Red and Dead Elliptical Galaxies

Elliptical Galaxies: Four elliptical galaxies with very low levels of star formation.

This four-panel of images represents a sample of giant elliptical galaxies observed by Chandra and the Hershel Space Observatory in a study to investigate why these objects have such low levels of star formation. In six galaxies, Herschel detected surprisingly large amounts of cold gas – the fuel for star formation. Chandra revealed that the hot gas in the center of these galaxies appears to be much more disturbed than in the cold gas-free systems. This is a sign that material has been ejected from regions close to the central black hole. The energy from these outbursts helps to prevent the cold gas from cooling sufficiently to form stars. In two other galaxies, jets pushing against the hot gas are creating enormous cavities that are observed in the Chandra images. These jets may be heating the hot, X-ray emitting gas, preventing it from cooling and forming cold gas and stars.

Image credit: X-ray: NASA/CXC/Stanford University/N.Werner et al; Optical: DSS

Note: For more information, see Elliptical Galaxies: Chandra Helps Explain "Red and Dead Galaxies".

Artist's Conception of Cassini Observing Sunsets on Titan

Using data collected by Cassini's Visual and Infrared Mapping Spectrometer, or VIMS, while observing Titan's sunsets, researchers created simulated spectra of Titan as if it were a planet transiting across the face of a distant star. The research helps scientists to better understand observations of exoplanets with hazy atmospheres.

Image Credit: NASA/JPL-Caltech

Note: For more information, see Sunsets on Titan Reveal the Complexity of Hazy Exoplanets.

Young Stellar Objects in the Serpens Cloud Core

Within the swaddling dust of the Serpens Cloud Core, astronomers are studying one of the youngest collections of stars ever seen in our galaxy. This infrared image combines data from NASA's Spitzer Space Telescope with shorter-wavelength observations from the Two Micron All Sky Survey (2MASS), letting us peer into the clouds of dust wrapped around this stellar nursery.

At a distance of around 750 light-years, these young stars reside within the confines of the constellation Serpens, or the "Serpent." This collection contains stars of only relatively low to moderate mass, lacking any of the massive and incredibly bright stars found in larger star-forming regions like the Orion nebula. Our sun is a star of moderate mass. Whether it formed in a low-mass stellar region like Serpens, or a high-mass stellar region like Orion, is an ongoing mystery.

The stellar "hatchlings" in the Serpens Cloud Core represent the very youngest stages of stellar development. They appear as red, orange and yellow points clustered near the center of the image. Other red features include jets of material ejected from these young stars. Some mature stars that are not in the nebula appear yellowish due to dust obscuring our view at shorter, bluer wavelengths.

This region also includes a population of prenatal stars that are so deeply enshrouded in their dusty cocoons to be completely hidden in this view. They only become detectable at much longer wavelengths of light.

The inner Serpens Cloud Core is remarkably detailed in this image, as it was assembled from 82 separate snapshots totaling a whopping 16.2 hours of Spitzer observing time. Serpens is one of several star-forming regions targeted by the Young Stellar Object Variability (YSOVAR) project, which conducted repeated observations in each area to look for changes in brightness in the baby stars. Such fluctuations can provide valuable clues to how stars gobble up gas and dust as they grow and mature.

Spitzer observations at wavelengths of 3.5 and 4.6 microns are shown in green and red, respectively. 2MASS data at 1.3 microns is displayed as blue. These observations date from Spitzer's warm mission phase, following the depletion of its liquid coolant in 2009.

Image credit: NASA/JPL-Caltech/2MASS

Note: For more information, see The 'Serpent' Star-forming Cloud Hatches New Stars.

Black Holes and Dark Matter in the Fornax Galactic Cluster

Active, supermassive black holes at the hearts of galaxies tend to fall into two categories: those that are hidden by dust, and those that are exposed. Data from NASA's Wide-field Infrared Survey Explorer, or WISE, have shown that galaxies with hidden supermassive black holes tend to clump together in space more than the galaxies with exposed, or unobscured, black holes.

