samedi 18 avril 2015

Rosetta new image of Comet 67P/Churyumov-Gerasimenko

ESA - Rosetta Mission patch.

April 18, 2015

Single frame NAVCAM image obtained on 15 April, from a distance of 170 km from the centre of Comet 67P/Churyumov-Gerasimenko. At this distance, the resolution is 14.5 m/pixel; the image has been cropped to 11.4 km (the original frame, provided at the end of the post, measures 14.8 km across).

Comet on 15 April 2015 – NavCam

Image above: Cropped and processed single frame NAVCAM image of Comet 67P/C-G taken on 15 April 2015 from a distance of 170 km to the comet centre. Credits: ESA/Rosetta/NAVCAM – CC BY-SA IGO 3.0.

Image above shows 67P/C-G from an unusual angle, revealing some regions on the comet nucleus that in previously published images were partly cast in shadow.

In this orientation, the small comet lobe is on the left, and the large one on the right. The image has been processed to bring out the comet’s activity, showing majestic jets of material emanating from 67P/C-G. Parts of both lobes are visible, in the lower half of the image, as dark silhouettes against the diffuse glow that envelops the nucleus.

Image above: The original 1024 x 1024 image. Cropped and processed single frame NAVCAM image of Comet 67P/C-G taken on 15 April 2015 from a distance of 170 km to the comet centre. Credits: ESA/Rosetta/NAVCAM – CC BY-SA IGO 3.0.

The large circular depression on the small lobe is Hatmehit and, to its right, parts of the Bastet region are visible. The large lobe provides an interesting view on the Aker region (the bright-looking portion pointing upwards in this orientation) and on the rough terrains of Khepry (to the right).

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Images (mentioned), Text, Credit: European Space Agency (ESA).


vendredi 17 avril 2015

White Dwarf May Have Shredded Passing Planet

NASA - Chandra X-ray Observatory patch.

April 16, 2015

The destruction of a planet may sound like the stuff of science fiction, but a team of astronomers has found evidence that this may have happened in an ancient cluster of stars at the edge of the Milky Way galaxy.

Using several telescopes, including NASA’s Chandra X-ray Observatory, researchers have found evidence that a white dwarf star – the dense core of a star like the Sun that has run out of nuclear fuel – may have ripped apart a planet as it came too close.

Image above: In this Chandra image of ngc6388, researchers have found evidence that a white dwarf star may have ripped apart a planet as it came too close. When a star reaches its white dwarf stage, nearly all of the material from the star is packed inside a radius one hundredth that of the original star. Image Credit: NASA/CXC/IASF Palermo/M.Del Santo et al; NASA/STScI.

How could a white dwarf star, which is only about the size of the Earth, be responsible for such an extreme act? The answer is gravity. When a star reaches its white dwarf stage, nearly all of the material from the star is packed inside a radius one hundredth that of the original star. This means that, for close encounters, the gravitational pull of the star and the associated tides, caused by the difference in gravity’s pull on the near and far side of the planet, are greatly enhanced. For example, the gravity at the surface of a white dwarf is over ten thousand times higher than the gravity at the surface of the Sun.

Researchers used the European Space Agency's INTErnational Gamma-Ray Astrophysics Laboratory (INTEGRAL) to discover a new X-ray source near the center of the globular cluster NGC 6388. Optical observations had hinted that an intermediate-mass black hole with mass equal to several hundred Suns or more resides at the center of NGC 6388. The X-ray detection by INTEGRAL then raised the intriguing possibility that the X-rays were produced by hot gas swirling towards an intermediate-mass black hole.

Image above: X-ray image of NGC 6388. Image Credits: NASA/CXC/IASF Palermo/M.Del Santo et al.

In a follow-up X-ray observation, Chandra’s excellent X-ray vision enabled the astronomers to determine that the X-rays from NGC 6388 were not coming from the putative black hole at the center of the cluster, but instead from a location slightly off to one side. A new composite image shows NGC 6388 with X-rays detected by Chandra in pink and visible light from the Hubble Space Telescope in red, green, and blue, with many of the stars appearing to be orange or white. Overlapping X-ray sources and stars near the center of the cluster also causes the image to appear white.

With the central black hole ruled out as the potential X-ray source, the hunt continued for clues about the  actual source in NGC 6388. The source was monitored with the X-ray telescope on board NASA's Swift Gamma Ray Burst mission for about 200 days after the discovery by INTEGRAL.

The source became dimmer during the period of Swift observations. The rate at which the X-ray brightness dropped agrees with theoretical models of a disruption of a planet by the gravitational tidal forces of a white dwarf. In these models, a planet is first pulled away from its parent star by the gravity of the dense concentration of stars in a globular cluster. When such a planet passes too close to a white dwarf, it can be torn apart by the intense tidal forces of the white dwarf. The planetary debris is then heated and glows in X-rays as it falls onto the white dwarf. The observed amount of X-rays emitted at different energies agrees with expectations for a tidal disruption event.

Image above: Optical image of NGC 6388. Image Credits: NASA/STScI.

The researchers estimate that the destroyed planet would have contained about a third of the mass of Earth, while the white dwarf has about 1.4 times the Sun’s mass.

While the case for the tidal disruption of a planet is not iron-clad, the argument for it was strengthened when astronomers used data from the multiple telescopes to help eliminate other possible explanations for the detected X-rays. For example, the source does not show some of the distinctive features of a binary containing a neutron star, such as pulsations or rapid X-ray bursts. Also, the source is much too faint in radio waves to be part of a binary system with a stellar-mass black hole.

A paper describing these results was published in an October 2014 issue of the Monthly Notices of the Royal Astronomical Society. The first author is Melania Del Santo of the National Institute for Astrophysics (INAF), IASF-Palermo, Italy, and the co-authors are Achille Nucita of the Universitá del Salento in Lecce, Italy; Giuseppe Lodato of the Universitá Degli Studi di Milano in Milan, Italy; Luigi Manni and Francesco De Paolis of the Universitá del Salento in Lecce, Italy; Jay Farihi of University College London in London, UK; Giovanni De Cesare of the National Institute for Astrophysics in IAPS-Rome, Italy and Alberto Segreto of the National Institute for Astrophysics (INAF), IASF-Palermo, Italy.

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.

For more information about Chandra X-ray Observatory, visit:

Images (mentioned), Text, Credits: NASA/Chandra X-ray Center/Megan Watzke/Marshall Space Flight Center/Janet Anderson.


Dragon is Berthed to the International Space Station

SpaceX - Falcon 9/Dragon CRS-6 Mission patch.

April 17, 2015

Image above: The SpaceX Dragon space freighter is in the grips of the Canadarm2 robotic arm. Credit: NASA TV.

