New Way to Peer at Distant Galaxies

A team including University of Hertfordshire astronomers have discovered a new way of finding cosmic zoom lenses, which allows astronomers to peer at galaxies in the distant Universe.

The cosmic lenses, discovered with the European Space Agency's Herschel Space Observatory, allow astronomers to see galaxies which are otherwise too distant to study. This provides key insights into how galaxies have changed over the history of the cosmos. Herschel looks at far-infrared light, which is emitted not by stars, but by the gas and dust from which they form.

The results, which are from the very first data taken as part of the Herschel-ATLAS project, the largest imaging survey conducted so far with Herschel, are published in the scientific journal Science on November 5).

Dr Mattia Negrello, of the Open University and lead researcher of the study, explained, "Our survey of the sky looks for sources of sub-millimetre light. The big breakthrough is that we have discovered that many of the brightest sources are being magnified by lenses, which means that we no longer have to rely on the rather inefficient methods of finding lenses which are used at visible and radio wavelengths."

The Herschel-ATLAS images contain thousands of galaxies, most so far away that the light has taken billions of years to reach us. Dr Negrello and his team investigated five surprisingly bright objects in this small patch of sky. Looking at the positions of these bright objects with optical telescopes on the Earth, they found galaxies that would not normally be bright at the far-infrared wavelengths observed by Herschel. This led them to suspect that the galaxies seen in visible light might be gravitational lenses magnifying much more distant galaxies seen by Herschel.

At the University of Hertfordshire, Dr David Bonfield used visible and near-infrared measurements taken from existing visible images to estimate distances to the galaxies believed to be acting as lenses. He explained, "More distant galaxies have their light stretched to longer, redder wavelengths, because the light travels through more of the expanding Universe before reaching us. So we can use the colours they appear to figure out how far away they are."

To find the true distances to the Herschel sources behind the lenses, Negrello and his team looked for a tell-tale signature of molecular gas. Using radio and sub-millimetre telescopes on the ground, they showed that this signature implies the galaxies are being seen as they were when the Universe was just 2-4 billion years old -- less than a third of its current age. The galaxies seen by the optical telescopes are much closer, each ideally positioned to create a gravitational lens.

Dr Negrello said: "Previous searches for magnified galaxies have targeted clusters of galaxies where the huge mass of the cluster makes the gravitational lensing effect unavoidable. Our results show that gravitational lensing is at work in not just a few, but in all of the distant and bright galaxies seen by Herschel."

Hubble captures new star birth in an ancient galaxy

Elliptical galaxies were once thought to be aging star cities whose star-making heyday was billions of years ago.

But new observations with NASA's Hubble Space Telescope are helping to show that elliptical galaxies still have some youthful vigor left, thanks to encounters with smaller galaxies.

Images of the core of NGC 4150, taken in near-ultraviolet light with the sharp-eyed Wide Field Camera 3 (WFC3), reveal streamers of dust and gas and clumps of young, blue stars that are significantly less than a billion years old. Evidence shows that the star birth was sparked by a merger with a dwarf galaxy.

The new study helps bolster the emerging view that most elliptical galaxies have young stars, bringing new life to old galaxies.

"Elliptical galaxies were thought to have made all of their stars billions of years ago," says astronomer Mark Crockett of the University of Oxford, leader of the Hubble observations. "They had consumed all their gas to make new stars. Now we are finding evidence of star birth in many elliptical galaxies, fueled mostly by cannibalizing smaller galaxies.

"These observations support the theory that galaxies built themselves up over billions of years by collisions with dwarf galaxies," Crockett continues. "NGC 4150 is a dramatic example in our galactic back yard of a common occurrence in the early universe."

The Hubble images reveal turbulent activity deep inside the galaxy's core. Clusters of young, blue stars trace a ring around the center that is rotating with the galaxy. The stellar breeding ground is about 1,300 light-years across. Long strands of dust are silhouetted against the yellowish core, which is composed of populations of older stars.

From a Hubble analysis of the stars' colors, Crockett and his team calculated that the star-formation boom started about a billion years ago, a comparatively recent event in cosmological history. The galaxy's star-making factory has slowed down since then.

"We are seeing this galaxy after the major starburst has occurred," explains team member Joseph Silk of the University of Oxford. "The most massive stars are already gone. The youngest stars are between 50 million and 300 to 400 million years old. By comparison, most of the stars in the galaxy are around 10 billion years old."

The encounter that triggered the star birth would have been similar to our Milky Way swallowing the nearby Large Magellanic Cloud.

"We believe that a merger with a small, gas-rich galaxy around one billion years ago supplied NGC 4150 with the fuel necessary to form new stars," says team member Sugata Kaviraj of the Imperial College London and the University of Oxford. "The abundance of 'metals'--elements heavier than hydrogen and helium--in the young stars is very low, suggesting the galaxy that merged with NGC 4150 was also metal-poor. This points towards a small, dwarf galaxy, around one-twentieth the mass of NGC 4150."

Minor mergers such as this one are more ubiquitous than interactions between hefty galaxies, the astronomers say. For every major encounter, there are probably up to 10 times more frequent clashes between a large and a small galaxy. Major collisions are easier to see because they create incredible fireworks: distorted galaxies, long streamers of gas, and dozens of young star clusters. Smaller interactions are harder to detect because they leave relatively little trace.

Over the past five years, however, ground- and space-based telescopes have offered hints of fresh star formation in elliptical galaxies. Ground-based observatories captured the blue glow of stars in elliptical galaxies, and satellites such as the Galaxy Evolution Explorer (GALEX), which looks in far- and near-ultraviolet light, confirmed that the blue glow came from fledgling stars much less than a billion years old. Ultraviolet light traces the glow of hot, young stars.

Crockett and his team selected NGC 4150 for their Hubble study because a ground-based spectroscopic analysis gave tantalizing hints that the galaxy's core was not a quiet place. The ground-based survey, called the Spectrographic Areal Unit for Research on Optical Nebulae (SAURON), revealed the presence of young stars and dynamic activity that was out of sync with the galaxy.

"In visible light, elliptical galaxies such as NGC 4150 look like normal elliptical galaxies," Silk says. "But the picture changes when we look in ultraviolet light. At least a third of all elliptical galaxies glow with the blue light of young stars."

Adds Crockett: "Ellipticals are the perfect laboratory for studying minor mergers in ultraviolet light because they are dominated by old red stars, allowing astronomers to see the faint blue glow of young stars."

The astronomers hope to study other elliptical galaxies in the SAURON survey to look for the signposts of new star birth. The team's results have been accepted for publication in The Astrophysical Journal.

Atoms-for-Peace: A galactic collision in action

European Southern Observatory astronomers have produced a spectacular new image of the famous Atoms-for-Peace galaxy. This galactic pile-up, formed by the collision of two galaxies, provides an excellent opportunity for astronomers to study how mergers affect the evolution of the universe.

Atoms-for-Peace is the curious name given to a pair of interacting and merging galaxies that lie around 220 million light-years away in the constellation of Aquarius. It is also known as NGC 7252 and Arp 226 and is just bright enough to be seen by amateur astronomers as a very faint small fuzzy blob. This very deep image was produced by ESO's Wide Field Imager on the MPG/ESO 2.2-metre telescope at ESO's La Silla Observatory in Chile.

A galaxy collision is one of the most important processes influencing how our Universe evolves, and studying them reveals important clues about galactic ancestry. Luckily, such collisions are long drawn-out events that last hundreds of millions of years, giving astronomers plenty of time to observe them.

This picture of Atoms-for-Peace represents a snapshot of its collision, with the chaos in full flow, set against a rich backdrop of distant galaxies. The results of the intricate interplay of gravitational interactions can be seen in the shapes of the tails made from streams of stars, gas and dust. The image also shows the incredible shells that formed as gas and stars were ripped out of the colliding galaxies and wrapped around their joint core. While much material was ejected into space, other regions were compressed, sparking bursts of star formation. The result was the formation of hundreds of very young star clusters, around 50 to 500 million years old, which are speculated to be the progenitors of globular clusters.

Atoms-for-Peace may be a harbinger of our own galaxy's fate. Astronomers predict that in three or four billion years the Milky Way and the Andromeda Galaxy will collide, much as has happened with Atoms-for-Peace. But don't panic: the distance between stars within a galaxy is vast, so it is unlikely that our Sun will end up in a head-on collision with another star during the merger.

The object's curious nickname has an interesting history. In December 1953, President Eisenhower gave a speech that was dubbed Atoms for Peace. The theme was promoting nuclear power for peaceful purposes -- a particularly hot topic at the time. This speech and the associated conference made waves in the scientific community and beyond to such an extent that NGC 7252 was named the Atoms-for-Peace galaxy. In many ways, this is oddly appropriate: the curious shape that we can see is the result of two galaxies merging to produce something new and grand, a little like what occurs in nuclear fusion. Furthermore, the giant loops resemble a textbook diagram of electrons orbiting an atomic nucleus.

Coronal mass ejections: Scientists unlock the secrets of exploding plasma clouds on the Sun

The Sun sporadically expels trillions of tons of million-degree hydrogen gas in explosions called coronal mass ejections (CMEs). Such clouds are enormous in size (spanning millions of miles) and are made up of magnetized plasma gases, so hot that hydrogen atoms are ionized. CMEs are rapidly accelerated by magnetic forces to speeds of hundreds of kilometers per second to upwards of 2,000 kilometers per second in several tens of minutes. CMEs are closely related to solar flares and, when they impinge on Earth, can trigger spectacular auroral displays. They also induce strong electric currents in Earth's plasma atmosphere (i.e., the magnetosphere and ionosphere), leading to outages in telecommunications and GPS systems and even the collapse of electric power grids if the disturbances are very severe.

Since the first observation of a solar flare in 1859, solar eruptions ("explosions") have attracted much attention from scientists around the world and have been studied with a succession of increasingly sophisticated international satellite missions in the past three decades. A major challenge has been that enormous and complicated plasma structures accelerating away from the Sun can only be observed remotely. As a result, it has been difficult to test theoretical models to establish a correct understanding of the mechanisms that cause such eruptions. But in 2006, an international twin-satellite mission called STEREO was launched to continuously observe the erupting plasma structures from the Sun to Earth.

