vendredi 23 mars 2012

A glow in the Martian night throws light on atmospheric circulation












ESA - Mars Express Mission patch.

23 Mar 2012

A faint, infrared glow above the winter poles of Mars is giving new insights into seasonal changes in the planet's atmospheric circulation. The tell-tale night emission was first detected in 2004 in observations made by the OMEGA imaging spectrometer on ESA's Mars Express orbiter.

Writing in a recent issue of the Journal of Geophysical Research, a team of French scientists reported on the first detection of an infrared emission above the polar regions of Mars. The emission, at a wavelength of 1.27 microns, was detected on three occasions (in 2004, 2005 and 2006) during a series of 40 observations made by OMEGA above the planet's limb.

video
Production of oxygen nightglow on Mars. Credit: ESA

This animation depicts the process that is believed to account for this nightglow:

When exposed to solar ultraviolet radiation above an altitude of 70 km, carbon dioxide molecules - the main atmospheric constituent of Mars' atmosphere - are split into carbon monoxide and oxygen atoms. Those oxygen atoms (depicted as red spheres) are transported by a gigantic Hadley cell, which features an ascending branch above the daytime summer pole and a descending branch over the winter pole, which is in the night hemisphere. The oxygen atoms recombine into molecular oxygen in the descending branch of the Hadley cell, at an altitude of 30-50 km, emitting infrared radiation at 1.27 microns.

Infrared emissions are not unusual in planetary atmospheres. In the upper atmospheres of both Venus and Mars, carbon dioxide (CO2) and nitrogen (N2) molecules are split or photodissociated by solar ultraviolet (UV) light. This produces oxygen and nitrogen atoms in the region known as the thermosphere, at an altitude of about 80-90 km above each planet's dayside.

Spacecraft observations show that the thermospheric circulation of Venus is characterised by a strong flow of air from the warmer, sub-solar point (local midday) toward the anti-solar point (local midnight). The cooler gas on the night side then begins to descend.

As the sinking gas comes into contact with carbon dioxide molecules in the atmosphere, the atoms of oxygen and nitrogen recombine. This recombination process results in an ultraviolet nightglow from nitric oxide (NO), as well as a near-infrared oxygen (O2) emission at 1.27 microns.

A comparable NO emission in the atmosphere of Mars was detected by the SPICAM instrument on Mars Express in 2005. Since this was also attributed to atmospheric circulation, scientists expected to see the associated O2 emission, but the nighttime glow from excited molecular oxygen was not confirmed until the OMEGA observations first reported in 2010.

OMEGA detection of oxygen nightglow on Mars. Image courtesy of J.-L. Bertaux et al.

The OMEGA instrument on Mars Express has detected oxygen emission at the night side of Mars. The emission, at a wavelength of 1.27 µm, was detected on three occasions during a series of 40 observations made by OMEGA above the planet's limb.

The panels above show, from left to right:

- A 2.2° wide swath of the observed limb at night with emission coded in pink;
    the vertical distribution of the intensity observed in megaRayleigh (MR) - integration over azimuth.

- The red line is a smoothed version of the distribution;
    the integrated observed spectrum, showing emission only at 1.27 µm.

"We think that the faintness of the infrared oxygen emission over the nightside of Mars may result from the slower descent of the cold air – which means less recombination of the oxygen atoms – and a less intense bombardment by solar UV light, which reduces the rate of photodissociation," explained Jean-Loup Bertaux from LATMOS / Université de Versailles Saint-Quentin, who was lead author of the paper.

The authors believe that the natural light emissions from the atmosphere are clearly associated with the planet's atmospheric circulation. Although few direct observations of Martian high level winds have been made, it is believed that air rises above the warmer, summer pole, moves across the equator and then descends near the winter pole, on the planet's night side. This circulation apparently takes the form of a simple Hadley cell, very much like the atmospheric motion which occurs on either side of Earth's equator.

As predicted by general circulation models of Mars, all of the OMEGA oxygen nightglow observations were obtained at high latitudes, during the winter night. This location coincides with the region where cooler gas is sinking above the pole which is experiencing long-term darkness – similar to the winter pole on Earth.

"When exposed to solar UV radiation above an altitude of 70 km, carbon dioxide molecules - the main atmospheric constituent of Mars' atmosphere - are split into carbon monoxide and oxygen atoms," said Jean-Loup Bertaux.

"Those oxygen atoms are transported by a gigantic Hadley cell, which features an ascending branch above the daytime summer pole and a descending branch over the winter pole, which is in the night hemisphere. The oxygen atoms recombine into molecular oxygen in the descending branch of the Hadley cell, at an altitude of 30-50 km."

