ABSOLUTE BEGINNERS
This article featured in
the June 2001 Beginners Magazine
OUR SOLAR SYSTEM
Before thinking about our Sun the family of
planets, moons Asteroids, Comets and Meteors we must go back long before the
Sun was formed to when the Universe began.
The almost universally accepted theory of how the
universe was formed is the Big Bang Theory.
This states that every thing we can see and even time itself came into
being about 15 billion (15 million million) years ago in an enormous bang. After about a million years atoms had formed
from the fireball of the Big Bang and light was able to shine. Nearly all matter at that time was in the
form of the basic element Hydrogen. From
huge swirls of Hydrogen gas, galaxies and stars began to form. It is believed that these early stars were
very large compared to the stars we see today because they were formed of
almost pure Hydrogen and could disperse
their energy into space quicker and easier.
Some of these old stars are thought to have been up to 300 times as massive
as our Sun. Very few stars today
achieve a size of more than 50 times the Sun.
These huge stars consumed hydrogen at an enormous
rate, converting it into heavier elements.
Being so large these stars could only survive for a short time (probably
less than a million years) then they destroyed themselves in colossal
explosions. All the elements formed in
these stars were blasted off into space along with the remaining Hydrogen. Great shock waves blasted across space from
these unbelievable explosions. The shock waves pushed the gas and dust from
other exploding stars into clumps which formed into new stars but these stars
were not pure Hydrogen they were contaminated with Helium, Carbon, Oxygen,
Calcium, Iron and even Gold all the elements we see around us today.
About 4500 million years ago the blast from an
exploding star formed a swirling mass of gas and dust into a spinning
disc. At the centre the gas became so
compressed and hot that a nuclear fusion furnace ignited and our Sun was
born. At first the Sun was much more
powerful and violent than it is today.
It probably had huge jets of material blasting out of its poles and the
radiation created a powerful solar wind.
The solar wind blasted away all the light volatile material from the
area of the disc closest to the Sun leaving only the heavier materials. The heavier dust particles drifted together
to form larger and larger lumps until planet sized lumps had grown. The lighter gases were pushed to the outer
parts of the disc where it was cooler and they froze into various kinds of ices
which in turn coalesced into the gas giants.
These gas giant were so big that the compression caused them to produce
internal heat and the ices again became gas.
It is thought that there may have been many more
planets in the beginning but there would have been many collisions and near
misses. Some planets may have been
destroyed and the debris reformed into new planets or may have been absorbed by
other planets which grew bigger. Close
encounters could move planets out of there orbits and driven some to their
death in the Sun. Others may have been
thrown out of the Sun’s family to wander through empty space forever. Eventually all calmed down and the planets
cooled and the Sun became the quiet stable star we see today.
Now lets have a look at the family of our Sun but
first we must look at the Sun, the dominating matriarch of the family. The Sun is about a million kilometres in
diameter and contains nearly all the material of the solar system. The centre of the Sun has a temperature of
millions of degrees centigrade and the surface has a temperature of about 6400
degrees centigrade. Virtually all the
light and heat in the solar system comes from the Sun , without that light and
heat even the atmospheres of the planets would be frozen solid.
The Main members of the Solar Family are the
planets and their moons there a 9 planets and most of these have moons. Below
is a list of the planets and their main moons.
DIST DIAMETER YEAR DAY
millions of miles Miles Earth
time Earth time
MURCURY 36 3030 88 days 58d 5hr
VENUS 67.2 7700 224.7 days 243 days
EARTH 93 7927 365 days 23h 56m
MARS 141.5 4200 687 days 24h 37m
JUPITER 483.3 88700 11.86 yrs 9h
50m
SATURN 886.1 75100 29.46 yrs 10h
14m
URANUS 1783 29300 84.01 yrs 10h 48m
NEPTUNE 2793 31200 164.79 yrs 14h
PLUTO 3666 4000 247.7 yrs 6d 9h
MOONS
NAME DIAMETER ORBIT
miles thousands miles
MERCURY None
VENUS None
EARTH The Moon 2160 239
MARS Phobos 10 5.8
Deimos 5 14.6
JUPITER Amalthea 150 113
Io 2310 262
Europa 1950 417
Ganymede 3270 666
Callisto 3220 1170
Hestia 100 7120
Hera 35 7290
Demeter 15 7300
Adrastea 14 13000
Pan 19 14000
Poseidon 35 14600
Hades 17 14700
SATURN Janus 150 98
Mimas 300 113
Enceladus 400 149
Tethys 800 183
Dione 1000 235
Rhea 1100 328
Titan 3500 760
Hyperion 200 920
Phoebe 150 8050
Iapetus 1500 2200
URANUS Miranda 200 76
Ariel 1500 119
Umbriel 800 166
Titania 1500 272
Oberon 1500 364
NEPTUNE Triton 3300 220
Nereid 200 3500
PLUTO Charon 750 12
The planets orbit as two main groups with Pluto
being a bit of an oddity. The inner
four planets Mercury, Venus, Earth and Mars are small rocky world whereas the
outer four Jupiter, Saturn, Uranus and Neptune are gaseous giants.
