samedi 14 novembre 2015

‘WT1190F’ Safely Reenters Earth’s Atmosphere, Provides Research Opportunity

Catalina Sky Survey logo.

Nov. 14, 2015

Just after 1:18 AM EST (6:18 AM UTC) on Friday, Nov. 13 an object tagged as WT1190F reentered Earth’s atmosphere as predicted above the Indian Ocean, just off the southern tip of Sri Lanka. The object - most likely man-made space debris from some previous lunar or interplanetary mission – burned up on reentry and was not a threat to anyone on Earth due to its low density and small size (3-6 feet or 1-2 meters).

Image above: Object tagged as ‘WT1190F’ reenters Earth’s atmosphere south of Sri Lanka on Nov. 13, 2015.  Image Credits: IAC/UAE/NASA/ESA.

The object was detected while still on a large elongated orbit about the Earth on Oct. 3 by the Catalina Sky Survey (CSS), one of the NASA-funded asteroid search projects operated by the University of Arizona and located near Tucson.

The U.S. Air Force Space Command had primary responsibility for tracking it, though NASA was also interested in tracking this object because its final trajectory was entering Earth’s atmosphere at an angle more like an asteroid from interplanetary space than of a typical piece of space debris. This event was therefore good to practice some of the procedures that NASA’s Near-Earth Object Observations Program would follow if a small asteroid were on a collision course with Earth.

WT1190F Reentry on 2015 November 13

Video above: Dr. Peter Jenniskens of the SETI Institute, in cooperation with NASA Ames Research Center in California, organized a team of U.S. and German observers to collect data of reentry from an aircraft provided by Abu Dhabi flying nearby over the Indian Ocean. Video Credits: IAC/UAE/NASA/ESA.

Those procedures include detecting and tracking of the object, characterizing its physical parameters, calculating its trajectory with high precision modeling, and delivering accurate predictions to scientists who would like to observe the entry through Earth’s atmosphere.

Related links:

Catalina Sky Survey (CSS):

NASA’s Near-Earth Object Observations Program (NEO):

Image (mentioned), Video (mentioned), Text, Credits: NASA/Tricia Talbert.


vendredi 13 novembre 2015

NASA's Fermi Mission Finds Hints of Gamma-ray Cycle in an Active Galaxy

NASA - Fermi Gamma-ray Space Telescope logo.

Nov. 13, 2015

Astronomers using data from NASA's Fermi Gamma-ray Space Telescope have detected hints of periodic changes in the brightness of a so-called "active" galaxy, whose emissions are powered by a supersized black hole. If confirmed, the discovery would mark the first years-long cyclic gamma-ray emission ever detected from any galaxy, which could provide new insights into physical processes near the black hole.

Fermi Gamma-ray Space Telescope. Image Credit: NASA

"Looking at many years of data from Fermi's Large Area Telescope (LAT), we picked up indications of a roughly two-year-long variation of gamma rays from a galaxy known as PG 1553+113," said Stefano Ciprini, who coordinates the Fermi team at the Italian Space Agency's Science Data Center (ASDC) in Rome. "This signal is subtle and has been seen over less than four cycles, so while this is tantalizing we need more observations."

Supermassive black holes weighing millions of times the sun's mass lie at the hearts of most large galaxies, including our own Milky Way. In about 1 percent of these galaxies, the monster black hole radiates billions of times as much energy as the sun, emission that can vary unpredictably on timescales ranging from minutes to years. Astronomers refer to these as active galaxies.

More than half of the gamma-ray sources seen by Fermi's LAT are active galaxies called blazars, like PG 1553+113. As matter falls toward its supermassive black hole, some subatomic particles escape at nearly the speed of light along a pair of jets pointed in opposite directions. What makes a blazar so bright is that one of these particle jets happens to be aimed almost directly toward us.

"In essence, we are looking down the throat of the jet, so how it varies in brightness becomes our primary tool for understanding the structure of the jet and the environment near the black hole," said Sara Cutini, an astrophysicist at ASDC.

Motivated by the possibility of regular gamma-ray changes, the researchers examined a decade of multiwavelength data. These included long-term optical observations from Tuorla Observatory in Finland, Lick Observatory in California, and the Catalina Sky Survey near Tucson, Arizona, as well as optical and X-ray data from NASA's Swift spacecraft. The team also studied observations from the Owens Valley Radio Observatory near Bishop, California, which has observed PG 1553+113 every few weeks since 2008 as part of an ongoing blazar monitoring program in support of the Fermi mission.

