Download Origin of SS - Independence High School

Origin of the Solar System
Stars spew out 1/2 their mass as gas & dust as they die
In the interstellar medium, dust and gas coalesces into clouds
New generations of stars (and their planets, if any) form in
these clouds
Nebular theory
•
•
•
•
Interstellar cloud of gas &
dust collapsed under its own
gravity
Prediction: protoplanetary
nebulae should be observed
Explains all of the major
features of solar system, and
also the exceptions
Observations continue to
support this theory
H, He gas is present throughout the disk
Icy compounds and rock/metal
Rock & metal
ice line
Condensation: gas becomes solid
The next billion years: Debris disks
•
•
•
•
•
•
Gas and fine dust blows away after
~ 10 million years
Jupiter must have formed by then
Older stars have ‘debris disks’
around them
Need a supply of larger objects to
regenerate the dust that gets
blown away
evidence of planets forming around
other stars
Debris disks are analogous to the
Oort cloud and Kuiper belt of
comets, and the asteroid belt
Debris disks around stars > 100 million years old are very
common!
Any GOOD hypothesis about the origin of the solar system
must explain most - if not all - of its characteristics:
1. All of the planets orbit the sun in the same direction,
and in the same plane
2. The planets closest to the sun are small and rocky,
have few moons
3. The planets further from the sun are large and
contain more gas and icy materials
4. Most of the Moons orbit their planets in the same
direction as the planets orbit the sun
5. Oldest meteorites are about 4.566 billion years old
6. Planetary surfaces are all younger than the oldest
meteorites
Sun-planet distance (relative to Earth: AU)
Mercury
Venus
Earth
Mars
Jupiter
Saturn
Uranus
Neptune
0.4 AU
0.7
1.0
1.5
5.2
9.5
19
30
1 AU = 150 million km
Other residents of the solar system:
1. Dwarf planets
diameter = 1000-3000 km, smaller than Moon, orbit the sun
QuickTime™ and a
decompressor
are needed to see this picture.
QuickTime™ and a
decompressor
are needed to see this picture.
Other residents of the solar system
2. Asteroids - rocky, d < 1000 km, orbit the sun
Asteroid belt
QuickTime™ and a
decompressor
are needed to see this picture.
Asteroids are
really quite rare…
QuickTime™ and a
decompressor
are needed to see this picture.
Other residents of the solar system
3. Comets - rock & ice, wide
range of sizes (~10 m to
100 km)
Other residents of the solar system
4. Moons - orbit planets, some are larger than Mercury
QuickTime™ and a
decompressor
are needed to see this picture.
QuickTime™ and a
decompressor
are needed to see this picture.
Asteroids and comets
are leftover
planetesimals
Some moons are
captured
planetesimals
Other residents of the solar system
5. Meteoroids - small fragments of asteroids that enter
earth’s atmosphere (dust to boulder sized)
QuickTime™ and a
decompressor
are needed to see this picture.
Meteor!
What are the planets made of?
Element
how many atoms gas or solid at
(total)
Earth
Jupiter
________________________________________________
Hydrogen
705,700
gas
gas
Helium
275,200
gas
gas
Carbon
3,032
gas
soot (solid)
Nitrogen
1,105
gas
ice
Oxygen
5,920
H2O gas
H2O ice
Silicon
653
rock
rock
Iron
1,169
metal
metal
Planet formation: Terrerstrial vs. giant planets
Giant (“jovian”)
1. Lots of solids in the
disk (cold > 5 AU)
2. Cores form from
ice, rock and metal
3. Grow large, quickly
(~1 million years)
4. Big enough to trap
H and He gas from
disk
Terrestrial (“earth like”)
1. Very little solid material in
disk at 1 AU
2. Form from rock and metal
only
3. Grow slowly (~100 million
years)
4. Too small to trap any gas
from disk
Terrestrial planets form by accretion of solids
Dust >rocks >planetesimals >embryos >planets
Formation of Jovian Planets: Fast! (< 10 Myr)
Core accretion: icy planetesimals clump together first
Gravitational instability: dense clump of nebular gas
forms first
The Nebular theory predicts
most other sun-like stars
should have planets
Do they?
358 planets have been found around other stars!!!
http://www.exoplanets.org