Now, using the data from STEREO, scientists at the Naval Research Laboratory (NRL) in Washington, D.C., have demonstrated for the first time that the observed motion of erupting plasma clouds driven by magnetic forces can be correctly explained by a theoretical model.

The theory, controversial when it was first proposed in 1989 by Dr. James Chen of NRL, is based on the concept that an erupting plasma cloud is a giant "magnetic flux rope," a rope of "twisted" magnetic field lines shaped like a partial donut. Chen and Valbona Kunkel, a doctoral student at George Mason University, have applied this model to the new STEREO data of CMEs and shown that the theoretical solutions agree with the measured trajectories of the ejected clouds within the entire field of view from the Sun to Earth.

The position of the leading edge (LE) of a CME that erupted on December 24, 2007 were tracked by the STEREO-A spacecraft from the earliest stages of eruption to its arrival at 1 AU approximately five days later. The magnetic field and plasma parameters were measured by the STEREO-B spacecraft. The agreement between theory and data is within 1 percent of the measured position of the LE. Chen and Kunkel's results show that the theoretically predicted magnetic field and plasma properties are in excellent agreement with the measurements aboard STEREO-B. This is the first model that can replicate directly observed quantities near the Sun and Earth as well as the actual trajectories of CMEs. Prior to STEREO, the motion of CMEs in the region corresponding to HI1 and HI2 data was not observed.

Interestingly, the basic forces acting on solar flux ropes are the same as those in laboratory plasma structures such as tokamaks developed to produce controlled fusion energy. The mechanism described by the theory is also potentially applicable to eruptions on other stars.

Researchers presented their work at the 52nd annual meeting of the American Physical Society's Division of Plasma Physics, held in Chicago Nov. 8-12.

NASA's EPOXI flyby reveals new insights into comet features

NASA's EPOXI mission spacecraft successfully flew past comet Hartley 2 at 7 a.m. PDT (10 a.m. EDT) Thursday, Nov. 4. Scientists say initial images from the flyby provide new information about the comet's volume and material spewing from its surface.

"Early observations of the comet show that, for the first time, we may be able to connect activity to individual features on the nucleus," said EPOXI Principal Investigator Michael A'Hearn of the University of Maryland, College Park. "We certainly have our hands full. The images are full of great cometary data, and that's what we hoped for."

EPOXI is an extended mission that uses the already in-flight Deep Impact spacecraft. Its encounter phase with Hartley 2 began at 1 p.m. PDT (4 p.m. EDT) on Nov. 3, when the spacecraft began to point its two imagers at the comet's nucleus. Imaging of the nucleus began one hour later.

"The spacecraft has provided the most extensive observations of a comet in history," said Ed Weiler, associate administrator for NASA's Science Mission Directorate at the agency's headquarters in Washington. "Scientists and engineers have successfully squeezed world-class science from a re-purposed spacecraft at a fraction of the cost to taxpayers of a new science project."

Images from the EPOXI mission reveal comet Hartley 2 to have 100 times less volume than comet Tempel 1, the first target of Deep Impact. More revelations about Hartley 2 are expected as analysis continues.

Initial estimates indicate the spacecraft was about 700 kilometers (435 miles) from the comet at the closest-approach point. That's almost the exact distance that was calculated by engineers in advance of the flyby.

"It is a testament to our team's skill that we nailed the flyby distance to a comet that likes to move around the sky so much," said Tim Larson, EPOXI project manager at NASA's Jet Propulsion Laboratory in Pasadena, Calif. "While it's great to see the images coming down, there is still work to be done. We have another three weeks of imaging during our outbound journey."

The name EPOXI is a combination of the names for the two extended mission components: the Extrasolar Planet Observations and Characterization (EPOCh), and the flyby of comet Hartley 2, called the Deep Impact Extended Investigation (DIXI). The spacecraft has retained the name "Deep Impact." In 2005, Deep Impact successfully released an impactor into the path of comet Tempel 1.

NASA's Jet Propulsion Laboratory, a division of the California Institute of Technology, manages the EPOXI mission for NASA's Science Mission Directorate. The spacecraft was built for NASA by Ball Aerospace & Technologies Corp., in Boulder, Colo.

For more information about EPOXI, visit: http://www.nasa.gov/epoxi and http://epoxi.umd.edu/.

Discovery could reveal secrets of ancient Martian and terrestrial atmospheres

Chemists at UC San Diego have uncovered a new chemical reaction on tiny particulates in the atmosphere that could allow scientists to gain a glimpse from ancient rocks of what the atmospheres of the Earth and Mars were like hundreds of millions years ago.

Their discovery also provides a simple chemical explanation for the unusual carbonate inclusions found in a meteorite from Mars that was once thought by some scientists to be evidence of ancient Martian life.

"We never knew before how the atmosphere could be trapped in carbonate," said Mark Thiemens, dean of UC San Diego's Division of Physical Sciences who headed the team of scientists that detailed its discovery in the early online edition of the Proceedings of the National Academy of Sciences. "This chemical reaction, which takes place on the surface of aerosols in the atmosphere, not only provides us with an understanding of how these carbonates can form on the Earth and Mars. It gives us a new tool to better understand climate change, as our planet warms and becomes more dusty."

Robina Shaheen, a postdoctoral researcher in Thiemens' laboratory, discovered the chemical reaction and detailed its importance in the Earth's atmosphere after four years of painstaking experiments in which she found a higher than expected proportion of oxygen 17 isotopes in the carbonates found on dust grains, aerosols and dirt from various parts of the world.

Martian meteorites, such as ALH84001, which was once thought to exhibit evidence of extraterrestrial life, have carbonates with similarly high oxygen 17 anomalies. Scientists have long attributed those anomalies to photochemical processes involving ozone and carbon dioxide in the thin atmosphere on Mars, which is bathed by intense ultraviolet radiation. But after finding similar anomalies on terrestrial carbonates formed in atmospheric aerosols, Shaheen surmised they might be the result of another chemical process more common to both planets.

She analyzed in painstaking detail in the laboratory and in the Earth's atmosphere how ozone molecules interacted with oxygen-bearing mineral aerosols from dust, sea spray and other sources to form hydrogen peroxide and carbonates containing this same oxygen-isotope anomaly.

"What she found is that the tiny little layer on the outside of the grain is where this chemistry all happens," said Thiemens. "It's the ozone in the atmosphere mixing with water and carbon dioxide that drives a completely different kind of chemistry, one that's not in any of the models."

While current models of atmospheric processes assume that the mixing of large volumes of gases drives the chemistry of the Earth's atmosphere, the UCSD chemists think their discovery may force a rethinking of this idea, particularly as the Earth's atmosphere becomes warmer and more dusty, providing more opportunities for this sort of chemistry to take place on aerosols.

"You can do chemistry on a grain that's a lot quicker and easier in many respects than is possible in other atmospheric processes," said Thiemens.

Shaheen, who analyzed the carbonates in the Martian meteorite ALH84001 and found that they could have been formed on aerosols in ancient Martian atmosphere, said that NASA's Phoenix lander recently detected carbonates associated with particulates in the dusty atmosphere of Mars. "We think it might be this same mechanism that is operating," she added.

Besides understanding current and future atmospheric processes on the Earth and Mars, the new discovery offers the possibility of mining information about the Earth's atmosphere, particularly its oxygen levels, from carbonates found in ancient rocks millions of years ago, far beyond the time period from which scientists can now obtain information about the ancient atmosphere from ice cores. The development of this new tool to probe ancient atmospheres could be the most significant aspect of the UCSD chemists' discovery.

"We've found a new way to measure the earth's atmosphere for time periods when we previously could not do it," said Thiemens. "What happened to ozone and oxygen levels 65 million years ago during the Cretaceous-Tertiary period when the dinosaurs and many other forms of life were killed in a mass extinction? Who died first? Did the food chain disappear before the dinosaurs? What happened 251 million years ago during the Permian-Triassic period, the most severe extinction of life on Earth, when 85 percent of life disappeared and no one knows why? There's no record of what happened in the atmosphere. But if you can find a record of what happened to oxygen levels, you can answer questions like that."

Other researchers at UCSD involved in the study in Thiemens' laboratory were undergraduates Anna Abramian and John Horn. The research was partially supported by grants from National Aeronautics and Space Administration, the National Science Foundation and the UC San Diego Chancellor's Associates.

Close-up of hidden galaxies with new cosmic zoom lenses

Astronomers have discovered a new way of locating a natural phenomenon that acts like a zoom lens and allows astronomers to peer at galaxies in the distant and early Universe. These results are from the very first data taken as part of the "Herschel-ATLAS" project, the largest imaging survey conducted so far with the European Space Agency's Herschel Space Observatory, and are published in the journal Science.

The magnification allows astronomers to see galaxies otherwise hidden from us when the Universe was only a few billion years old. This provides key insights into how galaxies have changed over the history of the cosmos.

Dr Loretta Dunne from the School of Physics and Astronomy at The University of Nottingham is joint-leader of the Herschel-ATLAS survey. Dr Dunne said: "What we've seen so far is just the tip of the iceberg. Wide area surveys are essential for finding these rare events and since Herschel has only covered one thirtieth of the entire Herschel-ATLAS area so far, we expect to discover hundreds of lenses once we have all the data. Once found, we can probe the early Universe on the same physical scales as we can in galaxies next door.

"The data from the area of sky used for this work has now been released to the astronomical community and we hope that now astronomers not directly involved in H-ATLAS will dive into this data set and exploit the wealth of science which is bursting to be done with it."

A century ago Albert Einstein showed that gravity can cause light to bend. The effect is normally extremely small, and it is only when light passes close to a very massive object such as a galaxy containing hundreds of billions of stars that the results become easily noticeable. When light from a very distant object passes a galaxy much closer to us, its path can be bent in such a way that the image of the distant galaxy is magnified and distorted. These alignment events are called "gravitational lenses" and many have been discovered over recent decades, mainly at visible and radio wavelengths.

