Where did our Sun come from?

How did our Solar System form?

Solar Nebular Hypothesis: Accretionary Disk ModelHow our solar system formed

Nebular Hypothesis• The most widely accepted model

explaining the formation and evolution of the solar system. • Proposed in 1734 by Emanuel

Swedenborg.• Also known as: Accretionary Disk

Model

The beginning…1. A large cloud

of gas began to collapse under its own gravity becoming denser and hotter, forming a central star.

Formation of the planets2. The cloud of gas and dust begins to

contract (get smaller) and rotate more rapidly.

3. The cloud flattens into a pancake like disk.

Nebular Contraction

• Why does it spin faster as it contracts?

Think Ice skating: which is spinning faster?

Next…4. Gases and dust grains in the original

solar nebula begin to attract additional matter, forming clumps that rotate within the disk.

• Accretion: gradual accumulation of mass.

Question:• Which object, a large or a small

object, would accumulate more matter? Why?

Next…• Planetesimals formed (size of small

moon)• Protoplanets formed (immature full

scale planet• Then mature planets form.

So basically…• Our star formed at

the center of this cloud of gas while the outer, cooler parts of the disk are where the planets were created.

Inner Planets vs. Outer Planets• Inner planets

are small, solid and made with dense minerals. • Outer planets

are large, mostly gas with a solid core.

Review: how the solar system formedNebular theory / Accretionary model• Huge cloud of dust and gas• Begins to condense at center due to

gravity• Some areas in cloud become

concentrated by accretion (particles sticking together due to gravity)• Areas near sun high in heavier elements

(form inner planets)• Areas far from sun low in heavy

elements (form outer planets)

Solar System Characteristics

Solar System Characteristics• Gas Expulsion•Strong solar wind blew away any left over dust and gas.

• Planetesimal Ejection•Uranus and Neptune pushed planetesimals out to the Kuiper Belt.• Jupiter and Saturn Kicked planetesimals out to the Oort cloud

Solar System Characteristics• Scientists believe the Solar system is

at least 4.6 Billion years old!• Evidence:•Measuring rock age and composition on Moon, other moons, comets, asteroids, meteors

• How big is our solar system?•Remember what an Astronomical Unit is?•Mercury is 0.39 AU from the sun.•Pluto is 39.5 AU from the sun.

Solar System Characteristics• We are

approximately 27,000 ly away from the center of the Milky way galaxy.

Solar System Characteristics• Planets all orbit the Sun in the same

direction: counterclockwise. This is the same direction as the sun rotates on its axis.• The orbits of almost all the planets all

lie in nearly the same plane (the ecliptic plane)•Except: Mercury = 7; It is so close to the sun which exerts too much gravity causing it to orbit off of the ecliptic plane• Except: Pluto = 17; It is believed to be a satellite captured by the Suns gravity and not a planet that formed in the evolution of our star and solar system.

Mercury

7o

Pluto17o

2 Types of Planets• Terrestrial: • Inner planets• Mercury• Venus• Earth• Mars

•Rocky•Denser•Smaller

• Gas Giants (Jovian): •Outer planets• Jupiter• Saturn• Uranus• Neptune

•Balls of gas•Less dense•Larger•Rings

Solar System Characteristics

Size and Scale

Size and Scale