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

Wallpaper: Bug Nebula

Image credit: Hubble
The Bug Nebula, NGC 6302, is one of the brightest and most extreme planetary nebulae known. At its centre lies a superhot dying star smothered in a blanket of ?hailstones?. A new Hubble image reveals fresh detail in the wings of this ?cosmic butterfly?.

This image of the Bug Nebula, taken with the NASA/ESA Hubble Space Telescope (HST), shows impressive walls of compressed gas. A torus (?doughnut?) shaped mass of dust surrounds the inner nebula (seen at the upper right).

At the heart of the turmoil is one of the hottest stars known. Despite an extremely high temperature of at least 250 000 degrees Celsius, the star itself has never been seen, as it shines most brightly in the ultraviolet and is hidden by the blanket of dust, making it hard to observe.

Chemically, the composition of the Bug Nebula also makes it one of the more interesting objects known. Earlier observations with the European Space Agency’s Infrared Space Observatory (ISO) have shown that the dusty torus contains hydrocarbons, carbonates such as calcite, as well as water ice and iron. The presence of carbonates is interesting. In the Solar System, their presence is taken as evidence for liquid water in the past, because carbonates form when carbon dioxide dissolves in liquid water and forms sediments. But its detection in nebulae such as the Bug Nebula, where no liquid water has existed, shows that other formation processes cannot be excluded.

Albert Zijlstra from UMIST in Manchester, UK, who leads a team of astronomers probing the secrets of this extreme object, says: ?What caught our interest in NGC 6302 was the mixture of minerals and crystalline ice – hailstones frozen onto small dust grains. Very few objects have such a mixed composition.?

The dense, dark dust torus around the central star contains the bulk of the measured dust mass and is something of a mystery to astronomers. They believe the nebula was expelled around 10 000 years ago, but do not understand how it formed or how long the dust torus can survive evaporation by the very hot central star.

Original Source: ESA News Release

Wallpaper: Galaxy with a Ring of Star Formation

Image credit: Hubble
Resembling a diamond-encrusted bracelet, a ring of brilliant blue star clusters wraps around the yellowish nucleus of what was once a normal spiral galaxy in this new image from NASA’s Hubble Space Telescope (HST). This image is being released to commemorate the 14th anniversary of Hubble’s launch on April 24, 1990 and its deployment from the space shuttle Discovery on April 25, 1990.

The sparkling blue ring is 150,000 light-years in diameter, making it larger than our entire home galaxy, the Milky Way. The galaxy, cataloged as AM 0644-741, is a member of the class of so- called “ring galaxies.” It lies 300 million light-years away in the direction of the southern constellation Dorado.

Ring galaxies are an especially striking example of how collisions between galaxies can dramatically change their structure, while also triggering the formation of new stars. They arise from a particular type of collision, in which one galaxy (the “intruder”) plunges directly through the disk of another one (the “target”). In the case of AM 0644-741, the galaxy that pierced through the ring galaxy is out of the image but visible in larger-field images. The soft spiral galaxy that is visible to the left of the ring galaxy in the image is a coincidental background galaxy that is not interacting with the ring.

The resulting gravitational shock imparted due to the collision drastically changes the orbits of stars and gas in the target galaxy’s disk, causing them to rush outward, somewhat like ripples in a pond after a large rock has been thrown in. As the ring plows outward into its surroundings, gas clouds collide and are compressed. The clouds can then contract under their own gravity, collapse, and form an abundance of new stars.

The rampant blue star formation explains why the ring is so blue: It is continuously forming massive, young, hot stars, which are blue in color. Another sign of robust star formation is the pink regions along the ring. These are rarefied clouds of glowing hydrogen gas, fluorescing because of the strong ultraviolet light from the newly formed massive stars.

Anyone who lives on planets embedded in the ring would be treated to a view of a brilliant band of blue stars arching across the heavens. The view would be relatively short-lived because theoretical studies indicate that the blue ring will not continue to expand forever. After about 300 million years, it will reach a maximum radius, and then begin to disintegrate.

The Hubble Heritage Team used the Hubble Advanced Camera for Surveys to take this image in January 2004. The team used a combination of four separate filters that isolate blue, green, red, and near-infrared light to create the color image.