Further observations are required to confirm what happens around the time of the Martian equinoxes, when the Sun is overhead at the equator and neither pole is in darkness. Around those dates, the OMEGA data and the general circulation model show that a different pattern establishes, with two symmetrical Hadley cells. Air rises near the equator, and divides into two branches, one going north and the other going south, with air descending simultaneously over both poles.

The paper also addresses whether OMEGA nightglow observations may help to solve the mystery of Martian methane. Although it is easily destroyed by solar UV, the gas is still present on the red planet today.

The authors consider the impact of Hadley circulation on the long-term stability of methane and conclude that recycling of the atmosphere at high altitude seems far too slow to significantly decrease the lifetime of the gas near the surface.

"These findings provide important constraints on the overall aeronomy and atmospheric dynamics of Mars," said Olivier Witasse, ESA's project scientist for Mars Express. "They should also stimulate research into Earth's atmosphere, through comparisons of the processes influencing the global circulations of the two neighbouring planets."

Reference publication:

Bertaux, J.-L., et al., "First detection of O2 1.27 µm nightglow emission at Mars with OMEGA/MEX and comparison with general circulation model predictions", J. Geophys. Res., 117, E00J04, 2012. doi:10.1029/2011JE003890.

Related publications:

Gondet, B., et al., "O2 nightglow emission detected in Mars atmosphere by OMEGA/Mars Express", paper presented at the European Geosciences Union General Assembly, Vienna, 3 May, 2010.

Clancy, R. T., et al., "CRISM limb observations of O2 singlet delta nightglow in the polar winter atmosphere of Mars", Bull. Am. Astron. Soc., 42, 1041 2010. http://adsabs.harvard.edu/abs/2010DPS....42.4202C

Notes for editors:

The results described here are based on measurements of O2 emission at 1.27 microns obtained from limb observations with the OMEGA imaging spectrometer on board Mars Express. This emission was detected in observations performed on 22 November 2004, 21 April 2005 and 27 January 2006.

Detections of the oxygen nightglow on Mars with the CRISM instrument on board NASA's Mars Reconnaissance Orbiter have also been reported.

The other scientists involved in this study with OMEGA data are: B. Gondet (IAS-Orsay, France), F. Lefèvre (LATMOS/IPSL/UPMC, France), J. P. Bibring (IAS-Orsay, France), and F. Montmessin (LATMOS/IPSL/UVSQ, France).

Mars Express, launched in June 2003, represents ESA's first visit to another planet in the Solar System. The scientific payload, provided by research institutes throughout Europe, consists of seven instruments that provide remote sensing measurements of the atmosphere, ground and below the surface. Since arrival in orbit around Mars in December 2003, Mars Express has been helping to answer fundamental questions about the geology, atmosphere, surface environment, history of water and potential for life on Mars.

For more information about Mars Express Mission, visit: http://www.esa.int/esaMI/Mars_Express/index.html

Images (mentioned), Text, Credit: LATMOS/IPSL/UVSQ/Université de Versailles Saint-Quentin/CNRS/France/Jean-Loup Bertaux/ESA Mars Express Project Scientist/Olivier Witasse.

Greetings, Orbiter.ch

European Space Agency's Edoardo Amaldi ATV liftoff













CERN - European Organization for Nuclear  Research logo.

23 March 2012

Artist's impression of the ESA's first Automated Transfer Vehicle. Image: D. Ducros /ESA

The Italian physicist Edoardo Amaldi was CERN's first Secretary General and a driving force for the creation of the laboratory. He was also one of the founding fathers of the European Space Agency (ESA).

Edoardo Amaldi

On Friday 23 March ESA's third Automated Transfer Vehicle (ATV), named in honour of Amaldi, began its journey to the International Space Station on board an Ariane rocket.

video
 CERN - Trailer Live Webcast Edoardo Amaldi ATV 3 launch

More information:

ESA's ATV blog: http://blogs.esa.int/atv/

Edoardo Amaldi ATV-3 launch: http://orbiterchspacenews.blogspot.com/2012/03/edoardo-amaldi-atv-3-launch.html

ESA press release: ATV-3 set to provide ESA's annual service to Space Station:
http://www.esa.int/esaCP/SEMBET4Y1ZG_index_0.html

CERN: http://public.web.cern.ch/public/Welcome.html

Follow CERN on Twitter: http://twitter.com/cern/

Images, Video, Text, Credits: CERN / ESA / D. Ducros.

Greetings, Orbiter.ch

jeudi 22 mars 2012

Edoardo Amaldi ATV-3 launch












ESA - Edoardo Amaldi ATV-3 Mission patch.