While the International Space Station was traveling 257 statue miles over the Pacific Ocean just east of Japan, Expedition 43 Flight Engineer Samantha Cristoforetti of the European Space Agency, with the assistance of Expedition 43 Commander Terry Virts of NASA, successfully captured the SpaceX Dragon spacecraft with the station’s robotic arm at 6:55 a.m. EDT.

Dragon arrival at the Space Station and Robotic Arm Capture

Video above: SpaceX Dragon Commercial Cargo Ship Arrives at the International Space Station. Video Credit: NASA TV.

The SpaceX Dragon cargo spacecraft was berthed to the Harmony module of the International Space Station at 9:29 a.m. EDT. The hatch between the newly arrived spacecraft and the Harmony module of the space station is scheduled to be opened Saturday.

The spacecraft is loaded with more than 4,300 pounds of supplies, science experiments, and technology demonstrations, including critical materials to support about 40 of more than 250 science and research investigations during the station's Expeditions 43 and 44.

For more information about the International Space Station (ISS), visit:

For more information about SpaceX and Falcon 9 reusable rocket, visit:

Image (mentioned), Video (mentioned), Text, Credit: NASA.


ALMA Reveals Intense Magnetic Field Close to Supermassive Black Hole

ALMA - Atacama Large Millimeter/submillimeter Array logo.

17 April 2015

Illuminating the mysterious mechanisms at play at the edge of the event horizon

The Atacama Large Millimeter/submillimeter Array (ALMA) has revealed an extremely powerful magnetic field, beyond anything previously detected in the core of a galaxy, very close to the event horizon of a supermassive black hole. This new observation helps astronomers to understand the structure and formation of these massive inhabitants of the centres of galaxies, and the twin high-speed jets of plasma they frequently eject from their poles. The results appear in the 17 April 2015 issue of the journal Science.

Artist’s impression of a supermassive black hole at the centre of a galaxy

Supermassive black holes, often with masses billions of times that of the Sun, are located at the heart of almost all galaxies in the Universe. These black holes can accrete huge amounts of matter in the form of a surrounding disc. While most of this matter is fed into the black hole, some can escape moments before capture and be flung out into space at close to the speed of light as part of a jet of plasma. How this happens is not well understood, although it is thought that strong magnetic fields, acting very close to the event horizon, play a crucial part in this process, helping the matter to escape from the gaping jaws of darkness.

Up to now only weak magnetic fields far from black holes — several light-years away — had been probed [1]. In this study, however, astronomers from Chalmers University of Technology and Onsala Space Observatory in Sweden have now used ALMA to detect signals directly related to a strong magnetic field very close to the event horizon of the supermassive black hole in a distant galaxy named PKS 1830-211. This magnetic field is located precisely at the place where matter is suddenly boosted away from the black hole in the form of a jet.

The team measured the strength of the magnetic field by studying the way in which light was polarised, as it moved away from the black hole.

“Polarisation is an important property of light and is much used in daily life, for example in sun glasses or 3D glasses at the cinema,” says Ivan Marti-Vidal, lead author of this work. “When produced naturally, polarisation can be used to measure magnetic fields, since light changes its polarisation when it travels through a magnetised medium. In this case, the light that we detected with ALMA had been travelling through material very close to the black hole, a place full of highly magnetised plasma.”

Artist’s impression of a supermassive black hole at the centre of a galaxy

The astronomers applied a new analysis technique that they had developed to the ALMA data and found that the direction of polarisation of the radiation coming from the centre of PKS 1830-211 had rotated [2]. These are the shortest wavelengths ever used in this kind of study, which allow the regions very close to the central black hole to be probed [3].

"We have found clear signals of polarisation rotation that are hundreds of times higher than the highest ever found in the Universe," says Sebastien Muller, co-author of the paper. "Our discovery is a giant leap in terms of observing frequency, thanks to the use of ALMA, and in terms of distance to the black hole where the magnetic field has been probed — of the order of only a few light-days from the event horizon. These results, and future studies, will help us understand what is really going on in the immediate vicinity of supermassive black holes.”


[1] Much weaker magnetic fields have been detected in the vicinity of the relatively inactive supermassive black hole at the centre of the Milky Way. Recent observations have also revealed weak magnetic fields in the active galaxy NGC 1275, which were detected at millimetre wavelengths.

[2] Magnetic fields introduce Faraday rotation, which makes the polarisation rotate in different ways at different wavelengths. The way in which this rotation depends on the wavelength tells us about the magnetic field in the region.

[3] The ALMA observations were at an effective wavelength of about 0.3 millimetres, earlier investigations were at much longer radio wavelengths. Only light of millimetre wavelengths can escape from the region very close to the black hole, longer wavelength radiation is absorbed.

More information:

This research was presented in a paper entitled “A strong magnetic field in the jet base of a supermassive black hole” to appear in Science on 17 April 2015

The team is composed of I. Martí-Vidal (Onsala Space Observatory and Department of Earth and Space Sciences, Chalmers University of Technology, Sweden), S. Muller (Onsala Space Observatory and Department of Earth and Space Sciences, Chalmers University of Technology, Sweden), W. Vlemmings (Department of Earth and Space Sciences and Onsala Space Observatory, Chalmers University of Technology, Sweden), C. Horellou (Department of Earth and Space Sciences, Chalmers University of Technology, Sweden) and S. Aalto (Department of Earth and Space Sciences, Chalmers University of Technology, Sweden).

The Atacama Large Millimeter/submillimeter Array (ALMA), an international astronomy facility, is a partnership of ESO, the US National Science Foundation (NSF) and the National Institutes of Natural Sciences (NINS) of Japan in cooperation with the Republic of Chile. ALMA is funded by ESO on behalf of its Member States, by NSF in cooperation with the National Research Council of Canada (NRC) and the National Science Council of Taiwan (NSC) and by NINS in cooperation with the Academia Sinica (AS) in Taiwan and the Korea Astronomy and Space Science Institute (KASI).

ALMA construction and operations are led by ESO on behalf of its Member States; by the National Radio Astronomy Observatory (NRAO), managed by Associated Universities, Inc. (AUI), on behalf of North America; and by the National Astronomical Observatory of Japan (NAOJ) on behalf of East Asia. The Joint ALMA Observatory (JAO) provides the unified leadership and management of the construction, commissioning and operation of ALMA.

