The team's findings suggest the moon possesses a solid, iron-rich inner core with a radius of nearly 150 miles and a fluid, primarily liquid-iron outer core with a radius of roughly 205 miles. Where it differs from Earth is a partially molten boundary layer around the core estimated to have a radius of nearly 300 miles. The research indicates the core contains a small percentage of light elements such as sulfur, echoing new seismology research on Earth that suggests the presence of light elements -- such as sulfur and oxygen -- in a layer around our own core.

The researchers used extensive data gathered during the Apollo-era moon missions. The Apollo Passive Seismic Experiment consisted of four seismometers deployed between 1969 and 1972, which recorded continuous lunar seismic activity until late-1977.

Live Web Chat

On Thursday, Jan. 20 from 3:00 to 4:00 EST, NASA planetary scientist Dr. Renee Weber will answer your questions about the inner workings of our nearest neighbor.

Joining the chat is easy! Simply return to this page http://www.nasa.gov/connect/chat/moon_core_chat.html a few minutes before 3:00 p.m. EST on Thursday, Jan. 20. The chat module will appear at the bottom of this page. After you log in, wait for the chat module to be activated, then ask your questions!

About Chat Expert Dr. Renee Weber

Dr. Renee Weber is a planetary scientist at NASA's Marshall Space Flight Center. She serves as the project scientist for the Lunar Mapping and Modeling Project, a software project designed to provide lunar maps and surface feature information to mission planners and other lunar researchers. Renee's scientific research focuses on planetary seismology, in particular the re-processing of seismic data from the Apollo missions. She is involved in several international efforts with goals of sending modern, broad-band seismometers to both the moon and Mars.

For more information visit http://www.nasa.gov/connect/chat/moon_core_chat.html

The image at left, taken in visible light, highlights the attributes of a typical spiral galaxy, including graceful, curving arms, pink star-forming regions, and brilliant blue strands of star clusters.

In the image at right, most of the starlight has been removed, revealing the Whirlpool's skeletal dust structure, as seen in near-infrared light. This new image is the sharpest view of the dense dust in M51. The narrow lanes of dust revealed by Hubble reflect the galaxy's moniker, the Whirlpool Galaxy, as if they were swirling toward the galaxy's core.

To map the galaxy's dust structure, researchers collected the galaxy's starlight by combining images taken in visible and near-infrared light. The visible-light image captured only some of the light; the rest was obscured by dust. The near-infrared view, however, revealed more starlight because near-infrared light penetrates dust. The researchers then subtracted the total amount of starlight from both images to see the galaxy's dust structure.

The red color in the near-infrared image traces the dust, which is punctuated by hundreds of tiny clumps of stars, each about 65 light-years wide. These stars have never been seen before. The star clusters cannot be seen in visible light because dense dust enshrouds them. The image reveals details as small as 35 light-years across.

Astronomers expected to see large dust clouds, ranging from about 100 light-years to more than 300 light-years wide. Instead, most of the dust is tied up in smooth and diffuse dust lanes. An encounter with another galaxy may have prevented giant clouds from forming.

Probing a galaxy's dust structure serves as an important diagnostic tool for astronomers, providing invaluable information on how the gas and dust collapse to form stars. Although Hubble is providing incisive views of the internal structure of galaxies such as M51, the planned James Webb Space Telescope (JWST) is expected to produce even crisper images.

Researchers constructed the image by combining visible-light exposures from Jan. 18 to 22, 2005, with the Advanced Camera for Surveys (ACS), and near-infrared light pictures taken in December 2005 with the Near Infrared Camera and Multi-Object Spectrometer (NICMOS).

For more information visit http://www.nasa.gov/mission_pages/hubble/science/two-faced.html

The unlikely pair, named Messier 81 and Messier 82, got to know each other a lot better during an encounter that occurred a few hundred million years ago. As they swept by each other, gravitational interactions triggered new bursts of star formation. In the case of Messier 82, also known as the Cigar galaxy, the encounter has likely triggered a tremendous wave of new star birth at its core. Intense radiation from newborn massive stars is blowing copious amounts of gas and smoky dust out of the galaxy, as seen in the WISE image in yellow hues.

"What's unique about the WISE view of this duo is that we can see both galaxies in one shot, and we can really see their differences," said Ned Wright of UCLA, the principal investigator of WISE. "Because the Cigar galaxy is bursting with star formation, it's really bright in the infrared, and looks dramatically different from its less active companion."

The WISE mission completed its main goal of mapping the sky in infrared light in October 2010, covering it one-and-one-half times before its frozen coolant ran out, as planned. During that time, it snapped pictures of hundreds of millions of objects, the first batch of which will be released to the astronomy community in April 2011. WISE is continuing its scan of the skies without coolant using two of its four infrared channels -- the two shorter-wavelength channels not affected by the warmer temperatures. The mission's ongoing survey is now focused primarily on asteroids and comets.

Because WISE has imaged the entire sky, it excels at producing large mosaics like this new picture of Messier 81 and Messier 82, which covers a patch of sky equivalent to three-by-three full moons, or 1.5 by 1.5 degrees.

It is likely these partner galaxies will continue to dance around each other, and eventually merge into a single entity. They are both spiral galaxies, but Messier 82 is seen from an edge-on perspective, and thus appears in visible light as a thin, cigar-like bar. When viewed in infrared light, Messier 82 is the brightest galaxy in the sky. It is what scientists refer to as a starburst galaxy because it is churning out large amounts of new stars.

"The WISE picture really shows how spectacular Messier 82 shines in the infrared even though it is relatively puny in both size and mass compared to its big brother, Messier 81," said Tom Jarrett, a member of the WISE team at the California Institute of Technology in Pasadena.

