Wallpaper: Little Ghost Nebula

Known to amateur astronomers as the ‘Little Ghost Nebula’, because it appears as a small, ghostly cloud surrounding a faint dying star, NGC 6369 lies in the direction of the constellation Ophiuchus.

The NASA/ESA Hubble Space Telescope has took this image of the planetary nebula NGC 6369, at a distance estimated to be between about 2000 and 5000 light-years from Earth.

When a star with a mass similar to that of our own Sun nears the end of its lifetime, it expands in size to become a ‘red giant’. The red-giant stage ends when the star expels its outer layers into space, producing a faintly glowing nebula.

Astronomers call such an object a planetary nebula, because its round shape resembles that of a planet when viewed with a small telescope.

The Hubble photograph of NGC 6369, captured with the Wide Field Planetary Camera 2 (WFPC2) in 2002, reveals remarkable details of the ejection process that are not visible from ground-based telescopes because of the blurring produced by the Earth’s atmosphere.

The remnant stellar core in the centre is now sending out a flood of ultraviolet (UV) light into the surrounding gas. The prominent blue-green ring, nearly a light-year in diameter, marks the location where the energetic UV light has stripped electrons off of atoms in the gas. This process is called ionisation.

In the redder gas at larger distances from the star, where the UV light is less intense, the ioniszation process is less advanced. Even farther outside the main body of the nebula, one can see fainter wisps of gas that were lost from the star at the beginning of the ejection process.

This colour image has been produced by combining WFPC2 pictures taken through filters that isolate light emitted by three different chemical elements with different degrees of ionisation.

The doughnut-shaped blue-green ring represents light from ionised oxygen atoms that have lost two electrons (blue) and from hydrogen atoms that have lost their single electrons (green). Red marks emission from nitrogen atoms that have lost only one electron. Our own Sun may eject a similar nebula, but not for another 5000 million years.

The gas will expand away from the star at about 15 miles per second, dissipating into interstellar space after some 10 000 years. After that, the remnant stellar member in the centre will gradually cool off for millions of years as a tiny white dwarf star, and eventually wink out.

Original Source: ESA News Release

Wallpaper: NGC 3949

Our Sun and solar system are embedded in a broad pancake of stars deep within the disk of the Milky Way galaxy. Even from a distance, it is impossible to see our galaxy’s large-scale features other than the disk.

The next best thing is to look farther out into the universe at galaxies that are similar in shape and structure to our home galaxy. Other spiral galaxies like NGC 3949, pictured in the Hubble image, fit the bill. Like our Milky Way, this galaxy has a blue disk of young stars peppered with bright pink star-birth regions. In contrast to the blue disk, the bright central bulge is made up of mostly older, redder stars.

NGC 3949 lies about 50 million light-years from Earth. It is a member of a loose cluster of some six or seven dozens of galaxies located in the direction of the Big Dipper, in the constellation Ursa Major (the Great Bear). It is one of the larger galaxies of this cluster.

This image was created from Hubble data taken with the Wide Field Planetary Camera 2 in October 2001. Separate exposures through blue, visible, and near-infrared filters have been combined to make the natural color picture. This image was produced by the Hubble Heritage Team (STScI).

Original Source: Hubble News Release

Wallpaper: Saturn’s Rings in Colour

Nine days before it entered orbit, Cassini captured this exquisite natural color view of of Saturn?s rings. The images that comprise this composition were obtained from Cassini?s vantage point beneath the ring plane with the narrow angle camera on June 21, 2004, from a distance of 6.4 million kilometers (4 million miles) from Saturn and a phase angle of 66 degrees. The image scale is 38 kilometers (23 miles) per pixel.

The brightest part of the rings, curving from the upper right to the lower left in the image, is the B ring. Many bands throughout the B ring have a pronounced sandy color. Other color variations across the rings can be seen. Color variations in Saturn’s rings have previously been seen in Voyager and Hubble Space Telescope images. Cassini’s images show that color variations in the rings are more pronounced in this viewing geometry than they are when seen from Earth. Saturn’s rings are made primarily of water ice. Since pure water ice is white, it is believed that different colors in the rings reflect different amounts of contamination by other materials such as rock or carbon compounds. In conjunction with other Cassini instruments, Cassini images will help to determine the composition of different parts of Saturn’s ring system.

The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. The Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the Cassini-Huygens mission for NASA’s Office of Space Science, Washington, D.C. The imaging team is based at the Space Science Institute, Boulder, Colorado.

For more information about the Cassini-Huygens mission, visit http://saturn.jpl.nasa.gov and the Cassini imaging team home page, http://ciclops.org.