ESO is the foremost intergovernmental astronomy organisation in Europe and the world’s most productive ground-based astronomical observatory by far. It is supported by 16 countries: Austria, Belgium, Brazil, the Czech Republic, Denmark, France, Finland, Germany, Italy, the Netherlands, Poland, Portugal, Spain, Sweden, Switzerland and the United Kingdom, along with the host state of Chile. ESO carries out an ambitious programme focused on the design, construction and operation of powerful ground-based observing facilities enabling astronomers to make important scientific discoveries. ESO also plays a leading role in promoting and organising cooperation in astronomical research. ESO operates three unique world-class observing sites in Chile: La Silla, Paranal and Chajnantor. At Paranal, ESO operates the Very Large Telescope, the world’s most advanced visible-light astronomical observatory and two survey telescopes. VISTA works in the infrared and is the world’s largest survey telescope and the VLT Survey Telescope is the largest telescope designed to exclusively survey the skies in visible light. ESO is a major partner in ALMA, the largest astronomical project in existence. And on Cerro Armazones, close to Paranal, ESO is building the 39-metre European Extremely Large Telescope, the E-ELT, which will become “the world’s biggest eye on the sky”.


Photos of ALMA:

The Atacama Large Millimeter/submillimeter Array (ALMA):

Image, Video, Text, Credits: ESO/L. Calçada.

Best regards,

NASA, USGS Begin Work on Landsat 9 to Continue Land Imaging Legacy

NASA / USGS - Landsat LDCM logo.

April 17, 2015

NASA and the U.S. Geological Survey (USGS) have started work on Landsat 9, planned to launch in 2023, which will extend the Earth-observing program’s record of land images to half a century.

The Landsat program has provided accurate measurements of Earth’s land cover since 1972. With data from Landsat satellites, ecologists have tracked deforestation in South America, water managers have monitored irrigation of farmland in the American West, and researchers have watched the growth of cities worldwide. With the help of the program’s open archive, firefighters have assessed the severity of wildfires and scientists have mapped the retreat of mountain glaciers.

Image above: NASA and the U.S. Geological Survey have started work on Landsat 9, an upgraded rebuild of the Landsat 8 spacecraft launched in 2013, to extend the Landsat program’s decades-long observations of Earth’s land cover. Image Credit: NASA.

The President’s fiscal year 2016 budget calls for initiation of a Landsat 9 spacecraft as an upgraded rebuild of Landsat 8, as well as development of a low-cost thermal infrared (TIR) free-flying satellite for launch in 2019 to reduce the risk of a data gap in this important measurement. The TIR free flyer will ensure data continuity by flying in formation with Landsat 8. The budget also calls for the exploration of technology and systems innovations to provide more cost effective and advanced capabilities in future land-imaging missions beyond Landsat 9, such as finding ways to miniaturize instruments to be launched on smaller, less expensive satellites.

“Moving out on Landsat 9 is a high priority for NASA and USGS as part of a sustainable land imaging program that will serve the nation into the future as the current Landsat program has done for decades,” said John Grunsfeld, associate administrator for science at NASA Headquarters, Washington. “Continuing the critical observations made by the Landsat satellites is important now and their value will only grow in the future, given the long term environmental changes we are seeing on planet Earth.”

Because an important part of the land imaging program is to provide consistent long-term observations, this mission will largely replicate its predecessor Landsat 8. The mission will carry two instruments, one that captures views of the planet in visible, near infrared and shortwave-infrared light, and another that measures the thermal infrared radiation, or heat, of Earth’s surfaces. These instruments have sensors with moderate resolution and the ability to detect more variation in intensity than the first seven satellites in the Landsat program.

The Landsat 9 mission is a partnership between NASA and the USGS. NASA will build, launch, perform the initial check-out and commissioning of the satellite; USGS will operate Landsat 9 and process, archive, and freely distribute the mission’s data.

"Landsat is a remarkably successful partnership," said Sarah Ryker, USGS deputy associate director for climate and land use change, Reston, Virginia. "Last year the White House found that GPS, weather satellites, and Landsat are the three most critical types of Earth-orbiting assets for civil applications, because they're used by many economic sectors and fields of research. Having Landsat 9 in progress, and a long-term commitment to sustainable land imaging, is great for natural resource science and for data-driven industries such as precision agriculture and insurance."

NASA’s Goddard Space Flight Center in Greenbelt, Maryland, will lead development of the Landsat 9 flight segment. Goddard will also build the Thermal Infrared Sensor (TIRS), which will be similar to the TIRS that the center built for Landsat 8. The new improved TIRS will have a five-year design lifetime, compared to the three-year design lifetime of the sensor on Landsat 8.

"This is good news for Goddard, and it’s great news for the Landsat community to get the next mission going," said Del Jenstrom, the Landsat 9 project manager at NASA Goddard. "It will provide data consistent with, or better than, Landsat 8."

With decades of observations, scientists can tease out subtle changes in ecosystems, the effects of climate change on permafrost, changes in farming technologies, and many other activities that alter the landscape.

“With a launch in 2023, Landsat 9 would propel the program past 50 years of collecting global land cover data,” said Jeffrey Masek, Landsat 9 Project Scientist at Goddard. "That’s the hallmark of Landsat: the longer the satellites view the Earth, the more phenomena you can observe and understand. We see changing areas of irrigated agriculture worldwide, systemic conversion of forest to pasture – activities where either human pressures or natural environmental pressures are causing the shifts in land use over decades.”

"We have recognized for the first time that we’re not just going to do one more, then stop, but that Landsat is actually a long-term monitoring activity, like the weather satellites, that should go on in perpetuity," Masek said.

NASA uses the vantage point of space to increase our understanding of our home planet, improve lives, and safeguard our future. NASA develops new ways to observe and study Earth's interconnected natural systems with long-term data records. The agency freely shares this unique knowledge and works with institutions around the world to gain new insights into how our planet is changing.

For more information on NASA’s Earth science activities, visit:

For more information on the Landsat program, visit: and

Image (mentioned), Text, Credits: NASA/Steve Cole.


Giant Galaxies Die from the Inside Out

ESO - European Southern Observatory logo.

17 April 2015

VLT and Hubble observations show that star formation shuts down in the centres of elliptical galaxies first

Astronomers have shown for the first time how star formation in “dead” galaxies sputtered out billions of years ago. ESO’s Very Large Telescope and the NASA/ESA Hubble Space Telescope have revealed that three billion years after the Big Bang, these galaxies still made stars on their outskirts, but no longer in their interiors. The quenching of star formation seems to have started in the cores of the galaxies and then spread to the outer parts. The results will be published in the 17 April 2015 issue of the journal Science.

Galaxies die from the inside out

A major astrophysical mystery has centred on how massive, quiescent elliptical galaxies, common in the modern Universe, quenched their once furious rates of star formation. Such colossal galaxies, often also called spheroids because of their shape, typically pack in stars ten times as densely in the central regions as in our home galaxy, the Milky Way, and have about ten times its mass.

Astronomers refer to these big galaxies as red and dead as they exhibit an ample abundance of ancient red stars, but lack young blue stars and show no evidence of new star formation. The estimated ages of the red stars suggest that their host galaxies ceased to make new stars about ten billion years ago. This shutdown began right at the peak of star formation in the Universe, when many galaxies were still giving birth to stars at a pace about twenty times faster than nowadays.

