Hubble discovers water vapour venting from Jupiter’s moon Europa

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Water vapour plumes on Jupiter's moon Europa (artist's impression) 

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Water vapour plumes on Jupiter's moon Europa (artist's impression) 

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Water vapour plumes on Jupiter's moon Europa (artist's impression)

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Water vapour plumes on Jupiter’s moon Europa (artist’s impression)

 

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Water vapour plumes over Europa

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Illustrated fly-by of Europa's plumes (artist's impression)

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Flying past Europa’s plumes (artist’s impression)

The NASA/ESA Hubble Space Telescope has discovered water vapour erupting from the frigid surface of Jupiter’s moon Europa, in one or more localised plumes near its south pole.

Europa is already thought to harbour a liquid ocean beneath its icy crust, making the moon one of the main targets in the search for habitable worlds away from Earth. This new finding is the first observational evidence of water vapour being ejected off the moon's surface.

"The discovery that water vapour is ejected near the south pole strengthens Europa's position as the top candidate for potential habitability," said lead author Lorenz Roth of the Southwest Research Institute in San Antonio, Texas. "However, we do not know yet if these plumes are connected to subsurface liquid water or not." The Hubble findings will be published in the 12 December online issue of Science Express, and are being reported today at the meeting of the American Geophysical Union in San Francisco, California, USA.

The Hubble discovery makes Europa only the second moon in the Solar System known to have water vapour plumes. In 2005, plumes of water vapour and dust were detected by NASA's Cassini orbiter spewing off the surface of the Saturnian moon Enceladus.

The Europa plumes were discovered by Hubble observations in December 2012. The Space Telescope Imaging Spectrograph (STIS) detected faint ultraviolet light from an aurora at the moon's south pole. This aurora is driven by Jupiter's intense magnetic field, which causes particles to reach such high speeds that they can split the water molecules in the plume when they hit them, resulting in oxygen and hydrogen ions which leave their telltale imprint in the colours of the aurora.

So far, only water vapour has been detected — unlike the plumes on Enceladus, which also contain ice and dust particles.

"We pushed Hubble to its limits to see this very faint emission," said co-lead author and principal investigator of the Hubble observing campaign Joachim Saur of the University of Cologne, Germany. "Only after a particular camera on the Hubble Space Telescope had been repaired on the last servicing mission by the Space Shuttle did we gain the sensitivity to really search for these plumes."

Roth suggests long cracks on Europa's surface, known as linea, might be venting water vapour into space. Similar fissures have been photographed near Enceladus's south pole by the Cassini spacecraft. It is unknown how deep inside Europa's crust the source of the water may be. Roth asks, "Do the vents extend down to a subsurface ocean or are the ejecta simply from warmed ice caused by friction stresses near the surface?"

Also like Enceladus, the Hubble team found that the intensity of the plumes varies with Europa's orbital position. Active geysers have only been seen when the moon is furthest from Jupiter. But the researchers could not detect any sign of venting when Europa is closer to Jupiter.

One explanation is that the long fractures in the ice crust experience more stress as gravitational tidal forces push and pull on the moon and so open vents at larger distances from Jupiter. The vents are narrowed or closed when at closest approach to the gas giant planet [1]. Team member Kurt Retherford, also of the Southwest Research Institute, points out that "the plume variability supports a key prediction that we should see this kind of tidal effect if there is a subsurface ocean on Europa".

Future space probe missions to Europa could confirm that the exact locations and sizes of vents and determine whether they connect to liquid subsurface reservoirs. It is important news for missions such as ESA's JUpiter ICy moons Explorer, a mission planned for launch in 2022, and which aims to explore both Jupiter and three of its largest moons: Ganymede, Callisto, and Europa.

Notes

[1] When Europa orbits around Jupiter, the moon experiences varying tidal forces at different points in its orbit. The tidal stresses compress the vents at the south pole region when Europa is closest to Jupiter, and stretch them when Europa is furthest away, making it possible for the vents to open up. A subsurface ocean would allow the stresses on Europa's surface to be much stronger as the interior would be malleable and flexible.

Notes for editors

The Hubble Space Telescope is a project of international cooperation between ESA and NASA.

The international team of astronomers in this study consists of L. Roth (Southwest Research Institute, USA; University of Cologne, Germany), J. Saur (University of Cologne, Germany), K. D. Retherford (Southwest Research Institute, USA), D. F. Strobel (The Johns Hopkins University, USA), P. D. Feldman (The Johns Hopkins University, USA), M. A. McGrath (NASA Marshall Space Flight Center, USA), F. Nimmo (University of California, USA).

More information

Image credit: NASA, ESA, L. Roth (Southwest Research Institute, USA/University of Cologne, Germany) and M. Kornmesser.

Links

• Science paper
• NASA press release
• Images of Hubble

Contacts

Lorenz Roth
Southwest Research Institute, San Antonio, Texas, USA
University of Cologne, Germany
Tel: +1-210-522-2225
Email: lorenz.roth@swri.org

Joachim Saur
University of Cologne
Germany
Tel: +49-221-470-2310
Email: jsaur@uni-koeln.de

Nicky Guttridge
ESA/Hubble Public Information Officer
Garching, Germany
Tel: +49-89-3200-6855
Cell: +44 7512 318322
Email: nguttrid@partner.eso.org

Ray Villard
Space Telescope Science Institute
Baltimore, Maryland, USA
Tel: +1-410-338-4514
Email: villard@stsci.edu

A members-only galaxy club

 

Credit: ESA/Hubble & NASA
Acknowledgement: Luca Limatola

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This new Hubble image shows a handful of galaxies in the constellation of Eridanus (The River). NGC 1190, shown here on the right of the frame, stands apart from the rest; it belong to an exclusive club known as Hickson Compact Group 22 (HCG 22).

There are four other members of this group, all of which lie out of frame: NGC 1189, NGC 1191, NGC 1192, and NGC 1199. The other galaxies shown here are nearby galaxies 2MASS J03032308-1539079 (centre), and dCAZ94 HCG 22-21 (left), both of which are not part of HCG 22.

Hickson Compact Groups are incredibly tightly bound groups of galaxies. Their discoverer Paul Hickson observed only 100 of these objects, which he described in his HCG catalogue in the 1980s. To earn the Hickson Compact Group label, there must be at least four members — each one fairly bright and compact. These short-lived groups are thought to end their lives as giant elliptical galaxies, but despite knowing much about their form and destiny, the role of compact galaxy groups in galactic formation and evolution is still unclear.

These groups are interesting partly for their self-destructive tendencies. The group members interact, circling and pulling at one another until they eventually merge together, signalling the death of the group, and the birth of a large galaxy.

A version of this image was entered into the Hubble's Hidden Treasures image processing competition by contestant Luca Limatola.

Source: ESA/Hubble - Space Telescope

Clay-Like Minerals Found on Icy Crust of Europa

This image, using data from NASA's Galileo mission, shows the first detection of clay-like minerals on the surface of Jupiter's moon Europa. Image credit: NASA/JPL-Caltech/SETI.  Full image and caption

This artist's concept shows a possible explosion resulting from a high-speed collision between a space rock and Jupiter's moon Europa. Image credit: NASA/JPL-Caltech.  Full image and caption  - enlarge image

A new analysis of data from NASA's Galileo mission has revealed clay-type minerals at the surface of Jupiter's icy moon Europa that appear to have been delivered by a spectacular collision with an asteroid or comet. This is the first time such minerals have been detected on Europa's surface. The types of space rocks that deliver such minerals typically also often carry organic materials.

