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Historic spacewalk
This history flashback remembers the first spacewalk by an American astronaut as Ed White leaves the Gemini 4 spacecraft for an EVA on June 3, 1965. (5min 51sec file)
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Cassini preview
The Cassini spacecraft's arrival at Saturn is previewed in this detailed news conference from NASA Headquarters on June 3. (50min 01sec file)
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Saturn arrival explained
Cassini's make-or-break engine firing to enter orbit around Saturn is explained with graphics and animation. Expert narration is provided by Cassini program manager Robert Mitchell. (3min 33sec file)
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Cassini mission science
The scientific objectives of the Cassini mission to study the planet Saturn, its rings and moons are explained by Charles Elachi, director of the Jet Propulsion Laboratory. (4min 54sec file)
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Huygens mission science
After entering orbit around Saturn, the Cassini spacecraft will launch the European Huygens probe to make a parachute landing on the surface of the moon Titan. The scientific objectives of Huygens are explained by probe project manager Jean-Pierre Lebreton. (3min 14sec file)
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Saturn's moon Titan
Learn more about Saturn's moon Titan, which is believed to harbor a vast ocean, in this narrated movie. (4min 01sec file)
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Relive Cassini's launch
An Air Force Titan 4B rocket launches NASA's Cassini spacecraft at 4:43 a.m. October 15, 1997 from Cape Canaveral, Florida. (5min 15sec file)
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Exploring the hills
"A brand new mission" is beginning for the Mars Exploration Rover Spirit as it nears the Columbia Hills as described in this presentation by science team member James Rice. (5min 57sec file)
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Exploring Endurance
New pictures from the Mars rover Opportunity as it drives around the rim of Endurance Crater are presented with narration by science team member Wendy Calvin. (5min 25sec file)
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Mars rover update
Mission officials and scientists discuss the condition and progress of Mars rovers Spirit and Opportunity plus the latest science news in this briefing from June 2. (40min 55sec file)
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Options to save Hubble
NASA Administrator Sean O'Keefe announces plans to examine a robotic servicing mission to the Hubble Space Telescope. (33min 51sec file)
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New theory for first stars
UNIVERSITY OF CHICAGO NEWS RELEASE
Posted: June 7, 2004

The very first stars that formed early in the history of the universe were smaller than the massive giants implied by the results of a NASA research satellite, but still larger than the typical stars found in our galaxy today, according to a research team led by the University of Chicago's Jason Tumlinson.


Credit: National Science Foundation and NASA
 
"We have managed to reconcile within a single theory the two very different leading indicators of the nature of the first stars," said Tumlinson, the Edwin Hubble Scientist in Astronomy & Astrophysics at the University of Chicago. Tumlinson presented the theory at the American Astronomical Society meeting in Denver. His co-authors are the University of Colorado's Aparna Venkatesan and J. Michael Shull.

No telescope is powerful enough yet to see the first stars, but astronomers can guess at their existence based on the stellar clues they leave behind. In 2001 and 2002, NASA's Wilkinson Microwave Anistropy Probe (WMAP) looked at the oldest light in the universe left over from the big bang, the cosmic microwave background, and found one such clue in the form of ionized (electrically charged) gas floating between the galaxies. WMAP showed that this intergalactic gas was ionized approximately 200 million years after the big bang.

"Very massive stars, with roughly 200 to 500 times the mass of the sun, and more massive than we see anywhere today, are extremely efficient at producing this ionizing radiation," Tumlinson said. This implies that the earliest stars were massive enough to cause the ionization.

But the oldest stars in our galaxy that astronomers can see in the sky today are on average approximately 13 billion years old. "They would have formed just after the first stars and out of the very gas and heavy elements that were strewn into space when the earliest stars exploded as supernovae," said Venkatesan, a National Science Foundation Fellow at Colorado and 2000 University of Chicago Ph.D. alumna.