The Space Telescope Science Institute (STScI) is operated by the Association of Universities for Research in Astronomy, Inc. (AURA), for NASA, under contract with the Goddard Space Flight Center, Greenbelt, MD. The Hubble Space Telescope is a project of international cooperation between NASA and the European Space Agency (ESA).

Original Source: Hubble News Release

Wallpaper: Louros Valles

Image credit: ESA
These latest images show a system of sapping channels, called Louros Valles (named in 1982 after river in Greece), south of the Ius Chasma canyon which runs east to west.

These images were taken by the High Resolution Stereo Camera (HRSC) on board ESA’s Mars Express during orbit 97 from an altitude of 269 kilometres. The images have a resolution of about 13 metres per pixel and are centred at 278.8? East and 8.3? South. The colour image has been created from the nadir and three colour channels. North is at the right.

The Ius Chasma belongs to the giant Valles Marineris canyon system on Mars. The Geryon Montes, visible at the right of this image, is a mountain range which divides the Ius Chasma into two parallel trenches. The dark deposits at the bottom of the Ius Chasma are possibly related to water and wind erosion.

‘Sapping’ is erosion by water that emerges from the ground as a spring or seeps from between layers of rock in a wall of a cliff, crater or other type of depression. The channel forms from water and debris running down the slope from the seepage area.

This is known from similar features on Earth, but on Mars it is thought that most of the water had probably either evaporated or frozen by the time it reached the bottom of the slope.

Original Source: ESA News Release

Wallpaper: Getting Closer to Saturn

Image credit: CICLOPS
As Cassini closes in on Saturn, its view is growing sharper with time and now reveals new atmospheric features in the planet’s southern hemisphere.

The spacecraft’s narrow angle camera took several exposures on March 8, 2004 which have been combined to create this natural color image. The image contrast and colors have been slightly enhanced to aid visibility. The spacecraft was then 56.4 million kilometers (35 million miles) from Saturn, or slightly more than one-third of the distance from Earth to the Sun. The image scale is approximately 338 kilometers (210 miles) per pixel. The planet is 23 percent larger in this image than it appeared in the preceding color image, taken four weeks earlier.

Atmospheric features such as two small, faint dark spots, visible in the planet’s southern hemisphere, will become clearer in the coming months. The spots are located at 38 degrees South latitude.

Moons visible in the lower half of this image: Mimas (398 kilometers, 247 miles across) at left, just below the rings; Dione (1,118 kilometers, 695 miles across) at left, below Mimas; and Enceladus (499 kilometers, 310 miles across) at right. The moons have had their brightness enhanced to aid 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: Bonneville Crater

Image credit: NASA/JPL
NASA’s Spirit rover has taken a beautiful panoramic image of the Bonneville crater. Here’s a 1024×768 wallpaper of the crater. The original image was quite wide, covering 180-degrees, so it doesn’t quite fit a computer screen normally – this image has been cropped a bit. Spirit recorded this photo on March 12, 2004, using its panoramic camera. By taking such a detailed image, scientists can get a good idea about the surface material at the crater.

Wallpaper: Hubble’s New Image of V838 Monocerotis

Image credit: Hubble
“Starry Night,” Vincent van Gogh’s famous painting, is renowned for its bold whorls of light sweeping across a raging night sky. Although this image of the heavens came only from the artist’s restless imagination, a new picture from NASA’s Hubble Space Telescope bears remarkable similarities to the van Gogh work, complete with never-before-seen spirals of dust swirling across trillions of miles of interstellar space.

This Hubble wallpaper, obtained with the Advanced Camera for Surveys on February 8, 2004, is Hubble’s latest view of an expanding halo of light around a distant star, named V838 Monocerotis (V838 Mon). The illumination of interstellar dust comes from the red supergiant star at the middle of the image, which gave off a flashbulb-like pulse of light two years ago. V838 Mon is located about 20,000 light-years away from Earth in the direction of the constellation Monoceros, placing the star at the outer edge of our Milky Way galaxy.

Called a light echo, the expanding illumination of a dusty cloud around the star has been revealing remarkable structures ever since the star suddenly brightened for several weeks in early 2002. Though Hubble has followed the light echo in several snapshots, this new image shows swirls or eddies in the dusty cloud for the first time. These eddies are probably caused by turbulence in the dust and gas around the star as they slowly expand away. The dust and gas were likely ejected from the star in a previous explosion, similar to the 2002 event, which occurred some tens of thousands of years ago. The surrounding dust remained invisible and unsuspected until suddenly illuminated by the brilliant explosion of the central star two years ago.