"Organic materials, which are important building blocks for life, are often found in comets and primitive asteroids," said Jim Shirley, a research scientist at NASA's Jet Propulsion Laboratory, Pasadena, Calif. Shirley is giving a talk on this topic at the American Geophysical Union meeting in San Francisco on Friday, Dec. 13. "Finding the rocky residues of this comet crash on Europa's surface may open up a new chapter in the story of the search for life on Europa," he said.

Many scientists believe Europa is the best location in our solar system to find existing life. It has a subsurface ocean in contact with rock, an icy surface that mixes with the ocean below, salts on the surface that create an energy gradient, and a source of heat (the flexing that occurs as it gets stretched and squeezed by Jupiter's gravity). Those conditions were likely in place shortly after Europa first coalesced in our solar system.

Scientists have also long thought there must be organic materials at Europa, too, though they have yet to detect them directly. One theory is that organic material could have arrived by comet or asteroid impacts, and this new finding supports that idea.

Shirley and colleagues, funded by a NASA Outer Planets Research grant, were able to see the clay-type minerals called phyllosilicates in near-infrared images from Galileo taken in 1998. Those images are low resolution by today's standards, and Shirley's group is applying a new technique for pulling a stronger signal for these materials out of the noisy picture. The phyllosilicates appear in a broken ring about 25 miles (40 kilometers) wide, which is about 75 miles (120 kilometers) away from the center of a 20-mile-diameter (30 kilometers) central crater site.

The leading explanation for this pattern is the splash back of material ejected when a comet or asteroid hits the surface at an angle of 45 degrees or more from the vertical direction. A shallow angle would allow some of the space rock's original material to fall back to the surface. A more head-on collision would likely have vaporized it or driven that space rock's materials below the surface. It is hard to see how phyllosilicates from Europa's interior could make it to the surface, due to Europa's icy crust, which scientists think may be up to 60 miles (100 kilometers) thick in some areas.

Therefore, the best explanation is that the materials came from an asteroid or comet. If the body was an asteroid, it was likely about 3,600 feet (1,100 meters) in diameter. If the body was a comet, it was likely about 5,600 feet (1,700 meters) in diameter. It would have been nearly the same size as the comet ISON before it passed around the sun a few weeks ago.

"Understanding Europa's composition is key to deciphering its history and its potential habitability," said Bob Pappalardo of JPL, the pre-project scientist for a proposed mission to Europa. "It will take a future spacecraft mission to Europa to pin down the specifics of its chemistry and the implications for this moon hosting life."

For more information about Europa, visit: http://solarsystem.nasa.gov/europa/home.cfm .

JPL is a division of the California Institute of Technology in Pasadena.
Jia-Rui C. Cook 818-354-0850
Jet Propulsion Laboratory, Pasadena, Calif.
jccook@jpl.nasa.gov

Discovery of Hot Oxygen Gas Streaming Away from Distant Galaxies: Witnessing the Final Stage of Galaxy Buildup

The following release was received from the Institute for Cosmic Ray Research at the University of Tokyo and is reprinted here in its entirety for the convenience of our readers:  Original Article: (http://www.icrr.u-tokyo.ac.jp/2013/12/09140001.html)

Figure 1: The color composite Subaru images around the largest OIIB1 (center), zoom-in image of OIIB1 (top right), and the eleven other OIIBs (left and right). The size of each small panel corresponds to 400 thousand light years. The picture of Andromeda galaxy (by Robert Gendler) in the top right panel was scaled as if it were at the same distance as OIIB. Credit: NAOJ, the University of Tokyo (Suraphong YUMA) 

Using wide-field imaging data of Subaru Telescope, a team of international astronomers led by Dr. Suraphong Yuma (JSPS Fellow) and Dr. Masami Ouchi (Associate Professor) at ICRR, the University of Tokyo has discovered twelve galaxies expelling hot oxygen gas extending up to 250 thousand light years, beyond the sizes of the galaxies. These galaxies are located 9 billion light years from the Earth. Some of these galaxies host a super massive black hole (SMBH), while some show violent star formation with no SMBH. The vast amount of energy produced by the SMBH or star formation activity is able to heat up the gas in the galaxies, and drive the strong outflow of hot oxygen gas. These distant galaxies are thought to be in their final phase of galaxy growth, with star formation being quenched by the expulsion of gas needed to produce new stars. This is the first discovery of the large physical extents of these energetic oxygen-gas outflows driven by SMBH and star formation.

Astronomers attempt to understand how galaxies like our Milky Way have formed and evolved over time by observing galaxies at the present and in the past. Some galaxies are converting gas to stars from a large reservoir of gas in the galaxy, while others have ceased their star formation and are just letting their stars dying out. In the latter galaxies, known as elliptical galaxies, there are almost no stars younger than several billion years old, and so the quenching of star formation is believed to have taken place several billion years previously. This quenching takes place in the final stage of galaxy growth, but the physical mechanism is not clear. It is thought that the gas can escape from distant galaxies through heating by SMBH and/or star-formation. However, existing observations do not make it possible to determine which quenching mechanism is the most important.

"Because oxygen in the Universe is only produced within galaxies by nuclear fusion in the cores of stars, we conceived of the idea to identify distant galaxies with gas outflows from their extended profiles of oxygen gas. We therefore looked for distant galaxies associated with large clouds of ionized oxygen emission, which were efficiently located with Subaru's prime focus camera, Suprime-Cam, at optical wavelengths," explains Dr. Yuma. "So far, outflows have been studied separately in galaxies with either SMBH or star formation, whereas our search technique works regardless of the energy source. Our search was conducted in the Subaru/XMM-Newton Deep Survey (SXDS) field that has the ideal Subaru data sets."

Dr. Alyssa Drake, who recently completed her Ph.D. at Liverpool John Moores University, UK, picks up the story. "As the Universe expands, the light emitted by galaxies is stretched out on its way to us, changing the colors of galaxies and making them redder. We can use this fact to calculate the distances to galaxies if we measure their colors accurately.

From the search the team pinpointed 12 galaxies whose oxygen gas emission extends over more than 100,000 light years, corresponding to the size of the Milky Way. Due to their spatial extent, they call these galaxies [OII] blobs or OIIB. Subaru images (Figure 1) show diffuse oxygen emission extending beyond the stellar components of the galaxies.

While OIIBs are producing tens to hundreds of stars per year from gas, the star-formation rates of well-matured OIIBs are lower than those of typical star-forming galaxies with the same stellar mass. "This would be a signature of quenching star-formation activity in the process of gas outflow," remarks Associate Prof. Ouchi. "According to our estimates, about 3% of star-forming galaxies at this epoch are right in the middle of the gas outflow phase, which is a new and important insight for understanding galaxy formation."