As with a normal glass lens the alignment is crucial, requiring the position of the lens -- in this case a galaxy -- to be just right. This is very rare and astronomers have to rely on chance alignments, often involving sifting through large amounts of data from telescopes. Most methods of searching for gravitational lenses have a very poor success rate with fewer than one in 10 candidates typically being found to be real.

Herschel looks at far-infrared light, which is emitted not by stars, but by the gas and dust from which they form. Its panoramic imaging cameras have allowed astronomers to find examples of these lenses by scanning large areas of the sky in far-infrared and sub-millimetre light.

Dr Mattia Negrello, of the Open University and lead researcher of the study, said: "Our survey of the sky looks for sources of sub-millimetre light. The big breakthrough is that we have discovered that many of the brightest sources are being magnified by lenses, which means that we no longer have to rely on the rather inefficient methods of finding lenses which are used at visible and radio wavelengths."

The Herschel-ATLAS images contain thousands of galaxies, most so far away that the light has taken billions of years to reach us. Dr Negrello and his team investigated five surprisingly bright objects in this small patch of sky. Looking at the positions of these bright objects with optical telescopes on the Earth, they found galaxies that would not normally be bright at the far-infrared wavelengths observed by Herschel. This led them to suspect that the galaxies seen in visible light might be gravitational lenses magnifying much more distant galaxies seen by Herschel.

To find the true distances to the Herschel sources, Negrello and his team looked for a tell-tale signature of molecular gas. Using radio and sub-millimetre telescopes on the ground, they showed that this signature implies the galaxies are being seen as they were when the Universe was just 2-4 billion years old -- less than a third of its current age. The galaxies seen by the optical telescopes are much closer, each ideally positioned to create a gravitational lens. Dr Negrello commented that "previous searches for magnified galaxies have targeted clusters of galaxies where the huge mass of the cluster makes the gravitational lensing effect unavoidable. Our results show that gravitational lensing is at work in not just a few, but in all of the distant and bright galaxies seen by Herschel."

The magnification provided by these cosmic zoom lenses allows astronomers to study much fainter galaxies, and in more detail than would otherwise be possible. They are the key to understanding how the building blocks of the Universe have changed since they were in their infancy. Professor Rob Ivison of the Royal Observatory, Edinburgh, part of the team that created the images, said "This relatively simple technique promises to unlock the secrets of how galaxies like our Milky Way formed and evolved. Not only does the lensing allow us to find them very efficiently, but it helps us peer within them to figure out how the individual pieces of the jigsaw came together, back in the mists of time."

Professor Steve Eales from Cardiff University and the other leader of the survey added: "We can also use this technique to study the lenses themselves. This is exciting because 80 per cent of the matter in the Universe is thought to be dark matter, which does not absorb, reflect or emit light and so can't be seen directly with our telescopes. With the large number of gravitational lenses that we'll get from our full survey, we'll really be able to get to grips with this hidden Universe."

The University of Nottingham has broad research portfolio but has also identified and badged 13 research priority groups, in which a concentration of expertise, collaboration and resources create significant critical mass. Key research areas at Nottingham include energy, drug discovery, global food security, biomedical imaging, advanced manufacturing, integrating global society, operations in a digital world, and science, technology & society.

Through these groups, Nottingham researchers will continue to make a major impact on global challenges.

NASA extends TIMED mission for fourth time

Nine years after beginning its unprecedented look at the gateway between Earth's environment and space, not to mention collecting more data on the upper atmosphere than any other satellite, NASA's Thermosphere Ionosphere Mesosphere Energetics and Dynamics (TIMED) mission has been extended again.

Before the launch of TIMED, the mesosphere and lower thermosphere/ionosphere -- which help protect us from harmful solar radiation -- had been one of the least explored and understood regions of our environment.

"The middle part of the atmosphere was the part we kind of ignored," says John Sigwarth, the deputy project scientist for TIMED at NASA's Goddard Space Flight Center in Greenbelt, MD. "It's too high for balloons and too low for spacecraft. So the understanding of this middle atmosphere and its impact on the upper atmosphere has been tremendously increased due to TIMED."

The mission will now continue to study the influences of the sun and humans on our upper atmosphere. TIMED began its extended mission on Oct. 1, 2010, and will collect data through 2014. This is its fourth extension since the original 2-year mission began in January 2002. TIMED will focus this time on a problem that has long puzzled scientists: differentiating between human-induced and naturally occurring changes in this atmospheric region. This extension also allows TIMED to continue collecting data for longer than a full 11-year solar cycle.

"The sun is a variable star with an 11 year cycle," says Sigwarth. "So, if things change in the mesosphere, you don't know if it's because the sun changed or because human activity has caused the change. By getting back to the same point in the cycle, we can compare what it was like then, and what it's like now, and see if there's a long term trend of changes that's not solar related."

In addition to checking for effects from humans, TIMED scientists would like to understand how cooling temperatures in the middle atmosphere are causing the thermosphere to become less dense and its composition to change. With fewer particles in the thermosphere, there's less drag on satellites in space, which affects how long spacecraft and space debris stay in orbit -- information that must be integrated into calculations for orbit models.

Composition changes in the thermosphere can also alter ionospheric structures that affect radio wave propagation and communications. To help with this is an instrument called SEE (or the Solar EUV Experiment) built at the University of Colo., which looks at the sun's x-rays and extreme ultraviolet rays to see how they impact our atmosphere.

TIMED will also collaborate with NASA's newest eye on the Sun, the Solar Dynamics Observatory, which provides continuing solar radiation measurements and new views of how solar activity is created.

NASA's Goddard Space Flight Center in Greenbelt, Md. manages the TIMED mission for the agency's Science Mission Directorate at NASA Headquarters in Washington. The spacecraft was built by the Johns Hopkins University Applied Physics Laboratory in Laurel, Md.

Students fly in zero gravity to protect satellites from tiny meteoroids

Stanford researchers have completed the first successful tests in zero gravity of a canopy for CubeSats -- the tiny satellites that hitch rides on rockets sending larger satellites into orbit. The goal is to gather data on what happens when micrometeoroids slam into a satellite. Such impacts often knock out electronic equipment on satellites. The encounters are poorly understood, but the canopies could be a first step in eventually building "black boxes" for satellites similar to airplane flight recorders.

Orbiting the Earth is risky business for a satellite. Over a hundred billion meteoroids enter Earth's atmosphere every day, and while big, fierce, spacecraft-crushing meteoroids are rare, even the tiniest ones are a hazard.

What happens when a really tiny meteoroid (so small a stack of 500 would stand less than an inch tall) hits a satellite is not fully understood, but Stanford researchers have successfully done preliminary testing of a device that may help shed light on these collisions in space.

The testing was in zero gravity, aboard a diving airplane flying over the ocean.

Nicolas Lee, a graduate student in aeronautics and astronautics, and several colleagues have designed a canopy to pop out of a tiny satellite called a CubeSat and absorb the impacts of these micrometeoroids, sometimes referred to as "interplanetary flyspecks."

"The canopy might eventually be deployed to protect a spacecraft from meteoroids or shield it from the sun, but for now, we just want it to get hit," Lee said.

Even tiny meteoroids travel at tremendous speeds in orbit around the sun (more than 250,000 kilometers per hour) and pack a hefty punch when they strike a spacecraft.

"It is pretty much an explosion," Lee said.

Since the impact disrupts the satellite's electronics, no one knows exactly how the micrometeoroid causes the damage. But Lee's advisor, Sigrid Close, assistant professor of aeronautics and astronautics, has a theory.

She suspects the meteoroid instantly vaporizes into free electrons and ions that float around in a little ball. As that ball expands in the vacuum of space, it gives off energy at radio frequencies that interfere with the electronic equipment on the satellite, disrupting communications and other essential functions.

"We want to fly a dedicated mission that can study this effect and make sure that we can protect against it," Lee said. For that mission, the team would work with Andrew Kalman, a consulting professor of aeronautics and astronautics, to equip a CubeSat with plasma sensors and radio antennas to measure radio frequency emissions.

As a first step in field-testing their canopy, Lee and fellow graduate students Shandor Dektor and Joseph Johnson recently tested their canopies in zero gravity aboard a NASA-hire airplane flying over the Gulf of Mexico.

The plane flew a flight path any rollercoaster lover would die for: up and down in a series of parabolas, from about 22,000 to 32,000 feet. At the top of each parabola, the plane's occupants experienced weightlessness for about 20 seconds, which was when the team tested how their canopies opened. Over the course of two flights and 80 parabolas, the students did 37 successful trial runs.

Operating in zero gravity took some getting used to. "You don't realize gravity is gone so you are still pushing against it," Lee said. "And so you end up feeling like you are falling upwards."

The team tested three prototypes of the canopy, each a square meter in area. One design was thin mylar, rolled up in a spiral pattern inside the little black CubeSat box. Another design had the mylar folded to expand in a radial pattern. The third design used the spiral unfolding, but with a thicker membrane for the canopy. For all the designs, the unfolding was powered by struts made of common metal tape measures rolled up with the canopies.

The thin membrane rolled in a spiral pattern was the most successful. Lee thinks with proper folding, a thicker membrane could work well, too. Although Lee had some prior experience in origami, he said getting the proper folding was initially just trial and error.

"I folded so many prototypes," he said. But after figuring out the basic geometry of the folding, he developed a mathematical algorithm to employ.

"We are also hoping to deploy some metallic sheets, which might give us a different effect than the plastic mylar we've been using," he said. "For the purpose of a meteoroid impact screen, we would need a thicker membrane so the screen doesn't break when it gets hit by a large meteoroid."

When the CubeSat is deployed in space, in addition to zero gravity, it will have to open in a vacuum, so the researchers want to take their canopies into a vacuum chamber and shoot high velocity particles at it to supplement the zero gravity tests.

As the CubeSat canopy testing progresses, Close sees long-term potential not only in protecting satellites but also in recording what spacecraft experience in orbit.

"This could lead to devices that could be attached to satellites just like a black box in an airplane," Close said.

The zero-gravity flight was sponsored by the National Aeronautics and Space Administration.