In this WISE view, infrared light has been color coded so that we can see it with our eyes. The shortest wavelengths (3.4 and 3.6 microns) are shown in blue and blue-green, or cyan, and the longer wavelengths (12 and 22 microns) are green and red. Messier 82 appears in yellow hues because its cocoon of dust gives off longer wavelengths of light (the yellow is a result of combining green and red). This dust is made primarily of polycyclic aromatic hydrocarbons, which are found on Earth as soot.

Messier 81, also known as Bode's galaxy, appears blue in the infrared image because it is not as dusty. The blue light is from stars in the galaxy. Knots of yellow seen dotting the spiral arms are dusty areas of recent star formation, most likely triggered by the galaxy's encounter with its rowdy partner.

"It's striking how the same event stimulated a classic spiral galaxy in Messier 81, and a raging starburst in Messier 82," said WISE Project Scientist Peter Eisenhardt of NASA's Jet Propulsion Laboratory in Pasadena, Calif. "WISE is finding the most extreme starbursts across the whole sky, out to distances over a thousand times greater than Messier 82."

Messier 81 is one of the brightest galaxies in the sky in visible light. Both it and its partner can be seen with binoculars on a dark, clear night in the northern constellation of Ursa Major, which contains the Big Dipper. The galaxies are 12 million light-years away from Earth.

JPL manages WISE for NASA's Science Mission Directorate. The mission was competitively selected under NASA's Explorers Program, which NASA's Goddard Space Flight Center in Greenbelt, Md., manages. The Space Dynamics Laboratory in Logan, Utah, built the science instrument, and Ball Aerospace & Technologies Corp. of Boulder, Colo., built the spacecraft. Science operations and data processing take place at the Infrared Processing and Analysis Center at the California Institute of Technology in Pasadena.

For more information visit http://www.jpl.nasa.gov/news/news.cfm?release=2011-016

"For 40 years, most astronomers regarded the Crab as a standard candle," said Colleen Wilson-Hodge, an astrophysicist at NASA's Marshall Space Flight Center in Huntsville, Ala., who presented the findings today at the American Astronomical Society meeting in Seattle. "Now, for the first time, we're clearly seeing how much our candle flickers."

The Crab Nebula is the wreckage of an exploded star whose light reached Earth in 1054. It is one of the most studied objects in the sky. At the heart of an expanding gas cloud lies what's left of the original star's core, a superdense neutron star that spins 30 times a second. All of the Crab's high-energy emissions are thought to be the result of physical processes that tap into this rapid spin.

For decades, astronomers have regarded the Crab's X-ray emissions as so stable that they've used it to calibrate space-borne instruments. They also customarily describe the emissions of other high-energy sources in "millicrabs," a unit derived from the nebula's output.

"The Crab Nebula is a cornerstone of high-energy astrophysics," said team member Mike Cherry at Louisiana State University in Baton Rouge, La. (LSU), "and this study shows us that our foundation is slightly askew." The story unfolded when Cherry and Gary Case, also at LSU, first noticed the Crab's dimming in observations by the Gamma-ray Burst Monitor (GBM) aboard NASA's Fermi Gamma-ray Space Telescope.

The team then analyzed GBM observations of the object from August 2008 to July 2010 and found an unexpected but steady decline of several percent at four different "hard" X-ray energies, from 12,000 to 500,000 electron volts (eV). For comparison, visible light has energies between 2 and 3 eV.

With the Crab's apparent constancy well established, the scientists needed to prove that the fadeout was real and was not an instrumental problem associated with the GBM. "If only one satellite instrument had reported this, no one would have believed it," Wilson-Hodge said.

So the team amassed data from the fleet of sensitive X-ray observatories now in orbit: NASA's Rossi X-Ray Timing Explorer (RXTE) and Swift satellites and the European Space Agency's International Gamma-Ray Astrophysics Laboratory (INTEGRAL). The results confirm a real intensity decline of about 7 percent at energies between 15,000 to 50,000 eV over two years. They also show that the Crab has brightened and faded by as much as 3.5 percent a year since 1999.

The scientists say that astronomers will need to find new ways to calibrate instruments in flight and to explore the possible effects of the inconstant Crab on past findings. A paper on the results will appear in the Feb. 1 issue of The Astrophysical Journal Letters.

Fermi's other instrument, the Large Area Telescope, has detected unprecedented gamma-ray flares from the Crab, showing that it is also surprisingly variable at much higher energies. A study of these events was published Thursday, Jan. 6, in Science Express.

The nebula's power comes from the central neutron star, which is also a pulsar that emits fast, regular radio and X-ray pulses. This pulsed emission exhibits no changes associated with the decline, so it cannot be the source. Instead, researchers suspect that the long-term changes probably occur in the nebula's central light-year, but observations with future telescopes will be needed to know for sure.

This region is dominated by four high-energy structures: an X-ray-emitting jet; an outflow of particles moving near the speed of light, called a "pulsar wind"; a disk of accumulating particles where the wind terminates; and a shock front where the wind abruptly slows.

"This environment is dominated by the pulsar's magnetic field, which we suspect is organized precariously," said Roger Blandford, who directs the Kavli Institute for Particle Astrophysics and Cosmology, jointly located at the Department of Energy's SLAC National Accelerator Laboratory and Stanford University. "The X-ray changes may involve some rearrangement of the magnetic field, but just where this happens is a mystery."

The Crab Nebula is a supernova remnant located 6,500 light-years away in the constellation Taurus.

NASA's Fermi is an astrophysics and particle physics partnership managed by NASA's Goddard Space Flight Center in Greenbelt, Md., and developed in collaboration with the U.S. Department of Energy, with important contributions from academic institutions and partners in France, Germany, Italy, Japan, Sweden and the United States.

The GBM Instrument Operations Center is located at the National Space Science Technology Center in Huntsville, Ala. The team includes a collaboration of scientists from UAH, NASA's Marshall Space Flight Center in Huntsville, the Max Planck Institute for Extraterrestrial Physics in Germany and other institutions.