Gas outflow has been confirmed in two OIIBs by optical spectroscopic observations with the Subaru telescope and the Very Large Telescope operated by the European Southern Observatory (ESO). "The spectra present absorption features made of cold gas outflowing from the galaxy. The intense activity of star formation and/or SMBH would trigger the outflow," explains co-author Dr. Chris Simpson, a senior lecturer at Liverpool John Moores University.

One of the OIIBs has a very fast outflow velocity of 600 km/s, suggesting a strong gas flow energized by a powerful SMBH. "This object, dubbed OIIB1, is the largest OIIB that we found in this study. OIIB1 is more than twice as large as Milky Way; its oxygen emission extends over 250,000 light years," adds Dr. Yuma. This giant blob has been detected in X-rays, a clear signature of SMBH activity. Prof. Masayuki Umemura of Tsukuba University comments, "This kind of object is very rare and can be a milestone to reveal gas outflow powered by SMBH."

This research is published in the December 10, 2013 issue of The Astrophysical Journal. The work was supported by KAKENHI (23244025) Grant-in-Aid for Scientific Research (A) through Japan Society for the Promotion of Science (JSPS).

Publication Details:

Suraphong Yuma*, Masami Ouchi, Alyssa B. Drake, Chris Simpson, Kazuhiro Shimazaku, Kimihiko Nakajima, Yoshiaki Ono, Rieko Momose, Masayuki Akiyama, Masao Mori, and Masayuki Umemura, "First Systematic Search for Oxygen-Line Blobs at High Redshift: Uncovering AGN Feedback and Star Formation Quenching," Astrophysical Journal Online Edition: 2013/12/10 (Japan time).

Member of the research team are

• Suraphong Yuma (The University of Tokyo)
• Masami Ouchi (The University of Tokyo)
• Alyssa B. Drake (Liverpool John Moores University)
• Chris Simpson (Liverpool John Moores University)
• Kazuhiro Shimasaku (The University of Tokyo)
• Kimihiko Nakajima (The University of Tokyo)
• Yoshiaki Ono (The University of Tokyo)
• Rieko Momose (The University of Tokyo)
• Masayuki Akiyama (Tohoku University)
• Masao Mori (University of Tsukuba)
• Masayuki Umemura (University of Tsukuba)

 

Souce: Subaru Telescope

 

Fire vs. Ice: The Science of ISON at Perihelion

After several days of continued observations, scientists continue to work to determine and understand the fate of Comet ISON: There's no doubt that the comet shrank in size considerably as it rounded the sun and there's no doubt that something made it out on the other side to shoot back into space. Image Credit: ESA/NASA/SOHO

This image from NASA's Solar Dynamics Observatory shows the sun, but no Comet ISON was seen. A white plus sign shows where the Comet should have appeared. Image Credit: NASA/SDO

After a year of observations, scientists waited with bated breath on Nov. 28, 2013, as Comet ISON made its closest approach to the sun, known as perihelion. Would the comet disintegrate in the fierce heat and gravity of the sun? Or survive intact to appear as a bright comet in the pre-dawn sky?

Some remnant of ISON did indeed make it around the sun, but it quickly dimmed and fizzled as seen with NASA's solar observatories. This does not mean scientists were disappointed, however. A worldwide collaboration ensured that observatories around the globe and in space, as well as keen amateur astronomers, gathered one of the largest sets of comet observations of all time, which will provide fodder for study for years to come.

On Dec. 10, 2013, researchers presented science results from the comet's last days at the 2013 Fall American Geophysical Union meeting in San Francisco, Calif. They described how this unique comet lost mass in advance of reaching perihelion and most likely broke up during its closest approach, as well, as summarized what this means for determining what the comet was made of.

"The comet's story begins with the very formation of the solar system," said Karl Battams, an astrophysicist at the Naval Research Lab in Washington, D.C. "The dirty snowball that we came to call Comet ISON was created at the same time as the planets."
 
ISON circled the solar system in the Oort cloud, more than 4.5 trillion miles away from the sun. At some point a few million years ago, something occurred – perhaps the passage of a nearby star – to knock ISON out of its orbit and send it hurtling along a path for its first trip into the inner solar system.

The comet was first spotted 585 million miles away in September 2012 by two Russian astronomers: Vitali Nevski and Artyom Novichonok. The comet was named after the project that discovered it, the International Scientific Optical Network, or ISON, and given an official designation of CC/2012 S1 (ISON). When comet scientists mapped out Comet ISON's orbit they learned that the comet would swing within 1.1 million miles of the sun's surface, making it what's known as a sungrazing comet, providing opportunities to study this pristine bit of the early solar system as it lost material while approaching the higher temperatures of the sun. With this knowledge, an international campaign to observe the comet was born. The number of space-based, ground-based, and amateur observations was unprecedented, including 12 NASA space-based assets observing Comet ISON over the past year.

Near the beginning of October, 2013, two months before perihelion, NASA's Mars Reconnaissance Observer, or MRO, turned its HiRISE instrument to view the comet during its closest approach to Mars in October 2013.

"The size of ISON's nucleus could be a little over half a mile across --- at the most.  Very likely it could have been as small as several hundred yards," said Alfred McEwen, the principal investigator for the HiRISE instrument at Arizona State University, in Tucson.

In other words, Comet ISON might have been the length of five or six football fields. This small size was near the borderline of how big ISON needed to be to survive its trip around the sun.

During that trip around the sun, Geraint Jones, a comet scientist at University College London's Mullard Space Science Laboratory in the UK studied the comet's dust tails to better understand what happened as it rounded the sun. By fitting models of the dust tail to the actual observations from NASA's Solar Terrestrial Observatory, or STEREO, and the joint European Space Agency/NASA Solar and Heliospheric Observatory, or SOHO, Jones showed that very little dust was produced after perihelion, which may suggest that the comet's nucleus had already broken up by that time.

While the comet was visible in STEREO and SOHO images going into perihelion, it was not visible in the data from NASA's Solar Dynamics Observatory, or SDO, or from ground based solar observatories during its closest approach to the sun. Dean Pesnell, project scientist for SDO at NASA's Goddard Space Flight Center in Greenbelt, Md., explained why Comet ISON wasn't visible in SDO and what could be learned from that: SDO is tuned to see wavelengths of light that would indicate the presence of oxygen, which is very common in comets.

"The fact that ISON did not show oxygen despite how close it came to the sun provides information about how high was the evaporation temperature of ISON's material," said Pesnell. "This limits what it could have been made of."

When Comet ISON was first spotted in September 2012, it was relatively bright for a comet at such a great distance from the sun. Consequently, many people had high hopes it would provide a beautiful light show visible in the night sky throughout December 2013. That potential ended when Comet ISON disrupted during perihelion. However, the legacy of the comet will go on for years as scientists analyze the tremendous data set collected during ISON's journey.

Related Links
› NASA's Comet ISON website
› Download high resolution media.
› Briefing Presentation

Karen C. Fox
NASA's Goddard Space Flight Center, Greenbelt, Md.

