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The Origin of the Solar System
Movie: The History of the Solar System
Please swipe your ID for attendance tracking and take your assigned transmitter.
How old is the Solar System?
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1) 1.3 million years
2) 350 million years
3) 1.7 billion years
4) 4.5 billion years
5) 13 billion years
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Visible
Barnard 68
Star formation ← collapse of the cores of giant molecular clouds: Dark, cold, dense clouds obscuring the light of stars behind them.
The Formation of Stars:Giant Molecular Clouds
Which wavelength range is adjacent to the visible spectrum and has longer
wavelengths than visible light?
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1) X-rays2) Gamma-Rays3) Stingrays4) Infrared light5) Ultraviolet light
VisibleInfrared
Barnard 68
Star formation ← collapse of the cores of giant molecular clouds: Dark, cold, dense clouds obscuring the light of stars behind them.
(More transparent in infrared light.)
The Formation of Stars:Giant Molecular Clouds
Parameters of Giant Molecular Clouds
Size: r ~ 50 pcMass: > 100,000 Msun
Dense cores:
Temp.: a few 0K
R ~ 0.1 pcM ~ 1 Msun
(Bok) Globules
~ 10 – 1000 solar masses;
Contracting to form protostars
Compact, dense pockets of gas which may contract to form stars.
ProtostarsProtostars =
pre-birth state of stars:
Hydrogen to Helium fusion not yet ignited
Still enshrouded in opaque
“cocoons” of dust => barely visible in the optical, but
bright in the infrared.
Do you expect stars to form isolated?
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1) Yes.2) No, they should form in
groups of a few (2 – 5)3) No, they should form in
large groups (several 100s or 1000s)
4) No, actually all stars in a galaxy (several billions) should form at the same time.
Open Clusters of Stars
Large masses of Giant Molecular Clouds => Stars
do not form isolated, but in large groups, called Open
Clusters of Stars.
Open Cluster M7
What happens to a spinning object if it contracts?
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1) It stops rotating.
2) Its rotation slows down.
3) Its rate of rotation remains unchanged.
4) Its rotation speeds up.
Protostellar Disks
Conservation of angular momentum leads to the formation of protostellar disks → birth place of
planets and moons
The Solar Nebula Hypothesis
Planets form at the same time from the
same cloud as the star.
Sun and our Solar system formed ~ 4.6 billion years ago.
Planet formation sites observed today as dust disks of T Tauri stars.
Would you expect that other stars have planetary systems too?
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1) Yes.
2) No.
Extrasolar PlanetsAll stars have gone through basically the
same formation process as the sun.→ Many stars should have planets!
Extrasolar planets can not be imaged directly.
→ planets orbiting around other stars = “Extrasolar planets”
Detection using the “wobbling” technique:
Look for “wobbling” motion of the star due to the gravitational pull of the planet on the star.
Would you expect that there are still new solar systems being formed at this time?
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1) Yes.
2) No.
Evidence for Ongoing
Planet Formation
Many young stars in the Orion
Nebula are surrounded by
dust disks:
Probably sites of planet formation
right now!
Dust Disks around
Forming Stars
Dust disks around some T Tauri stars
can be imaged directly (HST).
What is radioactivity?
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1) The decay of atomic nuclei, resulting in the emission of radio waves.
2) The decay of atomic nuclei, resulting in the emission of gamma-rays.
3) The fusion of atomic nuclei, resulting in the emission of radio waves.
4) The fusion of atomic nuclei, resulting in the emission of gamma-rays.
5) The emission of radio waves by stars like our sun.
The Age of the Solar SystemSun and planets should
have about the same age.
Ages of rocks can be measured through radioactive dating:
Measure abundance of a radioactively decaying element to find the time
since formation of the rock
Dating of rocks on Earth, on the Moon, and
meteorites all give ages of ~ 4.6 billion years.
If you start out with 1 kg of a radioactive substance with a half-life of 150 years, how long does it take until there is nothing left?
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1) 150 years.2) 300 years.3) 1,500 years.4) An infinite amount of
time (in principle).5) Impossible to tell with
the given information.
What is “condensation”?
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1) The melting of a substance.2) The transition of a substance
from the liquid to the gas phase.
3) The transition of a substance from the gas to the liquid phase.
4) The transition of a substance from the liquid to the solid phase.
Condensation in the Early Solar System
Only condensed materials could stick together to
form planets
Temperature in the protostellar cloud
decreases outward.
Further out → Protostellar cloud cooler → metals with lower melting point condensed → change of
chemical composition throughout solar system Lighter substances
condense at lower temperatures.
→ Average density of planets decreases outwards!
Formation and Growth of Planetesimals
Planet formation starts with clumping together of
grains of solid matter: Planetesimals
Planetesimals (few cm to km in size) collide to
form planets.
Planetesimals grow through condensation
and accretion.
What happens if you try to mix oil and water?
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1) They will mix to a uniform solution.
2) The oil will sink to the bottom, the water will “swim” on top of it.
3) The water will sink to the bottom, the oil will “swim” on top of it.
The Growth of Protoplanets
As rocks melted, heavier elements sink
to the center → differentiation
→ Terrestrial planets have heavy-metal (iron)
cores and mantles of lighter substances
The Story of Planet BuildingPlanets formed from the same protostellar material as the sun.
Rocky planet material formed from clumping together of dust grains in the protostellar cloud.
Mass of less than ~ 15 Earth masses:
Planets can not grow by gravitational collapse
Mass of more than ~ 15 Earth masses:
Planets can grow by gravitationally attracting material
from the protostellar cloud
Earthlike planetsJovian planets (gas giants)
Which features on the surface of the moon tell us that there were many small bodies (rocks) remaining in the solar system after it formed?
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1) A dense atmosphere.
2) The large, uncratered maria.
3) Lots of impact craters in the lunar highlands.
4) High mountains.
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Clearing the Nebula
Surfaces of the Moon and Mercury show evidence for heavy bombardment by asteroids.
Remains of the protostellar nebula were cleared away by:
• Sweeping-up of space debris by planets
• Ejection by close encounters with planets
Ejection of small bodies by massive planets
Clearing the Nebula
Surfaces of the Moon and Mercury show evidence for heavy bombardment by asteroids.
Remains of the protostellar nebula were cleared away by:
• Radiation pressure of the sun
• Solar wind• Sweeping-up of space debris by planets
• Ejection by close encounters with planets
Final overview movie