23 March 2012

 ATV-3 Launch

ESA’s third Automated Transfer Vehicle, Edoardo Amaldi, has been launched from Europe’s Spaceport in Kourou, French Guiana, with a night-time liftoff at 05:34 CET (04:34 GMT). Edoardo Amaldi is the heaviest payload ever launched by an Ariane rocket.

video
Liftoff of Ariane 5 VA205 with ATV-3

Using the Ariane 5 ES version of Arianespace’s heavy-lift workhorse, this flight will deploy the ATV into a 260-kilometer orbit – positioning the payload for its docking with the International Space Station.

Liftoff of Ariane 5 VA205 with ATV-3

The mission has a total lift performance of over 20,000 kg., which includes the ATV’s mass of more than 19,700 kg. – representing the heaviest payload ever to be orbited by Ariane 5.

Its payload is named after Italian physicist and spaceflight pioneer Edoardo Amaldi, and carries 6.6 metric tons of cargo for the International Space Station – including experiments, food, clothing, tools and spare parts, along with propellant for the multi-national crewed orbital facility.

Liftoff of Ariane 5 VA205 with ATV-3

Related links:

Arianespace: http://www.arianespace.com/index/index.asp

European Space Agency: http://www.esa.int/esaCP/index.html
 
Astrium: http://www.astrium.eads.net/

Images, Video, Text, Credits: ESA / S. Corvaja / Arianespace.

Best regards, Orbiter.ch

Dusty Mars Rover's Self Portrait











NASA - Mars Exploration Rover "Opportunity" (MER-B) patch.

March 22, 2012


This self portrait from NASA's Mars Exploration Rover Opportunity shows dust accumulation on the rover's solar panels as the mission approached its fifth Martian winter. The dust reduces the rover's power supply, and the rover's mobility is limited until the winter is over or wind cleans the panels.

This is a mosaic of images taken by Opportunity's panoramic camera (Pancam) during the 2,111th to 2,814th Martian days, or sols, of the rover's mission (Dec. 21 to Dec. 24, 2011). The downward-looking view omits the mast on which the camera is mounted.

The portrait is presented in approximate true color, the camera team's best estimate of what the scene would look like if humans were there and able to see it with their own eyes.

Mars Exploration Rover description

Opportunity has worked through four Martian southern hemisphere winters since it landed in in January 2004 about 14 miles (23 kilometers) northwest of its current location. Closer to the equator than its twin rover, Spirit, Opportunity has not needed to stay on a sun-facing slope during the previous winters. Now, however, Opportunity's solar panels carry a thicker coating of dust, and the team is using a strategy employed for three winters with Spirit: staying on a sun-facing slope. The sun will pass relatively low in the northern sky from the rover's perspective for several months of shortened daylight before and after the southern Mars winter solstice on March 30, 2012. Opportunity is conducting research while located on the north-facing slope of a site called "Greeley Haven."

For more information about Mars Exploration Rover Mission, visit: http://marsrover.nasa.gov/home/index.html

Images, Text, Credit: NASA / JPL-Caltech / Cornell / Arizona State Univ.

Greetings, Orbiter.ch

mercredi 21 mars 2012

Dawn Sees New Surface Features on Giant Asteroid













NASA - DAWN Mission patch.

March 21, 2012


In this image from NASA's Dawn spacecraft, bright material extends out from the crater Canuleia on Vesta. The bright material appears to have been thrown out of the crater during the impact that created it. Image credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA/UMD.

NASA's Dawn spacecraft has revealed unexpected details on the surface of the giant asteroid Vesta. New images and data highlight the diversity of Vesta's surface and reveal unusual geologic features, some of which were never previously seen on asteroids.

These results were discussed today at the Lunar and Planetary Science Conference at The Woodlands, Texas.

Vesta is one of the brightest objects in the solar system and the only asteroid in the so-called main belt between Mars and Jupiter visible to the naked eye from Earth. Dawn has found that some areas on Vesta can be nearly twice as bright as others, revealing clues about the asteroid's history.


This image, made from data obtained by NASA's Dawn spacecraft, shows a perspective view of a layered young crater in the Rheasilvia basin at Vesta. Image credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA/PSI.

"Our analysis finds this bright material originates from Vesta and has undergone little change since the formation of Vesta over 4 billion years ago," said Jian-Yang Li, a Dawn participating scientist at the University of Maryland, College Park. "We're eager to learn more about what minerals make up this material and how the present Vesta surface came to be."

Bright areas appear everywhere on Vesta but are most predominant in and around craters. The areas vary from several hundred feet to around 10 miles (16 kilometers) across. Rocks crashing into the surface of Vesta seem to have exposed and spread this bright material. This impact process may have mixed the bright material with darker surface material.