Astrophysicists launch ambitious assessment of galaxy formation simulations

Inconsistencies in supercomputer simulations to be compared in the AGORA project are clearly evident in this test galaxy produced by each of nine different versions of participating codes using the same astrophysics and starting with the same initial conditions. [Credit: Simulations performed by Samuel Leitner (ART-II), Ji-hoon Kim (ENZO), Oliver Hahn (GADGET-2- CFS), Keita Todoroki (GADGET-3), Alexander Hobbs (GADGET-3-CFS and GADGET-3-AFS), Sijing Shen (GASOLINE), Michael Kuhlen (PKDGRAV-2), and Romain Teyssier (RAMSES)].  Large image

AGORA, an international collaboration led by UC Santa Cruz, will perform systematic comparisons of high-resolution computer simulations of galaxy formation and evolution

One of the most powerful tools for understanding the formation and evolution of galaxies has been the use of computer simulations--numerical models of astrophysical processes run on supercomputers and compared with astronomical observations. Getting computer simulations to produce realistic-looking galaxies has been a challenge, however, and different codes (simulation programs) produce inconsistent results.

Now, an international collaboration led by astrophysicists at the University of California, Santa Cruz, aims to resolve these issues through an ambitious multi-year project named AGORA (Assembling Galaxies of Resolved Anatomy). AGORA will run direct comparisons of different codes using a common set of initial conditions and astrophysical assumptions. Each code treats some aspects of the physics differently, especially the way that energy from stars and supernovas is fed back into the simulated galaxies. The simulations are being run at the best resolutions currently possible, and they are using the same input physics as much as possible. The simulation results will be systematically compared with each other and against a variety of observations using a common analysis and visualization tool.

These comparisons will help researchers determine which of their simulation results are due to a particular code platform and which are due to the underlying theoretical assumptions common to all of the simulations.

"The physics of galaxy formation is extremely complicated, and the range of lengths, masses, and timescales that need to be simulated is immense," explained Piero Madau, professor of astronomy and astrophysics at UCSC and co-chair of the AGORA steering committee. "You incorporate gravity, solve the equations of hydrodynamics, and include prescriptions for gas cooling, star formation, and energy injection from supernovae into the code. After months of number crunching on a powerful supercomputer, you look at the results and wonder if that is what nature is really doing or if some of the outcomes are actually artifacts of the particular numerical implementation you used."

Dark matter

The AGORA project will explore the fundamental astrophysics of galaxy formation in the cosmological context of a "cold dark matter" universe. Although the nature of dark matter remains a mystery, it accounts for about 84 percent of the matter in the universe. As a result, the evolution of structure in the universe has been driven by the gravitational interactions of dark matter ("dark" because it can't be seen, and "cold" because the particles are moving slowly). The ordinary matter that forms stars and planets has fallen into the "gravitational wells" created by clumps of dark matter, giving rise to galaxies in the centers of dark matter halos.

The project's first major task will be to model a realistic isolated disk galaxy using various codes and their feedback recipes, varying both the feedback parameters and the resolution. The second task will be to compare the codes in cosmological simulations. Specifically, all the participating codes will model the evolution of eight individual galaxies from the big bang to the present, resulting in final masses representing a range of galaxy sizes, from that of a dwarf galaxy to one more massive than the Milky Way. For each mass, one set of simulations would model a galaxy having a quiescent merger history (having few mergers with another galaxy its own size) and another would model a galaxy having a violent merger history with many major mergers. The final task will be to compare the results, including such observable characteristics as the shape, internal structure and velocities, and spectral energy distribution (distribution of light at different wavelengths) between simulations and with observations of real galaxies.

The AGORA project will take advantage of new infrastructure for computational astrophysics at UC Santa Cruz, including the "Hyades" supercomputer and a high-capacity data storage system. "Our ability to store and analyze the data here, and make the output of the simulations available to the community at large, has made it possible for us to set up such a large project," Madau said.

The project was initiated in a workshop at UCSC in August 2012, under the sponsorship of the University of California High-Performance AstroComputing Center (UC-HiPACC). A second workshop was held at UCSC a year later. The project now involves more than 90 astrophysicists from 45 institutions in eight nations.

A paper describing the project in detail has been accepted for publication in the Astrophysical Journal Supplement. The first author is Ji-hoon Kim, formerly a postdoctoral researcher at UCSC and now at CalTech, who is coordinating the project along with the steering committee led by Madau and Joel Primack, a professor of physics at UCSC and director of the UC-HiPACC. Other members of the AGORA steering committee are Tom Abel (Stanford), Nick Gnedin (Fermilab and University of Chicago), Lucio Mayer and Romain Teyssier (University of Zurich), and James Wadsley (McMaster University, Canada).

AGORA is not the first such comparison of supercomputer simulations of galaxy evolution, but it is the most comprehensive and the highest-resolution (finest detail). Previous astronomical simulation comparison studies were the Santa Barbara Cluster comparison project (1999) and the Aquila comparison project (2012). The AGORA project is an open collaboration and welcomes new participants. AGORA is making all of its initial conditions and common assumptions public, both to make it easy for astrophysicists to join the collaboration and also to raise the level of galaxy simulations worldwide.

"This project will tell us what are the key ingredients that produce realistic galaxies regardless of the numerical codes. It will also challenge the community to put more effort in cross-checking their results against others'," Kim said.

More information about AGORA is available in the paper, "The AGORA High-Resolution Galaxy Simulations Comparison Project," preprint available at arxiv.org/abs/1308.2669. The official AGORA website is at www.agorasimulations.org.

By Tim Stephens 

Source: Universe of California Santa Cruz

NOAO/SOAR: Where do stars end and brown dwarfs begin?

The relation between size and temperature at the point where stars end and brown dwarfs begin (based on a figure from the publication) Image credit: P. Marenfeld & NOAO/AURA/NSF. 

The SOAR 4.1-m telescope on Cerro Pachón, CTIO 

Stars come in a tremendous size range, from many tens of times bigger than the Sun to a tiny fraction of its size. But the answer to just how small an astronomical body can be, and still be a star, has never been known. What is known is that objects below this limit are unable to ignite and sustain hydrogen fusion in their cores: these objects are referred to as brown dwarfs.

In research accepted for publication in the Astronomical Journal, the RECONS (Research Consortium On Nearby Stars) group from Georgia State University has found clear observational evidence for the theoretically predicted break between very low mass stars and brown dwarfs. The data came from the SOAR (Southern Observatory for Astrophysical Research) 4.1-m telescope and the SMARTS (Small and Moderate Aperture Research Telescope System) 0.9-m telescope at the Cerro Tololo Inter-American Observatory (CTIO) in Chile.

For most of their lives, stars obey a relationship referred to as the main sequence, a relation between luminosity and temperature – which is also a relationship between luminosity and radius. Stars behave like balloons in the sense that adding material to the star causes its radius to increase: in a star the material is the element hydrogen, rather than air which is added to a balloon. Brown dwarfs, on the other hand, are described by different physical laws (referred to as electron degeneracy pressure) than stars and have the opposite behavior. The inner layers of a brown dwarf work much like a spring mattress: adding additional weight on them causes them to shrink. Therefore brown dwarfs actually decrease in size with increasing mass.

