SOHO's new catch: its first officially periodic comet

Credits: ESA/ NASA/ SOHO

The location of the comet P/2007 R5 (SOHO) is indicated in all three panels in the picture. The panels show pictures of observations taken with SOHO’s Large Angle and Spectrometric Coronagraph Experiment (LASCO). The comet has a small orbit, taking four years to once circle the Sun.

For the first time, LASCO has found a rare type of comet called a periodic comet (which flies by the Sun at regular intervals). While many SOHO comets are believed to be periodic, this is the first one that has been conclusively proven and officially declared as such.

The comet faded as quickly as it brightened, and soon became too faint for SOHO's instruments to see it. Estimates show that P/2007 R5 (SOHO) is probably only 100-200 metres in diameter. Given how small and faint this object is, and how close it still is to the Sun, it is an extremely difficult target for observers on Earth to pick out in the sky.

Radio Occultation: Unraveling Saturn's Rings

Credit: NASA/JPL

Specially designed Cassini orbits place Earth and Cassini on opposite sides of Saturn's rings, a geometry known as occultation. Cassini conducted the first radio occultation observation of Saturn's rings on May 3, 2005.

Three simultaneous radio signals of 0.94, 3.6, and 13 centimeter wavelength (Ka-, X-, and S-bands) were sent from Cassini through the rings to Earth. The observed change of each signal as Cassini moved behind the rings provided a profile of the distribution of ring material as a function of distance from Saturn, or an optical depth profile.

This simulated image was constructed from the measured optical depth profiles. It depicts the observed ring structure at about 10 kilometers (6 miles) in resolution. Color is used to represent information about ring particle sizes in different regions based on the measured effects of the three radio signals.

Purple color indicates regions where there is a lack of particles of size less than 5 centimeters (about 2 inches). Green and blue shades indicate regions where there are particles smaller than 5 centimeters (2 inches) and 1 centimeter (less than one third of one inch). The saturated broad white band near the middle of ring B is the densest region of ring B, over which two of the three radio signals were blocked at 10-kilometer (6-mile) resolution, preventing accurate color representation over this band. From other evidence in the radio observations, all ring regions appear to be populated by a broad range particle size distribution that extends to boulder sizes (several to many meters across).

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 mission for NASA's Science Mission Directorate, Washington, D.C. The Cassini orbiter was designed, developed and assembled at JPL. The radio science team is based at JPL.

Hubble Captures Stars Going Out in Style

Credit: NASA, ESA, and The Hubble Heritage Team (SRScI/AURA)

The colorful, intricate shapes in these NASA Hubble Space Telescope images reveal how the glowing gas ejected by dying Sun-like stars evolves dramatically over time.

These gaseous clouds, called planetary nebulae, are created when stars in the last stages of life cast off their outer layers of material into space. Ultraviolet light from the remnant star makes the material glow. Planetary nebulae last for only 10,000 years, a fleeting episode in the 10-billion-year lifespan of Sun-like stars.

The name planetary nebula has nothing to do with planets. They got their name because their round shapes resembled planets when seen through the small telescopes of the eighteenth century.

The Hubble images show the evolution of planetary nebulae, revealing how they expand in size and change temperature over time. A young planetary nebula, such as He 2-47, at top, left, for example, is small and is dominated by relatively cool, glowing nitrogen gas. In the Hubble images, the red, green, and blue colors represent light emitted by nitrogen, hydrogen, and oxygen, respectively.

Over thousands of years, the clouds of gas expand away and the nebulae become larger. Energetic ultraviolet light from the star penetrates more deeply into the gas, causing the hydrogen and oxygen to glow more prominently, as seen near the center of NGC 5315. In the older nebulae, such as IC 4593, at bottom, left, and NGC 5307, at bottom, right, hydrogen and oxygen appear more extended in these regions, and red knots of nitrogen are still visible.

These four nebulae all lie in our Milky Way Galaxy. Their distances from Earth are all roughly the same, about 7,000 light-years. The snapshots were taken with Hubble's Wide Field Planetary Camera 2 in February 2007. Like snowflakes, planetary nebulae show a wide variety of shapes, indicative of the complex processes that occur at the end of stellar life.

He 2-47, at top, left, is dubbed the "starfish" because of its shape. The six lobes of gas and dust, which resemble the legs of a starfish, suggest that He 2-47 puffed off material at least three times in three different directions. Each time, the star fired off a narrow pair of opposite jets of gas. He 2-47 is in the southern constellation Carina.

NGC 5315, the chaotic-looking nebula at top, right, reveals an x-shaped structure. This shape suggests that the star ejected material in two different outbursts in two distinct directions. Each outburst unleashed a pair of diametrically opposed outflows. NGC 5315 lies in the southern constellation Circinus.

IC 4593, at bottom, left, is in the northern constellation Hercules.

NGC 5307, at bottom, right, displays a spiral pattern, which may have been caused by the dying star wobbling as it expelled jets of gas in different directions. NGC 5307 resides in the southern constellation Centaurus.

Hubble and Spitzer Space Telescopes Find "Lego-Block" Galaxies in Early Universe

Credit: NASA, ESAl, and N. Pirzkal (STScI/ESA)

In this image of the Hubble Ultra Deep Field, several objects are identified as the faintest, most compact galaxies ever observed in the distant universe. They are so far away that we see them as they looked less than one billion years after the Big Bang. Blazing with the brilliance of millions of stars, each of the newly discovered galaxies is a hundred to a thousand times smaller than our Milky Way Galaxy.

The bottom row of pictures shows several of these clumps (distance expressed in redshift value). Three of the galaxies appear to be slightly disrupted. Rather than being shaped like rounded blobs, they appear stretched into tadpole-like shapes. This is a sign that they may be interacting and merging with neighboring galaxies to form larger structures.

The detection required joint observations between Hubble and NASA's Spitzer Space Telescope. Blue light seen by Hubble shows the presence of young stars. The absence of infrared light from Spitzer observations conclusively shows that these are truly young galaxies without an earlier generation of stars.

Children of Saturn

Credit: NASA/JPL/Space Science Institute

Two moons on opposite sides of the rings slide past each other in this stately portrait of Saturn.

Dione (1,126 kilometers, or 700 miles across), on the far side of Saturn, appears above the rings. Tethys (1,071 kilometers, or 665 miles across) poses directly in front of the ringplane.

This view looks toward the unilluminated side of the rings from less than a degree above the ringplane. The silhouette of the rings overlay the subtle texture of Saturn's atmosphere.

The image was taken in visible green light with the Cassini spacecraft wide-angle camera on July 29, 2007. The view was obtained at a distance of approximately 3.2 million kilometers (2 million miles) from Saturn and at a Sun-Saturn-spacecraft, or phase, angle of 32 degrees. Image scale is 188 kilometers (117 miles) per pixel.

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 mission for NASA's Science Mission Directorate, Washington, D.C. The Cassini orbiter and its two onboard cameras were designed, developed and assembled at JPL. The imaging operations center is based at the Space Science Institute in Boulder, Colo.