The problem is that the ratio of heavy elements observed in the second generation of stars could not have been produced in the most massive stars associated with the WMAP studies.

"It was our goal to reconcile these two conflicting pieces of evidence," Tumlinson said.

His team reconciled the evidence by formulating a theory showing how stars with a mass of 20 to 100 times that of the sun could both be large enough to satisfy the WMAP results, yet still produce the ratio of heavy elements detected by ground-based telescopes in very old stars.

"We're not saying the very massive stars couldn't have formed at some low level. We're saying that for early heavy element production you need mostly stars that are massive but not extremely massive."

This theory meshes well with what astronomers know about how stars of various masses form in the galaxy.

"There are a lot of very low-mass stars like the sun, and as you go up in stellar mass, the numbers get more rare," Tumlinson said. "There are a very few stars of high mass, say a hundred solar masses in our galaxy. According to our theory, these massive stars were much more common in the first generation."

Problems that remain to be solved include determining how long the conditions could be maintained for forming the first stars from primordial gas and how these objects can be detected in the future, Venkatesan said.

"Predicting how the first stars affect their environment and whether they resemble the stars in our own galactic backyard at all is a critical input for the planning of future telescopes and instruments and in interpreting their data," she said.

The project was funded by NASA and the National Science Foundation.

New Station
Crew Patch


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The Expedition 38 embroidered crew patch for the International Space Station is now available in our store!
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Apollo 12 tribute DVD set

New! Featuring the jovial crew of Pete Conrad, Dick Gordon and Alan Bean, the Apollo 12 mission was struck by lightning shortly after liftoff but proceeded on the second successful exploration voyage to the lunar surface. This three-disc DVD brings the mission to life with extraordinary detail.
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Fallen Heroes special patch
This special 12-inch embroidered patch commemorates the U.S. astronauts who made the ultimate sacrifice, honoring the crews of Apollo 1, Challenger and Columbia.
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Women in Space
Women of Space: Cool Careers on the Final Frontier is for girls, young women, and anyone else interested in learning about exciting careers in space exploration. Includes CD-ROM.
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Mars rover poster
This new poster features some of the best pictures from NASA's amazing Mars Exploration Rovers Spirit and Opportunity.
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Gemini 7
Gemini 7: The NASA Mission Reports covers this 14-day mission by Borman and Lovell as they demonstrated some of the more essential facts of space flight. Includes CD-ROM.
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Apollo patches
The Apollo Patch Collection: Includes all 12 Apollo mission patches plus the Apollo Program Patch. Save over 20% off the Individual price.
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Mars Rover mission patch
A mission patch featuring NASA's Mars Exploration Rover is available from our online.
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Apollo 9 DVD
On the road to the moon, the mission of Apollo 9 stands as an important gateway in experience and procedures. This 2-DVD collection presents the crucial mission on the voyage to the moon.
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Gemini 12
Gemini 12: The NASA Mission Reports covers the voyage of James Lovell and Buzz Aldrin that capped the Gemini program's efforts to prove the technologies and techniques that would be needed for the Apollo Moon landings. Includes CD-ROM.
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STS-134 Patch

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The final planned flight of space shuttle Endeavour is symbolized in the official embroidered crew patch for STS-134. Available in our store!
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Final Shuttle Mission Patch

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The crew emblem for the final space shuttle mission is now available in our store. Get this piece of history!
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Apollo Collage
This beautiful one piece set features the Apollo program emblem surrounded by the individual mission logos.
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STS-133 Patch

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The final planned flight of space shuttle Discovery is symbolized in the official embroidered crew patch for STS-133. Available in our store!
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Anniversary Shuttle Patch

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This embroidered patch commemorates the 30th anniversary of the Space Shuttle Program. The design features the space shuttle Columbia's historic maiden flight of April 12, 1981.
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Mercury anniversary

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Celebrate the 50th anniversary of Alan Shephard's historic Mercury mission with this collectors' item, the official commemorative embroidered patch.
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