NASA Goddard manages Swift, RXTE and a guest observer facility for U.S. participation in the European Space Agency's INTEGRAL mission.

For more information visit http://www.nasa.gov/mission_pages/GLAST/news/crab-nebula-surprise.html

Figuring out exactly which molecules are leaving these clues, known as "diffuse interstellar bands" (DIBs), is a puzzle that initially seemed straightforward but has gone unsolved for nearly a hundred years. The answer is expected to help explain how stars, planets and life form, so settling the matter is as important to astronomers who specialize in chemistry and biology as determining the nature of dark matter is to the specialists in physics.

Cordiner is presenting the team's research at the American Astronomical Society meeting in Seattle, Wash., on Jan. 10, 2011, and the results from Andromeda were published in an Astrophysical Journal paper on Jan. 1. The findings provide some evidence against one of the top candidates on the list of suspects: polycyclic aromatic hydrocarbons (PAHs), a group of molecules that is widespread in space. The research also reveals that some of the signatures found in Andromeda and the Triangulum are similar to ones seen in our own Milky Way, despite some big differences between those galaxies and ours.

"We have studied DIBs in incredibly diverse environments. Some have low levels of UV radiation. Some have radiation levels thousands of times higher. Some have different amounts of 'ingredients' available for making stars and planets," Cordiner says. "And throughout all of these, we see DIBs."

Missing in action

Until now, only two galaxies beyond our own have been investigated in detail for DIBs. Those are our nearest neighbors, the Large and Small Magellanic Clouds, which lie 160,000 to 200,000 light years away. (Researchers have conducted selective studies elsewhere, however.)

Andromeda and the Triangulum are located much farther away, at about 2.5 to 3 million light years from Earth. "At those distances, individual stars are so faint that we need to push even the largest telescopes in the world to their limits in order to observe them," Cordiner says.

That statement might seem strange to anyone who has looked into the night sky and seen either of these galaxies with the naked eye. Under favorable conditions, the galaxies appear as smudges in the constellations that bear their respective names.

But to study DIBs, researchers need to do much more than see that the galaxy is there. They have to pick out individual stars within the galaxy, and only a few telescopes worldwide are powerful enough to gather sufficient light for that. (The team used the Gemini Observatory's telescope in Hawaii.) This is why most DIBs found so far have been in the Milky Way.

Whichever galaxy an astronomer chooses, though, it will be made up of tens to hundreds of billions of stars. "The first step is choosing which stars to observe," Cordiner explains.

Cordiner's colleagues at Queen's University in Belfast, U.K., took the lead on finding good targets. They picked blue supergiants—stars that are very large, very hot and very bright. Supergiants also burn very clean: unlike our sun and other cooler stars, they contribute little background clutter to the observations being made.

To look for DIBs, an astronomer points the telescope at a star and scans through a rainbow made up of thousands of wavelengths of light. This rainbow, or spectrum, is extended a bit beyond visible light, into the UV at the blue end and into the infrared at the red end.

DIBs are not defined by what astronomers see while doing this, but by what they don't see. The colors missing from the rainbow, marked by black stripes, are the ones of interest. Each one is a wavelength being absorbed by some kind of atom or molecule.

A DIB is one of these regions where the color is missing. But compared to the nice, neat "absorption lines" that are identified with atoms or simple molecules, a DIB is not well-behaved, which is why it stands out.

"Astronomers were used to seeing quite sharp, narrow bands where typical atoms and molecules absorb," says Cordiner. "But DIBs are broad; that's why they are called 'diffuse.' Some DIBs have simple shapes and are quite smooth, but others have bumps and wiggles and may even be lopsided."

The mystery deepens

Over time, astronomers have been building up catalogs to show exactly which wavelengths are absorbed by all kinds of atoms and molecules. Each molecule has its own unique pattern, which can be used like a fingerprint: if a pattern found during an astronomical observation matches a pattern in one of the catalogs, the molecule can be identified.

It's a pretty straightforward concept. So, early researchers "would surely not have thought that the solution to the diffuse band problem would still be so elusive," wrote Peter Sarre in a 2006 review article about DIBs. Sarre, a professor of chemistry and molecular astrophysics at the University of Nottingham, U.K., supervised Cordiner's graduate-school work on DIBs.

The significance of the first DIBs, recorded in 1922 in Mary Lea Heger's Ph.D. thesis, was not immediately recognized. But once astronomers began systematic studies, starting with a 1934 paper by P. W. Merrill, they had every reason to believe the problem could be solved within a decade or two.

No such luck

More than 400 DIBs have been documented since then. But not one has been identified with enough certainty for astronomers to consider its case closed.

"With this many diffuse bands, you'd think we astronomers would have enough clues to solve this problem," muses Joseph Nuth, a senior scientist with the Goddard Center for Astrobiology who was not involved in this work. "Instead, it's getting more mysterious as more data is gathered."

Detailed analyses of the bumps and wiggles of the DIBs, suggest that the molecules which give rise to DIBs—called "carriers"—are probably large.

But like beauty, "large" is in the eye of the beholder. In this case, it means the molecule has at least 20 atoms or more. This is quite small compared to, say, a protein but huge compared to a molecule of carbon monoxide, a very common molecule in space.

Recently, though, more interest has been focused on at least one small molecule, a chain made from three carbon atoms and two hydrogen atoms (C3H2). This was tentatively identified with a pattern of DIBs.

Tenacious D

On the list of DIB-related suspects, all molecules have one thing in common: they are organic, which means they are built largely from carbon.

Carbon is great for building large numbers of molecules because it is available almost everywhere. In space, only hydrogen, helium and oxygen are more plentiful. Here on Earth, we find carbon in the planet's crust, the oceans, the atmosphere and all forms of life.

Likewise, astronomers "see DIBs pretty much in any direction we look," says Jan Cami, an astronomer at the University of Western Ontario, Canada. He has collaborated with Cordiner before but was not involved in this study. "And we see lots of DIBs."