The interplay of bright and dark material at the rim of Marcia crater on Vesta is visible in this image mosaic taken by NASA's Dawn spacecraft. Image credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA/LPI/ASU.

While scientists had seen some brightness variations in previous images of Vesta from NASA's Hubble Space Telescope, Dawn scientists also did not expect such a wide variety of distinct dark deposits across its surface. The dark materials on Vesta can appear dark gray, brown and red. They sometimes appear as small, well-defined deposits around impact craters. They also can appear as larger regional deposits, like those surrounding the impact craters scientists have nicknamed the "snowman."

"One of the surprises was the dark material is not randomly distributed," said David Williams, a Dawn participating scientist at Arizona State University, Tempe. "This suggests underlying geology determines where it occurs."

The dark materials seem to be related to impacts and their aftermath. Scientists theorize carbon-rich asteroids could have hit Vesta at speeds low enough to produce some of the smaller deposits without blasting away the surface.


This image from NASA's Dawn spacecraft shows a young crater on Vesta that is 9 miles (15 kilometers) in diameter. Image credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA.

Higher-speed asteroids also could have hit Vesta's surface and melted the volcanic basaltic crust, darkening existing surface material. That melted conglomeration appears in the walls and floors of impact craters, on hills and ridges, and underneath brighter, more recent material called ejecta, which is material thrown out from a space rock impact.

Vesta's dark materials suggest the giant asteroid may preserve ancient materials from the asteroid belt and beyond, possibly from the birth of the solar system.

"Some of these past collisions were so intense they melted the surface," said Brett Denevi, a Dawn participating scientist at the Johns Hopkins University Applied Physics Laboratory in Laurel, Md. "Dawn's ability to image the melt marks a unique find. Melting events like these were suspected, but never before seen on an asteroid."

Dawn launched in September 2007. It will reach its second destination, Ceres, in February 2015.

"Dawn's ambitious exploration of Vesta has been going beautifully," said Marc Rayman, Dawn chief engineer at NASA's Jet Propulsion Laboratory in Pasadena, Calif. "As we continue to gather a bounty of data, it is thrilling to reveal fascinating alien landscapes."

To view the new images, visit: http://www.nasa.gov/dawn and http://dawn.jpl.nasa.gov .

Dawn's mission is managed by JPL 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, Ala. UCLA is responsible for overall Dawn mission science. Orbital Sciences Corp. in Dulles, Va., 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. JPL is managed for NASA by the California Institute of Technology in Pasadena.

For more information about DAWN Mission, visit: http://dawn.jpl.nasa.gov/

Images (mentioned), Text, Credit: NASA / Dwayne Brown / JPL / Jia-Rui Cook.

Best regards, Orbiter.ch

At 10, GRACE Continues Defying, and Defining, Gravity












NASA - GRACE Mission patch.

March 21, 2012

Just as the lead characters in the popular Broadway musical “Wicked” sing about defying gravity, the low-Earth orbiting twin spacecraft of NASA’s Gravity Recovery and Climate Experiment (GRACE) continue to defy gravity 10 years after launch, while also continuing to help define it. Along the way, they’ve also produced an amazing array of breakthrough science that is giving us a new understanding of changes in Earth’s natural systems.

Launched from Northern Russia on March 17, 2002, on what was designed to be a three- to five-year mission, GRACE continues its task of making detailed measurements of Earth’s gravity field. It does so by noting minute changes in gravitational pull caused by local changes in Earth's mass. Masses of ice, air, water and solid Earth can be moved by weather patterns, seasonal change, climate change and even tectonic events such as large earthquakes. To track these changes, GRACE uses GPS and a microwave ranging system to measure micron-scale variations in the 220-kilometer (137-mile) separation between the two spacecraft, developed by NASA's Jet Propulsion Laboratory, Pasadena, Calif.


These measurements are used to produce monthly gravity maps that are more than 100 times more precise than previous models, providing the resolution necessary to characterize how Earth’s gravity field varies over time and space, and over land and sea. The data have substantially improved the accuracy of techniques used by oceanographers, hydrologists, glaciologists, geologists and climate scientists.

“GRACE essentially demonstrated a new form of remote sensing for climate research that has turned out even better than we hoped,” said GRACE Project Scientist Michael Watkins of JPL “We realized early on in the design of GRACE that we could measure the gravity field well enough to observe the critical indicators of climate change – sea level rise and polar ice melt.”

