Transcript Formation of the Solar System

Formation of the Solar System
Q of D: How did the solar system form?
Formation of Solar System
Current theory is called accretion (a process
of coming together) or Nebular Theory.
Accretion I
a.k.a “Solar Nebular Theory”
1. Start with a nebula – a cloud of dust and
gas.
Accretion II
2. A shock wave causes gas and dust and
start to condense – come together to
form small rocks.
3. Gravity takes over (!) Pieces begin to
clump into bigger and bigger pieces.
Accretion III
3. It begins to spin as it condenses, and the
group of rocks, dust and planetesimals
takes a flat disk shape.
4. Clumping pieces become planetesimals,
which become protoplanets, which
become planets and moons.
Accretion IV
5. The big clump in center is “protosun”. As
it gets bigger, it gets hotter and denser.
6. When it becomes big enough, it ignites
(nuclear fusion).
Accretion IV
7. Solar wind (from the sun) blows off
remaining dust and debris.
• Inner planets are rocky and have metals.
Heavy elements withstand the solar wind
(gravity, again).
• Outer planets are made of light
elements, H and He.
Other Facts
• We know from radioactive dating, the oldest
rocks (on earth, moon, and mars) are approx.
4.6 billion years old. That’s the generally
accepted age of the solar system.
• Over 150 planets have been identified on other
stars.
• This is a “theory”. It ties together all of the
available evidence, and it seems reasonable.
We think it’s right, but……..
Evidence that supports the theory:
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Over 150 planets have been identified on other stars.
What we believe to be accretion disks have been observed.
Materials from Moon, Mars, meteorites appear to be of similar
ages and composition
Composition of the planets (inner and outer)
Motion of planets and sun
Law of gravity
Existence of solar wind
Asteroids – a broken or unformed planet?
What appear to be accretion disks have been observed around
protostars (Hubble photos of the Horsehead nebula)
We are always learning more.
Kuiper Belt
• A collection of icy planetesimals in orbit
from Neptune to 100 AU or more.
Oort Cloud
The Oort Cloud was discovered in 1950 by Dutch Astronomer Jan
Oort. It lies beyond the Kuiper belt some 30,000 AU to 1 Light Year
away from the Sun. The Oort Cloud is thought to be the origin of
many of our long term comets. The short term comets originate
closer to home, in the Kuiper Belt, which lies just beyond the orbit of
Neptune.
Where does the Solar System end?
The distance from the sun to the earth is 1 astronomical unit (1AU).