Original Source: CICLOPS News Release

Wallpaper: Saturn’s Rings in Ultraviolet

The best view ever of Saturn’s rings in the ultraviolet indicates there is more ice toward the outer part of the rings, hinting at ring origin and evolution, say two University of Colorado at Boulder researchers involved in the Cassini mission.

Researchers from CU-Boulder’s Laboratory for Atmospheric and Space Physics, Joshua Colwell and Larry Esposito, said the UV spectra taken during the Cassini spacecraft’s orbital insertion June 30 show definite compositional variation in the A, B and C rings.

Esposito, who discovered the F ring around Saturn in 1979 using Pioneer 11 data, is the team leader for Cassini’s Ultraviolet Imaging Spectrograph, or UVIS, a $12.5 million instrument riding on the spacecraft. A UVIS team member and ring expert, Colwell created the color-enhanced images from the spectra.

The CU-Boulder built UVIS instrument is capable of resolving the rings to show features up to 60 miles across, roughly 10 times the resolution obtained by the Voyager 2 spacecraft. The instrument was able to resolve the “Cassini division,” discovered by Giovanni Domenico Cassini in the 17th century, which separates the A and B rings of Saturn, proving the rings are not one contiguous feature.

The ring system begins from the inside out with the D, C, B and A rings followed by the F, G and E rings. The red in both images indicates sparser ringlets likely made of “dirty,” and possibly smaller, particles than in the denser, icier turquoise ringlets.

Original Source: University of Colorado News Release

Wallpaper: Star Formation in Nearby Galaxy

NASA’s Hubble Space Telescope captures this iridescent tapestry of star birth in a neighboring galaxy in this panoramic view of glowing gas, dark dust clouds, and young, hot stars. The star-forming region, catalogued as N11B, lies in the Large Magellanic Cloud (LMC), located only 160,000 light-years from Earth. With its high resolution, the Hubble Space Telescope is able to view details of star formation in the LMC as easily as ground-based telescopes are able to observe stellar formation within our own Milky Way galaxy. This new Hubble image zooms in on N11B, which is a small subsection within an area of star formation cataloged as N11. N11 is the second largest star-forming region in the LMC. Within the LMC, N11 is surpassed in size and activity only by the immense Tarantula nebula (also known as 30 Doradus.)

The image illustrates a perfect case of sequential star formation in a nearby galaxy where new star birth is being triggered by previous-generation massive stars. A collection of blue- and white-colored stars near the left of the image are among the most massive stars known anywhere in the universe. The region around the cluster of hot stars in the image is relatively clear of gas, because the stellar winds and radiation from the stars have pushed the gas away. When this gas collides with and compresses surrounding dense clouds, the clouds can collapse under their own gravity and start to form new stars. The cluster of new stars in N11B may have been formed this way, as it is located on the rim of the large, central interstellar bubble of the N11 complex. The stars in N11B are now beginning to clear away their natal cloud, and are carving new bubbles in turn. Yet another new generation of stars is now being born in N11B, inside the dark dust clouds in the center and right-hand side of the Hubble image. This chain of consecutive star birth episodes has been seen in more distant galaxies, but it is shown very clearly in this new Hubble image.

Farther to the right of the image, along the top edge, are several smaller dark clouds of interstellar dust with odd and intriguing shapes. They are seen silhouetted against the glowing interstellar gas. Several of these dark clouds are bright-rimmed because they are illuminated and are being evaporated by radiation from neighboring hot stars.

This image was taken with Hubble’s Wide Field Planetary Camera 2 using filters that isolate light emitted by hydrogen and oxygen gas. The science team, led by astronomers You-Hua Chu (University of Illinois) and Y?el Naz? (Universite de Li?ge, Belgium) are comparing these images of N11B, taken in 1999, with similar regions elsewhere in the LMC. This color composite image was co-produced and is being co-released by the Hubble Heritage Team (STScI) and the Hubble European Space Agency Information Center (HEIC).

Original Source: Hubble News Release

Wallpaper: Phoebe

During its historic close encounter with Phoebe, the Cassini spacecraft captured a series of high resolution images of the small moon, six of which have been mosaicked together to create this detailed view.

Phoebe shows an unusual variation in brightness over its surface due to the existence on some crater slopes and floors of bright material ? thought to contain ice ? on what is otherwise one of the darkest known bodies in the solar system. Bright streaks on the rim of the large crater in the North (up in this image) may have been revealed by the collapse of overlying darker material from the crater wall. The large crater below right-of-center shows evidence of layered deposits of alternating bright and dark material. A possible mechanism for this apparent layering was discussed in an earlier image release (PIA 06067).