Cosmic curiosity reveals ghostly glow of dead quasar

While sorting through hundreds of galaxy images as part of the Galaxy Zoo citizen science project two years ago, Dutch schoolteacher and volunteer astronomer Hanny van Arkel stumbled upon a strange-looking object that baffled professional astronomers. Two years later, a team led by Yale University researchers has discovered that the unique object represents a snapshot in time that reveals surprising clues about the life cycle of black holes.

In a new study, the team has confirmed that the unusual object, known as Hanny's Voorwerp (Hanny's "object" in Dutch), is a large cloud of glowing gas illuminated by the light from a quasar -- an extremely energetic galaxy with a supermassive black hole at its center. The twist, described online in the Astrophysical Journal Letters, is that the quasar lighting up the gas has since burned out almost entirely, even though the light it emitted in the past continues to travel through space, illuminating the gas cloud and producing a sort of "light echo" of the dead quasar.

"This system really is like the Rosetta Stone of quasars," said Yale astronomer Kevin Schawinski, a co-founder of Galaxy Zoo and lead author of the study. "The amazing thing is that if it wasn't for the Voorwerp being illuminated nearby, the galaxy never would have piqued anyone's interest."

The team calculated that the light from the dead quasar, which is the nearest known galaxy to have hosted a quasar, took up to 70,000 years to travel through space and illuminate the Voorwerp -- meaning the quasar must have shut down sometime within the past 70,000 years.

Until now, it was assumed that supermassive black holes took millions of years to die down after reaching their peak energy output. However, the Voorwerp suggests that the supermassive black holes that fuel quasars shut down much more quickly than previously thought. "This has huge implications for our understanding of how galaxies and black holes co-evolve," Schawinski said.

"The time scale on which quasars shut down their prodigious energy output is almost entirely unknown," said Meg Urry, director of the Yale Center for Astronomy & Astrophysics and a co-author of the paper. "That's why the Voorwerp is such an intriguing -- and potentially critical -- case study for understanding the end of black hole growth in quasars."

Although the galaxy no longer shines brightly in X-ray light as a quasar, it is still radiating at radio wavelengths. Whether this radio jet played a role in shutting down the central black hole is just one of several possibilities Schawinski and the team will investigate next.

"We've solved the mystery of the Voorwerp," he said. "But this discovery has raised a whole bunch of new questions."

Other authors of the paper include Shanil Virani, Priyamvada Natarajan, Paolo Coppi (all of Yale University); Daniel Evans (Massachusetts Institute of Technology, Harvard-Smithsonian Center for Astrophysics and Elon University); William Keel and Anna Manning (University of Alabama and Kitt Peak National Observatory); Chris Lintott (University of Oxford and Adler Planetarium); Sugata Kaviraj (University of Oxford and Imperial College London); Steven Bamford (University of Nottingham); Gyula Józsa (Netherlands Institute for Radio Astronomy and Argelander-Institut für Astronomie); Michael Garrett (Netherlands Institute for Radio Astronomy, Leiden Observatory and Swinburne University of Technology); Hanny van Arkel (Netherlands Institute for Radio Astronomy); Pamela Gay (Southern Illinois University Edwardsville); and Lucy Fortson (University of Minnesota).

Deep impact spacecraft successfully flies by comet Hartley 2

The University of Maryland-led EPOXI mission successfully flew by comet Hartley 2 at 10 a.m. EDT Nov. 3, 2010, and the spacecraft has begun returning images. Hartley 2 is the fifth comet nucleus visited by any spacecraft and the second one visited by the Deep Impact spacecraft.

Scientists and mission controllers are studying never-before-seen images of Hartley 2 appearing on their computer terminal screens. See images at: http://epoxi.umd.edu/

"We are all holding our breath to see what discoveries await us in the observations near closest approach," said University of Maryland astronomer Michael A'Hearn, one of the originators of science team leader for both the Deep Impact mission and its follow on mission EPOXI.

At approximately 10 a.m. EDT, the spacecraft passed within 700 kilometers (435 miles) of the comet. Minutes after closest approach, the spacecraft's High-Gain Antenna was pointed at Earth and began downlinking vital spacecraft health and other engineering data stored aboard the spacecraft's onboard computer during the encounter. Twenty minutes later, the first images of the encounter made the 37 million kilometer (23 million mile) trip from the spacecraft to NASA's Deep Space Network antenna, appearing moments later on the mission's computer screens.

"The mission team and scientists have worked for this day," said Tim Larson, EPOXI project manager at NASA's Jet Propulsion Laboratory, Pasadena, Calif. "It's good to see Hartley 2 up close."

A Deeper Impact on Planetary Science

With the latest EPOXI mission data on Hartley 2, the Deep Impact spacecraft is adding to an already extensive scientific legacy. Launched in January 2005, the spacecraft made scientific history and world-wide headlines when it smashed a probe into comet Tempel 1 on July 4th of that year. Following the conclusion of that mission, a Maryland-led team of scientists won approval from NASA to fly the Deep Impact spacecraft to a second comet.

The name EPOXI itself is a combination of the names for the two extended mission components: the extrasolar planet observations, called Extrasolar Planet Observations and Characterization (EPOCh), and the flyby of comet Hartley 2, called the Deep Impact Extended Investigation (DIXI). During the EPOCh phase of EPOXI, the Deep Impact spacecraft provided information on possible extrasolar planets and was one of three spacecraft to find for the first time clear evidence of water on Moon. A study accepted for publication in The Astrophysical Journal and just released by NASA, provides "colorful" findings on Earth and other planets in our solar system that someday may help identify earthlike worlds around other stars.

The overall objective of the flyby of Hartley 2 is the same as that for the Deep Impact mission's trip to Tempel 1: to learn more about the origin and history of our solar system by learning more about the composition and diversity of comets. Comets contain material from the early days of the solar system before the planets formed. "If we understand the comets really well it will tell us how the planets got made," explained A'Hearn. "That's why we choose comets to study."

NASA's Jet Propulsion Laboratory, Pasadena, Calif., manages the EPOXI mission for NASA's Science Mission Directorate, Washington. The University of Maryland, College Park, is home to the mission's principal investigator, Michael A'Hearn and eight other members of the EPOXI science team. Drake Deming of NASA's Goddard Space Flight Center, Greenbelt, Md., is the science lead for the mission's extrasolar planet observations. The spacecraft was built for NASA by Ball Aerospace & Technologies Corp., Boulder, Colo.

NASA's Chandra finds youngest nearby black hole

Astronomers using NASA's Chandra X-ray Observatory have found evidence of the youngest black hole known to exist in our cosmic neighborhood. The 30-year-old black hole provides a unique opportunity to watch this type of object develop from infancy.

The black hole could help scientists better understand how massive stars explode, which ones leave behind black holes or neutron stars, and the number of black holes in our galaxy and others.

The 30-year-old object is a remnant of SN 1979C, a supernova in the galaxy M100 approximately 50 million light years from Earth. Data from Chandra, NASA's Swift satellite, the European Space Agency's XMM-Newton and the German ROSAT observatory revealed a bright source of X-rays that has remained steady during observation from 1995 to 2007. This suggests the object is a black hole being fed either by material falling into it from the supernova or a binary companion.

"If our interpretation is correct, this is the nearest example where the birth of a black hole has been observed," said Daniel Patnaude of the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass. who led the study.

The scientists think SN 1979C, first discovered by an amateur astronomer in 1979, formed when a star about 20 times more massive than the sun collapsed. Many new black holes in the distant universe previously have been detected in the form of gamma-ray bursts (GRBs).

However, SN 1979C is different because it is much closer and belongs to a class of supernovas unlikely to be associated with a GRB. Theory predicts most black holes in the universe should form when the core of a star collapses and a GRB is not produced.

"This may be the first time the common way of making a black hole has been observed," said co-author Abraham Loeb, also of the Harvard-Smithsonian Center for Astrophysics. "However, it is very difficult to detect this type of black hole birth because decades of X-ray observations are needed to make the case."

The idea of a black hole with an observed age of only about 30 years is consistent with recent theoretical work. In 2005, a theory was presented that the bright optical light of this supernova was powered by a jet from a black hole that was unable to penetrate the hydrogen envelope of the star to form a GRB. The results seen in the observations of SN 1979C fit this theory very well.

Although the evidence points to a newly formed black hole in SN 1979C, another intriguing possibility is that a young, rapidly spinning neutron star with a powerful wind of high energy particles could be responsible for the X-ray emission. This would make the object in SN 1979C the youngest and brightest example of such a "pulsar wind nebula" and the youngest known neutron star. The Crab pulsar, the best-known example of a bright pulsar wind nebula, is about 950 years old.

"It's very rewarding to see how the commitment of some of the most advanced telescopes in space, like Chandra, can help complete the story," said Jon Morse, head of the Astrophysics Division at NASA's Science Mission Directorate.

The results will appear in the New Astronomy journal in a paper by Patnaude, Loeb, and Christine Jones of the Harvard-Smithsonian Center for Astrophysics. NASA's Marshall Space Flight Center in Huntsville, Ala., manages the Chandra program for the agency's Science Mission Directorate in Washington. The Smithsonian Astrophysical Observatory controls Chandra's science and flight operations from Cambridge.

For more information about Chandra, including images and other multimedia, visit: http://chandra.nasa.gov and http://chandra.harvard.edu

Primordial dry ice fuels comet jets

One of the biggest comet findings coming out of the amazing images and data taken by the University of Maryland-led EPOXI mission as it zipped past comet Hartley 2 last week is that dry ice is the 'jet' fuel for this comet and perhaps many others.

Images from the flyby show spectacular jets of gas and particles bursting from many distinct spots on the surface of the comet. This is the first time images of a comet have been sharp enough to allow scientists to link jets of dust and gas with specific surface features. Analysis of the spectral signatures of the materials coming from the jets shows primarily CO2 gas (carbon dioxide) and particles of dust and ice.

"Previously it was thought that water vapor from water ice was the propulsive force behind jets of material coming off of the body, or nucleus, of the comet," said University of Maryland Astronomy Professor Jessica Sunshine, who is deputy principal investigator for the EPOXI mission. "We now have unambiguous evidence that solar heating of subsurface frozen carbon dioxide (dry ice), directly to a gas, a process known as sublimation, is powering the many jets of material coming from the comet. This is a finding that only could have been made by traveling to a comet, because ground based telescopes can't detect CO2 and current space telescopes aren't tuned to look for this gas," Sunshine said.

