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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.
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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
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: All of the planets orbit the sun in the same direction, and in the same plane The planets closest to the sun are small and rocky, have few moons The planets further from the sun are large and contain more gas and icy materials Most of the Moons orbit their planets in the same direction as the planets orbit the sun Oldest meteorites are about 4.566 billion years old Planetary surfaces are all younger than the oldest meteorites
Sun-planet distance (relative to Earth: AU) Mercury 0.4 AU Venus 0.7 Earth 1.0 Mars 1.5 Jupiter 5.2 Saturn 9.5 Uranus 19 Neptune 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
Other residents of the solar system 2. Asteroids - rocky, d < 1000 km, orbit the sun
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
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)
Any GOOD hypothesis about the origin of the solar system must explain most - if not all - of its characteristics: All of the planets orbit the sun in the same direction, and in the same plane The planets closest to the sun are small and rocky, have few moons The planets further from the sun are large and contain more gas and icy materials Most of the Moons orbit their planets in the same direction as the planets orbit the sun Oldest meteorites are about 4.566 billion years old Planetary surfaces are all younger than the oldest meteorites
H, He gas is present throughout the disk Icy compounds and rock/metal Rock & metal ice line Condensation: gas becomes solid
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
Giant (“jovian”) Terrestrial (“earth like”) Lots of solids in the disk (cold > 5 AU) Cores form from ice, rock and metal Grow large, quickly (~1 million years) Big enough to trap H and He gas from disk Very little solid material in disk at 1 AU Form from rock and metal only Grow slowly (~100 million years) Too small to trap any gas from disk Planet formation: Terrerstrial vs. giant planets
Connecting the dots: From planet formation to early Earth Computational astrophysics meets field geology!
Hot+Dry (H2O gas) H2O ice habitable zone 1 million years 10 million years Jupiter >100 million years, 3.8 billion years ago
Terrestrial planets form by accretion of solids Dust >rocks >planetesimals >embryos >planets
The Moon-Forming Event t=0 : IMPACT! 6 minutes 20 minutes 32 minutes • A protoplanet the size of Mars (1/10 Earth’s mass) struck Earth, forming the Moon 4.5 billion years ago • Oceans boiled away, silicate-vapor atmosphere for at least 1 Myr • Earth had already differentiated into core & mantle structure by this time
But what if you don’t know: • the initial number of parent & daughter atoms? • how much of the P & D’s have entered or left the rock?
Solution: Isochron dating, requires a 4th measurement (the amount of a stable isotope of one of the elements) 48.8 Gyr Slope = D(now)/P(now)
solid melt
Make measurements for different minerals in rock. If data are linear, there is a strong correlation between: • The amount of P in each sample • The extent to which the sample has been enriched in D
Stable isotope geochronology 87Sr/86Sr 87Rb/86Sr
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