This enhanced image shows galaxies clumped together in the Fornax cluster, located 60 million light-years from Earth. The picture was taken by WISE, but has been artistically enhanced to illustrate the idea that clumped galaxies will, on average, be surrounded by larger halos of dark matter (represented in purple). Because dark matter, like normal matter, has gravity, it will pull galaxies toward it, causing them to clump.

Astronomers don't know why the hidden black holes would have larger halos of dark matter, but are intrigued by the surprising finding and are investigating further.

Image credit: NASA/JPL-Caltech

Note: For more information, see PIA18013: Unified, or 'Doughnut,' Theory of Active, Black Holes and NASA's WISE Findings Poke Hole in Black Hole 'Doughnut' Theory.

Fresh Impact Crater Northeast of Gordii Dorsum on Mars

On 20 March 2014, a dark spot on the surface of Mars, about 5 miles (8 kilometers) in diameter was seen for the first time in low-resolution (approximately 1 kilometer) imaging from the Mars Color Imager (MARCI) camera on Mars Reconnaissance Orbiter (MRO). Because MARCI sees essentially the whole planet every day, the sudden appearance of a dark spot was of note.

To follow up, the Context Camera (CTX) obtained a high resolution picture of the area in question in early April. Before and after imaging revealed two new large impact craters within the blast zone. At 6 meters per pixel, CTX can detect the dark blast locations but usually cannot resolve the crater that formed the blast, because most fresh impact craters are only a few meters across.

This is where the high resolution of HiRISE comes in: our camera was able to show the fine surface details within the blast zone. The largest of the new craters, appears slightly asymmetric in shape, and measures 159 x 143 feet (48.5 x 43.5 meters) in diameter, making it the largest new crater detected on Mars by MRO to date. Both HiRISE and CTX images also show numerous, new, small landslides within the blast zone.

All of these coordinated observations also demonstrate how different teams on the same spacecraft can work together to examine interesting features in greater detail.

Note: a newer image of this area, is also available and has an anaglyph.

Image credit: NASA/JPL/University of Arizona

Note: This impact crater is located just to the northeast of Gordii Dorsum. For more information, see PIA18380: Impact Scar Detected in Mars Weathercam Image, PIA18381: Best-Ever Pinning Down When a Space Rock Hit Mars, PIA18382: Fresh Mars Crater Confirmed Within Impact Scar, PIA18383: Before-and-After Views Confirm Fresh Craters, PIA18384: Large, Fresh Crater Surrounded by Smaller Craters, PIA18385: Landslides Near Fresh Crater on Mars, and NASA Mars Weathercam Helps Find Big New Crater.

Mapping the Densest Dusty Cloud Cores

Astronomers have found cosmic clumps so dark, dense and dusty that they throw the deepest shadows ever recorded. The clumps were discovered within a huge cosmic cloud of gas and dust. Infrared observations from NASA's Spitzer Space Telescope of these blackest-of-black regions in the cloud paradoxically light the way to understanding how the brightest stars form.

The large cloud looms in the center of this image of the galactic plane from Spitzer. The zoom in Figure 1 shows details of the cloud, revealing the dense clumps. A new study takes advantage of the shadows cast by these dark clumps to measure the cloud's overall structure and mass. These dense, clumpy pockets of star-forming material within the cloud are so thick with dust that they scatter and block not only visible light, but almost all background infrared light as well.

The dusty cloud, the results suggest, will likely evolve into one of the most massive young clusters of stars in our galaxy. The densest clumps will blossom into the cluster's biggest, most powerful stars, called O-type stars, the formation of which has long puzzled scientists. These hulking stars have major impacts on their local stellar environments while also helping to create the heavy elements needed for life.

Figure 2 reveals the overall darkness of the cloud, calculated using Spitzer's infrared observations at a wavelength of 8 microns. Artifacts left by individual stars have been removed from the data.

The background image combines data from Spitzer surveys. Blue represents 3.6-micron light and green shows light of 8 microns, both captured by Spitzer's infrared array camera. Red is 24-micron light detected by Spitzer's multiband imaging photometer. The red spot in the center of the zoom oval, unrelated to the new study's findings, is a young star whose radiating heat has lit up a surrounding cocoon of dust.