As Dr. Sergio Dieterich, the lead author, explained, “In order to distinguish stars from brown dwarfs we measured the light from each object thought to lie close to the stellar/brown dwarf boundary. We also carefully measured the distances to each object. We could then calculate their temperatures and radii using basic physical laws, and found the location of the smallest objects we observed (see the attached illustration, based on a figure in the publication). We see that radius decreases with decreasing temperature, as expected for stars, until we reach a temperature of about 2100K. There we see a gap with no objects, and then the radius starts to increase with decreasing temperature, as we expect for brown dwarfs. “

Dr. Todd Henry, another author, said: “We can now point to a temperature (2100K), radius (8.7% that of our Sun), and luminosity (1/8000 of the Sun) and say ‘the main sequence ends there’ and we can identify a particular star (with the designation 2MASS J0513-1403) as a representative of the smallest stars.”

Aside from answering a fundamental question in stellar astrophysics about the cool end of the main sequence, the discovery has significant implications in the search for life in the universe. Because brown dwarfs cool on a time scale of only millions of years, planets around brown dwarfs are poor candidates for habitability, whereas very low mass stars provide constant warmth and a low ultraviolet radiation environment for billions of years. Knowing the temperature where the stars end and the brown dwarfs begin should help astronomers decide which objects are candidates for hosting habitable planets.

Also, because brown dwarfs cool forever, they eventually become a type of macroscopic dark matter, so it is important to know how much dark matter is trapped in the form of extremely old and cold brown dwarfs.

The research highlights the capabilities of the National Optical Astronomy Observatory system in a single project. The SOAR observations provided the missing link to a wealth of data that had previously been obtained using telescopes under the auspices of NOAO. As Dieterich explains: “We used the SOAR 4.1-m telescope to measure the visible light of faint stars and brown dwarfs, and the CTIO 0.9-m telescope to obtain precise measurements of their distances. We then combined these measurements with infrared data taken at the CTIO 1.3-m telescope and the WISE space telescope. Three out of four of these telescopes are public telescopes located at CTIO, and the fourth explores wavelengths that are only accessible from space.”

CTIO is a division of the National Optical Astronomy Observatory, which is operated by the Association of Universities for Research in Astronomy Inc. (AURA) under a cooperative agreement with the National Science Foundation.

Science Contact

Dr. Sergio Dieterich
Astronomy Department
Georgia State University
Atlanta, GA
E-mail: dieterich@chara.gsu.edu
phone: +1 678-350-4741

 

Marching to the Beat: Subaru's FMOS Reveals the Well-Orchestrated Growth of Massive Galaxies in the Early Universe

Using the Fiber Multi-Object Spectrograph (FMOS) mounted on the Subaru Telescope, a team of astronomers participating in the Cosmological Evolution Survey (COSMOS) has found that galaxies, over nine billion years ago, provided a nurturing environment for the birth of new stars at remarkable rates while at the same time as orderly as commuters on a typical Tokyo workday. Even at these early times, there are signs of maturation, since the surroundings of massive galaxies were relatively dusty and enriched by heavier elements.

"These findings center on a major question: What was the Universe like when it was maximally forming its stars?" says John Silverman, the principal investigator of the FMOS-COSMOS project at the Kavli Institute for the Physics and Mathematics of the Universe (Kavli IPMU). The COSMOS team wants to find the answers. COSMOS's research is designed to examine the role of the environment of large-scale structures on the formation and evolution of galaxies with cosmic time. Determining whether the individual properties of galaxies, such as their rate of growth, are connected to the larger-scale environment catapults us into discovering what factors in the early Universe have shaped the current form of local galaxies. One part of that investigation is carrying out an intensive program of research using FMOS on the Subaru Telescope to map the distribution of over 1000 galaxies when the Universe was maximally forming its stars over nine billion years ago.

"One key to generating fruitful results is collaboration between COSMOS researchers to maximize optimal use of FMOS". Silverman continues, "In this project, researchers from Kavli IPMU in Japan and the Institute for Astronomy (IfA) at the University of Hawaii formed an effective collaboration to implement their goal." The observations spanned 10 clear nights starting in March 2012.

Another important key to making their ambitious goal a reality is the advanced technology that FMOS offers to researchers. FMOS is a fiber-fed, near-infrared spectrograph that can acquire spectra from 400 galaxies simultaneously with a wide field of coverage of 30 arc minutes at prime-focus. Being able to capture so many objects in such a wide field of view is useful for a range of purposes: from studying galaxy evolution and variation with the galaxy environment to investigating star-forming regions, cluster formation, and cosmology. FMOS provides unprecedented views of the distant Universe by using fiber optic cables to collect the light of multiple objects over an area of the sky equal to that spanned by our Moon and also by using a built-in filter to remove unwanted bright emissions from the warm night sky.

As David Sanders, the principal investigator of the FMOS-COSMOS project at IfA put it, "FMOS has clearly revolutionized our ability to study how galaxies form and evolve across cosmic time. It is currently the most powerful instrument we have to study the large numbers of objects needed to understand galaxies of all sizes, shapes and masses -- from the largest ellipticals to the smallest dwarfs. We are extremely fortunate that the Kavli IPMU-IfA collaboration is giving us this unique opportunity to study the distant universe in such exquisite detail."

FMOS has now been operating in a high spectral resolution mode, and its highly successful rate of detection is testimony to the realization of the instrument's full potential. Figure 1 displays the emission lines from a single FMOS pointing, which detected the following chemical species from the interstellar medium of high-redshift galaxies: hydrogen: Hα and Hβ, nitrogen: [NII], and oxygen: [OIII]. These so-called "spectral signatures" provide a measure of the distance to the galaxy (i.e., its redshift). The ratio of the intensity of Hβ relative to Hα provides a measure of obscuring dust. The strength of the emission lines indicates the rate at which stars are forming while the ratio of [Nll] relative to Hα is indicative of the level of chemical enrichment of the interstellar medium (i.e., metallicity).

 

Figure 1:  FMOS spectra in the J-band (left panel) and H-band (right panel), each of which filters light so that only specific wavelengths can pass through. The horizontal axis refers to the wavelength direction while the vertical axis indicates individual spectra observed through each fiber. Small blue circles indicate the detection of emission lines (left: Hβ and [OIII]; right: Hα, [NII]). The inset box shows the intensity of the emission lines for one galaxy. The vertical bands indicate the masked regions where bright sky (OH) emissions are prevented from entering science fibers placed on high-redshift galaxies. (Credit: FMOS-COSMOS team)

The FMOS-COSMOS survey is the largest near-infrared spectroscopic survey of galaxies at high spectral resolution and high redshift yet to be undertaken. Early scientific results include the following:

1) Galaxy growth and a star-forming 'main sequence'. There is a highly ordered, general decline in the rate at which galaxies form stars over cosmic time. The FMOS observations shown in Figure 2 confirm that the rate of star formation varies with the total mass of stars available. Although this relationship was first seen locally, this research shows that star formation not only persisted in early epochs but also that its rates of star formation were 20 times higher then! The star formation rate increases with a look-back time out to a corresponding redshift of z~1.6. "While this has been observed using other indicators (ultraviolet or infrared) at high redshift," says Daichi Kashino (Nagoya University) who led the study of the star formation rates, "FMOS's detection of the Hα emission line in the near infrared provides a consistent way to measure star formation in the early Universe and compare it with that of local galaxies."

