Orion Nebula: Star-forming Region

Solar Nebula

Flattening the Solar Nebula

Disks Around Other Stars

Steps in Planet Formation

1. Condensation

2. Accretion

3. Nebular Capture (Jovian Planets only)

• After planets form, the solar wind clears the nebula: gas and dust are blown away

Condensation and Temperature

• Metals: iron, nickel, aluminum, and other metals can solidify around 1600 K

• Rocks: primarily silicon-based minerals solidify around 500-1300 K

• Hydrogen Compounds: molecules of methane, ammonia, and water freeze into ices below 150 K

• Light gases: hydrogen and helium never condense in the solar nebula

Accretion into Planetesimals

• Condensed materials collide and stick together forming planetesimals

• Planetesimals would continue to grow from further accretion and gravity

• Larger planetesimals would form spherical shapes because of stronger self-gravity

• Some planetesimals would fragment due to collisions

Planetesimals to Planets

Self-gravity

Uncompressed Densities

Nebular Capture: Jovian Planets

• Larger planetesimals of the Jovian planets resulting in a stronger gravitational force

• Stronger gravity allowed the Jovian plantes to capture more gas and planetesimals

• Hydrogen and Helium gas could be captured despite low mass of these gases

• Jovian planets formed disk-shaped nebulae• Lower temperatures meant Hydrogen and Helium

gas would not escape from the Jovian planets

Nebular Capture: Jovian Planets

The Sun’s Lost Spin

• Magnetic field of the Sun drags charged particles in the disk of the solar nebula.

• This causes friction which slows down the rotation of the Sun

• Otherwise, the Sun should have a faster spin than is observed

A History of Impacts

Captured Moons of Mars

Leftover Planetesimals

Radioactive Dating

Detecting Extrasolar Planets

Detecting Extrasolar Planets

Extrasolar Planets

More Extrasolar Planets

First Direct Detection!

• Planet Orbiting the star HD209548

• Eclipsed by planet