Transcript Planetary system

Objectives:
1. Understand how stars and planets form
2. Relate how a variety of forces shape planetary
system
3. Evaluate multiple pieces of evidence to a variety
of planetary system hypothesis’.
4. Compare 3 different methods scientists use to
discover extraplanetary systems.
Planetary system
Nebular hypothesis
Nebula
Protostar
Protoplanetary disk
Accretion disk
Angular momentum
Planetesimals
Refractory materials
Volitiles
Atmospheres
Terrestrial planets
Giant planets asteroid belt
Extrasolar 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 selfgravity.
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 rotating
2. The mass of the object
3. 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.