“Massive dead spheroids contain about half of all the stars that the Universe has produced during its entire life,” said Sandro Tacchella of ETH Zurich in Switzerland, lead author of the article. “We cannot claim to understand how the Universe evolved and became as we see it today unless we understand how these galaxies come to be.”

Tacchella and colleagues observed a total of 22 galaxies, spanning a range of masses, from an era about three billion years after the Big Bang [1]. The SINFONI instrument on ESO’s Very Large Telescope (VLT) collected light from this sample of galaxies, showing precisely where they were churning out new stars. SINFONI could make these detailed measurements of distant galaxies thanks to its adaptive optics system, which largely cancels out the blurring effects of Earth’s atmosphere.

The researchers also trained the NASA/ESA Hubble Space Telescope on the same set of galaxies, taking advantage of the telescope’s location in space above our planet’s distorting atmosphere. Hubble’s WFC3 camera snapped images in the near-infrared, revealing the spatial distribution of older stars within the actively star-forming galaxies.

Elliptical galaxy IC 2006

“What is amazing is that SINFONI’s adaptive optics system can largely beat down atmospheric effects and gather information on where the new stars are being born, and do so with precisely the same accuracy as Hubble allows for the stellar mass distributions,” commented Marcella Carollo, also of ETH Zurich and co-author of the study.

According to the new data, the most massive galaxies in the sample kept up a steady production of new stars in their peripheries. In their bulging, densely packed centres, however, star formation had already stopped.

“The newly demonstrated inside-out nature of star formation shutdown in massive galaxies should shed light on the underlying mechanisms involved, which astronomers have long debated,” says Alvio Renzini, Padova Observatory, of the Italian National Institute of Astrophysics.

A leading theory is that star-making materials are scattered by torrents of energy released by a galaxy’s central supermassive black hole as it sloppily devours matter. Another idea is that fresh gas stops flowing into a galaxy, starving it of fuel for new stars and transforming it into a red and dead spheroid.

“There are many different theoretical suggestions for the physical mechanisms that led to the death of the massive spheroids,” said co-author Natascha Förster Schreiber, at the Max-Planck-Institut für extraterrestrische Physik in Garching, Germany. “Discovering that the quenching of star formation started from the centres and marched its way outwards is a very important step towards understanding how the Universe came to look like it does now.”


[1] The Universe’s age is about 13.8 billion years, so the galaxies studied by Tacchella and colleagues are generally seen as they were more than 10 billion years ago.

More information:

This research was presented in a paper entitled “Evidence for mature bulges and an inside-out quenching phase 3 billion years after the Big Bang” by S. Tacchella et al., to appear in the journal Science on 17 April 2015.

The team is composed of Sandro Tacchella (ETH Zurich, Switzerland), Marcella Carollo (ETH Zurich), Alvio Renzini (Italian National Institute of Astrophysics, Padua, Italy), Natascha Förster Schreiber (Max-Planck-Institut für Extraterrestrische Physik, Garching, Germany), Philipp Lang (Max-Planck-Institut für Extraterrestrische Physik), Stijn Wuyts (Max-Planck-Institut für Extraterrestrische Physik), Giovanni Cresci (Istituto Nazionale di Astrofisica), Avishai Dekel (The Hebrew University, Israel), Reinhard Genzel (Max-Planck-Institut für extraterrestrische Physik and University of California, Berkeley, California, USA), Simon Lilly (ETH Zurich), Chiara Mancini (Italian National Institute of Astrophysics), Sarah Newman (University of California, Berkeley, California, USA), Masato Onodera (ETH Zurich), Alice Shapley (University of California, Los Angeles, USA), Linda Tacconi (Max-Planck-Institut für Extraterrestrische Physik, Garching, Germany), Joanna Woo (ETH Zurich) and Giovanni Zamorani (Italian National Institute of Astrophysics, Bologna, Italy).

ESO is the foremost intergovernmental astronomy organisation in Europe and the world’s most productive ground-based astronomical observatory by far. It is supported by 16 countries: Austria, Belgium, Brazil, the Czech Republic, Denmark, France, Finland, Germany, Italy, the Netherlands, Poland, Portugal, Spain, Sweden, Switzerland and the United Kingdom, along with the host state of Chile. ESO carries out an ambitious programme focused on the design, construction and operation of powerful ground-based observing facilities enabling astronomers to make important scientific discoveries. ESO also plays a leading role in promoting and organising cooperation in astronomical research. ESO operates three unique world-class observing sites in Chile: La Silla, Paranal and Chajnantor. At Paranal, ESO operates the Very Large Telescope, the world’s most advanced visible-light astronomical observatory and two survey telescopes. VISTA works in the infrared and is the world’s largest survey telescope and the VLT Survey Telescope is the largest telescope designed to exclusively survey the skies in visible light. ESO is a major partner in ALMA, the largest astronomical project in existence. And on Cerro Armazones, close to Paranal, ESO is building the 39-metre European Extremely Large Telescope, the E-ELT, which will become “the world’s biggest eye on the sky”.


Photos of the VLT:

The SINFONI instrument on ESO’s Very Large Telescope (VLT):

NASA/ESA Hubble Space Telescope:

Hubble’s WFC3 camera:

ETH Zurich:

Padova Observatory:

Italian National Institute of Astrophysics:

Images, Text, Credits: ESO/ESA/Hubble & NASA Image acknowledgement: Judy Schmidt and J. Blakeslee (Dominion Astrophysical Observatory). Note that the image is not related to science release content. Science acknowledgement: M. Carollo (ETH, Switzerland).


jeudi 16 avril 2015

NASA Spacecraft Achieves Unprecedented Success Studying Mercury

NASA - MESSENGER Mission patch.

April 16, 2015

After extraordinary science findings and technological innovations, a NASA spacecraft launched in 2004 to study Mercury will impact the planet’s surface, most likely on April 30, after it runs out of propellant.

NASA’s MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) spacecraft will impact the planet at more than 8,750 miles per hour (3.91 kilometers per second) on the side of the planet facing away from Earth. Due to the expected location, engineers will be unable to view in real time the exact location of impact.

On Tuesday, mission operators in mission control at the Johns Hopkins University Applied Physics Laboratory (APL) in Laurel, Maryland, completed the fourth in a series of orbit correction maneuvers designed to delay the spacecraft’s impact into the surface of Mercury. The last maneuver is scheduled for Friday, April 24.

Image above: NASA’s MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) spacecraft traveled more than six and a half years before it was inserted into orbit around Mercury on March 18, 2011. Image Credit: NASA/JHU APL/Carnegie Institution of Washington.

