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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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Astronomers examine the evolution of a supernova
Posted: December 2, 2005

Scientists using NASA's Chandra X-ray Observatory have witnessed a cosmic rite of passage, the transition from a supernova to a supernova remnant, a process that has never seen in much detail until now, leaving it poorly defined.

The Chandra image in the inset shows X-rays from SN 1970G, a supernova that was observed to occur in the galaxy M101 35 years ago. The bright cloud in the box in the optical image is not related to the supernova, which is located immediately to the upper right (arrow) of the cloud. Credit: X-ray: NASA/CXC/GFSC/S.Immler & K.Kuntz; Optical: NOAO/AURA/NSF/G.Jacoby, B.Bohannan & M.Hanna
A supernova is a massive star explosion; the remnant is the beautiful glowing shell that evolves afterwards. When does a supernova become supernova remnant? When does the shell appear and what powers its radiant glow?

A science team led by Dr. Stefan Immler of NASA's Goddard Space Flight Center, Greenbelt, Md., has taken a fresh look at a supernova that exploded in 1970, called SN 1970G, just off the handle of the Big Dipper. This is the oldest supernova ever seen by X-ray telescopes.

"Some astronomers have thought there's a moment when the supernova remnant magically turns on years after the supernova itself has faded away, when the shock wave of the explosion finally hits and lights up the interstellar medium," said Immler. "By contrast, our results show that a new supernova quickly and seamlessly evolves into a supernova remnant. The star's own debris, and not the interstellar medium gas, fuels the remnant."

These results appear in The Astrophysical Journal, co-authored by Dr. Kip Kuntz, also of Goddard. They support previous Chandra observations of SN 1987A by Dr. Sangwook Park of Penn State.

Using new data from Chandra and archived data from the European-led ROSAT and XMM-Newton observatories, Immler and Kuntz pieced together how SN 1970G evolved over the years. They found telltale signs of a supernova remnant---bright X-ray light---yet no evidence of interstellar gas, even across a distance around the site of the explosion 35 times larger than our solar system.

Instead, the material that is heated by the supernova shock to glow in X-ray light, what we call the remnant, is from the stellar wind of the star itself and not distant gas in the interstellar medium. This wind, comprising energetic ions, was shed by the progenitor star thousands to million of years before the explosion. If this were from the interstellar medium, it would be much denser than this stellar wind.

Immler and Kuntz next studied the density profiles of all other supernovae that have been detected over the past two decades. Sure enough, the low-density circumstellar matter from the stellar wind was the source of X-rays, not the interstellar medium. Immler said that historical supernova remnants such as Cassiopeia A, which exploded some 320 years ago, also show no signs of activity from the interstellar medium.

This is more than just a name game, more than hypothetically changing SN 1970G to SNR 1970G. "We have to rethink this notion that a shock wave from the supernova crashes into the interstellar medium to create a supernova remnant," said Immler. "The luminous supernova remnants that we see can be created without the need of a dense interstellar medium. In fact, our study showed that all supernovae detected in X-rays over the past 25 years live in a low-density environment."

SN 1970G is located in the galaxy M101, also called the Pinwheel Galaxy, a stunning spiral galaxy about 22 million light years away in the constellation Ursa Major, home of the Big Dipper. Although the galaxy itself is visible from dark skies with binoculars, telescopes cannot resolve much structure in SN 1970G, unlike for supernova remnants in our Milky Way galaxy. Discovered with an optical telescope in 1970, SN 1970G was not seen with X-ray telescopes until the 1990s.

Immler's work at NASA Goddard is supported through the Universities Space Research Association. Kuntz is supported through University of Maryland, Baltimore County. NASA’s Marshall Space Flight Center in Huntsville, Ala., manages the Chandra program for the Agency’s Science Mission Directorate. The Smithsonian Astrophysical Observatory controls science and flight operations from the Chandra X-ray Center in Cambridge, Mass.