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The Discovery crew
The seven astronauts to fly the return to flight space shuttle mission hold a news conference at the Kennedy Space Center runway Jan. 7 to talk about delivery of the external tank, tile/RCC repair options and other issues. (44min 24sec file)

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Shuttle news conference
Senior space shuttle program officials hold a news conference at Kennedy Space Center on Jan. 6 following delivery of the redesigned external fuel tank to be used on the return-to-flight launch. (51min 47sec file)

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External tank arrives
The external tank for space shuttle Discovery's return-to-flight launch arrives at Kennedy Space Center. The tank is offloaded from the barge and moved into the Vehicle Assembly Building. (3min 15sec file)
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Tank leaves New Orleans
The redesigned external fuel tank to be used on the return-to-flight space shuttle launch is rolled out of the Michoud Assembly Facility and place on a barge for shipment from New Orleans to Kennedy Space Center. (1min 29sec file)
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Final touches
Technicians put the final touches on the Lockheed Martin-built space shuttle external fuel tank in advance of its shipment to the Cape. (1min 44sec file)
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Mars rover cake
NASA Administrator Sean O'Keefe is presented with a commemorative birthday cake marking the one-year anniversary of the Mars rover Spirit's landing. (1min 21sec file)
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Rover news briefing
On the one-year anniversary of Spirit's landing on Mars, mission officials hold a status news conference on the twin exploration rovers to discuss the latest findings and future plans for the craft. (31min 20sec file)
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NASA chief speech
During celebrations marking the Mars rover milestone on Jan. 3, NASA Administrator Sean O'Keefe gave this speech at the Jet Propulsion Laboratory. (10min 20sec file)
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The Mars rover story
Storyteller Syd Lieberman presents "Twelve Wheels on Mars" that describes the adventure to build, launch and explore with the Mars rovers Spirit and Opportunity. (54min 57sec file)
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Delta 4-Heavy launch
The Boeing Delta 4-Heavy rocket is launched from Cape Canaveral on its demonstration flight. (4min 35sec file)
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Onboard the Heavy
An onboard camera records the launch of Boeing's Delta 4-Heavy rocket from liftoff through separation of the outer boosters. (4min 40sec file)
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Launch of Atlas 5
The Lockheed Martin Atlas 5 rocket launches at 7:07 a.m. EST from Cape Canaveral carrying the AMERICOM 16 communications spacecraft. (6min 22sec file)
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Encountering Iapetus
Posted: January 9, 2004

On New Year's Eve 2004, Cassini flew past Saturn's intriguing moon Iapetus, capturing the four visible light images that were put together to form this global view.

The scene is dominated by a dark, heavily-cratered region, called Cassini Regio, that covers nearly an entire hemisphere of Iapetus. Iapetus is 1,436 kilometers (892 miles) across. The view is centered on the moon's equator and on roughly 90 degrees west longitude -- a location that always faces the direction of Iapetus's orbital motion around Saturn.

Credit: NASA/JPL/Space Science Institute
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Within Cassini Regio, and especially near the equator, dark deposits with a visual reflectivity of only about 4 percent coat nearly everything with remarkable uniformity. However, at latitudes of about 40 degrees, the surface transitions to a much brighter, icy terrain near the pole where the brightest icy materials have reflectivity over 60 percent. However, this region is not uniform: Close inspection reveals that the surface is stained by crudely north-south trending wispy streaks of darker material, typically a few kilometers wide and sometimes tens of kilometers long.

An ancient, 400-kilometer wide (250 miles) impact basin appears just above the center of the disc. The basin is heavily overprinted by more recent, smaller impact craters. The basin rim is delineated by steep scarps that descend to the basin floor. Many of these scarps, as well as walls of nearby craters, appear bright, probably due to exposed outcrops of relatively clean ice. Particularly at mid-latitudes, the brightest scarp exposures appear to face away from the equator (i.e. toward the pole). Often, the opposite south-facing scarps are stained with the lower-brightness material.

The most unique, and perhaps most remarkable feature discovered on Iapetus in Cassini images is a topographic ridge that coincides almost exactly with the geographic equator. The ridge is conspicuous in the picture as an approximately 20-kilometer wide (12 miles) band that extends from the western (left) side of the disc almost to the day/night boundary on the right. On the left horizon, the peak of the ridge reaches at least 13 kilometers (8 miles) above the surrounding terrain. Along the roughly 1,300 kilometer (800 mile) length over which it can be traced in this picture, it remains almost exactly parallel to the equator within a couple of degrees. The physical origin of the ridge has yet to be explained. It is not yet clear whether the ridge is a mountain belt that has folded upward, or an extensional crack in the surface through which material from inside Iapetus erupted onto the surface and accumulated locally, forming the ridge.

The origin of Cassini Regio is a long-standing debate among scientists. One theory proposes that its dark material may have erupted onto Iapetus's icy surface from the interior. Another theory holds that the dark material represented accumulated debris ejected by impact events on dark, outer satellites of Saturn. Details of this Cassini image mosaic do not definitively rule out either of the theories. However, they do provide important new insights and constraints.

The uniform appearance of the dark materials at the equator, the apparent thinning and spottiness of the dark materials at progressively higher latitudes and dark wispy streaks near the distal margin of Cassini Regio strongly suggest that dark material was emplaced as a coating. One of the important new results is that no clear evidence can be found that erupted fluids have resurfaced Cassini Regio. The high density of impact craters argues that the terrain underlying the dark coating is relatively ancient and has not been eradicated by its emplacement. Thus, Cassini Regio may have had its origin in plume-style eruptions in which dark particulate materials accumulated on the surface as fallout, perhaps in conjunction with the creation of the equatorial ridge. On the other hand, the dark deposits in Cassini Regio may be a surface coating consistent with, and perhaps more simply explained by, the fall of dark materials from outside.

The view has been oriented so that the north pole is toward the top of the picture.

Cassini acquired the images in this mosaic with its narrow angle camera on Dec. 31, 2004, at a distance of about 172,400 kilometers (107,124 miles) from Iapetus and at a Sun-Iapetus-spacecraft, or phase, angle of 50 degrees. The image scale is 1 kilometer (0.6 miles) per pixel. The image has been contrast enhanced to aid visibility of surface features.

The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. The Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the mission for NASA's Science Mission Directorate, Washington, D.C. The Cassini orbiter and its two onboard cameras were designed, developed and assembled at JPL. The imaging team is based at the Space Science Institute, Boulder, Colo.



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