"Following this last maneuver, we will finally declare the spacecraft out of propellant, as this maneuver will deplete nearly all of our remaining helium gas,” said Daniel O’Shaughnessy, mission systems engineer at APL. “At that point, the spacecraft will no longer be capable of fighting the downward push of the sun's gravity.”

Although Mercury is one of Earth’s nearest planetary neighbors, little was known about the planet prior to the MESSENGER mission.

“For the first time in history we now have real knowledge about the planet Mercury that shows it to be a fascinating world as part of our diverse solar system,” said John Grunsfeld, associate administrator for the Science Mission Directorate at NASA Headquarters in Washington. “While spacecraft operations will end, we are celebrating MESSENGER as more than a successful mission. It’s the beginning of a longer journey to analyze the data that reveals all the scientific mysteries of Mercury.”

The spacecraft traveled more than six and a half years before it was inserted into orbit around Mercury on March 18, 2011. The prime mission was to orbit the planet and collect data for one Earth year. The spacecraft’s healthy instruments, remaining fuel, and new questions raised by early findings resulted in two approved operations extensions, allowing the mission to continue for almost four years and resulting in more scientific firsts.

One key science finding in 2012 provided compelling support for the hypothesis that Mercury harbors abundant frozen water and other volatile materials in its permanently shadowed polar craters.

Data indicated the ice in Mercury's polar regions, if spread over an area the size of Washington, would be more than two miles thick. For the first time, scientists began seeing clearly a chapter in the story of how the inner planets, including Earth, acquired water and some of the chemical building blocks for life.

A dark layer covering most of the water ice deposits supports the theory that organic compounds,  as well as water, were delivered from the outer solar system to the inner planets and may have led to prebiotic chemical synthesis and, thusly, life on Earth.

“The water now stored in ice deposits in the permanently shadowed floors of impact craters at Mercury’s poles most likely was delivered to the innermost planet by the impacts of comets and volatile-rich asteroids,” said Sean Solomon, the mission’s principal investigator, and director of Columbia University's Lamont-Doherty Earth Observatory in Palisades, New York. “Those same impacts also likely delivered the dark organic material.”

In addition to science discoveries, the mission provided many technological firsts, including the development of a vital heat-resistant and highly reflective ceramic cloth sunshade that isolated the spacecraft’s instruments and electronics from direct solar radiation – vital to mission success given Mercury’s proximity to the sun. The technology will help inform future designs for planetary missions within our solar system.


“The front side of the sunshade routinely experienced temperatures in excess of 300° Celsius (570° Fahrenheit), whereas the majority of components in its shadow routinely operated near room temperature (20°C or 68°F),” said Helene Winters, mission project manager at APL. “This technology to protect the spacecraft’s instruments was a key to mission success during its prime and extended operations.”

The spacecraft was designed and built by APL. The lab manages and operates the mission for NASA's Science Mission Directorate. The mission is part of NASA's Discovery Program, managed for the directorate by the agency's Marshall Space Flight Center in Huntsville, Alabama.

For a complete listing of science findings and technological achievements of the mission visit:

Image (mentioned), Text, Credits: NASA/Dwayne Brown/Johns Hopkins University Applied Physics Laboratory/Paulette Campbell.

Best regards,

NASA's Curiosity Rover Making Tracks and Observations

NASA - Mars Science Laboratory (MSL) patch.

April 16, 2015

NASA's Curiosity Mars rover is continuing science observations while on the move this month. On April 16, the mission passed 10 kilometers (6.214 miles) of total driving since its 2012 landing, including about a fifth of a mile (310 meters) so far this month.

The rover is trekking through a series of shallow valleys between the "Pahrump Hills" outcrop, which it investigated for six months, and the next science destination, "Logan Pass," which is still about 200 yards, or meters, ahead toward the southwest.

(Click on the image for enlarge)

Image above: NASA's Curiosity Mars rover used its Navigation Camera (Navcam) to capture this scene toward the west just after completing a drive that took the mission's total driving distance on Mars past 10 kilometers (6.214 miles). Image Credit: NASA/JPL-Caltech.

"We've not only been making tracks, but also making important observations to characterize rocks we're passing, and some farther to the south at selected viewpoints," said John Grant of the National Air and Space Museum, Washington. Grant is a Curiosity science team member who has been the team's long-term planner in recent days.

A drive of 208 feet (63.5 meters) during the mission's 957th Martian day, early Thursday, took Curiosity past a cumulative 10 kilometers of total Martian ground-distance covered. This is based on mapped distance covered by each drive; by wheel odometery, the rover reached 10 kilometers last week, but the mapped tally is considered a more precise measure of distance covered, excluding wheel slippage.

Curiosity is examining the lower slopes of a layered mountain, Mount Sharp, to investigate how the region's ancient environment evolved from lakes and rivers to much drier conditions. Sites at Pahrump Hills exposed the mountain's basal geological layer, named the Murray formation. Nearby, high-standing buttes are examples of terrain called the Washboard unit, from its corrugated appearance as seen from orbit.

Image above: A green star marks the location of NASA's Curiosity Mars rover after a drive on the mission's 957th Martian day, or sol, (April 16, 2015). The map covers an area about 1.25 miles (2 kilometers) wide. Image Credit: NASA/JPL-Caltech/Univ. of Arizona.

"The trough we’re driving through is bounded by exposures of the Washboard unit, with gaps at some places that allow us to see farther south to higher exposures of it," Grant said. "At Logan Pass, we hope to investigate the relationship between the Murray formation and the Washboard unit, to help us understand the ancient depositional setting and how environmental conditions were changing. The observations we're making now help establish the context for what we'll see there."

"The rover's mobility has been crucial, because that's what allows us to get to the best sites to investigate," Grant said. "The ability to get to different sections of the rock record builds more confidence in your interpretation of each section."

From observations made by NASA's Mars Reconnaissance Orbiter, topographically ridged terrain that has beenategorized as the Washboard unit has been mapped at many locations around Mount Sharp -- on the south flank of the mountain as well as the northern flank Curiosity is climbing -- and on the surrounding plains.

Mars Science Laboratory (MSL) or Curiosity rover. Image Credits: NASA/JPL-Caltech

"Understanding the Washboard unit and what processes formed it could put what we've been studying into a wider context," Grant said.

Curiosity spent much of its first 12 months on Mars investigating locations close to its landing site north of Mount Sharp. Findings during that period included evidence for ancient rivers and a lakebed environment that offered conditions favorable for microbial life, if Mars has ever hosted life. After leaving the landing vicinity, Curiosity drove to reach Mount Sharp, with a few extended stops at science waypoints along the route before arriving in September 2014.

