Our Solar System
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About It
Our solar
neighborhood is an exciting place. The Solar System is full of planets,
moons, asteroids, comets, minor planets, and many other exciting
objects. Learn about Io, the explosive moon that orbits the planet
Jupiter, or explore the gigantic canyons and deserts on Mars.
What Is The Solar System?
The Solar System
is made up of all the planets that orbit our Sun. In addition to
planets, the Solar System also consists of moons, comets, asteroids,
minor planets, and dust and gas.
Everything in the Solar System
orbits or revolves around the Sun. The Sun contains around 98% of all
the material in the Solar System. The larger an object is, the more
gravity it has. Because the Sun is so large, its powerful gravity
attracts all the other objects in the Solar System towards it. At the
same time, these objects, which are moving very rapidly, try to fly away
from the Sun, outward into the emptiness of outer space. The result of
the planets trying to fly away, at the same time that the Sun is trying
to pull them inward is that they become trapped half-way in between.
Balanced between flying towards the Sun, and escaping into space, they
spend eternity orbiting around their parent star.
How Did The Solar System form?
This is an
important question, and one that is difficult for scientists to
understand. After all, the creation of our Solar System took place
billions of years before there were any people around to witness it. Our
own evolution is tied closely to the evolution of the Solar System.
Thus, without understanding from where the Solar System came from, it is
difficult to comprehend how mankind came to be.
Scientists believe that the Solar
System evolved from a giant cloud of dust and gas. They believe that
this dust and gas began to collapse under the weight of its own gravity.
As it did so, the matter contained within this could begin moving in a
giant circle, much like the water in a drain moves around the center of
the drain in a circle.
At the center of this spinning
cloud, a small star began to form. This star grew larger and larger as
it collected more and more of the dust and gas that collapsed into it.
Further away from the center of
this mass where the star was forming, there were smaller clumps of dust
and gas that were also collapsing. The star in the center eventually
ignited forming our Sun, while the smaller clumps became the planets,
minor planets, moons, comets, and asteroids.
A Great Storm
Once
ignited, the Sun's powerful solar winds began to blow. These winds,
which are made up of atomic particles being blown outward from the Sun,
slowly pushed the remaining gas and dust out of the Solar System.
With no more
gas or dust, the planets, minor planets, moons, comets, and asteroids
stopped growing. You may have noticed that the four inner planets are
much smaller than the four outer planets. Why is that?
Because the inner planets are
much closer to the Sun, they are located where the solar winds are
stronger. As a result, the dust and gas from the inner Solar System was
blown away much more quickly than it was from the outer Solar System.
This gave the planets of the inner Solar System less time to grow.
Another important difference is
that the outer planets are largely made of gas and water, while the
inner planets are made up almost entirely of rock and dust. This is also
a result of the solar winds. As the outer planets grew larger, their
gravity had time to accumulate massive amounts of gas, water, as well as
dust.
The Solar System Has Over 100 Worlds
It is
true that there are only eight planets. However, the Solar System is
made up of over 100 worlds that are every bit as fascinating. Some of
these minor planets, and moons are actually larger than the planet
Mercury!
Others, such as Io, have
active volcanoes. Europa has a liquid water ocean, while Titan has
lakes, rivers, and oceans of liquid Methane. You can read more about
these amazing worlds by clicking here.
The Asteroid Belt, The Kuiper Belt, And The Oort Cloud
You have
probably heard about the Asteroid Belt. This band of asteroids sits
between the orbits of the planets Jupiter and Mars. It is made up of
thousands of objects too small to be considered planets. Some of them no
larger than a grain of dust, while others, like Eros can be more than
100 miles across. A few, like Ida, even have their own moons.
Further out, beyond the
orbit of the minor planet Pluto, sits another belt known as the Kuiper
Belt. Like the Asteroid Belt, the Kuiper Belt is also made up of
thousands, possibly even millions of objects too small to be considered
planets. A few of these objects, like Pluto, are large enough that their
gravity has pulled them into a sphere shape.
These objects are made out
of mostly frozen gas with small amounts of dust. They are often called
dirty snowballs. However, you probably know them by their other name...
comets.
Every
once in a while one of these comets will be thrown off of its orbit in
the Kuiper Belt and hurled towards the inner Solar System where it
slowly melts in a fantastic show of tail and light.
Beyond the Kuiper Belt sits a
vast area known as the Oort Cloud. Here within this jumbled
disorganized cloud live millions of additional comets. These comets do
not orbit the Sun in a ring or belt. Instead, each one buzzes around in a
completely random direction, and at extremely high velocities.
