samedi 9 janvier 2016

NASA Research Reveals Biological Clock Misalignment Effects on Sleep for Astronauts











NASA logo.

Jan. 9, 2016

Since the beginning of the space program, astronauts have dealt with the realities of spaceflight from microgravity in weak muscles and space radiation, to sleep deprivation and disorientation. Both before and during astronauts’ flights, changes in biological clocks, or circadian rhythms, contribute to sleep deficiency and increase the use of sleep-promoting medications.

For most people, the circadian rhythm is a little longer than 24 hours. On Earth, our daily exposure to light from the sun keeps us synchronized to the 24-hour day. As they circle around Earth in orbit, astronauts experience a sunrise or sunset every 45 minutes. Understanding the effects of spaceflight on astronauts may help prepare NASA for planning longer crew stays in deep space and possible missions to Mars, where the day length is a little longer than 24 hours. Most importantly, investigating these effects can reveal new ways to reduce the general consequences of the exposure of spaceflight on the human body.

At NASA’s Ames Research Center in California's Silicon Valley, Erin Flynn-Evans has been investigating the quality of astronauts’ sleep during spaceflight to better understand how sleep disturbances, such as noise and uncomfortable temperatures, cause sleep deficiency, which can throw off their circadian rhythms. Docking and undocking with the International Space Station requires astronauts to “slam-shift” their sleep patterns, which causes sleep disruption, much like people on the Earth who work rotating night shifts.

ISS sleeping astronaut. Image Credit: NASA

“Imagine flying across the country and getting jet-lagged,” said Flynn-Evans, a researcher at the Fatigue Countermeasures Laboratory at Ames. “It’s very similar to what astronauts deal with on the International Space Station, only the stakes are higher.”

Flynn-Evans and her team at Ames worked with Harvard Medical School and Brigham and Women's Hospital, both in Boston, to conduct a study to evaluate causes of sleep deficiency and the use of sleep-promoting medication by astronauts during spaceflight. Because mission operations often dictate completion of tasks during the biological night and sleep during the biological day, the team investigated whether circadian misalignment was associated with adverse sleep outcomes before and during spaceflight missions.

For a recently published paper in Nature Microgravity about the topic, Flynn-Evans and her team collected data from 21 astronauts over 3,248 days of long-duration spaceflight on the space station, including 11 days prior to launch, and reviewed sleep logs to determine sleep medication use and sleep quality. 

Astronauts wore activity monitors similar to popular fitness monitoring wristbands during the study. The researchers evaluated data about the astronauts’ sleep episodes, including bedtime, wake time and number and cause of awakenings, ratings of sleep quality, medication and caffeine use for one week during their spaceflight.

“Rapid schedule changes are a problem, but so is exposure to light at times when the astronauts are scheduled to sleep,” said Flynn-Evans. “The crewmembers will often look out the cupola window to get a view of Earth during their scheduled sleep time, which can expose them to a bright blast of sunlight and inhibit their ability to sleep.”

Flynn-Evans says crewmembers often use tablet computers, which expose them to even more light before bed. The additional light exposure disrupts their natural sleep cycles and can prevent them from sleeping well during the day.

With the support of NASA grants, researchers at Brigham and Women's Hospital designed Circadian Performance Simulation Software (CPSS) to consistently predict the effects of sleep-wake schedules and light exposure on the human biological clock. When crewmembers slept when their biological clocks were promoting sleep, they slept longer and used fewer sleep medications. When they slept when their biological clocks were not promoting sleep, they had more disrupted sleep and used more sleep medication.

During the experiment, NASA researchers interviewed the astronauts and evaluated journal entries in order to better understand how they were being affected by sleep loss. They discovered that space station astronauts as well as shuttle astronauts slept for just six hours per night on average, when most mission schedules called for 8.5 hours. Another finding revealed that where astronauts launched into space made a significant difference in disruptions to sleep patterns. In the weeks before astronauts took flight, those launching from Baikonur, Kazakhstan, compared to launching from Cape Canaveral, Florida, experienced better sleep. This could be due to other variables, such as training and preflight preparations and/or social activities or recovery from jet lag to get to Baikonour. In any case, astronauts used sleep aids to help them sleep most nights during preflight.

International Space Station (ISS). Image Credit: NASA

NASA is working to make improvements that promote astronaut crew health during spaceflight. Suggestions include special blue LED lights to help fight insomnia experienced by astronauts, spacecraft designed with luxuries of Earth to make sure astronauts are more comfortable while in space and more efficient schedules to balance the astronaut work-sleep times. 

Still, more needs to be understood about the limitations of the human body in space. As the first one-year mission of living onboard the space station concludes in March 2016, studying the patterns of sleeping and waking is crucial to ensuring a well-rested astronaut crew for future deep space exploration missions.

For more information about living in space on the International Space Station, visit: http://www.nasa.gov/mission_pages/station/main/index.html

Related link:

One-Year Crew: http://www.nasa.gov/content/one-year-crew/index.html

Images (mentioned), Text, Credits: NASA/Ames Research Center/Kimberly Williams.

Best regards, Orbiter.ch

New command for Philae












ESA - Rosetta Mission patch.

January 9, 2016


Image above: Philae's home. The Optical, Spectroscopic and Infrared Remote Imaging System (OSIRIS) on ESA's Rosette spacecraft aquired this image of Comet 67P/Churyumov-Gerasimenko on 20 December 2015 from a distance of 91,5 kilometres. Image Credits: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA.

The last clear sign of life was received from Philae, the Rosetta mission's comet lander, on 9 July 2015; since then, it has remained silent. Now, Comet 67P/Churyumov-Gerasimenko is moving away from the Sun and the temperature on the comet's surface and the amount of sunlight are both decreasing. By the end of January 2016, conditions on the comet will be 'lander-hostile' and Philae's mission is expected to come to a natural end. Engineers and scientists at the German Aerospace Center (Deutsches Zentrum für Luft- und Raumfahrt; DLR) have been listening in vain since last September for a signal from Philae. On 10 January 2016, they will, for the first time, send a command to Philae to spin up its flywheel. "Time is running out, so we want to explore all possibilities," says DLR Project Leader Stephan Ulamec.

Waiting for a signal

During the comet landing on 12 November 2015, the flywheel stabilised Philae during its descent. Now, it might impart some angular momentum to the lander as it sits silently on 67P/Churyumov-Gerasimenko. "At best, the spacecraft might shake dust from its solar panels and better align itself with the Sun," explains Technical Project Manager Koen Geurts. In the worst case, the lander will not receive the commands sent by the DLR team.

