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This is Cassini’s closest pass yet by one of Saturn’s smaller icy satellites since its arrival around the ringed giant on June 30 of this year. The next close flyby of Iapetus is not until 2007. Iapetus is a world of sharp contrasts. The leading hemisphere is as dark as a freshly-tarred street, and the white, trailing hemisphere resembles freshly-fallen snow. Cassini will fly by the two-toned moon at a distance of approximately 123,400 kilometers (76,700 miles) on Friday, Dec. 31. This flyby brings to an end a year of major accomplishments and rings in what promises to be a year filled with new discoveries about Saturn and its moons. "I can think of no better way than this to wrap up what has been a whirlwind year," said Robert T. Mitchell, program manager for the Cassini mission at NASA’s Jet Propulsion Laboratory, Pasadena, Calif. "The new year offers new opportunities, and 2005 will be the year of the icy satellites." In 2005 Cassini will have 13 targeted encounters with five of Saturn’s moons. "We have 43 close flybys of Titan still ahead of us during the four-year tour. Next year, eight of our 13 close flybys will be of Titan. We will also have a number of more distant flybys of the icy satellites, and let’s not forget Saturn and the rings each time we come around," said Mitchell.With a diameter of about 1,400 kilometers (890 miles), Iapetus is Saturn’s third largest moon. It was discovered by Jean-Dominique Cassini in 1672. It was Cassini, for whom the Cassini-Huygens mission is named, who correctly deduced that one side of Iapetus was dark, while the other was white.
Scientists still do not agree on whether the dark material originated from an outside source or was created from Iapetus’ own interior. One scenario for the outside deposit of material would involve dark particles being ejected from Saturn’s little moon Phoebe and drifting inward to coat Iapetus. The major problem with this model is that the dark material on Iapetus is redder than Phoebe, although the material could have undergone chemical changes that made it redder after its expulsion from Phoebe. One observation lending credence to the theory of an internal origin is the concentration of material on crater floors, which implies that something is filling in the craters. In one model proposed by scientists, methane could erupt from the interior and then become darkened by ultraviolet radiation. Iapetus is odd in other respects. It is the only large Saturn moon in a highly inclined orbit, one that takes it far above and below the plane in which the rings and most of the moons orbit. It is less dense than objects of similar brightness, which implies it has a higher fraction of ice or possibly methane or ammonia in its interior. The last look at Iapetus was by NASA’s Voyager 1 and 2 spacecraft in 1980 and 1981. The Cassini images will be the highest resolution images yet of this mysterious moon. The Iapetus flyby by Cassini follows the successful release of the Huygens probe on December 24. The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. JPL, a division of the California Institute of Technology in Pasadena, manages the Cassini mission for NASA’s Science Mission Directorate, Washington, D.C. JPL designed, developed and assembled the Cassini orbiter. The European Space Agency built and managed the development of the Huygens probe and is in charge of the probe operations. The Italian Space Agency provided the high-gain antenna, much of the radio system and elements of several of Cassini’s science instruments. Cassini spacecraft targeted satellite encounters for 2005: **
Titan:
January 14, 2005 Titan-Bound Huygens Probe Detaches from Cassini
The Huygens probe, built and managed by the European Space Agency, was bolted to Cassini and has been riding along during the nearly seven-year journey to Saturn largely in a "sleep" mode. Huygens will be the first human-made object to explore on-site the unique environment of Titan, whose chemistry is assumed to be very similar to that of early Earth before life formed. Huygens will tell us whether this assumption is correct. "We wish to congratulate our European partners as their journey begins and wish them well on their descent to Titan," said Robert T. Mitchell, Cassini program manager at NASA’s Jet Propulsion Laboratory, Pasadena, Calif. "We are very excited to see the probe off and to have accomplished this part of our job. Now we’re ready to finish our part — receiving and relaying the Huygens data back to Earth." "Today’s release is another successful milestone in the Cassini- Huygens odyssey," said Dr. David Southwood, director of science program for the European Space Agency. "This was an amicable separation after seven years of living together. Our thanks to our partners at NASA for the lift. Each spacecraft will now continue on its own but we expect they’ll keep in touch to complete this amazing mission. Now all our hopes and expectations are focused on getting the first in-situ data from a new world we’ve been dreaming of exploring for decades." The Huygens probe will remain dormant until the onboard timer wakes it up just before the probe reaches Titan’s upper atmosphere on Jan. 14, 2005. Then it will begin a dramatic plunge through Titan’s murky atmosphere, tasting its chemical makeup and composition as it descends to touch down on its surface. The data gathered during this 2-1/2 hour descent will be transmitted from the probe to the Cassini orbiter (Click Here for the animation of the full descent). Afterward, Cassini will point its antenna to Earth and relay the data through NASA’s Deep Space Network to JPL and on to the European Space Agency’s Space Operations Center in Darmstadt, Germany, which serves as the operations center for the Huygens probe mission. From this control center, ESA engineers will be tracking the probe and scientists will be standing by to process the data from the probe’s six instruments. On Monday, Dec. 27, the Cassini orbiter will perform a deflection maneuver to keep it from following Huygens into Titan’s atmosphere. This maneuver will also establish the required geometry between the probe and the orbiter for radio communications during the probe descent. The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. JPL, a division of the California Institute of Technology in Pasadena, manages the Cassini mission for NASA’s Science Mission Directorate, Washington, D.C. JPL designed, developed and assembled the Cassini orbiter. The European Space Agency built and managed the development of the Huygens probe and is in charge of the probe operations. The Italian Space Agency provided the high-gain antenna, much of the radio system and elements of several of Cassini’s science instruments. For more in-depth information on the Huygens Probe Click Here Successful Getaway for Cassini
The Huygens probe successfully detached from the Cassini orbiter on 25 December. All systems performed as expected. The Huygens probe will be the first human-made object to explore on-site the unique environment of Titan, whose chemistry is thought to be very similar to that of early Earth before life arose. Next for Cassini
is a flyby of Saturn’s icy moon Iapetus on 31 December. Iapetus
is Saturn’s two-faced moon – one side is very bright, and the
other is very dark. One scenario for this striking difference
is that the moon’s surface is being resurfaced by some material
spewing from within. |