Hints of Phoebe?s irregular topography can be seen peeking out from the shadows near the lower left and upper left parts of the image. These are real features ? possibly crater rims or mountain peaks ? that are just being hit by the first light of sunrise on Phoebe.

Phoebe?s surface shows many large- and small-scale craters. The emerging view of Phoebe is that it might have been part of an ancestral population of icy, comet-like bodies, some of which now reside in the Kuiper Belt beyond Neptune.

The images in this mosaic were taken in visible light with the narrow-angle camera at distances ranging from 15,974 kilometers (9,926 miles) to 12,422 kilometers (7,719 miles). The image scale is 74 meters (243 feet) per pixel. Contrast in the image has been enhanced slightly to improve visibility.

The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. The Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the Cassini-Huygens mission for NASA’s Office of Space Science, Washington, D.C. The imaging team is based at the Space Science Institute, Boulder, Colorado.

For more information about the Cassini-Huygens mission, visit http://saturn.jpl.nasa.gov and the Cassini imaging team home page, http://ciclops.org.

Original Source: CICLOPS News Release

Wallpaper: The Valles Marineris Canyon

Image credit: ESA
On 2 May 2004, the High-Resolution Stereo Camera (HRSC) on board the ESA Mars Express spacecraft obtained images from the central area of the Mars canyon called Valles Marineris.

The images were taken at a resolution of approximately 16 metres per pixel. The displayed region is located at the southern rim of the Melas Chasma at Mars latitude 12?S and Mars longitude 285?E. The images were taken on orbit 360 of Mars Express.

This region shows several clues to the morphological and geological development of the Valles Marineris. The images show many traces of volcanic activity and possibly water-related acitivity. However, a lot of the surface has been altered by subsequent geological processes, such as wind erosion and quakes.

Although many questions about the geological development of the Valles Marineris canyon have remained unanswered until now, the detailed HRSC image data may help to find some answers. Using HRSC data, scientists can focus on morphology – the evolution of rocks and land forms. They can also analyse the light relected by the canyon to understand which type of rocks it is made out of.

Original Source: ESA News Release

Wallpaper: Flood Plains on Mars

Image credit: ESA
These images of fluvial surface features at Mangala Valles on Mars were obtained by the High Resolution Stereo Camera (HRSC) on board the ESA Mars Express spacecraft.

The HRSC has imaged structures several times which are related to fluvial events in the past on Mars.

The region seen here is situated on the south-western Tharsis bulge and shows the mouth of the Mangala Valles and Minio Vallis outflow channels.

The source of the outflow channel is related to the Mangala Fossa, a fissure running east-west for several hundred kilometres.

One theory about its formation is related to a process known on Earth as ?dyke emplacement?.

This is when hot molten rock finds its way to the surface through a fissure, releasing large amounts of water by the melting of subsurface ice.

It is still unclear for how long and to what extent water, mud or even ice masses and wind have carved the channel here.

This theory on its formation has several analogues on Earth. Events like the one proposed for Mangala Valles occur on Earth, for example in Iceland, where volcanic activity causes episodic releases of water from subsurface reservoirs, causing catastrophic floods.

Along the channel troughs, areas with so-called ?chaotic terrain? features favour the idea of the existence of subsurface ice.

The small-scale chaotic terrain is characterised by isolated blocks of surface material which have been randomly arranged during the release of subsurface water and subsequent collapse of the surface.

Huge areas of chaotic terrain can be found near the source areas of the outflow channels around Chryse Planitia, such as Kasei, Maja and Ares Valles.

Beside the large outflow channels, a variety of smaller ?dendritic? valley networks with a number of tributary valleys can be seen near the main channels. This indicates possible precipitation.

The images were taken during orbit 299 with a resolution of 28 metres per pixel. The image centre is located at 209? E longitude and 5? S latitude. For practical use on the internet, the images have been reduced in resolution.

The red/cyan 3D anaglyph image was created using the stereo- and nadir channels of the HRSC. The perspective view was calculated from the digital terrain model derived from the stereo and colour information of the image data.

Original Source: ESA News Release

Wallpaper: Comet NEAT

Image credit: NOAO/AURA/NSF
This image of Comet C/2001 Q4 (NEAT) was taken at the WIYN 0.9-meter telescope at Kitt Peak National Observatory near Tucson, AZ, on May 7, 2004.