Following its long silence, the current status of Philae is unclear. The last data about the health of the lander was received in the summer of 2015. The DLR team now believes that one of the lander's two radio transmitters and one of its two receivers have both failed. The second transmitter and receiver are also though to be no longer fully functional. The team continues to hope that Philae has not tilted over or become covered with too much dust. On an active comet, which is ejecting gas and dust into space, the lander is not in a particularly safe location. "Unfortunately, Philae's silence does not bode well," says Ulamec. During the night of 21 December 2015, a weak signal was received by the Rosetta spacecraft and examined by the mission team. Their analysis revealed that this was not a transmission from the lander.


Image above: Rosetta flies above the Philae lander on Comet 67P/Churyumov-Gerasimenko in this artist’s impression from 2002. Image Credits: Astrium/E. Viktor.

On a journey through space

No later than the end of January, things will become increasingly uncomfortable for Philae. By then, 67P/Churyumov-Gerasimenko will be more than 300 million kilometres from the Sun. Once the temperature falls below minus 51 degrees Celsius, the lander will no longer operate. The command to spin up the flywheel and move Philae will be one of the last attempts to obtain a response from the lander. "There is a small chance," says Cinzia Fantinati, an Operations Manager on the DLR control room team. "We want to leave no stone unturned." The communications unit on board Rosetta will remain active and continue to listen for a signal from Philae beyond mid-January. ESA’s Rosetta orbiter will remain active until September 2016.

The mission

Rosetta is an ESA mission with contributions from its member states and NASA. Rosetta's Philae lander is provided by a consortium headed by DLR, the Max Planck Institute for Solar System Research (MPS), the French Space Agency (CNES) and the Italian Space Agency (ASI).

For more information about Rosetta mission, visit: http://www.esa.int/Our_Activities/Space_Science/Rosetta

Rosetta overview: http://www.esa.int/Our_Activities/Space_Science/Rosetta_overview

Rosetta in depth:http://sci.esa.int/rosetta

Rosetta at Astrium: http://www.astrium.eads.net/en/programme/rosetta-1go.html

Rosetta at DLR: http://www.dlr.de/dlr/en/desktopdefault.aspx/tabid-10394/

Ground-based comet observation campaign: http://www.rosetta-campaign.net/home

Rosetta factsheet: http://www.esa.int/Our_Activities/Space_Science/Rosetta/Rosetta_factsheet

Frequently asked questions: http://www.esa.int/Our_Activities/Space_Science/Rosetta/Frequently_asked_questions

Images (mentioned), Text, Credits: German Aerospace Center (DLR)/Manuela Braun/ Dr Koen Geurts/ Dr Stephan Ulamec.

Greetings, Orbiter.ch

vendredi 8 janvier 2016

Hubble Sees a Supermassive and Super-hungry Galaxy











NASA - Hubble Space Telescope patch.

Jan. 8, 2016


This NASA/ESA Hubble Space Telescope image shows the spiral galaxy NGC 4845, located over 65 million light-years away in the constellation of Virgo (The Virgin). The galaxy’s orientation clearly reveals the galaxy’s striking spiral structure: a flat and dust-mottled disk surrounding a bright galactic bulge.

NGC 4845’s glowing center hosts a gigantic version of a black hole, known as a supermassive black hole. The presence of a black hole in a distant galaxy like NGC 4845 can be inferred from its effect on the galaxy’s innermost stars; these stars experience a strong gravitational pull from the black hole and whizz around the galaxy’s center much faster than otherwise.

From investigating the motion of these central stars, astronomers can estimate the mass of the central black hole — for NGC 4845 this is estimated to be hundreds of thousands times heavier than the sun. This same technique was also used to discover the supermassive black hole at the center of our own Milky Way — Sagittarius A* — which hits some four million times the mass of the sun.

video
Hubble and the sunrise over Earth

The galactic core of NGC 4845 is not just supermassive, but also super-hungry. In 2013 researchers were observing another galaxy when they noticed a violent flare at the center of NGC 4845. The flare came from the central black hole tearing up and feeding off an object many times more massive than Jupiter. A brown dwarf or a large planet simply strayed too close and was devoured by the hungry core of NGC 4845.

Hubble Space Telescope websites:

    http://www.nasa.gov/hubble
    http://hubblesite.org/
    http://www.spacetelescope.org/

Image, Video, Credits: ESA/Hubble & NASA and S. Smartt (Queen's University Belfast)/Text credits: European Space Agency/Ashley Morrow.

Best regards, Orbiter.ch

Particles ‘Go with the Flow’ on Pluto’s Surface & Icy Plains in Highest-Resolution Views












NASA - New Horizons Mission logo.

Jan. 8, 2016

Scientists from NASA’s New Horizons mission have combined data from two instruments to create this composite image of Pluto’s informally named Viking Terra area.


The combined data includes pictures taken by the spacecraft’s Long Range Reconnaissance Imager (LORRI) on July 14, 2015, from a range of about 31,000 miles (49,000 kilometers), showing features as small as 1,600 feet (480 meters) across. Draped over the LORRI mosaic is enhanced color data from the Ralph/Multispectral Visible Imaging Camera (MVIC), gathered about 20 minutes after the LORRI snapshots were taken, from a range of 21,000 miles (34,000 kilometers) and at a resolution of about 2,100 feet (650 meters) per pixel. The entire scene is 160 miles (250 kilometers) across.

Among the features scientists find particularly interesting are the bright methane ices that condensed on many crater rims; the collection of dark red tholins (small soot-like particles generated from reactions involving methane and nitrogen in the atmosphere) in low areas, like the bottoms of craters; and the layering on the faces of steep cliffs and on crater walls.


In areas where the reddish material is thickest and the surface appears smooth, the material seems to have flowed into some channels and craters. Scientists say tholin deposits of that thickness aren’t usually mobile on large scales, suggesting that they might be riding along with ice flowing underneath, or being blown around by Pluto’s winds.

Pluto’s Icy Plains in Highest-Resolution Views from New Horizons 


NASA’s New Horizons spacecraft continues to transmit the sharpest views of Pluto that it obtained (and recorded) during its July 14, 2015 flyby. 

The newest image, returned on Dec. 24, extends New Horizons’ highest-resolution swath of Pluto to the center of the informally named Sputnik Planum, and nearly completes the set of highest-resolution images taken by New Horizons.