Steamy Star in NGC 1333

Credit: NASA/JPL-Caltech/R. A. Gutermuth (Harvard-Smithsonian CfA)

This image from NASA's Spitzer Space Telescope shows a stellar nursery called NGC 1333. Spitzer discovered that a pre-planetary disk of dust surrounding an embryonic star within this region, called NGC 1333-IRAS 4B, is drenched with water vapor.

NGC 1333 is located about 1,000 light-years away in the Perseus constellation. It is a cloud of gas and dust that is busy manufacturing new stars. Spitzer surveyed four of the very youngest stars in this region and 26 others elsewhere, but found only one, NGC 1333-IRAS 4B, with water vapor. This might be because NGC 1333-IRAS 4B is in just the right orientation for Spitzer to view deep inside the developing star system and detect the water vapor.

Hubble Captures Uranus's Rings on Edge

Credit:NASA, ESA, and M. Showalter (SETI Institute)

This series of images from NASA's Hubble Space Telescope shows how the ring system around the distant planet Uranus appears at ever more oblique (shallower) tilts as viewed from Earth - culminating in the rings being seen edge-on in three observing opportunities in 2007. The best of these events appears in the far right image taken with Hubble's Wide Field Planetary Camera 2 on August 14, 2007.

The edge-on rings appear as two spikes above and below the planet. The rings cannot be seen running fully across the face of the planet because the bright glare of the planet has been blocked out in the Hubble photo (a small amount of residual glare appears as a fan- shaped image artifact). A much shorter color exposure of the planet has been photo- composited to show its size and position relative to the ring plane.

Earthbound astronomers only see the rings' edge every 42 years as the planet follows a leisurely 84-year orbit about the Sun. However, the last time the rings were tilted edge-on to Earth astronomers didn't even know they existed.

With further analysis of the Hubble data, astronomer Mark Showalter of the SETI Institute in Mountain View, Calif., hopes to detect some of the small moons that may shepherd the debris into distinct rings.

Until Voyager 2 flew by Uranus in January 1986, the rings were only known from the way they temporarily blocked the light of stars passing behind the planet. Hubble provided some of the first images of the ring system as viewed from Earth's distance of approximately 2 billion miles. The advent of adaptive optics gave ground-based observers using large telescopes comparatively sharp views.

The rings were discovered in 1977, so this is the first time for a Uranus ring crossing to be observed from Earth. Earth's orbit around the Sun permits three opportunities to view the rings edge-on: Uranus made its first ring crossing as seen from Earth on May 3; it made its second crossing on August 16; and will cross for the third time on February 20, 2008. Though the last ring crossing relative to Earth will be hidden behind the Sun, most of Earth's premier telescopes, including Keck, Hubble, the European Southern Observatory's Very Large Telescope and the Hale Telescope on Mt. Palomar, plan to focus on the planet again in the days following December 7, 2007. On December 7 the rings will be perfectly edge-on to the Sun.

Showalter is a member of a team led by Imke de Pater of the University of California, Berkeley, who reported that the rings of micron-sized dust have changed significantly since the Voyager 2 spacecraft photographed the Uranus system 21 years ago. Observations were also gleaned from near-infrared adaptive optics observations with the Keck II telescope on May 28, 2007, and reported in an article appearing on August 23 in Science Express, the online edition of Science Magazine.

Speeding-Bullet Star Leaves Enormous Streak Across Sky

Speeding-Bullet Star Leaves Enormous Streak Across Sky

NASA's Galaxy Evolution Explorer has spotted an amazingly long comet-like tail behind a star streaking through space at supersonic speeds. The star, named Mira after the Latin word for "wonderful," has been a favorite of astronomers for about 400 years. It is a fast-moving, older star called a red giant that sheds massive amounts of surface material.

The space-based Galaxy Evolution Explorer scanned the popular star during its ongoing survey of the entire sky in ultraviolet light. Astronomers then noticed what looked like a comet with a gargantuan tail. In fact, material blowing off Mira is forming a wake 13 light-years long, or about 20,000 times the average distance of Pluto from the sun. Nothing like this has ever been seen before around a star.

Astronomers say Mira's tail offers a unique opportunity to study how stars like our sun die and ultimately seed new solar systems. As Mira hurtles along, its tail sheds carbon, oxygen and other important elements needed for new stars, planets and possibly even life to form. This tail material, visible now for the first time, has been released over the past 30,000 years.

"This is an utterly new phenomenon to us, and we are still in the process of understanding the physics involved," said co-author Mark Seibert of the Observatories of the Carnegie Institution of Washington in Pasadena. "We hope to be able to read Mira's tail like a ticker tape to learn about the star's life."

Billions of years ago, Mira was similar to our sun. Over time, it began to swell into what's called a variable red giant - a pulsating, puffed-up star that periodically grows bright enough to see with the naked eye. Mira will eventually eject all of its remaining gas into space, forming a colorful shell called a planetary nebula. The nebula will fade with time, leaving only the burnt-out core of the original star, which will then be called a white dwarf.

Some Images

1. Johnny Appleseed of the Cosmos

A new ultraviolet mosaic from NASA's Galaxy Evolution Explorer shows a speeding star named Mira (pronounced my-rah) that is leaving an enormous trail of "seeds" for new solar systems.

2. A Real Shooting Star

This artist's animation illustrates a star flying through our galaxy at supersonic speeds, leaving a 13-light-year-long trail of glowing material in its wake.

3. Evolution of Mira's Enormous Tail

This chart illustrates the length (top) and age (bottom) of a long comet-like tail of material trailing behind a speeding star called Mira (pronounced My-rah).

4. Anatomy of a Shooting Star

A close-up view of a star racing through space faster than a speeding bullet can be seen in this image from NASA's Galaxy Evolution Explorer.

5. Supersonic Bullet

A bullet traveling through air at about 1.5 times the speed of sound can be seen in this image.

6. Mira's Tail There All Along

As this composite demonstrates, Mira's tail is only visible in ultraviolet light (top), and does not show up in visible light (bottom).

Quadruple Galaxy Merger - CL0958+4702

Credit: NASA/JPL-Caltech/K. Rines (Harvard-Smithsonian CfA)

Whopper Galaxy Collision

One of the biggest galaxy collisions ever observed is taking place at the center of this image. The four white blobs in the middle are large galaxies that have begun to tangle and ultimately merge into a single gargantuan galaxy. The whitish cloud around the colliding galaxies contains billions of stars tossed out during the messy encounter. Other galaxies and stars appear in yellow, orange and red hues. Blue shows hot gas that permeates this distant region of tightly packed galaxies.

NASA's Spitzer Space Telescope spotted the four-way collision, or merger, in a giant cluster of galaxies, called CL0958+4702, located nearly five billion light-years away. The dots in the picture are a combination of galaxies in the cluster; background galaxies located behind the cluster; and foreground stars in our own Milky Way galaxy.

Infrared data from Spitzer are colored red in this picture, while visible-light data from a telescope known as WIYN are green. Areas where green and red overlap appear orange or yellow. Since most galaxies in the cluster contain old stars that are visible to Spitzer and WIYN, those galaxies appear orange. Blue represents X-ray light captured by NASA's Chandra X-ray Observatory. The colliding galaxies appear white because they are in areas where all the colors overlap.

The WIYN telescope, located near Tucson, Ariz., is owned and operated by the WIYN Consortium, which consists of the University of Wisconsin, Indiana University, Yale University, and the National Optical Astronomy Observatory.

