NGC 1929

NGC 1929: A star cluster embedded within the N44 nebula, which is located about 160,000 light years from Earth.

The star cluster NGC 1929 contains massive stars that produce intense radiation, expel matter at high speeds, and race through their evolution to explode as supernovas. The winds and shock waves carve out huge cavities called superbubbles in the surrounding gas. X-rays from Chandra (blue) in this composite image reveal the regions created by these winds and shocks, while infrared data from Spitzer (red) outline where the dust and cooler gas are found. Optical light from an ESO telescope in Chile (yellow) shows where ultraviolet radiation from the young stars is causing the gas to glow.

Scale: Image is: 25 arcmin across (1200 light years).

Image credit: X-ray: NASA/CXC/U.Mich./S.Oey, IR: NASA/JPL, Optical: ESO/WFI/2.2-m)

Note: For more information, see NGC 1929 in N44: A Surprisingly Bright Superbubble.

Rho Ophiuchi Nebula

This image shows the Rho Ophiuchi star-forming region in infrared light, as seen by NASA’s Wide-field Infrared Explorer (WISE). Blue and cyan represent light emitted at wavelengths of 3.4 and 4.6 micrometers, which is predominantly from stars. Green and red represent light from 12 and 22 micrometers, respectively, which is mostly emitted by dust.

Photo credit: NASA/JPL-Caltech/WISE Team

Note: For more information, see Sweet Result from ALMA.

Neil Armstrong, 1930-2012

The following is a statement from NASA Administrator Charles Bolden regarding the death of former test pilot and NASA astronaut Neil Armstrong. He was 82.

"On behalf of the entire NASA family, I would like to express my deepest condolences to Carol and the rest of Armstrong family on the passing of Neil Armstrong. As long as there are history books, Neil Armstrong will be included in them, remembered for taking humankind's first small step on a world beyond our own.

"Besides being one of America's greatest explorers, Neil carried himself with a grace and humility that was an example to us all. When President Kennedy challenged the nation to send a human to the moon, Neil Armstrong accepted without reservation.

"As we enter this next era of space exploration, we do so standing on the shoulders of Neil Armstrong. We mourn the passing of a friend, fellow astronaut and true American hero."

Photo credit: NASA

Note: For more information, see neilarmstronginfo.com

Phobos Anaglyph

Mars Express HRSC (High Resolution Stereo Camera) image of Phobos taken on 9 January 2011 at a distance of 100 km with a resolution of 8.1 m/pixel. Use red-blue glasses to fully appreciate this image.

Phobos is approximately 27 × 22 × 18 km and orbits Mars at a distance of 6000 km above the planet’s surface, or 9400 km from the center of the planet.

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

The Phoenix Cluster

The image on the left shows the newly discovered Phoenix Cluster, located about 5.7 billion light years from Earth. This composite includes an X-ray image from NASA's Chandra X-ray Observatory in purple, an optical image from the 4m Blanco telescope in red, green and blue, and an ultraviolet (UV) image from NASA's Galaxy Evolution Explorer (GALEX) in blue. The Chandra data show hot gas in the cluster and the optical and UV images show galaxies in the cluster and in nearby parts of the sky.

This galaxy cluster has been dubbed the "Phoenix Cluster" because it is located in the constellation of the Phoenix, and because of its remarkable properties, as explained here and in our press release. Stars are forming in the Phoenix Cluster at the highest rate ever observed for the middle of a galaxy cluster. The object is also the most powerful producer of X-rays of any known cluster, and among the most massive of clusters. The data also suggest that the rate of hot gas cooling in the central regions of the cluster is the largest ever observed.

