Objectives:1.Understand how stars and planets form2.Relate how a variety of forces shape planetary system3.Evaluate multiple pieces of evidence to a variety of planetary system hypothesis’.4.Compare 3 different methods scientists use to discover extraplanetary systems.

Planetary systemNebular hypothesis

NebulaProtostar

Protoplanetary diskAccretion disk

Angular momentumPlanetesimals

Refractory materialsVolitiles

AtmospheresTerrestrial planets

Giant planets asteroid beltExtrasolar planets

• Planetary system: A collection of planets, moons, and other smaller bodies surrounding a host star

• Solar system: Our planetary system

• Nebula: a rotating cloud of interstellar gas• Nebula Hypothesis: Planetary systems form

from a nebula that gradually collapses and flattens out to form a disk by its own self-gravity.

Meteorites: include bits and pieces of material stuck together with filler, resembling concrete.

Conclusion: the larger bodies in the solar system had grown from the aggregation of smaller bodies.

Our solar system formed roughly 5 billion years ago (bya).

Protostar: a large hot ball of gas whose nuclear fires had not yet ignited.

Protoplanetary disk: (proplyd). A flay rotating disk surrounding a protostar made of gas and dust.

Angular momentum: momentum of a rotating object. Depends on three things:

1.How fast the object is rotating2.The mass of the object3.How the mass of the object is distributed.An object that is rotating slowly but is more

spread out may have more angular momentum than an object that is rotating more rapidly that is more compact.

It might seem natural that the rotation nebula would collapse into an ever smaller ball under it’s self gravity, but……

The cloud’s own angular momentum causes it to flatten out, like pizza dough being spun through the air.

1. As a slowly rotating interstellar cloud collapses it rotates faster.

2. Rotation slows collapse perpendicular to but not parallel to the axis, so the cloud flattens.

3. Eventually the cloud collapses from the inside out, and an accretion disk and protostar form.

Accretion disk: a thin rotating structure that serves as a way station for material on its way to becoming part of the star that is forming at its center.

Motion of the accretion disk pushes smaller grains of dust back and forth past larger grains causing them to stick together via static electricy.

Creating clumps the size of pebbles and then boulders which are less susceptible to being pushed around by the gas.

When clumps grow to 100 meters across their growth rate slows.

As clumps reach the size of kilometer they are considered planetesimals, and are massive enough that their gravity begins to dominate their growth.

The inner disk is hot, the outer disk is cold

As matter falls toward the protostar it lands on the disk.

The gravitational potential energy of this falling matter is transformed into heat energy as it lands on the disk.

Since the center of the disk (the protostar) has the greatest gravitational potenetial energy, the inner disk is how and the outer disk is cold.

Refractory Materials: rocky materails and metals that remain solid at high temperatures.

Volitile materials: water, ammonia, methane, that remain in the solid form only if their temperature remain low.

Difference in temperature have a significant effect on the makeup of the dust grains on different parts of the disk.

Volitiles can survive only in the outer disk, but….Refractory materials can survive anywhere.

Planets that form close to the central star are made up of rock and metals (refractory materials).

Planets that form farther out also contain refractory materials, but in addition they contain large quantities of volitiles and organic materials.

Terrestrial planets: include mercury, venus, earth, and mars which are made up of mostly refractory materials.

Giant planets: include Jupiter, Saturn, Uranus, and Neptune which are made up of volatile materials.

The search for Extrasolar Planets

The spectroscopic radial velocity method: has been the most successful with a few exoplanets being detected every week this way.

Mostly find large Jupiter like planets.The orbits of large planets cause a star to

wobble, causing a Doppler effect shifting from red to blue wavelengths.

Transit Method

Astronmers measure the diminishment of light as planet passes between its star and us.

Enables us to measure the size of a planet.

Planetary systems seem to common place

More than 500 extrasolar planets have been detected, and new ones are being discovered on a daily or weekly basis.

Most of these planets are large gas giants like Jupiter because they are easy to detect, only a handful of terrestrial planets have been detected, but soon our technology will allow us to measure and detect these easily.