Launched in 1997, the Cassini-Huygens mission is a seven-year project that reached Saturn in June 2004. Upon arrival Cassini began four years of data gathering on Saturn and nine of its twenty known moons. In November 2004 the probe Huygens was released and descended to the surface of Titan, Saturn's largest moon. Some scientists view this as a way to travel back in time because Titan is predicted to be under the same conditions as Earth was before life began. During the 2.5 hour descent, data will be gathered on the chemicals contained in Titan's atmosphere, as well as the environmental conditions on the moon, and transmitted back to Earth. Most importantly, scientists will get the first glimpse of the surface with the pictures taken during the descent. This data could possibly change all theories about the origin of life.
A Journey to Unseen Territory
In four years a whole new range of possibilities will open up in the search for the origin of life. This will occur when the spacecraft Cassini reaches Saturn. After a few months of orbiting the planet and relaying pictures back to Earth, Cassini will release the probe Huygens. Huygens is scheduled to land on Titan (see Fig. 1), Saturn's largest moon, in November of 2004. After years of planning, this seven-year journey will come to a climax during the three hours of data that the Huygens probe will gather. The data found on Titan will either change or confirm every theory scientists have about the origin of life.
NASA/Photo Journal of JPL
Most people can easily identify a picture of Saturn. This is thanks to the Voyager mission, the spacecraft that passed Jupiter, Saturn, and Uranus during the early 80's and took many pictures of Saturn and some of its moons; these pictures are easily available for everyone to see. There is just one problem: not everything is visible from a fly-by mission. While the Voyager was able to get pictures of Titan, the haze of Titan's atmosphere clouded any possible view of the surface. This haze intrigued many scientists who believe that Titan could be under the same conditions as the Earth was before signs of life. Enter Huygens, the probe that scientists are hoping will gather valuable information about the atmosphere of Titan as well as take pictures of the surface.
Cassini and Huygens?
Christiaan Huygens was a Dutch scientist who developed techniques to improve lenses used in telescopes. In 1655, Huygens discovered Titan and categorized Saturn's rings . Using these improved techniques, in 1675, Italian astronomer Giovanni Domenico Cassini discovered four other moons as well as a gap in Saturn's rings known as the Cassini division . Both of these men helped increase our knowledge of Saturn and have successfully aroused our interest in the topic. Thus, it is only fitting to name the spacecraft and probe that will be going to Saturn after these two men.
Planning, Planning, Planning
The Cassini-Huygens mission is the second global project undertaken by NASA. The European Space Agency (ESA) built the probe Huygens. Lockheed Martin Federal Systems, an American aerospace company, developed computers for the complex command and data subsystem that keeps Cassini on the right trajectory path. Lockheed included fault-protection software in the event of an emergency where the spacecraft will remain "in a neutral condition" for as long as two weeks at a time while a solution is being engineered here on Earth. While earlier projects had the danger of jamming, TRW, another American aerospace company, solved the problem by designing the solid-state data recorders. Cassini contains two recorders that can each hold up to two gigabytes. In all, Cassini is equipped with 12 sets of scientific instruments and subsystems for "mapping, measuring, and analyzing" the planet and its environment .
Since Cassini has to travel so far into the outer solar system where solar energy is weak, it is not possible to fuel the spacecraft with solar panels like the ones used on recent missions to Mars. Instead Cassini receives all of its electric power from 72.2 pounds of radioactive plutonium dioxide. The heat generated by the natural decay of the compound is turned into electric power with the use of three thermo-electric converters. NASA was confident that this large amount of radioactive material was securely packaged, and that the chance of radio active explosion during take off was very rare, 1 in 5,000 .
The Scenic Route
The Cassini-Huygens mission was designed as a seven year journey from Earth to Saturn. This is mainly due to the number of "gravity assists" that occur as the spacecraft travels by Venus, Earth and Jupiter before it heads for its final destination. As the craft gets closer to a planet it is drawn into its orbit due to gravity. The craft will then be swung around the planet and shot out again at a greater speed. This is often referred to as a "slingshot effect." Cassini passed Venus twice, in April '98 and June '99, then Earth in August '99 . Right now the spacecraft is heading towards Jupiter with a scheduled fly-by in December 2000. Each of these fly-bys is necessary in order for the craft to gain enough speed to head out into the outer solar system.
To incorporate another project into the Cassini-Huygens mission, scientists and engineers are planning to take pictures of Jupiter as well. A team of researchers is interested in possible volcanic activity on Io, one of Jupiter's largest moons. Once this is completed, the spacecraft will not come in contact with any other planets until it reaches Saturn in July 2004.
What Happens When Cassini Reaches Saturn?