Sunshine and other members of the EPOXI science team are meeting all this week at the University of Maryland to analyze the very large amount of data from the closest approach, and new data continues to come down at a rate of some 2000 images a day.

The Deep Impact spacecraft that flew past comet Hartley 2 has three instruments -- two telescopes with digital color cameras and an infrared spectrometer. The spectrometer measures the absorption, emission and reflection of light (spectroscopic signature) that is unique to each molecular compound. This allows Maryland scientists to determine the composition of the material on the comet's surface, in the jets, and in the coma, or cloud of particles around it. They have found that water and carbon dioxide dominate the infrared spectrum of comet Hartley 2's environment and that organics, including methanol, are present at lower levels.

This is no surprise to scientists. But what is surprising is that there is a lot more carbon dioxide escaping this comet than expected. "The distribution of carbon dioxide and dust around the nucleus is much different than the water distribution, and that tells us that the carbon dioxide rather than water takes dust grains with it into the coma as it leaves the nucleus, said Assistant Research Scientist Lori Feaga. "The dry ice that is producing the CO2 jets on this comet has probably been frozen inside it since the formation of the solar system."

From Deep Impact to Hartley 2

According to University of Maryland Research Scientist Tony Farnham, findings from the team's 2005 Deep Impact mission to comet Tempel 1, though less conclusive, nonetheless indicate that the Hartley 2 findings that super-volatiles (CO2) and not water drive the activity, probably are a common characteristic of comets. "Tempel 1 was most active before perihelion when its southern hemisphere, the hemisphere that appeared to be enhanced in CO2, was exposed to sunlight," said Farnham, a member of both the Deep Impact and EPOXI science teams. "Unlike our Hartley encounter, during the flyby with Tempel 1, we were unable to directly trace the CO2 to the surface, because the pole was in darkness during encounter."

The Maryland scientists devised the plan to reuse the Deep Impact spacecraft and travel to a second comet in order to learn more about the diversity of comets and the processes that govern them. This became the EPOXI mission on which the spacecraft has flown to comet Hartley 2.

The spacecraft's images show that Hartley 2 has an elongated nucleus, 2 kilometers in length and 0.4 kilometers wide at the narrow neck. Hartley 2 is only the 5th cometary nucleus ever seen and exhibits similarities and differences to the bodies or nuclei of other comets. Mission Principal Investigator and science team leader Michael A'Hearn, a University of Maryland professor of astronomy, said the mission has provided, and continues to provide, a tremendous wealth of data about Hartley 2 and the team expects to announce more science findings in the coming weeks.

Story Source:

The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by University of Maryland.

Note: If no author is given, the source is cited instead.

Neutron stars may be too weak to power some gamma-ray bursts; Black holes may be power source

A gamma-ray burst is an immensely powerful blast of high-energy light thought to be generated by a collapsing star in a distant galaxy, but what this collapse leaves behind has been a matter of debate.

A new analysis of four extremely bright bursts observed by NASA's Fermi satellite suggests that the remnant from a long-duration gamma-ray burst is most likely a black hole -- not a rapidly spinning, highly magnetized neutron star, or magnetar since such a burst emits more energy than is theoretically possible from a magnetar.

"Some of the events we have been finding seem to be pushing right up against this total limit for a neutron star progenitor system," said S. Bradley Cenko, a post-doctoral fellow from the University of California, Berkeley.

Cenko is presenting these findings Nov. 3 at the Nov. 1-4 Gamma Ray Bursts 2010 conference in Annapolis, Md. Cenko is a member of an international team that includes astronomers from UC Berkeley and the National Radio Astronomy Observatory (NRAO) in New Mexico.

The group has submitted a paper detailing its analysis to The Astrophysical Journal.

Long-duration gamma-ray bursts (GRBs) are presumed to be created by the explosive collapse in distant galaxies of massive stars. The explosion is visible from Earth because the light is emitted in a narrow cone, like a beam from a lighthouse. First discovered in 1967 by satellites looking for nuclear blasts on Earth, gamma-ray bursts have been the focus of several satellite missions, most recently NASA's Fermi gamma-ray space telescope, launched in 2008, and NASA's Swift satellite, launched in 2004.

With accumulating observations, astronomers have been able to create models of how the collapse of a rapidly rotating, massive star can accelerate matter to nearly the speed of light and collimate it into two oppositely directed, tightly focused beams along the spin axis. They have also studied how these particles generate gamma rays and other emissions.

The two leading candidates for powering these long-duration bursts are a magnetar and a black hole, sometimes referred to as a collapsar. In both cases, material from the star falls inward and is catapulted out by the spinning neutron star or black hole. What distinguishes these models is that magnetar-powered bursts cannot be as powerful as black hole-powered bursts.

"The question we have been trying to answer is: What is the true energy release from these events?" Cenko said. "We can measure all the light emitted -- very high energy gamma rays, and, at later times, X-ray, optical and radio afterglow emissions -- but that doesn't provide a very good estimate, because GRBs emit in relatively narrow jets. We have to get an idea of the geometry of this outflow, that is, how collimated the jets are."

Previous studies have shown that light measured in the afterglow begins to drop steeply at a certain point, and the sooner this drop-off, called a jet break, the narrower the jet. Typically, the gamma-ray burst itself lasts from a few seconds to as long as 100 seconds, but the afterglow, produced when the jets interact with gas and dust surrounding the star, emits visible light for a couple of weeks and radio radiation for several months.

While Swift has observed hundreds of bursts in the past five years and notified astronomers within seconds of detection, the instruments aboard the satellite detect mostly medium-sized bursts that are not as highly collimated and that have a jet break many days or weeks after the burst.

Fermi's Large Area Telescope, however, is sensitive to very bright bursts with jet breaks within several days of the burst, making follow-up observations easier with Swift's X-ray and ultraviolet-optical telescopes and the ground-based Very Large Array, a radio telescope operated by NRAO.

Fermi detects few extremely bright bursts, however -- only four in 2009, Cenko said -- and does not notify astronomers for nearly a day afterward. Once alerted, however, Cenko's team was able to observe the optical, X-ray and radio afterglow of these four events, find the jet break and use this information, along with the star's distance calculated from its redshift, to estimate the total energy output.

If the energy from these bright bursts were emitted in all directions, it would be equivalent to the mass of the sun being converted instantaneously into pure energy. Because the gamma-ray burst was focused in a cone only a few degrees wide, however, the energies for all four bursts were about 100-1,000 times less than this.

Theoretical models of how these beams are produced place a limit on how much energy a magnetar can generate in one of these explosive bursts: about 100 times less than if one converted the sun entirely into energy. Several of these bright bursts exceed this limit.

"The magnetar model is in serious trouble for such incredibly powerful events," noted coauthor Alex Filippenko, UC Berkeley professor of astronomy. "Even if the magnetar energy limit is not strictly violated, the tremendous efficiency required by this process strains credulity."

"In the future, we will be trying to make more precise measurements and be looking for more events to rule out a neutron star model," Cenko said.

Cenko and Filippenko's colleagues are post-doctoral fellows Nat R. Butler and Bethany E. Cobb, astronomy professor Joshua S. Bloom and graduate students Daniel A. Perley and Adam N. Morgan of UC Berkeley; Dale A. Frail of NRAO; Fiona A. Harrison, Mansi M. Kasliwal, Shrinivas R. Kulkarni and Vikram R. Rana of the California Institute of Technology; Joshua B. Haislip, Daniel E. Reichart, Aaron P. LaCluyze and Kevin M. Ivarsen of the University of North Carolina, Chapel Hill; Antonio Cucchiara and Derek B. Fox of Pennsylvania State University in University Park; Edo Berger of the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass.; Poonam Chandra of the Royal Military College of Canada in Kingston, Ontario; Jason X. Prochaska of the UCO/Lick Observatory at UC Santa Cruz; Karl Glazebrook of the Swinburne University of Technology in Victoria, Australia; Sebastian Lopez of the Universidad de Chile in Santiago; and Max Pettini of the University of Western Australia in Crawley.

The work of Cenko and Filippenko is supported by Gary and Cynthia Bengier, the Richard and Rhoda Goldman Fund, NASA and the National Science Foundation.

Formation of bulge on far side of moon explained

A bulge of elevated topography on the far side of the moon -- known as the lunar far side highlands -- has defied explanation for decades. But a new study led by researchers at the University of California, Santa Cruz, shows that the highlands may be the result of tidal forces acting early in the moon's history when its solid outer crust floated on an ocean of liquid rock.

Ian Garrick-Bethell, an assistant professor of Earth and planetary sciences at UC Santa Cruz, found that the shape of the moon's bulge can be described by a surprisingly simple mathematical function. "What's interesting is that the form of the mathematical function implies that tides had something to do with the formation of that terrain," said Garrick-Bethell, who is the first author of a paper on the new findings published in the November 11 issue of Science.

The paper describes a process for formation of the lunar highlands that involves tidal heating of the moon's crust about 4.4 billion years ago. At that time, not long after the moon's formation, the crust was decoupled from the mantle below it by an intervening ocean of magma. As a result, the gravitational pull of the Earth caused tidal flexing and heating of the crust. At the polar regions, where the flexing and heating was greatest, the crust became thinner, while the thickest crust would have formed in the regions in line with the Earth.

This process still does not explain why the bulge is now found only on the far side of the moon. "You would expect to see a bulge on both sides, because tides have a symmetrical effect," Garrick-Bethell said. "It may be that volcanic activity or other geological processes over the past 4.4 billion years have changed the expression of the bulge on the nearside."

The paper's coauthors include Francis Nimmo, associate professor of Earth and planetary sciences at UCSC, and Mark Wieczorek, a planetary geophysicist at the Institut de Physique du Globe in Paris. The researchers analyzed topographical data from NASA's Lunar Reconnaissance Orbiter and gravitational data from Japan's Kaguya orbiter.

