The Gas Giant (Jovian) Planets Jupiter Uranus Saturn Neptune The Terrestrial (Rocky/Metal) Planets Mercury Earth Venus Mars

Pluto (and Other Dwarf Planets) Much smaller than major planets, and not like a Jovian or terrestrial Icy, comet-like composition (not as much rock and little/no gas) Also Ceres (rocky/metal asteroid), Haumea, Makemake, Eris

Swarms of Smaller Bodies  Many rocky/metal asteroids and icy comets populate the Solar System. Asteroid Belt – small rocky/metal objects between Mars/Jupiter Kuiper Belt – icy comets outside Neptune’s orbit (including Pluto) at AU from Sun Oort Cloud – icy comets at ~50,000 AU or about a light year (not actually discovered yet)

Which of the following pairs of objects are primarily rocky objects? A) Terrestrial planets and asteroids B) Gas giant (Jovian) planets and comets C) Terrestrial planets and comets D) Gas giant (Jovian) planets and asteroids A) Terrestrial planets and asteroids B) Gas giant (Jovian) planets and comets C) Terrestrial planets and comets D) Gas giant (Jovian) planets and asteroids

Which of the following pairs of objects are primarily rocky objects? A)Terrestrial planets and asteroids B)Gas giant (Jovian) planets and comets C) Terrestrial planets and comets D) Gas giant (Jovian) planets and asteroids asteroid = rock (and some metal) comet = icy (and a little rock and metal) A)Terrestrial planets and asteroids B)Gas giant (Jovian) planets and comets C) Terrestrial planets and comets D) Gas giant (Jovian) planets and asteroids asteroid = rock (and some metal) comet = icy (and a little rock and metal)

Rules of the Solar System Our Solar System follows a set of rules that give us clues about how the Solar System formed. This helps us to form a theory about how planetary systems form around other stars. Exceptions to these rules in our Solar System challenge our theory. Theory also challenged by discovery of other solar systems around other stars within last 20 years. Our Solar System follows a set of rules that give us clues about how the Solar System formed. This helps us to form a theory about how planetary systems form around other stars. Exceptions to these rules in our Solar System challenge our theory. Theory also challenged by discovery of other solar systems around other stars within last 20 years.

Motion of Large Bodies  All large bodies in the Solar System orbit in the same direction as the Sun rotates and in nearly the same plane.  Most (but not all) also rotate in that direction.  Planets do not orbit in random directions or random inclinations, but in nearly the same plane (like a flat pancake).  All large bodies in the Solar System orbit in the same direction as the Sun rotates and in nearly the same plane.  Most (but not all) also rotate in that direction.  Planets do not orbit in random directions or random inclinations, but in nearly the same plane (like a flat pancake).

Two Major Planet Types  Terrestrial planets made of rock/metal (high density), relatively small, and close to the Sun with few/no moons and no rings.  Gas giant (Jovian) planets are mostly gaseous + ice (low density), larger, and farther from the Sun with many moons and rings.  Terrestrial planets made of rock/metal (high density), relatively small, and close to the Sun with few/no moons and no rings.  Gas giant (Jovian) planets are mostly gaseous + ice (low density), larger, and farther from the Sun with many moons and rings.

What properties of our Solar System must a formation theory explain? 1.Patterns of motion of the large bodies Orbit in same direction and plane 2.Existence of two types of planets Terrestrial and Jovian 3.Existence of smaller bodies Rocky/metal asteroids and icy comets 4.Notable exceptions to usual patterns Rotations of Uranus and Venus, Earth’s Moon 1.Patterns of motion of the large bodies Orbit in same direction and plane 2.Existence of two types of planets Terrestrial and Jovian 3.Existence of smaller bodies Rocky/metal asteroids and icy comets 4.Notable exceptions to usual patterns Rotations of Uranus and Venus, Earth’s Moon

What theory best explains the features of our solar system? The nebular theory states that our Solar System formed from the gravitational collapse of a giant interstellar gas cloud—the solar nebula. (Nebula is the Latin word for cloud.) A large amount of evidence now supports this idea. The nebular theory states that our Solar System formed from the gravitational collapse of a giant interstellar gas cloud—the solar nebula. (Nebula is the Latin word for cloud.) A large amount of evidence now supports this idea.

Galactic Recycling  Heavy elements that formed planets were made in stars and then recycled through interstellar space.  Sun is a second or third (or later) generation star to explain 1% heavier element (non- hydrogen/helium) content of the Solar System.  Heavy elements that formed planets were made in stars and then recycled through interstellar space.  Sun is a second or third (or later) generation star to explain 1% heavier element (non- hydrogen/helium) content of the Solar System.

What caused the orderly patterns of motion in our solar system? Why do planets all go around Sun the same direction in the same plane?

