Download Nebular Theory

Nebular Theory
E5.3A Explain how the solar system
formed from a nebula of dust and gas in a
spiral arm of the Milky Way Galaxy about
4.6 Ga (billion years ago).
Milky Way Galaxy
As viewed from Earth. Appears to be a milky band of stars across the sky.
Milky Way Galaxy (Artist’s Interpretation)
Observations suggest that it is a spiral galaxy. It is made up of a central bulge with
spiral density arms radiating outward. The arms are areas with a concentration of
matter, usually in the form of hydrogen gas, contained in clouds called nebulae. The
Sun is located about ½ way out from the center to the edge on the Orion (local) Arm.
Nebula
Cloud of gas and dust. Sight of new star formation.
Protostars
• Gravity causes contraction of matter in clouds. Gravitational
energy is converted into heat energy causing them to glow red.
Protostars
Protoplanetary Disk
As gravity causes matter to contract toward the center, the cloud
spins, creating a disk of unconsolidated matter surrounding this
newly forming protostar.
Protoplanetary disk
Star blocked out to make
protoplanetary disk visible
Infrared allows astronomers to
see dust surrounding stars.
Accretion
Matter not collected in the center is swept up in the protoplanetary disk forming early
planets (protoplanets) through a process called accretion.
Disks around young stars
Meteorite evidence for
accretion
Evidence for the Nebular Theory
1. Observations of star forming regions
(nebulae) and protoplanetary disks.
2. Age of rocks
3. Meteorite samples
4. Meteor craters throughout solar system
5. Asteroid belt