origin of the solar system. stars spew out 1/2 their mass as gas & dust as they die
TRANSCRIPT
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
• 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
Nebular 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 old6. Planetary surfaces are all younger than the oldest
meteorites
Sun-planet distance (relative to Earth: AU)
Mercury 0.4 AUVenus 0.7 Earth 1.0Mars 1.5Jupiter 5.2Saturn 9.5Uranus 19Neptune 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
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Other residents of the solar system
2. Asteroids - rocky, d < 1000 km, orbit the sun
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Asteroid belt
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Asteroids are really quite rare…
3. Comets - rock & ice, wide range of sizes (~10 m to 100 km)
Other residents of the solar system
Other residents of the solar system
4. Moons - orbit planets, some are larger than Mercury
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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)
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Meteor!
What are the planets made of?
Element how many atoms gas or solid at (total) Earth Jupiter
________________________________________________Hydrogen 705,700 gas gasHelium 275,200 gas gasCarbon 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
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