Like other galaxy clusters, Phoenix contains a vast reservoir of hot gas -- containing more normal matter than all of the galaxies in the cluster combined -- that can only be detected with X-ray telescopes like Chandra. This hot gas is giving off copious amounts of X-rays and cooling quickly over time, especially near the center of the cluster, causing gas to flow inwards and form huge numbers of stars. These features are shown in the artist's impression of the central galaxy, with hot gas in red, cooler gas in blue. The gas flows appear as the ribbon-like features and the newly formed stars are blue. An animation portrays the process of cooling and star formation in action. A close-up of the middle of the optical and UV image shows that the central galaxy has much bluer colors than the nearby galaxies in the cluster, revealing the presence of large numbers of hot, massive stars forming.

These results are striking because most galaxy clusters have formed very few stars over the last few billion years. Astronomers think that the supermassive black hole in the central galaxy of clusters pumps energy into the system. The famous Perseus Cluster is an example of a black hole bellowing out energy and preventing the gas from cooling to form stars at a high rate. Repeated outbursts from the black hole in the center of Perseus in the form of powerful jets, created giant cavities and produced sound waves with an incredibly deep B-flat note 57 octaves below middle C. Shock waves, akin to sonic booms in Earth's atmosphere, and the very deep sound waves release energy into the gas in Perseus, preventing most of it from cooling.

In the case of Phoenix, jets from the giant black hole in its central galaxy are not powerful enough to prevent the cluster gas from cooling. Correspondingly, any deep notes produced by the jets must be much weaker than needed to prevent cooling and star formation.

Based on the Chandra data and also observations at other wavelengths, the supermassive black hole in the central galaxy of Phoenix is growing very quickly, at a rate of about 60 times the mass of the Sun every year. This rate is unsustainable, because the black hole is already very large with a mass of about 20 billion times the mass of the Sun. Therefore, its growth spurt cannot last much longer than about a hundred million years or it would become much bigger than its counterparts in the nearby Universe. A similar argument applies to the growth of the central galaxy. Eventually powerful jets should be produced by the black hole in repeated outbursts, forming the deep notes seen in objects like Perseus and stopping the starburst.

The Phoenix Cluster was originally detected by the South Pole Telescope, using the Sunyaev-Zeldovich effect, as explained in more detail in a blog interview with the first author of the paper, Michael McDonald. In a separate article more details about the Sunyaev-Zeldovich effect are given, including a historical perspective, in an interview with one of its co-discoverers, Rashid Sunyaev.

Photo and illustration credits: X-ray: NASA/CXC/MIT/M.McDonald; UV: NASA/JPL-Caltech/M.McDonald; Optical: AURA/NOAO/CTIO/MIT/M.McDonald; Illustration: NASA/CXC/M.Weiss

Barnard 59, The Pipe Nebula

This picture shows Barnard 59, part of a vast dark cloud of interstellar dust called the Pipe Nebula. This new and very detailed image of what is known as a dark nebula was captured by the Wide Field Imager on the MPG/ESO 2.2-meter telescope at ESO’s La Silla Observatory.

Photo credit: ESO

Note: For more information, see Ceci N’est Pas Une Pipe.

Meteor Smoke and Noctilucent Clouds

Anyone who's ever seen a noctilucent cloud or “NLC” would agree: They look alien. The electric-blue ripples and pale tendrils of NLCs reaching across the night sky resemble something from another world.

Researchers say that's not far off. A key ingredient for the mysterious clouds comes from outer space.

"We've detected bits of 'meteor smoke' embedded in noctilucent clouds," reports James Russell of Hampton University, principal investigator of NASA's AIM mission to study the phenomenon. "This discovery supports the theory that meteor dust is the nucleating agent around which NLCs form."

Noctilucent clouds are a mystery dating back to the late 19th century. Northern sky watchers first noticed them in 1885 about two years after the eruption of Krakatoa. Ash from the Indonesian volcano caused such splendid sunsets that evening sky watching became a worldwide pastime. One observer in particular, a German named T.W. Backhouse who is often credited with the discovery of NLCs, noticed something odd. He stayed outside longer than most people, long enough for the twilight to fully darken, and on some nights he saw wispy filaments glowing electric blue against the black sky. Scientists of the day figured they were some manifestation of volcanic dust.

