Voyager Celebrates 25 Years Since Uranus Visit

Uranus in "natural" light, left and "enhanced" light on the right Miranda, innermost of Uranus' large satellites, is seen at close range Ariel's complex structure, seen close up.
As NASA's Voyager 2 spacecraft made the only close approach to date of our mysterious seventh planet Uranus 25 years ago, Project Scientist Ed Stone and the Voyager team gathered at NASA's Jet Propulsion Laboratory, Pasadena, Calif., to pore over the data coming in.

Images of the small, icy Uranus moon Miranda were particularly surprising. Since small moons tend to cool and freeze over rapidly after their formation, scientists had expected a boring, ancient surface, pockmarked by crater-upon-weathered-crater. Instead they saw grooved terrain with linear valleys and ridges cutting through the older terrain and sometimes coming together in chevron shapes. They also saw dramatic fault scarps, or cliffs. All of this indicated that periods of tectonic and thermal activity had rocked Miranda's surface in the past.

The scientists were also shocked by data showing that Uranus' magnetic north and south poles were not closely aligned with the north-south axis of the planet's rotation. Instead, the planet's magnetic field poles were closer to the Uranian equator. This suggested that the material flows in the planet's interior that are generating the magnetic field are closer to the surface of Uranus than the flows inside Earth, Jupiter and Saturn are to their respective surfaces.

"Voyager 2's visit to Uranus expanded our knowledge of the unexpected diversity of bodies that share the solar system with Earth," said Stone, who is based at the California Institute of Technology in Pasadena. "Even though similar in many ways, the worlds we encounter can still surprise us."

Voyager 2 was launched on Aug. 20, 1977, 16 days before its twin, Voyager 1. After completing its prime mission of flying by Jupiter and Saturn, Voyager 2 was sent on the right flight path to visit Uranus, which is about 3 billion kilometers (2 billion miles) away from the sun. Voyager 2 made its closest approach – within 81,500 kilometers (50,600 miles) of the Uranian cloud tops – on Jan. 24, 1986.

Before Voyager 2's visit, scientists had to learn about Uranus by using Earth-based and airborne telescopes. By observing dips in starlight as a star passed behind Uranus, scientists knew Uranus had nine narrow rings. But it wasn't until the Voyager 2 flyby that scientists were able to capture for the first time images of the rings and the tiny shepherding moons that sculpted them. Unlike Saturn's icy rings, they found Uranus' rings to be dark gray, reflecting only a few percent of the incident sunlight.

Scientists had also determined an average temperature for Uranus (59 Kelvin, or minus 350 degrees Fahrenheit) before this encounter, but the distribution of that temperature came as a surprise. Voyager showed there was heat transport from pole to pole in Uranus' atmosphere that maintained the same temperature at both poles, even though the sun was shining directly for decades on one pole and not the other.

By the end of the Uranus encounter and science analysis, data from Voyager 2 enabled the discovery of 11 new moons and two new rings, and generated dozens of science papers about the quirky seventh planet.

Voyager 2 moved on to explore Neptune, the last planetary target, in August 1989. It is now hurtling toward interstellar space, which is the space between stars. It is about 14 billion kilometers (9 billion miles) away from the sun. Voyager 1, which explored only Jupiter and Saturn before heading on a faster track toward interstellar space, is about 17 billion kilometers (11 billion miles) away from the sun.

"The Uranus encounter was one of a kind," said Suzanne Dodd, Voyager project manager, based at JPL. "Voyager 2 was healthy and durable enough to make it to Uranus and then to Neptune. Currently both Voyager spacecraft are on the cusp of leaving the sun's sphere of influence and once again blazing a trail of scientific discovery."

Color View from Orbit Shows Mars Rover Beside Crater

The High Resolution Imaging Science Experiment (HiRISE) camera on NASA's Mars Reconnaissance Orbiter acquired this color image on March 9, 2011, of "Santa Maria" crater, showing NASA's Mars Exploration Rover Opportunity perched on the southeast rim.

Cassini Sees Seasonal Rains Transform Titan's Surface

"Arrow" shaped storm clouds form over Titan's equator.