Image above: Fermi observations suggest possible years-long cyclic changes in gamma-ray emission from the blazar PG 1553+113. The graph shows Fermi Large Area Telescope data from August 2008 to July 2015 for gamma rays with energies above 100 million electron volts (MeV). For comparison, visible light ranges between 2 and 3 electron volts. Vertical lines on data points are error bars. Background: One possible explanation for the gamma-ray cycle is an oscillation of the jet produced by the gravitational pull of a second massive black hole, seen at top left in this artist's rendering. Image Credits: NASA's Goddard Space Flight Center/CI Lab.

"The cyclic variations in visible light and radio waves are similar to what we see in high-energy gamma-rays from Fermi," said Stefan Larsson, a researcher at the Royal Institute of Technology in Stockholm and a long-time collaborator with the ASDC team. "The fact that the pattern is so consistent across such a wide range of wavelengths is an indication that the periodicity is real and not just a fluctuation seen in the gamma-ray data."

Ciprini, Cutini, Larsson and their colleagues published the findings in the Nov. 10 edition of The Astrophysical Journal Letters. If the gamma-ray cycle of PG 1553+113 is in fact real, they predict it will peak again in 2017 and 2019, well within Fermi's expected operational lifetime.

The scientists identified several scenarios that could drive periodic emission, including different mechanisms that could produce a years-long wobble in the jet of high-energy particles emanating from the black hole. The most exciting scenario involves the presence of a second supermassive black hole closely orbiting the one producing the jet we observe. The gravitational pull of the neighboring black hole would periodically tilt the inner part of its companion's accretion disk, where gas falling toward the black hole accumulates and heats up. The result would be a slow oscillation of the jet much like that of a lawn sprinkler, which could produce the cyclic gamma-ray changes we observe.   

PG 1553+113 lies in the direction of the constellation Serpens, and its light takes about 5 billion years to reach Earth.

NASA's Fermi Gamma-ray Space Telescope was launched in June 2008. The mission is an astrophysics and particle physics partnership, developed in collaboration with the U.S. Department of Energy and with important contributions from academic institutions and partners in France, Germany, Italy, Japan, Sweden and the United States.

Related links:

The Astrophysical Journal Letters. If the gamma-ray cycle of PG 1553+113:

Fermi Gamma-Ray Space Telescope:

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

Best regards,

NASA's RapidScat Sees OLYMPEX Winds

NASA - ISS-RapidScat Mission logo.

Nov. 13, 2015

A low pressure system in the Pacific Ocean south of Alaska has moved far enough eastward that it is bringing rain and strong winds to the Pacific Northwest where the OLYMPEX field campaign is under way. NASA's RapidScat instrument analyzed those strong coastal winds from space.

On Nov. 12, the RapidScat instrument aboard the International Space Station measured surface winds between 1300 and 1500 UTC (5 a.m. and 7 a.m. PST. The strongest winds were along the north and northwest of Vancouver Island at a rate of 27 meters per second/60.4 mph/97.2 kph. Along the west coast of Washington State where OLYMPEX is occurring, RapidScat saw sustained winds near 18 meters per second/40.2 mph/ 64.8 kph.

RapidScat measures wind speed at the surface which is always lower than speeds at higher altitude. RapidScat is managed by NASA's Jet Propulsion Laboratory in Pasadena, California.

ISS-RapidScat in action. Animation Credit: NASA

The Olympic Mountain Experiment, or OLYMPEX, is a NASA-led field campaign, which will take place on the Olympic Peninsula of Washington State from November 2015 through February 2016. The goal of the campaign is to collect detailed atmospheric measurements that will be used to evaluate how well rain-observing satellites measure rainfall and snowfall from space. In particular, OLYMPEX will be assessing satellite measurements made by the Global Precipitation Measurement (GPM) mission Core Observatory, a joint mission by NASA and the Japan Aerospace Exploration Agency (JAXA), which launched in 2014.

For more information about OLYMPEX, visit:

For more information about ISS-RapidScat, visit:

Image & Animation (mentioned), Text, Credits: NASA/JPL/Doug Tyler/GSFC/Rob Gutro/Rob Garner.


Hubble Views a Lonely Galaxy

NASA - Hubble Space Telescope patch.

Nov. 13, 2015

Only three local stars appear in this image, quartered by right-angled diffraction spikes. Everything besides them is a galaxy; floating like a swarm of microbes in a drop of water, and brought into view here not by a microscope, but by the Advanced Camera for Surveys on the Hubble Space Telescope.