The pictures are part of a sequence taken near New Horizons’ closest approach to Pluto, with resolutions of about 250-280 feet (77-85 meters) per pixel – revealing features smaller than half a city block on Pluto’s surface. The images illustrate the polygonal or cellular pattern of the plains, which are thought to result from the convective churning of a deep layer solid, but mobile, nitrogen ice.

The images shown here form a strip 50 miles (80 kilometers) wide and more than 400 miles (700 kilometers) long, trending from the northwestern shoreline of Sputnik Planum and out across its icy plains. They were made with the telescopic Long Range Reconnaissance Imager (LORRI) aboard New Horizons, from a range of approximately 10,000 miles (17,000 kilometers), about 15 minutes before New Horizons’ closest approach to Pluto.

The surface of Sputnik Planum appears darker toward the shore (at top), possibly implying a change in composition or surface texture. The occasional raised, darker blocks at the cell edges are probably dirty water “icebergs” that are floating in denser solid nitrogen.

The images are six times better than the resolution of the global Pluto map New Horizons obtained, and five times better than the best images of Pluto’s cousin Triton, Neptune’s large moon, obtained by Voyager 2 in 1989.

For more information about New Horizons, visit: http://www.nasa.gov/mission_pages/newhorizons/main/index.html

Images, Text, Credits: Credits: NASA/JHUAPL/SwRI/Bill Keeter.

Greetings, Orbiter.ch

jeudi 7 janvier 2016

NASA's Fermi Space Telescope Sharpens its High-energy Vision











NASA - Fermi Gamma-ray Space Telescope logo.

Jan. 7, 2016

Major improvements to methods used to process observations from NASA's Fermi Gamma-ray Space Telescope have yielded an expanded, higher-quality set of data that allows astronomers to produce the most detailed census of the sky yet made at extreme energies. A new sky map reveals hundreds of these sources, including 12 that produce gamma rays with energies exceeding a trillion times the energy of visible light. The survey also discovered four dozen new sources that remain undetected at any other wavelength.


Image above: This image, constructed from more than six years of observations by NASA's Fermi Gamma-ray Space Telescope, is the first to show how the entire sky appears at energies between 50 billion (GeV) and 2 trillion electron volts (TeV). For comparison, the energy of visible light falls between about 2 and 3 electron volts. A diffuse glow fills the sky and is brightest in the middle of the map, along the central plane of our galaxy. The famous Fermi Bubbles, first detected in 2010, appear as red extensions north and south of the galactic center and are much more pronounced at these energies. Discrete gamma-ray sources include pulsar wind nebulae and supernova remnants within our galaxy, as well as distant galaxies called blazars powered by supermassive black holes. Labels show the highest-energy sources, all located within our galaxy and emitting gamma rays exceeding 1 TeV. Image Credits: NASA/DOE/Fermi LAT Collaboration.

"What made this advance possible was a complete reanalysis, which we call Pass 8, of all data acquired by Fermi's Large Area Telescope (LAT)," said Marco Ajello, a Fermi team member at Clemson University in South Carolina. "The end result is effectively a complete instrument upgrade without our ever having to leave the ground."

By carefully reexamining every gamma-ray and particle detection by the LAT since Fermi's 2008 launch, scientists improved their knowledge of the detector's response to each event and to the background environment in which it was measured. This enabled the Fermi team to find many gamma rays that previously had been missed while simultaneously improving the LAT's ability to determine the directions of incoming gamma rays. These improvements effectively sharpen the LAT's view while also significantly widening its useful energy range.

video
Fermi Sharpens its High-Energy View - 4K

Video above: Watch Fermi scientists explain why they're so excited about Pass 8, a complete reprocessing of all data collected by the mission's Large Area Telescope. This analysis increased the LAT's sensitivity, widened its energy range, and effectively sharpened its view through improved backtracking of incoming gamma rays. Video Credits: NASA's Goddard Space Flight Center.

Using 61,000 Pass 8 gamma rays collected over 80 months, Ajello and his colleagues constructed a map of the entire sky at energies ranging from 50 billion (GeV) to 2 trillion electron volts (TeV). For comparison, the energy of visible light ranges from about 2 to 3 electron volts.

video
Best-Ever View of the High-Energy Gamma-ray Sky - 4K

Video above: Tour the best view of the high-energy gamma-ray sky yet seen. This video highlights the plane of our galaxy and identifies objects producing gamma rays with energies greater than 1 TeV. Video Credits: NASA's Goddard Space Flight Center.

"Of the 360 sources we cataloged, about 75 percent are blazars, which are distant galaxies sporting jets powered by supermassive black holes," said co-investigator Alberto Domínguez at the Complutense University in Madrid. "The highest-energy sources, all located in our galaxy, are mostly remnants of supernova explosions and pulsar wind nebulae, places where rapidly rotating neutron stars accelerate particles to near the speed of light." One famous example, the Crab Nebula, tops the list of the highest-energy Fermi sources, producing a steady drizzle of gamma rays exceeding 1 TeV.

Astronomers think these very high-energy gamma rays are produced when lower-energy light collides with accelerated particles. This results in a small energy loss for the particle and a big gain for the light, transforming it into a gamma ray.

video
How Fast Electrons Make Gamma-rays

Video above: Gamma-ray emission from the highest-energy sources detected by Fermi is likely produced by what scientists call the inverse Compton process. When an electron moving near the speed of light strikes a low-energy photon, the collision slightly slows the electron and boosts the light's energy into the gamma-ray regime. Video Credits: NASA's Goddard Space Flight Center.

For the first time, Fermi data now extend to energies previously seen only by ground-based detectors. Because ground-based telescopes have much smaller fields of view than the LAT, which scans the whole sky every three hours, they have detected only about a quarter of the objects in the catalog. This study provides ground facilities with more than 280 new targets for follow-up observations.

"An exciting aspect of this catalog is that we find many new sources that emit gamma rays over a comparatively large patch of the sky," explained Jamie Cohen, a University of Maryland graduate student working with the Fermi team at NASA's Goddard Space Flight Center in Greenbelt. "Finding more of these objects enables us to probe their structures as well as better understand mechanisms that accelerate the subatomic particles that ultimately produce gamma-ray emission." The new catalog identifies 25 of these extended objects, including three new pulsar wind nebulae and two new supernova remnants.

Ajello presented the findings Thursday at the 227th meeting of the American Astronomical Society in Kissimmee, Florida. A paper describing the catalog has been accepted for publication in The Astrophysical Journal Supplement.