Evidence of methane "rain" on surface

PASADENA, Calif. -- As spring continues to unfold at Saturn, April showers on the planet's largest moon, Titan, have brought methane rain to its equatorial deserts, as revealed in images captured by NASA's Cassini spacecraft. This is the first time scientists have obtained current evidence of rain soaking Titan's surface at low latitudes. Extensive rain from large cloud systems, spotted by Cassini's cameras in late 2010, has apparently darkened the surface of the moon. The best explanation is these areas remained wet after methane rainstorms. The observations released today in the journal Science, combined with earlier results in Geophysical Research Letters last month, show the weather systems of Titan's thick atmosphere and the changes wrought on its surface are affected by the changing seasons. "It's amazing to be watching such familiar activity as rainstorms and seasonal changes in weather patterns on a distant, icy satellite," said Elizabeth Turtle, a Cassini imaging team associate at the Johns Hopkins University Applied Physics Lab in Laurel, Md., and lead author of today's publication. "These observations are helping us to understand how Titan works as a system, as well as similar processes on our own planet." The Saturn system experienced equinox, when the sun lies directly over a planet's equator and seasons change, in August 2009. (A full Saturn "year" is almost 30 Earth years.) Years of Cassini observations suggest Titan's global atmospheric circulation pattern responds to the changes in solar illumination, influenced by the atmosphere and the surface, as detailed in the Geophysical Research Letters paper. Cassini found the surface temperature responds more rapidly to sunlight changes than does the thick atmosphere. The changing circulation pattern produced clouds in Titan's equatorial region. Clouds on Titan are formed of methane as part of an Earth-like cycle that uses methane instead of water. On Titan, methane fills lakes on the surface, saturates clouds in the atmosphere, and falls as rain. Though there is evidence that liquids have flowed on the surface at Titan's equator in the past, liquid hydrocarbons, such as methane and ethane, had only been observed on the surface in lakes at polar latitudes. The vast expanses of dunes that dominate Titan's equatorial regions require a predominantly arid climate. Scientists suspected that clouds might appear at Titan's equatorial latitudes as spring in the northern hemisphere progressed. But they were not sure if dry channels previously observed were cut by seasonal rains or remained from an earlier, wetter climate. An arrow-shaped storm appeared in the equatorial regions on Sept. 27, 2010 -- the equivalent of early April in Titan's "year" -- and a broad band of clouds appeared the next month. As described in the Science paper, over the next few months, Cassini's imaging science subsystem captured short-lived surface changes visible in images of Titan's surface. A 193,000-square-mile (500,000-square-kilometer) region along the southern boundary of Titan's Belet dune field, as well as smaller areas nearby, had become darker. Scientists compared the imaging data to data obtained by other instruments and ruled out other possible causes for surface changes. They concluded this change in brightness is most likely the result of surface wetting by methane rain. These observations suggest that recent weather on Titan is similar to that over Earth's tropics. In tropical regions, Earth receives its most direct sunlight, creating a band of rising motion and rain clouds that encircle the planet. "These outbreaks may be the Titan equivalent of what creates Earth's tropical rainforest climates, even though the delayed reaction to the change of seasons and the apparently sudden shift is more reminiscent of Earth's behavior over the tropical oceans than over tropical land areas," said Tony Del Genio of NASA's Goddard Institute for Space Studies, New York, a co-author and a member of the Cassini imaging team. On Earth, the tropical bands of rain clouds shift slightly with the seasons but are present within the tropics year-round. On Titan, such extensive bands of clouds may only be prevalent in the tropics near the equinoxes and move to much higher latitudes as the planet approaches the solstices. The imaging team intends to watch whether Titan evolves in this fashion as the seasons progress from spring toward northern summer. "It is patently clear that there is so much more to learn from Cassini about seasonal forcing of a complex surface-atmosphere system like Titan's and, in turn, how it is similar to, or differs from, the Earth's," said Carolyn Porco, Cassini imaging team lead at the Space Science Institute, Boulder, Colo. "We are eager to see what the rest of Cassini's Solstice Mission will bring."

Cassini Finds Saturn Sends Mixed Signals

Recent data from NASA's Cassini spacecraft show that the variation in radio waves controlled by the planet's rotation is different in the northern and southern hemispheres. Moreover, the northern and southern rotational variations also appear to change with the Saturnian seasons, and the hemispheres have actually swapped rates. These two radio waves, converted to the human audio range, can be heard in a new video available online at: http://www.nasa.gov/multimedia/videogallery/index.html?media_id=74390781

"These data just go to show how weird Saturn is," said Don Gurnett, Cassini's radio and plasma wave science instrument team lead and professor of physics at the University of Iowa, Iowa City. "We thought we understood these radio wave patterns at gas giants, since Jupiter was so straightforward. Without Cassini's long stay, scientists wouldn't have understood that the radio emissions from Saturn are so different."

Saturn emits radio waves known as Saturn Kilometric Radiation, or SKR for short. To Cassini, they sound a bit like bursts of a spinning air raid siren, since the radio waves vary with each rotation of the planet. This kind of radio wave pattern had been previously used at Jupiter to measure the planet's rotation rate, but at Saturn, as is the case with teenagers, the situation turned out to be much more complicated.

When NASA's Voyager spacecraft visited Saturn in the early 1980s, the radiation emissions indicated the length of Saturn's day was about 10.66 hours. But as its clocking continued by a flyby of the joint ESA-NASA Ulysses spacecraft and Cassini, the radio burst varied by seconds to minutes. A paper in Geophysical Research Letters in 2009 analyzing Cassini data showed that the Saturn Kilometric Radiation was not even a solo, but a duet, with two singers out of sync. Radio waves emanating from near the north pole had a period of around 10.6 hours; radio waves near the south pole had a period of around 10.8 hours.

A new paper led by Gurnett that was published in Geophysical Research Letters in December 2010 shows that, in recent Cassini data, the southern and northern SKR periods crossed over around March 2010, about seven months after equinox, when the sun shines directly over a planet's equator. The southern SKR period decreased from about 10.8 hours on Jan. 1, 2008 and crossed with the northern SKR period around March 1, 2010, at around 10.67 hours. The northern period increased from about 10.58 hours to that convergence point.

Seeing this kind of crossover led the Cassini scientists to go back into data from previous Saturnian visits. With a new eye, they saw that NASA's Voyager data taken in 1980, about a year after Saturn's 1979 equinox, showed different warbles from Saturn's northern and southern poles. They also saw a similar kind of effect in the Ulysses radio data between 1993 and 2000. The northern and southern periods detected by Ulysses converged and crossed over around August 1996, about nine months after the previous Saturnian equinox.

Cassini scientists don't think the differences in the radio wave periods had to do with hemispheres actually rotating at different rates, but more likely came from variations in high-altitude winds in the northern and southern hemispheres. Two other papers involving Cassini investigators were published in December, with results complementary to the radio and plasma wave science instrument -- one by Jon Nichols, University of Leicester, U.K., in the same issue of Geophysical Research Letters, and the other led by David Andrews, also of University of Leicester, in the Journal of Geophysical Research.

In the Nichols paper, data from the NASA/ESA Hubble Space Telescope showed the northern and southern auroras on Saturn wobbled back and forth in latitude in a pattern matching the radio wave variations, from January to March 2009, just before equinox. The radio signal and aurora data are complementary because they are both related to the behavior of the magnetic bubble around Saturn, known as the magnetosphere. The paper by Andrews, a Cassini magnetometer team associate, showed that from mid-2004 to mid-2009, Saturn's magnetic field over the two poles wobbled at the same separate periods as the radio waves and the aurora.