NASA's Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, built the rover and manages the project for NASA's Science Mission Directorate in Washington. For more information about Curiosity, visit: and

You can follow the mission on Facebook and Twitter at: and

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


Crew Gets Ready for New Dragon and New Science

ISS - Expedition 43 Mission patch.

April 16, 2015

The SpaceX Dragon commercial cargo craft is less than a day away from arriving at the International Space Station. The Expedition 43 crew is getting ready for its arrival and five-week stay at the Earth-facing port of the Harmony module.

Read more about the SpaceX CRS-6 mission:

Commander Terry Virts set up hardware inside Harmony to assist Dragon’s installation after its capture tomorrow. Virts and Italian astronaut Samantha Cristoforetti also brushed up on robotics skills necessary to capture Dragon with the Canadarm2.

Image above: Astronaut Samantha Cristoforetti operates the Canadarm2 from inside the cupola. Image Credit: NASA.

NASA TV will begin rendezvous coverage Friday at 5 a.m. EDT. Dragon is scheduled to be grappled about 7 a.m. by Cristoforetti inside the cupola at the controls of Canadarm2 with Virts assisting.

NASA TV coverage:

Though it was a light day, the rest of the crew worked on human research and advanced microgravity experiments. Dragon is also delivering new science gear to support hundreds of experiments aboard the orbital laboratory.

Read more about research on the space station:

For more information about the International Space Station (ISS), visit:

Image (mentioned), Text, Credit: NASA.


Dawn Glimpses Ceres' North Pole

NASA - Dawn Mission patch.

April 16, 2015

After spending more than a month in orbit on the dark side of dwarf planet Ceres, NASA's Dawn spacecraft has captured several views of the sunlit north pole of this intriguing world. These images were taken on April 10 from a distance of 21,000 miles (33,000 kilometers), and they represent the highest-resolution views of Ceres to date.

Subsequent images of Ceres will show surface features at increasingly better resolution.

Animation above: This animation shows the north pole of dwarf planet Ceres as seen by the Dawn spacecraft on April 10, 2015. Dawn was at a distance of 21,000 miles (33,000 kilometers) when its framing camera took these images. Image Credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA.

Dawn arrived at Ceres on March 6, marking the first time a spacecraft has orbited a dwarf planet. Previously, the spacecraft explored giant asteroid Vesta for 14 months from 2011 to 2012. Dawn has the distinction of being the only spacecraft to orbit two extraterrestrial targets.

Ceres, with an average diameter of about 590 miles (950 kilometers), is the largest body in the main asteroid belt between Mars and Jupiter. Dawn has been using its ion propulsion system to maneuver to its first science orbit at Ceres, which it will reach on April 23.  The spacecraft will remain at a distance of 8,400 miles (13,500 kilometers) from the dwarf planet until May 9. Afterward, it will make its way to lower orbits.

Dawn's mission is managed by NASA's Jet Propulsion Laboratory, Pasadena, California, for NASA's Science Mission Directorate in Washington. Dawn is a project of the directorate's Discovery Program, managed by NASA's Marshall Space Flight Center in Huntsville, Alabama. UCLA is responsible for overall Dawn mission science. Orbital ATK, Inc., in Dulles, Virginia, designed and built the spacecraft. The German Aerospace Center, the Max Planck Institute for Solar System Research, the Italian Space Agency and the Italian National Astrophysical Institute are international partners on the mission team. For a complete list of acknowledgements, visit:

For more information about Dawn, visit:

Animation (mentioned), Text, Credits: NASA/JPL/Elizabeth Landau.


The Hard-won Triumph of the Apollo 13 Mission - 45 Years Later

NASA - Apollo 13 Mission patch.

April 16, 2015

When their spaceship was severely damaged 200,000 miles from Earth – 45 years ago this week, it was like a bad dream from which the Apollo 13 crew could not wake.

Moments after they finished a TV broadcast late on April 13, 1970, a spark ignited one of the oxygen tanks on the Apollo 13 spacecraft. The resulting explosion plunged an entire nation into an anxious three-and-a-half day drama.

Image above: Astronauts Fred Haise (left), Jack Swigert and James Lovell pose with the Apollo 13 patch and spacecraft models the day before launch. Image Credit: NASA.

The blast obliterated one of three fuel cells and an oxygen tank. Oxygen jetted into space from the command module’s remaining tank.

“Houston, we’ve had a problem here,” astronaut Jack Swigert told mission control in Houston at what was then NASA’s Manned Spacecraft Center (now Johnson Space Center).

“We’ve had a main B bus undervolt,” Mission Commander James Lovell said. One of the command module’s two main electrical circuits had experienced a drop in power.

The Manned Space Flight Network at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, made Swigert and Lovell’s reports possible. The network’s tracking stations linked the spacecraft to Earth, where its signals were transmitted through Goddard. Nearly three million circuit miles of communication channels in the NASA Communication Network conveyed the messages received at Goddard to the Mission Control Center in Houston.

Image above: From their key positions in this control center at Goddard, the Manned Space Flight Network operations director and staff controlled Apollo mission communications activities throughout a far-flung worldwide complex of stations. Image Credit: NASA's Goddard Space Flight Center.

Less than two hours after Swigert’s message was transmitted to Houston, mission control pronounced the command module mortally wounded. With only 15 minutes of power left, astronauts Swigert, Jim Lovell and Fred Haise escaped to the “life boat” of the lunar module.

President Richard Nixon learned of the crisis shortly after the explosion, and he met with Goddard Center Director John F. Clark the following day for an update. William C. Schneider, director of NASA’s Skylab program, briefed the president on the status of the rescue mission in Goddard’s Manned Space Flight Network control room, through which communications to and from Apollo 13 passed.

The nation watched for the latest updates from their television sets, transfixed, as the rescue mission unfolded.

Image above: Then-Goddard Center Director John Clark greets President Richard Nixon, who visited the center for an Apollo 13 briefing on April 14, 1970. At right is Henry Thompson, deputy director of manned flight support at Goddard. Image Credit: NASA's Goddard Space Flight Center.

The crew spent three-and-a-half grueling days in the lunar module. They rationed food and water, which mission designers had only intended to last two men a day and a half, not three men three days. Carbon dioxide reached dangerous levels in the lunar module before the team managed to convert square filters from the command module to fit in the round openings on the lunar module. When the crew shut the instruments off to conserve power, the inside temperature reached an icy 38 F.

But reorienting the lunar module to a return-to-Earth trajectory from a lunar landing course proved to be one of the most difficult and important obstacles to hurdle.

Navigation and targeting functions were unavailable. Debris from the explosion made it impossible for the crew to navigate by the stars using the on-board sextant. In a nail-biting maneuver, the astronauts improvised by using the limb of Earth, or the horizon where Earth meets the atmosphere, as a reference point. They were then able to perform a controlled fuel burn to shorten the time ’til splashdown on Earth.