Image credit: NASA/JPL-Caltech/University of Zurich

Note: For more information, see Pitch Black: Cosmic Clumps Cast the Darkest Shadows.

NGC 3590

This colorful new image from the MPG/ESO 2.2-meter telescope at ESO's La Silla Observatory in Chile shows the star cluster NGC 3590. These stars shine brightly in front of a dramatic landscape of dark patches of dust and richly hued clouds of glowing gas. This small stellar gathering gives astronomers clues about how these stars form and evolve — as well as giving hints about the structure of our galaxy's pinwheeling arms.

Photo credit: ESO/G. Beccari

Note: For more information, see A Star Cluster in the Wake of Carina.

Endeavour Crater Rim from Murray Ridge

This vista of the Endeavour Crater rim was acquired by NASA's Mars Exploration Rover Opportunity from the southern end of "Murray Ridge" on the western rim of the crater. It combines several exposures taken by the rover's panoramic camera (Pancam) on the 3,637th Martian day, or sol, of the mission (April 18, 2014).

The view extends from the east-southeast on the left to southward on the right. It encompasses the far rim of Endeavour Crater on the left and the crater's western rim on the right. Endeavour is 14 miles (22 kilometers) in diameter.

The small impact crater visible in the distance on the slopes of the far rim is about 740 feet (about 225 meters) in diameter and is 13 miles (21 kilometers) away. The high peak in the distance on the right is informally named "Cape Tribulation" and is about 1.2 miles (2 kilometers) to the south of Opportunity's position when this view was recorded. The rim curves off to the left from Cape Tribulation in a series of peaks towards the far southern crater rim.

The floor of Endeavour crater is filled with dark sand, brighter dust, and, in the distance, dusty haze. Outcrops here on the western rim are crater ejecta covered in the foreground by dark sand ripples. On Sol 3662 (May 13, 2014), Opportunity approached the dark outcrops about halfway down on the right side of the image.

The view merges exposures taken through three of the Pancam's color filters, centered on wavelengths of 753 nanometers (near-infrared), 535 nanometers (green) and 432 nanometers (violet). It is presented in approximately true color.

Image credit: NASA/JPL-Caltech/Cornell University/Arizona State University

Note: For more information, see PIA18094: Endeavour Crater Rim From 'Murray Ridge' on Mars, False Color, PIA18095: Approaching a Target Deposit on Mars Crater Rim, PIA18096: Approaching a Target Deposit on Mars Crater Rim (Stereo), PIA18098: Opportunity's Tracks Near Crater Rim Ridgeline, PIA18099: Opportunity's Tracks Near Crater Rim Ridgeline (Stereo), and NASA Rover Gains Martian Vista From Ridgeline.

Auroras on Saturn

Astronomers using the NASA/ESA Hubble Space Telescope have captured new images of the dancing auroral lights at Saturn’s north pole. Taken in April and May 2013 from Hubble’s perspective in orbit around Earth, these observations provide a detailed look at previously unseen dynamics in the choreography of the auroral glow.

The ultraviolet images, taken by Hubble’s super-sensitive Advanced Camera for Surveys, capture moments when Saturn’s magnetic field is affected by bursts of particles streaming from the Sun.

Saturn’s magnetosphere – the vast magnetic ‘bubble’ that surrounds the planet – is compressed on the Sunward side of the planet, and streams out into a long ‘magnetotail’ on the nightside.

It appears that when particles from the Sun hit Saturn, the magnetotail collapses and later reconfigures itself, an event that is reflected in the dynamics of its auroras.

Saturn was caught during a very dynamic light show – some of the bursts of light seen shooting around Saturn’s polar regions traveled more than three times faster than the speed of the gas giant’s roughly 10-hour rotation period!

The new observations were taken as part of a three-year Hubble observing campaign, and are presented in a paper published in the journal Geophysical Research Letters. The images complement those taken by the international Cassini spacecraft orbiting Saturn.

