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The Cassini mission, which is named after a seventeenth-century
astronomer named Jean Dominique Cassini, will send a two-story tall
robotic spacecraft to Saturn (shown on the right). There, the Cassini
spacecraft will orbit Saturn while it looks at Saturn's rings,
atmosphere, and moons. It will also drop a smaller spacecraft, called
the Huygens probe (named after another astronomer named Christiaan
Huygens), onto Saturn's largest moon, Titan.
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Saturn is the sixth planet from our sun, and the second largest (only
Jupiter is bigger). Saturn is so huge that you could easily fit 750
Earths inside! Saturn is called a "gas giant" because it is made up of
mostly gas, unlike the Earth which is mostly rock. Saturn's atmosphere
is composed mainly of Hydrogen and Helium, and is very cold: -218
degrees Fahrenheit! We don't know for sure if Saturn has a surface or
not, but the pressure near the center is about 100 times the Earth's
atmospheric pressure. That's enough to crush any spacecraft we could
build! (Click on the picture of Saturn to the right to see it close-up.
Notice the two moons visible to the lower right of Saturn.)
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Saturn's rings are among its most famous features: they are easily
visible from earth with a small telescope. The rings are mostly
chunks of water ice that come in many sizes, from as small as a grain of sand
to as large as a house. The rings circle Saturn around it's equator,
and are separated into distinct rings, including some which can be
seen individually through a larger telescope. To find out more about Saturn
and it's rings, go to the
Saturn
web page.
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What will the Cassini spacecraft do there?
The Cassini spacecraft will orbit Saturn for 4 years, taking measurements of different aspects of the planet and it's moons. Cassini will travel in 60 different orbits so it can see many different views of Saturn, it's rings and moons. Cassini will make more than 30 close flybys of Titan, as well as many close approaches to other moons such as Mimas, Dione, Rhea and Iapetus. The Cassini spacecraft will take RADAR images of Titan's surface, measure the magnetic field of Saturn, examine the wind speed and temperature of Saturn's atmosphere, and take a closer look at what Saturn's rings are made of. Cassini will also take many pictures in the visual range, as well as in the infrared and ultraviolet.
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Saturn has 18 known moons, many of which are very interesting. Mimas
(shown on the right) has a huge crater that has walls 3 miles high --
which is pretty amazing since Mimas is only 250 miles in diameter.
Rhea appears to be make mostly of water ice. Depending on where it is
in it's orbit, Iapetus looks like two different moons, because one side
of the moon is covered with a very dark material, while the other side
is very bright! And Titan may be the most interesting of all.
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Titan's atmosphere may resemble the chemical environment of a primitive Earth, although it is unlikely that life could have arisen there, since it is very, very cold -- nearly -300 degrees Fahrenheit! Titan's atmosphere is brownish-orange, hazy mixture of nitrogen, methane, and complex carbon-based molecules. This thick atmosphere shields the surface from the prying eyes of astronomers. They theorize, though, that the surface contains lakes of methane or ethane, underneath which might lie a surface of frozen water ice. Using RADAR, we can see that the surface is not smooth, and by using infrared light, we can see a surface feature, similar to a continent.
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Titan is actually larger than the planets Mercury and Pluto, and is 40%
as large as the Earth, which makes Titan the second largest moon in the
Solar System (second only to Jupiter's Ganymede). It takes Titan only
16 days to make a complete orbit around Saturn. (Click on the
picture to the left to see a closer view of Titan. Notice the
uniform dark orange atmosphere.)
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In order to answer these questions, the Cassini spacecraft will carry a probe that it will drop into Titan's atmosphere. This probe, named Huygens, will look at the clouds, atmosphere, and surface of Titan as it descends on a parachute through the atmosphere. As the probe falls, it will take measurements of the pressure, temperature, and composition of the atmosphere. Click here to see an artist's idea of what the surface of Titan would look like. Imagine living on a planet where you could see Saturn and it's rings in all their glory up close and personal! The spacecraft in the upper left of the painting is the Cassini orbiter, while the object to the right is the Huygens probe, descending on it's parachute.
What is this I hear about plutonium?
Many stories have been published in the media discussing the possible dangers of launching the Cassini spacecraft, with it's RTG power source. The debate focuses on the plutonium that is the heart of the RTG power source. Environmental activists claim that the accidental detonation of the rocket could pulverize the plutonium and spread it throughout the Earth's atmosphere, causing lung cancer if it is inhaled. NASA claims that the plutonium cannot be damaged, citing numerous studies it performed in which the RTG was subjected to extreme heat and shocks, and did not fracture. The debate is complex, and will not be further discussed here, but you can check out NASA's comments on the debate.
On October 3rd, after an extensive review of the assessments of the potential risk, the White House office of Science and Technology Policy announced it's formal approval for the launch of the Cassini spacecraft. The Cassini mission was launched from Cape Canaveral, Florida on October 15, 1997 at 4:53 am EDT.
Where can I go to get more information?
NASA's Jet Propulsion Laboratory has lots of information about the Mission:
www.jpl.nasa.gov/Cassini
How will Cassini get to Saturn? See:
JPL's
Explanation
How to build a scale model of the Cassini spacecraft:
JPL's Instructions
Cassini Spacecraft movies:
Quicktime and
MPEG movies