Beyond The Oort Cloud
The Sun's
solar winds continue pushing outward until they finally begin to mix
into the interstellar medium, becoming lost with the winds from other
stars. This creates a sort of bubble called the Heliosphere. Scientists
define the boundaries of the Solar System as being the border of the
Heliosphere, or at the place where the solar winds from the Sun mix with
the winds from other stars.
The Heliosphere extends
out from the Sun to a distance of about 15 billion miles, which is more
than 160 times further from the Sun than is the Earth.
Solar System Facts
Each page is full of fun and
exciting facts about our Solar System. Take your time, and enjoy
exploring our solar family.
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Did you know that moons are also called satellites?
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The Sun's Name Means:
The Romans called the sun Sol, which
in English means sun. In ancient Greece, the sun was called Helios.
Our Sun is not
unique in the universe. It is a common middle-sized yellow star which
scientists have named Sol, after the ancient Roman name. This is why our
system of planets is called the Solar System. There are trillions of
other stars in the universe just like it. Many of these stars have their
own systems of planets, moons, asteroids, and comets.
The Sun was born in a vast cloud of
gas and dust around 5 billion years ago. Indeed, these vast nebulae are
the birth places of all stars. Over a period of many millions of years,
this gas and dust began to fall into a common center under the force of
its own gravity.
At the center, an ever growing body
of mass was forming. As the matter fell inward, it generated a
tremendous amount of heat and pressure. As it grew, the baby Sun became
hotter and hotter. Eventually, when it reached a temperature of around 1
million degrees, its core ignited, causing it to begin nuclear fusion.
When this happened, the Sun began producing its own light, heat, and energy.
What is Thermonuclear Fusion?
Thermonuclear fusion is the process in which a
star produce its light, heat, and energy. This happens at the core of
the star. The core is superheated to millions of degrees. This heat
travels towards the surface and radiates out into the universe. Through
this thermonuclear process, stars "burn" a fuel known as hydrogen. The
result is that they create another type of fuel known as helium.
However, stars do not burn in the same way that a fire does, because
stars are not on fire.
Convection
Heat rises,
while cooler gas falls. Have you ever noticed that your basement is
always much cooler than upstairs. The same laws of physics apply within
stars. Because heat rises while cooler gases fall, the gas within a star
is constantly rising and falling. This creates massive streams of
circular motion within the star. This is called convection.
As the gases near the core of the
Sun are heated, they begin to rise towards the surface. As they do so,
they cool somewhat. Eventually they become cool enough that they begin
to sink back down towards the core. It can take an atom millions of
years to complete one complete cycle around a convection stream. As a
result of this process, the temperature on the surface of the Sun is
around 10,000 degrees Fahrenheit, which is much cooler than its
superheated core.
Sun Spots
We don't often
think of the Sun as having cooler areas on its surface. The Sun is far
too hot for an astronaut to ever visit, but there are areas which are
slightly cooler than others. These areas are known as sun spots. Sun
spots are still very hot. However, because they are slightly cooler than
the rest of the surface of the Sun, they appear slightly darker in
color. The gravitational forces in Sun spots are also stronger than the
other hotter areas. Of course, you cannot look directly at the Sun to
see these spots because you would damage your eyes. Astronomers have to
use special telescopes with filters and other instruments to be able to
see the cooler spots on the surface of the Sun.
Sun spots come and go on a regular
basis. At times, there are very few, if any sun spots. At other times
there are far more. They generally increase in intensity and then
decrease over a period of 11 years. This 11 year cycle is known as the
Saros Cycle.
To learn more, click here.
Solar Flares
During
periods of high solar activity, the Sun commonly releases massive
amounts of gas and plasma into its atmosphere. These ejections are known
as solar flares. Some solar flares can be truly massive, and contain
impressive power. On occasion, these more powerful flares can even cause
satellites orbiting the Earth to malfunction. They can also interact
with Earth's magnetic field to create impressive and beautiful light
shows known as the
Northern and Southern lights. In the northern hemisphere, these lights are commonly known as the Aurora Borealis.
Solar Winds
As the Sun
burns hydrogen at its core, it releases vast amounts of atomic
particles, or pieces of atoms, into outer space. These atomic particles
along with the Sun's radiation create a sort of wind, known as the solar
wind.