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MERCURY
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MERCURY is the nearest planet to the Sun and is the
smallest of all the planets at 3030 miles in diameter, only half as big again
as the Earths Moon. In fact both
Jupiter and Saturn have moons larger than Mercury. The surface of Mercury is cratered and looks very moon like. One face of Mercury always faces the Sun and
therefore roasts in a blistering heat of 400ºC but the other side facing away
from the Sun freezes at a temperature of only -170ºC. As it is so close to the Sun it is always quite difficult to
see. This is because the sky is always
bright and because mercury always rises just before the Sun or sets just after
it is always close to the horizon. When
it is seen in a telescope it often has a crescent shape like the Moon. Mercury has no known moons.
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VENUS
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VENUS is almost Earth’s twin
being the same size but is definitely not an identical twin. With a thick atmosphere of Carbon Dioxide Venus
is suffering a runaway greenhouse effect. The surface temperature is almost hot enough to melt Lead at a 470ºC.
Earth has as much carbon dioxide as Venus so it begs the question ,
why is Venus so different ? The answer is most of the Carbon dioxide on
Earth has been absorbed by the oceans and then deposited as rocks such as
Limestone. Most of the Carbon dioxide
on Venus is still in the atmosphere. Ordinary
telescopes even if carried on probes orbiting Venus cannot see any more than
the top of the thick white cloud covering the whole surface. Radar has been used to penetrate the clouds
and has recorded huge mountains and valleys.
Venus has few recognisable craters because only the largest of meteors
can penetrate the thick atmosphere and the craters which are formed are soon
eroded by the harsh atmospheric conditions.
Most have been eroded by powerful acid rain. Venus has no moons.
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EARTH
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EARTH is the third planet from the Sun and the
only planet known, known to support life.
One of the major ingredients required for life in all the form we know
about is liquid water. Earth is right
at the centre of a zone which is known as the Goldielocks Zone, where the
temperature is not too hot, and not too cold but is ‘just right’ for water to
exist as a liquid. It is becoming more
evident that the presence of our large moon may have played an important roll
in the origins of life on Earth by producing the strong tides. Earth like Venus has few craters these have
been eroded by weather and land movements caused by continental drift and plate
tectonics. It is now thought that our
moon was formed when a large planet sized object struck the Earth with a
glancing blow in the early stages of it formation. The debris circled the Earth and eventually formed into the moon
we see today.
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MARS
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MARS is the outer member of the inner rocky
planets. Mars has only a very thin
atmosphere and no liquid water. Because
it is on the very edge of the ‘Goldielocks Zone’ it is probably just too cold
for liquid water on its surface.
Another problem here is that the planet is quite small and doesn’t have
a strong enough gravity to hold on to a thicker atmosphere. Without a thick atmosphere water boils
instantly into a vapour and can then be lost into space. There are gigantic extinct volcanoes on the
surface of Mars some up to five time the height of Mount Everest, Earth’s highest
mountain. It is thought by many scientists
that Mars had and atmosphere and even oceans, early after its formation but it
was lost into space about 3 billion years ago.
Mars has two small moons which may be captured asteroids (see below).
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ASTEROID IDA
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ASTEROIDS are chunks of rock, ice and metals which orbit
the Sun between the small rocky inner planets and the gaseous outer giants.
In the space between Mars and Jupiter are hundreds of thousands of
small planets known as Planetoids or Asteroids.
It is likely that this belt of asteroids is material which might have
formed into a planet but was prevented from doing so my the immense gravity
of Jupiter which kept pulling them apart as soon as the tried to aggregate
into a new planet. Asteroids vary in size from a few meters across
up to the largest which may be hundreds of kilometres. Some meteors originate from asteroids when
they collide and knock chunks off each other.
These chunks of rock and metal fly off in all directions and a few
head towards Earth and enter the atmosphere as meteors. Some larger ones may even make it to the surface and cause craters.
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JUPITER
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JUPITER is the largest of all the planets and is
over ten times the diameter of Earth.