Carbon is also great for building molecules in all kinds of configurations—millions of carbon compounds have been identified—and especially for building very stable molecules.

DIB carriers also seem to be quite stable. They survive the harsh physical conditions in the interstellar medium—the material found in the space between the stars. They also hang tough in the Large Magellanic Cloud, where radiation levels are thousands of times stronger than in the Milky Way. In fact, says Cordiner, DIB carriers seem comfortable almost everywhere except in the clouds of dense gas where stars are born.

"The carriers are readily formed but not readily destroyed in a wide range of different environments," says Cordiner. "It's remarkable how tenacious these molecules really are."

In short, carriers are thought to be made of carbon, Cami says, "because it's a lot easier to build strong and stable molecules from carbon atoms than from other elements, such as silicon or sulfur. Using those elements rather than carbon would be like building a house from a bucket of sand while there's a huge pile of bricks at the construction site."

The top three carrier candidates are: chain-like molecules, like the one now tentatively associated with a pattern of DIBs; PAHs, which often come up in studies of how planets formed; and compounds related to fullerenes, the soccer-ball-shaped molecules also known as buckyballs.

"This list covers most types of carbon molecules," notes Cami. "Chains are essentially the one-dimensional carbon molecules, PAHs are the two-dimensional ones, and fullerene compounds are the three-dimensional ones."

Present and accounted for

In spite of the challenges of looking for DIBs in other galaxies, it's worth the effort to astronomers because they need to see what DIBs look like under different conditions.

Granted, conditions are not uniform everywhere within a galaxy. Some stars have planets near them; others don't. Between the stars, in the vast tracts of interstellar medium, the relative amounts of gas and dust floating around can be different from one region to the next. And the exact mixture of chemicals can vary a little from place to place.

"But being on Earth and looking at another object in the Milky Way is like being in the crowd at Times Square in New York City on New Year's Eve and trying to find your friend," explains Nuth. "It's much easier to spot the person if you are on a balcony rather than standing in the crowd yourself." Likewise, it's much easier to get a clear overview of a galaxy when you are outside of it.

In some respects, Andromeda and the Triangulum are similar to the Milky Way. All three are spiral galaxies that belong to a collection of more than 30 nearby galaxies called the Local Group. The Milky Way is the largest member of this group. Andromeda is the second-largest, and the Triangulum is third.

Like the Milky Way, Andromeda and the Triangulum are thought to be good places to synthesize large organic molecules, which is what DIBs carriers are thought to be. And yet, says Cordiner, "nobody knew until now whether DIBs actually existed in either galaxy."

The team found that, indeed, DIBs do exist in both places, and they are strong, which implies there are many carriers.

In the Milky Way, when researchers find strong DIBs, they tend to find a lot of dust, too. This makes sense, because whenever there's more raw material available to make DIBs carriers, there's also more available to make dust. The team found the same situation in Andromeda, Cordiner says.

Of greater interest in Andromeda was whether the strength of the DIBs was related to the amount of PAHs, which are high on the list of candidates for carriers. The researchers knew going into the study that PAHs are plentiful in Andromeda, as they are in the Milky Way.

"The details of the PAH population seem to be somewhat different in Andromeda, though," says Cami. "This makes it interesting to try and find out exactly what is different."

But after checking to see if the PAH levels were related to DIBs strength, "we didn't find any correlation between the two," Cordiner says. That finding doesn't rule out a connection, but it might shift more attention to chains of carbon atoms or to fullerene compounds.

The carriers are not pure, isolated fullerenes, says Cami, who led the team that first detected fullerenes in space. More likely, "atoms or molecules are either locked up in fullerene cages or attached to the outside surface, " he explains. "This might even hold for some of the other proposed molecules. For example, you could think of carbon chains dangling from other molecules or even from dust grains."

The more things change . . .

One big difference between the Milky Way and Andromeda is the number of massive young stars. The Milky Way has more than Andromeda. Because those young stars generate a lot of UV radiation, the Milky Way's interstellar medium has higher levels of this radiation than Andromeda's does.

More radiation means a harsher environment, so organic molecules should survive better in an environment with less radiation. In that sense, Andromeda should be more favorable for the carriers of DIBs and, in theory, should be able to boast more of them. But Cordiner and his colleagues found that the DIBs in Andromeda were only slightly stronger than those in the Milky Way, implying that Andromeda can only claim slightly more carriers.

The observations in the Triangulum add even more intrigue. There, the researchers found strong DIBs even though this galaxy differs in its metallicity, which is a measure of the availability of ingredients for making stars and planets.

The consistency from galaxy to galaxy is surprising, given how much the conditions are thought to vary among them. "But there are no detailed studies of Andromeda to tell us everything we want to know about conditions there," says Cordiner. "And even less is known about the Triangulum."

As is usually the case in cutting-edge astronomy, some assumptions had to be made, and a lot depends on how well those assumptions hold up as more information becomes available.

Meanwhile, researchers will try to learn everything they can about DIBs near and far and the organic molecules they represent. "If we're going to understand fully how interstellar chemistry works—how stars and planets form," says Cordiner, "then we need a full understanding of the ingredients they use."

For more information visit http://www.nasa.gov/topics/universe/features/molecule-fingerprints.html

"NASA is pleased to support this important mission, and we have eagerly awaited Planck's first discoveries," said Jon Morse, NASA's Astrophysics Division director at the agency's headquarters in Washington. "We look forward to continued collaboration with ESA and more outstanding science to come."

Planck launched in May 2009 on a mission to detect light from just a few hundred thousand years after the Big Bang, an explosive event at the dawn of the universe approximately 13.7 billion years ago. The spacecraft's state-of-the-art detectors ultimately will survey the whole sky at least four times, measuring the cosmic microwave background, or radiation left over from the Big Bang. The data will help scientists decipher clues about the evolution, fate and fabric of our universe. While these cosmology results won't be ready for another two years or so, early observations of specific objects in our Milky Way galaxy, as well as more distant galaxies, are being released.