This wind blows particles
outward in all directions from the Sun. Even as you read this, there are
atomic particles which are traveling from the Sun towards you. Often,
particles pass right through your body without you ever realizing it.
Eventually this wind reaches
out beyond the Solar System and begins to mix with the winds from other
stars. The bubble around the Sun where the solar winds are still strong
enough to blow outward is known as the heliosphere (note the Greek name
Helios). The area of space where the winds are too weak to continue
pushing outward and instead begin to mix with the winds of other stars
is known as the interstellar medium.
The Sun's Family
The Sun is
by far the largest object in the Solar System. 98% of all matter within
the Solar System is found within the Sun. This means that all the
planets, moons, asteroids, minor planets, comets, gas, and dust would
all combine to make up only 2% of all the matter in the Solar System.
The Sun is so large that the Earth could easily fit inside the Sun a
million times.
Because the Sun is so large
compared to everything else, it is easily able to hold on to the rest of
the matter, causing everything else to orbit around it.
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Light from the
Sun can reach the Earth in only 8 minutes! This is called the speed of
light. The Sun is nearly 93 million miles (approx 145 million km) from
Earth.
What are asteroids?
An asteroid is a large rock in outer space. Some,
like Ceres, can be very large, while others are as small as a grain
of sand. Due to their smaller size, asteroids do not have enough
gravity to pull themselves into the shape of a ball.
Astronomers group asteroids into different categories based on the
way they reflect sunlight.
The asteroid belt is divided into an inner belt
and an outer belt. The inner belt, which is made up of asteroids that
are within 250 million miles (402 million km) of the Sun, contains asteroids that are
made of metals.
The outer belt, which includes asteroids 250
million miles (402 million km) beyond the Sun, consists of rocky asteroids. These
asteroids appear darker than the asteroids of the inner belt, and are
rich in carbon.
Where did the Asteroid Belt come from? |
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Asteroids are left over materials from
the formation of the Solar System. These materials were never
incorporated into a planet because of their proximity to Jupiter's
strong gravity.
omets Among the most brilliant and most rare
objects in the night sky. These soaring beacons with their beautiful
tails come from the outer realms of the Solar System
Wishing on a meteorite!
Written for the KidsKnowIt Network by:
Gemma Lavender, MPhys, FRAS
Image: NASA
You have
probably heard of a shooting or falling star, but have you ever seen
one? If you have ever spent any amount of time looking up at the night
sky, then you probably have - a flash of light streaking high above
through the darkness for just a moment, disappearing just as quickly as
it appeared - sometimes so quick that you cannot be sure if you have
really seen something or imagined it. You might think that your eyes
are playing tricks on you, but shooting stars are definitely real! Your
parents may have told you to quickly make a wish on a shooting star
before it vanishes - what will your next wish be when you get to see
one?
Here’s
another question for you, a little bit harder this time: do you know
what a shooting star is? Their names are a little misleading and this
causes some people to think that these fast moving trails of light
really are stars that have fallen out of the sky. However, this is not
true. Our Sun is a star, our closest star, and the other stars are many
many miles away (it would take more than your lifetime to travel to
them!) and since they are much bigger than a shooting star, they are
certainly not responsible, so we can count them out. If you are still
not sure of the answer, then you might be surprised to learn that
shooting stars are just tiny bits of dust entering the Earth’s
atmosphere from space. Tiny particles, like grains of sand or pebbles
on a beach, like to crash into the atmosphere at amazingly fast speeds -
some faster than a car travelling at his highest speed along the
motorway! But don’t worry - they are not big enough to harm you! If you
pick up a stone from the beach, however, you will find that a fast
moving pebble does not quite look the same as a shooting star, no
matter how hard you throw it. This is because the light that you see is
the heat of the air around them as they fly into the atmosphere and
burn up.
Image: NASA
Sometimes something a little
bigger than a pebble will shoot through the atmosphere and we seem them
as fireballs - if you are lucky enough to see one of these then you
might see flames shooting from it! But don’t worry, fireballs are not
dangerous - like shooting stars, they are high above us.
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The
point in the sky where a meteor shower originates is called the radiant
point. It is much like the center of a bicycle wheel with the meteors
radiating outward from the center. During a meteor shower, the radiant
point will move across the sky as the Earth continues to rotate. Keep
reading below to see all the different meteor showers that occur during
the year, and learn how the showers got their names.