In the foreground, the spiral arms of MCG+01-02-015 seem to wrap around one another, cocooning the galaxy. The scene suggests an abundance of galactic companionship for MCG+01-02-015, but this is a cruel trick of perspective. Instead, MCG+01-02-015’s unsentimental naming befits its position within the cosmos: it is a void galaxy, the loneliest of galaxies.

The vast majority of galaxies are strung out along galaxy filaments — thread-like formations that make up the large-scale structure of the universe — drawn together by the influence of gravity into sinuous threads weaving through space. Between these filaments stretch shallow but immense voids; the universe’s wastelands, where, outside of the extremely rare presence of a galaxy, there is very little matter — about one atom per cubic meter. One such desolate stretch of space is what MCG+01-02-015 reluctantly calls home.

Hubble and the sunrise over Earth

The galaxy is so isolated that if our galaxy, the Milky Way, were to be situated in the same way, we would not even have known of the existence of other galaxies until the development of strong telescopes and detectors in the 1960s.

For images and more information about Hubble, visit: and and

Image, Video, Credits: ESA/Hubble & NASA and N. Gorin (STScI), Acknowledgement: Judy Schmidt/Text Credits: European Space Agency (ESA)/Ashley Morrow.


jeudi 12 novembre 2015

In Greenland, Another Major Glacier Comes Undone

USGS / NASA - Landsat-8 Mission logo.

Nov. 12, 2015

It's big. It's cold. And it's melting into the world’s ocean.

It's Zachariae Isstrom, the latest in a string of Greenland glaciers to undergo rapid change in our warming world. A new NASA-funded study published today in the journal Science finds that Zachariae Isstrom broke loose from a glaciologically stable position in 2012 and entered a phase of accelerated retreat. The consequences will be felt for decades to come.

Animation above: Image time series of Greenland’s Zachariæ Isstrøm glacier as seen by the NASA/USGS Landsat satellite. Retreat of the glacier front is indicated by lines, color-coded from dark green (2003) to light green (2015). Animation Credits: NASA/USGS.

The reason? Zachariae Isstrom is big. It drains ice from an area of 35,440 square miles (91,780 square kilometers). That’s about 5 percent of the Greenland Ice Sheet. All by itself, it holds enough water to raise global sea level by more than 18 inches (46 centimeters) if it were to melt completely. And now it's on a crash diet, losing 5 billion tons of mass every year. All that ice is crumbling into the North Atlantic Ocean.

“North Greenland glaciers are changing rapidly,” said lead author Jeremie Mouginot, an assistant researcher in the Department of Earth System Science at the University of California, Irvine. “The shape and dynamics of Zachariae Isstrom have changed dramatically over the last few years. The glacier is now breaking up and calving high volumes of icebergs into the ocean, which will result in rising sea levels for decades to come.”

Mouginot and his colleagues from NASA's Jet Propulsion Laboratory, Pasadena, California; and the University of Kansas, Lawrence, set out to study the changes taking place at Zachariae Isstrom.

The team used data from aerial surveys conducted by NASA’s Operation IceBridge and satellite-based observations acquired by multiple international space agencies (NASA, ESA, CSA, DLR, JAXA and ASI) coordinated by the Polar Space Task Group. The NASA satellite data used are from the joint NASA/USGS Landsat program. The various tools used -- including a highly sensitive radar sounder, gravimeter and laser profiling systems, coupled with radar and optical images from space -- monitor and record changes in the shape, size and position of glacial ice over long time periods, providing precise data on the state of Earth’s polar regions.

Image above: Landsat-8 image of Greenland’s Zachariae Isstrom and Nioghalvfjerdsfjorden glaciers, acquired on Aug. 30, 2014. Image Credits: NASA/USGS.

The scientists determined the bottom of Zachariae Isstrom is being rapidly eroded by warmer ocean water mixed with growing amounts of meltwater from the ice sheet surface. “Ocean warming has likely played a major role in triggering [the glacier’s] retreat,” Mouginot said, “but we need more oceanographic observations in this critical sector of Greenland to determine its future.”

“Zachariae Isstrom is being hit from above and below,” said the study’s senior author Eric Rignot, Chancellor’s Professor of Earth system science at UCI, and Joint Faculty Appointee at JPL. “The top of the glacier is melting away as a result of decades of steadily increasing air temperatures, while its underside is compromised by currents carrying warmer ocean water, and the glacier is now breaking away into bits and pieces and retreating into deeper ground.”