A map of crustal thickness based on the gravity data showed that an especially thick region of the moon's crust underlies the lunar far side highlands. The variations in crustal thickness on the moon are similar to effects seen on Jupiter's moon Europa, which has a shell of ice over an ocean of liquid water. Nimmo has studied the effects of tidal heating on the structure of Europa, and the researchers applied the same analytical approach to the moon.

"Europa is a completely different satellite from our moon, but it gave us the idea to look at the process of tidal flexing of the crust over a liquid ocean," Garrick-Bethell said.

The mathematical function that describes the shape of the moon's bulge can account for about one-fourth of the moon's shape, he said. Although mysteries still remain, such as what made the nearside so different, the new study provides a mathematical framework for further investigations into the shape of the moon.

"It's still not completely clear yet, but we're starting to chip away at the problem," Garrick-Bethell said.

Simulating black hole radiation with lasers: Lasers produce the first Hawking radiation ever detected

A team of Italian scientists has fired a laser beam into a hunk of glass to create what they believe is an optical analogue of the Hawking radiation that many physicists expect is emitted by black holes.

Although the laser experiment superficially bears little resemblance to ultra-dense black holes, the mathematical theories used to describe both are similar enough that confirmation of laser-induced Hawking radiation would bolster confidence that black holes also emit Hawking radiation.

When Stephen Hawking first predicted the radiation bearing his name in 1974, he hypothesized that photons could be spontaneously generated from the vacuum at the edge of a black hole. However, Hawking radiation emitted from a black hole would be so weak that many scientists believe it to be nearly impossible to detect.

Scientists have turned to lasers before in attempts to create Hawking radiation, but have had difficulty isolating Hawking radiation from other forms of light emitted during experiments. Franco Belgiorno et al. combined a tunable laser beam with a bulk glass target, which allowed them to limit the Hawking radiation to certain wavelengths of infrared light and to capture the apparent Hawking radiation with an infrared sensitive digital camera.

A paper describing the possible production of a laser induced analogue of Hawking radiation appears in the current issue of Physical Review Letters, and is the subject of a Viewpoint article by John Dudley (CNRS, France) and Dmitry Skryabin (University of Bath, UK) in this week's edition of Physics.

WISE image reveals strange specimen in starry sea: Dying star surrounded by fluorescing gas, unusual rings

A new image from NASA's Wide-field Infrared Survey Explorer shows what looks like a glowing jellyfish floating at the bottom of a dark, speckled sea. In reality, this critter belongs to the cosmos -- it's a dying star surrounded by fluorescing gas and two very unusual rings.

"I am reminded of the jellyfish exhibition at the Monterey Bay Aquarium -- beautiful things floating in water, except this one is in space," said Edward (Ned) Wright, the principal investigator of the WISE mission at UCLA, and a co-author of a paper on the findings, reported in The Astronomical Journal.

The object, known as NGC 1514 and sometimes the "Crystal Ball" nebula, belongs to a class of objects called planetary nebulae, which form when dying stars toss off their outer layers of material. Ultraviolet light from a central star, or in this case a pair of stars, causes the gas to fluoresce with colorful light. The result is often beautiful -- these objects have been referred to as the butterflies of space.

NGC 1514 was discovered in 1790 by Sir William Herschel, who noted that its "shining fluid" meant that it could not be a faint cluster of stars, as originally suspected. Herschel had previously coined the term planetary nebulae to describe similar objects with circular, planet-like shapes.

Planetary nebulae with asymmetrical wings of nebulosity are common. But nothing like the newfound rings around NGC 1514 had been seen before. Astronomers say the rings are made of dust ejected by the dying pair of stars at the center of NGC 1514. This burst of dust collided with the walls of a cavity that was already cleared out by stellar winds, forming the rings.

"I just happened to look up one of my favorite objects in our WISE catalogue and was shocked to see these odd rings," said Michael Ressler, a member of the WISE science team at NASA's Jet Propulsion Laboratory in Pasadena, Calif., and lead author of the Astronomical Journal paper. Ressler first became acquainted with the object years ago while playing around with his amateur telescope on a desert camping trip. "It's funny how things come around full circle like this."

WISE was able to spot the rings for the first time because their dust is being heated and glows with the infrared light that WISE can detect. In visible-light images, the rings are hidden from view, overwhelmed by the brightly fluorescing clouds of gas.

"This object has been studied for more than 200 years, but WISE shows us it still has surprises," said Ressler.

Infrared light has been color-coded in the new WISE picture, such that blue represents light with a wavelength of 3.4 microns; turquoise is 4.6-micron light; green is 12-micron light; and red is 22-micron light. The dust rings stand out in orange. The greenish glow at the center is an inner shell of material, blown out more recently than an outer shell that is too faint to be seen in WISE's infrared view. The white dot in the middle is the central pair of stars, which are too close together for WISE to see separately.

Ressler says NGC 1514's structure, though it looks unique, is probably similar in overall geometry to other hour-glass nebulae, such as the Engraved Hourglass Nebula (http://hubblesite.org/newscenter/archive/releases/1996/07). The structure looks different in WISE's view because the rings are detectable only by their heat; they do not fluoresce at visible wavelengths, as do the rings in the other objects.

Serendipitous findings like this one are common in survey missions like WISE, which comb through the whole sky. WISE has been surveying the sky in infrared light since January 2010, cataloguing hundreds of millions of asteroids, stars and galaxies. In late September, after covering the sky about one-and-a-half times, it ran out of the frozen coolant needed to chill its longest-wavelength detectors. The mission, now called NEOWISE, is still scanning the skies with two of its infrared detectors, focusing primarily on comets and asteroids, including near-Earth objects, which are bodies whose orbits pass relatively close to Earth's orbit around the sun.

The WISE science team says that more oddballs like NGC 1514 are sure to turn up in the plethora of WISE data -- the first batch of which will be released to the astronomical community in spring 2011.

Other study authors are Martin Cohen of the Monterey Institute for Research in Astronomy, Marina, Calif.; Stefanie Wachter and Don Hoard of NASA's Spitzer Science Center at the California Institute of Technology in Pasadena; and Amy Mainzer of JPL.

JPL manages and operates the Wide-field Infrared Survey Explorer for NASA's Science Mission Directorate, Washington. The mission was competitively selected under NASA's Explorers Program managed by the Goddard Space Flight Center, Greenbelt, Md. The science instrument was built by the Space Dynamics Laboratory, Logan, Utah, and the spacecraft was built by Ball Aerospace & Technologies Corp., Boulder, Colo. Science operations and data processing take place at the Infrared Processing and Analysis Center at Caltech. Caltech manages JPL for NASA. More information is online at http://www.nasa.gov/wise , http://wise.astro.ucla.edu and http://www.jpl.nasa.gov/wise .

What will Webb see? Supercomputer models yield sneak previews

As scientists and engineers work to make NASA's James Webb Space Telescope a reality, they find themselves wondering what new sights the largest space-based observatory ever constructed will reveal. With Webb, astronomers aim to catch planets in the making and identify the universe's first stars and galaxies, yet these are things no telescope -- not even Hubble -- has ever shown them before.

"It's an interesting problem," said Jonathan Gardner, the project's deputy senior project scientist at NASA's Goddard Space Flight Center in Greenbelt, Md. "How do we communicate the great scientific promise of the James Webb Space Telescope when we've never seen what it can show us?"

So the project turned to Donna Cox, who directs the Advanced Visualization Laboratory (AVL) at the National Center for Supercomputing Applications (NCSA). Located at the University of Illinois in Urbana-Champaign, NCSA provides enormous computing resources to researchers trying to simulate natural processes at the largest and smallest scales, from the evolution of the entire universe to the movement of protein molecules through cell walls.

Cox and her AVL team developed custom tools that can transform a model's vast collection of ones and zeroes into an incredible journey of exploration. "We take the actual data scientists have computed for their research and translate them into state-of-the-art cinematic experiences," she said.

Armed with an ultra-high-resolution 3D display and custom software, the AVL team choreographs complex real-time flights through hundreds of gigabytes of data. The results of this work have been featured in planetariums, IMAX theaters and TV documentaries. "Theorists are the only scientists who have ventured where Webb plans to go, and they did it through complex computer models that use the best understanding of the underlying physics we have today," Cox said. "Our challenge is to make these data visually understandable -- and reveal their inherent beauty."

The new visualizations reflect the broad science themes astronomers will address with Webb. Among them: How did the earliest galaxies interact and evolve to create the present-day universe? How do stars and planets form?

"When we look at the largest scales, we see galaxies packed into clusters and clusters of galaxies packed into superclusters, but we know the universe didn't start out this way," Gardner said. Studies of the cosmic microwave background -- the remnants of light emitted when the universe was just 380,000 years old -- show that the clumpy cosmic structure we see developed much later on. Yet the farthest galaxies studied are already more than 500 million years old.

"Webb will show us what happened in between," Gardner added.

Cox and her AVL team visualized this epoch of cosmic construction from a simulation developed by Renyue Cen and Jeremiah Ostriker at Princeton University in New Jersey. It opens when the universe was 20 million years old and continues to the present-day, when the universe is 13.7 billion years old.

AVL team members Robert Patterson, Stuart Levy, Matthew Hall, Alex Betts and A. J. Christensen visualized how stars, gas, dark matter and colliding galaxies created clusters and superclusters of galaxies. Driven by the gravitational effect of dark matter, these structures connect into enormous crisscrossing filaments that extend over vast distances, forming what astronomers call the "cosmic web."

"We worked with nine scientists at five universities to visualize terabytes of computed data in order to take the viewer on a visual tour from the cosmic web, to smaller scales of colliding galaxies, to deep inside a turbulent nebula where stars and disks form solar systems like our own," Cox said. "These visuals represent current theories that scientists will soon re-examine through the eyes of Webb."

Closer to home, Webb will peer more deeply than ever before into the dense, cold, dusty clouds where stars and planets are born. Using data from models created by Aaron Boley at the University of Florida in Gainesville and Alexei Kritsuk and Michael Norman at the University of California, San Diego, the AVL team visualized the evolution of protoplanetary disks over tens of thousands of years.