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Occasionally, however, the piece of
rock can be big enough so that it does not all burn up while entering
the atmosphere and it will hit the ground. We call these meteorites
(while they are flying through the atmosphere as shooting stars we call
them meteors, and while they are in space we call them meteoroids - it
is important to remember the difference!). A whopping 38,000
meteorites have been found on Earth so far, from all over the world,
but most are found in the hot desert or in freezing cold Antarctica.
You may have heard stories of someone you know that has found a
meteorite or maybe you have even found one yourself! If you have never
had the chance to touch or see a meteorite, then you might not know
that these space rocks are quite different to the ones that you are
likely to find in your backyard, but not in the way that you might
think.
Image courtesy of Lunar and Planetary Institute
This map shows some of the locations in Antartica where many meteorites have been found.
There are three main types of meteorites:
stony, iron and stony-iron. A lot of them have been smashed off from
very large chunks of rock, called asteroids, in collisions before
eventually finding their way to our planet. Iron meteorites, for
example, are bits of metal iron cores of large asteroids that were once
hot enough to have melted, causing all of their iron to sink to the
centre. Stony meteorites look most like the stones that you find on
Earth and come from the outer layer of asteroids, whereas stony-iron
meteorites are a mixture of the two.
Image courtesy of NASA Johnson Space Center
This meteorite came from the moon.
Comets
and asteroids are leftover debris from the when the planets were being
built in the Solar System. Just like asteroids, comets make falling
stars, but rather than seeing one of them every so often (that are easy
to miss!), there is a shower of them - astronomers call these meteor
showers and they are made when the Earth moves through the tail of a
comet that has been left behind after one of these icy and dusty bodies
have swooped past us. You can usually see at least a few meteors
during a shower, but on a particularly good show, you can sometimes see
hundreds of shooting stars per hour - you can be sure not to miss one
then! The best meteor showers are the Quadrantids that are at their
best on the 3rd January every year, the Lyrids that are at their best
on 22nd April, the famous Perseids on 12th August, the Orionids on 22nd
October, the Leonids on 17th November and the Geminids on 14th
December. The Geminids, it is thought, are actually dust from an
asteroid called Phaethon rather than a comet - and it has been shown
that Phaethon was originally part of the second biggest asteroid
Pallas, but was smashed off in a mighty collision with another asteroid
billions of years ago. Meteor showers are named after the
constellation that they appear to be falling from. For example, the
Geminids will be shooting away from the constellation, Gemini (The
Twins), whereas the Perseids are from Perseus (The Hero). Why don’t you
grab a map of the constellations and, with your friends, see if you
can find them in the night sky before the meteor showers start?
So, ready to go meteor spotting? Check out the box, How to watch a meteor shower, to find out how!
Image: NASA
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How to watch a meteor shower
Watching a meteor shower can be one of the most enjoyable things about
observing the night sky, waiting with tense excitement to see the
next shooting star. The best meteor shower is the Perseids - not just
because it has the most meteors (although it does have as many as 100
per hour) - but because you can sit out in the garden during the warm
summer night to watch them, rather than having to wrap up in your
scarf, bobble hat and wooly mittens during the middle of winter, as you
would have to for watching the Geminids in December!
Image: NASA
For the best meteor viewing, it is best to find a dark corner of your
garden or from wherever you are observing them. Give time for your eyes
to get used to the darkness, and use a red light flashlight rather
than a normal flashlight, so that you do not ruin your night vision when
looking at maps of the night sky. If you do not have a red light
flashlight, then you can just cellotape some red see-through paper over a
normal flashlight - it works just as well! To avoid going back inside,
bring a water bottle and some snacks out into the garden with you.
Make sure that you wrap up warm - even in August for the Perseids, it
can still get chilly late at night. Remember that a hat is essential,
as your body loses much of its heat through your head.
Now,
you have probably found that when looking at the stars that straining
your neck to look up all the time can quickly become uncomfortable. For
meteor watching, a deck chair is ideal - you are angled comfortably so
you do not have to strain your neck.
Image: NASA
Simply watching for meteors and counting
up how many you see in your head is fun, but if you want to be a proper
scientist then you need to record your results, as you would during a
real science experiment. With a clipboard, pen and paper, write down
the time that you see each meteor, in which direction the meteor comes
from, its colour (if you can see any colour!), and how bright it was
compared to other stars in the constellations that surround it.
Remember that a star map will be able to help you with how bright
certain stars are in a constellation.
