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Space shuttle update
A status report on the space shuttle program's efforts to fly the second post-Columbia test flight, including changes to the external fuel tank, is provided in this news conference from Kennedy Space Center on Feb. 28. The participants are Wayne Hale, shuttle program manager, Mike Leinbach, shuttle launch director, and Tim Wilson, external tank tiger team lead.

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NASA employee briefing
Space science funding, the Vision for Space Exploration and the recent controversy over public affairs clashing with agency scientists. These topics and more are discussed in this NASA employee question and answer session with Administrator Mike Griffin and Deputy Administrator Shana Dale held Feb. 27 from agency headquarters in Washington.

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Lockheed's CEV plans
As part of Lockheed Martin's plans for the Crew Exploration Vehicle, the company has announced that final assembly and testing of the capsules will be performed at the Kennedy Space Center's Operations and Checkout Building. Lockheed Martin officials, Florida's lieutenant governor, the local congressman and a county economic development leader held this press conference Feb. 22 to unveil the plans.

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Mars orbiter briefing
With two weeks until its arrival at the red planet, NASA and Lockheed Martin officials hold this Feb. 24 news conference on the Mars Reconnaissance Orbiter. The briefing explains how the MRO spacecraft will fire its engines to enter into orbit around Mars and the mission's scientific goals to examine the planet like never before.

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STS-8: Night launch
The space shuttle program performed its first dazzling nighttime launch with Challenger's August 1983 mission. A cockpit camera mounted beside commander Dick Truly captured amazing footage of night turning to day inside the shuttle from the brilliant flame of ascent. STS-8 also featured the first African-American astronaut, Guion Bluford. Challenger's astronauts tell the story of their six-day mission, which deployed an Indian satellite, used the robot arm to look at the orbiter's belly and examined the glow around the shuttle, during this narrated post-flight film.

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Andromeda's origin similar to the Milky Way
Posted: March 4, 2006

For the last decade, astronomers have thought that the Andromeda galaxy, our nearest galactic neighbor, was rather different from the Milky Way. But a group of researchers have determined that the two galaxies are probably quite similar in the way they evolved, at least over their first several billion years.

In an upcoming issue of the Astrophysical Journal, Scott Chapman of the California Institute of Technology, Rodrigo Ibata of the Observatoire de Strasbourg, and their colleagues report that their detailed studies of the motions and metals of nearly 10,000 stars in Andromeda show that the galaxy's stellar halo is "metal-poor." In astronomical parlance, this means that the stars lying in the outer bounds of the galaxy are pretty much lacking in all the elements heavier than hydrogen.

This is surprising, says Chapman, because one of the key differences thought to exist between Andromeda and the Milky Way was that the former's stellar halo was metal-rich and the latter's was metal-poor. If both galaxies are metal-poor, then they must have had very similar evolutions.

"Probably, both galaxies got started within a half billion years of the Big Bang, and over the next three to four billion years, both were building up in the same way by protogalactic fragments containing smaller groups of stars falling into the two dark-matter haloes," Chapman explains.

While no one yet knows what dark matter is made of, its existence is well established because of the mass that must exist in galaxies for their stars to orbit the galactic centers the way they do. Current theories of galactic evolution, in fact, assume that dark-matter wells acted as a sort of "seed" for today's galaxies, with the dark matter pulling in smaller groups of stars as they passed nearby. What's more, galaxies like Andromeda and the Milky Way have each probably gobbled up about 200 smaller galaxies and protogalactic fragments over the last 12 billion years.

Chapman and his colleagues arrived at the conclusion about the metal-poor Andromeda halo by obtaining careful measurements of the speed at which individual stars are coming directly toward or moving directly away from Earth. This measure is called the radial velocity, and can be determined very accurately with the spectrographs of major instruments such as the 10-meter Keck-II telescope, which was used in the study.

Of the approximately 10,000 Andromeda stars for which the researchers have obtained radial velocities, about 1,000 turned out to be stars in the giant stellar halo that extends outward by more than 500,000 light-years. These stars, because of their lack of metals, are thought to have formed quite early, at a time when the massive dark-matter halo had captured its first protogalactic fragments.

The stars that dominate closer to the center of the galaxy, by contrast, are those that formed and merged later, and contain heavier elements due to stellar evolution processes.

In addition to being metal-poor, the stars of the halo follow random orbits and are not in rotation. By contrast, the stars of Andromeda's visible disk are rotating at speeds upwards of 200 kilometers per second.

According to Ibata, the study could lead to new insights on the nature of dark matter. "This is the first time we've been able to obtain a panoramic view of the motions of stars in the halo of a galaxy," says Ibata. "These stars allow us to weigh the dark matter, and determine how it decreases with distance."

In addition to Chapman and Ibata, the other authors are Geraint Lewis of the University of Sydney; Annette Ferguson of the University of Edinburgh; Mike Irwin of the Institute of Astronomy in Cambridge, England; Alan McConnachie of the University of Victoria; and Nial Tanvir of the University of Hertfordshire.