Image credit: NASA/ESA, Acknowledgement: J. Nichols (University of Leicester)

Comet 67P Churyumov–Gerasimenko and M107

Comet 67P/Churyumov–Gerasimenko seen towards the constellation of Ophiuchus (note that from the vantage point of Earth, both the comet and Rosetta are presently in Sagittarius), with the globular cluster M107 also clearly visible in the field of view. The image was taken on 30 April 2014 by the OSIRIS Narrow Angle Camera and the comet is already displaying a coma, which extends over 1300 km from the nucleus.

Image credit: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA

Note: For more information, see PIA18376: Rosetta's Comet Comes Alive, Rosetta Puts on the Brakes, Comet 67P/C-G on 30 April 2014, Rosetta's Target Comet is Becoming Active, and Rosetta Comet Comes Alive (NASA Science News).

Jupiter and Its Not-So-Great Red Spot

Jupiter's Great Red Spot is a churning anticyclonic storm. It shows up in images of the giant planet as a conspicuous deep red eye embedded in swirling layers of pale yellow, orange and white. Winds inside this Jovian storm rage at immense speeds, reaching several hundreds of kilometers per hour.

Historic observations as far back as the late 1800s gauged this turbulent spot to span about 41 000 kilometers at its widest point – wide enough to fit three Earths comfortably side by side. In 1979 and 1980 the NASA Voyager fly-bys measured the spot at a shrunken 23,335 kilometers across. Now, Hubble has spied this feature to be smaller than ever before.

This full-disc image of Jupiter was taken on 21 April 2014 with Hubble's Wide Field Camera 3 (WFC3).

Image credit: NASA, ESA, and A. Simon (Goddard Space Flight Center)

Note: For more information, see The Shrinking of Jupiter's Great Red Spot, Jupiter's Great Red Spot is Smaller Than Ever Measured, and Jupiter's Great Red Spot is Shrinking.

Artist’s Impression of the Magnetar in the Star Cluster Westerlund 1

This artist’s impression shows the magnetar in the very rich and young star cluster Westerlund 1. This remarkable cluster contains hundreds of very massive stars, some shining with a brilliance of almost one million suns. European astronomers have for the first time demonstrated that this magnetar — an unusual type of neutron star with an extremely strong magnetic field — probably was formed as part of a binary star system. The discovery of the magnetar’s former companion elsewhere in the cluster helps solve the mystery of how a star that started off so massive could become a magnetar, rather than collapse into a black hole.

Illustration credit: ESO/L. Calçada

Note: For more information, see Magnetar Formation Mystery Solved?

Saturn Ring Spokes

The spokes in Saturn's rings continue to be active and Cassini scientists continue to study them in order to unravel their mysteries. The spokes, visible near the center of the image, appear bright against the dense core of the B ring, which is the darkest section of the rings shown here in silhouette. Conditions favorable to the production of spokes are expected to wane as Saturn approaches its northern summer solstice. Scientists are eager to monitor the transition, the timing of which could yield valuable insight into the mechanisms that form these intriguing and ethereal features.

This view looks toward the unilluminated side of the rings from about 47 degrees below the ringplane. The image was taken in visible light with the Cassini spacecraft wide-angle camera on October 19, 2013.

The view was acquired at a distance of approximately 1.2 million miles (1.9 million kilometers) from Saturn and at a Sun-Saturn-spacecraft, or phase, angle of 122 degrees. Image scale is 72 miles (115 kilometers) per pixel.

Image credit: NASA/JPL-Caltech/Space Science Institute

Phobos and Jupiter Conjunction

Even though it may only be a lump of porous rock, Phobos isn’t shy about hogging the limelight in this sequence taken by ESA’s Mars Express. These three images show Phobos, the larger of the two Martian moons, darting across the frame in front of Jupiter, visible as the pale dot in the center. From right to left, the frames show snapshots before, during and after the small moon’s journey in front of the gas giant.