"The rain of electrons into the atmosphere that produces the auroras also produces the radio emissions and affects the magnetic field, so scientists think that all these variations we see are related to the sun's changing influence on the planet," said Stanley Cowley, a co-author on both papers, co-investigator on Cassini's magnetometer instrument, and professor at the University of Leicester.

As the sun continues to climb towards the north pole of Saturn, Gurnett's group has continued to see the crossover trend in radio signals through Jan. 1, 2011. The period of the southern radio signals continued to decrease to about 10.54 hours, while the period of the northern radio signals increased to 10.71 hours.

"These papers are important in helping to explain the complicated dance between the sun and Saturn's magnetic bubble, something normally invisible to the human eye and imperceptible to the human ear," said Marcia Burton, a Cassini fields and particles scientist at NASA's Jet Propulsion Laboratory, Pasadena, Calif., who was not involved in the work. "Cassini will continue to keep an eye on these changes."

Astronomers have detected a new candidate for the coldest known star – one whose temperature is roughly equivalent to a fresh cup of tea. The object is part of a double system and is a type of star known as a brown dwarf, which is essentially a failed star. Brown dwarfs lack enough mass for gravity to trigger the nuclear reactions that make stars shine, but they’re more massive than what’s typically considered to be a planet. This newly discovered brown dwarf is identified as CFBDSIR 1458+10B, and is the dimmer member of the binary brown dwarf system, which is located only 75 light-years from Earth. The system was detected from observations made by the Very Large Telescope at the European Southern Observatory's Paranal Observatory in Chile. The telescope's powerful spectrograph was used to study the object’s infrared spectrum and measure its temperature, which was found to be extraordinarily cold by brown dwarf standards. [Video: Getting WISE to Brown Dwarfs] "We were very excited to see that this object had such a low temperature, but we couldn't have guessed that it would turn out to be a double system and have an even more interesting, even colder component," said Philippe Delorme of the French National Center for Scientific Research and the Joseph Fourier University in Grenoble, France. Delorme is the co-author of a paper on the brown dwarf finding that will appear in an upcoming issue of the Astrophysical Journal. The dimmer of the two failed stars has been found to have a temperature of approximately 212 degrees Fahrenheit (100 degrees Celsius), which is the boiling point of water and not much different from the temperature inside a sauna. Our sun, in comparison, averages a temperature of about 10,000 degrees Fahrenheit (5,500 degrees Celsius), researchers have said. "At such temperatures we expect the brown dwarf to have properties that are different from previously known brown dwarfs and much closer to those of giant exoplanets – it could even have water clouds in its atmosphere," said Michael Liu of the University of Hawaii's Institute for Astronomy, who is the lead author of the study. "In fact, once we start taking images of gas-giant planets around sun-like stars in the near future, I expect that many of them will look like CFBDSIR 1458+10B." The hunt for cool objects in the cosmos is an active field of astronomy. NASA's Spitzer Space Telescope recently identified two other very faint objects as other possible contenders for the coldest known brown dwarfs, but the temperatures of these stars have not been measured as precisely. The brown dwarfs seen by the Spitzer Space Telescope have temperatures that range from 350 to 620 degrees Fahrenheit (177 to 327 degrees Celsius). Future observations will better determine how the objects found by Spitzer compare to CFBDSIR 1458+10B. Liu and his colleagues are planning to observe this newly detected brown dwarf again to better determine its properties, and to begin mapping the binary's orbit, which, after about a decade of observation, should allow astronomers to determine the system's mass

PASADENA, Calif. -- The Planck mission released a new data catalogue Tuesday from initial maps of the entire sky. The catalogue includes thousands of never-before-seen dusty cocoons where stars are forming, and some of the most massive clusters of galaxies ever observed. Planck is a European Space Agency mission with significant contributions from NASA.

"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 189 massive clusters of galaxies; 15,000 objects within and outside our galaxy, in addition to the 10,000 cold cores; 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

NASA's Kepler Mission Discovers Its First Rocky Planet

PASADENA, Calif. -- NASA's Kepler mission confirmed the discovery of its first rocky planet, named Kepler-10b. Measuring 1.4 times the size of Earth, it is the smallest planet ever discovered outside our solar system.

The discovery of this planet, called an exoplanet, is based on more than eight months of data collected by the spacecraft from May 2009 to early January 2010.

"All of Kepler's best capabilities have converged to yield the first solid evidence of a rocky planet orbiting a star other than our sun," said Natalie Batalha, Kepler's deputy science team lead at NASA's Ames Research Center in Moffett Field, Calif., and primary author of a paper on the discovery accepted by the Astrophysical Journal. "The Kepler team made a commitment in 2010 about finding the telltale signatures of small planets in the data, and it's beginning to pay off."

Kepler's ultra-precise photometer measures the tiny decrease in a star's brightness that occurs when a planet crosses in front of it. The size of the planet can be derived from these periodic dips in brightness. The distance between the planet and the star is calculated by measuring the time between successive dips as the planet orbits the star.

Kepler is the first NASA mission capable of finding Earth-size planets in or near the habitable zone, the region in a planetary system where liquid water can exist on the planet's surface. However, since it orbits once every 0.84 days, Kepler-10b is more than 20 times closer to its star than Mercury is to our sun and not in the habitable zone.

Kepler-10 was the first star identified that could potentially harbor a small transiting planet, placing it at the top of the list for ground-based observations with the W.M. Keck Observatory 10-meter telescope in Hawaii. Scientists waiting for a signal to confirm Kepler-10b as a planet were not disappointed. Keck was able to measure tiny changes in the star's spectrum, called Doppler shifts, caused by the telltale tug exerted by the orbiting planet on the star.