GRACE is a joint mission with the German Aerospace Center (DLR) and the German Research Center for Geosciences (GFZ), in partnership with the University of Texas at Austin. During its first decade of operations, the mission has made remarkable contributions to many scientific disciplines, expanding our knowledge of ice loss from the polar ice sheets and mountain glaciers, groundwater storage on land, sea level variations and large-scale ocean circulation, to name but a few.

GRACE also pioneered the study technique now being used by NASA’s Gravity Recovery and Interior Laboratory (GRAIL) mission, which recently began mapping the gravitational field of the moon to learn about its internal structure and composition in unprecedented detail. GRAIL data will also provide a better understanding of how Earth and other rocky planets in the solar system formed and evolved.

In June 2010, NASA and DLR signed an agreement to continue GRACE through 2015—a full 10 years past the planned mission duration. Recognizing the importance of extending this long-term dataset, NASA has approved the development and launch of the GRACE Follow-On mission, also developed jointly with Germany, and planned for launch in 2017.

For more information on GRACE, visit: http://www.csr.utexas.edu/grace/ , http://www.nasa.gov/grace , and http://grace.jpl.nasa.gov/ . For more information on GRAIL, visit: http://www.nasa.gov/grail

View GRACE slideshow: http://www.nasa.gov/mission_pages/Grace/multimedia/gallery-index.html

Image, Text Credit: NASA / JPL / Alan Buis.

Cheers, Orbiter.ch

Cassini Sees Saturn Stressing out Enceladus













NASA / ESA - Cassini Mission to Saturn logo.

March 21, 2012


These images, based on ones obtained by NASA's Cassini spacecraft, show how the pull of Saturn's gravity can deform the surface of Saturn's moon Enceladus in the south polar region crisscrossed by fissures known as "tiger stripes." Image credit: NASA/JPL-Caltech/SSI/LPI/GSFC.

Images from NASA's Cassini spacecraft have, for the first time, enabled scientists to correlate the spraying of jets of water vapor from fissures on Saturn's moon Enceladus with the way Saturn's gravity stretches and stresses the fissures. The result is among the Cassini findings presented today at the Lunar and Planetary Science Conference at The Woodlands, Texas.

"This new work gives scientists insight into the mechanics of these picturesque jets at Enceladus and shows that Saturn really stresses Enceladus," said Terry Hurford, a Cassini associate based at NASA Goddard Space Flight Center in Greenbelt, Md.

Enceladus is unique in the Saturn system in having jets of water vapor and organic particles spray from long fissures in its south polar region. The long fissures have been nicknamed the "tiger stripes."

Hurford and colleagues suggested a few years ago that tidal pulls from Saturn's gravity could explain the existence of the jets, but they had not been able to correlate specific jets with calculated stresses until now. They studied the jets emerging from the warmest regions within the tiger stripes Baghdad Sulcus and Damascus Sulcus.

The scientists found that the greatest stresses pulling apart the tiger stripes, occurred right after Enceladus made its closest approach to Saturn in its orbit. The scientists found that Saturn's gravitational pull could also deform the fissure by making one side move relative to the other side. That kind of deformation seemed to occur quite often during Enceladus' orbit around the planet, even when Enceladus was very far away.

The finding suggests that a large reservoir of liquid water – a global or local ocean – would be necessary to allow Enceladus to flex enough to generate stresses great enough to deform the surface, Hurford said. That process would control the timing of the jet eruptions. The finding also suggests that Saturn's tides create an enormous amount of heat in the area.

Enceladus

The conference will also include a talk presenting highlights of the Cassini mission by Linda Spilker, Cassini project scientist at NASA's Jet Propulsion Laboratory, Pasadena, Calif. She will present images showing the evolution of an enormous storm that roiled the northern hemisphere of Saturn, the effect of seasonal rain storms on Saturn's moon Titan, and what Cassini will hope to observe in the next few years of its extended mission.

"Cassini's seven-plus years roaming the Saturn system have shown us how beautifully dynamic and unexpected the Saturn system is over time," Spilker said. "We're looking forward to new discoveries as the seasons turn."

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

For more information about the Cassini-Huygens mission visit http://www.nasa.gov/cassini and http://saturn.jpl.nasa.gov

Enceladus' image gallery: http://www.nasa.gov/mission_pages/cassini/multimedia/gallery-indexEnceladus.html

ESA Cassini website: http://www.esa.int/esaMI/Cassini-Huygens/

Images, Text, Credit: NASA / JPL / ia-Rui C. Cook / ESA.

Greetings, Orbiter.ch

VISTA Stares Deep into the Cosmos













ESO - European Southern Observatory logo.