Eventually Krakatoa’s ash settled and the sunsets faded, but strangely the noctilucent clouds didn’t go away. They’re still present today, stronger than ever. Researchers aren’t sure what role Krakatoa’s ash played in those early sightings. One thing is clear, however: The dust behind the clouds we see now is space dust.

Mark Hervig of the company GATS, Inc, led the team that found the extraterrestrial connection.

"Using AIM's Solar Occultation for Ice Experiment (SOFIE), we found that about 3% of each ice crystal in a noctilucent cloud is meteoritic," says Hervig.

The inner solar system is littered with meteoroids of all shapes and sizes--from asteroid-sized chunks of rock to microscopic specks of dust. Every day Earth scoops up tons of the material, mostly the small stuff. When meteoroids hit our atmosphere and burn up, they leave behind a haze of tiny particles suspended 70 km to 100 km above Earth's surface.

It's no coincidence that NLCs form 83 km high, squarely inside the meteor smoke zone.

Specks of meteor smoke act as gathering points where water molecules can assemble themselves into ice crystals. The process is called "nucleation."

Nucleation happens all the time in the lower atmosphere. In ordinary clouds, airborne specks of dust and even living microbes can serve as nucleation sites. Tiny ice crystals, drops of water, and snowflakes grow around these particles, falling to Earth if and when they become heavy enough.

Nucleating agents are especially important in the ethereal realm of NLCs. The clouds form at the edge of space where the air pressure is little more than vacuum. The odds of two water molecules meeting is slim, and of sticking together slimmer still.

Meteor smoke helps beat the odds. According AIM data, ice crystals can grow around meteoritic dust to sizes ranging from 20 to 70 nanometers. For comparison, cirrus clouds in the lower atmosphere where water is abundant contain crystals 10 to 100 times larger.

The small size of the ice crystals explains the clouds' blue color. Small particles tend to scatter short wavelengths of light (blue) more strongly than long wavelengths (red). So when a beam of sunlight hits an NLC, blue is the color that gets scattered down to Earth.

Meteor smoke explains much about NLCs, but a key mystery remains: Why are the clouds brightening and spreading?

In the 19th century, NLCs were confined to high latitudes—places like Canada and Scandinavia. In recent times, however, they have been spotted as far south as Colorado, Utah and Nebraska. The reason, Russell believes, is climate change. One of the greenhouse gases that has become more abundant in Earth's atmosphere since the 19th century is methane. It comes from landfills, natural gas and petroleum systems, agricultural activities, and coal mining.

It turns out that methane boosts NLCs.

Russell explains: "When methane makes its way into the upper atmosphere, it is oxidized by a complex series of reactions to form water vapor. This extra water vapor is then available to grow ice crystals for NLCs."

If this idea is correct, noctilucent clouds are a sort of "canary in a coal mine" for one of the most important greenhouse gases.

And that, says Russell, is a great reason to study them. "Noctilucent clouds might look alien, but they're telling us something very important about our own planet."

Photo credit: NASA; video credit: NASA

SNR G272.2-03.2

Composite optical and X-ray picture of supernova remnant G272.2-03.2, taken on 11 December 2001 by ESA’s XMM-Newton. The remnant was discovered in 1994 with ROSAT. The image is 40 x 40 arc minutes.

Photo credit: XMM-Newton/ESA

Soyuz Docked to the ISS

ESA astronaut André Kuipers looks at night-time Earth from his vantage point on the International Space Station. A Russian Progress ferry and his Soyuz spacecraft (left) are attached to the Station.

Photo credit: ESA/NASA

Note: This image is of the eastern Mediterranean Ocean with the Nile River and its delta being the long meandering line of lights in the distance; Cairo is the bright spot at the base of the delta. Israel is the bright patch of lights to the lower left, behind the Soyuz spacecraft, and you can just barely see a sliver of Cyprus at the bottom right.

