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2009 SPACE ODYSSEY
a guide to the PLANETS
THE SOLAR SYSTEM
Our Solar System consists of the Sun and everything that revolves around it.
As well as the planets that orbit the Sun, many other bodies inhabit the Solar System.
They include satellites of the main planets, such as our moon, and various asteroids
and comets. Even as you read these words, you are travelling at around
500 miles per hour as the Earth spins on its axis.
As the Earth goes round the Sun, it moves at
almost 19 miles every second.
MERCURY
VENUS
EARTH
MARS
JUPITER
Discovered: Known since 3,000 years BC.
Mercury is the closest planet to the Sun and
the smallest in our Solar System. Named
after the Roman messenger god, the planet
is not much larger than the Earth's Moon and
superficially resembles it with a surface
pock-marked by enormous craters.
These craters were caused by meteorites
smashing into the planet's surface in the early
stages of the Solar System's evolution, some
four billion years ago. Although it's only a third
the size of Earth, Mercury is almost as dense.
Scientists put this down to a massive iron
core, which is also responsible for
Mercury's magnetic field.
Discovered: In the prehistoric age
Venus is the second planet from the Sun and is
named after the Roman goddess of love and
beauty. The landscape consists of rolling plains,
mountain ranges, lava flows and volcanoes. A
compass wouldn't work on Venus because there
is no discernible magnetic field. Venus has a
similar chemical composition and density to the
Earth but any water the planet might have had
evaporated long ago due to its closeness to the
Sun and the planet's runaway greenhouse
effect. Also, its thick clouds of sulphuric acid
and carbon dioxide make Venus one of the
most inhospitable places in the Solar System.
The surface temperature is hot enough to melt
lead. There are 217mph winds at high altitude
and the surface pressure is equivalent to
7 miles below sea level on Earth.
Age: 4.6 billion years
The third planet from the Sun, Earth is an
average-sized green and blue planet with a
single moon. But it is distinctly special for
humankind because it occupies a so-called
'Goldilocks' zone of space. It is neither too hot,
nor too cold, possessing the perfect conditions
for life. The name Earth comes from the
Anglo-Saxon word Erda, meaning ground, soil
and earth. Three quarters of the planet is
covered by vast oceans of water, thought to
have arrived from a shower of comets.
Discovered: Prehistoric times
Mars is named after the Roman God of war
and is often known as the Red Planet. Mars'
orange-red appearance results from soil rich
in iron oxide (more commonly known as rust).
Galileo was the first person to observe the
planet through a telescope in the early 1600s.
Its distinctive colour, associated by the Romans
with blood, makes Mars a highly visible planet
in the night sky and it can be seen with the
naked eye. Mars' orbit is closest to the
Earth every 26 months.
Discovered: Prehistoric times
The largest object in our Solar System, Jupiter
is a planetary tour de force. More than a
thousand Earths would fit inside it and Jupiter
has moons larger than planets. It is also home
to storms that have raged for hundreds of
years. No wonder it was named after the
Roman king of the gods. This enormous orange
gas giant is made up of 90 per cent hydrogen.
The atmosphere is not only poisonous, its
pressure is so strong deep down that hydrogen
gas is compressed into a liquid and any
spacecraft would be crushed.
The thick atmosphere contains a complex
weather system and its layers extend more than
347 miles from the Earth's surface. It is made up
of 77 per cent nitrogen and 21 per cent oxygen
as well as small amounts of other gases such as
carbon dioxide and protects us from harmful
ultraviolet radiation from the Sun.
Although relatively small - its radius is about
half that of the Earth's - Mars boasts scenery
on a massive scale, including Olympus Mons the highest volcano in the Solar System
Although it takes 12 years to orbit the Sun,
Jupiter only has a ten hour day. As a result,
the planet rotates so fast that it produces
violent winds, bulges 9,000 km at its equator
and stretches the striped white clouds of
ammonia ice. Its distinctive Red Spot is a
40,000 km storm system and could
swallow the entire Earth.
SATURN
Discovered: Prehistoric times
Named after the Roman god of agriculture,
Saturn is the second largest planet in our Solar
System. Its icy rocky core is surrounded by
hydrogen and helium with traces of methane,
ammonia and water ice. Saturn, like Jupiter, is
known as a gas giant. Engulfed in yellow clouds
of ammonia, the planet's wispy orange stripes
result from 1,770 km per hour winds and hot air
from the planet's interior. It also spins rapidly
on its axis, completing a full rotation every 10
hours 39 minutes. Saturn is circled by a majestic
halo of concentric rings and is the most distant
planet visible to the naked eye.
