Formation of the Solar System

Questions for this chapter… How old is the Earth? How do we know???

Questions for this chapter… How old are the Sun and other planets? How old are the Sun and other planets? Were they created during the “Big Bang”? Were they created during the “Big Bang”? How do we know? How do we know?

Questions for this chapter… What is the value to exploring our solar system, and spending tax dollars for these missions? value

Observe patterns, characteristics, motions How do we start?

Analyze and Research data How do we start?

Develop models and test them with hypotheses. How do we start?

NASA super- computer models of our solar system (2010)

Clear patterns of motion, composition, and distribution. What does the solar system look like?

The solar system exhibits clear patterns of composition and motion and distribution. These patterns are far more important and interesting than numbers, names, and other trivia.

Patterns of Motion

Patterns of Composition

Patterns of Distribution

But don’t get too confident…

Planets are very tiny compared to distances between them.

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 (day), –170°C (night) Mercury

Mariner 10 (1974) Messenger spacecraft ( …)Messenger spacecraft Mercury

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

Mariner (1960s) Pioneer & Venera (1970s) Magellan (1989)

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

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

Mariner (1960s) Viking (1970s) Pathfinder (1990s) Odyssey Spirit & Opportunity Phoenix Mars

MRO (Mars Reconnaissance Orbiter) Curiosity (Mars Science Laboratory) MAVEN (Mars Atmosphere and Volatile EvolutioNMAVEN Mars

Mars Express (ESA) Mars Orbiter Mission ( Mangalyaan ) - India Mars

Mars

Mars failures… Mars Phobos-Grunt (Russia/China) Mars Polar Lander Mars Climate Orbiter Nozomi (Japan)

Much farther from Sun Much farther from Sun Mostly H/He; no solid surface Mostly H/He; no solid surface 300+ times mass of Earth 300+ times mass of Earth Many moons, rings Many moons, rings Jupiter

Pioneer (1970s) Pioneer (1970s) Voyager (1970s) Voyager (1970s) Galileo ( s) Galileo ( s) Juno ( ) Juno ( ) Jupiter

Jupiter’s moons can be as interesting as planets themselves, especially Jupiter’s four Galilean moons IO, EUROPA, GANYMEDE, & CALLISTO

Saturn Giant and gaseous like Jupiter Giant and gaseous like Jupiter Spectacular rings Spectacular rings Many moons, including cloudy Titan Many moons, including cloudy Titan

Pioneer (1970s) Voyager (1980s) Cassini (2004- )

Cassini probe arrived in July 2004 (launched in 1997). Cassini probe arrived in July 2004 (launched in 1997).

Rings are NOT solid Countless small chunks of ice and rock Each orbiting like a tiny moon. Artist’s conception

Smaller than Jupiter/Saturn; much larger than Earth Smaller than Jupiter/Saturn; much larger than Earth H/He gas and hydrogen compounds (H 2 O, NH 3, CH 4 ) H/He gas and hydrogen compounds (H 2 O, NH 3, CH 4 ) Extreme axis tilt Extreme axis tilt Uranus

Similar to Uranus (except for axis tilt) Similar to Uranus (except for axis tilt) Many moons (including Triton with geysers) Many moons (including Triton with geysers) Neptune

Pluto and Eris Much smaller than other planets Much smaller than other planets Icy, comet-like composition Icy, comet-like composition Pluto’s moon Charon is similar in size to Pluto Pluto’s moon Charon is similar in size to Pluto

Pluto and Other Dwarf Planets Much smaller than other planets Much smaller than other planets Icy, comet-like composition Icy, comet-like composition Charon is similar in size to Pluto Charon is similar in size to Pluto

What features and patterns of our solar system provide clues to how it formed?

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

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

Swarms of Smaller Bodies Rocky asteroids populate the inner solar system. Rocky asteroids populate the inner solar system. Pluto-like bodies beyond Neptune Pluto-like bodies beyond Neptune Icy comets populate the outer solar system Icy comets populate the outer solar system

Notable Exceptions Several exceptions to normal patterns must be explained. Several exceptions to normal patterns must be explained. Venus’ rotation Earth’s Moon Uranus’ tilt

What theory best explains the features of our solar system?