"The discovery of Kepler 10-b is a significant milestone in the search for planets similar to our own," said Douglas Hudgins, Kepler program scientist at NASA Headquarters in Washington. "Although this planet is not in the habitable zone, the exciting find showcases the kinds of discoveries made possible by the mission and the promise of many more to come."

Knowledge of the planet is only as good as the knowledge of the star it orbits. Because Kepler-10 is one of the brighter stars being targeted by Kepler, scientists were able to detect high-frequency variations in the star's brightness generated by stellar oscillations, or starquakes. This analysis allowed scientists to pin down Kepler-10b's properties.

There is a clear signal in the data arising from light waves that travel within the interior of the star. Kepler Asteroseismic Science Consortium scientists use the information to better understand the star, just as earthquakes are used to learn about Earth's interior structure. As a result of this analysis, Kepler-10 is one of the most well-characterized planet-hosting stars in the universe.

That's good news for the team studying Kepler-10b. Accurate stellar properties yield accurate planet properties. In the case of Kepler-10b, the picture that emerges is of a rocky planet with a mass 4.6 times that of Earth and with an average density of 8.8 grams per cubic centimeter -- similar to that of an iron dumbbell

Partial Solar Eclipse - 4 Jan 2011

Image Documenting California Earthquake

This UAVSAR image, covering the time period from October 21, 2009 to April 13, 2010, shows ground deformation that is largely a result of the April 4, 2010 earthquake in Baja California. Black lines indicate interpreted faults, and red lines show where surface rupture was confirmed by geologists in the field. Image credit: NASA JPL/USGS/California Geological Survey/Google

Hot Plasma Explosions Inflate Saturn's Magnetic Field

A new analysis based on data from NASA's Cassini spacecraft finds a causal link between mysterious, periodic signals from Saturn's magnetic field and explosions of hot ionized gas, known as plasma, around the planet.

Scientists have found that enormous clouds of plasma periodically bloom around Saturn and move around the planet like an unbalanced load of laundry on spin cycle. The movement of this hot plasma produces a repeating signature "thump" in measurements of Saturn's rotating magnetic environment and helps to illustrate why scientists have had such a difficult time measuring the length of a day on Saturn.

"This is a breakthrough that may point us to the origin of the mysteriously changing periodicities that cloud the true rotation period of Saturn," said Pontus Brandt, the lead author on the paper and a Cassini team scientist based at the Johns Hopkins University Applied Physics Laboratory in Laurel, Md. "The big question now is why these explosions occur periodically."
The data show how plasma injections, electrical currents and Saturn's magnetic field -- phenomena that are invisible to the human eye -- are partners in an intricate choreography. Periodic plasma explosions form islands of pressure that rotate around Saturn. The islands of pressure "inflate" the magnetic field.

A new animation showing the linked behavior is available at http://www.nasa.gov/cassini and http://saturn.jpl.nasa.gov .

The visualization shows how invisible hot plasma in Saturn's magnetosphere – the magnetic bubble around the planet -- explodes and distorts magnetic field lines in response to the pressure. Saturn's magnetosphere is not a perfect bubble because it is blown back by the force of the solar wind, which contains charged particles streaming off the sun.

The force of the solar wind stretches the magnetic field of the side of Saturn facing away from the sun into a so-called magnetotail. The collapse of the magnetotail appears to kick off a process that causes the hot plasma bursts, which in turn inflate the magnetic field in the inner magnetosphere.

Scientists are still investigating what causes Saturn's magnetotail to collapse, but there are strong indications that cold, dense plasma originally from Saturn's moon Enceladus rotates with Saturn. Centrifugal forces stretch the magnetic field until part of the tail snaps back.

The snapping back heats plasma around Saturn and the heated plasma becomes trapped in the magnetic field. It rotates around the planet in islands at the speed of about 100 kilometers per second (200,000 mph). In the same way that high and low pressure systems on Earth cause winds, the high pressures of space cause electrical currents. Currents cause magnetic field distortions.

A radio signal known as Saturn Kilometric Radiation, which scientists have used to estimate the length of a day on Saturn, is intimately linked to the behavior of Saturn's magnetic field. Because Saturn has no surface or fixed point to clock its rotation rate, scientists inferred the rotation rate from timing the peaks in this type of radio emission, which is assumed to surge with each rotation of a planet. This method has worked for Jupiter, but the Saturn signals have varied. Measurements from the early 1980s taken by NASA's Voyager spacecraft, data obtained in 2000 by the ESA/NASA Ulysses mission, and Cassini data from about 2003 to the present differ by a small, but significant degree. As a result, scientists are not sure how long a Saturn day is.

"What's important about this new work is that scientists are beginning to describe the global, causal relationships between some of the complex, invisible forces that shape the Saturn environment," said Marcia Burton, the Cassini fields and particles investigation scientist at NASA's Jet Propulsion Laboratory, Pasadena, Calif. "The new results still don't give us the length of a Saturn day, but they do give us important clues to begin figuring it out. The Saturn day length, or Saturn's rotation rate, is important for determining fundamental properties of Saturn, like the structure of its interior and the speed of its winds."

Plasma is invisible to the human eye. But the ion and neutral camera on Cassini's magnetospheric imaging instrument provides a three-dimensional view by detecting energetic neutral atoms emitted from the plasma clouds around Saturn. Energetic neutral atoms form when cold, neutral gas collides with electrically-charged particles in a cloud of plasma. The resulting particles are neutrally charged, so they are able to escape magnetic fields and zoom off into space. The emission of these particles often occurs in the magnetic fields surrounding planets.