Uncovering the Veil Nebula

NASA's Hubble Space Telescope photographed three magnificent sections of the Veil Nebula — the shattered remains of a supernova that exploded thousands of years ago. This series of images provides beautifully detailed views of the delicate, wispy structure resulting from this cosmic explosion. The Veil Nebula is one of the most spectacular supernova remnants in the sky. The entire shell spans about 3 degrees on the sky, corresponding to about 6 full moons.

The Veil Nebula is a prototypical middle-aged supernova remnant, and is an ideal laboratory for studying the physics of supernova remnants because of its unobscured location in our Galaxy, its relative closeness, and its large size. Also known as the Cygnus Loop, the Veil Nebula is located in the constellation of Cygnus, the Swan. It is about 1,500 light-years away from Earth.

Stars in our Galaxy, and in other galaxies, are born and then die. How long a star lives depends on how massive it is. The more massive the star, the shorter its life. When a star significantly more massive than our Sun runs out of fuel, it collapses and blows itself apart in a catastrophic supernova explosion. A supernova releases so much light that it can outshine a whole galaxy of stars put together. The exploding star sweeps out a huge bubble in its surroundings, fringed with actual stellar debris along with material swept up by the blast wave. This glowing, brightly colored shell of gas forms a nebula that astronomers call a "supernova remnant."

Such a remnant can remain visible long after the initial explosion fades away. Scientists estimate that the Veil supernova explosion occurred some 5,000 to 10,000 years ago.

The small regions captured in these Hubble images provide stunning close-ups of the Veil. Fascinating smoke-like wisps of gas are all that remain visible of what was once a star in our Milky Way Galaxy. The intertwined rope-like filaments of gas in the Veil Nebula result from the enormous amounts of energy released as the fast-moving debris from the explosion plows into its surroundings and creates shock fronts. These shocks, driven by debris moving at 600,000 kilometers per hour, heat the gas to millions of degrees. It is the subsequent cooling of this material that produces the brilliant glowing colors.

The Hubble images of the Veil Nebula are striking examples of how processes that take place hundreds of light-years away can sometimes resemble effects we see around us in our daily life. Although caused by different forces, the structures show similarities to the patterns formed by the interplay of light and shadow on the bottom of a swimming pool, rising smoke, or a ragged cirrus cloud.

Although only about one star per century in our Galaxy will end its life in this spectacular way, these explosions are responsible for making all chemical elements heavier than iron, as well as being the main producers of oxygen in the universe. Elements such as copper, mercury, gold, and lead are forged in these violent events. The expanding shells of supernova remnants mix with other clouds in the Milky Way and become the raw material for new generations of stars and planets. The chemical elements that constitute Earth, and indeed those of which we ourselves are made, were formed deep inside ancient stars and distributed by supernova explosions in nebulae like the one we see here.

The images were taken with Hubble's Wide Field Planetary Camera 2 (WFPC2) in November 1994 and August 1997. The color is produced by creating a composite of three different images. The colors indicate emission from different kinds of atoms excited by the shock: blue shows oxygen, green shows sulfur, and red shows hydrogen.

Credit: NASA, ESA, and theHubble Heritage(STScI/AURA)-ESA/Hubble Collaboration

Planets with four parents?

Planets with four parents?

SPITZER SCIENCE CENTER NEWS RELEASE
Posted: July 24, 2007

How many stars does it take to "raise" a planet? In our own solar system, it took only one -- our Sun. However, new research from NASA's Spitzer Space Telescope shows that planets might sometimes form in systems with as many as four stars.

This artist concept depicts a quadruple-star system called HD 98800.
The system is approximately 10 million years old, and is located 150 light-years away in the constellation TW Hydrae.
Credit: NASA/JPL-Caltech/T. Pyle (SSC)

Astronomers used Spitzer's infrared vision to study a dusty disk that swirls around a pair of stars in the quadruple-star system HD 98800. Such disks are thought to give rise to planets. Instead of a smooth, continuous disk, the telescope detected gaps that could be caused by a unique gravitational relationship between the system's four stars. Alternatively, the gaps could indicate planets have already begun to form, carving out lanes in the dust.

"Planets are like cosmic vacuums. They clear up all the dirt that is in their path around the central stars," said Dr. Elise Furlan, of the NASA Astrobiology Institute at the University of California at Los Angeles. Furlan is the lead author of a paper that has been accepted for publication in The Astrophysical Journal.

HD 98800 is approximately 10 million years old, and is located 150 light-years away in the constellation TW Hydrae.

Before Spitzer set its gaze on HD 98800, astronomers had a rough idea of the system's structure from observations with ground-based telescopes. They knew the system contains four stars, and that the stars are paired off into doublets, or binaries. The stars in the binary pairs orbit around each other, and the two pairs also circle each other like choreographed ballerinas. One of the stellar pairs, called HD 98800B, has a disk of dust around it, while the other pair has none.

Although the four stars are gravitationally bound, the distance separating the two binary pairs is about 50 astronomical units (AU) -- slightly more than the average distance between our Sun and Pluto. Until now, technological limitations have hindered astronomers' efforts to look at the dusty disk around HD 98800B more closely.

With Spitzer, scientists finally have a detailed view. Using the telescope's infrared spectrometer, Furlan's team sensed the presence of two belts in the disk made of large dust grains. One belt sits at approximately 5.9 AU away from the central binary, HD 98800B, or about the distance from the Sun to Jupiter. This belt is likely made up of asteroids or comets. The other belt sits at 1.5 to 2 AU, comparable to the area where Mars and the asteroid belt sit, and probably consists of fine grains.

"Typically, when astronomers see gaps like this in a debris disk, they suspect that a planet has cleared the path. However, given the presence of the diskless pair of stars sitting 50 AU away, the inward-migrating dust particles are likely subject to complex, time-varying forces, so at this point the existence of a planet is just speculation," said Furlan.

Astronomers believe that planets form like snowballs over millions of years, as small dust grains clump together to form larger bodies. Some of these cosmic rocks then smash together to form rocky planets, like Earth, or the cores of gas-giant planets like Jupiter. Large rocks that don't form planets often become asteroids and comets. As these rocky structures violently collide, bits of dust are released into space. Scientists can see these dust grains with Spitzer's supersensitive infrared eyes.

According to Furlan, the dust generated from the collision of rocky objects in the outer belt should eventually migrate toward the inner disk. However, in the case of HD 98800B, the dust particles do not evenly fill out the inner disk as expected, due to either planets or the diskless binary pair sitting 50 AU away and gravitationally influencing the movement of dust particles.

"Since many young stars form in multiple systems, we have to realize that the evolution of disks around them and the possible formation of planetary systems can be way more complicated and perturbed than in a simple case like our solar system," Furlan added.

Astronomers Find Highly Elliptical Disk Around Young Star

Credit: NASA, ESA, and P. Kalas (University of California, Berkeley)

Astronomers Find Highly Elliptical Disk Around Young Star

This image taken by NASA's Hubble Space Telescope shows a lopsided debris disk around the young star HD 15115.