URANUS
Discovered: 1781 by William Herschel
The seventh planet from the Sun is blue-green
in colour with bright clouds, multiple rings and
strange moons. The third largest planet in the
Solar System, Uranus is named after the Greek
god of the heavens and was the first planet to
be discovered through a telescope.
Uranus has a total of 13 rings and 27 known
moons, all named after characters in works
by William Shakespeare and Alexander Pope.
A day on the planet lasts 17 hours while a year
on Uranus is equivalent to 84 Earth years.
NEPTUNE
Discovered: 1846
(proved mathematically 1845)
Named after the Roman god of the sea,
Neptune is about four times larger than Earth
and is the fourth largest planet in our Solar
System. Now that Pluto has been officially
demoted to a dwarf planet, Neptune is the only
planet in our Solar System that cannot be seen
with the naked eye. Although Pluto is further
away from the Sun, every 248 years it moves
inside Neptune's orbit for around 20 years.
A day on Neptune lasts 17 hours but each year
is the equivalent of 165 years on Earth. It has a
ring system, which is not as pronounced as
Saturn's, and several moons. The largest
moon is Triton (1,680 miles in diameter).
PLUTO
Discovered in 1930,
Pluto is smaller than our Moon.
It is thought to have a surface
of frozen methane and nitrogen and a thin
atmossphere. In 2006 was re classified
as a ‘Dwarf Planet’ as it does not meet the
criteria for a planet.
It takes 248 years to orbit the Sun.
MERCURY
VENUS
EARTH
MARS
JUPITER
SATURN
URANUS
NEPTUNE
PLUTO
Average miles
from sun
36,000,000
67,000,000
93,000,000
141,000,000
483,000,000
886,000,000
1,782,000,000
2,794,000,000
3,661,000,000
Diameter
3,031 miles
7,521 miles
7,926 miles
4,221 miles
88,734 miles
74,566 miles
31,556 miles
30,199 miles
1,450 miles
THE PIONEER AND VOYAGER MISSIONS
In 1977 NASA launched Voyagers 1 and 2. About the size of a small car,
both probes were designed to study and photograph Jupiter and Saturn,
but went on to send back data on all the outer planets except for Pluto,
and made amazing discoveries such as volcanoes on Jupiter’s moons and
the previously unknown rings of Neptune. The earlier Pioneer probes
carried metal plaques with diagrams identifying their origin, but the
Voyagers carried greetings in many languages plus sounds and images
from Earth with pictorial instructions for how to play the disc in the
event that they are discovered by intelligent extra terrestrials.
These tiny space ships have now gone beyond all the planets in our
Solar System and are approaching interstellar space.
Assuming they survive the journey, and even though they are travelling
at more than 36,000 miles per hour, it will be over 40,000 years
before they come close to another solar system.
ASTEROIDS
Asteroids are irregular fragments of rock and metal left
over from the formation of the Solar System 4.6 billion years
ago. Millions of asteroids are thought to orbit the Sun and are
largely concentrated in a belt, 111 million miles wide, between the
orbits of Mars and Jupiter. They range in size from less than half
a mile across to the largest known asteroid, Ceres, which is 584
miles in diameter, and has recently been reclassified as a dwarf
planet. Stray asteroids have hit Earth in the past. Many scientists
believe one impact, around 65 million years ago in an area now
known as Mexico, was responsible for a sudden change in
climate and the extinction of dinosaurs. In February 2001 the
Near Earth Asteroid Rendezvous (NEAR) mission achieved
the first ever landing on the asteroid ‘Eros’.
OUR NEAREST NEIGHBOURS
The nearest planet to us is usually Venus,
but sometimes Mars or Mercury are closer.
The distances constantly vary because not
all planets are in the same orbit. Venus is
the closest planet to Earth in terms of size but
has an atmosphere 90 times as dense as ours,
composed mainly of carbon dioxide.
Mars is roughly half the size of Earth and has a
very thin atmosphere. It is known as ‘the red
planet’ due to iron oxide dust (rust) on the
surface. Mars has seasons like ours and frozen
poles, although these are made of frozen carbon
dioxide (dry ice). The Phoenix Mars Lander has
recently discovered water ice on Mars, raising
speculation that it once supported life forms
and might still do. Slightly smaller than Mars,
Mercury is the innermost planet in the solar
system, orbiting the Sun every 88 days.
It is heavily cratered like our Moon, but its
surface temperature can range from 427oC to minus 183oC.
