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Pegasus abort
During the final seconds prior to the planned launch of the Space Technology 5 mission on March 15, a retention pin that holds the starboard-side fin aerosurface on the Pegasus rocket first stage did not retract. That forced the launch team to call an abort. This movie shows the scrub as it happened.

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Shuttle launch delay
Space Shuttle Program Manager Wayne Hale announces his decision to replace suspect fuel-level sensors inside the liquid hydrogen portion of Discovery's external tank. The three-week job means Discovery will miss its May launch window, delaying the second post-Columbia test flight to the next daylight period opening July 1. Hale made the announcement during a news conference from Johnson Space Center on March 14.

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Stardust science
NASA's Stardust spacecraft returned to Earth in January with the first samples ever retrieved from a comet. This briefing with mission scientists held March 13 from the Johnson Space Center offers an update on the initial research into the comet bits.

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Exploring Enceladus
The Cassini spacecraft orbiting the planet Saturn has found evidence indicating pockets of liquid water may exist near the surface on the icy moon Enceladus, raising the question of whether the small world could support life. This movie includes stunning images of Enceladus taken by Cassini and animation of geysers seen erupting from the moon.

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MRO's orbit insertion explained
The make-or-break engine firing by the Mars Reconnaissance Orbiter to enter orbit around Mars and the subsequent aerobraking to reach the low-altitude perch for science observations are explained by project manager Jim Graf in this narrated animation package.

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MRO overview briefing
Fuk Li, Mars program manager at JPL, Jim Graf, MRO project manager, Rich Zurek, MRO project scientist, and Dan McCleese, the principal investigator for the Mars Climate Sounder instrument, provide an overview on the Mars Reconnaissance Orbiter on March 8, about 48 hours before arrival at Mars.

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Water may not have formed Mars' recent gullies
Posted: March 17, 2006

If you're a scientist studying the surface of Mars, few discoveries could be more exciting than seeing recent gullies apparently formed by running water.

And that's what scientists believed they saw in Mars Orbital Camera (MOC) images five years ago. They published a paper in Science on MOC images that show small, geologically young ravines. They concluded that the gullies are evidence that liquid water flowed on Mars' surface sometime within the last million years.

A word of caution, though: The moon has gullies that look like that, a University of Arizona Lunar and Planetary Laboratory researcher has found. And water certainly didn't form gullies on the waterless moon.

Gwendolyn D. Bart presented the work at the 37th Lunar and Planetary Science Conference in Houston.

"We'd all like to find liquid water on Mars," Bart said. "That would be really, really exciting. If there were liquid water on Mars, humans wouldn't have to ship water from Earth when they go to explore the planet. That would be an enormous cost savings. And liquid water near the surface of Mars would greatly increase the chances for native life on Mars."

The 2000 Science paper was provocative, Bart said. "But I was skeptical. I wondered if there is another explanation for the gullies."

Then last year she heard a talk by Allan Treiman of the Lunar and Planetary Institute. Treiman suggested the martian gullies might be dry landslides, perhaps formed by wind and not formed by water at all.

Recently, Bart was studying the lunar landscape in high-resolution images taken in 1969, prior to the Apollo landings, for her research on processes that modify the lunar surface.

"Totally by accident, I saw gullies that looked strikingly like the gullies on Mars," she said.

"If the dry landslide hypothesis for the formation of martian gullies is correct, we might expect to see similar features on the moon, where there is no water," she said. "We do."

Gullies in the moon's 10-mile-diameter (17 kilometer) crater Dawes are similar in structure and size to those in a martian crater that MOC photographed. Micrometeorites hitting the smooth slopes and crater on the airless moon could easily trigger small avalanches that form gullies, Bart said.

However, the martian gullies also resemble gullies on Earth that were formed by water, she noted.

"My point is that you can't just look at the Mars gullies and assume they were formed by water. It may be, or may be not. We need another test to know."