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The meteorites you
see during a meteor shower might appear to be very close, but did you
know that those tiny particles of burning space debris are actually
about 30 to 40 miles (48 to 64km) above Earth's surface? Pretty amazing
that you are able to see such a tiny piece of space dust from so far
away!
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So you’ve spent some time out in the garden, watching and recording
meteors. What do you do with your results then? Some scientists can use
your results, such as those at astronomical associations, and they
will look for trends in the meteor shower - for example, were they more
or less active than in previous years? If so, why? If you are unsure
of who to contact, you should ask your teacher or parents to help you.
Who knew that by watching a meteor shower and reporting what you see
could allow you to contribute to real life science! How exciting is
that?!
Near
the Grand Canyon in Arizona is Meteor Crater (above). It was formed
about 50,000 years ago when a meteor about 30 meters wide and weighing
100,000 tons struck the Arizona desert at an estimated speed of 20
kilometers per second (12 miles per second).
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What are comets?
A comet is a small world which
scientists sometimes call a planetesimal. They are made out of dust and
ice, kind of like a dirty snow ball.
Where do they come from?
Comets come from two places: The Kuiper Belt and the Oort Cloud.
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Many people think that a comet's tail is always following behind it,
but actually the coma, or tail, can either be behind the comet or
in front of it. Which way the tail is pointing depends on where the Sun
is. That's right, the Sun's heat and radiation produce a wind called
the Solar Wind, as a comet gets close to the Sun it begins
to melt. The gas and dust that melt off are blown away from the Sun by
the solar winds. So if a comet is traveling towards the Sun then the
tail will follow behind, but if the comet is traveling away from the Sun
the tail will be in front of the comet.
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Imagine a place far, far away at the very edge of the Solar System. A
place where millions of comets can be seen swishing around in every
direction. These icy comets are orbiting the Sun in two different
places, both of which are very distant. One place is called the Oort
cloud, and the other is called the Kuiper Belt.
Why do Comets leave their home in the Oort Cloud or Kuiper Belt?
A comet will spend billions of years
in the Kuiper Belt or Oort Cloud. Sometimes two comets will come very
close to each other, or even crash into one another. When this happens
the comets change directions. Sometimes their new path will bring them
into the Inner Solar System.
This is when a comet begins to shine. Up until now the comet has been
among millions of others exactly the same, but as they approach the
warmer Inner Solar System they begin to melt leaving behind magnificent
tails.
Unfortunately, comets don't live very long once they enter the warmer
part of the Solar System. Just like a snowman melts in the summer,
comets melt in the Inner Solar System. Although it is the most
glorious part of their lives, traveling through the Inner Solar System
eventually kills them. After several thousand years they melt down to a
little bit of ice and dust, not nearly enough to leave a tail. Some
even melt away completely.
Would it be safe to fly through the tail of a comet?
Unlike a recent blockbuster movie
showing a space ship flying past giant rocks the size of houses, a
comet's tail is actually quite safe. The only thing that would hit your
ship would be microscopic pieces of dust.
Enjoy these pictures of real comets.
| How many asteroids are there? |
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26 very large asteroids have been
discovered, which is probably most of the big ones. But there are
still millions of smaller ones that we have yet to see because they
are too tiny, only a mile or so across.
If we stuck all the asteroids
together, how big would the new planet be?
If all the materials of all the
asteroids were squashed up into one planet it would be smaller than
our moon.
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While most asteroids can be
found in the Asteroid Belt, others are in strange orbits straying far
from home. It is currently believed that at least 5000 asteroids
cross the Earth's orbit, some coming very close. Don't worry though,
asteroids and comets only hit the Earth every 100 million years or so.
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Quaoar
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Quaoar is the largest known non-planet
object in the Solar System. It is one tenth the size of the
Earth, and is larger than all other asteroids put together.
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No picture currently available
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Ceres
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For many years Ceres was thought to be the
biggest asteroid in the Solar System. It is about 600 miles wide and
contains about 25% of the mass of all the asteroids combined.
However, in the summer of 2001 scientists discovered an even bigger
asteroid orbiting the Sun near Pluto.
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No picture currently available
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2001 KX76
The New
Asteroid King
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On August 23, 2001, astronomers announced the
discovery of a new asteroid. The new asteroid is even bigger
than Ceres, which for over two hundred years had been thought to be
the largest asteroid in the Solar System.
It was discovered looking at old photographs
taken of the sky.
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Ida and Dactyl
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Ida is a neat little asteroid about 36 miles
wide. It is unique because it has its own little moon called Dactyl.
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