The Hubble telescope has imaged V838 Mon and its light echo several times since the star’s outburst in January 2002, in order to follow the constantly changing appearance of the dust as the pulse of illumination continues to expand away from the star at the speed of light. During the outburst event, the normally faint star suddenly brightened, becoming 600,000 times more luminous than our Sun. It was thus one of the brightest stars in the entire Milky Way, until it faded away again in April 2002. The star has some similarities to a class of objects called “novae,” which suddenly increase in brightness due to thermonuclear explosions at their surfaces; however, the detailed behavior of V838 Mon, in particular its extremely red color, has been completely different from any previously known nova.

Nature’s own piece of performance art, this structure will continue to change its appearance in coming years as the light from the stellar outburst continues to propagate outward and bounce off more distant black clouds of dust. Astronomers expect the echoes to remain visible for at least the rest of the current decade.

Original Source: Hubble News Release

Wallpaper: Cassini’s Latest View of Saturn

Image credit: NASA/JPL
Four months before its scheduled arrival at Saturn, the Cassini- Huygens spacecraft sent its best color postcard back to Earth of the ringed world. The spacecraft is expected to send weekly postcards, as it gets closer to the ringed giant.

The view from Cassini shows Saturn growing larger and more defined as the spacecraft nears a July 1, 2004, arrival date. On February 9, Cassini’s narrow angle camera, one of two cameras onboard the spacecraft, took a series of exposures through different filters, which were combined to form the color image released today.

“We very much want everyone to enjoy Cassini’s tour of this magnificent planetary system,” said Dr. Carolyn Porco, leader of the Cassini imaging science team at the Space Science Institute in Boulder, Colo. “And I can say right now the views out the window will be stunning.”

Cassini was 69.4 million kilometers (43.2 million miles) from Saturn when the images were taken. The smallest features visible in the image are approximately 540 kilometers (336 miles) across. Finer details in the rings and atmosphere than previously seen are beginning to emerge and will grow in sharpness and clarity over the coming months. The thickness of the middle B ring of Saturn, and the comparative translucence of the outer A ring, when seen against the planet, as well as subtle color differences in the finely-banded Saturn atmosphere, are more apparent.

“I feel like a kid on a road trip at the beginning of our tour,” said Dr. Dennis Matson, project scientist for the Cassini-Huygens mission to Saturn and its largest moon Titan. “We’ve been driving this car for nearly 3.5 billion kilometers (2.2 billion miles) and it’s time to get off and explore this ringed world and its many moons. I can hardly wait, but in the meantime, these weekly color images offer a glimpse of our final destination.”

In the coming months, imaging highlights will include near daily, multi-wavelength imaging of Saturn and its rings; imaging of Titan beginning in April; Titan movie sequences starting in late May, when the resolution exceeds that obtainable from Earth; and a flyby of Saturn’s distant moon, Phoebe, in June, at a spacecraft altitude of 2,000 kilometers (1,243 miles).

Through Cassini, about 260 scientists from 17 countries hope to gain a better understanding of Saturn, its famous rings, its magnetosphere, Titan, and its other icy moons. “Cassini is probably the most ambitious exploration mission ever launched and is the fruit of an active international collaboration,” said Dr. Andre Brahic, imaging team member and professor at Universit? Paris 7-Denis Diderot, France. “It should be the prelude of our future, the exploration of our surroundings by humanity.”

Cassini will begin a four-year prime mission in orbit around Saturn when it arrives July 1. It will release its piggybacked Huygens probe about six months later for descent through Titan’s thick atmosphere. The probe could impact in what may be a liquid methane ocean.

JPL, a division of the California Institute of Technology in Pasadena, manages the mission for NASA’s Office of Space Science, Washington. The Space Science Institute is a non-profit organization of scientists and educators engaged in research in astrophysics, planetary science, Earth sciences, and in integrating research with education and public outreach. Cassini- Huygens is a cooperative mission of NASA, the European Space Agency and the Italian Space Agency.

For the first image and other weekly images on the Internet each Friday, visit:

http://www.nasa.gov/

http://saturn.jpl.nasa.gov

http://ciclops.org/

For information about Cassini-Huygens on the Internet, visit:

http://saturn.jpl.nasa.gov/

Original Source: NASA/JPL News Release