Adjacent to Zachariae Isstrom is another large glacier, Nioghalvfjerdsfjorden, which is also melting rapidly but is receding at a slower rate because it’s protected by an inland hill. The two glaciers make up 12 percent of the Greenland ice sheet and would boost global sea levels by more than 39 inches (99 centimeters) if they fully collapsed.

The sector where these two glaciers reside is one of three major marine-based basins in Greenland, along with Jakobshavn Isbrae in central west Greenland and the Petermann-Humboldt sector in central north Greenland. The latter two sectors hold enough water to raise global sea level by 2 feet (0.6 meters) each, and both are also undergoing significant changes at present. The authors conclude it is likely that Nioghalvfjerdsfjorden and Petermann-Humboldt glaciers will lose their ice shelves in coming years, further increasing Greenland’s future contributions to global sea level rise.

Image above: Aerial photo of all of lower Zachariae Isstrom glacier taken from aboard a NASA Falcon jet on Sept. 30, 2015. Image Credit: John Sonntag.

“Not long ago, we wondered about the effect on sea levels if Earth’s major glaciers in the polar regions were to start retreating,” Rignot noted. “We no longer need to wonder; for a couple of decades now, we’ve been able to directly observe the results of climate warming on polar glaciers. The changes are staggering and are now affecting the four corners of Greenland.”

In 2015, NASA kicked off a new six-year field campaign, Oceans Melting Greenland, which will examine ocean conditions around Greenland affecting the Ice Sheet. For more information on OMG, visit: 

Ongoing research into the health of ice sheets and glaciers in Greenland and Antarctica is supported by funding from NASA’s Cryospheric Sciences Program.

For more information on the study, visit:

Related links:

NASA’s Cryospheric Sciences Program:

Polar Space Task Group:

NASA’s Operation IceBridge:

Images (mentioned), Text, Credits: NASA/JPL/Alan Buis/Tony Greicius.


35th Anniversary of the Voyager 1 Saturn Flyby

NASA - Voyager 1 & 2 Mission patch.

Nov. 12, 2015

Image above: Artist's concept of the Voyager spacecraft in space. Image Credits: NASA.

On November 12, 1980, 35 years ago, Voyager 1 became the second spacecraft to flyby Saturn. Its main objectives were to conduct close-up studies of Jupiter and Saturn, Saturn’s rings, and the larger moons of the two planets. Built to last 5 years, the spacecraft is in interstellar space today and still operating 38 years after launch.

Voyager 1 launched on September 5, 1977, on a short and fast trajectory toward Jupiter and Saturn aboard the Titan-Centaur III expendable rocket. At the time, our solar system’s outer planets were in a rare geometric arrangement, which only occurs about every 175 years. The advantage of this alignment, is that it allows a spacecraft to swing from one planet to the next without the need for large onboard propulsion systems, also known as the gravity assist technique. Voyager 1 passed Jupiter on March 5, 1979, and Saturn on November 12, 1980. It’s current velocity is about 38,000 miles per hour.

Image above: Voyager 1 color-enhanced image of Saturn taken on October 18, 1980, 25 days before closest approach. Image Credits: NASA/JPL-Caltech.

On its flyby of Saturn, Voyager 1 found an abundance of new data regarding the planet and its moons. Specifically, it found three new moons, Prometheus, Pandora, and Atlas. Prometheus and Pandora are shepherding moons of the F-rings, and Atlas is a shepherd of the A-rings. Finding these moons confirmed that Saturn’s moons are mostly composed of water ice. Most significantly, the spacecraft found new information regarding Saturn’s largest moon, Titan. It found that Titan has a thick atmosphere, which hides its surface from visible-light cameras and telescopes trying to obtain images. In addition, it found that Titan’s atmosphere was mostly composed of nitrogen like the Earth; however, its surface pressure is 1.6 times as high as Earth’s. Similarly, it found Saturn’s upper atmosphere to be composed of 7% helium and the rest mostly made up of hydrogen. Scientists inferred that because of Saturn’s atmospheric composition, Saturn radiates more heat than what it receives from the sun. Voyager 1 also discovered the G-rings of Saturn.

Thirty two years after the encounter with Saturn, in August 2012, Voyager 1 entered interstellar space and became the most distant human-made object in space. Redesignated the Voyager Interstellar Mission (VIM) at this time, the mission was extended to explore the solar system beyond our outer planets. The goals of the new mission were to collect data on the heliopause boundary, the outer limits of the sun’s magnetic field, and the outward flow of solar wind.