Gale Crater Panorama

This is the first 360-degree panorama in color of the Gale Crater landing site taken by NASA's Curiosity rover. The panorama was made from thumbnail versions of images taken by the Mast Camera.

Scientists will be taking a closer look at several splotches in the foreground that appear gray. These areas show the effects of the descent stage's rocket engines blasting the ground. What appeared as a dark strip of dunes in previous, black-and-white pictures from Curiosity can also be seen along the top of this mosaic, but the color images also reveal additional shades of reddish brown around the dunes, likely indicating different textures or materials.

The images were taken late August 8 PDT (August 9 EDT) by the 34-millimeter Mast Camera. This panorama mosaic was made of 130 images of 144 by 144 pixels each. Selected full frames from this panorama, which are 1,200 by 1,200 pixels each, are expected to be transmitted to Earth later. The images in this panorama were brightened in the processing. Mars only receives half the sunlight Earth does and this image was taken in the late Martian afternoon.

Photo credit: NASA/JPL-Caltech/MSSS

Note: For more information, see NASA's Curiosity Beams Back a Color 360 of Gale Crater.

Signs Changing Fast for Voyager at Solar System Edge

Two of three key signs of changes expected to occur at the boundary of interstellar space have changed faster than at any other time in the last seven years, according to new data from NASA's Voyager 1 spacecraft.

For the last seven years, Voyager 1 has been exploring the outer layer of the bubble of charged particles the sun blows around itself. In one day, on July 28, data from Voyager 1's cosmic ray instrument showed the level of high-energy cosmic rays originating from outside our solar system jumped by five percent. During the last half of that same day, the level of lower-energy particles originating from inside our solar system dropped by half. However, in three days, the levels had recovered to near their previous levels.

A third key sign is the direction of the magnetic field, and scientists are eagerly analyzing the data to see whether that has, indeed, changed direction. Scientists expect that all three of these signs will have changed when Voyager 1 has crossed into interstellar space. A preliminary analysis of the latest magnetic field data is expected to be available in the next month.

"These are thrilling times for the Voyager team as we try to understand the quickening pace of changes as Voyager 1 approaches the edge of interstellar space," said Edward Stone, the Voyager project scientist based at the California Institute of Technology, Pasadena, California. "We are certainly in a new region at the edge of the solar system where things are changing rapidly. But we are not yet able to say that Voyager 1 has entered interstellar space."

The levels of high-energy cosmic ray particles have been increasing for years, but more slowly than they are now. The last jump -- of five percent -- took one week in May. The levels of lower-energy particles from inside our solar system have been slowly decreasing for the last two years. Scientists expect that the lower-energy particles will drop close to zero when Voyager 1 finally crosses into interstellar space.

"The increase and the decrease are sharper than we've seen before, but that's also what we said about the May data," Stone said. "The data are changing in ways that we didn't expect, but Voyager has always surprised us with new discoveries."

Voyager 1, which launched on September 5, 1977, is 11 billion miles (18 billion kilometers) from the sun. Voyager 2, which launched on August 20, 1977, is close behind, at 9.3 billion miles (15 billion kilometers) from the sun.

"Our two veteran Voyager spacecraft are hale and healthy as they near the 35th anniversary of their launch," said Suzanne Dodd, Voyager project manager based at NASA's Jet Propulsion Laboratory, Pasadena. "We know they will cross into interstellar space. It's just a question of when."

Illustration credit: NASA/JPL-Caltech

Note: This story was actually released by JPL on August 3rd, but had to be pushed back due to other stories, especially those related to Curiosity.

Star Formation in the Small Magellanic Cloud

This image shows the Small Magellanic Cloud galaxy in infrared light from the Herschel Space Observatory, a European Space Agency-led mission, and NASA's Spitzer Space Telescope. Considered dwarf galaxies compared to the big spiral of the Milky Way, the Large and Small Magellanic Clouds are the two biggest satellite galaxies of our home galaxy.