By stringing together images obtained every half hour, scientists produced movies of plasma as it drifted around the planet. Scientists used these images to reconstruct the 3-D pressure produced by the plasma clouds, and supplemented those results with plasma pressures derived from the Cassini plasma spectrometer. Once scientists understood the pressure and its evolution, they could calculate the associated magnetic field perturbations along the Cassini flight path. The calculated field perturbation matched the observed magnetic field "thumps" perfectly, confirming the source of the field oscillations.

"We all know that changing rotation periods have been observed at pulsars, millions of light years from our solar system, and now we find that a similar phenomenon is observed right here at Saturn," said Tom Krimigis, principal investigator of the magnetospheric imaging instrument, also based at the Applied Physics Laboratory and the Academy of Athens, Greece. "With instruments right at the spot where it's happening, we can tell that plasma flows and complex current systems can mask the real rotation period of the central body. That's how observations in our solar system help us understand what is seen in distant astrophysical objects."

NASA Aids in Characterizing Super-Earth Atmosphere

PASADENA, Calif. -- A team of astronomers, including two NASA Sagan Fellows, has made the first characterizations of a super-Earth's atmosphere, by using a ground-based telescope. A super-Earth is a planet up to three times the size of Earth and weighing up to 10 times as much. The findings, reported in the Dec. 2 issue of the journal Nature, are a significant milestone toward eventually being able to probe the atmospheres of Earth-like planets for signs of life.

The team determined the planet, GJ 1214b, is either blanketed with a thin layer of water steam or surrounded by a thick layer of high clouds. If the former, the planet itself would have an icy composition. If the latter, the planet would be rocky or similar to the composition of Neptune, though much smaller.

"This is the first super-Earth known to have an atmosphere," said Jacob Bean, a NASA Sagan Fellow and astronomer at the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass. "But even with these new measurements, we can't say yet what that atmosphere is made of. This world is being very shy and veiling its true nature from us."

GJ 1214b, first discovered in December 2009, is 2.7 times the size of Earth and 6.5 times as massive. Previous observations of the planet's size and mass demonstrated it has a low density for its size, leading astronomers to conclude the planet is some kind of solid body with an atmosphere.

The planet orbits close to its dim star, at a distance of 0.014 astronomical units. An astronomical unit is the distance between Earth and the sun, approximately 93 million miles. GJ 1214b circles too close to its star to be habitable by any life forms.

Bean and his team observed infrared light as the planet crossed in front of its star. During such transits, the star's light filters through the atmosphere. Gases absorb the starlight at particular wavelengths, leaving behind chemical fingerprints detectable from Earth. This same type of technique has been used to study the atmospheres of distant "hot Jupiters," or Jupiter-like planets orbiting close to their stars, and found gases like hydrogen, methane and sodium vapor.

In the case of the super-Earth, no chemical fingerprints were detected; however, this doesn't mean there are no chemicals present. Instead, this information ruled out some possibilities for GJ 1214b's atmosphere, and narrowed the scope to either an atmosphere of water steam or high clouds. Astronomers believe it's more likely the atmosphere is too thin around the planet to let enough light filter through and reveal chemical fingerprints.

"A steamy atmosphere would have to be very dense - about one-fifth water vapor by volume -- compared to our Earth, with an atmosphere that's four-fifths nitrogen and one-fifth oxygen with only a touch of water vapor," Bean said. "During the next year, we should have some solid answers about what this planet is truly like."

The team, which included Bean's co-authors -- Eliza Miller-Ricci Kempton, a NASA Sagan Fellow at the University of California in Santa Cruz, and Derek Homeier of the Institute for Astrophysics in Gottingen, Germany -- examined GJ 1214b using the ground-based Very Large Telescope at Paranal Observatory in Chile.

"This is an important step forward, narrowing our understanding of the atmosphere of this planet," said NASA Exoplanet Exploration Program Scientist Douglas Hudgins at NASA Headquarters in Washington. "Bizarre worlds like this make exoplanet science one of the most compelling areas in astrophysics today."

Cassini Finds Warm Cracks on Enceladus

PASADENA, Calif. – New images and data from NASA's Cassini spacecraft give scientists a unique Saturn-lit view of active fissures through the south polar region of Saturn's moon Enceladus. They reveal a more complicated web of warm fractures than previously thought.

The new images are available at: http://www.nasa.gov/cassini and http://saturn.jpl.nasa.gov.

Scientists working jointly with Cassini's composite infrared spectrometer and its high-resolution imaging camera have constructed the highest-resolution heat intensity maps yet of the hottest part of a region of long fissures spraying water vapor and icy particles from Enceladus. These fissures have been nicknamed "tiger stripes." Additional high-resolution spectrometer maps of one end of the tiger stripes Alexandria Sulcus and Cairo Sulcus reveal never-before-seen warm fractures that branch off like split ends from the main tiger stripe trenches. They also show an intriguing warm spot isolated from other active surface fissures.

"The ends of the tiger stripes may be the places where the activity is just getting started, or is winding down, so the complex patterns of heat we see there may give us clues to the life cycle of tiger stripes," said John Spencer, a Cassini team scientist based at Southwest Research Institute in Boulder, Colo.

The images and maps come from the Aug. 13, 2010, Enceladus flyby, Cassini's last remote sensing flyby of the moon until 2015. The geometry of the many flybys between now and 2015 will not allow Cassini to do thermal scans like these, because the spacecraft will be too close to scan the surface and will not view the south pole. This Enceladus flyby, the 11th of Cassini's tour, also gave Cassini its last look at any part of the active south polar region in sunlight.

The highest-resolution spectrometer scan examined the hottest part of the entire tiger stripe system, part of the fracture called Damascus Sulcus. Scientists used the scan to measure fracture temperatures up to190 Kelvin (minus 120 degrees Fahrenheit). This temperature appears slightly higher than previously measured temperatures at Damascus, which were around 170 Kelvin (minus 150 degrees Fahrenheit).

