Planet formation
- H, He represent 90% of the mass of the Solar Nebula
- plenty of mass to build a giant planet
- Jupiter and Saturn are primarily H and He
- Uranus and Neptune about 50% H, He by mass
- Something “clears out” the abundant gaseous component of the solar nebula disk after ~ 10 million years
- strong “T-Tauri” wind
- or perhaps accretion on to star
- Leaving behind planets and other debris
- asteroids, comets, Kuiper-Belt objects, Pluto
Ages of the Solar System
- Fundamentally based on radioactive decay
- example 14C -> 14N with half-life of ~ 104 y
- Shroud of Turin only 800 +/- 100 y old
- can’t be Christ’s shadow on it
- Long half-lives for dating Solar System