Chapter 6 Notes Jessica Brandon

Chapter 6 Formation of Planetary Systems Our Solar System and Beyond

·      The solar system exhibits clear patterns of composition and motion.

·      These patterns are far more important and interesting than numbers, names, and other trivia.

·      Planets are very tiny compared to distances between them.

Sun

·      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

Mercury

·      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)

Venus

·      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

Earth

·      An oasis of life

·      The only surface liquid water in the solar system

·      A surprisingly large moon

Mars

·      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?

Jupiter

·      Much farther from Sun than inner planets

·      Mostly H/He; no solid surface

·      300 times more massive than Earth

·      Many moons, rings Jupiter Jupiter’s moons can be as interesting as planets themselves, especially Jupiter’s four Galilean moons

·      Io (shown here): Active volcanoes all over

·      Europa: Possible subsurface ocean

·      Ganymede: Largest moon in solar system

·      Callisto: A large, cratered “ice ball”Saturn

·      Giant and gaseous like Jupiter

·      Spectacular rings

·      Many moons, including cloudy Titan

·      Cassini spacecraft currently studying it

·      Rings are NOT solid; they are made of countless small chunks of ice and rock, each orbiting like a tiny moon.

Uranus

·      Smaller than Jupiter/Saturn; much larger than Earth

·      Made of H/He gas and hydrogen compounds (H2O, NH3, CH4)

·      Extreme axis tilt

·      Moons and rings

Neptune

·      Similar to Uranus (except for axis tilt)

·      Many moons (including Triton)

Neptune Pluto and Eris

·      Much smaller than other planets

·      Icy, comet-like composition

·      Pluto’s moon Charon is similar in size to Pluto

****What features 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.

·      Most also rotate in that direction.

Two Major Planet Types

·      Terrestrial planets are rocky, relatively small, and close to the Sun.

·      Jovian planets are gaseous, larger, and farther from the Sun.

Swarms of Smaller Bodies

·      Many rocky asteroids and icy comets populate the solar system. Notable Exceptions

·      Several exceptions to normal patterns need to be explained.

·      Swarms of Smaller Bodies

·      According to the nebular theory, our solar system formed from a giant cloud of interstellar gas.

****Where did the solar system come from? ****

·      Galactic Recycling

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

·      Evidence from Other Gas Clouds

·      We can see stars forming in other interstellar gas clouds, lending support to the nebular theory.

·      The Orion Nebula with Proplyds

****What caused the orderly patterns of motion in our solar system? ****

·      Orbital and Rotational Properties of the Planets 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.

·      Collisions between particles in the cloud caused it to flatten into a disk.

·      Flattening Collisions between gas particles in a cloud gradually reduce random motions.

·      Formation of Circular Orbits Collisions between gas particles also reduce up and down motions.

****Why does the Disk Flatten? ****

·      The spinning cloud flattens as it shrinks.

·      Formation of the Protoplanetary Disk Disks Around Other Stars

·      Observations of disks around other stars support the nebular hypothesis.

****Why are there two major types of planets? ****

·      As gravity causes the cloud to contract, it heats up.

·      Conservation of Energy Collapse of the Solar Nebula Inner parts of the disk are hotter than outer parts.

·      Rock can be solid at much higher temperatures than ice.

·      Temperature Distribution of the Disk and the Frost Line

·      Inside the frost line: Too hot for hydrogen compounds to form ices Outside the frost line: Cold enough for ices to form

·      Formation of Terrestrial Planets

·      Small particles of rock and metal were present inside the frost line.

·      Planetesimals of rock and metal built up as these particles collided.

·      Gravity eventually assembled these planetesimals into terrestrial planets

·      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.

·      Formation of Jovian Planets

·      Ice could also form small particles outside the frost line.

·      Larger planetesimals and planets were able to form.

·      The gravity of these larger planets was able to draw in surrounding H and He gases.

·      The gravity of rock and ice in jovian planets draws in H and He gases.

·      Nebular Capture and the Formation of the Jovian Planets Moons of jovian planets form in miniature disks.

·      Radiation and outflowing matter from the Sun — the solar wind — blew away the leftover gases. The Solar Wind

****Where did asteroids and comets come from? ****

·      Asteroids and Comets

·      Leftovers from the accretion process

·      Rocky asteroids inside frost line

·      Icy comets outside frost line Heavy Bombardment

·      Leftover planetesimals bombarded other objects in the late stages of solar system formation

·      Origin of Earth’s Water

·      Water may have come to Earth by way of icy planetesimals from the outer solar system.

***How do we explain the existence of our Moon and other exceptions to the rules?*

·      Captured Moons

·      The unusual moons of some planets may be captured planetesimals.

·      Odd Rotation

·      Giant impacts might also explain the different rotation axes of some planets.

·      Review of nebular theory

·      There are two main types of planets: terrestrial and jovian.

·      Planets orbit in the same direction and plane.

·      Asteroids and comets exist.

·      There are four terrestrial and four jovian planets.

·      There are two main types of planets: terrestrial and jovian.

·      Planets orbit in the same direction and plane.

·      Asteroids and comets exist.

·      There are four terrestrial and four jovian planets.

****When did the planets form? ****

·      We cannot find the age of a planet, but we can find the ages of the rocks that make it up.

·      We can determine the age of a rock through careful analysis of the proportions of various atoms and isotopes within it.

·      Radioactive Decay

·      Some isotopes decay into other nuclei.

·      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 Dating the Solar System

·      Radiometric dating tells us that the oldest moon rocks are 4.4 billion years old.

·      The oldest meteorites are 4.55 billion years old.

·      Planets probably formed 4.5 billion years ago.