21 March 2012

Treasure trove of new infrared data made available to astronomers

 Highlights of VISTA’s deep infrared view of the COSMOS field

ESO's VISTA telescope has created the widest deep view of the sky ever made using infrared light. This new picture of an unremarkable patch of sky comes from the UltraVISTA survey and reveals more than 200 000 galaxies. It forms just one part of a huge collection of fully processed images from all the VISTA surveys that is now being made available by ESO to astronomers worldwide. UltraVISTA is a treasure trove that is being used to study distant galaxies in the early Universe as well as for many other science projects.

ESO’s VISTA telescope has been trained on the same patch of sky repeatedly to slowly accumulate the very dim light of the most distant galaxies. In total more than six thousand separate exposures with a total effective exposure time of 55 hours, taken through five different coloured filters, have been combined to create this picture. This image from the UltraVISTA survey is the deepest [1] infrared view of the sky of its size ever taken.

Highlights of VISTA’s deep infrared view of the COSMOS field

The VISTA telescope at ESO’s Paranal Observatory in Chile is the world’s largest survey telescope and the most powerful infrared survey telescope in existence. Since it started work in 2009 (eso0949) most of its observing time has been devoted to public surveys, some covering large parts of the southern skies and some more focused on small areas. The UltraVISTA survey has been devoted to the COSMOS field ([2], eso1124, heic0701), an apparently almost empty patch of sky which has already been extensively studied using other telescopes, including the NASA/ESA Hubble Space Telescope [3]. UltraVISTA is the deepest of the six VISTA surveys by far and reveals the faintest objects.

The COSMOS field in the constellation of Sextans

Data from the VISTA surveys —  totalling more than 6 terabytes of images — are now being processed in data centres in the United Kingdom, and in the case of UltraVISTA in France, and are flowing back into the ESO science archive and being made available to astronomers around the world.

Wide-field view of the COSMOS field

At first glance the UltraVISTA image looks unremarkable, a few bright stars and a sprinkling of fainter ones. But in fact almost all of those fainter objects are not stars in the Milky Way, but very remote galaxies, each containing billions of stars. Enlarging the image to fill the screen, and zooming in reveals more and more of them, and the image records more than 200 000 galaxies in total.

The expansion of the Universe shifts light from distant objects towards longer wavelengths. For starlight coming from the most distant galaxies that we can observe, this means that most of the light falls in the infrared part of the spectrum when it gets to Earth. As a highly sensitive infrared telescope with a wide field of view, VISTA is uniquely powerful for spotting distant galaxies in the early Universe. By studying galaxies in redshifted light at successively larger distances, astronomers can also trace how galaxies were built up and evolved over the history of the cosmos.

video
Zooming into VISTA's deep view of the COSMOS field

Close inspection of the picture reveals tens of thousands of previously unknown reddish objects scattered between the more numerous cream-coloured galaxies. These are mostly very remote galaxies seen when the Universe was only a small fraction of its present age. Early studies of the UltraVISTA images, in combination with images from other telescopes, have revealed the presence of many galaxies that are seen when the Universe was less than a billion years old and a few are seen at even earlier times.

Although the current UltraVISTA image is already the deepest infrared image of its size in existence observations are continuing. The final result, a few years from now, will be significantly deeper still.

video
Panning over VISTA's deep view of the COSMOS field

Surveys are vital resources for astronomers and ESO has put in place a programme [4] so that the rich heritage from both VISTA and its visible-light companion, the VLT Survey Telescope (VST, eso1119), will be accessible to astronomers for decades to come.

Notes:

[1] Astronomers use the word deep to mean images taken with very long total exposures that can detect the faintest possible objects. Normally many shorter exposures are taken and later digitally combined.

[2] UltraVISTA has imaged the COSMOS field in the constellation of Sextans (The Sextant). This region of sky has been mapped by a multitude of telescopes so that a series of studies and investigations can benefit from this wealth of data. UltraVISTA covers 1.5 square degrees, about eight times the area of the full Moon and slightly smaller than the full COSMOS field.

[3] The new UltraVISTA observations provide the very deep infrared observations of the COSMOS field that complement observations at different wavelengths of light from other telescopes, both on Earth and in space.

[4] Data from ESO’s telescopes normally goes straight into a huge digital archive. But a new initiative, called Phase 3 is collecting highly processed ESO data from groups of astronomers around Europe and making them available in ready-to-use form. The processing of large astronomical images, such as those from survey telescopes, is challenging and requires major computing resources and specialist expertise. So the provision of fully processed and comprehensively described uniform data, rather than raw data from the telescopes, greatly helps the community to fully exploit the data.

