Download The Origin of Our Solar System

The Origin of Our Solar System
Early Hypotheses
Objectives
• SWBAT evaluate varying hypotheses and their
evidence about the origin of the solar system.
• SWBAT compare, and contrast hypotheses
about the origin of our solar system.
Early Hypotheses - Examples
• René Descartes (Early 17th century)
– Created first recorded physical theory.
– Did not recognize gravitation as the universe’s
central force.
– Believed force was exerted by contact betwn
physical entities and the universe was filled with
vortices of “whirling invisible particles.”
– Posited that the sun and planets formed when a
large vortex contracted and condensed.
Early Hypotheses - Examples
• Louis de Buffon (mid to late 17th century) was
a French naturalist.
– Proposed that the planets formed when a comet
collided with the sun and pulled matter out of it.
– Buffon knew nothing of the actual size of a comet;
however, later astronomers took his idea and
replaced the comet with a passing star.
– Matter ripped from the two stars condensed to
form planets.
Catastrophic V. Evolutionary (these
ideas are found throughout science)
• Descartes’ Hypothesis – is an “evolutionary”
type hypothesis.
– An evolutionary hypothesis involves gradual
processes to produce the sun and planets.
– If an evolutionary perspective were correct, and
the origin of planets, solar systems, and galaxies
were through gradual, common, process, then
stars and planets would be very common.
Catastrophic V. Evolutionary
• Buffon’s hypothesis depends on highly
improbable, sudden events.
– If a catastrophic hypothesis were true, then
planetary systems should be very rare.
• The catastrophic versus evolutionary debate
has mostly been settled.
• Scientists have mostly sided with the
gradualist perspective; however,
catastrophism does play a real role and should
not be dismissed.
Evolutionary Processes Are Favored
• The modern theory for the origin of the
planets, which is based on large amounts of
data, is without a doubt evolutionary.
• The modern theory began to form in the late
17th early 18th centuries when Pierre-Simon de
Laplace combined Decartes’ vortex idea with
Newton’s laws of gravity.
Laplace’s Nebular Hypothesis
• Many of science’s greatest advances come
when there is a synthesis of two seemingly
different disciplines (astronomy and physics in
this case.
Laplace posited that vortices
had been acted on by gravity –
applying Newton’s laws.
Gravitational forces pulled on
the vortices and flattened them
out into a disk. The center of
the vortex became the sun.
Nebular Hypothesis Continued
• Disks grew smaller as gravity acted on them.
– In order to maintain angular momentum the sun,
the source of the spin, and the resulting disks had
to spin faster:
Angular momentum =
moment of inertia x
angular velocity.
The increased “spin” was
necessary to keep the
evolving disk rotating.
Nebular Hypothesis Continued
• When our cloud of spinning matter was
spinning as “fast as it could,” the disk began to
shed layers – leaving behind rings of matter.
This is a painting
of the early solar
system, according
to Laplace, from
NASA’s website.
Nebular Hypothesis Continued
• As the cloud spun, it created many rings.
– The rings would become the newborn planets
orbiting a new sun at the center of what was the
cloud of gas (which remember, is matter).
• As with most hypotheses in science, this one
was a very good try but the evidence did not
support it.
Nebular Hypothesis Continued
• The hypothesis depended on the sun having
most of the angular momentum in the solar
system.
– Angular momentum (re-stated in easier to
understand form): the tendency of a rotating
object to continue to rotate.
– In fact, the sun rotates relatively slowly – having
little angular momentum.
– The planets rotate much faster and have greater
angular momentum.
Nebular Hypothesis Continued
• The Nebular Hypothesis could not adequately
explain the angular momentum problem (sun
low, planets high).
• Therefore it was rejected, however, it was
absolutely key because of its incorporation of
Newton’s laws of motion.
• It was the first “modern” theory.
• In the 1940s, the Solar Nebula Hypothesis
was proposed.
Solar Nebula Theory (SNT)
• Proposes that the planets, including Earth,
formed in a rotating disk of gas and dust that
surrounded the sun as it, the sun, formed.
Laplace’s nebular hypothesis included a disk but
depended on rings of matter left behind by disk
contraction.
He did not take into account how gas and dust behave
in such a disk.
In the SNT, the planets grew within the disk by carefully
described physical processes – an evolutionary process
(called uniformitarianism in geology.
Solar Nebula Theory (SNT)
• Disks of gas and dust are common around
young stars.
• Modern astronomical tools can image the
disks directly and evidence is strong that our
own planetary system formed in such a disk
shaped cloud.
• So, evidence comes from direct observation as
well as the laws of physics and chemistry –
and now biology and geology.
Solar Nebula Theory (SNT)
• If planet formation is a natural part of star
formation, from the disks of gas and dust,
then most stars should have planets orbiting
them.
This is a borrowed slide
Neil deGrasse Tyson, from Nova Now
• http://www.pbs.org/wgbh/nova/space/origins
-solar-system.html