Back in October 1989, a NASA spacecraft that was named after the famous astronomer Galileo,
launched into space, beginning a 14-year mission that would reveal the solar systems largest
planet like never before. The mission involved over 800 people from
multiple countries and achieved many firsts, including being the first spacecraft to orbit
an outer planet, being the first to deploy an entry probe into an outer planets atmosphere
and being the first to closely image an asteroid. Galileo's journey to Jupiter started when
it was released from the cargo bay of space shuttle Atlantis, while in orbit around the
Earth. Because the spacecraft did not carry enough
fuel for a direct trip to the giant gas planet, it was set on a cleverly designed flight path
that would take it hurtling past Venus once and Earth twice, in order to increase its
speed and propel it outwards into the solar system, a technique known as a gravity assist
manoeuvre. Galileo reached our shrouded neighbour, Venus
in February 1990, presenting the first opportunity for the spacecraft to properly test and calibrate
its scientific instruments. It studied the thick Venusian clouds as it
swung past the hellish planet, sending back fascinating images of its toxic atmosphere.
This dark almost eerie image exposes the planets thick clouds as they circle above a scorching
surface. The image was captured 5 days after Galileo's closest approach and was taken through
a violet filter and coloured blue to enhance the contrast, allowing us to see the structure
of the clouds in much greater detail. After gaining a boost from Venus, Galileo
made its way home, where it would complete two more gravity assist flybys. The first
taking place in December 1990. During the first flyby, Galileo captured this
magnificent true colour image, when it was around 1.5 million miles away, which is 2.4
million kilometres away. You can see Africa stretching upwards from
the centre of our majestic planet, while the sunlit continent of Antarctica silently sits
at the bottom, all of which is slightly shrouded by swirling clouds.
Close up images of Earth were also captured, such as this beautiful bird's eye view of
Antarctica during the day, as the darkness of night roles in from the side.
You can see the thin, envelope of Earths blueish atmosphere as it follows the curvature of
the planet, a reminder of how fragile our existence really is.
After passing Earth the spacecraft swung outwards on an ever-growing orbit and in October 1991,
it clipped the edge of the asteroid belt, a vast region between Mars and Jupiter. Within
this mysterious region, Galileo was able to make history by snapping the first-ever close
up images of an asteroid. Named Gaspra, this asteroid is roughly 11
miles long, which 18 kilometres long and is a heavily pockmarked object, that may have
a relatively recent origin. The Sun's light, which is shining from the
right-hand side of the image is clearly illuminating the asteroids surface features, causing dark
shadows to be cast across its scarred, cratered landscape.
But there seems to be a lack of larger craters, and scientists think this could indicate that
Gaspra was once apart of a much larger body that was broken up during a catastrophic collision
event. Once passed Gaspra, Galileo swung inwards
for its next encounter with Earth and in December 1992 it successfully completed the second
flyby, boosting its velocity for the last time and saying goodbye to its home planet
forever. Now Galileo had finally built up enough speed
to start its long journey to the outer solar system, where it would eventually begin its
primary mission. But before it would arrive at Jupiter, it would first encounter one more
object and In August 1993, the spacecraft passed a second asteroid, with a small surprise.
Named Ida, this asteroid is the first ever to be discovered to have its own moon, which
was later named Dactyl. The enormous asteroid is about 35 miles long,
which is 58 kilometres long, while its little companion is just 1 mile across, which 1.6
kilometres across. Where dactyl originated from is uncertain, but scientists think that
it is likely a fragment of a much larger object that broke apart at some point in the past.
After passing Ida and dactyl, Galileo continued on its long journey, eventually leaving the
asteroid belt and entering the final stages of its trip.
From here, the spacecraft had no more planned encounters before arriving at the gas giant,
but it was able to capture a historic moment from a distance.
In July 1994 The spacecraft was perfectly positioned to watch 21 fragments of comet
shoemaker levy 9 crash into Jupiter. It was able to make a direct observation of the impact
and send back stunning images. These four frames were captured at the moment
part of the comet collided, smashing into Jupiter's cloud tops with an estimated force
of 300 million atomic bombs. Since it launched, Galileo visited Venus,
swung by Earth twice and encountered two separate asteroids, as well as getting a front-row
seat to a comet vs Jupiter showdown. After a journey that spanned 6 years and 2.3 billion
miles, or 3.7 billion kilometres, Galileo had finally arrived at Jupiter.