Spencer said he isn't sure if this tiger stripe is just more active than it was the last time Cassini's spectrometer scanned it, in 2008, or if the hottest part of the tiger stripe is so narrow that previous scans averaged its temperature out over a larger area. In any case, the new scan had such good resolution, showing details as small as 800 meters (2,600 feet), that scientists could see for the first time warm material flanking the central trench of Damascus, cooling off quickly away from the trench. The Damascus thermal scan also shows large variations in heat output within a few kilometers along the length of the fracture. This unprecedented resolution will help scientists understand how the tiger stripes deliver heat to the surface of Enceladus.

Cassini acquired the thermal map of Damascus simultaneously with a visible-light image where the tiger stripe is lit by sunlight reflecting off Saturn. The visible-light and thermal data were merged to help scientists understand the relationships between physical heat processes and surface geology.

"Our high-resolution images show that this section of Damascus Sulcus is among the most structurally complex and tectonically dynamic of the tiger stripes," said imaging science team associate Paul Helfenstein of Cornell University, Ithaca, N.Y. Some details in the appearance of the landforms, such as a peculiar pattern of curving striations along the flanks of Damascus, had not previously been noticed in ordinary sunlit images.

The day after the Enceladus flyby, Cassini swooped by the icy moon Tethys, collecting images that helped fill in gaps in the Tethys global map. Cassini's new views of the heavily cratered moon will help scientists understand how tectonic forces, impact cratering, and perhaps even ancient resurfacing events have shaped the moon's appearance.

Dawn of the Universe Recreated

Just weeks after the world's largest particle accelerator began smashing together heavy lead ions to create little Big Bangs, the experiment has produced a primordial state of matter akin to what existed at the dawn of the universe.

The Large Hadron Collider (LHC), a 17-mile-long (27 kilometer) underground ring run by the European Organization for Nuclear Research (CERN) near Geneva, began colliding lead ions together Nov. 8. These atomic nuclei contain 82 protons, and are much heavier than the lone protons the accelerator was previously colliding.

Now two experiments at the LHC – called ATLAS and CMS, respectively – have reported a phenomenon called "jet quenching" that scientists say could reveal secrets about the nature of matter and the evolution of the universe.

After two ions crash into each other, detectors measure jets of particles that emerge from the high-energy collision. Jets are formed as the basic constituents of nuclear matter, called quarks and gluons, fly away from the collision point.

In proton collisions, jets usually appear in pairs, emerging back to back. However, in the tumultuous conditions created by heavy ion collisions such as those made by lead nuclei, the jets interact with a hot dense medium created when temperatures are so high that the basic constituents of matter break apart.

This leads to a characteristic signal, known as jet quenching, in which the energy of the jets can be severely degraded, signaling interactions with the medium more intense than ever seen before.

"ATLAS is the first experiment to report direct observation of jet quenching," said ATLAS spokesperson Fabiola Gianotti in a statement. "The excellent capabilities of ATLAS to determine jet energies enabled us to observe a striking imbalance in energies of pairs of jets, where one jet is almost completely absorbed by the medium."

Jet quenching is a powerful tool for studying nature, especially the behavior of the medium of broken-down particles, called quark-gluon plasma. This plasma is created when super-high temperatures break apart protons into their constituent quarks and gluons. The quarks and gluons then float around in a kind of primordial soup that resembles the universe shortly after the Big Bang.

"It is truly amazing to be looking, albeit on a microscopic scale, at the conditions and state of matter that existed at the dawn of time," said CMS spokesperson Guido Tonelli. "Since the very first days of lead-ion collisions, the quenching of jets appeared in our data while other striking features, like the observation of Z particles, never seen before in heavy-ion collisions, are under investigation. The challenge is now to put together all possible studies that could lead us to a much better understanding of the properties of this new, extraordinary state of matter." (A Z particle is nearly identical to a massless photon yet is very massive.)

The quark-gluon plasma was created for the first time ever at a smaller particle accelerator called the Relativistic Heavy Ion Collider (RHIC) at Brookhaven National Laboratory on Long Island. That finding was announced in February 2010.

The ATLAS and CMS measurements offer a new possibility to use jets, which interact with the primordial soup, to probe this unique state of matter, scientists said. Future jet quenching and other measurements from the LHC experiments will provide powerful insight into the properties of the primordial plasma and the interactions among its quarks and gluons, they said.

Thin Air - Cassini Finds Ethereal Atmosphere at Rhea

NASA's Cassini spacecraft has detected a very tenuous atmosphere known as an exosphere, infused with oxygen and carbon dioxide around Saturn's icy moon Rhea. This is the first time a spacecraft has directly captured molecules of an oxygen atmosphere – albeit a very thin one -- at a world other than Earth.

The oxygen appears to arise when Saturn's magnetic field rotates over Rhea. Energetic particles trapped in the planet's magnetic field pepper the moon’s water-ice surface. They cause chemical reactions that decompose the surface and release oxygen. The source of the carbon dioxide is less certain.

Oxygen at Rhea's surface is estimated to be about 5 trillion times less dense than what we have at Earth. But the new results show that surface decomposition could contribute abundant molecules of oxygen, leading to surface densities roughly 100 times greater than the exospheres of either Earth's moon or Mercury. The formation of oxygen and carbon dioxide could possibly drive complex chemistry on the surfaces of many icy bodies in the universe.

"The new results suggest that active, complex chemistry involving oxygen may be quite common throughout the solar system and even our universe," said lead author Ben Teolis, a Cassini team scientist based at Southwest Research Institute in San Antonio. "Such chemistry could be a prerequisite for life. All evidence from Cassini indicates that Rhea is too cold and devoid of the liquid water necessary for life as we know it."