Observed on 1 June 2011, this unusual alignment is known as a conjunction, and occurs when two Solar System bodies appear to pass close to one another on the sky. This is an optical illusion caused by our perspective–when these pictures were taken there was a distance of almost 11,400 km between the spacecraft and Phobos, and a further 529 million km to Jupiter.

These three frames are part of a set of 104 taken over a period of 68 seconds by the high-resolution stereo camera on Mars Express. Some of the images were also processed to form a video. The images and the video were originally released in June 2011.

Image credit: ESA/DLR/FU Berlin (G. Neukum)

Partial Eclipses of the Sun by Proba-2

ESA's Proba-2 Sun-watcher saw Australia's 29 April 2014 partial solar eclipse from orbit - footage captured by the Royal Observatory of Belgium.

Video credit: ESA

Star Cluster NGC 2024 in the Flame Nebula

Stars are often born in clusters or groups, in giant clouds of gas and dust. Astronomers have studied two star clusters using NASA's Chandra X-ray Observatory and infrared telescopes and the results show that the simplest ideas for the birth of these clusters cannot work.

This composite image shows one of the clusters, NGC 2024, which is found in the center of the so-called Flame Nebula about 1,400 light years from Earth. In this image, X-rays from Chandra are seen as purple, while infrared data from NASA's Spitzer Space Telescope are colored red, green and blue.

A study of NGC 2024 and the Orion Nebula Cluster, another region where many stars are forming, suggest that the stars on the outskirts of these clusters are older than those in the central regions. This is different from what the simplest idea of star formation predicts, where stars are born first in the center of a collapsing cloud of gas and dust when the density is large enough.

The research team developed a two-step process to make this discovery. First, they used Chandra data on the brightness of the stars in X-rays to determine their masses. Next, they found out how bright these stars were in infrared light using data from Spitzer, the 2MASS telescope and the United Kingdom Infrared Telescope. By combining this information with theoretical models, the ages of the stars throughout the two clusters could be estimated.

According to the new results, the stars at the center of NGC 2024 were about 200,000 years old while those on the outskirts were about 1.5 million years in age. In Orion, the age spread went from 1.2 million years in the middle of the cluster to nearly 2 million years for the stars toward the edges.

Explanations for the new findings can be grouped into three broad categories. The first is that star formation is continuing to occur in the inner regions. This could have happened because the gas in the outer regions of a star-forming cloud is thinner and more diffuse than in the inner regions. Over time, if the density falls below a threshold value where it can no longer collapse to form stars, star formation will cease in the outer regions, whereas stars will continue to form in the inner regions, leading to a concentration of younger stars there.

Another suggestion is that old stars have had more time to drift away from the center of the cluster, or be kicked outward by interactions with other stars. Finally, the observations could be explained if young stars are formed in massive filaments of gas that fall toward the center of the cluster.

These results will be published in two separate papers in The Astrophysical Journal and are available online (papers 1 and 2). They are part of the MYStIX (Massive Young Star-Forming Complex Study in Infrared and X-ray) project led by Penn State astronomers.

Image credit: X-ray: NASA/CXC/PSU/K.Getman, E.Feigelson, M.Kuhn and the MYStIX team; Infrared: NASA/JPL-Caltech

Note: For more information, see NASA Delivers New Insight into Star Cluster Formation and Flame Nebula: NASA's Chandra Delivers New Insight into Formation of Star Clusters.

The Milky Way's Magnetic Field and Dust Polarization

The magnetic field of our Milky Way Galaxy as seen by ESA's Planck satellite. This image was compiled from the first all-sky observations of polarized light emitted by interstellar dust in the Milky Way. The magnetic field is displayed using a visualization technique called line integral convolution (LIC).

Darker regions correspond to stronger polarized emission, and the striations indicate the direction of the magnetic field projected on the plane of the sky. The dark band running horizontally across the center corresponds to the Galactic Plane. Here, the polarization reveals a regular pattern on large angular scales, which is due to the magnetic field lines being predominantly parallel to the plane of the Milky Way. The data also reveal variations of the polarization direction within nearby clouds of gas and dust. This can be seen in the tangled features above and below the plane, where the local magnetic field is particularly disorganized.

