SETI Reasons for Cassini mission to Saturn


Larry Klaes (lklaes@bbn.com)
Mon, 14 Jun 1999 12:51:58 -0400


http://www.flatoday.com/space/explore/stories/1999b/061299d.htm June 12, 1999 Reasons for Cassini mission to Saturn By Dr. Carl Pilcher A FLORIDA TODAY guest column "Only when we have flown missions to every part of the solar system will we have the vital statistics of all its components and be able to turn back the pages of the book of cosmology to the origins of our own world, and perhaps of the universe itself." Arthur C. Clark, Beyond Jupiter, 1972 CAPE CANAVERAL, Fla. - This visionary passage was written during the earliest stages of planetary exploration. But it still rings true today, an era when data from space probes are recorded on silicon chips instead of magnetic tape, and rocket engines can eject electrically charged particles instead of burning chemicals. About a decade after Dr. Clarke's book, the two NASA Voyager missions together flew by the four gaseous outer planets and their moons, giving Earthlings our first detailed look at \ their cold beauty and surprising complexity. The logical next step: orbit these planets to study their mysteries close up. Subsequently, NASA's still-running Galileo mission has answered many major questions about Jupiter during its three-plus years in orbit around the orange-tinted giant. Galileo also has shown us that Jupiter's icy moon Europa is covered with tantalizing fractures, ridges and iceberg-like features that merit more focused exploration to determine whether they cover a slushy ocean or even a liquid body of water. If confirmed, it would be the first such ocean discovered outside of Earth, and a prime candidate for hosting some kind of primitive life. In October 1997, NASA and international partners from 16 countries launched the Cassini mission to Saturn, the most capable and ambitious robotic expedition ever sent into space. The mission is actually a pair of spacecraft: the Cassini orbiter, packed with 12 state-of-the-art science instruments, including a radar to penetrate the natural smog of the mysterious moon Titan; and, a saucer-shaped probe built by the European Space Agency. This probe, called Huygens, will ride a parachute through Titan's thick, nitrogen-rich atmosphere all the way down to its unseen surface, where it might find lakes of liquid hydrocarbons amidst a bizarre landscape. All of these missions - the Voyagers, Galileo and Cassini - seek to address basic questions about how the planets were formed and what conditions existed at the time life was beginning on Earth. For example, why is Jupiter about 9 percent helium, while Saturn has only one-third that fraction? Why does Jupiter have four large moons but Saturn only one among its 18 natural satellites? What can each planet's amazing but very different ring systems tell us about these puzzles? And perhaps most importantly, which of these bodies, if any, might have harbored the first stirrings of life? These missions also share a common element of design: They all utilize devices called Radioisotope Thermoelectric Generators to provide their electrical power, using heat from the natural decay of non-weapons grade plutonium. These devices have been used safely and successfully for 30 years. They are used only when solar panels or batteries cannot provide adequate power for a mission, and their safety is assured by rigorous engineering, physical testing and overall design of the mission. Cassini must fly by Earth (on Aug. 17) to gain enough speed to reach Saturn, one billion miles from Earth, using a flight plan very similar to Galileo, which performed this well-understood maneuver twice with incredible accuracy. Cassini's trajectory is never pointed at Earth, and all of the procedures and analyses related to this Earth swingby were reviewed by experts outside of NASA and were found to be sound and reasonable. These analyses concluded that the chances of an accidental entry into Earth's atmosphere are less than 1 in 1 million, and even if this extremely unlikely event did occur, the expected radiation does to an exposed person is equivalent to the amount of radiation a person receives from natural sources during a one-way airline flight from New York to Los Angeles. Many people know that the great Italian scientist Galileo was the first person to observe the rings of Saturn. But many people do not know that Galileo did not understand that these "handles" were truly rings - it took Dutch scientists Christiaan Huygens, for whom the Cassini Huygens probe is named, to provide that special and ultimately profound insight. In that same way, Cassini will build upon the successes of Galileo and Voyager missions to help us answer some of the most basic questions of human existence: How did the planets form? How did life begin? And, are we alone in the universe? Join us in the adventure. http://www.jpl.nasa.gov/cassini/ Dr. Carl Pilcher is the science director for Solar Systems exploration in the Office of Space Science at NASA Headquarters in Washington, D.C. Use of this site signifies your agreement to the Terms of Service updated February 1998. Please e-mail comments or questions about this page to Space Online Editor Mark DeCotis. Contact Space Online Manager Jim Banke to inquire about becoming a sponsor. This World Wide Web site is copyright 1999 FLORIDA TODAY.



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