In combined data from Herschel and Spitzer, the irregular distribution of dust in the Small Magellanic Cloud becomes clear. A stream of dust extends to the left in this image, known as the galaxy's "wing," and a bar of star formation appears on the right.

The colors in this image indicate temperatures in the dust that permeates the Cloud. Colder regions show where star formation is at its earliest stages or is shut off, while warm expanses point to new stars heating surrounding dust. The coolest areas and objects appear in red, corresponding to infrared light taken up by Herschel's Spectral and Photometric Imaging Receiver at 250 microns, or millionths of a meter. Herschel's Photodetector Array Camera and Spectrometer fills out the mid-temperature bands, shown here in green, at 100 and 160 microns. The warmest spots appear in blue, courtesy of 24- and 70-micron data from Spitzer.

Photo credit: ESA/NASA/JPL-Caltech/STScI

Cluster Spacecraft Flying Through the Thin Boundary in the Magnetotail

This illustration shows the magnetic environment of Earth, which arises from the interaction between the solar wind, a stream of electrically charged particles released by the Sun, and our planet's internal magnetic field. In fact, the magnetosphere acts as a shield that prevents most of the solar wind particles from infiltrating Earth's atmosphere.

Highlighted in purple is the plasma sheet boundary layer, a thin boundary in the magnetotail – the long and cylindrical end of the magnetosphere that extends in the direction opposite the Sun. This thin boundary divides various regions of the magnetotail, which are populated by plasma with significantly different properties. To the north and south of the boundary are the lobes, two plasma layers characterized by very low density and strong magnetic field. Enclosed within the thin boundary is the plasma sheet, a denser layer where the magnetic field is weaker than in the lobes. Due to the drastically different properties of plasma at either side, thin boundaries such as the one in the magnetotail host most of the energy exchanges that take place in a plasma.

In the illustration, the four spacecraft of ESA's Cluster mission are shown as they fly in the magnetotail, in the configuration they had on 31 August 2007: two of them were separated by only a few tens of kilometers and located in the thin boundary of the magnetotail, while the other two were much farther away. This was a very favorable event to probe the behavior of plasma on the small scales where electrons become dominant. Using data from this event, scientists have for the first time characterized lower hybrid drift waves – plasma waves that develop in thin boundaries and play an important role in the dynamics of electrons and in the transfer of energy between different layers of plasma in Earth's magnetosphere.

Illustration credit: ESA / AOES Medialab

Note: For more information, see Cluster Looks into Waves in the Magnetosphere's Thin Boundaries.

Earth

MSG-3 first image of Earth, acquired on 7 August 2012 by its Spinning Enhanced Visible and Infrared Imager (SEVIRI).

Photo credit: Eumetsat

Curiosity Descending Into Gale Crater

NASA's Curiosity rover and its parachute were spotted by NASA's Mars Reconnaissance Orbiter as Curiosity descended to the surface on August 5 PDT (August 6 EDT). The High-Resolution Imaging Science Experiment (HiRISE) camera captured this image of Curiosity while the orbiter was listening to transmissions from the rover. Curiosity and its parachute are in the center of the white box; the inset image is a cutout of the rover stretched to avoid saturation. The rover is descending toward the etched plains just north of the sand dunes that fringe "Mt. Sharp." From the perspective of the orbiter, the parachute and Curiosity are flying at an angle relative to the surface, so the landing site does not appear directly below the rover.

The parachute appears fully inflated and performing perfectly. Details in the parachute, such as the band gap at the edges and the central hole, are clearly seen. The cords connecting the parachute to the back shell cannot be seen, although they were seen in the image of NASA's Phoenix lander descending, perhaps due to the difference in lighting angles. The bright spot on the back shell containing Curiosity might be a specular reflection off of a shiny area. Curiosity was released from the back shell sometime after this image was acquired.