Um… What really is a scientific theory?

What is a scientific theory? An explanation that is right all of the time An explanation that everyone agrees with An explanation that most people agree with An explanation that has been proven by a scientist

A scientific theory is a well-substantiated explanation of some aspect of the natural world, based on knowledge that has been repeatedly confirmed through observation and experimentation. Scientific theory. (2013, October 22). In Wikipedia, The Free Encyclopedia. Retrieved 16:46, October 23, 2013, from What is a scientific theory?

A scientific theory is not the end result of the scientific method; theories can be proven or rejected, just like hypotheses. scientific method Zimmerman, K. (2012) “What is a Scientific Theory?” LiveScience. theory.html theory.html What is a scientific theory?

A scientific theory summarizes a hypothesis or group of hypotheses that have been supported with repeated testing. What is a scientific theory? “If enough evidence accumulates to support a hypothesis, it … becomes accepted as a valid explanation of a phenomenon” – a scientific theory.

What is a scientific theory? An explanation that is right all of the time An explanation that everyone agrees with An explanation that most people agree with An explanation that has been proven by a scientist

A scientific theory can be falsified (proven wrong) with just ONE test. Can scientific theories be proven absolutely? But… a scientific theory can never be proven absolutely true with just one test!

A scientific theory MUST change when new evidence is discovered. Can scientific theories change? So… what qualifies as “evidence”?

What theory best explains the features of our solar system? Assemble evidence from many sources Integrate many observations and results of many prior experiments Test the general theory against all known facts But…

What theory best explains the features of our solar system? But… Always be aware, you can’t PROVE the theory correct! You can, however, disprove it or cause it to be re-evaluated with new evidence!

What theory best explains the features of our solar system? We have only ONE example to study Could we over-generalize based on a unique case? Are there mutliple ways to “build” a solar system?

We know space is filled with gas and dust – the raw materials from which planetary systems form! Space isn’t empty…

…and its composition changes Spectra of exploding and old stars shows heavier elements being ejected, too

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

Why would it “contract”? Mass of material could be ~100 x Mass of the Sun Mass of material could be ~100 x Mass of the Sun Universal Law of Gravity

Why would it “flatten”? Rotation speed of the cloud increased as cloud contracted. Rotation speed of the cloud increased as cloud contracted. Conservation of Angular Momentum

Why would it “flatten”? Collisions within the rotating disk even out motions Collisions within the rotating disk even out motions Conservation of Angular Momentum

Rotation of a contracting cloud speeds up Same reason a skater speeds up as she pulls in her arms. Collapse of the Solar Nebula

Why would it develop planets? Collisions of material form “planetary seeds” Collisions of material form “planetary seeds” Gravity, Static Electricity, Accretion

Why would it develop planets? Temperature rises in the center; cooler on the outer edges Temperature rises in the center; cooler on the outer edges Conservation of Energy

Why would it develop two kinds of planets? Temperature varies from inside to outside Temperature varies from inside to outside Condensation Sequence Theory

Why two major types of planets?

~ 99% of material is Hydrogen & Helium gas ~ 1% Small bits of Dust (Carbon, Silicates, Iron, etc.)

Inside the frost line: Too hot for hydrogen compounds to form ices Very Little Material to grow solid planets!

Outside the frost line: Cold enough for ices of Hydrogen (H 2 0, NH 3, CH 4 ) to form HUGE amounts of material to grow planets from

Observational Evidence

BETA Pictoris – a Hint at Stars with Planetary Disks?

Computer Model Evidence

Jupiter & Saturn as “miniature” solar systems Jupiter & Saturn as “miniature” solar systems Moon systems mirror planet systems? Moon systems mirror planet systems? Show trends in density of moons from inside to outside Show trends in density of moons from inside to outside Additional Evidence

Moons of jovian planets form in miniature disks.