More information:

The year 2012 marks the 50th anniversary of the founding of the European Southern Observatory (ESO). ESO is the foremost intergovernmental astronomy organisation in Europe and the world’s most productive astronomical observatory. It is supported by 15 countries: Austria, Belgium, Brazil, the Czech Republic, Denmark, France, Finland, Germany, Italy, the Netherlands, Portugal, Spain, Sweden, Switzerland and the United Kingdom. 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 the European partner of a revolutionary astronomical telescope ALMA, the largest astronomical project in existence. ESO is currently planning a 40-metre-class European Extremely Large optical/near-infrared Telescope, the E-ELT, which will become “the world’s biggest eye on the sky”.

Links:

    Photos of VISTA: http://www.eso.org/public/images/archive/search/?adv=&subject_name=Visible%20and%20Infrared%20Survey%20Telescope%20for%20Astronomy

    The UltraVISTA project site: http://www.ultravista.org/

    VISTA public data release: http://www.eso.org/sci/archive/VISTA-Public-Release.html

    More information about the COSMOS survey: http://cosmos.astro.caltech.edu/

Images, Text, Credits: ESO / UltraVISTA team. Acknowledgement: TERAPIX/CNRS/ INSU / CASU / IAU and Sky & Telescope/ESO and Digitized Sky Survey 2. Acknowledgement: Davide De Martin/Videos: ESO/A. Fujii / Digitized Sky Survey 2 / UltraVISTA teamESO. Music: John Dyson (from the album Moonwind)/ESO / UltraVISTA team. Acknowledgement: TERAPIX / CNRS / INSU / CASU. Music: John Dyson (from the album Moonwind).

Greetings, Orbiter.ch

mardi 20 mars 2012

NASA'S Swift Narrows Down Origin of Important Supernova Class













NASA - SWIFT Mission patch.

March 20, 2012

Studies using X-ray and ultraviolet observations from NASA's Swift satellite provide new insights into the elusive origins of an important class of exploding star called Type Ia supernovae.


Three types of systems, illustrated here, may host Type Ia supernovae. The first two panels depict a white dwarf in a binary system accumulating matter transferred from a red supergiant companion many times the sun's mass (left) or similar to the sun (middle). The transferred matter is thought to accumulate on the white dwarf and ultimately cause it to explode. Swift data on dozens of supernovae essentially eliminate the first model. Mounting evidence suggests that some Type Ia supernovae occur when binary white dwarfs (right) merge and collide. Credit: NASA/Swift/ Aurore Simonnet, Sonoma State Univ.

These explosions, which can outshine their galaxy for weeks, release large and consistent amounts of energy at visible wavelengths. These qualities make them among the most valuable tools for measuring distance in the universe. Because astronomers know the intrinsic brightness of Type Ia supernovae, how bright they appear directly reveals how far away they are.

"For all their importance, it's a bit embarrassing for astronomers that we don't know fundamental facts about the environs of these supernovae," said Stefan Immler, an astrophysicist at NASA's Goddard Space Flight Center in Greenbelt, Md. "Now, thanks to unprecedented X-ray and ultraviolet data from Swift, we have a clearer picture of what's required to blow up these stars."

Astronomers have known for decades that Type Ia supernovae originate with a remnant star called a white dwarf, which detonates when pushed to a critical mass. The environment that sets the stage for the explosion, however, has been harder to pin down.

According to the most popular scenario, a white dwarf orbits a normal star and pulls a stream of matter from it. This gas flows onto the white dwarf, which gains mass until it reaches a critical threshold and undergoes a catastrophic explosion.


This image combines all Swift X-ray Telescope observations for 53 Type Ia supernovae. The images are stacked to align the supernovae at the center (circled in inset), giving a total effective exposure of 35.3 days -- the deepest-ever X-ray observation of Type Ia supernovae. Unresolved hot gas within the host galaxies produces the diffuse orange glow, while yellow and orange blobs reveal X-ray binaries in the host galaxies as well as foreground stars in our own. No additional X-ray emission is visible at the position of the stacked supernovae, placing strong limits on their host systems. Credit: NASA/Swift/Stefan Immler.

"A missing detail is what types of stars reside in these systems. They may be a mix of stars like the sun or much more massive red- and blue-supergiant stars," said Brock Russell, a physics graduate student at the University of Maryland, College Park, and lead author of the X-ray study.

In a competing model, the supernova arises when two white dwarfs in a binary system eventually spiral inward and collide. Observations suggest both scenarios occur in nature, but no one knows which version happens more often.

Swift's primary mission is to locate gamma-ray bursts, which are more distant and energetic explosions associated with the birth of black holes. Between these bursts, astronomers can use Swift's unique capabilities to study other objects, including newly discovered supernovae. The satellite's X-ray Telescope (XRT) has studied more than 200 supernovae to date, with about 30 percent being Type Ia.

