock that lies beneath.

Strength of Rock Rock stretches when pulled slowly but breaks when pulled rapidly. The gravity of a large world pulls slowly on its rocky content, shaping the world into a sphere.

Heat Drives Geological Activity Convection: hot rock rises, cool rock falls. One convection cycle takes 100 million years on Earth.

Sources of Internal Heat 1.Gravitational potential energy of accreting planetesimals 2.Differentiation 3.Radioactivity

Heating of Interior over Time Accretion and differentiation when planets were young ____________ _______is most important heat source today

Cooling of Interior Convection transports heat as hot material rises and cool material falls Conduction transfers heat from hot material to cool material Radiation sends energy into space

Planetary Magnetic Fields Moving charged particles create magnetic fields. A planet’s interior can create magnetic fields if its core is electrically conducting, convecting, and rotating.

Earth’s Magnetosphere Earth’s magnetic fields protects us from charged particles from the Sun. The charged particles can create aurorae (“Northern lights”).

Tectonics Convection of the mantle creates stresses in the crust called tectonic forces. Compression forces make mountain ranges. A valley can form where the crust is pulled apart.

Role of Size Smaller worlds cool off faster and harden earlier. Moon and Mercury are now geologically “dead.”

Surface Area to Volume Ratio Heat content depends on volume. Loss of heat through radiation depends on surface area. Time to cool depends on surface area divided by volume: Larger objects have a smaller ratio and cool more slowly.

Impact Cratering Most cratering happened soon after the solar system formed. Craters are about ___ times wider than objects that made them. Small craters greatly outnumber large ones. The Production of a CraterProduction

Impact Craters Meteor Crater (Arizona) Tycho (Moon)

Volcanism Volcanism happens when molten rock (magma) finds a path through lithosphere to the surface. Molten rock is called lava after it reaches the surface.

Lava and Volcanoes Runny lava makes flat lava plains. Slightly thicker lava makes broad shield volcanoes. Thickest lava makes steep stratovolcanoes.

Outgassing Volcanism also releases gases from Earth’s interior into the atmosphere.

Plate Tectonics on Earth Earth’s continents slide around on separate plates of crust. Plate Tectonics on EarthTectonics

Effects of Atmosphere on Earth 1.Erosion 2.Radiation protection 3.Greenhouse effect 4.Makes the sky blue!

Erosion Erosion is a blanket term for weather-driven processes that break down or transport rock. Processes that cause erosion include —Glaciers —Rivers —Wind

Radiation Protection All X-ray light is absorbed very high in the atmosphere. Ultraviolet light is absorbed by ozone (O 3 ).

Earth’s atmosphere absorbs light at most wavelengths.

Why the sky is blue Atmosphere scatters blue light from the Sun, making it appear to come from different directions. Sunsets are red because less of the red light from the Sun is scattered.

Over 99.9% of solar system’s mass Made mostly of H/He gas (plasma) Converts 4 million tons of mass into energy each second Sun

Made of metal and rock; large iron core Desolate, cratered; long, tall, steep cliffs Very hot and very cold: 425°C/ 797°F (day), –170°C/ -274°F (night) Mercury

Cratering of Mercury Mercury has a mixture of heavily cratered and smooth regions like the Moon. The smooth regions are likely ancient lava flows.

Cratering of Mercury The Caloris basin is the largest impact crater on Mercury Region opposite the Caloris Basin is jumbled from seismic energy of impact

Tectonics on Mercury Long cliffs indicate that Mercury shrank early in its history.

Nearly identical in size to Earth; surface hidden by clouds Hellish conditions due to an extreme greenhouse effect Even hotter than Mercury: 470°C/ 878°F, day and night Venus

Cratering on Venus Impact craters, but fewer than Moon, Mercury, Mars

Volcanoes on Venus Many volcanoes, including both shield volcanoes and stratovolcanoes

Tectonics on Venus Fractured and contorted surface indicates tectonic stresses

Erosion on Venus Photos of rocks taken by lander show little erosion

Does Venus have plate tectonics? Most of Earth’s major geological features can be attributed to plate tectonics, which gradually remakes Earth’s surface. Venus does not appear to have plate tectonics, but its entire surface seems to have been “repaved” 750 million years ago.

Why is Venus so hot? The greenhouse effect on Venus keeps its surface temperature at 470°C. But why is the greenhouse effect on Venus so much stronger than on Earth?

Atmosphere of Venus Venus has a very thick carbon dioxide atmosphere with a surface pressure 90 times that of Earth. Reflective clouds contain droplets of sulfuric acid. The upper atmosphere has fast winds that remain unexplained.

Greenhouse Effect on Venus Thick carbon dioxide atmosphere produces an extremely strong greenhouse effect. Earth escapes this fate because most of its carbon and water are in rocks and oceans.

Runaway Greenhouse Effect The runaway greenhouse effect would account for why Venus has so little water. Greater heat, more evaporation More evaporation, stronger greenhouse effect

An oasis of life The only surface liquid water in the solar system A surprisingly large moon Earth and Moon to scale Earth

What unique features of Earth are important for life? 1.Surface liquid water 2.Atmospheric oxygen 3.Plate tectonics 4.Climate stability

Continental Motion Motion of continents can be measured with GPS

Carbon Dioxide Cycle 1.Atmospheric CO 2 dissolves in rainwater. 2.Rain erodes minerals that flow into the ocean. 3.Minerals combine with carbon to make rocks on ocean floor.

