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STS-1 anniversary event
This 25th anniversary celebration of the first space shuttle launch took place April 12 at Space Center Houston. Speakers included Johnson Space Center Director Mike Coats, NASA Administrator Mike Griffin, Congressman Tom DeLay, Senator Kay Bailey Hutchison, STS-1 commander John Young and pilot Bob Crippen.

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New lunar mission
During this NASA news conference on April 10, agency officials unveil the Lunar Crater Observation and Sensing Satellite, or LCROSS, that will launch piggyback with the Lunar Reconnaissance Orbiter spacecraft in October 2008. LCROSS will use the launch vehicle's spent upper stage to crash into the moon's south pole in an explosive search for water.

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LCROSS mission plan
Daniel Andrews, the LCROSS project manager from NASA's Ames Research Center, narrates this animation depicting the mission from launch through impact on the lunar surface.

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STS-1 crew looks back
In this highly entertaining program, commander John Young and pilot Bob Crippen of the first space shuttle crew tell stories and memories from STS-1. The two respected astronauts visited Kennedy Space Center on April 6 to mark the upcoming 25th anniversary of Columbia's maiden voyage.

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STS-41G crew film
The October 1984 flight of space shuttle Challenger featured a diverse set of accomplishments. The Earth Radiation Budget Satellite environmental spacecraft was deployed and a planet-mapping radar was tested. The seven-person crew was led by Bob Crippen and included the first Canadian in space, Marc Garneau, and the first time two women, Sally Ride and Kathryn Sullivan, had flown aboard one flight. Sullivan and Dave Leestma also conducted a spacewalk to demonstrate techniques for refueling satellites. The crew narrates this post-flight film of STS-41G.

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STS-37 anniversary
On April 5, 1991, space shuttle Atlantis lifted off from Kennedy Space Center carrying the Compton Gamma Ray Observatory -- NASA's second Great Observatory. Launch occurred at 9:23 a.m. from pad 39B.

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Crew news conference
The combined Expedition 12 and 13 crews, along with visiting Brazilian astronaut Marcos Pontes, hold this in-flight news conference with reporters in Houston, Cape Canaveral and Moscow on April 3. The crews are handing over duties during this week-long handover before Expedition 12 returns to Earth from the space station.

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Next station crew
Full coverage of the Expedition 13 crew's launch aboard a Russian Soyuz spacecraft to begin a six-month mission aboard the International Space Station.

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Deadly cosmic event unlikely in our galaxy
Posted: April 18, 2006

Are you losing sleep at night because you're afraid that all life on Earth will suddenly be annihilated by a massive dose of gamma radiation from the cosmos?

Well, now you can rest easy.

Some scientists have wondered whether a deadly astronomical event called a gamma ray burst could happen in a galaxy like ours, but a group of astronomers at Ohio State University and their colleagues have determined that such an event would be nearly impossible.

Gamma ray bursts (GRBs) are high-energy beams of radiation that shoot out from the north and south magnetic poles of a particular kind of star during a supernova explosion, explained Krzysztof Stanek, associate professor of astronomy at Ohio State. Scientists suspect that if a GRB were to occur near our solar system, and one of the beams were to hit Earth, it could cause mass extinctions all over the planet.

The GRB would have to be less than 3,000 light years away to pose a danger, Stanek said. One light year is approximately 6 trillion miles, and our galaxy measures 100,000 light years across. So the event would not only have to occur in our galaxy, but relatively close by, as well.

In the new study, which Stanek and his coauthors submitted to the Astrophysical Journal, they found that GRBs tend to occur in small, misshapen galaxies that lack heavy chemical elements (astronomers often refer to all elements other than the very lightest ones -- hydrogen, helium, and lithium -- as metals). Even among metal-poor galaxies, the events are rare -- astronomers only detect a GRB once every few years.

But the Milky Way is different from these GRB galaxies on all counts -- it's a large spiral galaxy with lots of heavy elements.

The astronomers did a statistical analysis of four GRBs that happened in nearby galaxies, explained Oleg Gnedin, a postdoctoral researcher at Ohio State. They compared the mass of the four host galaxies, the rate at which new stars were forming in them, and their metal content to other galaxies catalogued in the Sloan Digital Sky Survey.

Though four may sound like a small sample compared to the number of galaxies in the universe, these four were the best choice for the study because astronomers had data on their composition, Stanek said. All four were small galaxies with high rates of star formation and low metal content.

Of the four galaxies, the one with the most metals -- the one most similar to ours -- hosted the weakest GRB. The astronomers determined that the odds of a GRB occurring in a galaxy like that one to be approximately 0.15 percent.

And the Milky Way's metal content is twice as high as that galaxy, so our odds of ever having a GRB would be even lower than 0.15 percent.

"We didn't bother to compute the odds for our galaxy, because 0.15 percent seemed low enough," Stanek said.

He figures that most people weren't losing sleep over the possibility of an Earth-annihilating GRB. "I wouldn't expect the stock market to go up as a result of this news, either," he said. "But there are a lot of people who have wondered whether GRBs could be blamed for mass extinctions early in Earth's history, and our work suggests that this is not the case."

Astronomers have studied GRBs for more than 40 years, and only recently determined where they come from. In fact, Stanek led the team that tied GRBs to supernovae in 2003.

He and Gnedin explained that when a very massive, rapidly rotating star explodes in a supernova, its magnetic field directs gamma radiation to flow only out of the star's north and south magnetic poles, forming high-intensity jets.

Scientists have measured the energies of these events and assumed -- rightly so, Stanek said -- that such high-intensity radiation could destroy life on a planet. That's why some scientists have proposed that a GRB could have been responsible for a mass extinction that occurred on Earth 450 million years ago.

Now it seems that gamma ray bursts may not pose as much a danger to Earth or any other potential life in the universe, either, since they are unlikely to occur where life would develop.

Planets need metals to form, Stanek said, so a low-metal galaxy would probably have fewer planets, and fewer chances for life.

He added that he didn't originally intend to address the question of mass extinctions. The study grew out of a group discussion during the Ohio State Department of Astronomy's "morning coffee" -- a daily half-hour where faculty and students review new astronomy journal articles that have been posted to Internet preprint servers overnight. In February, Stanek published a paper on a GRB he had observed, and during coffee someone asked whether he thought it was just a coincidence that these events seem to happen in small, metal-poor galaxies.

"My initial reaction was that it's not a coincidence, and everyone just knows that GRBs happen in metal-poor galaxies. But then people asked, 'Is it really that well known? Has anybody actually proven it to be true?' And we realized that nobody had."

As a result, the list of coauthors on the paper includes astronomers across a broad range of expertise, which Stanek said is somewhat unusual in these days of specialized research. The coauthors were among faculty gathered for coffee that day, plus a few friends they recruited to help them: Stanek and Gnedin; John Beacom, assistant professor of physics and astronomy; Jennifer Johnson, assistant professor of astronomy; Juna Kollmeier, a graduate student; Andrew Gould, Marc Pinsonneault, Richard Pogge, and David Weinberg, all professors of astronomy at Ohio State; and Maryam Modjaz, a graduate student at the Harvard-Smithsonian Center for Astrophysics.

This work was sponsored by the National Science Foundation.



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