Dense clumps develop far out in a disk's fringes, and if these clumps survive they may become gas giant planets or substellar objects called brown dwarfs. The precise outcome depends on the detailed makeup of the disk. "Dr. Boley was interested in what happened in the disk and did not include the central star," Cox said, "so to produce a realistic view we worked with him to add a young star."

This is astrophysics with a pinch of Hollywood sensibility, work at the crossroads of science and art. "The theoretical digital studies that form the basis of our work are so advanced that cinematic visualization is the most effective way to share them with the public," Cox said. "It's the art of visualizing science."

"What AVL has done for the Webb project is truly amazing and inspiring," Gardner noted. "It really whets our appetites for the science we'll be doing when the telescope begins work a few years from now."

Pushing black-hole mergers to the extreme: Scientists achieve 100:1 mass ratio in simulation

Scientists have simulated, for the first time, the merger of two black holes of vastly different sizes, with one mass 100 times larger than the other. This extreme mass ratio of 100:1 breaks a barrier in the fields of numerical relativity and gravitational wave astronomy.

Until now, the problem of simulating the merger of binary black holes with extreme size differences had remained an unexplored region of black-hole physics.

"Nature doesn't collide black holes of equal masses," says Carlos Lousto, associate professor of mathematical sciences at Rochester Institute of Technology and a member of the Center for Computational Relativity and Gravitation. "They have mass ratios of 1:3, 1:10, 1:100 or even 1:1 million. This puts us in a better situation for simulating realistic astrophysical scenarios and for predicting what observers should see and for telling them what to look for.

"Leaders in the field believed solving the 100:1 mass ratio problem would take five to 10 more years and significant advances in computational power. It was thought to be technically impossible."

"These simulations were made possible by advances both in the scaling and performance of relativity computer codes on thousands of processors, and advances in our understanding of how gauge conditions can be modified to self-adapt to the vastly different scales in the problem," adds Yosef Zlochower, assistant professor of mathematical sciences and a member of the center.

A paper announcing Lousto and Zlochower's findings was submitted for publication in Physical Review Letters.

The only prior simulation describing an extreme merger of black holes focused on a scenario involving a 1:10 mass ratio. Those techniques could not be expanded to a bigger scale, Lousto explained. To handle the larger mass ratios, he and Zlochower developed numerical and analytical techniques based on the moving puncture approach -- a breakthrough, created with Manuela Campanelli, director of the Center for Computational Relativity and Gravitation, that led to one of the first simulations of black holes on supercomputers in 2005.

The flexible techniques Lousto and Zlochower advanced for this scenario also translate to spinning binary black holes and for cases involving smaller mass ratios. These methods give the scientists ways to explore mass ratio limits and for modeling observational effects.

Lousto and Zlochower used resources at the Texas Advanced Computer Center, home to the Ranger supercomputer, to process the massive computations. The computer, which has 70,000 processors, took nearly three months to complete the simulation describing the most extreme-mass-ratio merger of black holes to date.

"Their work is pushing the limit of what we can do today," Campanelli says. "Now we have the tools to deal with a new system."

Simulations like Lousto and Zlochower's will help observational astronomers detect mergers of black holes with large size differentials using the future Advanced LIGO (Laser Interferometer Gravitational-wave Observatory) and the space probe LISA (Laser Interferometer Space Antenna). Simulations of black-hole mergers provide blueprints or templates for observational scientists attempting to discern signatures of massive collisions. Observing and measuring gravitational waves created when black holes coalesce could confirm a key prediction of Einstein's general theory of relativity.

Pulsating star mystery solved in rare alignment of Cepheid variable and another star

By discovering the first double star where a pulsating Cepheid variable and another star pass in front of one another, an international team of astronomers has solved a decades-old mystery. The rare alignment of the orbits of the two stars in the double star system has allowed a measurement of the Cepheid mass with unprecedented accuracy. The new result shows that the prediction from stellar pulsation theory is spot on, while the prediction from stellar evolution theory is at odds with the new observations.

The new results, from a team led by Grzegorz Pietrzynski (Universidad de Concepción, Chile, Obserwatorium Astronomiczne Uniwersytetu Warszawskiego, Poland), appear in the Nov. 25, 2010 edition of the journal Nature.

Grzegorz Pietrzynski introduces this remarkable result: "By using the HARPS instrument on the 3.6-metre telescope at ESO's La Silla Observatory in Chile, along with other telescopes, we have measured the mass of a Cepheid with an accuracy far greater than any earlier estimates. This new result allows us to immediately see which of the two competing theories predicting the masses of Cepheids is correct."

Classical Cepheid Variables, usually called just Cepheids, are unstable stars that are larger and much brighter than the Sun [1]. They expand and contract in a regular way, taking anything from a few days to months to complete the cycle. The time taken to brighten and grow fainter again is longer for stars that are more luminous and shorter for the dimmer ones. This remarkably precise relationship makes the study of Cepheids one of the most effective ways to measure the distances to nearby galaxies and from there to map out the scale of the whole Universe [2].

Unfortunately, despite their importance, Cepheids are not fully understood. Predictions of their masses derived from the theory of pulsating stars are 20% less than predictions from the theory of the evolution of stars. This embarrassing discrepancy has been known since the 1960s.

To resolve this mystery, astronomers needed to find a double star containing a Cepheid where the orbit happened to be seen edge-on from Earth. In these cases, known as eclipsing binaries, the brightness of the two stars dims as one component passes in front of the other, and again when it passes behind the other star. In such pairs astronomers can determine the masses of the stars to high accuracy [3]. Unfortunately neither Cepheids nor eclipsing binaries are common, so the chance of finding such an unusual pair seemed very low. None are known in the Milky Way.

Wolfgang Gieren, another member of the team, takes up the story: "Very recently we actually found the double star system we had hoped for among the stars of the Large Magellanic Cloud. It contains a Cepheid variable star pulsating every 3.8 days. The other star is slightly bigger and cooler, and the two stars orbit each other in 310 days. The true binary nature of the object was immediately confirmed when we observed it with the HARPS spectrograph on La Silla."

The observers carefully measured the brightness variations of this rare object, known as OGLE-LMC-CEP0227 [4], as the two stars orbited and passed in front of one another. They also used HARPS and other spectrographs to measure the motions of the stars towards and away from the Earth -- both the orbital motion of both stars and the in-and-out motion of the surface of the Cepheid as it swelled and contracted.

This very complete and detailed data allowed the observers to determine the orbital motion, sizes and masses of the two stars with very high accuracy -- far surpassing what had been done before for a Cepheid. The mass of the Cepheid is now known to about 1% and agrees exactly with predictions from the theory of stellar pulsation. However, the larger mass predicted by stellar evolution theory was shown to be significantly in error.

The much-improved mass estimate is only one outcome of this work, and the team hopes to find other examples of these remarkably useful pairs of stars to exploit the method further. They also believe that from such binary systems they will eventually be able to pin down the distance to the Large Magellanic Cloud to 1%, which would mean an extremely important improvement of the cosmic distance scale.

Notes

[1] The first Cepheid variables were spotted in the 18th century and the brightest ones can easily be seen to vary from night to night with the unaided eye. They take their name from the star Delta Cephei in the constellation of Cepheus (the King), which was first seen to vary by John Goodricke in England in 1784. Remarkably, Goodricke was also the first to explain the light variations of another kind of variable star, eclipsing binaries. In this case two stars are in orbit around each other and pass in front of each other for part of their orbits and so the total brightness of the pair drops. The very rare object studied by the current team is both a Cepheid and an eclipsing binary. Classical Cepheids are massive stars, distinct from similar pulsating stars of lower mass that do not share the same evolutionary history.

[2] The period luminosity relation for Cepheids, discovered by Henrietta Leavitt in 1908, was used by Edwin Hubble to make the first estimates of the distance to what we now know to be galaxies. More recently Cepheids have been observed with the Hubble Space Telescope and with the ESO VLT on Paranal to make highly accurate distance estimates to many nearby galaxies.

[3] In particular, astronomers can determine the masses of the stars to high accuracy if both stars happen to have a similar brightness and therefore the spectral lines belonging to each of the two stars can be seen in the observed spectrum of the two stars together, as is the case for this object. This allows the accurate measurement of the motions of both stars towards and away from Earth as they orbit, using the Doppler effect.

[4] The name OGLE-LMC-CEP0227 arises because the star was first discovered to be a variable during the OGLE search for gravitational microlensing. More details about OGLE are available at: http://ogle.astrouw.edu.pl/.

Detailed dark matter map yields clues to galaxy cluster growth

Astronomers using NASA's Hubble Space Telescope took advantage of a giant cosmic magnifying glass to create one of the sharpest and most detailed maps of dark matter in the universe. Dark matter is an invisible and unknown substance that makes up the bulk of the universe's mass.

The new dark matter observations may yield new insights into the role of dark energy in the universe's early formative years. The result suggests that galaxy clusters may have formed earlier than expected, before the push of dark energy inhibited their growth. A mysterious property of space, dark energy fights against the gravitational pull of dark matter. Dark energy pushes galaxies apart from one another by stretching the space between them, thereby suppressing the formation of giant structures called galaxy clusters. One way astronomers can probe this primeval tug-of-war is through mapping the distribution of dark matter in clusters.

A team led by Dan Coe at NASA's Jet Propulsion Laboratory in Pasadena, Calif., used Hubble's Advanced Camera for Surveys to chart the invisible matter in the massive galaxy cluster Abell 1689, located 2.2 billion light-years away. The cluster's gravity, the majority of which comes from dark matter, acts like a cosmic magnifying glass, bending and amplifying the light from distant galaxies behind it. This effect, called gravitational lensing, produces multiple, warped, and greatly magnified images of those galaxies, like the view in a funhouse mirror. By studying the distorted images, astronomers estimated the amount of dark matter within the cluster. If the cluster's gravity only came from the visible galaxies, the lensing distortions would be much weaker.

Based on their higher-resolution mass map, Coe and his collaborators confirm previous results showing that the core of Abell 1689 is much denser in dark matter than expected for a cluster of its size, based on computer simulations of structure growth. Abell 1689 joins a handful of other well-studied clusters found to have similarly dense cores. The finding is surprising, because the push of dark energy early in the universe's history would have stunted the growth of all galaxy clusters.