"The data we're releasing now are from what lies between us and the cosmic microwave background," said Charles Lawrence, the U.S. project scientist for Planck at NASA's Jet Propulsion Laboratory in Pasadena, Calif. We ultimately will subtract these data out to get at our cosmic microwave background signal. But by themselves, these early observations offer up new information about objects in our universe -- both close and far away, and everything in between."

Planck observes the sky at nine wavelengths of light, ranging from infrared to radio waves. Its technology has greatly improved sensitivity and resolution over its predecessor missions, NASA's Cosmic Background Explorer and Wilkinson Microwave Anisotropy Probe.

The result is a windfall of data on known and never-before-seen cosmic objects. Planck has catalogued approximately 10,000 star-forming "cold cores," thousands of which are newly discovered. The cores are dark and dusty nurseries where baby stars are just beginning to take shape. They also are some of the coldest places in the universe. Planck's new catalogue includes some of the coldest cores ever seen, with temperatures as low as seven degrees above absolute zero, or minus 447 degrees Fahrenheit. In order to see the coldest gas and dust in the Milky Way, Planck's detectors were chilled to only 0.1 Kelvin.

The new catalogue also contains some of the most massive clusters of galaxies known, including a handful of newfound ones. The most massive of these holds the equivalent of a million billion suns worth of mass, making it one of the most massive galaxy clusters known.

Galaxies in our universe are bound together into these larger clusters, forming a lumpy network across the cosmos. Scientists study the clusters to learn more about the evolution of galaxies and dark matter and dark energy -- the exotic substances that constitute the majority of our universe.

"Because Planck is observing the whole sky, it is giving us a comprehensive look at how all the smaller structures of the universe are connected to the whole," said Jim Bartlett, a U.S. Planck team member at JPL and the Astroparticule et Cosmologie-Universite Paris Diderot in France.

Planck's new catalogue also includes unique data on the pools of hot gas that permeate roughly 14,000 smaller clusters of galaxies; the best data yet on the cosmic infrared background, which is made up of light from stars evolving in the early universe; and new observations of extremely energetic galaxies spewing radio jets. The catalogue covers about one-and-a-half sky scans.

Planck is a European Space Agency mission, with significant participation from NASA. NASA's Planck Project Office is based at JPL. JPL contributed mission-enabling technology for both of Planck's science instruments. European, Canadian and U.S. Planck scientists will work together to analyze the Planck data. JPL is managed for NASA by the California Institute of Technology in Pasadena.

For more information visit http://www.nasa.gov/mission_pages/planck/planck20110111.html

Stone drew a crude sketch of this scalloped, multi-stranded ring, known as the F ring, in his notebook, but with no explanation next to it. The innumerable particles comprising the broad rings are in near-circular orbits about Saturn. So, it was a surprise to find that the F ring, discovered just a year before by NASA's Pioneer 11 spacecraft, had clumps and wayward kinks. What could have created such a pattern?

"It was clear Voyager was showing us something different at Saturn," said Stone, now based at the California Institute of Technology in Pasadena. "Over and over, the spacecraft revealed so many unexpected things that it often took days, months and even years to figure them out."

The F ring curiosity was only one of many strange phenomena discovered in the Voyager close encounters with Saturn, which occurred on Nov. 12, 1980, for Voyager 1, and Aug. 25, 1981, for Voyager 2. The Voyager encounters were responsible for finding six small moons and revealing the half-young, half-old terrain of Enceladus that had to point to some kind of geological activity.

Images from the two encounters also exposed individual storms roiling the planet's atmosphere, which did not show up at all in data from Earth-based telescopes. Scientists used Voyager data to resolve a debate about whether Titan had a thick or thin atmosphere, finding that Titan was shrouded in a thick haze of hydrocarbons in a nitrogen-rich atmosphere. The finding led scientists to predict there could be seas of liquid methane and ethane on Titan's surface.

"When I look back, I realize how little we actually knew about the solar system before Voyager," Stone added. "We discovered things we didn't know were there to be discovered, time after time."

In fact, the Voyager encounters sparked so many new questions that another spacecraft, NASA's Cassini, was sent to probe those mysteries. While Voyager 1 got to within about 126,000 kilometers (78,300 miles) above Saturn's cloud tops, and Voyager 2 approached as close as about 100,800 kilometers (62,600 miles), Cassini has dipped to this altitude and somewhat lower in its orbits around Saturn since 2004.

Because of Cassini's extended journey around Saturn, scientists have found explanations for many of the mysteries first seen by Voyager. Cassini has uncovered a mechanism to explain the new terrain on Enceladus – tiger stripe fissures with jets of water vapor and organic particles. It revealed that Titan indeed does have stable lakes of liquid hydrocarbons on its surface and showed just how similar to Earth that moon really is. Data from Cassini have also resolved how two small moons discovered by Voyager – Prometheus and Pandora – tug on the F ring to create its kinked shape and wakes that form snowballs.

"Cassini is indebted to Voyager for its many fascinating discoveries and for paving the way for Cassini," said Linda Spilker, Cassini project scientist at JPL, who started her career working on Voyager from 1977 to 1989. "On Cassini, we still compare our data to Voyager's and proudly build on Voyager's heritage."

But Voyager left a few mysteries that Cassini has not yet solved. For instance, scientists first spotted a hexagonal weather pattern when they stitched together Voyager images of Saturn's north pole. Cassini has obtained higher-resolution pictures of the hexagon – which tells scientists it's a remarkably stable wave in one of the jet streams that remains 30 years later – but scientists are still not sure what forces maintain the hexagon.

