The Formation of the Solar System
There are several theories that attempt to explain
how the solar system began, but the most widely
accepted one is known as the nebular theory.
Astronomers and physicists believe the solar
system started as a large, shapeless cloud of gas,
dust and ice, but something disrupted the mass and
set things in motion -- perhaps the explosion of a
nearby star.
If you've ever watched figure skating, 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 same thing happened
with our solar system. 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.
Eventually, dust began to stick together and form
larger bodies called planetesimals. Even more
matter flying around collided with these
planetesimals and stuck to them in a process called accretion. As the bodies spun themselves and gravity brought in
more dust and gas, the planetesimals accreted into protoplanets, and soon into the eight planets we currently know and
love -- Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune (sorry,Pluto).
It's the area in between the fourth planet, Mars, and the fifth, Jupiter, that's important. An astronomical unit (AU) is the
distance between the Earth and the sun, which is about 150 million kilometers -- astronomers use this distance as a ruler
to measure other distances within the solar system and the Milky Way galaxy. Mars lies about 1.5 AU from the sun, or 225
million kilometers away. Jupiter, meanwhile, is about 5.2 AU from the sun, or 780 million kilometers away. If we subtract
the two distances, there's about 3.7 AU between Mars and Jupiter, or 555 million kilometers. It seems like there's enough
room between the two planets for yet another planet, right? What happened in between Mars and Jupiter during the
formation of the solar system?
The Main Asteroid Belt
So how do we explain the vast distance between Mars and Jupiter? Some astronomers have suggested that a separate
planet or protoplanet actually formed between the two planets, but the impact of a high-speed comet broke up and
scattered the newly formed body to create what we now know as the main asteroid belt.
While it's possible that comets and other large
objects were flying around the solar system and
breaking up material during the early stages, most
scientists accept a much simpler theory - asteroids are leftover matter from the solar
system's formation that never successfully came
together as one planet. But how come nothing
came together?
If you look at Jupiter's mass, you'll notice it's
extremely large. People refer to it as a gas giant for
good reason -- while the Earth's mass is about
6x10^24 kilograms, Jupiter's mass is estimated to
be 2x10^27 kilograms. It's a much closer relative to
our sun than to rocky planets like Earth or Mars.
Jupiter's massive size would be enough to disturb
the rocky matter that fell in between it and Mars -its strong gravitational pull would cause any
potential protoplanets to collide and break apart into
smaller bits. We're then left with a large, spread-out
collection of asteroids that orbits around the sun in
the same direction as Earth -- the main asteroid
belt. With its center around 2.7 AU from the sun, the
belt separates Mars and the other rocky planets
from the massive, cold gas giants like Jupiter and
Saturn.
THE KIRKWOOD GAPS
The gravitational force of Jupiter still affects the belt to this day -- its giant mass disturbs the path of asteroids and creates
large gaps in the main belt known as Kirkwood gaps. This happens due to orbital resonance, which is the point when
one body lines up with the orbit of another body and experiences a force. For example, an asteroid might make two full
orbits around the sun in the time it takes Jupiter to make one orbit. Every other orbit, that asteroid would line up with
Jupiter, and its orbit would experience a slight change. This causes several different groups of asteroids to cluster
together, depending on how frequently they circle the sun -- it also leaves several gaps where there aren't any asteroids.
There are also two "clouds" of asteroids in front of and behind Jupiter's path, known as Jupiter Trojans, which act
somewhat like bodyguards around the planet. Two similar groups are found along Mars's orbit called Martian Trojans.
Left side:
On page 54 in notebooks:
Draw and explain the four steps for the formation of the solar system. Your sequencing map should look like this:
Step 1
Step 2
Picture of Step
Explain the step (what’s happening in this step)
Step 3
Explain the step (what’s happening in this step)
Explain the step (what’s happening in this step)
Step 4
Explain the step (what’s happening in this step)