Origin of Our Solar SystemOrigin of Our Solar System

TEK Objective 5: Earth in space and time. The student understands the solar nebular accretionary disk model. The student is expected to:

analyze how gravitational condensation of solar nebular gas and dust can lead to the accretion of planetesimals and protoplanets;

Where did we come from?Where did we come from?The origin of the planets

in our Solar System has

been debated since

1755 when Immanuel

Kant proposed the first theory

Scientists

debated whether

the origin of our

Solar System

was usual, or a

common

consequence of

star formationDuring the 1900s, many

believed we are not a

unique occurrence because

of the recent discovery of

other planetary systems

around other stars

Two Main TheoriesTwo Main Theories

The Nebular The Nebular

HypothesisHypothesis The The Protoplanet Protoplanet HypothesisHypothesis

Nebula are star “nurseries”, where stars are born. This nebular photograph was taken by the Hubble Space

Telescope

Sun-like stars usually take around 100 million years to form.

A nebula is the product of a supernova event. The death of one system, may well be the birth of another!

The Nebular Hypothesis The Nebular Hypothesis In 1755 Immanuel Kant proposed that a solar nebulae was pulled together by gravity so that it collapsed into a flat, rotating disk that eventually coalesced into the Sun and planets

Solar nebulae are huge clouds of dust and

gas

Pierre Laplace expanded

the theory in 1796 and

proposed that the planets

were formed by rings of

matter split off a rotating

nebulae by centrifugal

force

The Nebular Hypothesis The Nebular Hypothesis

Laplace stated that after the matter split off, it coalesced into a planet. The process repeated itself, resulting in a planet each time. The matter left over was the Sun.

The spinning nebula

formed planets

because as the masses

became more

concentrated the more

they began to spin.

Much like a figure skater. You may

have noticed that skaters can spin

much faster if they pull their arms closer to their bodies. The more concentrated their body masses

are, the faster they'll be able to rotate.

The hypothetical explosion squeezed the unformed gas and dust

together, which began to spin faster and faster in a circle

As the sun formed

in the middle, the

cloud started to

flatten out into a

disc, sort of like a

Frisbee or a

pancake, with tiny

dust grains making

up the rest of the

disc.

Problems With the Nebular Problems With the Nebular Hypothesis Hypothesis

Used a flat, rotating nebula as the Solar System's origin to explain why all

the planets orbit in nearly the same plane and in the same direction

Contradicted the observation that the Sun contains most of the Solar System's mass but only a small fraction of its

angular momentum.

All planets revolve around the Sun in a counterclockwise direction within a 7° band of the equatorial region of the Sun, and nearly all of them also turn on their individual axes in a counterclockwise direction as well.

Angular momentum is the measure of the tendency of a rotating body to remain rotating

Problems With the Nebular Problems With the Nebular Hypothesis Hypothesis

If rings of matter were split off, If rings of matter were split off, as Laplace stated, they as Laplace stated, they

wouldn't be pulled together wouldn't be pulled together to form planets but would to form planets but would

disperse into space.disperse into space.

Process of Nebular Accretion Disk Process of Nebular Accretion Disk Formation HypothesisFormation Hypothesis

Starts with Solar NebulaeStarts with Solar Nebulae Disturbance (possibly a Supernova) cause Disturbance (possibly a Supernova) cause

gradual collapse of Solar Nebulaegradual collapse of Solar Nebulae Gravity causes cloud to shrink and

compress the center which begins to heat up

Accretion disk forms as matter spins around the center and forms a flat disk Thermal energy evaporates the disk

Protostar forms with opaque coreProtostar forms with opaque core Energy is given off by protostar causing a

cooling Cooling causes gas to condense into tiny specs

of metal, rock, & ice “Stellar Debris” Stellar Debris begins to stick together to

form Planetesimals Accrection of Planetesimals forms

Protoplanets Some Planetsimals will form into asteroids,

comets, and moons

Process of Nebular Nebular Accretion Process of Nebular Nebular Accretion Disk Formation HypothesisDisk Formation Hypothesis

Planetesimals- Baby Planets

Accretion – gradual growth of planets by the accumulation of other smaller bodies

Protoplanet – small body that could later form a planet

The Protoplanet Hypothesis The Protoplanet Hypothesis Because of faults in the nebular hypothesis, other explanations of planet formation were sought.

After many failures, such as the

encounter theory, astronomers

returned to the nebular hypothesis

to find improvements during the mid

1900s.

The Protoplanet Hypothesis The Protoplanet Hypothesis

Formed independently

byCarl von Weizsacker

Gerard Kuiper

The solar system begins to form as a rotating cloud, or nebulae, collapses

Instabilities in the nebulae cause dust particles to stick together and accrete into billions of planetesimals with diameters of about 10 meters. The planetesimals then collide and form protoplanets.

Meanwhile, the protosun in the center of the nebular disk becomes massive and hot enough to "turn on" by fusing hydrogen.

The Protoplanet HypothesisThe Protoplanet Hypothesis

The Sun begins to radiate energy and vaporize dust in the inner part of the Solar System. The remaining gas is blown away by solar winds.