The disk, seen edge-on, is the dense blue line extending from the star to the upper right and lower left of the image. As seen from Earth, the edge-on disk resembles a needle sticking out from the star. The disk appears thicker and longer at upper right than at lower left, evidence of the disk's lopsided structure.

Astronomers think the disk's odd imbalanced look is caused by dust particles following a highly elliptical orbit around the star, which is slightly brighter than the Sun. The lopsidedness may have been caused by planets sweeping up debris in the disk or by the gravity of a nearby star.

Astronomers used an occulting mask on Hubble's Advanced Camera for Surveys to block out the bright starlight so they could see the dim disk. The occulting masks can be seen in the image as the dark circle in the center and the dark bar on the left. The star is behind the central mask.

HD 15115 is among nearly 30 stars that belong to the Beta Pictoris Moving Group. Moving groups are expanded clusters of stars believed to have a common birthplace and age, in this case about 12 million years, that are traveling together loosely through space. HD 15115 is 150 light-years from Earth.

Dusty disks are known to exist around at least 100 stars, but because of the difficulty in observing material close to the brightness of a star, less than a dozen have been studied closely.

Astronomers described the disk as one of the most peculiar debris disks that Hubble has ever imaged. They in fact made follow-up observations with the W.M. Keck Observatory in Hawaii to confirm the disk's presence.

Hubble's Advanced Camera for Surveys snapped the image on July 17, 2006.

An intriguing bright clump in Saturn's F ring

An Intriguing Bright Clump in Saturn's F ring

The Cassini spacecraft spies an intriguing bright clump in Saturn's F ring. Also of interest is the dark gash that appears to cut through the ring immediately below the clump. Scientists continue to monitor this ring for small, transient clumps of material, as well as the effects of the shepherd moon Prometheus.

This view looks toward the unilluminated side of the rings from about 28 degrees above the ringplane.

The image was taken in visible light with the Cassini spacecraft narrow-angle camera on May 5, 2007 at a distance of approximately 2.1 million kilometers (1.3 million miles) from Saturn. Image scale is 12 kilometers (8 miles) per pixel.

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 mission for NASA's Science Mission Directorate, Washington, D.C. The Cassini orbiter and its two onboard cameras were designed, developed and assembled at JPL. The imaging operations center is based at the Space Science Institute in Boulder, Colo.

For more information about the Cassini-Huygens mission visit http://saturn.jpl.nasa.gov
The Cassini imaging team homepage is at http://ciclops.org

Credit: NASA/JPL/Space Science Institute

Astronomers Measure Mass of Largest Dwarf Planet

Credit: NASA, ESA, and M. Brown (California Institute of Technology)

ASA's Hubble Space Telescope has teamed up with the W.M. Keck Observatory to precisely measure the mass of Eris, the largest member of a new class of dwarf planets in our solar system. Eris is 1.27 times the mass of Pluto, formerly the largest member of the Kuiper Belt of icy objects beyond Neptune.

Hubble observations in 2006 showed that Eris is slightly physically larger than Pluto. But the mass could only be calculated by observing the orbital motion of the moon Dysnomia around Eris. Multiple images of Dysnomia's movement along its orbit were taken by Hubble and Keck.

Astronomer Mike Brown of the California Institute of Technology in Pasadena, Calif. and colleagues also report in this week's Science Magazine that Dysnomia is in a nearly circular 16-day orbit. This favors the idea that Dysnomia was born out of a collision between Eris and another Kuiper Belt object (KBO). A gravitationally captured object would be expected to be in a more elliptical orbit.

The satellites of Pluto, as well as the Earth-Moon system are also believed to have been born out of a collision process where debris from the smashup goes into orbit and coalesces into a satellite.

By comparing the mass and diameter, Brown has calculated a density for Eris of 2.3 grams per cubic centimeter. This is very similar to the density of Pluto, the large Kuiper Belt object 2003 EL61, and Neptune's moon Triton which is likely a captured KBO. These higher densities imply that these bodies are not pure ice but must have a significant rocky composition.

The discovery of Eris in 2005 (originally nicknamed Xena, and officially cataloged 2003 UB313) prompted a debate over the planetary status of Pluto because astronomers realized they would have to call it the "10th" planet if Pluto retained its own planetary status, which was already under debate. This led the International Astronomical Union, in 2006, to make a new class of solar system object called dwarf planets. These are spherical bodies in hydrostatic equilibrium (objects that have sufficient gravity to overcome their own rigidity and form a spherical shape) like the planets, but unlike the major planets in the solar system, they have not gravitationally cleared out the neighborhood of particles and small debris along their orbits.

Dark Matter Ring in CI 0024+17

Credit: NASA, ESA, M.J. Jee and H. Ford (Johns Hopkins University)

This Hubble Space Telescope composite image shows a ghostly "ring" of dark matter in the galaxy cluster Cl 0024+17.

The ring-like structure is evident in the blue map of the cluster's dark matter distribution. The map is superimposed on a Hubble image of the cluster. The ring is one of the strongest pieces of evidence to date for the existence of dark matter, an unknown substance that pervades the universe.

The map was derived from Hubble observations of how the gravity of the cluster Cl 0024+17 distorts the light of more distant galaxies, an optical illusion called gravitational lensing. Although astronomers cannot see dark matter, they can infer its existence by mapping the distorted shapes of the background galaxies. The mapping also shows how dark matter is distributed in the cluster.

Astronomers suggest that the dark-matter ring was produced from a collision between two gigantic clusters.

Dark matter makes up the bulk of the universe's material and is believed to make up the underlying structure of the cosmos.

The Hubble observations were taken in November 2004 by the Advanced Camera for Surveys (ACS). Thanks to the exquisite resolution of the ACS, astronomers saw the detailed cobweb tracery of gravitational lensing in the cluster.

Star-Forming Region in the Carina Nebula

Credit for Hubble Image: NASA, ESA, N. Smith (University of California, Berkeley),

and The Hubble Heritage Team (STScI/AURA)

[Left] — A towering "mountain" of cold hydrogen gas laced with dust is the site of new star formation in the Carina Nebula. The great gas pillar is being eroded by the ultraviolet radiation from the hottest newborn stars in the nebula.

[Right] — A close-up look at the peak of one of these "pillars of creation" reveals unequivocal evidence that stars are being born inside the columns. A pencil-like streamer of gas shoots out in both directions from the pillar and plows into surrounding gas like a fire hose hitting a wall of sand. The jet is being launched from a newly forming star hidden inside the column. A similar jet appears near the bottom of the image. These stellar jets are a common signature of the birth of a new star.

Carina Nebula Details

Credit for Hubble Image: NASA, ESA, N. Smith (University of California, Berkeley),
and The Hubble Heritage Team (STScI/AURA)

This Hubble Space Telescope view of the central region of the Carina Nebula reveals a violent maelstrom of star birth. The fantasy-like landscape of the nebula is sculpted by the intense pressure of starlight from monster stars and their accompanying star clusters, as well as the hydrodynamics of their stellar winds of charged particles.

[Top] — An approximately one-light-year tall "pillar" of cold hydrogen towers above the wall of the molecular cloud. The 2.5-million-year-old star cluster called Trumpler 14 appears at the right side of the image. A small nugget of cold molecular hydrogen, called a Bok globule, is silhouetted against the star cluster.