2) Early dust formation and chemical enrichment. The galaxies observed with FMOS have significantly lower levels of chemical enrichment of gas in their interstellar medium than galaxies of the same mass in the local Universe near us. This finding agrees with a portrait of galaxies that have room to grow and are accreting pristine gas that fuels their intense star formation. Larger amounts of dust and metal content indicate that the more massive galaxies at z~1.6 have evolved more fully and are similar to fully-mature local galaxies that have stopped star formation.

Figure 2: Rates at which new stars are forming in galaxies with a given total stellar mass. The galaxies observed with FMOS are shown in red. The y-axis shows the number of units of solar masses formed in a year. Star formation rates show a clear increase with mass, reaching over 500 M☉ per. As the age of the Universe increases, star formation decreases uniformly across the population. (Credit: FMOS-COSMOS team)

The FMOS-COSMOS survey has reached the halfway mark towards completing its goals of having over 1000 galaxies with redshifts to map the large-scale structure. While the current survey spans a sky area of one square degree in high-resolution mode, future efforts with FMOS may expand the areal coverage and complement instruments at other telescopes, which have wider spectral coverage or deeper penetrating power but are limited by a small area of coverage. Such complementarity may allow FMOS to detect the first structures (i.e., sites of higher than average density of galaxies) that likely evolved into the massive clusters that we see today.

Publications:

"The FMOS-Cosmos Survey of Star-Forming Galaxies at z ~ 1.6 I. Hα-Based Star Formation Rates and Dust Extinction," D. Kashino, J. D. Silverman, G. Rodighiero et al. 2013, Astrophysical Journal Letters, volume 777, L8, Published 11 October 2013

"The FMOS-Cosmos Survey of Star-Forming Galaxies at z~1.6 II. The Mass-Metallicity Relation and the Dependence on Star Formation Rate and Dust Extinction," J. Zahid, D. Kashino, J. D. Silverman, et al. 2013, arXiv:1310.4950, Submitted to Astrophysical Journal.

Participating Institutions/Members:

• Kavli Institute for the Physics and Mathematics of the Universe: John Silverman
• National Astronomical Observatory of Japan/Subaru Telescope: Nobuo Arimoto
• Nagoya University: Daichi Kashino, Naoshi Sugiyama
• Institute of Astronomy, University of Hawaii: Dave Sanders, Jabran Zahid, Lisa Kewley, Jason Chu
• Istituto Nazionale di Astrofisicai - Osservatorio Astronomico di Padova: Alvio Renzini, Giulia Rodighiero
• CEA Saclay: Emanuele Daddi
• National Optical Astronomy Observatory - Jeyhan Kartaltepe

Souce: Subaru Telescope

Subaru Telescope's Image Captures the Intricacy of Comet Lovejoy's Tail

A team of astronomers from Stony Brook University (the State University of New York at Stony Brook), the National Astronomical Observatory of Japan (NAOJ), and others used Suprime-Cam, Subaru Telescope's wide-field, prime-focus camera, to capture an image of the intricate flow of Comet Lovejoy's (C/2013 R1) ion tail. (Figure 1) The instrument's combination of a wide field of view and high spatial resolution provides a clear delineation of the complex, wiggling streams in the comet's tail. At the time of this observation, at around 5:30 am on December 3, 2013 (Hawaii Standard Time), Comet Lovejoy was 50 million miles (80 million km) distant from Earth and 80 million miles (130 million km) away from the Sun.

Figure 1: Image of Comet Lovejoy (C/2013 R1) captured by the Subaru Telescope's Suprime-Cam on December 3, 2013 (Hawaii Standard Time). The wavelength was at 450 nm (B-band), with a 180 second exposure. (Credit: NAOJ with data processing by Masafumi Yagi (NAOJ))

Comet Lovejoy was discovered in September this year (2013). At dawn on October 31, 2013, Subaru Telescope succeeded in capturing its image, which showed dust jets streaming from its nucleus. (Subaru Telescope Captures Visible-Light Images of the Comets ISON and Lovejoy) Although Comet ISON (C2012 S1) did not survive its closest encounter with the Sun (its perihelion) at the end of November (2013), Comet Lovejoy's visibility has been increasing in the eastern sky. The current image adds even more data about this newly-discovered comet. The variety of approaches used to image and analyze Comet Lovejoy will lead to a much clearer view of its detailed structure. As a member of the observation team commented, "Subaru Telescope offers a rare combination of large telescope aperture and a wide-field camera. This enabled us to capture a detailed look at the nucleus while also photogenically framing inner portions of Comet Lovejoy's impressive ion tail." (Figure 2)

Figure 2: Scientists in Subaru Telescope’s control room checking the details of Comet Lovejoy from the image that Suprime-Cam successfully captured. From left to right: the principal investigator of the observation, Dr. Jin Koda (Stony Brook University, New York), Alexandre Bouquin (U. Complutense, Spain), and David Thilker (Johns Hopkins University, Maryland). Dr. Masafumi Yagi (NAOJ), who promptly analyzed the data, was at NAOJ headquarters in Mitaka, Tokyo, Japan. He participated in the observation via Subaru Telescope’s remote observation system.

Source: Subaru Telescope

New Instrument Continues Gathering Sun's Effects on the Earth

Total solar irradiance (shown in color) over the past three solar cycles since 1978 adjusted to a ground-based cryogenic instrument funded by NASA in collaboration with the National Institute of Standards and Technology (NIST). Image Credit: Greg Kopp, LASP, University of Colorado / NASA

Total Irradiance Monitor used to measure solar irradiance on the TCTE and SORCE missions. Image Credit: LASP, University of Colorado

The SORCE satellite prior to its launch in January 2003. The satellite has three instruments designed to measure solar irradiance and the solar spectrum to better understand the sun's role in climate change and another instrument to measure high-energy radiation from the sun. Image Credit: NASA

Maintaining a record of solar measurements is important in understanding the sun's effect on Earth and the National Oceanic and Atmospheric Administration's (NOAA), Total solar irradiance Calibration Transfer Experiment, or TCTE, is now providing that information.

Many natural conditions on Earth such as the surface temperature or air temperature depend on energy that comes from the sun in the form of electromagnetic radiation. A solar cycle lasts about 11 years and typically has modest changes in solar radiation. There are also dramatic solar events that eject solar material, but the energy variation caused by these particle emissions, when averaged over a year or longer, is small compared to variations in the sun's electromagnetic radiation.

Scientists have noted these changes in the sun's energy by observing from Earth's surface for more than a hundred years, but were only able to begin to determine their magnitude and impact on Earth's climate with more accurate measurements from space, starting in 1978 with measurements of the "total solar irradiance," or TSI, made by NASA's Nimbus 7 satellite.

It is important to continue this TSI measurement record without a break in the data. The TCTE is designed to prevent such a break by continuing measurements from space to determine how solar changes are influencing Earth's climate.

A NOAA, Joint Polar Satellite System-sponsored mission, TCTE launched aboard U.S. Air Force Space Test Program Satellite-3, Tuesday, Nov. 19, 2013, from NASA's Wallops Flight Facility in Virginia. Since launch, TCTE successfully turned on and is transmitting information.