Even more perplexing are the somewhat wedge-shaped, transient clouds of tiny particles that Voyager discovered orbiting in Saturn's B ring. Scientists dubbed them "spokes" because they looked like bicycle spokes. Cassini scientists have been searching for them since the spacecraft first arrived. As Saturn approached equinox, and the sun's light hit the rings edge-on, the spokes did reappear in the outer part of Saturn's B ring. But Cassini scientists are still testing their theories of what might be causing these odd features.

"The fact that we still have mysteries today goes to show how much we still have to learn about our solar system," said Suzanne Dodd, Voyager's project manager, based at JPL. "Today, the Voyager spacecraft continue as pioneers traveling toward the edge of our solar system. We can't wait for the Voyager spacecraft to enter interstellar space – true outer space – and make more unexpected discoveries."

Voyager 1, which was launched on Sept. 5, 1977, is currently about 17 billion kilometers (11 billion miles) away from the sun. It is the most distant spacecraft. Voyager 2, which was launched on Aug. 20, 1977, is currently about 14 billion kilometers (9 billion miles) away from the sun.

The Voyagers were built by JPL, which continues to operate both spacecraft. Caltech manages JPL for NASA. The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. JPL manages Cassini for NASA. The Cassini orbiter and its two onboard cameras were designed, developed and assembled at JPL.

For more information visit http://www.nasa.gov/mission_pages/voyager/voyager20101111.html

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.

For more information visit http://www.nasa.gov/mission_pages/cassini/whycassini/dimmer-switch.html

"What we see are two gamma-ray-emitting bubbles that extend 25,000 light-years north and south of the galactic center," said Doug Finkbeiner, an astronomer at the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass., who first recognized the feature. "We don't fully understand their nature or origin."

The structure spans more than half of the visible sky, from the constellation Virgo to the constellation Grus, and it may be millions of years old. A paper about the findings has been accepted for publication in The Astrophysical Journal.

Finkbeiner and his team discovered the bubbles by processing publicly available data from Fermi's Large Area Telescope (LAT). The LAT is the most sensitive and highest-resolution gamma-ray detector ever launched. Gamma rays are the highest-energy form of light.

Other astronomers studying gamma rays hadn't detected the bubbles partly because of a fog of gamma rays that appears throughout the sky. The fog happens when particles moving near the speed of light interact with light and interstellar gas in the Milky Way. The LAT team constantly refines models to uncover new gamma-ray sources obscured by this so-called diffuse emission. By using various estimates of the fog, Finkbeiner and his colleagues were able to isolate it from the LAT data and unveil the giant bubbles.

Scientists now are conducting more analyses to better understand how the never-before-seen structure was formed. The bubble emissions are much more energetic than the gamma-ray fog seen elsewhere in the Milky Way. The bubbles also appear to have well-defined edges. The structure's shape and emissions suggest it was formed as a result of a large and relatively rapid energy release - the source of which remains a mystery.

One possibility includes a particle jet from the supermassive black hole at the galactic center. In many other galaxies, astronomers see fast particle jets powered by matter falling toward a central black hole. While there is no evidence the Milky Way's black hole has such a jet today, it may have in the past. The bubbles also may have formed as a result of gas outflows from a burst of star formation, perhaps the one that produced many massive star clusters in the Milky Way's center several million years ago.

"In other galaxies, we see that starbursts can drive enormous gas outflows," said David Spergel, a scientist at Princeton University in New Jersey. "Whatever the energy source behind these huge bubbles may be, it is connected to many deep questions in astrophysics."

Hints of the bubbles appear in earlier spacecraft data. X-ray observations from the German-led Roentgen Satellite suggested subtle evidence for bubble edges close to the galactic center, or in the same orientation as the Milky Way. NASA's Wilkinson Microwave Anisotropy Probe detected an excess of radio signals at the position of the gamma-ray bubbles.

The Fermi LAT team also revealed Tuesday the instrument's best picture of the gamma-ray sky, the result of two years of data collection.

"Fermi scans the entire sky every three hours, and as the mission continues and our exposure deepens, we see the extreme universe in progressively greater detail," said Julie McEnery, Fermi project scientist at NASA's Goddard Space Flight Center in Greenbelt, Md.

NASA's Fermi is an astrophysics and particle physics partnership, developed in collaboration with the U.S. Department of Energy, with important contributions from academic institutions and partners in France, Germany, Italy, Japan, Sweden and the United States.

"Since its launch in June 2008, Fermi repeatedly has proven itself to be a frontier facility, giving us new insights ranging from the nature of space-time to the first observations of a gamma-ray nova," said Jon Morse, Astrophysics Division director at NASA Headquarters in Washington. “These latest discoveries continue to demonstrate Fermi's outstanding performance.”

For more information visit http://www.nasa.gov/mission_pages/GLAST/news/new-structure.html

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."

The key instrument performing this work is known as SABER (or Sounding of the Atmosphere using Broadband Emission Radiometry), built by Hampton University in Hampton, Va. SABER can remotely sense composition and temperature in the mesosphere.

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.

For more information visit http://www.nasa.gov/topics/solarsystem/sunearthsystem/main/timed-extended.html

Radiation from the flare created a wave of ionization in Earth's upper atmosphere that altered the propagation of low-frequency radio waves. There was, however, no bright CME (plasma cloud) hurled in our direction, so the event is unlikely to produce auroras in the nights ahead.

This is the third M-flare in as many days from this increasingly active sunspot. So far none of the eruptions has been squarely Earth-directed, but this could change in the days ahead as the sun's rotation turns the active region toward our planet.

For more information visit http://www.nasa.gov/topics/solarsystem/sunearthsystem/main/News110610-Mflare.html

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.

The Hubble Space Telescope is a project of international cooperation between NASA and the European Space Agency. NASA's Goddard Space Flight Center manages the telescope. The Space Telescope Science Institute (STScI) conducts Hubble science operations. STScI is operated for NASA by the Association of Universities for Research in Astronomy, Inc., in Washington, D.C.