[Center] — A Bok globule nicknamed the "caterpillar" appears at the right. Its glowing edge indicates that it is being photoionized by the hottest stars in the cluster. It has been hypothesized that stars may form inside such dusty cocoons. The top of the Keyhole Nebula, the most prominent feature embedded inside Carina, is on the left. Another Bok globule is in the foreground.

[Bottom] — These great clouds of cold hydrogen resemble summer afternoon thunderheads. They tower above the surface of a molecular cloud on the edge of the nebula. So-called "elephant trunk" pillars resist being heated and eaten away by blistering ultraviolet radiation from the nebula's brightest stars.

Carina Nebula

Credit for Hubble Image:NASA, ESA, N. Smith (University of California, Berkeley),
and The Hubble Heritage Team (STScI/AURA)

In celebration of the 17th anniversary of the launch and deployment of NASA's Hubble Space Telescope, a team of astronomers is releasing one of the largest panoramic images ever taken with Hubble's cameras. It is a 50-light-year-wide view of the central region of the Carina Nebula where a maelstrom of star birth - and death - is taking place.

Hubble's view of the nebula shows star birth in a new level of detail. The fantasy-like landscape of the nebula is sculpted by the action of outflowing winds and scorching ultraviolet radiation from the monster stars that inhabit this inferno. In the process, these stars are shredding the surrounding material that is the last vestige of the giant cloud from which the stars were born.

The immense nebula contains at least a dozen brilliant stars that are roughly estimated to be at least 50 to 100 times the mass of our Sun. The most unique and opulent inhabitant is the star Eta Carinae, at far left. Eta Carinae is in the final stages of its brief and eruptive lifespan, as evidenced by two billowing lobes of gas and dust that presage its upcoming explosion as a titanic supernova.

The fireworks in the Carina region started three million years ago when the nebula's first generation of newborn stars condensed and ignited in the middle of a huge cloud of cold molecular hydrogen. Radiation from these stars carved out an expanding bubble of hot gas. The island-like clumps of dark clouds scattered across the nebula are nodules of dust and gas that are resisting being eaten away by photoionization.

The hurricane blast of stellar winds and blistering ultraviolet radiation within the cavity is now compressing the surrounding walls of cold hydrogen. This is triggering a second stage of new star formation.

Our Sun and our solar system may have been born inside such a cosmic crucible 4.6 billion years ago. In looking at the Carina Nebula we are seeing the genesis of star making as it commonly occurs along the dense spiral arms of a galaxy.

The immense nebula is an estimated 7,500 light-years away in the southern constellation Carina the Keel (of the old southern constellation Argo Navis, the ship of Jason and the Argonauts, from Greek mythology).

This image is a mosaic of the Carina Nebula assembled from 48 frames taken with Hubble Space Telescope's Advanced Camera for Surveys. The Hubble images were taken in the light of neutral hydrogen. Color information was added with data taken at the Cerro Tololo Inter-American Observatory in Chile. Red corresponds to sulfur, green to hydrogen, and blue to oxygen emission.

Hubble Sees 'Comet Galaxy' Being Ripped Apart By Galaxy Cluster

Credit: NASA, ESA, and J. -P. Kneib (Laboratorie d'Astrophysique de Marseille)

NASA's Hubble Space Telescope, in collaboration with several other ground- and space- based telescopes, has captured a galaxy being ripped apart by a galaxy cluster's gravitational field and harsh environment.

The finding sheds light on the mysterious process by which gas-rich spiral-shaped galaxies might evolve into gas-poor irregular- or elliptical-shaped galaxies over billions of years. The new observations also reveal one mechanism for forming the millions of "homeless" stars seen scattered throughout galaxy clusters.

There are many galaxies of different shapes and sizes around us today. Roughly half are gas-poor elliptical-shaped galaxies with little new star formation activity, and half are gas- rich spiral and irregular galaxies with high star formation activity. Observations have shown that gas-poor galaxies are most often found near the centers of crowded galaxy clusters, whereas spirals spend most of their lifetimes in less crowded circumstances.

But deep observations of the universe show that when the universe was half its present age, only one in five galaxies was a gas-poor object. So where do all of today's gas-poor galaxies come from? Scientists suspect that some kind of transformative process must have taken place, but because galaxy evolution occurs over billions of years, they previously have not been able to see this transformation at work.

The new Hubble observations, made by an international team of astronomers led by Luca Cortese of Cardiff University, United Kingdom, provide one of the best examples to date of this metamorphosis. While looking at galaxy cluster Abell 2667, astronomers found an odd- looking spiral galaxy (shown in the upper left hand corner of the image) that plows through the cluster after being accelerated to at least 3.5 million km/h by the enormous combined gravity of the cluster's dark matter, hot gas and hundreds of galaxies. As it speeds through, it rams into the hot gas that permeates the cluster. Its gas and stars are pulled away by the gravitational tidal forces exerted by the cluster, just as the forces exerted by our moon and sun pull the Earth's oceans.

The unique galaxy is situated 3.2 billion light-years from the Earth. It has an extended stream of bright blue knots and diffuse wisps of young stars whose formation and evolution have been driven by both the cluster's tidal forces and a mechanism called "ram pressure stripping." Abell 2667's hot gas is composed of charged particles with a temperature of 10-100 million degrees. During the ram pressure stripping process, the charged particles strip and push away the infalling galaxy's gas, just as the solar wind of charged particles pushes ionized gas away from a comet to create a gas tail. For this reason the scientists have nicknamed the stretched spiral the "comet galaxy."

In the midst of the destruction a baby-boom of star formation in the center of the infalling galaxy has been triggered by the tidal effect of the cluster's gravity. Millions of stars have been ripped from their host galaxy. The spiral galaxy will inevitably lose all its gas and dust in the collision, and become a gas-poor galaxy with an old population of red stars.

Scientists estimate that the total duration of the transformation process is close to one billion years. What is seen now in the Hubble image is not yet half-way through the transformation (i.e. roughly 200 million years).

The strong gravitational pull exerted by the galaxy cluster's collective mass has bent the light of other, more distant galaxies and distorted their shapes - an effect called gravitational lensing. The giant bright banana-shaped arc seen just to the right of the center in the photo corresponds to the magnified and distorted image of a distant galaxy that lies behind the cluster's core.

The Hubble image was taken by the Wide Field Planetary Camera 2 in October 2001 and is a composite of three observations through blue, green, and near-infrared filters.

The astronomers combined the Hubble observations with various ground- and space-based telescopes: the European Southern Observatory's Very Large Telescope in Chile, NASA's Spitzer Space Telescope, NASA's Chandra X-Ray Observatory, and the twin Keck Telescopes in Hawaii.

The Very Large Telescope was used for optical spectroscopy and near-infrared photometry. Spitzer Space Telescope provided mid-infrared photometry. The Chandra X-Ray Observatory took X-ray observations, and the twin Keck Telescopes were used for optical spectroscopy. Optical spectroscopy is used to measure the temperature, composition, and radial motion of stars and galaxies. Infrared photometry measures the brightness, and any change in brightness, of an object glowing at infrared wavelengths.

Supernova 1987A

This photo album of images from NASA's Hubble Space Telescope shows a ring of gas beginning to glow around an exploded star.