Flight Director Gerald Griffin in Houston later recalled of the alignment maneuver, “Some years later I went back to the log and looked up that mission. My writing was almost illegible, I was so damned nervous. And I remember the exhilaration running through me: My God, that's the last hurdle - if we can do that, I know we can make it. It was funny because only the people involved knew how important it was to have that platform properly aligned.”

On April 17, 1970, the crew splashed down in the Pacific Ocean near Samoa.

Image above: Then-NASA Administrator Thomas Paine (center), together with staff members from NASA Headquarters and the Manned Spacecraft Center, applaud the successful splashdown of the Apollo 13 mission. The splashdown occurred at 12:07 p.m., April 17, 1970, in the south Pacific Ocean. Image Credit: NASA.

The performance of Goddard’s Manned Space Flight Network contributed significantly to the safe return of the astronauts, said Dale Call, then-MSFN network director. He said the network performed better then than on any previous Apollo mission.

Houston’s flight operations director commended MSFN operators for their critical help with the mission.

Throughout the crisis, the network remained consistent and reliable in relaying communications to and from Apollo 13 despite the tracking difficulties imposed by the failure of the command module. As engineers on the ground hurriedly created workarounds for each challenge that arose, such as the carbon dioxide issue, they could only be communicated to the crew via the network.

 APOLLO 13 - Part 2

Films above: APOLLO 13 and APOLLO 13 - Part 2,  an Orbiter Films, a tribute for Apollo 13 mission, inspired by the scenario of the movie issued in 1995, made by Aerospace Studio, this film was made using Orbiter Space Flight Simulator 2010 and many add-ons made by the Orbiter Community. Musics: Original soundtracks of the movie Apollo 13 by James Horner.

Although the mission was not able to achieve its scientific goals, NASA’s rescue mission was an agency triumph.

“With astronauts Lovell, Haise and Swigert safely back on Earth, a surpassing human drama that gripped the world for three-and-a-half days at last has a happy ending,” President Richard Nixon said following the astronauts’ return. “Their safe return is a tribute to their own courage and also to the ingenuity and resourcefulness of those on the ground who helped transform potential tragedy into a heart-stopping rescue.”

Related link:

Apollo 13 Mission:

Images (mentioned), Film (mentioned), Text, Credits: NASA/Goddard Space Flight Center/Ashley Morrow/ Aerospace.

Best regards,

AMS days: experiments present latest results

CERN - European Organization for Nuclear Research logo.

April 16, 2015

The Alpha Magnetic Spectrometer (AMS) collaboration will present today the latest results in its quest to understand the origin of cosmic rays and dark matter. These intriguing results will be shared and discussed during the “AMS days” starting today at CERN with many of the world’s leading theoretical physicists and principal investigators of some of the major experiments exploring the field of cosmic-ray physics. The main objective of this scientific exchange is to understand the interrelation between AMS results and those of other major cosmic-ray experiments and current theories.

“I am very pleased that so many of the world's leading scientists are interested in AMS results and are coming to CERN for this meeting,” said AMS spokesperson Samuel Ting.

Image above: The Alpha Magnetic Spectrometer looks for dark matter, antimatter and missing matter from a module on the International Space Station (Image: NASA).

In particular, AMS is presenting unexpected new results on the antiproton/proton ratio in the cosmic rays, and on the proton and helium fluxes. Pre-existing models of ordinary cosmic rays cannot explain the AMS results. These new observations may provide important information on the understanding of cosmic-ray production and propagation. It is possible that the results may be explained by new astrophysical sources or new acceleration and propagation mechanisms, and the latest AMS results are also consistent with dark matter collisions.


CERN, the European Organization for Nuclear Research, is one of the world’s largest and most respected centres for scientific research. Its business is fundamental physics, finding out what the Universe is made of and how it works. At CERN, the world’s largest and most complex scientific instruments are used to study the basic constituents of matter — the fundamental particles. By studying what happens when these particles collide, physicists learn about the laws of Nature.

The instruments used at CERN are particle accelerators and detectors. Accelerators boost beams of particles to high energies before they are made to collide with each other or with stationary targets. Detectors observe and record the results of these collisions.

Founded in 1954, the CERN Laboratory sits astride the Franco–Swiss border near Geneva. It was one of Europe’s first joint ventures and now has 22 Member States.

Related link:

The Alpha Magnetic Spectrometer (AMS):

Read more:

"Physics community to discuss latest results of the AMS experiment" – CERN press release:

Don't miss:

- "Human Space Exploration" by NASA's William H. Gerstenmaier, as part of the AMS days at CERN. Webcast at 6:15pm today (15 April 2015):

- "The Odyssey of Voyager" by Prof. Edward C. Stone, as part of the AMS days at CERN. Webcast at 6:30pm tomorrow (16 April 2015):

For more information about the European Organization for Nuclear Research (CERN), visit:

Image (mentioned), Text, Credits: CERN/Cian O'Luanaigh.


Video: SpaceX Falcon 9 rocket still misses landing

SpaceX - Falcon 9/ Dragon CRS-6 Mission patch.

April 16, 2015

The first stage of the launch vehicle was scheduled to land on Tuesday to Earth for reuse. This is the third failure in as many attempts for the US company owned by billionaire Elon Musk.

SpaceX Falcon 9 crash on Tuesday April 14, 2015

The last mission entrusted to SpaceX is a partial success. Or partial failure. US private space company managed to take off its Falcon 9 rocket to resupply the International Space Station on Tuesday 14th April. The astronauts have received particular the first espresso machine sent into space. But the first stage of the launcher scheduled to return to Earth intact, has once again failed in his mission.

Incredible footage shows SpaceX Falcon 9 rocket crash landing

Three failures in as many attempts

As shown in the pictures from SpaceX, the launch vehicle attempted to land on an offshore platform off the coast of Jacksonville, Florida (USA). The rocket has slowed his fall with the approach of the site, and is well managed to ask. But his angle of approach, distorted by the side wind, caused a drop, causing an explosion and disintegration of the craft. This is the third time in as many attempts, the pitcher fails to return to Earth.

Image above: The 300-foot-long ship (Drone Barge) used for the landing attempt returned to port Jan. 12 in Jacksonville, Florida, showing no obvious signs of damage. Containers housing support equipment on the barge’s deck were blackened and crumpled from the blast of the second crash of the reusable rocket Falcon 9.

SpaceX for the success of this landing is crucial to the profitability of the company owned by billionaire Elon Musk. For recovering intact launcher would reuse for the next launch. Enough to drastically reduce the cost of space travel in the future.

For more information about SpaceX and Falcon 9 reusable rocket, visit:

Image, Video, Text, Credits: SpaceX/APTN/ Aerospace.


GOCE helps tap into sustainable energy resources

ESA - GOCE Mission logo.