Solar irradiance is currently measured by the Total Irradiance Monitor or TIM deployed in 2003 on NASA's Solar Radiation and Climate Experiment or SORCE mission. The TIM on TCTE is one of three nearly identical instruments built as part of NASA's investment in the Total Irradiance Monitor deployed in 2003 on the SORCE mission.

While SORCE was designed to last for five years, it is still recording data more than 10 years later, but the aging satellite is nearing the end of its battery life. It is critical for the continuity of the data stream to have both instruments overlap to allow for syncing the measurements, allowing the new more accurate TCTE calibration to be transferred to SORCE TIM, and then to earlier overlapping measurements, so greatly increasing the accuracy and value of the overall TSI record.

Mission scientists hope for an overlap period of about ten days for the two instruments in space. After that period, because there are other instruments on the Air Force satellite, TCTE will be turned on once a week for a few orbits of the Earth, typically lasting about an hour-and-a-half, with a view of the sun for about 45 minutes during each orbit.

"The basic input to the climate system is the sun. We need that basic measurement before we can do other science," said Jeffrey Privette, chief of Climate Services and Monitoring Division for NOAA's National Climatic Data Center in Asheville, N.C. "The important thing is to not lose this record. I'm very optimistic about the quality of the data and the ability to use it," he said.

The solar irradiance measurements achieved by the TIM deployed in 2003, and its near clone as part of TCTE, are significantly more accurate than their previous space-based predecessors, said Robert Cahalan, project scientist for SORCE and TCTE at NASA's Goddard Space Flight Center in Greenbelt, Md.

Prior to SORCE, the space-based solar irradiance measurements located their precision apertures, that control exposure to the sun's light, inside the instrument, requiring the light to travel past baffles and other instrument surfaces before reaching that aperture, allowing some unknown amount of sunlight to be reflected from those surfaces, and then to enter the aperture, resulting in lost precision. "The big innovation with the SORCE TIM is that the precision aperture is right out in front, so the exposure is known very precisely," said Cahalan.

Even though the TIM on TCTE was built at the same time as the TIM currently flying on SORCE, scientists now have had the advantage with the current TIM of calibrating it with a ground-based cryogenic system operating at very cold temperatures to establish a more accurate measurement. This cryogenic system did not exist when the instrument on SORCE was launched.

This innovation will benefit the previous space-based solar data recorded since 1978. "Because we have a calibrated instrument, we will transfer that information to the data from SORCE, allowing us to correct the last 11 years of TIM data. And all the earlier instruments can potentially be corrected by their instrument teams and principal investigators," Cahalan said.

Scientists acknowledge that there is evidence that Earth's relationship to the sun, including changes in Earth's orbit, is a cause of some changes to the climate.. Yet over the last few decades, there has been no significant trend in the sun's energy output, its TSI, and over a 1,000 year timescale, Earth's orbit is remains essentially fixed and unchanged. Known orbital changes require more than 10,000 years to occur.

"In recent decades Earth has experienced a dramatic rise in temperature over the planet as a whole, and as the temperature has risen, ice has melted and the ocean has acidified (become less basic). These changes are traceable to the same cause, namely the increasing concentration of carbon dioxide and other greenhouse gases being emitted from fossil fuel use, trapping heat near Earth's surface, and being absorbed in the oceans," Cahalan said.

"During these decades, the sun's brightness (energy) has undergone several up-and-down cycles, in sync with the sunspot cycle, but with no overall trend that could explain Earth's temperature trend," Cahalan said. "That doesn't mean we should stop measuring the sun. Just because the sun hasn't significantly brightened or dimmed since 1978, doesn't mean it won't brighten or dim between now and 2050. Even a very small trend in the sun would either enhance the warming, if the sun were brightening, or partially offset it, if the sun were dimming."

Related Links:

For more information about JPSS and its precursor, Suomi NPP, please visit: http://www.jpss.noaa.gov/ and http://www.nasa.gov/npp

For more information about TCTE please visit: http://lasp.colorado.edu/home/missions-projects/quick-facts-tcte/

For more information on the Total Irradiance Monitor please visit: http://lasp.colorado.edu/home/sorce/instruments/tim/

For more information on SORCE, please visit: http://science1.nasa.gov/missions/sorce/ and http://lasp.colorado.edu/home/sorce/

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NASA Goddard: Audrey Haar
NASA's Goddard Space Flight Center, Greenbelt, Md.
240-684-0808
audrey.j.haar@nasa.gov

NOAA: John Leslie
NOAA Office of Communications and External Affairs
301-713-0214
john.leslie@noaa.gov

NASA's Cassini Spacecraft Obtains Best Views of Saturn Hexagon

This colorful view from NASA's Cassini mission is the highest-resolution view of the unique six-sided jet stream at Saturn's north pole known as "the hexagon." This movie, made from images obtained by Cassini's imaging cameras, is the first to show the hexagon in color filters, and the first movie to show a complete view from the north pole down to about 70 degrees north latitude. Image credit: NASA/JPL-Caltech/SSI/Hampton University.  Full image and caption

This infrared movie from NASA's Cassini mission shows the churning of the curious six-sided jet stream at Saturn's north pole known as "the hexagon." The movie, which was sped up here, covers 2 hours and 45 minutes in real time. It was made from data obtained by Cassini's visual and infrared mapping spectrometer in the 5-micron wavelength of radiation. This channel shows clouds in silhouette against infrared light emanating from Saturn's interior. These clouds are composed of relatively large particles and are thick, blocking light so they appear dark. These kinds of clouds tend to lie deep in Saturn's atmosphere, at about 3 bars of pressure. Image credit: NASA/JPL-Caltech/University of Arizona. Full image and caption -  enlarge image

This black-and-white movie from NASA's Cassini mission shows a polar projection of the curious six-sided jet stream at Saturn's north pole known as "the hexagon" in the infrared. Image credit: NASA/JPL-Caltech/University of Arizona.  Full image and caption - enlarge image

NASA's Cassini spacecraft has obtained the highest-resolution movie yet of a unique six-sided jet stream, known as the hexagon, around Saturn's north pole.

This is the first hexagon movie of its kind, using color filters, and the first to show a complete view of the top of Saturn down to about 70 degrees latitude. Spanning about 20,000 miles (30,000 kilometers) across, the hexagon is a wavy jet stream of 200-mile-per-hour winds (about 322 kilometers per hour) with a massive, rotating storm at the center. There is no weather feature exactly, consistently like this anywhere else in the solar system.

"The hexagon is just a current of air, and weather features out there that share similarities to this are notoriously turbulent and unstable," said Andrew Ingersoll, a Cassini imaging team member at the California Institute of Technology in Pasadena. "A hurricane on Earth typically lasts a week, but this has been here for decades -- and who knows -- maybe centuries."

Weather patterns on Earth are interrupted when they encounter friction from landforms or ice caps. Scientists suspect the stability of the hexagon has something to do with the lack of solid landforms on Saturn, which is essentially a giant ball of gas.

Better views of the hexagon are available now because the sun began to illuminate its interior in late 2012. Cassini captured images of the hexagon over a 10-hour time span with high-resolution cameras, giving scientists a good look at the motion of cloud structures within.