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

For more information about NASA's Fermi, visit: http://www.nasa.gov/fermi

Image (mentioned), Videos (mentioned), Text, Credits: NASA's Goddard Space Flight Center/Francis Reddy/ Ashley Morrow.

Best regards, Orbiter.ch

NASA's Great Observatories Weigh Massive Young Galaxy Cluster












NASA - Chandra X-ray Observatory patch.

Jan. 7, 2016

Astronomers have used data from three of NASA's Great Observatories to make the most detailed study yet of an extremely massive young galaxy cluster. This rare cluster, which is located 10 billion light years from Earth, weighs as much as 500 trillion Suns. This object has important implications for understanding how these megastructures formed and evolved early in the Universe.

The galaxy cluster called IDCS J1426.5+3508 (IDCS 1426 for short), is so far away that the light detected is from when the universe was roughly a quarter of its current age. It is the most massive galaxy cluster detected at such an early age.


Image above: Galaxy Cluster IDCS 1426. Image Credits: X-ray: NASA/CXC/Univ of Missouri/M.Brodwin et al; Optical: NASA/STScI; Infrared: JPL/CalTech.

First discovered by the Spitzer Space Telescope in 2012, IDCS 1426 was observed using the Hubble Space Telescope and the Keck Observatory to determine its distance. Observations from the Combined Array for Millimeter Wave Astronomy indicated it was extremely massive. New data from the Chandra X-ray Observatory confirm the galaxy cluster mass and show that about 90% of the mass of the cluster is in the form of dark matter, a mysterious substance detected so far only through its gravitational pull on normal matter composed of atoms.

“We are really pushing the boundaries with this discovery,” said Mark Brodwin of the University of Missouri at Kansas City, who led the study. “As one of the earliest massive structures to form in the Universe, this cluster sets a high bar for theories that attempt to explain how clusters and galaxies evolve.”

Galaxy clusters are the largest objects in the Universe bound together by gravity. Because of their sheer size, scientists think it should take several billion years for them to form. The distance of IDCS J1426 means astronomers are observing it when the Universe was only 3.8 billion years old, implying that the cluster is seen at a very young age.

The data from Chandra reveal a bright knot of X-rays near the middle of the cluster, but not exactly at its center. This overdense core has been dislodged from the cluster center, possibly by a merger with another developing cluster 500 million years prior. Such a merger would cause the X-ray emitting, hot gas to slosh around like wine in a glass that is tipped from side to side.

“Mergers with other groups and clusters of galaxies should have been more common so early in the history of the Universe,” said co-author Michael McDonald of Massachusetts Institute of Technology in Cambridge, Massachusetts. “That appears to have played an important part in this young cluster’s rapid formation.”

Aside from this cool core, the hot gas in the rest of the cluster is very smooth and symmetric. This is another indication that IDCS 1426 formed very rapidly. In addition, astronomers found possible evidence that the amount of elements heavier than hydrogen and helium in the hot gas is unusually low. This suggests that this galaxy cluster might still be in the process of enriching its hot gas with these elements as supernovae create heavier elements and blast them out of individual galaxies.

“The presence of this massive galaxy cluster in the early Universe doesn’t upset our current understanding of cosmology,” said co-author of Anthony Gonzalez of University of Florida in Gainesville, Florida. “It does, however, give us more information to work with as we refine our models.”

Chandra X-ray Observatory. Image Credits: NASA/CXC

Evidence for other massive galaxy clusters at early times has been found, but none of these matches IDCS 1426 with its combination of mass and youth. The mass determination used three independent methods: a measurement of the mass needed to confine the hot X-ray emitting gas to the cluster, the imprint of the cluster's gaseous mass on the cosmic microwave background radiation, and the observed distortions in the shapes of galaxies behind the cluster, which are caused by the bending of light from the galaxies by the gravity of the cluster.

These results were presented at the 227th meeting of the American Astronomical Society meeting being held in Kissimmee, Florida. A paper describing these results has been accepted for publication in The Astrophysical Journal and is available online (http://arxiv.org/abs/1504.01397). NASA's Marshall Space Flight Center in Huntsville, Alabama, manages the Chandra program for NASA's Science Mission Directorate in Washington. The Smithsonian Astrophysical Observatory in Cambridge, Massachusetts, controls Chandra's science and flight operations.

Read More from NASA's Chandra X-ray Observatory: http://chandra.harvard.edu/photo/2016/idcs1426/

For more Chandra images, multimedia and related materials, visit: http://www.nasa.gov/chandra

Images (mentioned), Text, Credits: NASA/Lee Mohon/Marshall Space Flight Center/Molly Porter.

Greetings, Orbiter.ch

mercredi 6 janvier 2016

Spitzer & Hubble Find "Twins" of Superstar Eta Carinae in Other Galaxies














NASA - Spitzer Space Telescope patch / NASA - Hubble Space Telescope patch.

Jan. 6, 2016

Eta Carinae, the most luminous and massive stellar system within 10,000 light-years, is best known for an enormous eruption seen in the mid-19th century that hurled at least 10 times the sun's mass into space. This expanding veil of gas and dust, which still shrouds Eta Carinae, makes it the only object of its kind known in our galaxy. Now a study using archival data from NASA's Spitzer and Hubble space telescopes has found five objects with similar properties in other galaxies for the first time.    

"The most massive stars are always rare, but they have tremendous impact on the chemical and physical evolution of their host galaxy," said lead scientist Rubab Khan, a postdoctoral researcher at NASA's Goddard Space Flight Center in Greenbelt, Maryland. These stars produce and distribute large amounts of the chemical elements vital to life and eventually explode as supernovae.


Image above: Eta Carinae's great eruption in the 1840s created the billowing Homunculus Nebula, imaged here by Hubble, and transformed the binary into a unique object in our galaxy. Astronomers cannot yet explain what caused this eruption. The discovery of likely Eta Carinae twins in other galaxies will help scientists better understand this brief phase in the life of a massive star. Image Credits: NASA, ESA, and the Hubble SM4 ERO Team.

Located about 7,500 light-years away in the southern constellation of Carina, Eta Carinae outshines our sun by 5 million times. The binary system consists of two massive stars in a tight 5.5-year orbit. Astronomers estimate that the more massive star has about 90 times the sun’s mass, while the smaller companion may exceed 30 solar masses.