Carbon Dioxide Cycle 4.Subduction carries carbonate rocks down into the mantle. 5.Rock melts in mantle and outgases CO 2 back into atmosphere through volcanoes.

Long-Term Climate Change Changes in Earth’s axis tilt might lead to ice ages. Widespread ice tends to lower global temperatures by increasing Earth’s reflectivity. CO 2 from outgassing will build up if oceans are frozen, ultimately raising global temperatures again.

These unique features are intertwined: Plate tectonics create climate stability Climate stability allows liquid water Liquid water is necessary for life Life is necessary for atmospheric oxygen

Moon craters smooth plains

Earth’s Moon Diameter of 3475 kilometers (2150 miles) is unusually large compared to its parent planet Density 3.3 times that of water Comparable to Earth's crustal rocks Perhaps the Moon has a small iron core

Earth’s Moon Gravitational attraction is ____of Earth's No atmosphere Tectonics no longer active Surface is bombarded by micrometeorites from space which gradually makes the landscape smooth

Moon’s Formation Before Apollo missions, three hypotheses of the Moon’s origin: –Moon originally a small planet orbiting the Sun and was subsequently captured by Earth’s gravity during a close approach (capture theory) –Earth and Moon were twins, forming side by side from a common cloud of gas and dust (twin formation theory) –The Moon spun out of a very fast rotating Earth in the early day of the Solar System (fission theory)

Moon’s Formation Each of these hypotheses gave different predictions about Moon’s composition: –In capture theory, the Moon and Earth would be very different in composition, while twin theory would require they have the same composition –In fission theory, the Moon’s composition should be close to the Earth’s crust

Moon’s Formation Moon rock samples proved surprising –For some elements, the composition was the same, but for others, it was very different –None of the three hypotheses could explain these observations

Impact Theory of Moon’s Formation –Moon formed from debris blasted out of the Earth by the impact of a Mars-sized body –Age of lunar rocks and lack of impact site on Earth suggests collision occurred at least 4.5 billion years ago as the Earth was forming –The impact would vaporize low-melting-point materials (e.g., water) and disperse them explaining their lack in the Moon –Only surface rock blasted out of Earth leaving Earth’s core intact and little iron in the Moon –Easily explains composition difference with Earth

Giant Impact Giant impact stripped matter from Earth’s crust Stripped matter began to orbit Then accreted into Moon

Moon Some volcanic activity 3 billion years ago must have flooded lunar craters, creating lunar maria. The Moon is now geologically dead.

Looks almost Earth-like, but don’t go without a spacesuit! Giant volcanoes, a huge canyon, polar caps, and more Water flowed in the distant past; could there have been life? Mars

Mars versus Earth 50% Earth’s radius, 10% Earth’s mass 1.5 AU from the Sun Axis tilt about the same as Earth Similar rotation period Thin CO 2 atmosphere: little greenhouse Main difference: Mars is SMALLER

Seasons on Mars Seasons on Mars are more extreme in the southern hemisphere because of its elliptical orbit.

Storms on Mars Seasonal winds on Mars can drive huge dust storms.

The surface of Mars appears to have ancient riverbeds.

The condition of craters indicates surface history. Eroded crater

Low-lying regions may once have had oceans.

Opportunity Spirit

2004 Opportunity Rover provided strong evidence for abundant liquid water on Mars in the distant past. How could Mars have been warmer and wetter in the past?

Today, most water lies frozen underground (blue regions) Some scientists believe accumulated snowpack melts carve gullies even today.

Climate Change on Mars Mars has not had widespread surface water for 3 billion years. The greenhouse effect probably kept the surface warmer before that. Somehow Mars lost most of its atmosphere.

Climate Change on Mars Magnetic field may have preserved early Martian atmosphere. Solar wind may have stripped atmosphere after field decreased because of interior cooling.

Martian Surface –Martian Polar Ice Caps Change in size with seasons (Mars tilt similar to Earth’s) Southern cap –frozen CO 2 (dry ice) –diameter »5900 km (winter) »350 km (summer)

Martian Surface Northern –surface layer of CO 2 –primarily water ice –separate layers indicative of climate cycles (including “ice ages”) –Shrinks to 1000 km in summer Far less water than Earth’s caps

So, Are there Martians? Censored

Fossils of ancient Martian life? The tiny rod-shaped structures look similar to primitive fossils found in ancient rocks on Earth. However, some scientists think these structures formed chemically. (Courtesy NASA.)

Are there Martians? Maybe, extremophiles live on Earth and may exist at northern pole on Mars. Extremophiles exist at the “fringes” of livable conditions. –Tube worm communities at hydrothermal vents in the deep ocean (Chemosynthetic) –Bacteria communities under ice in Antarctica

What makes a planet habitable? Located at an optimal distance from the Sun for liquid water to exist

What makes a planet habitable? Large enough for geological activity to release and retain water and atmosphere

Planetary Destiny Earth is habitable because it is large enough to remain geologically active, and it is at the right distance from the Sun so oceans could form.