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JOURNEYS TO
JUPITER Jupiter is
the most visited planet of the four Outer Planets or Gas Giants (Jupiter,
Saturn, Uranus and Neptune). So far, eight unmanned space crafts have
visited the huge planet. Pioneer 10, Pioneer 11, Voyager 1, Voyager 2, Ulysses,
Cassini and New Horizons have all been flyby missions, meaning they observed
Jupiter and its moons while flying past it. Galileo was an orbiter which
spent several years in orbit of the planet. It also carried a probe which
was dropped into the planet's atmosphere. By
the early 1970s, missions had taken place to visit Earth's nearest
neighbours - the Moon, Venus and
Mars - and a mission to visit Mercury was
due to launch in 1973. Unsurprisingly, scientists wanted to go even further,
and the next logical step was Jupiter. Whereas the Moon,
Venus and Mars are
all relatively close to Earth, Jupiter is much further away. And to make the
journey even more of a challenge, Jupiter and the rest of the Outer Planets
are separated from the Inner Planets by the Asteroid Belt, a region of
thousands of asteroids. Even so, NASA mission planners, always up for a
challenge, decided to give the journey a go and in 1973 were ready to send a
couple of space crafts through it and on to Jupiter!  THE
PIONEER MISSION
Pioneer 10 launched 2nd
March 1972, Pioneer 11 launched 5th April 1973
Pioneer 10 was the first space craft to complete the treacherous journey
through the Asteroid Belt in July 1972 and achieved its aim of flying by
Jupiter in December 1973, getting as close as 200,000 kilometres (124,000
miles) from the cloud tops of the planet. It sent back the first close-up
images of Jupiter and discovered surprisingly high levels of radiation surrounding the
planet. It also analysed Jupiter's atmosphere and magnetic field and took a
look at some of the planet's moons. Pioneer 10's twin probe, Pioneer 11,
reached Jupiter about a year later, achieving its closest approach of 34,000
km (21,000 miles) on 3rd December 1974. From this distance, it sent back
spectacular images of Jupiter's Great Red Spot. After passing Jupiter,
Pioneer 10 continued on its journey heading out of the Solar System. Despite
not visiting anything else, it sent back regular data about outer space
until 31st March 1997. Contact was made occasionally afterwards, mainly for
training purposes, until contact was lost on 23rd January 2003. Of course,
the space craft still continues its journey, although no longer sends back
any information about its adventure. It is heading in the direction of a star called
Aldebaran, a red giant star in the Taurus constellation. It should get there
in about 2 million years, and just in case anybody/thing happens to be in
that region at that time, there is a plaque (pictured below)  onboard Pioneer 10
with a
diagram of a man and a woman and some other, apparently meaningful, doodles
for them to have a look at. Seeing as the diagram doesn't make much sense to
human beings without having it explained, who knows what extra-terrestrial
beings would make of it? Pioneer 11 also had an identical plaque onboard and
would also end up going on a journey out of the Solar System but not before
taking in the sights of Saturn. Pioneer 11 would use a method called gravity
assist to get it from Jupiter to Saturn. With this method, the space craft
would use the gravity of one planet to pick up speed (since the planet travels at a
greater velocity than the space craft). As it passes by the planet while
attracted by its gravity, it can be boosted out of this orbit and onto a
different trajectory, therefore getting to another destination quicker and
by using less fuel. The method had already been tried with Mariner 10
earlier in 1974 which used the gravity of Venus to get it to
Mercury, and
Pioneer's use of Jupiter's gravity to get it to Saturn paved the way for a
similar technique to be used for later missions, most notably Voyager.
THE VOYAGER
MISSION
Voyager 1 launched
5th September 1977, Voyager 2 launched 20th August 1977
(Go here for more information about the Voyager Mission)
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Originally planned as a "Grand Tour" of the Outer
Planets, Voyager
was officially a two-probe mission to visit just Jupiter and Saturn with the
possibility of mission extensions to go on to visit Uranus and
Neptune,
using the gravity assist method of Pioneer 11 to get from one planet to the
next. Although Voyager 1 was launched 16 days after Voyager 2, it actually
reached Jupiter four months before Voyager 2 in January 1979 (maybe it knew
a shortcut through the Asteroid Belt!). Achieving its closest approach on
5th March 1979 (349,000 km or 217,000 miles), Voyager 1 sent back amazing
images and other scientific data from Jupiter, completing its flyby by April
before going off on its way to Saturn. Shortly after Voyager 1 left Jupiter,
Voyager 2 turned up to take some more pictures and do some more analysing.