As one of the nearest laboratories for studying high-mass stars, Eta Carinae has been a unique astronomical touchstone since its eruption in the 1840s. To understand why the eruption occurred and how it relates to the evolution of massive stars, astronomers needed additional examples. Catching rare stars during the short-lived aftermath of a major outburst approaches needle-and-haystack levels of difficulty, and nothing matching Eta Carinae had been found prior to Khan's study. 

"We knew others were out there," said co-investigator Krzysztof Stanek, a professor of astronomy at Ohio State University in Columbus. "It was really a matter of figuring out what to look for and of being persistent."

Working with Scott Adams and Christopher Kochanek at Ohio State and George Sonneborn at Goddard, Khan developed a kind of optical and infrared fingerprint for identifying possible Eta Carinae twins, or "Eta twins" for short.

Dust forms in gas ejected by a massive star. This dust dims the star’s ultraviolet and visible light, but it absorbs and reradiates this energy as heat at longer mid-infrared wavelengths. "With Spitzer we see a steady increase in brightness starting at around 3 microns and peaking between 8 and 24 microns," explained Khan. "By comparing this emission to the dimming we see in Hubble's optical images, we could determine how much dust was present and compare it to the amount we see around Eta Carinae."


Image above: The nearby spiral galaxy M83 is currently the only one known to host two potential Eta Carinae twins. This composite of images from the Hubble Space Telescope's Wide Field Camera 3 instrument shows a galaxy ablaze with newly formed stars. A high rate of star formation increases the chances of finding massive stars that have recently undergone an Eta Carinae-like outburst. Bottom: Insets zoom into Hubble data to show the locations of M83's Eta twins. Image Credits: NASA, ESA, the Hubble Heritage Team (STScI/AURA) and R. Khan (GSFC and ORAU).

An initial survey of seven galaxies from 2012 to 2014 didn't turn up any Eta twins, underscoring their rarity. It did, however, identify a class of less massive and less luminous stars of scientific interest, demonstrating the search was sensitive enough to find Eta Carinae-like stars had they been present.

In a follow-on survey in 2015, the team found two candidate Eta twins in the galaxy M83, located 15 million light-years away, and one each in NGC 6946, M101 and M51, located between 18 and 26 million light-years away. These five objects mimic the optical and infrared properties of Eta Carinae, indicating that each very likely contains a high mass star buried in five to 10 solar masses of gas and dust. Further study will let astronomers more precisely determine their physical properties. The findings were published in the Dec. 20 edition of The Astrophysical Journal Letters.


Images above: Researchers found likely Eta twins in four galaxies by comparing the infrared and optical brightness of each candidate source. Infrared images from NASA's Spitzer Space Telescope revealed the presence of warm dust surrounding the stars. Comparing this information with the brightness of each source at optical and near-infrared wavelengths as measured by instruments on Hubble, the team was able to identify candidate Eta Carinae-like objects. Top: 3.6-micron images of candidate Eta twins from Spitzer's IRAC instrument. Bottom: 800-nanometer images of the same sources from various Hubble instruments. Image Credits: NASA, ESA, and R. Khan (GSFC and ORAU).

NASA's James Webb Space Telescope, set to launch in late 2018, carries an instrument ideally suited for further study of these stars. The Mid-Infrared Instrument (MIRI) has 10 times the angular resolution of instruments aboard Spitzer and is most sensitive at the wavelengths where Eta twins shine brightest. "Combined with Webb's larger primary mirror, MIRI will enable astronomers to better study these rare stellar laboratories and to find additional sources in this fascinating phase of stellar evolution," said Sonneborn, NASA's project scientist for Webb telescope operations. It will take Webb observations to confirm the Eta twins as true relatives of Eta Carinae.

The Spitzer Space Telescope is managed by NASA's Jet Propulsion Laboratory in Pasadena, California. The Spitzer Science Center at the California Institute of Technology in Pasadena conducts science operations.

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

For more information about Spitzer, visit: http://www.nasa.gov/spitzer

For more information about Hubble, visit: http://www.nasa.gov/hubble

ESA's Hubble website: http://www.spacetelescope.org/

Images (mentioned), Text, Credits: NASA's Goddard Space Flight Center/Francis Reddy/Ashley Morrow.

Greetings, Orbiter.ch

mardi 5 janvier 2016

Runaway Stars Leave Infrared Waves in Space














NASA - Spitzer Space Telescope logo / NASA - WISE Mission patch.

Jan. 5, 2016

Astronomers are finding dozens of the fastest stars in our galaxy with the help of images from NASA's Spitzer Space Telescope and Wide-field Infrared Survey Explorer, or WISE.

When some speedy, massive stars plow through space, they can cause material to stack up in front of them in the same way that water piles up ahead of a ship. Called bow shocks, these dramatic, arc-shaped features in space are leading researchers to uncover massive, so-called runaway stars.


Images above: Bow shocks thought to mark the paths of massive, speeding stars are highlighted in these images from NASA's Spitzer Space Telescope and Wide-field Infrared Survey Explorer, or WISE. Images Credits: NASA/JPL-Caltech/University of Wyoming.

"Some stars get the boot when their companion star explodes in a supernova, and others can get kicked out of crowded star clusters," said astronomer William Chick from the University of Wyoming in Laramie, who presented his team's new results at the American Astronomical Society meeting in Kissimmee, Florida. "The gravitational boost increases a star's speed relative to other stars."

Our own sun is strolling through our Milky Way galaxy at a moderate pace. It is not clear whether our sun creates a bow shock. By comparison, a massive star with a stunning bow shock, called Zeta Ophiuchi (or Zeta Oph), is traveling around the galaxy faster than our sun, at 54,000 mph (24 kilometers per second) relative to its surroundings. Zeta Oph's giant bow shock can be seen in this image from the WISE mission:

http://www.nasa.gov/mission_pages/WISE/multimedia/gallery/pia13455.html

Both the speed of stars moving through space and their mass contribute to the size and shapes of bow shocks. The more massive a star, the more material it sheds in high-speed winds. Zeta Oph, which is about 20 times as massive as our sun, has supersonic winds that slam into the material in front of it.

The result is a pile-up of material that glows. The arc-shaped material heats up and shines with infrared light. That infrared light is assigned the color red in the many pictures of bow shocks captured by Spitzer and WISE.

Chick and his team turned to archival infrared data from Spitzer and WISE to identify new bow shocks, including more distant ones that are harder to find. Their initial search turned up more than 200 images of fuzzy red arcs. They then used the Wyoming Infrared Observatory, near Laramie, to follow up on 80 of these candidates and identify the sources behind the suspected bow shocks. Most turned out to be massive stars.

