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Cassini Rendevouz
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11-06-2004 9:52pm#1Cassini spacecraft bears down on Saturn after 7-year trip
By Andrew Bridges, Associated Press
LOS ANGELES — Out so far in space that the sun is a tiny dot, the most sophisticated science spacecraft ever is nearing Saturn to begin a lengthy study of the ringed planet and its 31 known moons.
Nearly seven years after it left Earth, Cassini, an internationally built craft named for an early day astronomer, is on schedule to enter orbit June 30 after it dashes through a gap in Saturn's shimmering rings. Scientists hope its findings will reveal new secrets about the evolution of our solar system.
Cassini had its first encounter with the Saturn system Friday afternoon, hurtling within 1,240 miles of the outermost moon, Phoebe. The tiny moon is just 137 miles across. Saturn, in contrast, is nearly 75,000 miles in diameter.
Scientists believe Phoebe originated in the outer reaches of the solar system and that it was later flung toward Saturn, which captured it into orbit.
"If it is, this will be our first encounter with something from that far out in the solar system," said Carolyn Porco, one of the team of scientists on the project.
"The study of the outer planets is of great importance to us because of what they represent: Saturn, its ring system, its moons, are a miniature model of a disk of gas and dust that surrounded the early sun as the planets formed in the solar system," Orlando Figueroa, director of NASA's Solar System Exploration Division, said in a recent briefing.
Saturn is the sixth planet from the sun, between bigger Jupiter and smaller Uranus. It was previously visited in flybys by NASA's Pioneer 11 on Sept. 1, 1979, Voyager 1 on Nov. 12, 1980, and Voyager 2 on Aug. 25, 1981. But none of those visitors entered orbit around Saturn.
The $3.3 billion, U.S.-European spacecraft, which also carries a probe to explore the moon Titan, was launched in October 1997. NASA built the plutonium-powered spacecraft; the European Space Agency contributed the Huygens (pronounced Hoy'-genz) probe.
Cassini, weighing 5,384 pounds, carries 12 science instruments; Huygens has six.
Once at Saturn, Cassini should spend at least four years in orbit. Its two cameras could take as many as half a million pictures.
"Cassini-Huygens is the most sophisticated scientific spacecraft launched to the planets," Figueroa said.
In addition to studying the composition and structure of the planet itself and the moons, scientists want to learn more about the rings.
"Other giant planets do have rings also, but Saturn has the most spectacular rings," said Charles Elachi, director of NASA's Jet Propulsion Laboratory and team leader of Cassini's radar instrument.
"What we want to understand is, what are they made of, what's their dynamic, how old they are, and, in a sense, to shed some light on how dust disks lead to the formation of planets," he said.
Mission members caution that getting into orbit won't be a cakewalk. Cassini must fire its engine on cue for 96 minutes to slow itself sufficiently and allow Saturn to pull it into orbit. If the maneuver fails, the spacecraft would sail past.
Cassini is set to release Huygens in December. A month later, scientists expect the probe to parachute through the murky atmosphere of Titan, Saturn's largest moon, and land on its surface.
Titan, larger than the planet Mercury, is the only moon in the solar system with an atmosphere and is believed to resemble what the Earth was like several billion years ago.
"Titan may preserve in deep freeze many of the chemical compounds that preceded life on Earth," Figueroa said.
Friday's flyby of Phoebe is a warmup for what's to come: Mission planners expect Cassini to conduct more than 50 similar flights past other Saturn moons, said Bob Mitchell, the mission's program manager.
NASA this week released images of Phoebe taken by Cassini this month as it closed in on the moon. Cassini's best possible pictures of Phoebe could show features as small as 66 feet across.
The mission is named for two 17th century scientists, the Italian-French astronomer Jean Dominique Cassini and the Dutch scientist Christiaan Huygens.
Contributing: Associated Press writer John Antczak.
Mike.1
Comments
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From bbc.Cassini flies past Saturn moon
The Cassini spacecraft, which is en route to Saturn, has made a close pass of the planet's mysterious moon Phoebe.
The US-European spacecraft made its closest approach to the moon on Friday at 2156 BST at a distance of 2,000km.
As the probe flies past, it will gather data that will tell scientists about Phoebe's internal structure, its composition and its history.
Phoebe is 220km across and Cassini's images of it will be far superior to those taken by Voyager 2 in 1981.
By determining the mass and volume of the moon, the scientists can also determine its density. This will tell them whether the moon is solid all the way through or is essentially a mass of rubble.
A radar instrument aboard Cassini will be able to answer whether Phoebe is composed primarily of ice or of rock.
The moon is intriguingly dark - it reflects only 6% of the sunlight it receives - and it orbits Saturn in a direction opposite to that of the larger, and closer, Saturn moons.
Its darkness and retrograde orbit have led some scientists to wonder if Phoebe is a Centaur: an object that migrated from the outer Solar System.
Objects of this type - from the region known as the Kuiper Belt - are thought to have served as the building blocks of the outer planets.
If this is true then observations of Phoebe will provide valuable information about how the various worlds that inhabit the cold, outer reaches of our Solar System were formed.
Images taken by Cassini so far show a body heavily pitted with craters, including a very large one, roughly 50km (31 miles) across.
The photos reveal a substantial amount of variation in surface brightness on Phoebe. Features that appear to be cliffs may be the boundaries between large craters.
The pattern of cratering will give clues to Phoebe's history. By looking at the surface properties of the youngest crater, Researchers can begin to understand how Phoebe started out.
Long-distance images were obtained by the Voyager 2 flyby in 1981, but Cassini's images - with a resolution of a few tens of metres - will be far superior.
Cassini is a joint Nasa-European Space Agency probe which will enter orbit around Saturn on 1 July. Next year, it will deliver the Huygens probe into the atmosphere of Saturn's major moon, Titan.
The small moon was discovered in 1898 by the US astronomer William Henry Pi
Mike.0 -
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http://photojournal.jpl.nasa.gov/jpeg/PIA06075.jpg
Nice pic, you feel like you could er land on it.
Mike.0 -
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