Although Voyager 2's main receiver broke down ten months into its journey to
Jupiter, communications were maintained through its back-up receiver, and
still are to this day! Voyager 2's closest approach to Jupiter was on 9th
July 1979 and like Voyager 1, it was sent onwards to Saturn after completing
its flyby of Jupiter by August 1979. |
A Voyager probe before
launch
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Between
the two Voyager probes, three new moons of Jupiter
were discovered (Metis,
Adrastea and Thebe) as well as Jupiter's rings which proved that Saturn
isn't the only planet with rings. In fact, Voyager 2 would later discover
that rings orbit all of the Gas Giants. Analysis of Jupiter's largest moons
revealed them to be very interesting bodies, much more exciting than the one
orbiting Earth! Nine volcanic eruptions were observed on
Io, making it the
first place other than Earth where current volcanic activity has been
witnessed. Analysis of Europa suggests that the moon is possibly covered
with a surface of ice, probably 30 kilometres (18 miles) thick floating on a
deep ocean of water, preventing from freezing by the heat generated by the
moon's active core.
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Today,
about 30 years after their encounter with Jupiter, the two Voyager probes
are still active. After visiting Saturn, Voyager 1 was sent on its journey
out of the Solar System, and is now the most distant man-made object in
space somewhere at the edge of the Solar System and looking for the exit.
Voyager 2 benefited from a mission extension which took it to Uranus and
then Neptune before also being sent out of the Solar System. Like Pioneers
10 and 11, they were sent bearing gifts for any passing aliens/lost
astronauts/space craft collectors. Taking advantage of state-of-the-art
1970s technology, the Voyager crafts carry gold-plated records! Covering the
record is another plaque of confusing drawings. The records themselves contain images, sounds and
music from Earth, although quite annoyingly, nothing was sent with either
Voyager 1 or 2 to play them on! |
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THE
GALILEO MISSION
Galileo launched 18th October 1989
Named after the Italian astronomer who discovered Jupiter's largest moons
(Io, Europa, Ganymede and
Callisto), Galileo was launched in 1989 (the space
craft, not the astronomer!) on a mission dedicated to the exploration of
Jupiter and its moons. Galileo used gravity assist to gain speed and save
fuel, using the gravity of Earth and Venus to do so and took almost six
years to reach its destination. Whereas previous and future missions simply
flew by Jupiter, Galileo actually went into orbit of the planet and spent
several years there. On its approach to Jupiter, Galileo witnessed Comet
Shoemaker-Levy's spectacular collision into Jupiter in July 1994. It sent
back images of the collision (such as the one below) and the scars that remained visible in the
planet's atmosphere for the months following. This was the first time that a
collision of two space objects had been observed. 
As Galileo got closer to
Jupiter, it released a probe in July 1995 which would plunge into the
planet's atmosphere later that year. Galileo entered orbit of Jupiter on 8th
December 1995, a day after the probe released in July began its descent
through Jupiter's atmosphere. As the probe dropped through Jupiter's
virtually endless sky, it sent back information about the planet's
temperature, wind speed, atmospheric conditions and pressure. It
communicated for almost an hour but by the time it was being subjected to
pressures 22 times greater than surface pressure on Earth
and at temperatures of 153°C (307°F), it is likely to have
been crushed before melting and vapourising. Not a pleasant way to go! While
the Galileo probe was experiencing its violent end, the Galileo orbiter was
quite peacefully orbiting the planet and taking in the scenery. As well as
snapping photos of Jupiter and sending back scientific data, it had a look
at Jupiter's rings, discovering that they are formed from dust particles
being kicked up as meteoroids impact the four innermost moons (Metis,
Adrastea, Amalthea and Thebe). It also discovered that Jupiter's outer ring
is actually two rings embedded together. Mission extensions allowed Galileo
to pay Jupiter's moons some more attention. It confirmed more volcanic
activity on Io, discovering it to be 100 times more volcanically active than
Earth. It confirmed that Europa's surface is water ice and below it is
likely to be an ocean of salt water. It also suggested that Callisto and
Ganymede may also have a layer of saltwater. It also discovered that
Ganymede has a magnetic field, the only moon known to possess one, due to
having an iron core. After completing its mission, the Galileo orbiter met
the same fate as its descent probe when it was sent plunging into the
planet's atmosphere to be destroyed on 21st September 2003. This was to
prevent it from colliding with Europa and causing possible contamination of
the moon's water. During its time at Jupiter, Galileo completed 35 orbits of
the planet and several flybys of each of Jupiter's known moons. ULYSSES
Ulysses launched 6th
October 1990
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Diagram showing the
path Ulysses took to go into orbit of the Sun
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Ulysses is a mission to explore the Sun while in a polar orbit of the star.