Spitzer Space Telescope. Image Credit: NASA

The findings suggest that many of the bow shocks are the result of speedy runaways that were given a gravitational kick by other stars. However, in a few cases, the arc-shaped features could turn out to be something else, such as dust from stars and birth clouds of newborn stars. The team plans more observations to confirm the presence of bow shocks.

"We are using the bow shocks to find massive and/or runaway stars," said astronomer Henry "Chip" Kobulnicky, also from the University of Wyoming. "The bow shocks are new laboratories for studying massive stars and answering questions about the fate and evolution of these stars."

Another group of researchers, led by Cintia Peri of the Argentine Institute of Radio Astronomy, is also using Spitzer and WISE data to find new bow shocks in space. Only instead of searching for the arcs at the onset, they start by hunting down known speedy stars, and then they scan them for bow shocks.

Wide-field Infrared Survey Explorer, or WISE. Image Credit: NASA

"WISE and Spitzer have given us the best images of bow shocks so far," said Peri. "In many cases, bow shocks that looked very diffuse before, can now be resolved, and, moreover, we can see some new details of the structures."

Some of the first bow shocks from runaway stars were identified in the 1980s by David Van Buren of NASA's Jet Propulsion Laboratory in Pasadena, California. He and his colleagues found them using infrared data from the Infrared Astronomical Satellite (IRAS), a predecessor to WISE that scanned the whole infrared sky in 1983.

Kobulnicky and Chick belong to a larger team of researchers and students studying bow shocks and massive stars, including Matt Povich from the California State Polytechnic University, Pomona. The National Science Foundation funds their research.

Images from Spitzer, WISE and IRAS are archived at the NASA Infrared Science Archive housed at the Infrared Processing and Analysis Center at the California Institute of Technology in Pasadena. Caltech manages JPL for NASA.

More information about Spitzer is online at:

http://www.nasa.gov/spitzer

http://spitzer.caltech.edu

More information about WISE is at:

http://www.nasa.gov/wise

Images (mentioned), Text, Credits: NASA/Martin Perez/JPL/Whitney Clavin.

Best regards, Orbiter.ch

Chandra Finds Supermassive Black Hole Burping Nearby












NASA - Chandra X-ray Observatory patch.

Jan. 5, 2016

Evidence for powerful blasts produced by a giant black hole has been discovered using NASA’s Chandra X-ray Observatory. This is one of the nearest supermassive black holes to Earth that is currently undergoing such violent outbursts.

Astronomers found this outburst in the supermassive black hole centered in the small galaxy NGC 5195. This companion galaxy is merging with a large spiral galaxy NGC 5194, also known as “The Whirlpool.” Both of these galaxies are in the Messier 51 galaxy system, located about 26 million light years from Earth.


Image above: Galaxy NGC 5195. Image Credits: X-ray: NASA/CXC/Univ of Texas/E.Schlegel et al; Optical: NASA/STScI.

“For an analogy, astronomers often refer to black holes as 'eating' stars and gas.  Apparently, black holes can also burp after their meal,” said Eric Schlegel of The University of Texas in San Antonio, who led the study. “Our observation is important because this behavior would likely happen very often in the early universe, altering the evolution of galaxies. It is common for big black holes to expel gas outward, but rare to have such a close, resolved view of these events.”

In the Chandra data, Schlegel and his colleagues detect two arcs of X-ray emission close to the center of NGC 5195.

“We think these arcs represent fossils from two enormous blasts when the black hole expelled material outward into the galaxy,” said co-author Christine Jones of the Harvard-Smithsonian Center for Astrophysics (CfA) in Cambridge, Mass. “This activity is likely to have had a big effect on the galactic landscape.”

Just outside the outer X-ray arc, the researchers detected a slender region of emission of relatively cool hydrogen gas in an optical image from the Kitt Peak National Observatory 0.9-meter telescope. This suggests that the hotter, X-ray emitting gas has “snow-plowed,” or swept up, the hydrogen gas from the center of the galaxy. This is a clear case where a supermassive black hole is affecting its host galaxy in a phenomenon that astronomers call “feedback.”

In NGC 5195, the properties of the gas around the X-ray-glowing arcs suggest that the outer arc has plowed up enough material to trigger the formation of new stars.

“We think that feedback keeps galaxies from becoming too large,” said co-author Marie Machacek of CfA. “But at the same time, it can be responsible for how some stars form. This shows that black holes can create, not just destroy.”

The astronomers think the outbursts of the supermassive black hole in NGC 5195 may have been triggered by the interaction of this smaller galaxy with its large spiral companion, causing gas to be funneled in towards the black hole. The energy generated by this infalling matter would produce the outbursts. The team estimates that it took about one to three million years for the inner arc to reach its current position, and three to six million years for the outer arc.

Artist's view of Chandra X-ray Observatory. Image Credits: NASA/CXC

The arcs are also significant because of their location in the galaxy. They are well outside the region where rapid outflow, or winds, have been detected from active supermassive black holes in other galaxies, yet inside the much larger cavities and filaments observed in the hot gas around many massive galaxies.  As such they may represent a rare view an intermediate stage in the feedback process operating between the interstellar gas and the black hole.

These results were presented in January 2016 at the 227th meeting of the American Astronomical Society meeting in Kissimmee, FL, and have been submitted in a paper to The Astrophysical Journal. Laura Vega, of the Fisk University and Vanderbilt University Bridge Program, in Nashville, Tennessee was also a co-author of the paper. NASA's Marshall Space Flight Center in Huntsville, Alabama, manages the Chandra program for NASA's Science Mission Directorate in Washington. The Smithsonian Astrophysical Observatory in Cambridge, Massachusetts, controls Chandra's science and flight operations.

Read More from NASA's Chandra X-ray Observatory: http://chandra.harvard.edu/photo/2016/ngc5195/

For more Chandra images, multimedia and related materials, visit: http://www.nasa.gov/chandra

Images (mentioned), Text, Credits: NASA/Lee Mohon/Marshall Space Flight Center/Molly Porter.

Best regards, Orbiter.ch

Andromeda in High-Energy X-rays








NASA - NuSTAR Mission patch.

Jan. 5, 2016


Image above: NASA's Nuclear Spectroscope Telescope Array, or NuSTAR, has imaged a swath of the Andromeda galaxy -- the nearest large galaxy to our own Milky Way galaxy. Image Credits: NASA/JPL-Caltech/GSFC.

