Lesson 19: A Brief Tour of the Solar System
In this lesson, we will look at the solar system,
starting with an overall birds-eye view and moving on to
a more detailed look at the Sun and each of the planets.
Our Solar System is made up of the Sun with its orbiting planets, moons,
and celestial objects such as asteroids and comets.
The system is not random. All of the planets move around the Sun in nearly
circular orbits in the same direction in nearly the same plane, and most of the
large moons orbit their planets in this same direction as well.
The planets can be put into two main categories. Terrestrial planets are
small in mass and size, close to the Sun, made of metal and rock, and have few
moons and no rings. Terrestrial planets include Mercury, Venus, Earth, and Mars.
Jovian planets, on the other hand, are large in mass and size, far from
the Sun, and instead of metal and rock, are
made of Hydrogen, Helium, and Hydrogen compounds. They also have rings and many
moons. Jovian planets include Jupiter, Saturn, Uranus, and Neptune.
There are swarms of asteroids in the Solar System. Most of them orbit in
the asteroid belt between Mars and Jupiter.
Many comets can be found in
the Kuiper belt (pronounced kyper belt) beyond Neptune's orbit.
The Sun is the largest and
brightest object in the solar system,
containing more than 99.8% of the solar system's mass.
It is a gaseous ball of hot hydrogen and helium gas - about 5800 Kelvin or 10,
000 Fahrenheit on the surface with temperature and pressure increasing with
depth.
The Sun gets hotter as you go deeper to
its core. It functions like its own nuclear fusion plant.
The Sun is the most influential object in our solar system. Its gravity
controls the orbits of all of the planets in the system, its heat warms the
planetary surfaces and atmospheres, and its light is the source of virtually
all light in our system.
Mercury is the planet closest to
the Sun and is the smallest of the eight official planets. It has no active
volcanoes, no wind, no rain and no known life. It has a lot of craters and has
both hot and cold extremes.
Venus is the second planet from
the Sun and is almost identical in size to the Earth. Venus has a thick
atmosphere with an extreme greenhouse effect where carbon dioxide traps heat.
As a result, day and night, Venus is like a pizza oven with extreme heat. One
of the most interesting mysteries about Venus is its rotation - it is the only
planet in the solar system that rotates clockwise, causing the Sun to rise in
the west and set in the east.
Earth is the third planet from the sun and is the only known life-supporting
planet in the solar system, with life-supporting oxygen, ozone to protect
against solar radiation, and plentiful surface water. Earth's atmosphere
contains just the right balance of carbon dioxide and water vapor to maintain a
moderate greenhouse effect and keep our planet from getting too hot or too cold.
The Earth also has a moon which is unique in that
it is surprisingly large compared to the Earth. Nearly all other moons in the
solar system are much smaller relative to the planets they orbit.
Mars is the fourth inner planet and the last of the terrestrial planets. It is
larger than Mercury but half the Earth's diameter with 2 moons, Phobos
(pronounced FOE-bos) and Deimos (pronounced DIE-mos). Mars has ancient
volcanoes, a canyon, polar caps with frozen water, carbon dioxide and dried-up
riverbeds, which suggest that it may have once sustained life. Temperature is
below freezing on the surface, however, with very little oxygen and the lack of
atmospheric ozone would leave you exposed to deadly ultraviolet radiation from
the Sun.
After Mars is Jupiter, and
to get there, we would pass through the asteroid belt on the way.
Jupiter is the largest planet at 300 times the size of Earth. Its most famous
feature is its Giant Red Spot, a long-lived storm big enough to swallow at
least two Earths. Jupiter does NOT have a solid surface and, like the Sun, is
composed primarily of hydrogen and helium. It has many moons, with four of them
being large enough that they would be considered planets or dwarf planets if
they orbited the Sun independently. These four moons are Europa, Io (pronounced
EYE-oh), Ganymede and Callisto. Io is the most volcanically alive world in the
solar system and Europa has an icy crust that may hide a subsurface ocean of
liquid water.
The journey from Jupiter to
Saturn is very long as Saturn orbits almost twice as far away from the Sun as
Jupiter. Saturn is only slightly smaller than Jupiter but is much less dense.
Just like Jupiter and the other Jovian planets, Saturn does not have a solid
surface and is composed of hydrogen and helium.
Saturn is famous for its spectacular rings, made up of many small particles of
ice and rock. All four of the jovian planets have rings, but only Saturn's can
be seen easily. Saturn has many moons - two of which are geologically active -
Enceladus with ice fountains and Titan with a thick atmosphere but frigid
surface temperature.
Uranus lies twice as far from
the Sun as Saturn. Uranus is much larger than Earth but smaller than Jupiter
and Saturn. Again, it does not have a solid surface, being made up of hydrogen,
helium and hydrogen compounds such as water, ammonia and methane. The methane
is what gives it a pale blue-green color.
Uranus has over a dozen moons and rings that are hard to see. One of the most
unique features of Uranus is that its entire system - the planet, its rings and
moon orbits - are all tipped on its side relative to the other planets. One
result of this extreme axis tilt is that Uranus has the most extreme seasonal
variations of any planet in the solar system. For example, you could have a 42
year long span of daylight for one-half of an orbit and then a 42 year long
span of night.
The journey from
Uranus to Neptune is the longest so far. Neptune looks similar to Uranus but
has a more striking blue color. It also has a similar composition to Uranus but
is denser, giving it a slightly greater mass even though it is a little smaller
in size. Neptune has both rings and moons.
The largest moon, Triton, is larger than Pluto and is considered one of the
most interesting moons in the solar system for a variety of reasons. It has
geyser-like features on its surface that spew out nitrogen gas, and it is the
only moon in the solar system that orbits its planet backward - in other words,
it orbits Neptune in the opposite direction that Neptune rotates. Many
scientists believe this means it was an independent planet that orbited the Sun
before being captured into Neptune's orbit.
Pluto was considered the ninth planet in our solar system for around
seventy-five years but after the discovery of a larger object - Eris -
scientists created a new classification called a dwarf planet. Dwarf planets
are defined as being too small to qualify as official planets but large enough
to be round in shape, and include Pluto, Eris, and several other objects.
Pluto and
Eris, along with thousands of other icy objects make up the Kuiper belt. The
Kuiper belt is similar to the asteroid belt, but is composed of comet-like
objects rather than rocky asteroids.