The image is a Mollweide projection of the full celestial sphere, with the plane of the Galaxy aligned with the horizontal axis of the oval. Certain areas in the image, mostly at high Galactic latitude, have been masked out. The overall intensity in these regions is low, complicating the separation of foreground and CMB components. Further data analysis will improve this by the time of the full data release in late 2014.

Image credit: ESA and the Planck Collaboration

Note: For more information, see Planck Takes Magnetic Fingerprint of Our Galaxy, Milky Way's Magnetic Fingerprint, PIA18048: Magnetic Map of Milky Way and Planck Takes Magnetic Fingerprint of Our Galaxy.

Ganymede's Possible Internal Structure

This artist's concept of Jupiter's moon Ganymede, the largest moon in the solar system, illustrates the "club sandwich" model of its interior oceans. Scientists suspect Ganymede has a massive ocean under an icy crust. In fact, Ganymede's oceans may have 25 times the volume of those on Earth. Previous models of the moon showed the moon's ocean sandwiched between a top and bottom later of ice. A new model, based on experiments in the laboratory that simulate salty seas, shows that the ocean and ice may be stacked up in multiple layers, more like a club sandwich.

Ice comes in different forms depending on pressures. "Ice I," the least dense form of ice, is what floats in your chilled beverages. As pressures increase, ice molecules become more tightly packed and thus more dense. Because Ganymede's oceans are up to 500 miles (800 kilometers) deep, they would experience more pressure than Earth's oceans. The deepest and most dense form of ice thought to exist on Ganymede is called "Ice VI."

When researchers added in salt into their models of the ocean, they found the situation changed from what was previously thought. With enough salt, liquid in Ganymede can become dense enough to sink to the very bottom of the seafloor, below Ice VI. Their models also suggest a complex stacking of ocean and ice, as illustrated in the picture.

What's more, the model shows that a strange phenomenon might occur in the uppermost liquid layer, where ice floats upward. In this scenario, cold plumes cause Ice III to form. As the ice forms, salt precipitates out. The salt then sinks down while the ice "snows" upward. Eventually, this ice would melt, resulting in a slushy layer in Ganymede's club sandwich structure.

Scientists say this structure may not be stable. It's possible the moon goes through a club sandwich phase, while at other times goes back to being more like a regular sandwich, with one ocean sitting below the familiar Ice I found on Earth and on top of different high-pressure ices.

The fact that salty water may persist at the bottom of the rocky seafloor, rather than ice, is favorable for the development of life. Researchers think life emerges through a series of chemical interactions at water-mineral interfaces, so a wet seafloor on Ganymede might be a key ingredient for life there.

Illustration credit: NASA/JPL-Caltech

Note: For more information, see Ganymede May Harbor 'Club Sandwich' of Oceans and Ice.

Uranus from Saturn

This view from NASA's Cassini spacecraft features a blue planet, but unlike the view from July 19, 2013 (PIA17172) that featured our home planet, this blue orb is Uranus, imaged by Cassini for the first time.

Uranus is a pale blue in this natural color image because its visible atmosphere contains methane gas and few aerosols or clouds. Methane on Uranus -- and its sapphire-colored sibling, Neptune -- absorbs red wavelengths of incoming sunlight, but allows blue wavelengths to escape back into space, resulting in the predominantly bluish color seen here. Cassini imaging scientists combined red, green and blue spectral filter images to create a final image that represents what human eyes might see from the vantage point of the spacecraft.

Uranus has been brightened by a factor of 4.5 to make it more easily visible. The outer portion of Saturn's A ring, seen at bottom right, has been brightened by a factor of two. The bright ring cutting across the image center is Saturn's narrow F ring.

Uranus was approximately 28.6 astronomical units from Cassini and Saturn when this view was obtained. An astronomical unit is the average distance from Earth to the sun, equal to 93,000,000 miles (150,000,000 kilometers).