For more information visit http://www.nasa.gov/mission_pages/hubble/science/dark-matter-map.html

Cloud computing is a way to gain fast flexibility in computing ability by ordering capacity on demand -- as if from the clouds -- and paying only for what is used. NASA's Mars Exploration Rover Project moved to this strategy last week for the software and data that the rovers' flight team uses to develop daily plans for rover activities. NASA's Jet Propulsion Laboratory, Pasadena, Calif., which manages the project, gained confidence in cloud computing from experience with other uses of the technology, including public participation sites about Mars exploration.

"This is a change to thinking about computer capacity and data storage as a commodity like electricity, or even the money in your bank account," said JPL's John Callas, rover project manager. "You don't keep all your money in your wallet. Instead you go to a nearby ATM and get cash when you need it. Your money is safe, and the bank can hold as much or as little of the money as you want. Data is the same way: You don't need to have it on you all the time. It can be safely stored elsewhere and you can get it anytime via an Internet connection.

"When we need more computing capacity, we don't need to install more servers if we can rent more capacity from the cloud for just the time we need it. This way we don't waste electricity and air conditioning with servers idling waiting to be used, and we don't have to worry about hardware maintenance and operating system obsolescence."

Spirit and Opportunity landed on Mars in January 2004 for what were planned as three-month missions. Bonus, extended missions have continued for more than six years. Opportunity is currently active, requiring daily activity plans by a team of engineers at JPL, and scientists at many locations in North America and Europe. Spirit has been silent since March 2010 and is believed to be in a low-power hibernation mode for the Martian winter.

"The rover project is well suited for cloud computing," said Khawaja Shams, a JPL software engineer supporting the project. "It has a widespread user community acting collaboratively. Cloud enables us to deliver the data to each user from nearby locations for faster reaction time." Also, the unexpected longevity of the mission means the volume of data used has outgrown the systems originally planned for handling and sharing data, which makes the virtually limitless capacity of cloud computing attractive.

JPL collaborated with the cloud team of Amazon.com Inc., Seattle, to plan and implement the use of cloud computing in the Mars Exploration Rover Project's daily operations. JPL developed the rover project's activity-planning software, called Maestro.

"We have worked closely with multiple cloud vendors since 2007 to learn the best ways to gain the advantages of cloud computing," said Tomas Soderstrom, chief technology officer for the JPL Office of the Chief Information Officer. "To implement JPL CIO Jim Rinaldi's vision of renting instead of buying capacity, we pragmatically look past the hype about cloud computing to find the practical, cost-efficient real mission applications. The Mars Exploration Rover project's use of clouds is one example of this results-oriented partnership. More will follow."

In support of the federal Open Government Initiative, which increases public access to data collected by the federal government, JPL collaborated with the cloud team at Microsoft Corp., Redmond, Wash., to launch the "Be a Martian" website in November 2009. The site enables the public to participate as citizen scientists to improve Mars maps and take part in Mars research tasks.

For another early use of cloud computing, JPL worked with the cloud team at Google Inc., Mountain View, Calif. The Google cloud served a project in which JPL and computer science students at the University of California, San Diego, developed an educational application enabling fifth- and sixth-graders to tag labels onto images from Mars spacecraft.

In addition to establishing a private cloud and working with Amazon, Google and Microsoft, JPL has also collaborated with other vendors of public cloud computing. Soderstrom said, "We defined a 'cloud-oriented architecture' to use clouds as an extension of our own resources and to run the computing and storage where it is most appropriate for each application."

The extended missions of Spirit and Opportunity have provided a resource for testing innovations during an active space mission for possible use in future missions. New software uploads giving the rovers added autonomy have been one example, and cloud computing is another. JPL is currently building and testing NASA's next Mars rover, Curiosity, for launch in late 2011 in the Mars Science Laboratory mission. This rover will land on Mars in August 2012.

Shams said, "The experience we gain using cloud computing for planning Opportunity's activities may be valuable when Curiosity reaches Mars, too."

For more information visit http://www.nasa.gov/mission_pages/mer/news/mer20101102.html

Planets around other stars probably exhibit a rainbow of colors every bit as diverse as those in our solar system. And astronomers would like to eventually harness color to learn more about exoplanets. Are they rocky or gaseous — or earthlike?

In a study recently accepted for publication in The Astrophysical Journal, a team led by NASA astronomer Lucy McFadden and UCLA graduate student Carolyn Crow describe a simple way to distinguish between the planets of our solar system based on color information. Earth, in particular, stands out clearly among the planets, like a blue jay in a flock of seagulls.

"The method we developed separates the planets out," Crow says. "It makes Earth look unique."

This suggests that someday, when we have the technology to gather light from individual exoplanets, astronomers could use color information to identify earthlike worlds. "Eventually, as telescopes get bigger, there will be the light-gathering power to look at the colors of planets around other stars," McFadden says. "Their colors will tell us which ones to study in more detail."

Earth the Exoplanet

The project began in 2008, when Crow teamed up with McFadden, her faculty mentor at the University of Maryland in College Park. McFadden currently heads university and post-doctoral programs at NASA's Goddard Space Flight Center in Greenbelt, Maryland.

New color information about Earth, the moon, and Mars became available, thanks to NASA's Deep Impact spacecraft. En route to a planned encounter this November with Comet 103P/Hartley 2, Deep Impact observed Earth. The idea was to determine what our home looks like to alien astronomers and eventually use that insight to figure out how to spot earthlike worlds around other stars.

As Deep Impact cruised through space, its High Resolution Instrument (HRI) measured the intensity of Earth's light. HRI is an 11.8-inch (30 cm) telescope that feeds light through seven different color filters mounted on a revolving wheel. Each filter samples the incoming light at a different portion of the visible-light spectrum, from ultraviolet and blue to red and near-infrared. On May 28, 2008, Deep Impact even caught a glimpse of the moon's light as it crossed in front of Earth. Later, in 2009, HRI scoped Mars.