Russell and Immler combined X-ray data for 53 of the nearest known Type Ia supernovae but could not detect an X-ray point source. Stars shed gas and dust throughout their lives. When a supernova shock wave plows into this material, it becomes heated and emits X-rays. The lack of X-rays from the combined supernovae shows that supergiant stars, and even sun-like stars in a later red giant phase, likely aren't present in the host binaries.

In a companion study, a team led by Peter Brown at the University of Utah in Salt Lake City looked at 12 Type Ia events observed by Swift's Ultraviolet/Optical Telescope (UVOT) less than 10 days after the explosion. A supernova shock wave should produce enhanced ultraviolet light as it interacts with its companion, with larger stars producing brighter, longer enhancements. Swift's UVOT detected no such emission, leading the researchers to exclude large, red giant stars from Type Ia binaries.


These images from Swift's Ultraviolet/Optical Telescope (UVOT) show the nearby spiral galaxy M101 before and after the appearance of SN 2011fe (circled, right), which was discovered on Aug. 24, 2011. At a distance of 21 million light-years, it was the nearest Type Ia supernova since 1986 but appeared too late for inclusion in the published studies. Left: View constructed from images taken in March and April 2007. Right: The supernova was so bright that most UVOT exposures were short, so this view includes imagery from August through November 2011 to better show the galaxy. Credit: NASA/Swift/Peter Brown, Univ. of Utah.

Taken together, the studies suggest the companion to the white dwarf is either a smaller, younger star similar to our sun or another white dwarf. The X-ray findings will appear in the April 1 issue of The Astrophysical Journal Letters; the ultraviolet results appear in the April 10 edition of The Astrophysical Journal.

The ultraviolet studies rely on early, sensitive observations. As Brown's study was being written, nature provided a great case study in SN 2011fe, the closest Type Ia supernova since 1986. Early Swift UVOT observations show no ultraviolet enhancement. According to the findings in an unpublished study led also by Brown, this means any companion must be smaller than the sun.

Swift data on SN 2011fe also figure prominently in unpublished studies led by Alicia Soderberg at the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass. Preliminary results suggest that the explosion was caused by merging white dwarfs.

Swift launched in November 2004 and is managed by Goddard. It is operated in collaboration with Pennsylvania State University and other national and international partners.

Related links:

Type Ia Supernovae Typically Lack Sun-Like Companions: http://www.cfa.harvard.edu/news/2012/pr201205.html

Swift Supernovae: http://heasarc.nasa.gov/docs/swift/sne/swift_sn.html

NASA'S Chandra Finds New Evidence on Origin of Supernovas: http://chandra.harvard.edu/photo/2011/tycho2/index.html

NASA's Swift Sees Double Supernova in Galaxy: http://www.nasa.gov/mission_pages/swift/bursts/double_supernova.html

NASA's Swift Satellite Catches First Supernova in the Act of Exploding: http://www.nasa.gov/centers/goddard/news/topstory/2008/swift_supernova.html

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

Greetings, Orbiter.ch

lundi 19 mars 2012

Spider Web of Stars













NASA - SPITZER Space Telescope patch.

March 20, 2012


Looking like a spider's web swirled into a spiral, Galaxy IC 342 presents its delicate pattern of dust in this image from NASA's Spitzer Space Telescope. Seen in infrared light, faint starlight gives way to the glowing bright patterns of dust found throughout the galaxy's disk.

At a distance of about 10 million light-years, IC 342 is relatively close by galactic standards, however our vantage point places it directly behind the disk of our own Milky Way. The intervening dust makes it difficult to see in visible light, but infrared light penetrates this veil easily. IC 342 belongs to the same group as its even more obscured galactic neighbor, Maffei 2.

IC 342 is nearly face-on to our view, giving a clear, top-down view of the structure of its disk. It has a low surface brightness compared to other spirals, indicating a lower density of stars (seen here as a blue haze). Its dust structures show up much more vividly (red). Blue dots are stars closer to us, in our own Milky Way.

New stars are forming in the disk at a healthy rate. The very center glows especially brightly in the infrared, highlighting an enormous burst of star formation occurring in this tiny region. To either side of the center, a small bar of dust and gas is helping to fuel this central star formation.

Data from Spitzer's infrared array camera are shown in blue (3.6 microns), green (4.5 microns) and red (5.8 and 8.0 microns).

For more information about SPITZER Space Telescope, visit: http://www.spitzer.caltech.edu/

Image, Text, Credit: NASA / JPL-Caltech.

Greetings, Orbiter.ch