The stellar blast, called Supernova 1987A, was first spotted 20 years ago. The explosion is one of the brightest supernova blasts in more than 400 years. Hubble began watching the blast's aftermath shortly after it was launched in 1990.

The growing number of bright spots on the ring was produced by an onslaught of material unleashed by the blast. The shock wave of material is slamming into the ring's innermost regions, heating them up, and causing them to glow. The ring, about a light-year across, was probably shed by the star about 20,000 years before the star exploded.

Astronomers detected the first bright spot in 1997, but now they see dozens of spots around the ring. Only Hubble can see the individual bright spots. In the next few years, the entire ring will be ablaze as it absorbs the full force of the crash. The glowing ring is expected to become bright enough to illuminate the star's surroundings, providing astronomers with new information on how the star expelled material before the explosion.

The bright spot that appears to be on the ring at lower right is actually a foreground star. Supernova 1987A is 163,000 light-years away in the Large Magellanic Cloud.

The images were taken between 1994 and 2006 with Hubble's Wide Field Planetary Camera 2 and Advanced Camera for Surveys.

Credit: NASA, ESAP. Challis and R. Kirshner (Harvard-Smithsonian Center for Astrophysics)

Eagle Nebula (M16) Pillars

Credit: NASA/JPL-Caltech/N. Flagey (IAS/SSC) & A. Noriega-Crespo (SSC/Caltech)

Unwrapping the Pillars

This image composite highlights the pillars of the Eagle nebula, as seen in infrared light by NASA's Spitzer Space Telescope (bottom) and visible light by NASA's Hubble Space Telescope (top insets).

The top right inset focuses on the three famous pillars, dubbed the "Pillars of Creation," which were photographed by Hubble in 1995. Hubble's optical view shows the dusty towers in exquisite detail, while Spitzer's infrared eyes penetrate through the thick dust, revealing ghostly transparent structures. The same effect can be seen for the pillar outlined in the top left box.

In both cases, Spitzer's view exposes newborn stars that were hidden inside the cocoon-like pillars, invisible to Hubble. These stars were first uncovered by the European Space Agency's Infrared Satellite Observatory. In the Spitzer image, two embedded stars are visible at the tip and the base of the left pillar, while one star can be seen at the tip of the tallest pillar on the right.

Credit: NASA/JPL-Caltech/N. Flagey (IAS/SSC) & A. Noriega-Crespo (SSC/Caltech)

Eagle Nebula Flaunts Its Infrared Feathers

This set of images from NASA's Spitzer Space Telescope shows the Eagle nebula in different hues of infrared light. Each view tells a different tale. The left picture shows lots of stars and dusty structures with clarity. Dusty molecules found on Earth called polycyclic aromatic hydrocarbons produce most of the red; gas is green and stars are blue.

The middle view is packed with drama, because it tells astronomers that a star in this region violently erupted, or went supernova, heating surrounding dust (orange). This view also reveals that the hot dust is shell shaped, another indication that a star exploded.

The final picture highlights the contrast between the hot, supernova-heated dust (green) and the cooler dust making up the region's dusty star-forming clouds and towers (red, blue and purple).

The left image is a composite of infrared light with the following wavelengths: 3.6 microns (blue); 4.5 microns (green); 5.8 microns (orange); and 8 microns (red). The right image includes longer infrared wavelengths, and is a composite of light of 4.5 to 8.0 microns (blue); 24 microns (green); and 70 microns (red). The middle image is made up solely of 24-micron light.

Heavyweight Stars Light Up Nebula NGC 6357

The small open star cluster Pismis 24 lies in the core of the large emission nebula NGC 6357 in Sagittarius, about 8,000 light-years away from Earth. Some of the stars in this cluster are extremely massive and emit intense ultraviolet radiation.

The brightest object in the picture is designated Pismis 24-1. It was once thought to weigh as much as 200 to 300 solar masses. This would not only have made it by far the most massive known star in the galaxy, but would have put it considerably above the currently believed upper mass limit of about 150 solar masses for individual stars.

However, Hubble Space Telescope high-resolution images of the star show that it is really two stars orbiting one another (inset pictures at top right and bottom right). They are estimated to each be 100 solar masses.

In addition, spectroscopic observations with ground-based telescopes further reveal that one of the stars is actually a tight binary that is too compact to be resolved even by Hubble. This divides the estimated mass for Pismis 24-1 among the three stars. Although the stars are still among the heaviest known, the mass limit has not been broken thanks to the multiplicity of the system.

The observations were performed by a team of astronomers led by J. Maíz Apellániz of the Instituto de Astrofísica de Andalucía in Spain. The team imaged Pismis 24-1 with Hubble's Advanced Camera for Surveys in April 2006.

The images of NGC 6357 were taken with Hubble's Wide Field and Planetary Camera 2 in April 2002.

Credit: NASA, ESA, and J. Maíz Apellániz (Instituto de Astrofísica de Andalucía, Spain)

Hubble Finds Evidence for Dark Energy in the Young Universe

Credit: NASA, ESA, and A. Riess (STScI)

Scientists using NASA's Hubble Space Telescope have discovered that dark energy is not a new constituent of space, but rather has been present for most of the universe's history.
Dark energy is a mysterious repulsive force that causes the universe to expand at an increasing rate. Investigators used Hubble to find that dark energy was already boosting the expansion rate of the universe as long as nine billion years ago.
This picture of dark energy is consistent with Albert Einstein's prediction of nearly a century ago that a repulsive form of gravity emanates from empty space.
Data from Hubble provides supporting evidence to help astrophysicists to understand the nature of dark energy.
This will allow them to begin ruling out some competing explanations that predict that the strength of dark energy changes over time.

Cassini stares into the eye of monster storm on Saturn

NASA NEWS RELEASE
Posted: November 9, 2006

NASA's Cassini spacecraft has seen something never before seen on another planet -- a hurricane-like storm at Saturn's South Pole with a well-developed eye, ringed by towering clouds.

Cassini stares deep into the swirling hurricane-like vortex at Saturn's south pole, where the vertical structure of the clouds is highlighted by shadows. Such a storm, with a well-developed eye ringed by towering clouds, is a phenomenon never before seen on another planet.

Credit: NASA/JPL/Space Science Institute

The "hurricane" spans a dark area inside a thick, brighter ring of clouds. It is approximately 5,000 miles across, or two thirds the diameter of Earth.

"It looks like a hurricane, but it doesn't behave like a hurricane," said Andrew Ingersoll, a member of Cassini's imaging team at the California Institute of Technology, Pasadena. "Whatever it is, we're going to focus on the eye of this storm and find out why it's there."

A movie taken by Cassini's camera over a three-hour period reveals winds around Saturn's South Pole blowing clockwise at 350 miles per hour. The camera also saw the shadow cast by a ring of towering clouds surrounding the pole, and two spiral arms of clouds extending from the central ring. These ring clouds, 20 to 45 miles above those in the center of the storm, are two to five times taller than the clouds of thunderstorms and hurricanes on Earth.