Jupiter & Saturn as “miniature” solar systems Jupiter & Saturn as “miniature” solar systems Moon systems mirror planet systems? Moon systems mirror planet systems? Show trends in density of moons from inside to outside Show trends in density of moons from inside to outside Disks of Matter around other stars! Disks of Matter around other stars! Additional Evidence

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

Tiny solid particles stick to form planetesimals. Summary of the Condensates in the Protoplanetary Disk

Gravity draws planetesimals together to form planets. This process of assembly is called accretion. Summary of the Condensates in the Protoplanetary Disk

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

Formation of Jovian Planets Hydrogen-rich ices could also form small particles outside the frost line. Hydrogen-rich ices could also form small particles outside the frost line. Larger planetesimals and planets were able to form from these abundant elements Larger planetesimals and planets were able to form from these abundant elements The gravity of these larger planets then was able to draw in surrounding H and He gases. The gravity of these larger planets then was able to draw in surrounding H and He gases.

Where did asteroids and comets come from?

Asteroids and Comets Leftovers from the accretion process Leftovers from the accretion process Rocky asteroids inside frost line Rocky asteroids inside frost line Icy comets outside frost line Icy comets outside frost line

Asteroids Play A Role in Solar System Evolution! Leftover planetesimals bombarded other objects in late stages of solar system formation. Leftover planetesimals bombarded other objects in late stages of solar system formation. Craters on EVERY solid surface! Craters on EVERY solid surface!

Comets Play A Role in Solar System Evolution! Water may have come to Earth by way of collisions with icy comets & planetesimals from the outer solar system. Water may have come to Earth by way of collisions with icy comets & planetesimals from the outer solar system.

Explaining existence of our Moon & other exceptions?

Captured Moons The unusual moons of some planets may be captured planetesimals. The unusual moons of some planets may be captured planetesimals.

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

More Giant Impacts? Giant impacts might also explain the different rotation axes of some planets like Uranus & Venus Giant impacts might also explain the different rotation axes of some planets like Uranus & Venus

Review of Nebular Theory condensation sequence

Thought Question How would the solar system be different if the solar nebula had cooled with a temperature half its current value? A. Jovian planets would have formed closer to the Sun. B. There would be no asteroids. C. There would be no comets. D. Terrestrial planets would be larger.

Thought Question How would the solar system be different if the solar nebula had cooled with a temperature half its current value? A. Jovian planets would have formed closer to the Sun. B. There would be no asteroids. C. There would be no comets. D. Terrestrial planets would be larger.

Thought Question Which of these facts is NOT explained by the nebular theory? There are two main types of planets: terrestrial and jovian. There are two main types of planets: terrestrial and jovian. Planets orbit in the same direction and plane. Planets orbit in the same direction and plane. Asteroids and comets exist. Asteroids and comets exist. There are four terrestrial and four jovian planets. There are four terrestrial and four jovian planets.

Thought Question Which of these facts is NOT explained by the nebular theory? There are two main types of planets: terrestrial and jovian. There are two main types of planets: terrestrial and jovian. Planets orbit in the same direction and plane. Planets orbit in the same direction and plane. Asteroids and comets exist. Asteroids and comets exist. There are four terrestrial and four jovian planets. There are four terrestrial and four jovian planets.

When did the planets form? Cannot find age of a planet, but can find ages of rocks on a planet. Cannot find age of a planet, but can find ages of rocks on a planet. Determine age of rock through careful analysis of proportions of various atoms and isotopes within it. Determine age of rock through careful analysis of proportions of various atoms and isotopes within it. Radioactive Dating Radioactive Dating

Radioactive Decay Some isotopes decay into other nuclei. Some isotopes decay into other nuclei. A half-life is the time for half the nuclei in a substance to decay. A half-life is the time for half the nuclei in a substance to decay.

Age dating of meteorites that are unchanged since they condensed and accreted tells us that the solar system is about 4.6 billion years old. Dating the Solar System

Multiple Pieces of Evidence! Radiometric dating tells us that the oldest moon rocks are ~4.4 billion years old. Radiometric dating tells us that the oldest moon rocks are ~4.4 billion years old. The oldest meteorites are ~4.55 billion years old. The oldest meteorites are ~4.55 billion years old. Planets probably formed ~4.5 billion years ago. Planets probably formed ~4.5 billion years ago.