During its journey, Galileo also carried a small atmospheric probe that was released
in July 1995 as the spacecraft entered its final approach.
The probe made a solo flight into Jupiter's atmosphere, slicing through the clouds and
descending for 95 miles, which is 153 kilometres for 58 minutes before being vaporised.
Although the probe wasn't equipped with a camera, it did collect direct data on Jupiter's
local weather for the first time. It recorded wind speeds of up to 450 miles per hour, which
is 724 kilometres an hour and detected huge thunderstorms in the distance that were many
times larger than those we see here on Earth. Galileo successfully entered into orbit around
Jupiter in December 1995, marking the start of its primary mission. Over the next eight
years, it orbited the gas giant and captured thousands of incredible images of the planets
mesmerising atmosphere, including the famous storm, the Great Red Spot.
The orbit was also designed so that the spacecraft could complete close up flybys of Jupiters
largest moons, starting with the spectacular icy world, Europa.
Magnificent images such as this one, allowed us to view Europa in all its glory, as it
flaunted its fascinating surface features. They display a world with a diverse geology,
covered in long, linear cracks and ridges that crisscross around the moons icy crust.
A crust that Galileo also discovered is hiding a subsurface liquid ocean.
Close up, fascinating features such as these reddish coloured shallow pits, named Lenticulae,
which is Latin for freckles were also spotted. The unusual holes are thought to be caused
by warmer ice moving upwards from the bottom of Europa's ice shell, churning away like
a frigid lava lamp, and of course, providing further evidence of that concealed warm ocean.
Scientists found that Europa's linear ridges and bands that crisscross its frozen surface
are likely caused by Jupiter's strong gravity stretching and pulling the moon, which opens
and closes ridges repeatedly, resulting in these astonishing huge fractures.
After Europa, In September 1997, during Galileo's 10th orbit of the gas planet, the bizarre
moon Io was observed. A moon with a hellishly, active surface.
Io is the solar systems most volcanic world, as can be seen in this incredible colour image.
You can see irregular shaped mountains, layered materials that form vast plateaus and lava
flows erupting from enormous pits, all spread out across a bright sulphur-rich surface.
Close up images such as this one reveal beautiful colours mixing together within a volcanic
depression that has been named Tupan Patera, after the Brazilian thunder God.
Cooling lava is visible as black material, while the yellow is presumed to be a mix of
sulphurous compounds and the red is possibly sulphur gas that has condensed and coated
the ground after escaping volcanic vents. All of which is surrounded by cliffs 3000
feet tall, which is 900 metres tall. This image captures an active volcano in action
as it erupts hot lava out on to IO's bizarre surface.
IO's volcanic activity is a result of the strong gravitational pull from Jupiter on
one side and the large moons Europa, Ganymede and Callisto on the other. This gravitational
tug of war stretches and bends IO, causing it to heat up inside and erupt the colourful
materials that Galileo captured all those years ago.
Over the eight years that the spacecraft spent orbiting Jupiter it captured hundreds of fascinating
images of its largest moons, including Ganymede and Callisto.
Ganymede, which is the solar systems largest moon, has an icy surface that is speckled
with bright young craters, old darker craters and a frozen terrain that is laced with strange
grooves and ridges. Below its hard shell of ice, much like Europa,
scientists think an ocean layer also exists that may contain more water than here on Earth.
Callisto is Jupiters second largest moon and is the most heavily cratered object in the
solar system as these images reveal. The dark, icy, pummelled world clearly displays
a long violent history, although just like its neighbours, there is some evidence to
suggest that it too might be hiding a liquid ocean deep below its frozen crust.
The Galileo spacecraft completed 34 orbits of Jupiter while capturing thousands of stunning
images of its clouds, rings and mighty moons. Since its launch, back in October 1989, it
travelled a total of 2.8 billion miles, which is 4.6 billion kilometres, it achieved many
firsts and made multiple discoveries during its 14 years exploring space.
But like all things in life, the mission had to come to an end and in September 2003, the
spacecraft was commanded to deliberately plunge into Jupiter's atmosphere, destroying it forever
and eliminating any chance of contamination between the craft and one of Jupiter's large
moons. The Galileo mission remains one of the most
successful missions ever undertaken, it revealed our solar systems largest planet in astonishing
detail and provided the ambitious minds of planet Earth with a stepping stone into the
future.