McFadden wondered what combination of color information from the filters would best distinguish Earth from the other planets and moons of the solar system. She recruited Crow to work on the project. Eight other researchers from NASA, the University of Maryland, the University of Washington (Seattle), and the Johns Hopkins University Applied Physics Lab also joined the team.

The Magic Mix

The Deep Impact color data covered Earth, the moon, and Mars. The relative amounts of light passing through the filters vary for each planet or moon, providing a kind of color fingerprint. To this the team added existing color information about Mercury, Venus, Jupiter, Saturn, Uranus, Neptune, and Saturn's moon Titan.

A simple side-by-side comparison of color data on all the major planets was a confusing mess. The team finally found a combination of three different filters — one in the blue, one in the green, and one in the red — that highlights the differences between the planets.

On a special "color-color" diagram the team created, the planets cluster into groups based on similarities in the wavelengths of sunlight that their surfaces and atmospheres reflect. The gas giants Jupiter and Saturn huddle in one corner, Uranus and Neptune in a different one. The rocky inner planets Mars, Venus, and Mercury cluster off in their own corner of "color space."

But Earth is the true loner in color space. Its uniqueness traces to two factors. One is the scattering of blue light by the atmosphere. This is called Rayleigh scattering, after the English scientist who discovered it.

The other reason Earth stands out in color space is because it does not absorb a lot of infrared light. That's because our atmosphere is low in infrared-absorbing gases like methane and ammonia, compared to the gas giant planets Jupiter and Saturn.

"It is Earth's atmosphere that dominates the colors of Earth," Crow says. "It's the scattering of light in the ultraviolet and the absence of absorption in the infrared."

Colorful Future

Someday, the three-filter approach may provide a rough "first cut" look at exoplanet surfaces and atmospheres. "There are some things we can tell from the colors but there are some things that we can't quite tell without additional information," Crow says.

For example, if an exoplanet shows a similar color fingerprint to Earth's, it would not necessarily mean that the planet has the blue skies and vast oceans of our home. But it would tell us to look at that planet more closely.

And that would be an important first step toward making sense of the colorful complexity of the 490 (and counting) alien planets already discovered, and the scores more on the way.

For more information visit http://www.nasa.gov/topics/universe/features/planet-colors.html

This new insight, garnered from images of Saturn's most massive ring, the B ring, may answer another long-standing question: What causes the bewildering variety of structures seen throughout the very densest regions of Saturn's rings?

Another finding from new images of the B ring's outer edge was the presence of at least two perturbed regions, including a long arc of narrow, shadow-casting peaks as high as 3.5 kilometers (2 miles) above the ring plane. The areas are likely populated with small moons that might have migrated across the outer part of the B ring in the past and got trapped in a zone affected by the moon Mimas' gravity. This process is commonly believed to have configured the present-day solar system.

"We have found what we hoped we'd find when we set out on this journey with Cassini nearly 13 years ago: visibility into the mechanisms that have sculpted not only Saturn's rings, but celestial disks of a far grander scale, from solar systems, like our own, all the way to the giant spiral galaxies," said Carolyn Porco, co-author on the new paper and Cassini imaging team lead, based at the Space Science Institute, Boulder, Colo.

Since NASA's Voyager spacecraft flew by Saturn in 1980 and 1981, scientists have known that the outer edge of the planet's B ring was shaped like a rotating, flattened football by the gravitational perturbations of Mimas. But it was clear, even in Voyager's findings, that the outer B ring's behavior was far more complex than anything Mimas alone might do.

Now, analysis of thousands of Cassini images of the B ring taken over a four-year period has revealed the source of most of the complexity: at least three additional, independently rotating wave patterns, or oscillations, that distort the B ring's edge. These oscillations, with one, two or three lobes, are not created by any moons. They have instead spontaneously arisen, in part because the ring is dense enough, and the B ring edge is sharp enough, for waves to grow on their own and then reflect at the edge.

"These oscillations exist for the same reason that guitar strings have natural modes of oscillation, which can be excited when plucked or otherwise disturbed," said Joseph Spitale, lead author on today's article and an imaging team associate at the Space Science Institute. "The ring, too, has its own natural oscillation frequencies, and that's what we're observing."

Astronomers believe such "self-excited" oscillations exist in other disk systems, like spiral disk galaxies and proto-planetary disks found around nearby stars, but they have not been able to directly confirm their existence. The new observations confirm the first large-scale wave oscillations of this type in a broad disk of material anywhere in nature.

Self-excited waves on small, 100-meter (300-foot) scales have been previously observed by Cassini instruments in a few dense ring regions and have been attributed to a process called "viscous overstability." In that process, the ring particles' small, random motions feed energy into a wave and cause it to grow. The new results confirm a Voyager-era predication that this same process can explain all the puzzling chaotic waveforms found in Saturn's densest rings, from tens of meters up to hundreds of kilometers wide.

"Normally viscosity, or resistance to flow, damps waves -- the way sound waves traveling through the air would die out," said Peter Goldreich, a planetary ring theorist at the California Institute of Technology in Pasadena. "But the new findings show that, in the densest parts of Saturn's rings, viscosity actually amplifies waves, explaining mysterious grooves first seen in images taken by the Voyager spacecraft."

The two perturbed B ring regions found orbiting within Mimas' zone of influence stretch along arcs up to 20,000 kilometers (12,000 miles) long. The longest one was first seen last year when the sun's low angle on the ring plane betrayed the existence of a series of tall structures through their long, spiky shadows. The small moons disturbing the material are probably hundreds of meters to possibly a kilometer or more in size.

The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. The Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the mission for NASA's Science Mission Directorate, Washington. The Cassini orbiter and its two onboard cameras were designed, developed and assembled at JPL. The imaging operations center is based at the Space Science Institute in Boulder, Colo.

For more information visit http://www.nasa.gov/mission_pages/cassini/whycassini/cassini20101101.html