Solar Nebula Theory
Three things we need to examine:
1.
2.
3.
Some properties of our Solar System
Formation of the Solar System relative to these properties
Some differences between planets
Solar Nebula Theory
Recall the Solar System scale…
1.
2.
3.
4.
5.
The distance from the Sun
to Earth is 1.5 X 108 km or
1 Astronomical Unit (AU).
From the Sun to the dwarf
planet Pluto is 40 AU
Presently, we cannot fly
people to Mars…our
closest neighbour planet
The Sun is 98% of the mass
of the Solar System. If the
Sun were a basketball,
Mercury would be a tiny,
tiny ball bearing and a
large asteroid would be a
speck of dust
Jupiter is 318X larger than
Earth
Solar Nebula Theory
Some New Stuff…
All objects in the Solar System are about 4.6 billion years old. We
know this from radioactive dating. For example, the Half-Life of U238 is
4.5 billion years.
Oldest Earth rocks at 3.96 billion years old.
If we radioactive date a planet, we are actually looking at the time
the mass solidified. Thus, the Solar System is much older that 4.6 billion
years
Solar Nebula Theory
Formation of the Solar System
The Solar System formed from the collapse of a cloud of gas and dust.
The cloud was slowing rotating and formed a shape of a disk from
centrifugal forces. This process moved matter to its centre
Conservation of Angular Momentum (…recall that…) made the rotation
faster.
As well, the disk began rotating along one plane. This rotational pattern
explains why most of the planets orbit in the same direction and along
the same plane (see illustration).
Solar Nebula Theory
Formation of the Solar System…2
Dust , rock and ice joined to make small planetesimal bodies
This is the start of planet building
Via gravitational pull, larger planetesimals attract smaller ones.
They collide and possibly merge to form larger bodies…eventually
planets
The Sun is burning very hot. The heat prevents the formation of
atmospheres in the closest planets.
Solar Nebula Theory
Formation of the Solar System…3
The planets are mostly liquid-like.
Heavy elements start to sink , and as a
result, radioactive elements are
concentrated in the centre. NOTE: This
explains the intense heat at the Earth’s
core AND gravitational energy.
On Earth, gases such as H2S, SO2,
CO2, H2O, NH3 and N2 are released from
the hot interior. These gases react with
solar radiation to break apart and form
rudimentary atmospheres.
This explains the Inner Planets
which are terrestrial. How might the
process differ for the Outer or Gas
Planets?
Solar Nebula Theory
• This idea for planet formation
was originally proposed by
Immanuel Kent in 1755. Kent
thought a NEBULAE (huge cloud
of dust and gas) was pulled
together by gravity so that it
collapsed into a flat, rotating disk.
As suggested, increased
gravitational and centrifugal
forces from spinning and rotating
caused the disk to coalesced into
the Sun and planets.
• Is this correct? If so, should the
Sun not have most of the motion
caused by gravitational
forces….hmmm?
Solar Nebulae Theory
Modified, the new hypothesis
states (1) a nebulae rotates
and collapses to form a solar
system, (2) instabilities cause
dust particles to stick together
(planetesimals), (3) these
particles collide and form
protoplanets, (4) the centre of
the disk becomes so massive
and hot it “turns on” (i.e., Sun)
and (5) the Sun radiates
energy that vaporizes dust in
the inner Solar System.
Solar Nebula Theory
• This updated idea still did
not explain lack of Sun
momentum.
• Turns out, the Sun is
magnetic. The
momentum of the Sun is
offset (…slowed…) by the
counteracting magnetic
force, AND the force of
the Sun’s spin is
transferred to the planets
so all angular momentum
resides with the planets