Releasing oxygen through surface irradiation could help generate conditions favorable for life at an icy body other than Rhea that has liquid water under the surface, Teolis said. If the oxygen and carbon dioxide from the surface could somehow get transported down to a sub-surface ocean, that would provide a much more hospitable environment for more complex compounds and life to form. Scientists are keen to investigate whether life on icy moons with an ocean is possible, though they have not yet detected it.

The tenuous atmosphere with oxygen and carbon dioxide makes Rhea, Saturn's second largest moon, unique in the Saturnian system. Titan has a thick nitrogen-methane atmosphere, but very little carbon dioxide and oxygen.

"Rhea is turning out to be much more interesting than we had imagined," said Linda Spilker, Cassini project scientist at NASA's Jet Propulsion Laboratory, Pasadena, Calif. "The Cassini finding highlights the rich diversity of Saturn’s moons and gives us clues on how they formed and evolved."

Scientists had suspected Rhea could have a thin atmosphere with oxygen and carbon dioxide, based on remote observations of Jupiter's icy moons by NASA's Galileo spacecraft and Hubble Space Telescope. Other Cassini observations detected oxygen escaping from icy Saturn ring particles after ultraviolet bombardment. But Cassini was able to detect oxygen and carbon dioxide in the exosphere directly because of how close it flew to Rhea – 101 kilometers, or 63 miles – and its special suite of instruments.

In the new study, scientists combined data from Cassini's ion and neutral mass spectrometer and the Cassini plasma spectrometer during flybys on Nov. 26, 2005, Aug. 30, 2007, and March 2, 2010. The ion and neutral mass spectrometer "tasted" peak densities of oxygen of around 50 billion molecules per cubic meter (1 billion molecules per cubic foot). It detected peak densities of carbon dioxide of around 20 billion molecules per cubic meter (about 600 million molecules per cubic foot).

The plasma spectrometer saw clear signatures of flowing streams of positive and negative ions, with masses that corresponded to ions of oxygen and carbon dioxide.

"How exactly the carbon dioxide is released is still a puzzle," said co-author Geraint Jones, a Cassini team scientist based at University College London in the U.K. "But with Cassini's diverse suite of instruments observing Rhea from afar, as well as sniffing the gas surrounding it, we hope to solve the puzzle."

The carbon dioxide may be the result of “dry ice” trapped from the primordial solar nebula, as is the case with comets, or it may be due to similar irradiation processes operating on the organic molecules trapped in the water ice of Rhea. The carbon dioxide could also come from carbon-rich materials deposited by tiny meteors that bombarded Rhea's surface.

Astronomers have caught sight of an unusual galaxy that has illuminated new details about a celestial "sandbar" connecting two massive islands of galaxies. The research was conducted in part with NASA's Spitzer Space Telescope.

These "sandbars," or filaments, are known to span vast distances between galaxy clusters and form a lattice-like structure known as the cosmic web. Though immense, these filaments are difficult to see and study in detail. Two years ago, Spitzer's infrared eyes revealed that one such intergalactic filament containing star-forming galaxies ran between the galaxy clusters called Abell 1763 and Abell 1770.

Now these observations have been bolstered by the discovery, inside this same filament, of a galaxy that has a rare boomerang shape and unusual light emissions. Hot gas is sweeping the wandering galaxy into this shape as it passes through the filament, presenting a new way to gauge the filament's particle density. Researchers hope that other such galaxies with oddly curved profiles could serve as signposts for the faint threads, which in turn signify regions ripe for forming stars.

"These filaments are integral to the evolution of galaxy clusters -- among the biggest gravitationally bound objects in the universe -- as well as the creation of new generations of stars," said Louise Edwards, a postdoctoral researcher at the California Institute of Technology in Pasadena, and lead author of a study detailing the findings in the Dec. 1 issue of the Astrophysical Journal Letters. Her collaborators are Dario Fadda, also at Caltech, and Dave Frayer from the National Science Foundation's National Radio Astronomy Observatory, based in Charlottesville, Virginia.

Blowing in the cosmic breeze

Astronomers spotted the bent galaxy about 11 million light-years away from the center of the galaxy cluster Abell 1763 during follow-up observations with the WIYN Observatory near Tucson, Ariz., and radio-wave observations by the Very Large Array near Socorro, N.M. The WIYN Observatory is named after the consortium that owns and operates it, which includes the University of Wisconsin, Indiana University, Yale University, and the National Optical Astronomy Observatories.

The galaxy has an unusual ratio of radio to infrared light, as measured by the Very Large Array and Spitzer, making it stand out like a beacon. This is due in part to the galaxy having twin jets of material spewing in opposite directions from a supermassive black hole at its center. These jets have puffed out into giant lobes of material that emit a tremendous amount of radio waves.

Edwards and her colleagues noticed that these lobes appear to be bent back and away from the galaxy's trajectory through the filament. This bow shape, the astronomers reasoned, is due to particles in the filament pushing on the gas and dust in the lobes.

By measuring the angle of the arced lobes, Edwards' team calculated the pressure exerted by the filaments' particles and then determined the density of the medium. The method is somewhat like looking at streamers on a kite soaring overhead to judge the wind strength and the thickness of the air.

According to the data, the density inside this filament is indeed about 100 times the average density of the universe. This value agrees with that obtained in a previous X-ray study of filaments and also nicely matches predictions of supercomputer simulations.

Interconnected superclusters

Galaxies tend to bunch together as great islands in the void of space, called galaxy clusters. These galaxy groupings themselves often keep company with other clusters in "superclusters" that loom as gargantuan, gravitationally associated walls of galaxies. These structures evolved from denser patches of material as the universe rapidly expanded after the Big Bang, some 13.7 billion years ago.