NASA's Nuclear Spectroscopic Telescope Array, or NuSTAR, has captured the best high-energy X-ray view yet of a portion of our nearest large, neighboring galaxy, Andromeda. The space mission has observed 40 "X-ray binaries" -- intense sources of X-rays comprised of a black hole or neutron star that feeds off a stellar companion.

The results will ultimately help researchers better understand the role of X-ray binaries in the evolution of our universe. According to astronomers, these energetic objects may play a critical role in heating the intergalactic bath of gas in which the very first galaxies formed.

"Andromeda is the only large spiral galaxy where we can see individual X-ray binaries and study them in detail in an environment like our own," said Daniel Wik of NASA Goddard Space Flight Center in Greenbelt, Maryland, who presented the results at the 227th meeting of American Astronomical Society in Kissimmee, Florida.­­­­ "We can then use this information to deduce what's going on in more distant galaxies, which are harder to see."

Andromeda, also known as M31, can be thought of as the big sister to our own Milky Way galaxy. Both galaxies are spiral in shape, but Andromeda is slightly larger than the Milky Way in size. Lying 2.5 million light-years away, Andromeda is relatively nearby in cosmic terms. It can even be seen by the naked eye in dark, clear skies.

Other space missions, such as NASA's Chandra X-ray Observatory, have obtained crisper images of Andromeda at lower X-ray energies than the high-energy X-rays detected by NuSTAR. The combination of Chandra and NuSTAR provides astronomers with a powerful tool for narrowing in on the nature of the X-ray binaries in spiral galaxies. 

In X-ray binaries, one member is always a dead star or remnant formed from the explosion of what was once a star much more massive than the sun. Depending on the mass and other properties of the original giant star, the explosion may produce either a black hole or neutron star. Under the right circumstances, material from the companion star can "spill over" its outermost edges and then be caught by the gravity of the black hole or neutron star. As the material falls in, it is heated to blazingly high temperatures, releasing a huge amount of X-rays.

With NuSTAR's new view of a swath of Andromeda, Wik and colleagues are working on identifying the fraction of X-ray binaries harboring black holes versus neutron stars. That research will help them understand the population as a whole.

"We have come to realize in the past few years that it is likely the lower-mass remnants of normal stellar evolution, the black holes and neutron stars, may play a crucial role in heating of the intergalactic gas at very early times in the universe, around the cosmic dawn," said Ann Hornschemeier of NASA Goddard, the principal investigator of the NuSTAR Andromeda studies.

"Observations of local populations of stellar-mass-sized black holes and neutron stars with NuSTAR allow us to figure out just how much power is coming out from these systems."

NASA's Nuclear Spectroscopic Telescope Array, or NuSTAR. Image Credits: NASA/GFSC

The new research also reveals how Andromeda may differ from our Milky Way. Fiona Harrison, the principal investigator of the NuSTAR mission, added, "Studying the extreme stellar populations in Andromeda tells us about how its history of forming stars may be different than in our neighborhood."

Harrison will be presenting the 2015 Rossi Prize lecture at the AAS meeting. The prize, awarded by the AAS's High-Energy Astrophysics Division, honors physicist Bruno Rossi, an authority on cosmic-ray physics and a pioneer in the field of X-ray astronomy.

Related links:

Harrison will be presenting the 2015 Rossi Prize lecture: http://www.jpl.nasa.gov/news/news.php?feature=4447

AAS's High-Energy Astrophysics Division: http://head.aas.org/

For more information, visit http://www.nasa.gov/nustar and http://www.nustar.caltech.edu/

Images (mentioned), Text, Credits: NASA/Martin Perez/JPL/Whitney Clavin.

Greetings, Orbiter.ch

Tim Peake set for spacewalk












ESA - Principia Mission patch.

5 January 2016

December spacewalk

ESA astronaut Tim Peake and NASA astronaut Tim Kopra will exit the International Space Station next week to repair a power unit on the outside.

The two Tims arrived at the Space Station on 15 December but this will be their second involvement in a spacewalk: Tim Peake assisted Tim Kopra and Station commander Scott Kelly when they moved an equipment carrier on 21 December.

Tim Peake training at JSC

The new spacewalk will last around six hours on 15 January, with Tim Kopra and Tim Peake working closely together to replace a faulty unit.

The ESA astronaut explains: “Our primary task will be to replace a failed Solar Shunt Unit, which transfers electrical power generated by the solar panels.”

The unit is relatively easy to replace because it is a simple box that can be removed by undoing one bolt. Once done, the spacewalkers will lay cables in advance of new docking ports and reinstall a valve that was removed for the relocation of the Leonardo module last year.

Preparing for spacewalk

Inside the Station, Scott Kelly will help the spacewalkers into and out of their suits – a major operation in itself.

Before the astronauts leave they will breathe pure oxygen for two hours to purge their bodies of nitrogen. The spacesuit pressure is lower than in the Space Station and the drop could give them the ‘bends’, much like scuba divers rising too quickly to the sea surface.

Donning their spacesuits and safety equipment will take hours before they enter the airlock to reduce the pressure until it is safe to open the exterior hatch.

Tim Peake comments, “I am thrilled at this opportunity for a spacewalk. Right now we are focusing on preparing the tools, equipment and procedures. 

Quest airlock

“Maintaining the International Space Station from the outside requires intense operations - not just from the crew, but also from our ground support teams who are striving to make this spacewalk as safe and efficient as possible.”

The Station has eight shunt units to regulate power but has been operating with only seven since last November.

Tim concludes, “If the spacewalk is successful, this will restore the International Space Station to 100% of its operational capability.”

More information and live updates can be found on Tim Peake’s Principia blog: http://blogs.esa.int/tim-peake/

Related article:

Space Station Module Relocation Makes Way for Commercial Crew Spacecraft:
http://orbiterchspacenews.blogspot.ch/2015/05/space-station-module-relocation-makes.html

Related links:

Principia mission: http://www.esa.int/Our_Activities/Human_Spaceflight/Principia

Connect with Tim Peake: http://timpeake.esa.int/

Principia in UK: https://principia.org.uk/

Images, Text, Credits: ESA/NASA/Bill Stafford.

Greetings, Orbiter.ch

lundi 4 janvier 2016

Rover Rounds Martian Dune to Get to the Other Side












NASA - Mars Science Laboratory (MSL) patch.

Jan. 4, 2016


Image above: This Dec. 18, 2015, view of the downwind face of "Namib Dune" on Mars covers 360 degrees, including a portion of Mount Sharp on the horizon. Image Credits: NASA/JPL-Caltech/MSSS.

