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SOHO anniversary
10 years ago: The Solar and Heliospheric Observatory, a joint European and American Sun-watching probe, blasts off from Cape Canaveral aboard a Lockheed Martin Atlas 2AS rocket.

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Huygens science results
The European Space Agency's Huygens probe, launched from NASA's Cassini spacecraft, descended through the atmosphere of Saturn's moon Titan and landed on its mysterious surface in January. Scientists hold this news briefing to report on new results from the daring mission.

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Mars Express update
Project scientists working on the European Space Agency's Mars Express spacecraft now orbiting the Red Planet hold a news conference to announce some interesting results from the ongoing mission.

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Hubble Space Telescope
Scientists marvel at the achievements made by the orbiting Hubble Space Telescope in this produced movie looking at the crown jewel observatory that has served as our window on the universe.

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An American in orbit
Mercury astronaut John Glenn becomes the first American to orbit the Earth on February 20, 1962, when he is launched aboard Friendship 7.

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Space Thanksgiving
International Space Station commander Bill McArthur and flight engineer Valery Tokarev mark the Thanksgiving holiday in orbit during this downlinked message.

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Soyuz on the move
Expedition 12 Soyuz commander Valery Tokarev and station commander Bill McArthur temporarily leave the International Space Station. They undocked their Soyuz capsule from the Pirs module and then redocked the craft to the nearby Zarya module. The move clears Pirs for use as the airlock for an upcoming Russian-based spacewalk.

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Pluto New Horizons
Check out NASA's Pluto-bound New Horizons spacecraft undergoing thermal blanket installation inside the cleanroom at Kennedy Space Center's Payload Hazardous Servicing Facility in preparation for launch in January from the Cape.

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Mountains of creation
A new image from NASA's Spitzer Space Telescope reveals billowing mountains of dust ablaze with the fires of stellar youth. The majestic infrared view from Spitzer resembles the iconic "Pillars of Creation" picture taken of the Eagle Nebula in visible light by NASA's Hubble Space Telescope.

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Space history: STS-51A
This week marks the anniversary of arguably the most daring and complex space shuttle mission. The astronauts successfully launched two satellites and then recovered two others during extraordinary spacewalks by astronauts using jet-propelled backpacks and pure muscle power.

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Space station EVA
Commander Bill McArthur and flight engineer Valery Tokarev conduct a 5 1/2-hour spacewalk outside the International Space Station, installing a TV camera, doing repair chores and jettisoning a failed science probe.

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The Earth from space
Return to flight space shuttle commander Eileen Collins narrates an interesting slide show featuring some favorite photographs of Earth taken during her previous shuttle missions.

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When worlds collide: Forces that produce new galaxies
Posted: December 3, 2005

When galaxies collide -- as our galaxy, the Milky Way, eventually will with the nearby Andromeda galaxy -- what happens to matter that gets spun off in the collision's wake?

This false-color infrared image from the infrared array camera on NASA's Spitzer Space Telescope shows dwarf galaxies forming in the tails of two larger colliding galaxies. The big galaxies are at the center of the picture, while the dwarfs can be seen as red dots in the red streamers. Credit: NASA/JPL-Caltech/Cornell University
With help from the Spitzer Space Telescope's infrared spectrograph (IRS), Cornell astronomers are beginning to piece together an answer to that question. Specifically, they are gaining new insight into how some ubiquitous dwarf galaxies form, interact and arrange themselves into new systems.

Dwarf galaxies, with stellar masses around 0.1 percent that of the Milky Way, are far more common than their more massive spiral or starburst counterparts. Some may be primordial remnants of the big bang; but others -- called tidal dwarfs -- formed later as a result of gravitational interactions after galactic collisions.

To understand which dwarf galaxies are tidal in origin and how those galaxies differ from primordial dwarf galaxies, Cornell researcher Sarah Higdon and her colleagues studied a system called NGC 5291, which is 200 million light years from Earth and stretches a distance roughly four times the span of the Milky Way. At the system's center are two colliding galaxies; behind them trail a string of much smaller dwarfs.

The researchers focused on the system because they knew from earlier analyses that the trailing dwarfs were formed tidally as a result of the central collision. Until recently, though, they hadn't been able to look closely enough at the tidal dwarfs to catalog their properties for comparison with those of similar galaxies.

Spitzer's sharp eye has changed that. Using it to look for compounds that indicate star-forming activity, Higdon's team found that when it comes to fostering new star formation, the colliding galaxies at the system's center are fairly dull. The exciting place to be, they found, is in the tidal dwarfs at the system's edges.

Specifically, the team found that the tidal dwarfs show strong emission from organic compounds, found in crude petroleum, burnt toast and (more relevantly) stellar nurseries, known as PAHs -- for polycyclic aromatic hydrocarbons. And for the first time, the researchers detected warm molecular hydrogen -- another indicator of star formation, and one that has never before been directly measured in tidal dwarf galaxies.

"We know molecular hydrogen is out there. Now we have the sensitivity to measure it," Higdon said.

Higdon and Cornell colleagues James Higdon and Jason Marshall describe the features of the NGC 5291 system in a forthcoming issue of the Astrophysical Journal.

"Nearly everything at some stage interacts," Higdon said. "This is a part of the puzzle. But we've only just started looking. We don't know how long lived [the tidal dwarf galaxies] will be, or how many formed like this."

Next, the team plans to search for new tidal dwarf galaxies using the Spitzer surveys and compare their properties to the newly cataloged galaxies in NGC 5291.

The Spitzer telescope is the last of NASA's Great Observatories. The IRS, one of three science instruments on the observatory, is managed by NASA's Jet Propulsion Laboratory and was built by Ball Aerospace & Technologies Corp. under the direction of Cornell professor of astronomy Jim Houck.