"Galaxy clusters, therefore, would had to have started forming billions of years earlier in order to build up to the numbers we see today," Coe explains. "At earlier times, the universe was smaller and more densely packed with dark matter. Abell 1689 appears to have been well fed at birth by the dense matter surrounding it in the early universe. The cluster has carried this bulk with it through its adult life to appear as we observe it today."

Mapping the Invisible

Abell 1689 is among the most powerful gravitational lensing clusters ever observed. Coe's observations, combined with previous studies, yielded 135 multiple images of 42 background galaxies.

"The lensed images are like a big puzzle," Coe says. "Here we have figured out, for the first time, a way to arrange the mass of Abell 1689 such that it lenses all of these background galaxies to their observed positions." Coe used this information to produce a higher-resolution map of the cluster's dark matter distribution than was possible before.

Coe teamed with mathematician Edward Fuselier, who, at the time, was at the United States Military Academy at West Point, to devise a new technique to calculate the new map. "Thanks, in large part, to Eddie's contributions, we have finally `cracked the code' of gravitational lensing. Other methods are based on making a series of guesses as to what the mass map is, and then astronomers find the one that best fits the data. Using our method, we can obtain, directly from the data, a mass map that gives a perfect fit."

Astronomers are planning to study more clusters to confirm the possible influence of dark energy. A major Hubble program that will analyze dark matter in gigantic galaxy clusters is the Cluster Lensing and Supernova survey with Hubble (CLASH). In this survey, the telescope will study 25 clusters for a total of one month over the next three years. The CLASH clusters were selected because of their strong X-ray emission, indicating they contain large quantities of hot gas. This abundance means the clusters are extremely massive. By observing these clusters, astronomers will map the dark matter distributions and look for more conclusive evidence of early cluster formation, and possibly early dark energy.

Enigma of missing stars in local group of galaxies may be solved

In the local group of galaxies that also includes the Andromeda Nebula and our Milky Way, there are about 100 billion stars. According to astronomers' calculations, there should be many more. Now, physicists from the University of Bonn and the University of St. Andrews in Scotland may have found an explanation for this discrepancy.

Their study will appear in the upcoming issue of the Monthly Notices of the Royal Astronomical Society.

New stars are born in the Universe around the clock -- on the Milky Way, currently about ten per year. From the birth rate in the past, we can generally calculate how populated space should actually be. But the problem is that the results of such calculations do not match our actual observations. "There should actually be a lot more stars that we can see," says Dr. Jan Pflamm-Altenburg, astrophysicist at the Argelander-Institut für Astronomie of the University of Bonn.

So, where are those stars?

For years, astronomers worldwide have been looking for a plausible explanation for this discrepancy. In cooperation with Dr. Carsten Weidner from St. Andrews University, Dr. Pflamm-Altenburg and Professor Dr. Pavel Kroupa, Professor of Astrophysics at the University of Bonn, may now have found the solution. It seems that so far, the birth rate has simply been overestimated. But this answer is not quite as simple as it sounds. Apparently, the error of estimation only occurs during periods of particularly high star production.

The reason for this lies in the manner in which astronomers calculate the birth rate. "For the local Universe -- i.e., the Milky Way as our home and the adjacent galaxies -- it is relatively simple," explains Professor Kroupa. "Here we are able to count the young stars one by one, using huge telescopes."

The problem with this method is that it only works for our immediate vicinity. But many galaxies are so distant that even the best telescope simply overlooks their small stars. As luck would have it, however, occasionally there is an especially large whopper among the newbie's in the sky. Such a star will, even if it cannot be directly discovered as an individual star, leave its traces in the light of even the farthest galaxies. The number of large whoppers then determines the strength of this trace.

In our immediate vicinity, these large whoppers occur with a fixed probability. There are always about 300 lightweights to one "big star baby." This numerical ratio seemed to be universal. So it was sufficient for astronomers to know the number of the large whoppers, for this allowed them to determine the number of new-born stars by simply multiplying the former number by a factor of 300.

Population explosion in space

Recently, however, some Bonn astronomers around Professor Kroupa began doubting the fixed ratio. Their hypothesis is that at times when the galactic nurseries are booming, they generate a considerably higher number of stellar heavies than normal. The reason for this, according to this theory, is so-called stellar crowding. For stars are not single children; they are born in groups, as so-called star clusters. At birth, these clusters are always of a similar size -- no matter whether they contain 100 star embryos -- or 100,000.

Consequently, at times of a high birth rate, space can be at a premium in star clusters. Astronomers call such galaxies that are particularly rich in mass "ultra-compact dwarf galaxies," or UCD's for short. In these, things are so tight that some of the young stars fuse during formation. Thus, more stars rich in mass than normal emerge. The "small to large" ratio is then only about 50 to 1. "In other words, we used to estimate the number of newly formed small stars by far too high," explains Dr. Carsten Weidner.

The researchers from Bonn and St. Andrews have now corrected the birth rates according to the projections of the stellar crowding theory. With an encouraging result -- they actually arrived at the number of stars that can be seen today.

Saturn is on a cosmic dimmer switch, Cassini reveals

Like a cosmic light bulb on a dimmer switch, Saturn emitted gradually less energy each year from 2005 to 2009, according to observations by NASA's Cassini spacecraft. But unlike an ordinary bulb, Saturn's southern hemisphere consistently emitted more energy than its northern one. On top of that, energy levels changed with the seasons and differed from the last time a spacecraft visited in the early 1980s.

These never-before-seen trends came from an analysis of comprehensive data from the Composite Infrared Spectrometer (CIRS), an instrument built by NASA's Goddard Space Flight Center in Greenbelt, Md., as well as a comparison with earlier data from NASA's Voyager spacecraft. When combined with information about the energy coming to Saturn from the sun, the results could help scientists understand the nature of Saturn's internal heat source.

The findings were reported November 9 in the Journal of Geophysical Research-Planets by Liming Li of Cornell University in Ithaca, N.Y. (now at the University of Houston), and colleagues from several institutions, including Goddard and NASA's Jet Propulsion Laboratory in Pasadena Calif., which manages the Cassini mission. "The Cassini CIRS data are very valuable because they give us a nearly complete picture of Saturn," says Li. "This is the only single data set that provides so much information about this planet, and it's the first time that anybody has been able to study the power emitted by one of the giant planets in such detail."

The planets in our solar system lose energy in the form of heat radiation in wavelengths that are invisible to the human eye. The CIRS instrument picks up wavelengths in the thermal infrared region, which is beyond red light, where the wavelengths correspond to heat emission.

"In planetary science, we tend to think of planets as losing power evenly in all directions and at a steady rate," says Li. "Now we know Saturn is not doing that." (Power is the amount of energy emitted per unit of time.)

Instead, Saturn's flow of outgoing energy was lopsided, with its southern hemisphere giving off about one-sixth more energy than the northern one, Li explains. This effect matched Saturn's seasons: during those five Earth years, it was summer in the southern hemisphere and winter in the northern one. (A season on Saturn lasts about seven Earth years.) Like Earth, Saturn has these seasons because the planet is tilted on its axis, so one hemisphere receives more energy from the sun and experiences summer while the other receives less energy and is shrouded in winter. Saturn's equinox, when the sun was directly over the equator, occurred in August 2009.

In the study, Saturn's seasons looked Earth-like in another way: in each hemisphere, its effective temperature, which characterizes its thermal emission to space, started to warm up or cool down as a change of season approached. Because Saturn's weather is variable and the atmosphere tends to retain heat (called heat inertia), the temperature changes in complicated ways throughout the atmosphere. "The effective temperature provides us a simple way to track the response of Saturn's atmosphere, as a system, to the seasonal changes," says Li. Cassini's observations in the northern hemisphere revealed that the effective temperature gradually dropped from 2005 to 2008 and then started to warm up again by 2009. In Saturn's southern hemisphere, the effective temperature cooled from 2005 to 2009, as the equinox started to approach.

The emitted energy for each hemisphere rose and fell along with the effective temperature. Even so, during this five-year period, the planet as a whole seemed to be slowly cooling down and emitting less energy.

To find out if similar changes were happening one Saturn year ago, the researchers looked at data collected by Voyager in 1980 and 1981. Like Cassini CIRS, Voyager recorded fluctuations in the energy emitted by the planet and in the effective temperature. But Voyager did not see the imbalance between the southern and northern hemispheres; instead, the two regions were much more consistent with each other.

Why wouldn't Voyager have seen the same summer-versus-winter difference between the two hemispheres? The amount of energy coming from the sun (called solar radiance), which drives weather and atmospheric temperatures, could have fluctuated from one Saturn year to the next. The patterns in Saturn's cloud cover and haze could have, too.

"It's reasonable to think that the changes in Saturn's emitted power are related to cloud cover," says Amy Simon-Miller, who heads the Planetary Systems Laboratory at Goddard and is a co-author on the paper. "As the amount of cloud cover changes, the amount of radiation escaping into space also changes. This might vary during a single season and from one Saturn year to another. But to fully understand what is happening on Saturn, we will need the other half of the picture: the amount of power being absorbed by the planet."

Li is finishing an analysis of the solar energy that came to Saturn, based on data sets collected by two other Cassini instruments, the imaging science subsystem and the visual and infrared mapping spectrometer. He agrees that this information is crucial because Saturn, like its fellow giant planets Jupiter and Neptune, is thought to have its own source of internal energy. (The fourth giant planet, Uranus, does not seem to have an internal source.) By studying the changes in Saturn's outgoing energy along with the changes in incoming solar energy, scientists can learn about the nature of the planet's internal energy source and whether it, too, changes over time.

"The differences between Saturn's northern and southern hemisphere and that fact that Voyager did not see the same asymmetry raise a very important question: does Saturn's internal heat vary with time?" says Li. "The answer will significantly deepen our understanding of the weather, internal structure and evolution of Saturn and the other giant planets."

The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency, and the Italian Space Agency. NASA's Jet Propulsion Laboratory, Pasadena, Calif., 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 composite infrared spectrometer team is based at NASA Goddard, where the instrument was built.

More Cassini information is available at http://www.nasa.gov/cassini and http://saturn.jpl.nasa.gov.