This view is one product from an observation made by HiRISE targeted to the expected location of Curiosity about one minute prior to landing. It was captured in HiRISE CCD RED1, near the eastern edge of the swath width (there is a RED0 at the very edge). This means that the rover was a bit further east or downrange than predicted.

The image scale is 13.2 inches (33.6 centimeters) per pixel.

Photo credit: NASA/JPL-Caltech/Univ. of Arizona

Note: For more information, see NASA's Curiosity Rover Caught in the Act of Landing.

First Images from Curiosity

This image shows one of the first views from NASA's Curiosity rover, which landed on Mars the evening of August 5 PDT (early morning hours August 6 EDT). It was taken through a "fisheye" wide-angle lens on one of the rover's Hazard-Avoidance cameras. These engineering cameras are located at the rover's base. As planned, the early images are lower resolution. Larger color images are expected later in the week when the rover's mast, carrying high-resolution cameras, is deployed.

Photo credit: NASA/JPL-Caltech

This is one of the first images taken by NASA's Curiosity rover, which landed on Mars the evening of August 5 PDT (morning of August 6 EDT). It was taken through a "fisheye" wide-angle lens on the left "eye" of a stereo pair of Hazard-Avoidance cameras on the left-rear side of the rover. The image is one-half of full resolution. The clear dust cover that protected the camera during landing has been sprung open. Part of the spring that released the dust cover can be seen at the bottom right, near the rover's wheel.

On the top left, part of the rover's power supply is visible.

Some dust appears on the lens even with the dust cover off.

The cameras are looking directly into the sun, so the top of the image is saturated. Looking straight into the sun does not harm the cameras. The lines across the top are an artifact called "blooming" that occurs in the camera's detector because of the saturation.

As planned, the rover's early engineering images are lower resolution. Larger color images from other cameras are expected later in the week when the rover's mast, carrying high-resolution cameras, is deployed.

Photo credit: NASA/JPL-Caltech


Notes: For more information on the lower photo see NASA's New Mars Rover Sends Higher-Resolution Image. Are these blueberries in the sand?

Cloudy with a chance of...

This global map of Mars was acquired on August 2, 2012, by the Mars Color Imager instrument on NASA's Mars Reconnaissance Orbiter. One global map is generated each day to forecast weather conditions for the entry, descent and landing of NASA's Curiosity rover. The active dust storm observed south of Curiosity's landing site on July 31 has dissipated, leaving behind a dust cloud that will not pose a threat to the landing.

The map is a rectangular projection of Mars (from 90 degrees latitude to minus 90 degrees latitude, and minus 180 degrees longitude to 180 degrees east longitude). The landing site is located on the right side of the map, near 137 degrees east longitude and 4.5 degrees south latitude. The map shows water ice clouds at equatorial latitudes that are typical for late southern winter, when Mars is farther from the sun. Along the southern (bottom) part of the map there are patches of orange clouds, indicating dust lofted into the atmosphere. Small, short-lived dust storms are common at this time of year on Mars and were taken into account when Curiosity's landing system was designed and tested. Larger and more long-lived dust storms are very rare at this time of year.

This global map of Mars was acquired on October 28, 2008, by the Mars Color Imager instrument on NASA's Mars Reconnaissance Orbiter. It was acquired during the same season that NASA's Curiosity rover will land in, but two Mars years earlier. It is remarkably free of water ice clouds when compared with the maps acquired this year in the days leading up to Curiosity's landing.

In 2008, during this season, the planet was dustier than usual. Larger amounts of dust cause sunlight to warm the atmosphere and make it less dense, which means less stopping power for a landing rover. What's more, dusty conditions can lead to an increased chance for small, intense dust storms, another challenge for rover landings. So far, the weather forecast for Curiosity calls for a clearer atmosphere; nonetheless, the spacecraft has been designed to land safely under conditions similar to those observed in 2008.