THE GAS GIANTS
344 million miles beyond Mars is Jupiter, the largest planet in the solar system and
the first of the ‘Gas Giants’ (Jupiter, Saturn, Uranus and Neptune). These planets do
not have a suface as such, but consist of a small solid core surrounded by outer layer
of mostly hydrogen and helium. It has the largest moon in the solar system,
‘Ganymede’ which is bigger than Mercury. SATURN has a prominent system of rings
composed of ice, rocks and dust. Its moon Titan
has a nitrogen and methgane atmosphere and is
thought to have an underground ocean, possibly
hosting microbial life forms. URANUS was
discovered in 1781. 1.78 billion miles from the
Sun, It has a blue green appearance and
unusually is tipped on its side, thought to be
as the result of a planetary collision early in its
existance. It has a faint ring system like Saturn
and winds of up to 560 miles per hour.
NEPTUNE was the first planet to be discovered
by mathematical prediction as opposed to
optical observation. 2.8 billion miles from the Sun,
it takes 165 years to complete one orbit. Like Uranus,
the colour of its atmosphere comes from the presence of ‘methane’ gas,
but Neptune is a much deeper blue, the cause of which is still a mystery.
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Two American observatories, Harvard Observatory in Cambridge, Massachusetts and
Lowell Observatory in Flagstaff, Arizona devoted a good deal of resources in the early
decades of the 20th century to finding Planet X. Success finally came in 1930 when
Clyde Tombaugh at Lowell found a dim star-like point moving through a set of
photographic plates. This planet was called Pluto. When astronomers at the Lowell
observatory announced the discovery of Pluto in 1930, they claimed it was several
times larger than Earth, ensuring that it was quickly labelled the ninth planet.
But as it turned out, Pluto is substantially smaller than the moon. In 2006, Pluto was
re-classified as a ‘Dwarf Planet’ at a meeting of the International Astronomical Union,
officially reducing the Solar system back to eight planets.
DISCOVERING THE PLANETS
The five naked eye planets - Mercury, Venus, Mars, Jupiter
and Saturn - have been known for millennia. Therefore,
no one person can be said to have ‘discovered’ these
bodies. However, the case of the three outer planets Uranus, Neptune, and Pluto - is different. These planets
were discovered with telescopes by specific individuals,
and the first discovery, that of Uranus, caused a
sensation throughout the world.
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William Herschel
ASTEROID WATCHDOGS
JUPITER’S COMET STRIKE
Was Mars once a living world? Does life
continue, even today, in a holding pattern,
waiting until the next global warming event
comes along? Many people would like to
believe so. Scientists are no exception.
But so far no evidence has been found that
convinces even a sizable minority of the
scientific community that the red planet
was ever home to life. What the evidence
does indicate, though, is that Mars was once
a habitable world. Life, as we know it, could
have taken hold there. The discoveries made
by NASA's Opportunity rover at Eagle Crater
leave no doubt that the area was once
‘drenched’ in water. It might have been
shallow water. It might not have been there for long. And billions of years might have
passed since it dried up. But liquid water was there, at the martian surface, and that
means that living organisms might have been there, too. Liquid water may have flowed
episodically over the surface of Mars in the planet's distant past. Even if life did gain a
foothold on Mars, it's unlikely that it ever evolved beyond the martian equivalent of
terrestrial single-celled bacteria. It took life on Earth billions of years to evolve beyond
single-celled organisms. Bacteria are amazingly diverse, various species occupying
extreme niches of temperature from sub freezing
to above boiling, living in sulfuric acid and
surviving with or without oxygen. In fact, there
are few habitats on Earth where one or another
species of bacterium can't survive. Photosynthesis
came relatively late to life on Earth. Early life had
to get its energy from chemical interactions
between rocks and dirt, water, and gases in the
atmosphere. If life ever emerged on Mars, it might
never have evolved beyond this primitive stage.
Comet Shoemaker-Levy was a comet that
collided with Jupiter in 1994, providing the first
direct observation of an extraterrestrial collision
of solar system objects. This generated a large
amount of coverage in the popular media, and
was closely observed by astronomers worldwide.
The collision provided new information about
Jupiter and highlighted its role in attracting
space debris in the inner solar system and
reducing impacts on other planets - like ours.
Content & Images supplied courtesy of:
Poster design by Jonathan Simms
Urbain Le Verrier
The comet was discovered by astronomers Carolyn and Eugene M. Shoemaker
and David Levy. Shoemaker-Levy 9 was located on the night of March 24, 1993,
in a photograph taken at the Palomar Observatory in California. It was the first comet
observed to be orbiting a planet. As the comet got closer to the planet, it broke into
several fragments which collided with Jupiter's southern hemisphere between July 16
and July 22, 1994, at a speed of over 100,000 miles per hour. The prominent scars
from the impacts were more easily visible than the Great Red Spot and
persisted for many months.
