After a 7-year interplanetary voyage, NASA’s Cassini spacecraft will reach Saturn this July and begin what promises to be one of the most exciting missions in planetary exploration history.
After years of work, scientists have just completed plans for Cassini’s observations of Saturn’s largest moon, Titan.
"Of course, no battle plan survives contact with the enemy," said Ralph Lorenz, an assistant research scientist at the University of Arizona’s Lunar and Planetary Laboratory in Tucson.
The spacecraft will deploy the European Space Agency’s Huygens probe to Titan for a January 2005 landing. Nearly half the size of Earth, frigid Titan is the only moon in the solar system with a thick atmosphere. Smog has prevented scientists from getting more than a tantalizing hint of what may be on the moon’s amazing surface.
"Titan is a completely new world to us, and what we learn early on will likely make us want to adjust our plans. But we have 44 flybys of Titan in only four years, so we have to have a basic plan to work to."
Scientists have long thought that, given the abundant methane in Titan's atmosphere, there might be liquid hydrocarbons on Titan. Infrared maps taken by the Hubble Space Telescope and ground-based telescopes show bright and dark regions on Titan's surface. The maps indicate the dark regions are literally pitch-black, suggesting liquid ethane and methane.
Last year, data from the Arecibo telescope showed there are many regions on Titan that are both fairly radar-dark and very smooth. One explanation is that these areas are seas of methane and ethane. These two compounds, present in natural gas on Earth, are liquid at Titan's frigid surface temperature, 94 degrees Kelvin (minus 179 degrees Celsius).
Titan will be an outstanding laboratory for oceanography and meteorology, Lorenz predicts.
"Many important oceanographical processes, like the transport of heat from low to high latitudes by ocean currents, or the generation of waves by wind, are known only empirically on Earth," Lorenz said. "If you want to know how big waves get for a given windspeed, you just go out and measure both of them, get a lot of datapoints, and fit a line through them.
"But that's not the same as understanding the underlying physics and being able to predict how things will be different if circumstances change. By giving us a whole new set of parameters, Titan will really open our understanding of how oceans and climates work."
Cassini/Huygens will answer many questions, among them:
Are the winds strong enough to whip up waves that will cut cliffs in the lakesides? Will they form steep beaches, or will the strong tides caused by Saturn's gravity be a bigger effect, forming wide, shallow tidal flats?
How deep are Titan's seas? This question bears on the history of Titan's atmosphere, which is the only other significant nitrogen atmosphere in the solar system, apart from the one you're breathing now.
And do the oceans have the same composition everywhere? Just as there are salty seas and freshwater lakes on Earth, some seas on Titan may be more ethane-rich than others.
Lorenz is a member of both the Cassini spacecraft's radar mapping team and a co-investigator of the Surface Science Package on the Huygens probe. He spoke Saturday, Feb. 14, at the press conference, "What Will Titan Be Like?" at the American Association for the Advancement of Science meeting in Seattle.
Lorenz began working on the Huygens project as an engineer for the European Space Agency in 1990, then earned his doctorate from the University of Kent at Canterbury, England, while building one of the probe's experiments. He joined the University of Arizona in 1994 where he started work on Cassini's Radar investigation. He is a co-author of the book, "Lifting Titan's Veil" published in 2002 by Cambridge University Press.
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