Once Cassini gets to Saturn in the summer of 2004, it will begin a four-year scientific program. While orbiting Saturn, it will gather enormous amounts of information, including 300,000 pictures. It is also programmed to study the physics of Saturn's rings and shepherd moons, which appear to herd the rings. This program will begin when Cassini enters Saturn's orbit by firing braking rockets. Cassini will then pass through Saturn's rings. The entire spacecraft will rotate allowing the instruments to collect and transmit data to Earth . It is expected to circle Saturn about sixty times. While in orbit it will use its 13-foot diameter antenna to scan the surface of Saturn's nine major moons.
Using Titan's gravitational pull, Cassini will fly among Saturn's moons. It is expected that each moon will be visited at least five times, including circling Titan itself 30 to 40 times. Five months after Cassini arrives at Saturn, the saucer-shaped Huygens will be released. Twenty-two days after Huygens is released it will parachute into Titan's atmosphere. During the first three minutes of descent through the atmosphere, Huygens will slow from 11,250 mph to 1,060 mph. Then with the help of three separate parachutes the probe will reduce its speed even more and stabilize. It is scheduled to have a two and a half hour descent, during which it will obtain the majority of its data. The probe contains six experiment packages that will test the contents of the atmosphere and relay 1,100 pictures back to Earth through the help of Cassini .
Ralph Lorenz, a planetary scientist at University of Arizona's Lunar and Planetary Laboratory in Tucson, has predicted that the surface of Titan is like icebergs in lakes of methane . Scientists do not know what the surface of Titan will be but if all goes as planned, Huygens will touch down, or even splash down, at 12 mph. The largest "if" comes at this point. If the probe survives the landing, it is programmed to continue taking data for up to half an hour. After this time Cassini will move out of range of Huygens and any other data taken by Huygens will be lost forever .
What's the Big Deal?
Spectroscopy is widely used in chemistry to determine the chemical composition of a substance. Each element has its own unique spectrum, made up of lines in the visible light range, which can be seen when the substance is heated. Huygens is carrying a mass spectrometer that will analyze the chemical composition of the atmosphere, including the haze that mystified many scientists as well as the methane and nitrogen that is already known to be on the moon. The probe also contains thermometers and barometers to gather weather information.
NASA/Photo Journal of JPL
During the descent the camera onboard will also take pictures of the surface beneath. All of this data is highly anticipated due to the prediction that Titan is a sort of primordial Earth. Many scientists have been researching the Origin of Life and have come up with numerous theories. The late Carl Sagan performed a number of experiments in his laboratory attempting to simulate the haze on Titan's surface. He provided the elements that are on Titan with the same kinds of energy sources available to Titan. He was able to produce a dark organic solid that he called tholin, which is Greek for muddy. Current scientists also plan to use the data from Titan to simulate the planet's conditions in their own laboratories.
While most concede that conditions are not exactly the same as the primordial Earth, the lack of free oxygen makes Titan the best look at primitive earth. It is important to note that based on one of the many theories of the origin of life, oxygen was not present on Earth at the "inception of life" . Oxygen as we know it was produced by the life that was created with the substances on Earth. Titan is fascinating because it contains many of the same compounds that were believed to be on Earth. One other difference is that Titan is nearly 900 million miles from the Sun which gives it 100 times less solar energy . However, Titan also receives energy from Saturn's magnetosphere, cosmic rays and impacts (meteors or other fragments that run into the moon) as well as possible heat from volcanoes on Titan's surface .
Return to Saturn
Due to the amount of planning necessary for a mission like the Cassini-Huygens project, scientists, such as Lorenz, believe that planning the next mission to Saturn should already begin . If Huygens shows signs of life on Titan, scientists will have to change their requirements for organic life. Organic life is not predicted because of the extreme temperatures of Titan, as low as 95 degrees Kelvin, or -178 degrees Celsius . Scientists also look for a certain size organism, assuming that a living organism must be larger than the molecules that are required to sustain life. These assumptions, or standards, could be completely wiped out if Huygens finds signs of organic life on Titan.
Such an enormous change in the perception of life deserves return trips to Titan. Perhaps new predictions could be made or even confirmed. On the other hand, even if all of the data confirms the beliefs of the scientists, a deeper look at the "primordial Earth" will need to be considered. However, the planning for another mission does not have to wait until the data is sent back to Earth; based on the research that scientists conduct across the globe on Saturn and what is already known, planning the next tour of Titan could take place while Cassini-Huygens is still in flight. Until Cassini reaches Saturn, the theories of the origin of life will continue to be studied. But, in four years the answers to many scientists' questions could be transmitted back from Titan.
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