This view was acquired by the Cassini narrow-angle camera at a distance of approximately 614,300 miles (988,600 kilometers) from Saturn on April 11, 2014. Image scale at Uranus is approximately 16,000 miles (25,700 kilometers) per pixel. Image scale at Saturn's rings is approximately 4 miles (6 kilometers) per pixel. In the image, the disk of Uranus is just barely resolved. The solar phase angle at Uranus, seen from Cassini, is 11.9 degrees.

Image credit: NASA/JPL-Caltech/Space Science Institute

Note: For more information, see Cassini Spies the Ice-Giant Planet Uranus.

Saturn's C and B Rings in Ultraviolet Light

This colorful cosmic rainbow portrays a section of Saturn’s beautiful rings, four centuries after they were discovered by Galileo Galilei.

Saturn’s rings were first observed in 1610. Despite using his newly created telescope, Galileo was confounded by what he saw: he referred to the peculiar shapes surrounding the planet as “Saturn’s children”. Only later did Christiaan Huygens propose that the mysterious shapes were actually rings orbiting the planet. These were named in the order in which they were discovered, using the first seven letters of the alphabet: the D-ring is closest to the planet, followed by C, B, A, F, G and E.

The data for this image, which shows the portion of the C-ring closest to Saturn on the left, with the B-ring beginning just right of center, were acquired by Cassini’s Ultraviolet Imaging Spectrograph, or UVIS, as the spacecraft entered into orbit around Saturn on 30 June 2004.

UVIS, as its name suggests, carries out observations in ultraviolet wavelengths. During the Saturn orbit insertion maneuver, when Cassini flew closest to the rings, UVIS could resolve features up to 97 km across. The region shown in this image spans about 10,000 km.

The variation in the color of the rings arises from the differences in their composition. Turquoise-hued rings contain particles of nearly pure water ice, whereas reddish rings contain ice particles with more contaminants.

Saturn’s prominent and complex ensemble of rings is the best studied in the Solar System, but it is still not known how the rings formed. One suggestion is that they formed at the same time as the planet and that they are as old as the Solar System. Another idea is that they formed when icy material was pulled from another body into Saturn’s gravitational field, in which case the rings could be younger than the planet.

One thing is sure: as Cassini searches for answers it is providing amazing images of these rainbow rings.

The Cassini–Huygens mission is a cooperative project of NASA, ESA and Italy’s ASI space agency.

This image was first published at the NASA Cassini website, in 2004.

Image credit: NASA/JPL/University of Colorado

Caracalla Supernova in Galactic Cluster MACSJ1720+35

The heart of a vast cluster of galaxies called MACSJ1720+35 is shown in this image, taken in visible and near-infrared light by the NASA/ESA Hubble Space Telescope.

The galaxy cluster is so massive that its gravity distorts, brightens, and magnifies light from more distant objects behind it, an effect called gravitational lensing. In the top right an exploding star, located behind the cluster can just be made out. It is cataloged as SCP/SN-L2 and nicknamed Caracalla.

The supernova is a member of a special class of exploding star called Type Ia, prized by astronomers because it provides a consistent level of peak brightness that makes it reliable for making distance estimates.

Finding a gravitationally lensed Type Ia supernova gives astronomers a unique opportunity to check the optical "prescription" of the foreground lensing cluster. The supernova is one of three exploding stars discovered in the Cluster Lensing And Supernova survey with Hubble (CLASH), and was followed up as part of a Supernova Cosmology Project HST program. CLASH is a Hubble census that probed the distribution of dark matter in 25 galaxy clusters. Dark matter cannot be seen directly but is believed to make up most of the universe's matter.

The image of the galaxy cluster was taken between March and July 2012 by Hubble's Wide Field Camera 3 and Advanced Camera for Surveys.

Image credit: (top) NASA, ESA, S. Perlmutter (UC Berkeley, LBNL), A. Koekemoer (STScI), M. Postman (STScI), A. Riess (STScI/JHU), J. Nordin (LBNL, UC Berkeley), D. Rubin (Florida State), and C. McCully (Rutgers University); (bottom) NASA, ESA, S. Perlmutter (UC Berkeley, LBNL), A. Koekemoer (STScI), M. Postman (STScI), A. Riess (STScI/JHU), J. Nordin (LBNL, UC Berkeley), D. Rubin (Florida State), and C. McCully (Rutgers University)

Note: For more information, see Cosmic Lens MACS J1720+35 Helps Hubble to Find a Distant Supernova.