Unlike the inner planets Jupiter has no solid surface because it is
comprised of gas although it may have a small rocky or metallic core. Because Jupiter is so large the enormous
pressure in the centre produces a lot of heat.
This heat is conducted outwards through the gas and drives huge storms
in the outer atmosphere. The surface of
the planet has many coloured bands or ‘belts’ of different colours. These belts are mainly different shades of
browns with variations fro white through orange to chocolate brown. There are even vivid reds especially in the
famous giant Red Spot. The Red Spot is
a massive storm larger than the size of the Earth which has been raging since
before the invention of telescopes.
Jupiter has many moons and more are being discovered all the time. Many are small and may be captured asteroids
but four are large enough to have been planets, two, Ganymede and Callisto are
bigger than Mercury.
With space probes much more is now known about
the moons especially the four Galilean moons (named after Galileo who
discovered them). Io the inner, is the
most active volcanic place in the Solar System. It is so close to Jupiter that is nearly torn apart by the
gravitational forces. Europa is covered
in ice and may have a liquid salty ocean beneath. Ganymede is the largest moon in the solar system (3270 miles in
diameter). There are large areas on the
surface cover with thick dark dust. The
strangest features are the massive fault lines cause by movements on the
surface. Callisto has one of the most
heavily cratered surfaces in the Solar System.
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SATURN
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SATURN is the second largest planet but its most famous
feature is the magnificent ring system. The
ring or to be more precise rings are 275000km (170000 miles) across but only
a few hundred meters thick. They are
made up of millions of small pieces of ice and rock varying in size from a
few millimetres to a few meters across. The rings are thought to be the remains of a comet or a small moon
which was pulled apart by Saturn’s gravity. In theory the rings should not last for very long but they appear
to have been around for a very long time.
Small moonlets have been found orbiting within the rings which appear
to stop the rings falling apart. As
these small moons orbit their gravitational influence pushes and pulls the
ring particles into place, these moons are therefore called ‘Shepherd Moons’. There is a gap in the rings called the Cassini
Division, this can be seen quite clearly in medium sizes telescopes.
When space probes photographed the ring close up it was found that
there are in fact hundreds of rings and divisions.
Saturn, like Jupiter has dozens of moons with some large and some small. Titan is the largest moon at 3500 miles in
diameter and is one of the most intriguing of all the moons in the solar system.
It has a thick atmosphere and may have oceans, land, clouds and rain
not of water but all made of Methane. A
space probe called Cassini is due to land on Titan in 2004.
The probe has a camera on board and will film the decent of the craft
through the atmosphere by parachute. Saturn
has many other moons of various sizes. Titan
can be seen in most telescopes and perhaps three more may be seen in a 6 inch
telescope. Larger amateur telescopes
may pick out up to seven.
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URANUS
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NEPTUNE
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NEPTUNE is the last of the Gas
Giants and is approximately the same size as Uranus and also appears blue
/ green. Because it is even further
away than Uranus it is even harder to find.
Strangely the atmosphere on Neptune is much more turbulent than on
Uranus. This is because Neptune produces
much more heat in its core although the process is not yet fully understood.
Neptune boasts the largest moon is the Solar System in Triton which
has a diameter of 3300 miles and can be visible in medium sized telescopes.
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PLUTO AND CHARON
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PLUTO is considered, by
some people, not to be a true planet but just the largest of the icy bodies
orbiting the Sun beyond Neptune. With
it relatively large moon Charon, it can almost be considered to be a double
planet. At 4000 miles in diameter Pluto
is about the same size as Mars.
Although classed as the outermost planet, it has an odd orbit which
sometimes takes it inside the orbit of Neptune but most of the time it is the
most distant planet. Pluto is so remote
that the Sun looks more like a very bright star than the Sun we know. The surface is so cold that all the gases
there are frozen solid.
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COMET HALE-BOBB
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COMETS are like giant dirty
snowballs which originate in a vast area of space beyond the orbit of Pluto
and may be the left over remnants form the formation of the Solar System. The vary in size but are on average about 25
miles across. For some reason one
may get disturbed from its orbit a head in towards the Sun. As this huge ball of frozen gas and water mixed
with dust moves closer to the Sun it begins to melt. The gases and water vapour are pushed away
from the comet by the strong radiation from the Sun and the solar wind. The gas is pushed away from the Sun and forms
the familiar tail see on some comets. The
dust particles also form a trail in front and behind the nucleus.
If the Earth passes through this trail of particles the particles enter
the atmosphere they burn up and cause a glowing trail which we know as a Meteor. Some comets fall straight into the Sun others loop around the Sun
and return to the outer solar system sometimes to return years later.
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