Exam #2 Wednesday, March 31 Review session Monday, March 29 7:30 –9:30 pm Morrison Hall 007

TerrestrialJovian Two “flavors” of planets

 Size: smalllarge  Location:closer to Sundistant  Composition: rocky/metallicgaseous/icy  Temperature:hotter cold  Rings:noneubiquitous  Rotation rate:slowrapid  Surface:solidnot solid  Atmosphere:minimalsubstantial  Moons:few to nonemany Terrestrial Planets Jovian Planets

So how do we account for what we see in the solar system?

The Nebular Theory The Solar system was formed from a giant, swirling interstellar cloud of gas and dust (the solar nebula)‏

 Start with a giant, swirling interstellar cloud of gas and dust (the solar nebula)‏ The Nebular Theory

 Start with a giant, swirling interstellar cloud of gas and dust (nebula)‏  Perturb cloud to begin its collapse  Sit back and let physics take overSit back and let physics take over Recipe for solar system formation

Important physics in forming stars stars & planets  Gravity  Gas pressure  Conservation of Angular Momentum  Conservation of Energy  Phases of matter

Gravity vs Gas Pressure The struggle to form stellar/planetary systems

System initially in pressure balance – no collapse Protosolar nebula Slowly rotating

System initially in pressure balance – no collapse Gravity seeks to collapse cloud

System initially in pressure balance – no collapse Gas pressure seeks to expand cloud

System initially in balance – no collapse gravity gas pressure

gravity gas pressure Now, whack the cloud (don't use an actual hammer)‏

Perturbation triggers collapse – gravity is winning As collapse proceeds, rotation rate increases

As collapse continues, the rotation rate increases while nebula flattens

Building the Planets. I COLLAPSE OF PROTOSTELLAR CLOUD INTO A ROTATING DISK Composition of disk:  98% hydrogen and helium  2% heavier elements (carbon, nitrogen, oxygen, silicon, iron, etc.). Most of this was in gaseous form!

Collapse of the Solar Nebula As the solar nebula collapsed to a diameter of 200 A.U. (1 LY = 63, 240 AU), the following happened:  The temperature increased as it collapsed (conservation of energy; gravitational potential energy becomes thermal energy)  The rotation rate increased (conservation of angular momentum)  The nebula flattened into a disk (protoplanetary disk)  Motions of material in the disk became circularized

Material in the newly formed proto-planetary disk is: Orbiting in approximately the same plane Orbiting in approximately circular orbits This is the situation with the orbits of planets, so now we have the material in the proper location and moving in the proper manner.

Examples of proto- planetary disks

According to our theory of solar system formation, what three major changes occurred in the solar nebula as it shrank in size? (blue) It got hotter, its rate of rotation increased, and it flattened into a disk. (red) It gained energy, it gained angular momentum, and it flattened into a disk. (yellow) Its mass, temperature, and density all increased. (green) I have no idea

According to our theory of solar system formation, what three major changes occurred in the solar nebula as it shrank in size? (blue) It got hotter, its rate of rotation increased, and it flattened into a disk. (red) It gained energy, it gained angular momentum, and it flattened into a disk. (yellow) Its mass, temperature, and density all increased. (green) I have no idea

Which law best explains why the solar nebula spun faster as it shrank in size? (blue) Law of universal gravitation. (red) Einstein's law that E = mc 2. (yellow) Conservation of angular momentum. (green) Conservation of energy.

Which law best explains why the solar nebula spun faster as it shrank in size? (blue) Law of universal gravitation. (red) Einstein's law that E = mc 2. (yellow) Conservation of angular momentum. (green) Conservation of energy.

Why did the solar nebula end up with a disk shape as it collapsed? (blue) The force of gravity pulled the material downward into a flat disk. (red) It flattened as a natural consequence of collisions between particles in the nebula, changing random motions into more orderly ones. (yellow) The law of conservation of energy. (green) It was fairly flat to begin with, and retained this flat shape as it collapsed.

Why did the solar nebula ended up with a disk shape as it collapsed? (blue) The force of gravity pulled the material downward into a flat disk. (red) It flattened as a natural consequence of collisions between particles in the nebula, changing random motions into more orderly ones. (yellow) The law of conservation of energy. (green) It was fairly flat to begin with, and retained this flat shape as it collapsed.