Eye-wall clouds are a distinguishing feature of hurricanes on Earth. They form where moist air flows inward across the ocean's surface, rising vertically and releasing a heavy rain around an interior circle of descending air that is the eye of the storm itself. Though it is uncertain whether such moist convection is driving Saturn's storm, the dark "eye" at the pole, the eye-wall clouds and the spiral arms together indicate a hurricane-like system.

These images of Saturn's south pole were taken by two different instruments on Cassini. The four monochrome images displayed here were acquired by the imaging science subsystem; the blue and red images in the bottom row were taken by the visual and infrared mapping spectrometer. The images are arranged in order of increasing wavelength in nanometers as follows: (top row) 460 nm, 752 nm, 728 nm; (bottom row) 890 nm, 2,800 nm, 5,000 nm.

Credit: NASA/JPL/Space Science Institute/University of Arizona

Distinctive eye-wall clouds have not been seen on any planet other than Earth. Even Jupiter's Great Red Spot, much larger than Saturn's polar storm, has no eye or eye-wall, and is relatively calm at the center.

This giant Saturnian storm is apparently different than hurricanes on Earth because it is locked to the pole and does not drift around like terrestrial hurricanes. Also, since Saturn is a gaseous planet, the storm forms without an ocean at its base.

In the Cassini imagery the eye looks dark at light wavelengths where methane gas absorbs the light and only the highest clouds are visible.

"The clear skies over the eye appear to extend down to a level about twice as deep as the usual cloud level observed on Saturn," said Kevin H. Baines, of Cassini's visual and infrared mapping spectrometer team at NASA's Jet Propulsion Laboratory, Pasadena, Calif. "This gives us the deepest view yet into Saturn over a wide range of wavelengths, and reveals a mysterious set of dark clouds at the bottom of the eye."
The Cassini data presented in this view appear to confirm a region of warm atmospheric descent into the eye of a hurricane-like storm locked to Saturn's south pole. The view shows temperature data from the Cassini spacecraft composite infrared spectrometer overlaid onto an image from the imaging science subsystem wide-angle camera.

Credit: NASA/JPL/Space Science Institute/GSFC

Infrared images taken by the Keck I telescope in Mauna Kea, Hawaii, had previously shown Saturn's South Pole to be warm. Cassini's composite infrared spectrometer has confirmed this with higher resolution temperature maps of the area. The spectrometer observed a temperature increase of about 4 degrees Fahrenheit at the pole. The instrument measured high temperatures in the upper troposphere and stratosphere, regions higher in the atmosphere than the clouds seen by the Cassini imaging instruments.

"The winds decrease with height, and the atmosphere is sinking, compressing and heating over the South Pole," said Richard Achterberg, a member of Cassini's composite infrared spectrometer team at NASA's Goddard Spaceflight Center, Greenbelt, Md.

Observations taken over the next few years, as the South Pole season changes from summer to fall, will help scientists understand the role seasons play in driving the dramatic meteorology at the south pole of Saturn.

The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. The Jet Propulsion Laboratory manages the Cassini-Huygens mission for NASA's Science Mission Directorate, Washington.

Light Echo from Star V838 Monocerotis

Credit: NASA, ESA, and H. Bond (STScI)

These are the most recent NASA Hubble Space Telescope views of an unusual phenomenon in space called a light echo. Light from a star that erupted nearly five years ago continues propagating outward through a cloud of dust surrounding the star. The light reflects or "echoes" off the dust and then travels to Earth.

Because of the extra distance the scattered light travels, it reaches the Earth long after the light from the stellar outburst itself. Therefore, a light echo is an analog of a sound echo produced, for example, when sound from an Alpine yodeler echoes off of the surrounding mountainsides.

The echo comes from the unusual variable star V838 Monocerotis (V838 Mon), located 20,000 light-years away on the periphery of our Galaxy. In early 2002, V838 Mon increased in brightness temporarily to become 600,000 times brighter than our Sun. The reason for the eruption is still unclear.

Hubble has been observing the V838 Mon light echo since 2002. Each new observation of the light echo reveals a new and unique "thin-section" through the interstellar dust around the star. The new images of the light echo were taken with Hubble's Advanced Camera for Surveys in November 2005 (left) and September 2006 (right). Particularly noticeable in the images are numerous whorls and eddies in the interstellar dust, which are possibly produced by effects of magnetic fields.

In the Shadow of Saturn

Credit: SSI, JPL, ESA, NASA

In the shadow of Saturn, unexpected wonders appear. The robotic Cassini spacecraft now orbiting Saturn recently drifted in giant planet's shadow for about 12 hours and looked back toward the eclipsed Sun. Cassini saw a view unlike any other. First, the night side of Saturn is seen to be partly lit by light reflected from its own majestic ring system. Next, the rings themselves appear dark when silhouetted against Saturn, but quite bright when viewed away from Saturn and slightly scattering sunlight, in the above exaggerated color image. Saturn's rings light up so much that new rings were discovered, although they are hard to see in the above image. Visible in spectacular detail, however, is Saturn's E ring, the ring created by the newly discovered ice-fountains of the moon Enceladus, and the outermost ring visible above. Far in the distance, visible on the image left just above the bright main rings, is the almost ignorable pale blue dot of Earth.

Markarian's Chain of Galaxies

Across the heart of the Virgo Cluster of Galaxies lies a striking string of galaxies known as Markarian's Chain. The chain, pictured above, is highlighted on the lower right with two large but featureless lenticular galaxies, M84 and M86, and connects through several large spiral to the upper left, including M88. The home Virgo Cluster is the nearest cluster of galaxies, contains over 2,000 galaxies, and has a noticeable gravitational pull on the galaxies of the Local Group of Galaxies surrounding our Milky Way Galaxy. The center of the Virgo Cluster is located about 70 million light years away toward the constellation of Virgo. At least seven galaxies in the chain appear to move coherently, although others appear to be superposed by chance. The above image is just a small part of a mosaic dubbed the Big Picture taken by the Samuel Oschin Telescope at Palomar Observatory, in California, USA. A mural of the Big Picture will be displayed at the newly renovated Griffith Observatory near Los Angeles, California.

Credit & Copyright: The Palomar-Quest Survey Team, CalTech

Hubble Exoplanet Search Field in Sagittarius

This is an image of one-half of the Hubble Space Telescope field of view in the Sagittarius Window Eclipsing Extrasolar Planet Search (SWEEPS). The field contains approximately 150,000 stars, down to 30th magnitude. The stars in the Galactic disk and bulge have a mixture of colors and masses. The field is so crowded with stars because Hubble was looking across 26,000 light-years of space in the direction of the center of our galaxy.

Half of these stars are bright enough for Hubble to monitor for any small, brief and periodic dips in brightness caused by the passage of an exoplanet passing in front of the star, an event called a transit. Hubble took approximately 520 pictures of this field, at red and blue wavelengths, from Feb. 22-29, 2004. The green circles identify 9 stars that are orbited by planets with periods of a few days. Planets so close to their stars with such short orbital periods are called "hot Jupiters."

These are considered "candidate" exoplanets because most of them are too faint to allow for spectroscopic observations that would allow for a precise measure of the planet's mass. The Hubble observations allow for a robust statistical estimate of the possible "false positives," which suggests that at least 45 percent of the candidates must be genuine planets.