The map is a rectangular projection of Mars (from 90 degrees latitude to minus 90 degrees latitude, and minus 180 degrees longitude to 180 degrees east longitude). The landing site is located on the right side of the map, near 137 degrees east longitude and 4.5 degrees south latitude. Along the northern (top) and southern (bottom) parts of the map there are patches of orange clouds, indicating dust lofted into the atmosphere.

Map credit 1: NASA/JPL-Caltech/MSSS; map credit 2: NASA/JPL-Caltech/MSSS

Note: NASA has released an additional Martian weather map, that of August 5th, the day Curiosity landed in Gale Crater.

NGC 1187

This picture taken with ESO’s Very Large Telescope shows the galaxy NGC 1187. This impressive spiral lies about 60 million light-years away in the constellation of Eridanus (The River). NGC 1187 has hosted two supernova explosions during the last thirty years, the latest one in 2007.

Photo credit: ESO

Note: For more information, see A Blue Whirlpool in The River.

Dunes on the Move in Lyot Crater

HiRISE has been carrying out a dedicated survey of sand dunes on Mars, determining whether and how fast the dunes move by observing repeatedly at intervals of Martian years. More than 60 sites have been monitored so far, showing that sand dunes from the equator to the poles are advancing at rates of up to 1 meter per Martian year.

These observations are still spotty, however, and tend to be concentrated in the tropics and the North Polar erg (the sand sea that surrounds the North Pole). One latitude band that had not been sampled at all lies between 30 and 65 degrees north. This observation is among a set of images acquired to fill that gap.

This image shows a variety of different dune types in southern Lyot Crater in the northern lowlands at 48.9 degrees North. Transverse dunes to the west grade into longitudinal dunes downwind to the east and barchans to the south, possibly because of local winds channeled by topography in the impact basin. This image was intended to match the approximate illumination and viewing conditions of an earlier HiRISE observation that was made two Martian years earlier, in August 2008.

Detailed comparison of the two images shows movement on many of the dunes during this interval of nearly four Earth years. The subimage is an animation showing changes on one of the small barchans in the south of the dune field. The area pictured in the subimage is about 100 meters across. Winds from the west (left) have shifted the small ripples up the back of the dune towards the east. Sand has blown over the crest of the dune, cascaded down the steep slip face, and accumulated along the base of the slip face in the lee of the dune. In this way, the small dune advances slowly downwind.

Other images also show dune activity in this latitude band, adding to a growing suspicion that dunes are on the move everywhere on Mars, faster in some places than others.

Photo credit: NASA/JPL/University of Arizona

The Morphology of a Coronal Mass Ejection

This illustration shows the morphology of a Coronal Mass Ejection (CME) – a gigantic eruption that releases enormous amounts of matter and energy from the Sun through the corona and into space – as revealed by radio-sounding experiments.

Radio sounding of the solar corona is a technique that exploits radio transmissions from planetary missions to probe the corona of the Sun. This technique can be performed when a spacecraft is located at superior solar conjunction – meaning that Earth, Sun and the spacecraft lie on the same line, with the spacecraft located on the opposite side of the Sun with respect to our planet. In this configuration, or more precisely just before and after it, radio signals sent out by the spacecraft pass through the solar corona – the hot outer atmosphere of the Sun, which consists of turbulent plasma at temperatures of millions of degrees – as they travel towards Earth. Electrons in the coronal plasma interact with the radio signals, causing a frequency shift that can be measured on Earth and analyzed to infer the electron density in the corona.

The upper part of the illustration shows the limb of the Sun (on the right), a CME moving away from the Sun (in the center) and the path traveled by radio waves sent out by a spacecraft on their way to Earth (on the left); all components are shown as viewed from 'above', perpendicularly to the ecliptic plane. The lower part of the illustration shows a graph depicting how the density of electrons varies in time as a CME moves across the path of a radio signal that is traveling from the spacecraft to Earth.