Which law best explains why the central regions of the solar nebula got hotter as the nebula shrank in size? (blue) Newton's third law. (red) Law of conservation of energy. (yellow) Law of conservation of angular momentum (green) The two laws of thermal radiation.

Which law best explains why the central regions of the solar nebula got hotter as the nebula shrank in size? (blue) Newton's third law. (red) Law of conservation of energy. (yellow) Law of conservation of angular momentum (green) The two laws of thermal radiation.

Building the Planets. II There was a range of temperatures in the proto-solar disk, decreasing outwards Condensation: the formation of solid or liquid particles from a cloud of gas (from gas to solid or liquid phase)‏ Different kinds of planets and satellites were formed out of different condensates

Ingredients of the Solar Nebula Metals : Condense into solid form at 1000 – 1600 K iron, nickel, aluminum, etc. ; 0.2% of the solar nebula’s mass Rocks : Condense at 500 – 1300 K primarily silicon-based minerals; 0.4% of the mass Hydrogen compounds : condense into ices below ~ 150 K water (H 2 O), methane (CH 4 ), ammonia (NH 3 ), along with carbon dioxide (CO 2 ), 1.4% of the mass Light gases (H & He): Never condense in solar nebula hydrogen and helium.; 98% of the mass

The "Frost Line” - Situated near Jupiter Rock & Metals can form anywhere it is cooler than about 1300 K. Carbon grains & ices can only form where the gas is cooler than 300 K. Inner Solar System: * Too hot for ices & carbon grains. Outer Solar System: * Carbon grains & ices form beyond the "frost line".

Building the Planets. III Accretion Accretion is growing by colliding and sticking The growing objects formed by accretion – planetesimals (“pieces of planets”)‏ Small planetesimals came in a variety of shapes, reflected in many small asteroids Large planetesimals (>100 km across) became spherical due to the force of gravity

In the inner solar system (interior to the frost line), planetesimals grew by accretion into the Terrestrial planets. In the outer solar system (exterior to the frost line), accretion was not the final mechanism for planet building – nebular capture followed once accretion of planetesimals built a sufficiently massive protoplanet.

Building the Planets. IV. Nebular Capture Nebular capture – growth of icy planetesimals by capturing larger amounts of hydrogen and helium. Led to the formation of the Jovian planets Numerous moons were formed by the same processes that formed the proto-planetary disk Condensation and accretion created “mini-solar systems” around each Jovian planet

What do we mean by the frost line when we discuss the formation of planets in the solar nebula? (blue) It is another way of stating the temperature at which water freezes into ice. (red) It is the altitude in a planet's atmosphere at which snow can form. (yellow) It marks the special distance from the Sun at which hydrogen compounds become abundant; closer to the Sun, there are no hydrogen compounds. (green) It is the distance from the Sun, beyond which the temperature was low enough for ices to condense.

What do we mean by the frost line when we discuss the formation of planets in the solar nebula? (blue) It is another way of stating the temperature at which water freezes into ice. (red) It is the altitude in a planet's atmosphere at which snow can form. (yellow) It marks the special distance from the Sun at which hydrogen compounds become abundant; closer to the Sun, there are no hydrogen compounds. (green) It is the distance from the Sun, beyond which the temperature was low enough for ices to condense.

Which of the following types of material can condense into what we call ice at low temperatures? (blue) hydrogen and helium (red) metal (yellow) hydrogen compounds (green) rock

Which of the following types of material can condense into what we call ice at low temperatures? (blue) hydrogen and helium (red) metal (yellow) hydrogen compounds Examples: water (H 2 O), Methane (CH 3 ), Ammonia (NH 4 )

Building the Planets. V. Expulsion of remaining gas

The Solar wind is a flow of charged particles ejected by the Sun in all directions. It was stronger when the Sun was young. The wind swept out a lot of the remaining gas

Building the Planets. VI. Period of Massive Bombardment

Planetesimals remaining after the clearing of the solar nebula became comets and asteroids Rocky leftovers became asteroids Icy leftovers became comets Many of them impacted on objects within the solar system during first few 100 million years (period of massive bombardment - creation of ubiquitous craters).

Brief Summary