16 April 2015

Going far above and beyond its original mission objectives, results from the GOCE gravity satellite are now being used to produce maps for geothermal energy development.

Geothermal energy is heat from under Earth’s surface. From hot springs to magma, this energy provides a clean, sustainable resource that can be used to generate electricity, heat buildings, grow plants in greenhouses and many other applications.

Bouguer gravity anomaly

These energy sites exist underground, but often in remote areas, making them difficult, expensive and time-consuming to explore and measure. While the potential of geothermal energy worldwide remains vast, more effort is needed to develop and harness it.

To help facilitate their exploitation, scientists from ESA and the International Renewable Energy Agency (IRENA) have used gravity measurements from the GOCE mission to produce an online tool that indicates areas likely to possess geothermal potential, narrowing the search for prospectors.

The tool’s maps show certain characteristics that may help in the search for geothermal reservoirs, including areas with thin crusts, subduction zones and young magmatic activity.

“These maps can help make a strong business case for geothermal development where none existed before,” said Henning Wuester, Director of IRENA’s Knowledge, Policy and Finance Centre.

Free air gravity anomaly

“In doing so, the tool provides a shortcut for lengthy and costly explorations and unlocks the potential of geothermal energy as a reliable and clean contribution to the world’s energy mix.”

After a potential site location has been selected using the online tool, ground surveys and seismic measurements are still needed to determine the exact points for energy extraction, but the new resource is a step towards developing a comprehensive geothermal prospecting technique.

The maps outline two specific global gravity anomalies: ‘Bouguer’ and ‘free air’.

The free air gravity map provides information on geological structures, while the Bouguer gravity anomaly map combines GOCE data with information of global topography to show differences in crustal thickness. Together, the maps depict characteristics unique to geothermal reservoirs.

The two maps are complementary and form a basis to discriminate and classify different terrains at a country-wide scale.


GOCE’s mission ended in October 2013 when it ran out of fuel and subsequently reentered Earth’s atmosphere. But its wealth of data continues to be exploited to improve our understanding of ocean circulation, sea level, ice dynamics and Earth’s interior.

“This is the first time that global gravity data from GOCE have been used as a tool for geothermal energy site exploration,” said Volker Liebig, Director of ESA’s Earth Observation Programmes.

“ESA will continue its collaboration with IRENA to further improve space-based gravity data as a resource for sustainable energy development.”

Related links:


Global Atlas geothermal map:

More on the global gravity maps:


Images, Text, Credits: ESA/IRENA/AOES Medialab.

Best regards,

mercredi 15 avril 2015

Icy Tendrils Reaching into Saturn Ring Traced to Their Source

NASA - Cassini Mission International logo.

April 15, 2015

Images above: This collage, consisting of two Cassini images of long, sinuous, tendril-like features from Saturn's moon Enceladus and two corresponding computer simulations of the same, illustrates how well the structures, and the sizes of the particles composing them, can be modeled by tracing the trajectories of tiny, icy grains ejected from Enceladus' south polar geysers. Credit: NASA/JPL-Caltech/Space Science Institute.

Long, sinuous, tendril-like structures seen in the vicinity of Saturn's icy moon Enceladus originate directly from geysers erupting from its surface, according to scientists studying images from NASA's Cassini spacecraft.

This result is published online today in a study in the Astronomical Journal, along with additional insights into the nature of the structures.

"We've been able to show that each unique tendril structure can be reproduced by particular sets of geysers on the moon's surface," said Colin Mitchell, a Cassini imaging team associate at the Space Science Institute in Boulder, Colorado, and lead author of the paper. Mitchell and colleagues used computer simulations to follow the trajectories of

ice grains ejected from individual geysers. The geysers, which were discovered by Cassini in 2005, are jets of tiny water ice particles, water vapor and simple organic compounds.

Under certain lighting conditions, Cassini's wide-view images showing icy material erupting from Enceladus reveal faint, finger-like features, dubbed "tendrils" by the imaging team. The tendrils reach into Saturn's E ring -- the ring in which Enceladus orbits -- extending tens of thousands of miles (or kilometers) away from the moon. Since the tendrils were discovered, scientists have thought they were the result of the moon's geysering activity and the means by which Enceladus supplies material to the E ring. But the ghostly features had never before been traced directly to geysers on the surface.

Graphic above: This graphic plots the source locations of the geysers scientists have located on Enceladus' south polar terrain. Credit: NASA/JPL-Caltech/Space Science Institute.

Because the team was able to show that tendril structures of different shapes correspond to different sizes of geyser particles, the team was able to zero in on the sizes of the particles forming them. They found the tendrils are composed of particles with diameters no smaller than about a hundred thousandth of an inch, a size consistent with the measurements of E-ring particles made by other Cassini instruments.

As the researchers examined images from different times and positions around Saturn, they also found that the detailed appearance of the tendrils changes over time. "It became clear to us that some features disappeared from one image to the next," said John Weiss, an imaging team associate at Saint Martin's University in Lacey, Washington, and an author on the paper.

The authors suspect that changes in the tendrils' appearance likely result from the cycle of tidal stresses -- squeezing and stretching of the moon as it orbits Saturn -- and its control of the widths of fractures from which the geysers erupt. The stronger the tidal stresses raised by Saturn at any point on the fractures, the wider the fracture opening and the greater the eruption of material. The authors will investigate in future work whether this theory explains the tendrils' changing appearance.

Cassini spacecraft. Image Credit: NASA

There is even more that can be extracted from the images, the scientists say. "As the supply lanes for Saturn's E ring, the tendrils give us a way to ascertain how much mass is leaving Enceladus and making its way into Saturn orbit," said Carolyn Porco, team leader for the imaging experiment and a coauthor on the paper. "So, another important step is to determine how much mass is involved, and thus estimate how much longer the moon's sub-surface ocean may last." An estimate of the lifetime of the ocean is important in understanding the evolution of Enceladus over long timescales.

Because of its significance to the investigation of possible extraterrestrial habitable zones, Enceladus is a major target of investigation for the final years of the Cassini mission. Many observations, including imaging of the plume and tendril features, and thermal observations of the surface of its south polar geyser basin, are planned during the next couple of years.

The Cassini-Huygens mission is a cooperative project of NASA, ESA (European Space Agency) and the Italian Space Agency. NASA's Jet Propulsion Laboratory in Pasadena, California, manages the mission for the agency's Science Mission Directorate in Washington. JPL is a division of the California Institute of Technology in Pasadena. The Cassini imaging operations center is based at the Space Science Institute in Boulder, Colo.

New images released today can be found at:

More information about Cassini, visit: and and

Images (mentioned), Text, Credits: NASA/JPL/Preston Dyches/Space Science Institute/Steve Mullins.