Chapter 6 Notes: Jessica Horn

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 degrees Celsius (day), -170 degrees Celsius (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 degrees Celsius, 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.
• Giant volcanoes, a huge canyon, polar caps, and more.
• Water flowed in the distant past.
• Jupiter
• Much farther from Sun than inner planets.
• Mostly H/He; no solid surface.
• 300 times more massive than Earth.
• Many moons, rings.
• Saturn
• Giant and gaseous like Jupiter.
• Spectacular rings.
• Many moons, including cloudy Titan.
• Cassini spacecraft currently studying it.
• Uranus
• Smaller than Jupiter/Saturn; much larger than Earth.
• Made of H/He gas and hydrogen compounds.
• Extreme axis tilt.
• Moons and rings.
• Neptune
• Similar to Uranus, except for axis tilt.
• Many moons, including Triton.
• Pluto and Eris (Dwarf Planets)
• Much smaller than other planets.
• Icy, comet-like composition.
• Pluto's moon Charon is similar to Pluto.
• Motion of Large Bodies
• All large bodies in the solar system orbit in the same direction in nearly the same plane.
• Most also rotate in that direction.
• Two Major Planets
• 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.
• According to Nebular Theory, our solar system formed from a giant cloud of interstellar gas.
• 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.
• Conservation of Energy: As gravity causes the cloud to contract, it heats up.
• 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.
• 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. 
• Asteroids and Comets
• Leftovers from the accretion process.
• Rocky asteroids inside the frost line.
• Icy comets outside frost line.
• 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.
• Dating the Solar System
• 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.