The clumps and threads of this primordial matter eventually cooled, and some of it has condensed into the galaxies we see today. The leftover gas is strewn in filaments between galaxy clusters. Much of it is still quite hot -- about one million degrees Celsius (1.8 million degrees Fahrenheit) -- and blazes in high-energy X-rays that permeate galaxy clusters. Filaments are therefore best detected in X-ray light, and one direct density reading of the strands has previously been obtained in this band of frequencies.

But the X-ray-emitting gas in filaments is much more diffuse and weak than in clusters, just as submerged sandbars are extremely hard to spot at sea compared to islands poking above the water. Therefore, obtaining quality observations of filaments is time-consuming with current space observatories.

The technique by Edwards and her colleagues, which uses radio frequencies that can reach a host of ground-based telescopes, points to an easier way to probe the interiors of galaxy-cluster filaments. Instead of laboring to find subtle X-rays clues, astronomers could trust these arced "lighthouse" galaxies to indicate just where cosmic filaments lie.

Knowing how much material these filaments contain and how they interact with galaxy clusters will be very important for understanding the overall evolution of the universe, Edwards said.

The Spitzer observations were made before it ran out of its liquid coolant in May 2009 and began its warm mission.

Astronomers have discovered the most massive stars known, including one at more than 300 times the mass of our sun ? double the size that scientists thought heavyweight stars could reach.

These colossal stars are millions of times brighter than the sun and shed mass through very powerful winds.

The stellar discovery, which represents the first time that these hulking stars were individually identified, could help astronomers understand the behavior of massive stars, and how large they can be at birth.


A European research team led by Paul Crowther, professor of Astrophysics at the University of Sheffield in England, discovered the massive stars inside two young clusters of stars ? NGC 3603 and RMC 136a. They used a combination of instruments on the European Southern Observatory's Very Large Telescope, in addition to archival data from the Hubble Space Telescope, to study the stellar nurseries.

The NGC 3603 nebula, located 22,000 light-years from the sun, is a star-making factory where flurries of stars form from the extended clouds of gas and dust.

RMC 136a, which is more commonly referred to as simply R136, is another cluster of young, massive and hot stars, located within the Tarantula Nebula. This nebula is found in the Large Magellanic Cloud, a neighboring galaxy that is 165,000 light-years away.

Astronomers found several stars with scorching hot surface temperatures of over 71,500 degrees Fahrenheit (39,700 degrees Celsius), which is more than seven times hotter than the sun. The stars are also tens of times larger and several million times brighter.

The researchers compared their observations with models, and their findings suggest that a number of these stars were greater than 150 solar masses at birth.

In fact, the star R136a1, which is located in the R136 cluster, is the most massive star ever found. Its current mass is approximately 265 solar masses, and its estimated birth weight was as much as 320 times that of our sun. R136a1 also has the highest luminosity of any star found to date ? nearly 10 million times greater than the sun.

Big, fat baby stars
From the time of their birth, these massive stars produce outflows, such as powerful winds, which eventually reduce their mass, researchers said.

"Unlike humans, these stars are born heavy and lose weight as they age," Crowther said. "Being a little over a million years old, the most extreme star R136a1 is already 'middle-aged' and has undergone an intense weight loss program, shedding a fifth of its initial mass over that time, or more than 50 solar masses."

The stars are still, however, intensely bright.

For example, if the star R136a1 were to replace the sun in our solar system, it would outshine our closest star by as much as the sun currently outshines the full moon, and its powerful radiation would effectively sterilize our home planet.

"Its high mass would reduce the length of the Earth's year to three weeks, and it would bathe the Earth in incredibly intense ultraviolet radiation, rendering life on our planet impossible," said Raphael Hirschi, a research team member from Keele University in Staffordshire, England.

More massive than thought
In the NGC 3603 nebula, the astronomers were also able to directly measure the masses of two stars that belong to a double-star system. The stars A1, B and C in this cluster have estimated birth masses of close to or above 150 solar masses.

These ultra-heavy stars are extremely rare and only form within the densest star clusters. Detecting them requires the sharp resolving power of the Very Large Telescope's infrared instruments.

In the study, the researchers estimated the maximum possible mass for stars within the two clusters, and the relative number of the most massive stars. Their findings have caused them to reevaluate current estimates for how large these stars can be.?

"The smallest stars are limited to more than about 80 times more than Jupiter, below which they are 'failed stars' or brown dwarfs," said Olivier Schnurr, a research team member from the Astrophysikalisches Institut Potsdam in Germany. "Our new finding supports the previous view that there is also an upper limit to how big stars can get, although it raises the limit by a factor of two, to about 300 solar masses."

Within R136, only four of the approximately 100,000 stars found in the cluster weighed more than 150 solar masses at birth. Yet the sheer intensity of their wind and radiation account for nearly half of R136's entire wind and radiation power.

R136a1 alone emits energy by more than a factor of 50 compared to the entire Orion Nebula, which is the closest region of massive star formation to Earth.

Unraveling the mystery
Astronomers are still grappling to understand how these stars form ? a process further complicated by their very short life spans and powerful winds.

"Either they were born so big or smaller stars merged together to produce them," Crowther said.

Stars between approximately eight and 150 solar masses end their brief lives in supernova explosions, leaving behind exotic remnants in the form of either neutron stars or black holes.

With the discovery of stars weighing between 150 and 300 solar masses, the study's findings raise the prospect of the existence of exceptionally bright, "pair instability supernovae" that blow themselves apart. These exploding stars fail to leave any remnants, and disperse up to ten solar masses of iron into their surroundings. A few candidates for such explosions have been proposed in recent years.

Still, the title of most massive star ever found now belongs to R136a1, and the stellar heavyweight could hold the designation for quite some time, said Crowther.

"Owing to the rarity of these monsters, I think it is unlikely that this new record will be broken any time soon," he said.