The image was taken with the Mosaic I camera, which has a one-square degree field of view, or about five times the size of the Moon. Even with this large field, only the comet?s coma and the inner portion of its tail are visible. This color image was assembled by combining images taken through blue, green and red filters.

A small star cluster (C0736-105, or Melotte 72) is visible in the lower right of the image, between the head of the comet and the bright red star in the lower-right corner.

Comet C/2001 Q4 (NEAT) was discovered on August 24, 2001, by the Near Earth Asteroid Tracking (NEAT) system operated by NASA?s Jet Propulsion Laboratory, Pasadena, CA.

The comet will remain visible for several weeks with binoculars and small telescopes just after sunset, high in the western sky.

Image Credit: T. Rector (University of Alaska Anchorage), Z. Levay and L.Frattare (Space Telescope Science Institute) and WIYN/NOAO/AURA/NSF

Original Source: NOAO News Release

Wallpaper: Dying Star Spins a Spiderweb

Image credit: Hubble
Astronomers may not have observed the fabled “Stairway to Heaven,” but they have photographed something almost as intriguing: ladder-like structures surrounding a dying star.

A new image, taken with NASA’s Hubble Space Telescope, reveals startling new details of one of the most unusual nebulae known in our Milky Way. Cataloged as HD 44179, this nebula is more commonly called the “Red Rectangle” because of its unique shape and color as seen with ground-based telescopes.

Hubble has revealed a wealth of new features in the Red Rectangle that cannot be seen with ground-based telescopes looking through the Earth’s turbulent atmosphere. Details of the Hubble study were published in the April 2004 issue of The Astronomical Journal.

Hubble’s sharp pictures show that the Red Rectangle is not really rectangular, but has an overall X-shaped structure, which the astronomers involved in the study interpret as arising from outflows of gas and dust from the star in the center. The outflows are ejected from the star in two opposing directions, producing a shape like two ice-cream cones touching at their tips. Also remarkable are straight features that appear like rungs on a ladder, making the Red Rectangle look similar to a spider web, a shape unlike that of any other known nebula in the sky. These rungs may have arisen in episodes of mass ejection from the star occurring every few hundred years. They could represent a series of nested, expanding structures similar in shape to wine glasses, seen exactly edge-on so that their rims appear as straight lines from our vantage point.

The star in the center of the Red Rectangle is one that began its life as a star similar to our Sun. It is now nearing the end of its lifetime, and is in the process of ejecting its outer layers to produce the visible nebula. The shedding of the outer layers began about 14,000 years ago. In a few thousand years, the star will have become smaller and hotter, and will begin to release a flood of ultraviolet light into the surrounding nebula; at that time, gas in the nebula will begin to fluoresce, producing what astronomers call a planetary nebula.

At the present time, however, the star is still so cool that atoms in the surrounding gas do not glow, and the surrounding dust particles can only be seen because they are reflecting the starlight from the central star. In addition, there are molecules mixed in with the dust, which emit light in the red portion of the spectrum. Astronomers are not yet certain which types of molecules are producing the red color that is so striking in the Red Rectangle, but suspect that they are hydrocarbons that form in the cool outflow from the central star.

Another remarkable feature of the Red Rectangle, visible only with the superb resolution of the Hubble telescope, is the dark band passing across the central star. This dark band is the shadow of a dense disk of dust that surrounds the star. In fact, the star itself cannot be seen directly, due to the thickness of the dust disk. All we can see is light that streams out perpendicularly to the disk, and then scatters off of dust particles toward our direction. Astronomers found that the star in the center is actually a close pair of stars that orbit each other with a period of about 10 1/2 months. Interactions between these stars have probably caused the ejection of the thick dust disk that obscures our view of the binary. The disk has funneled subsequent outflows in the directions perpendicular to the disk, forming the bizarre bi- conical structure we see as the Red Rectangle. The reasons for the periodic ejections of more gas and dust, which are producing the “rungs” revealed in the Hubble image, remain unknown.

The Red Rectangle was first discovered during a rocket flight in the early 1970s, in which astronomers were searching for strong sources of infrared radiation. This infrared source lies about 2,300 light-years from Earth in the direction of the constellation Monoceros. Stars surrounded by clouds of dust are often strong infrared sources because the dust is heated by the starlight and radiates long-wavelength light. Studies of HD 44179 with ground-based telescopes revealed a rectangular shape in the dust surrounding the star in the center, leading to the name Red Rectangle which was coined in 1973 by astronomers Martin Cohen and Mike Merrill.

This image was made from observations taken on March 17-18, 1999 with Hubble’s Wide Field Planetary Camera 2.

Original Source: Hubble News Release