2009 SPACE ODYSSEY
LIFE ON MARS?
(1845) NEPTUNE While the discovery of Uranus was an
accident, Neptune was actively searched for. A detailed
study of Uranus’ orbit indicated that an unseen object
was making it deviate from the expected path.
Two astronomers, John Adams in England and Urbain
Le Verrier in France, made detailed mathematical
calculations that predicted where the planet would be
found. Both men gave the calculations to observational
astronomers, and observers in several countries found
the planet very close to the predicted location in 1845.
However, Le Verrier’s observational team was the first
to report the discovery and is usually given the credit.
The planet was christened Neptune, in keeping with
the classical theme of naming planets.
Today’s free poster
(1930) Pluto The fact that a planet had been discovered “mathematically” caused as
great a sensation among scientists as the original discovery of Uranus had a century
earlier. Thus the orbit of Neptune was carefully scrutinized to see if still other planets
lurked in the darkness beyond. By the turn of the twentieth century most planetary
astronomers had convinced themselves that Neptune was indeed showing the signs of
being tugged by an as yet undiscovered ninth planet. This effect was much smaller
than the corresponding effect on Uranus, and, therefore, the search for Planet X
(as the unseen planet came to be called) was much more difficult.
The astronomer William Herschel first used the word asteroid (Greek for star-like)
to describe these celestial objects. The asteroid belt is relatively stable but
occasionally gravity from a larger body, such as a planet, pulls one of them out of
orbit. Stray asteroids have hit Earth in the past. The chances of an impact similar to
the one which is thought to have wiped out the Dinosaurs are, thankfully, slim but
ground-based telescopes are monitoring Near Earth Asteroids (NEAs) - defined as
those whose orbits are able to approach or cross the orbit of Earth.
Telescopes on Earth track NEAs and detect new asteroids in case any
of them are in an orbit that might
collide with our planet. Even a
relatively small impact from space
would cause enormous damage.
Meteor Crater in Winslow, Arizona.
was formed 50,000 years ago when
a nickel-iron meteorite, 150 feet
in diameter and traveling at
40,000 mph, hit the earth.
The meteorite vaporized during
its descent. The crater is 4,500 feet
in diameter and 570 feet deep.
The impact was equivalent to 2.5 megatons of TNT, or 150 times the force of the
Hiroshima bomb. In 1908, what is thought to be a meteor exploded above a remote
area of Siberia. Although the meteor or comet burst in the air rather than directly
hitting the surface, this event is still referred to as an impact. Estimates of the energy
of the blast range from 5 megatons to as high as 30 megatons of TNT. The explosion
knocked over an estimated 80 million trees over 830 square miles. It is thought
that the earthquake from the blast would have measured 5.0 on the Richter scale.
THE PLANETS
(1781) URANUS William Herschel, at that time an amateur astronomer in Bath, England,
was making a systematic survey of the sky, noting nebulae, double stars, and the
occasional comet. In 1781 he discovered a small green object that he assumed was a
comet. However, after following it for a few days, it was clear that it was orbiting the
sun as a planet. He had discovered the planet we now know as Uranus, although his
original designation was ‘Georgium Sidus’ or George’s Star, after England’s reigning
monarch, George III. The effect on Herschel’s career was dramatic. George III awarded
Herschel a lifetime salary so that he could concentrate full time on astronomy.
2009 SPACE ODYSSEY
Today’s free poster
THE PLANETS
PIONEER 10
Pioneer 10 was launched on March 2,
1972, on a 21 month mission. It became
the first spacecraft to pass through the
asteroid belt and the first to obtain
close-up images of Jupiter. In 1983, it
became the first manmade object to
leave the Solar System when it passed
the orbit of Pluto. The Pioneer 10
spacecraft, destined to be the first
man-made object to escape our solar
system, carries this plaque. It is
designed to show scientifically educated inhabitants of some other star system who
might intercept it perhaps thousands of years from now. When Pioneer was launched,
from where, and by what kind of beings. The design is engraved into a gold-anodized
aluminum plate, 152 by 229 millimeters (6 by 9 inches), attached to the spacecraft's
antenna support struts in a position to help shield it from erosion by interstellar dust.
After travelling 12.2 billion kilometres from Earth, we have now lost contact with our
most distant spacecraft. The last signal received by Jet Propulsion Laboratory's Deep
Space Network was on 22 January 2003. The spacecraft was so distant that the signal,
travelling at the speed of light, took 11 hours and 20 minutes to arrive.
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