Star Cluster LH63 in Emission Nebula LHA 120-N51

This stunning new Hubble image shows a small part of the Large Magellanic Cloud, one of the closest galaxies to our own. This collection of small baby stars, most weighing less than the Sun, form a young stellar cluster known as LH63. This cluster is still half-embedded in the cloud from which it was born, in a bright star-forming region known as the emission nebula LHA 120-N 51, or N51. This is just one of the hundreds of star-forming regions filled with young stars spread throughout the Large Magellanic Cloud.

The burning red intensity of the nebulae at the bottom of the picture illuminates wisps of gas and dark dust, each spanning many light-years. Moving up and across, bright stars become visible as sparse specks of light, giving the impression of pin-pricks in a cosmic cloak.

This patch of sky was the subject of observation by Hubble's WFPC2 camera. Looking for and at low-mass stars can help us to understand how stars behave when they are in the early stages of formation, and can give us an idea of how the Sun might have looked billions of years ago.

Image credit: NASA, ESA, and D. Gouliermis (University of Heidelberg)

NGC 3455

Shown here is a spiral galaxy known as NGC 3455, which lies some 65 million light-years away from us in the constellation of Leo (The Lion). Galaxies are classified into different types according to their structure and appearance. This classification system is known as the Hubble Sequence, named after its creator Edwin Hubble. In this sequence, NGC 3455 is known as a type SB galaxy — a barred spiral. Barred spiral galaxies account for approximately two thirds of all spirals. Galaxies of this type appear to have a bar of stars slicing through the bulge of stars at their center. The SB classification is further sub-divided by the appearance of a galaxy's pinwheeling spiral arms; SBa types have more tightly wound arms, whereas SBc types have looser ones. SBb types, such as NGC 3455, lie in between. NGC 3455 is part of a pair of galaxies — its partner, NGC 3454, lies out of frame. This cosmic duo belong to a group known as the NGC 3370 group, which is in turn one of the Leo II groups, a large collection of galaxies scattered some 30 million light-years to the right of the Virgo cluster. This new image is from Hubble's Advanced Camera for Surveys (ACS).

Image credit: ESA/Hubble & NASA; Acknowledgement: Nick Rose

Messier 61

This new Hubble picture is the sharpest ever image of the core of spiral galaxy Messier 61. Taken using the High Resolution Channel of Hubble's Advanced Camera for Surveys, the central part of the galaxy is shown in striking detail. Also known as NGC 4303, this galaxy is roughly 100,000 light-years across, comparable in size to our galaxy, the Milky Way.

Both Messier 61 and our home galaxy belong to a group of galaxies known as the Virgo Supercluster in the constellation of Virgo (The Virgin) — a group of galaxy clusters containing up to 2000 spiral and elliptical galaxies in total. Messier 61 is a type of galaxy known as a starburst galaxy. Starburst galaxies experience an incredibly high rate of star formation, hungrily using up their reservoir of gas in a very short period of time (in astronomical terms). But this is not the only activity going on within the galaxy; deep at its heart there is thought to be a supermassive black hole that is violently spewing out radiation.

Despite its inclusion in the Messier Catalog, Messier 61 was actually discovered by Italian astronomer Barnabus Oriani in 1779. Charles Messier also noticed this galaxy on the very same day as Oriani, but mistook it for a passing comet — the comet of 1779.

Image credit: ESA/Hubble & NASA

Beta Pictoris B

This artist’s view shows the planet orbiting the young star Beta Pictoris. This exoplanet is the first to have its rotation rate measured. Its eight-hour day corresponds to an equatorial rotation speed of 100,000 kilometers/hour — much faster than any planet in the Solar System.

Illustration credit: ESO L. Calçada/N. Risinger (skysurvey.org)

Note: For more information, see Length of Exoplanet Day Measured for First Time.