Conservation of Angular Momentum Rotation speed of the large cloud from which our Solar System formed must have increased as the cloud contracted. As size speed

Rotation of a contracting cloud speeds up for the same reason a skater speeds up as she pulls in her arms. Cloud initially a light year or so in diameter.

Collisions between particles in the cloud caused it to flatten into a disk. Collisions between gas particles also reduce up and down motions.  flat, pancake structure forms, with everything revolving in the same direction Flattening

Collisions between gas particles in cloud gradually reduce random motions. Leads to nearly circular orbits of contracting gas.

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

Protoplanetary disks in Orion star-forming region. We see protoplanetary disks elsewhere!

Disks around Other Stars Observations of disks around other stars support the nebular hypothesis. AU MicroscopiiHD141569A

Summary of Solar System Formation 1)Initial large (1 light year diameter) barely rotating gas cloud begins to collapse gravitationally. 2)Cloud spins up (conserving angular momentum) and flattens (due to collisions) as it collapses. 3)Left with gas in a rapidly-rotating, thin, mostly circular pancake-shaped disk

Why are there two major types of planets?

As gravity causes cloud to contract, it heats up. Gravitational potential energy  kinetic energy of gas  thermal energy (heat) via collisions. Conservation of Energy

Inner parts of disk are hot; outer parts are cold. Rock and metal can be solid at much greater temperatures than ice.  rock/metal is present everywhere in Solar System Inner Solar System too hot for hydrogen compounds (water ice, ammonia ice, methane ice) to be solids.  ice, H compounds only survive as solids in outer Solar System Inner Solar System therefore contained only rock and metal in solid form  terrestrial planets + asteroids!

Inside the frost line: too hot for H/He/hydrogen compounds to form ices (get terrestrial planets and rocky/metal asteroids) Outside the frost line: cold enough for ices to form solids IN ADDITION to rock/metal (get Jovian planets and icy comets) Frost line between asteroid belt and Jupiter Important concept!

Tiny solid particles stick to form planetesimals Gravity draws planetesimals (tiny solid particles) together to form planets. This process of assembly is called accretion. Rock/me tal only Rock/metal/ice + H/He gas

Accretion of Planetesimals Many smaller objects collected into just a few large ones (dust grains to planetesimals to planets).

Dust grain – 0.02mm across from interplanetary space

Inside frost line: small metal/rock planets form – the terrestrial planets and asteroids Gravity of terrestrials too weak to draw in hydrogen/helium gas Outside the frost line: large planets form – the Jovians, plus comets The gravity of ice and rock in large Jovian planetesimals strong enough to draw in available H and He gas  grow big (ice/rock/metal core with large H/He gas envelope)

How would the Solar System be different if the solar nebula had cooled with a temperature half its actual value at every distance? A)Jovian planets would have formed closer to Sun. B) There would be no asteroids. C) There would be no comets. D) Terrestrial planets would be larger. How would the Solar System be different if the solar nebula had cooled with a temperature half its actual value at every distance? A)Jovian planets would have formed closer to Sun. B) There would be no asteroids. C) There would be no comets. D) Terrestrial planets would be larger.

How would the Solar System be different if the solar nebula had cooled with a temperature half its actual value at every distance? A) Jovian planets would have formed closer to Sun. B) There would be no asteroids. C) There would be no comets. D) Terrestrial planets would be larger. Frost line would have been closer to Sun, but everything else would have proceeded as before. How would the Solar System be different if the solar nebula had cooled with a temperature half its actual value at every distance? A) Jovian planets would have formed closer to Sun. B) There would be no asteroids. C) There would be no comets. D) Terrestrial planets would be larger. Frost line would have been closer to Sun, but everything else would have proceeded as before.

Which materials can be found in Jovian planets? A) hydrogen, helium B) hydrogen, helium, hydrogen compounds C) hydrogen, helium, hydrogen compounds, rock, metal

Which materials can be found in Jovian planets? A) hydrogen, helium B) hydrogen, helium, hydrogen compounds C) hydrogen, helium, hydrogen compounds, rock, metal Nothing precludes rock and metal from being in the outer part of the Solar System. It’s just that there is a lot more H/He/hydrogen compounds in the outer parts than rock and metal  Jovian planets have small rocky/metal cores covered by a lot of H/He/hydrogen compounds.

The gas giants are became “miniature solar systems” with their own miniature accretion disks which went to form moons. Many moons form in miniature disks of dust/gas around Jovians in a scaled-down version of how our entire Solar System formed.

Jovian systems formed like the Solar System in miniature. (form rocky moons)(form icy moons)

Most of the nebula material never gets incorporated into a (Jovian) planet. H/He gas is blown out of the young solar system by a strong solar wind — outflowing protons and electrons from the Sun. Planets stop growing at this point. What ended the era of planet formation?