NASA's Curiosity Mars rover, partway through the first up-close study ever conducted of  extraterrestrial sand dunes, is providing dramatic views of a dune's steep face, where cascading sand has sculpted very different textures than the wavy ripples visible on the dune's windward slope.

Panoramic scenes dominated by the steep face of a dune called "Namib Dune" are online at these sites:

http://www.jpl.nasa.gov/spaceimages/details.php?id=PIA20284

http://www.jpl.nasa.gov/spaceimages/details.php?id=PIA20281

Researchers are using Curiosity to examine examples of the Bagnold Dunes, a band of dark sand dunes lining the northwestern flank of Mt. Sharp, the layered mountain the rover is climbing. A characteristic that sets true dunes apart from other wind-shaped bodies of sand, such as drifts and ripples previously visited by Mars rovers, is a steep, downwind slope known as the slip face. Here, sand blowing across the windward side of the dune suddenly becomes sheltered from the wind by the dune itself. The sand falls out of the air and builds up on the slope until it becomes steepened and flows in mini-avalanches down the face.


Image above: This view from NASA's Curiosity Mars Rover shows the downwind side of a dune about 13 feet high within the Bagnold Dunes field on Mars. The rover's Navigation Camera took the component images on Dec. 17, 2015. Image Credits: NASA/JPL-Caltech.

The mission's dune-investigation campaign is designed to increase understanding about how wind moves and sorts grains of sand, in an environment with less gravity and much less atmosphere than well-studied dune fields on Earth. The Bagnold Dunes are active. Sequential images taken from orbit over the course of multiple years show that some of these dunes are migrating by as much as a yard, or meter, per Earth year.


Image above: This Dec. 17, 2015, view combines multiple images from the telephoto-lens camera of the Mast Camera (Mastcam) on NASA's Curiosity Mars rover to reveal fine details of the downwind face of "Namib Dune." Image Credits: NASA/JPL-Caltech/MSSS.

Curiosity has not caught a sand slide in action, but the rover's images of the Namib Dune slip face show where such slides have occurred recently. These dunes likely are most active in Mars' southern summer, rather than in the current late-fall season.


Image above: This Dec. 17, 2015, view combines multiple images from the telephoto-lens camera of the Mast Camera (Mastcam) on NASA's Curiosity Mars rover to reveal fine details of the downwind face of "Namib Dune." Sand on this face of the dark dune has cascaded down a slope of about 26 to 28 degrees. Image Credits: NASA/JPL-Caltech/MSSS.

A few days of rover operations were affected in December due to an arm-motion fault, diagnosed as a minor software issue. Normal use of the arm resumed Dec. 23.

Curiosity has been working on Mars since early August 2012. It reached the base of Mount Sharp in 2014 after fruitfully investigating outcrops closer to its landing site and then trekking to the mountain. The main mission objective now is to examine successively higher layers of Mount Sharp.

For more information about Curiosity, visit: http://mars.jpl.nasa.gov/msl

Images (mentioned), Text, Credits: NASA/Dwayne Brown/Laurie Cantillo/JPL/Guy Webster/Martin Perez.

Happy New Year! Best regards, Orbiter.ch

New Year Begins With Eye to Next Spacewalk











ISS - Expedition 46 Mission patch.

January 4, 2016

The Expedition 46 crew begins its first full week of the New Year planning for a spacewalk scheduled for Jan. 15. The orbiting residents are also busy with numerous science experiments benefitting life on Earth and future astronauts.


Image above: Tropical Cyclone Ula, a category 3 storm at the time this image was captured, is seen from the International Space Station. Image Credit: NASA TV.

A pair of spacewalkers will replace a failed voltage regulator to return power to one of eight power channels next Friday. Two crew members will exit the Quest airlock and work outside for 6.5 hours for the replacement work. They will also rig cables for the future installation of docking adapters that will enable commercial crew vehicles to dock at the International Space Station. Final spacewalking roles will be confirmed following spacesuit hardware checkouts taking place today.


Image above: NASA astronaut Tim Kopra is seen floating during a spacewalk on Dec. 21, 2015. Image Credit: NASA TV.

NASA astronauts Tim Kopra and Commander Scott Kelly collected and stowed blood and urine samples this morning for the Fluid Shifts study. That experiment observes the headward fluid shift caused by microgravity that increases brain pressure and pushes back on the eye. British astronaut Tim Peake also explored particles suspended in fluids, or colloids, which could benefit the design of advanced materials on Earth.

Related links:

Fluid Shifts study: http://www.nasa.gov/mission_pages/station/research/experiments/1257.html

One-Year Crew: https://www.nasa.gov/content/one-year-crew/

Expedition 46: https://blogs.nasa.gov/spacestation/category/expedition-46/

Stay up-to-date on the latest ISS news at: http://www.nasa.gov/station

Images (mentioned), Text, Credits: NASA/Mark Garcia.

Happy New Year! Greetings, Orbiter.ch

Triple Play













NASA - Cassini Mission to Saturn patch.

Jan. 4, 2016


What looks like a pair of Saturnian satellites is actually a trio upon close inspection.

Here, Cassini has captured Enceladus (313 miles or 504 kilometers across) above the rings and Rhea (949 miles or 1,527 kilometers across) below.  The comparatively tiny speck of Atlas (19 miles or 30 kilometers across) can also be seen just above and to the left of Rhea, and just above the thin line of Saturn's F ring.

This view looks toward the unilluminated side of the rings from about 0.34 degrees below the ring plane.

The image was taken in visible light with the Cassini spacecraft narrow-angle camera on Sept. 24, 2015.

The view was obtained at a distance of approximately 1.8 million miles (2.8 million kilometers) from Rhea. Image scale on Rhea is 10 miles (16 kilometers) per pixel. The distance to Enceladus was 1.3 million miles (2.1 million kilometers) for a scale of 5 miles (8 kilometers) per pixel. The distance to Atlas was 1.5 million miles (2.4 million) kilometers) for an image scale at Atlas of 9 miles (14 kilometers) per pixel.

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

For more information about the Cassini-Huygens mission visit http://saturn.jpl.nasa.gov or http://www.nasa.gov/cassini . The Cassini imaging team homepage is at http://ciclops.org and ESA's website: http://www.esa.int/Our_Activities/Space_Science/Cassini-Huygens

Image, Text, Credits: NASA/JPL/Martin Perez.

Happy New Year! Greetings, Orbiter.ch