Download Origin of the Solar System

Formation of our solar system:
The nebular hypothesis (Kant, 1755)
Hydrogen (H), He (He) and “stardust”
(heavier elements that were formed
in previous stars)
Our Solar System - Origins
• Observations
– Ordered motions of objects
– Two types of planets – Terrestrial (Solid) vs. Jovian
(Gas)
• For example, Mars vs. Jupiter
– Asteroids and comets
– Exceptions to ordered motions
• Tilt of Earth’s axis, Earth’s Moon, Pluto
• Is there a theory that can explain what we see?
Yes!!
Nebular Theory
• Solar System formed through
the collapse of a large cloud of
gas under its own gravity
Eagle Nebula
Lagoon Nebula
Formation of our solar system:
The nebular hypothesis (Kant, 1755)
Gravitational Collapse
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Lets look at an animation!
Angular Momentum Conservation also explains why objects
rotate faster as they shrink in radius:
Formation of our solar system:
The nebular hypothesis (Kant, 1755)
Formation of our solar system:
The nebular hypothesis (Kant, 1755)
From Cloud to Solar System
• Energy Conservation
– As the nebula contracts, the
energy is concentrated in a
smaller area. This, in turn,
heats the cloud
• Ang. Momentum Cons.
– Causes the cloud to spin
faster
• Cloud Flattens
– The lighter material floats
to the outer edges.
– The more dense material
stays towards the center.
– In our solar system, this
was the formation of our
inner solid and outer
gaseous planets.
Does this theory make sense?
• We observe many other stars forming from interstellar
clouds with circumstellar disks
• What has yet to be explained?
How do planets form?
• Through accretion (collecting of material)
– Small particles are able to build larger complexes of
particles through electromagnetic forces
– Eventually the complex becomes large enough to
“attract” pieces through gravitation – planetesimals
– Only the largest planetesimals survive to become
planets
– The smaller pieces collide and merge with the larger
ones or are broken up by gravitational forces
• Question: Why are all of the planets very nearly
spherical in structure?
Why are there two types of
planets?
• It all boils down to temperature
• Gas in the solar nebula was
mostly hydrogen and helium,
but there were trace amounts of
hydrogen compounds, rock, and
metals
• Condensation (gas solidifying
into solid) occurs at different
temperatures
• Warmer temperatures closer to
the center of the disk (Sun)
• Temperature decreases as we
move towards the edge of the
disk
Planet Formation
• Terrestrial planets (Mercury, Venus, Earth, and
Mars) all formed beyond a distance of 0.3 AU
– Rock could not condense within this distance
• Jovian planets (Jupiter, Saturn, Uranus, and
Neptune) all formed beyond the frost line (3.5
AU)
– Hydrogen compounds formed the cores of these planets
• Continues to support nebular theory
• What about planet orbits?
– But more questions remain
The solar system:
Sun, terrestrial, and Juvian planets
Terrestrial (inner) planets
Juvian (outer) planets
•Small
•contains the heavier elements (Fe, Si, O)
•rocky shell over a metallic core
•Accretion began 4.567 billion years ago
•It took about 0.1 billion years
(100 million years) for planets to form
•mostly volatile gases (H,He)
•same composition as the sun,
but internal pressure is too low
for nucleo-synthesis to take place
99.8 % of the total mass of the solar system resides in the sun
Earth formation
Nebula forms out of H, He clouds
and fusion products from now dead stars.
Gravity pulls gas and dust inward, and rotation
makes a accretionary disk. The proto-sun is at
the center and fusion begins when it is hot enough.
Gravity reshapes the
proto-Earth into a sphere
Heavier elements concentrate in the inner rings. Collisions and
gravitational attraction leads to the formation of planetesimals.
Soon after Earth formed, a Mars-size planet collided with
Earth, blasting debris into space that will form our Moon.
Volcanic gases form the atmosphere, and as Earth
cools, moisture condenses and rains into oceans.
Some gases may have come from passing comets.
Asteroids and Comets
Ida
• Asteroids – Rocky leftover planetesimals
• Comets - Icy leftover planetesimals
Hale-Bopp
Other Solar Systems?
• Detected over 100
planets
• Can not detect directly
– Even for the largest
planets, light from the
star overwhelms any
light from the planet
• Use indirect evidence
to search for planets
– Gravitational tugs