Based on data collected during four CMEs in 2004 using ESA's Mars Express spacecraft, scientists have been able to probe the morphology of a CME in great detail. According to the data, when the path of the radio signal is traversed by a CME, the electron density first undergoes a gentle rise, followed by a steeper increase and, eventually, by a smooth decline, as shown in the graph. This suggests that the proper, dense structure of a CME is preceded by a shock front and a series of smaller fronts that consist of less dense material. The smaller fronts build up as the CME itself propagates outward through the corona, pushing material ahead of it and piling it up in a similar way to a bulldozer. In contrast, material immediately behind the CME has extremely low density, as indicated by the eventual density decrease. These results have been presented by Pätzold et al., 2012.

Illustration credit: ESA/AOES Medialab

Note: For more information, see Planetary Missions Probe Giant Eruptions in the Sun's Corona.

SN 1957D in M83: X-Rays Discovered from Young Supernova Remnant

Over fifty years ago, a supernova was discovered in M83, a spiral galaxy about 15 million light years from Earth. Astronomers have used NASA's Chandra X-ray Observatory to make the first detection of X-rays emitted by the debris from this explosion.

Named SN 1957D because it was the fourth supernova to be discovered in the year of 1957, it is one of only a few located outside of the Milky Way galaxy that is detectable, in both radio and optical wavelengths, decades after its explosion was observed. In 1981, astronomers saw the remnant of the exploded star in radio waves, and then in 1987 they detected the remnant at optical wavelengths, years after the light from the explosion itself became undetectable.

A relatively short observation -- about 14 hours long -- from NASA's Chandra X-ray Observatory in 2000 and 2001 did not detect any X-rays from the remnant of SN 1957D. However, a much longer observation obtained in 2010 and 2011, totaling nearly 8 and 1/2 days of Chandra time, did reveal the presence of X-ray emission. The X-ray brightness in 2000 and 2001 was about the same as or lower than in this deep image.

This new Chandra image of M83 is one of the deepest X-ray observations ever made of a spiral galaxy beyond our own. This full-field view of the spiral galaxy shows the low, medium, and high-energy X-rays observed by Chandra in red, green, and blue respectively. The location of SN 1957D, which is found on the inner edge of the spiral arm just above the galaxy's center, is outlined in the box (or can be seen by mousing over the image.)

The new X-ray data from the remnant of SN 1957D provide important information about the nature of this explosion that astronomers think happened when a massive star ran out of fuel and collapsed. The distribution of X-rays with energy suggests that SN 1957D contains a neutron star, a rapidly spinning, dense star formed when the core of pre-supernova star collapsed. This neutron star, or pulsar, may be producing a cocoon of charged particles moving at close to the speed of light known as a pulsar wind nebula.

If this interpretation is confirmed, the pulsar in SN 1957D is observed at an age of 55 years, one of the youngest pulsars ever seen. The remnant of SN 1979C in the galaxy M100 contains another candidate for the youngest pulsar, but astronomers are still unsure whether there is a black hole or a pulsar at the center of SN 1979C.

An image from the Hubble Space Telescope (in the box labeled "Optical Close-Up") shows that the debris of the explosion that created SN 1957D is located at the edge of a star cluster less than 10 million years old. Many of these stars are estimated to have masses about 17 times that of the Sun. This is just the right mass for a star's evolution to result in a core-collapse supernova as is thought to be the case in SN 1957D.

Photo credit: X-ray: NASA/CXC/STScI/K.Long et al., Optical: NASA/STScI

Messier 68

Messier 68 is located about 33,000 light-years from Earth in the constellation Hydra (The Female Water Snake). French astronomer Charles Messier notched the object as the 68th entry in his famous catalog in 1780.

The image was taken by Hubble’s Wide Field Camera of the Advanced Camera for Surveys and combines visible and infrared light. It has a field of view of about 3.4 by 3.4 arcminutes.

Photo credit: ESA/Hubble & NASA