This means that instead of orbiting the Sun around its equator on a similar
plane to the orbits of Earth and the other planets, the probe goes around
the top and bottom of the Sun. In fact, if you want to sound clever, it
orbits on a plane with an 80.2 degree inclination of the ecliptic. However,
getting a space craft into an Out-of-the-Ecliptic (OOE) orbit around the Sun
would require one huge rocket and lots of fuel. Alternatively, it could use
the tried and tested gravity assist method. In the case of Ulysses, the
space craft was launched from the Space Shuttle Discovery and sent to
Jupiter. It was originally going to launch on 1986 from Space Shuttle
Challenger, but due to the Challenger disaster in January of that year, the
Ulysses mission was delayed. When it reached Jupiter, it used the planet's
gravity to propel the craft onto a different plane. This enables the craft
to travel around the Sun at a distance ranging from the distance of the
orbit of Jupiter (its aphelion) to the distance of the orbit of Earth (its
perihelion). While at Jupiter in February 1992, it took the opportunity to
do a spot of analysis, measuring the planet's magnetic and radiation fields.
As the craft isn't equipped with cameras, it didn't take any pictures. In
2004, the craft made further analysis of Jupiter at a distance of 240
million kilometres from the planet. As of today, the craft is still
active. |
CASSINI-HUYGENS
Cassini-Huygens
launched 15th October 1997
Cassini-Huygens is a mission to explore Saturn, but like previous visitors,
it used gravity assist to get there. Rather cleverly, it used the gravity of
Earth, Venus and Jupiter to get the craft to
Saturn in an effort to reduce
costs and increase speed, or perhaps just to show off. After
completing two gravity assist flybys of Venus in 1998 and 1999 and then a
gravity assist flyby of Earth, Cassini-Huygens went on its way to Jupiter.
While flying by Jupiter from December 2000, it sent back over 26,000 images
of the planet, providing the most detailed pictures of Jupiter to date. It
also provided new information about Jupiter's atmospheric conditions. The
craft is now in an active orbit around Saturn. NEW
HORIZONS
New Horizons launched 19th January 2006
New Horizons is a space craft on its way to visit Pluto and the Kuiper Belt
to complete the first mission in this region of space. Once again to get
there, it used the gravity assist method and, unsurprisingly, Jupiter was
the planet chosen to lend its gravity to the mission. In the case of New
Horizons, Jupiter was used to increase the speed of the craft (which was
already travelling at record speeds) and sent it onto a different orbital
plane to the rest of the planets seeing as Pluto, being a bit odd, also
orbits on a different elliptical plane. The craft began imaging Jupiter in
September 2006 and completed its flyby of the planet between January and May
2007, only a year after launch. While at Jupiter, it did the usual
scientific things, paying particular attention to its four largest moons.
New Horizons was also the first craft to analyse Jupiter's newly formed
Little Red Spot, or Oval BA to give it its official name (a spot with a
qualification?). It is now still en route to Pluto and should get there in
2015. |
Image of Jupiter from
Galileo data
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FUTURE MISSIONS
In 2011, NASA is
expected to launch Juno, a spacecraft which will explore Jupiter while in
orbit of its poles. As well as analysing Jupiter's magnetic and
gravitational fields from polar orbit, it will also try to uncover
information about the formation of the planet and attempt to discover
whether the planet has a rocky centre and how much water is present in its
atmosphere. A possible future spacecraft is Europe's Laplace probe.
Currently in its proposal stages, and expected to be launched in
collaboration with NASA and the Japanese Aerospace Exploration Agency if
approved, Laplace will go into orbit of Jupiter and analyse it and its moons
with particular attention being paid to Europa, with investigating the
possibility of the moon being able to harbour life. In addition to these
missions, missions to other destinations in the Solar System may rely on
Jupiter's gravity to get them there. And more than likely during these
missions, Jupiter will again be observed during the flybys.
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