They saw the storm around the pole, as well as small vortices rotating in the opposite direction of the hexagon. Some of the vortices are swept along with the jet stream as if on a racetrack. The largest of these vortices spans about 2,200 miles (3,500 kilometers), or about twice the size of the largest hurricane recorded on Earth.

Scientists analyzed these images in false color, a rendering method that makes it easier to distinguish differences among the types of particles suspended in the atmosphere -- relatively small particles that make up haze -- inside and outside the hexagon.

"Inside the hexagon, there are fewer large haze particles and a concentration of small haze particles, while outside the hexagon, the opposite is true," said Kunio Sayanagi, a Cassini imaging team associate at Hampton University in Virginia. "The hexagonal jet stream is acting like a barrier, which results in something like Earth's Antarctic ozone hole."

The Antarctic ozone hole forms within a region enclosed by a jet stream with similarities to the hexagon. Wintertime conditions enable ozone-destroying chemical processes to occur, and the jet stream prevents a resupply of ozone from the outside. At Saturn, large aerosols cannot cross into the hexagonal jet stream from outside, and large aerosol particles are created when sunlight shines on the atmosphere. Only recently, with the start of Saturn's northern spring in August 2009, did sunlight begin bathing the planet's northern hemisphere.

"As we approach Saturn's summer solstice in 2017, lighting conditions over its north pole will improve, and we are excited to track the changes that occur both inside and outside the hexagon boundary," said Scott Edgington, Cassini deputy project scientist at NASA's Jet Propulsion Laboratory in Pasadena, Calif.

A black-and-white version of the imaging camera movie and movies obtained by Cassini's visual and infrared mapping spectrometer are also tools Cassini scientists can use to look at wind speeds and the mini-storms inside the jet stream.

Cassini launched in 1997 and arrived at Saturn on July 1, 2004. Its mission is scheduled to end in September 2017. The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. JPL manages the mission for NASA's Science Mission Directorate in Washington. JPL designed, developed and assembled the Cassini orbiter and its two onboard cameras. The imaging team is based at the Space Science Institute, Boulder, Colo.

A Google+ Hangout to discuss these results and other Cassini images will take place today at 12:30 p.m. PST (3:30 p.m. EST): http://bit.ly/askcassini .

The event will be broadcast live on NASA Television and streamed on the agency's website. For information on NASA TV, visit: http://www.nasa.gov/ntv .

The event will also be streamed live on Ustream with a moderated chat available at: http://www.ustream.tv/nasajpl2 .

Questions can be asked on the Google Hangout event page, in the chat box on the Ustream site and via Twitter using the hashtag #askCassini.

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

Jia-Rui C. Cook 818-354-0850
Jet Propulsion Laboratory, Pasadena, Calif.
jccook@jpl.nasa.gov

Dwayne Brown 202-358-1726
NASA Headquarters, Washington
dwayne.c.brown@nasa.gov

A bizarre cosmic rarity: NGC 660

NGC 660

Credit: ESA/Hubble & NASA

This new Hubble image shows a peculiar galaxy known as NGC 660, located around 45 million light-years away from us.

NGC 660 is classified as a "polar ring galaxy", meaning that it has a belt of gas and stars around its centre that it ripped from a near neighbour during a clash about one billion years ago. The first polar ring galaxy was observed in 1978 and only around a dozen more have been discovered since then, making them something of a cosmic rarity.

Unfortunately, NGC 660’s polar ring cannot be seen in this image, but has plenty of other features that make it of interest to astronomers – its central bulge is strangely off-kilter and, perhaps more intriguingly, it is thought to harbour exceptionally large amounts of dark matter. In addition, in late 2012 astronomers observed a massive outburst emanating from NGC 660 that was around ten times as bright as a supernova explosion. This burst was thought to be caused by a massive jet shooting out of the supermassive black hole at the centre of the galaxy.

Source: ESA/Hubble - Space Telescope

Circinus X-1: Supernova Blast Provides Clues to Age of Binary Star System

Circinus X-1

Credit: X-ray: NASA/CXC/Univ. of Wisconsin-Madison/S.Heinz et al; 

Optical: DSS; Radio: CSIRO/ATNF/ATCA 

JPEG (485.1 kb) - Large JPEG (3 MB) - Tiff (11 MB) - More Images
View on the Sky (WWT)

The youngest member of an important class of objects has been found using data from NASA's Chandra X-ray Observatory and the Australia Compact Telescope Array. A composite image shows the X-rays in blue and radio emission in purple, which have been overlaid on an optical field of view from the Digitized Sky Survey. This discovery, described in the press release, allows scientists to study a critical phase after a supernova and the birth of a neutron star.

Systems known as "X-ray binaries" are some of the brightest X-ray sources in the sky. They consist of either an ultra-dense star packed with neutrons --- a.k.a., a "neutron star" --- or a black hole that is paired with a normal star like the Sun. As these two objects orbit one another, the neutron star or black hole pulls material from the companion star onto it.

A new study shows that the X-ray binary called Circinus X-1 is less than 4,600 years old, making it the youngest ever seen. Astronomers have detected hundreds of X-ray binaries throughout the Milky Way and other nearby galaxies. However, these older X-ray binaries only reveal information about what happens later in the evolution of these systems.

Circinus X-1 Infographic

Researchers have found that the neutron star in Circinus X-1 is less than 4,600 years old, making it much younger than any other X-ray binary known in the Milky Way. Credit: Univ. of Wisconsin-Madison/S.Heinz et al.

Astronomers were able to determine the age of Circinus X-1 by examining material around the orbiting pair. While the source itself has been known for decades, the neutron star is usually so bright that the glare from its X-ray light overwhelms any faint emission surrounding it. The new Chandra data were obtained while the neutron star was in a very faint state, which meant it was dim enough for astronomers to detect the faint afterglow created by the supernova explosion plowing through the surrounding interstellar gas. This, combined with characteristics of the radio emission, allowed the researchers to pinpoint the age of the supernova remnant. In turn, this information reveals the age of the neutron star since they were formed at the same time.

These results have been published in the December 4th issue of The Astrophysical Journal. In addition to those mentioned above, the other authors on this paper are Peter Jonker of the SRON Netherlands Institute for Space Research, Niel Brandt of Penn State University, Daniel Emilio Calvelo-Santos of the University of Southampton, Tasso Tzioumis of the Australia Telescope National Facility, Michael Nowak and Norbert Schultz of the Kavli Institute/MIT, Rudy Wijnands and Michiel van der Klis of the University of Amsterdam.

Fast Facts for Circinus X-1: 

Scale: Image is 10 arcmin across (about 76 light years) 
Category: Neutron Stars/X-ray Binaries 
Coordinates (J2000): RA 15h 20m 41.00s | Dec -51° 10' 00 
Constellation: Circinus 
Observation Date: 1 May 2009 
Observation Time: 27 hours 25 min (1 day 3 hours 25 min) 
Obs. ID: 10062 
Instrument: ACIS 

References: Heinz, S et al, 2013, ApJ accepted

Color Code: X-ray (Blue); Optical (Red, Green, Blue); Radio (Pink) D

Distance Estimate: About 26,000 light years