The bottom frame identifies one of two stars in the field where astronomers were able to spectroscopically measure the star's back-and-forth wobble due to the pull of the planet. The planet turns out to be less than 3.8 Jupiter masses.

The members of the SWEEPS science team are Kailash C. Sahu, Stefano Casertano, Howard E. Bond, Jeff Valenti, T. Ed Smith, Mario Livio, Nino Panagia, Thomas M. Brown, Will Clarkson and Stephen Lubow (Space Telescope Science Institute), Dante Minniti and Manuela Zoccali (Universidad Catolica de Chile), Nikolai Piskunov (Uppsala University), Timothy Brown (High Altitude Observatory), Alvio Renzini (INAF-Osservatorio Astronomico di Padova), and R. Michael Rich (University of California at Los Angeles).

Credit: NASA, ESA, K. Sahu (STScI) and the SWEEPS Science Team

Distant Galaxies in the Hubble Ultra Deep Field

Credit: NASA, ESA,R. Bouwens and G. Illingworth (University of California, Santa Cruz)

This Hubble Space Telescope image shows 28 of the more than 500 young galaxies that existed when the universe was less than 1 billion years old. The galaxies were uncovered in a study of two of the most distant surveys of the cosmos, the Hubble Ultra Deep Field (HUDF), completed in 2004, and the Great Observatories Origins Deep Survey (GOODS), made in 2003.

Just a few years ago, astronomers had not spotted any galaxies that existed significantly less than 1 billion years after the Big Bang. The galaxies spied in the HUDF and GOODS surveys are blue galaxies brimming with star birth.

The large image at left shows the Hubble Ultra Deep Field, taken by the Hubble telescope. The numbers next to the small boxes correspond to close-up views of 28 of the newly found galaxies at right. The galaxies in the postage-stamp size images appear red because of their tremendous distance from Earth. The blue light from their young stars took nearly 13 billion years to arrive at Earth. During the journey, the blue light was shifted to red light due to the expansion of space.

Visible-Light and X-Ray Composite Image of Galaxy Cluster 1E 0657-556

Credit: X-ray: NASA/CXC/M.Markevitch et al. Optical: NASA/STScI; Magellan/U.Arizona/D.Clowe et al. Lensing Map: NASA/STScI; ESO WFI; Magellan/U.Arizona/D.Clowe et al.

This composite image shows the galaxy cluster 1E 0657-556, also known as the "bullet cluster." This cluster was formed after the collision of two large clusters of galaxies, the most energetic event known in the universe since the Big Bang.

Hot gas detected by Chandra in X-rays is seen as two pink clumps in the image and contains most of the "normal," or baryonic, matter in the two clusters. The bullet-shaped clump on the right is the hot gas from one cluster, which passed through the hot gas from the other larger cluster during the collision. An optical image from Magellan and the Hubble Space Telescope shows the galaxies in orange and white. The blue areas in this image depict where astronomers find most of the mass in the clusters. The concentration of mass is determined by analyzing the effect of so-called gravitational lensing, where light from the distant objects is distorted by intervening matter. Most of the matter in the clusters (blue) is clearly separate from the normal matter (pink), giving direct evidence that nearly all of the matter in the clusters is dark.

The hot gas in each cluster was slowed by a drag force, similar to air resistance, during the collision. In contrast, the dark matter was not slowed by the impact because it does not interact directly with itself or the gas except through gravity. Therefore, during the collision the dark matter clumps from the two clusters moved ahead of the hot gas, producing the separation of the dark and normal matter seen in the image. If hot gas was the most massive component in the clusters, as proposed by alternative theories of gravity, such an effect would not be seen. Instead, this result shows that dark matter is required.

Comparing the optical image with the blue emission shows that the most of the galaxies in each cluster are located near the two dark matter clumps. This shows that the galaxies in each cluster did not slow down because of the collision, unlike the hot gas.

N 180B - Large Magellanic Cloud

Credit: NASA ESA, and the Hubble Heritag Team (STScI/AURA)

This active region of star formation in the Large Magellanic Cloud (LMC), as photographed by NASA's Hubble Space Telescope, unveils wispy clouds of hydrogen and oxygen that swirl and mix with dust on a canvas of astronomical size. The LMC is a satellite galaxy of the Milky Way.

This particular region within the LMC, referred to as N 180B, contains some of the brightest known star clusters. The hottest blue stars can be brighter than a million of our Suns. Their intense energy output generates not only harsh ultraviolet radiation but also incredibly strong stellar "winds" of high-speed, charged particles that blow into space. The ultraviolet radiation ionizes the interstellar gas and makes it glow, while the winds can disperse the interstellar gas across tens or hundreds of light-years. Both actions are evident in N 180B.

Also visible etched against the glowing hydrogen and oxygen gases are 100 light-year-long dust streamers that run the length of the nebula, intersecting the core of the cluster near the center of the image. Perpendicular to the direction of the dark streamers, bright orange rims of compact dust clouds appear near the bottom right of and top left corners of the image. These dark concentrations are on the order of a few light-years in size. Also visible among the dust clouds are so-called "elephant trunk" stalks of dust. If the pressure from the nearby stellar winds is great enough to compress this material and cause it to gravitationally contract, star formation might be triggered in these small dust clouds. These dust clouds are evidence that this is still a young star-formation region.

This image was taken with Hubble's Wide Field Planetary Camera 2 in 1998 using filters that isolate light emitted by hydrogen and oxygen gas. To create a color composite, the data from the hydrogen filter were colorized red, the oxygen filter were colorized blue, and a combination of the two filters averaged together was colorized green. The amalgamation yields pink and orange hydrogen clouds set amid a field of soft blue oxygen gas. Dense dust clouds block starlight and glowing gas from our view point.

Orion's Inner Beauty

Credit: NASA/JPL-Caltech/ T. Megeath (University of Toledo)

This infrared image from NASA's Spitzer Space Telescope shows the Orion nebula, our closest massive star-making factory, 1,450 light-years from Earth. The nebula is close enough to appear to the naked eye as a fuzzy star in the sword of the popular hunter constellation.

The nebula itself is located on the lower half of the image, surrounded by a ring of dust. It formed in a cold cloud of gas and dust and contains about 1,000 young stars. These stars illuminate the cloud, creating the beautiful nebulosity, or swirls of material, seen here in infrared.

This image shows infrared light captured by Spitzer's infrared array camera. Light with wavelengths of 8 and 5.8 microns (red and orange) comes mainly from dust that has been heated by starlight. Light of 4.5 microns (green) shows hot gas and dust; and light of 3.6 microns (blue) is from starlight.

NGC 2392 - Eskimo Nebula

Credit: Andrew Fruchter (STScI) et al., WFPC2, HST, NASA

In 1787, astronomer William Herschel discovered the Eskimo Nebula. From the ground, NGC 2392 resembles a person's head surrounded by a parka hood. In 2000, the Hubble Space Telescope imaged the Eskimo Nebula. From space, the nebula displays gas clouds so complex they are not fully understood. The Eskimo Nebula is clearly a planetary nebula, and the gas seen above composed the outer layers of a Sun-like star only 10,000 years ago. The inner filaments visible above are being ejected by strong wind of particles from the central star. The outer disk contains unusual light-year long orange filaments.