Like sister ship Voyager 2, Voyager 1 carries a Golden Record. The 12-inch gold-plated copper disc contains greetings in 60 languages, samples of music from different cultures and eras, and natural and human-made sounds from Earth to communicate the story of Earth in deep space. The disc also contains electronic information that an advanced technological civilization could convert into diagrams and photographs.

Image above: Layers of haze covering Saturn's moon Titan are seen in this image taken by Voyager 1 on November 12, 1980, at a range of 13,700 miles (22,000 kilometers). This false color image shows the details of the haze that covers Titan. The upper level of the thick aerosol above the moon's limb appears orange. Image Credits: NASA/JPL.

Voyager 2 flew by Saturn in August 1981 and the next mission to Saturn was an orbiter that arrived in 2004. The Cassini probe was designed to explore Saturn’s atmosphere, rings, magnetosphere, and moons. It has successfully found geysers on Saturn’s moon Enceladus, evidence that its moon Titan is Earth-like, and Saturn’s rings are active and dynamic. In 2016, Cassini will embark on The Grand Finale where it will fly between Saturn and its rings 22 times, the closest it has ever been to the planet. This more hazardous research will help us learn about Saturn’s gravity and magnetic fields, its rotation, and the composition of its rings. At the end of The Grand Finale, Cassini will plunge into the atmosphere of Saturn and be destroyed.  This step will make sure that the Cassini probe does not accidentally crash on one of the moons of Saturn and (perhaps) contaminate it with microbes from Earth.

For more information about Voyager 1 & 2, visit:

Images (mentioned), Text, Credits: NASA/Betsy Reimer/Yvette Smith.

Best regards,

More Than Meets the Eye: Delta Orionis in Orion's Belt

NASA - Chandra X-ray Observatory patch.

Nov. 12, 2015

One of the most recognizable constellations in the sky is Orion, the Hunter. Among Orion’s best-known features is the “belt,” consisting of three bright stars in a line, each of which can be seen without a telescope.

The westernmost star in Orion’s belt is known officially as Delta Orionis. (Since it has been observed for centuries by sky-watchers around the world, it also goes by many other names in various cultures, like “Mintaka”.) Modern astronomers know that Delta Orionis is not simply one single star, but rather it is a complex multiple star system.

Image above: Delta Orionis is a complex star system that contains five stars in total. Image Credits: X-ray: NASA/CXC/GSFC/M. Corcoran et al.; Optical: Eckhard Slawik.

Delta Orionis is a small stellar group with three components and five stars in total: Delta Ori A, Delta Ori B, and Delta Ori C. Both Delta Ori B and Delta Ori C are single stars and may give off small amounts of X-rays. Delta Ori A, on the other hand, has been detected as a strong X-ray source and is itself a triple star system as shown in the artist’s illustration.

In Delta Ori A, two closely separated stars orbit around each other every 5.7 days, while a third star orbits this pair with a period of over 400 years. The more massive, or primary, star in the closely-separated stellar pair weighs about 25 times the mass of the Sun, whereas the less massive, or secondary star, weighs about ten times the mass of the Sun.

Image above: This artist's illustration depicts the system of Delta Orionis A. Image Credits: NASA/CXC/M.Weiss.

The chance alignment of this pair of stars allows one star to pass in front of the other during every orbit from the vantage point of Earth. This special class of star system is known as an “eclipsing binary,” and it gives astronomers a direct way to measure the mass and size of the stars.

Massive stars, although relatively rare, can have profound impacts on the galaxies they inhabit. These giant stars are so bright that their radiation blows powerful winds of stellar material away, affecting the chemical and physical properties of the gas in their host galaxies. These stellar winds also help determine the fate of the stars themselves, which will eventually explode as supernovas and leave behind a neutron star or black hole.

By observing this eclipsing binary component of Delta Orionis A (dubbed Delta Ori Aa) with NASA’s Chandra X-ray Observatory for the equivalent of nearly six days, a team of researchers gleaned important information about massive stars and how their winds play a role in their evolution and affect their surroundings. The Chandra image is seen in the inset box in context with an optical view of the Orion constellation obtained from a ground-based telescope.

Since Delta Ori Aa is the nearest massive eclipsing binary, it can be used as a decoder key for understanding the relation between the stellar properties derived from optical observations, and the properties of the wind, which are revealed by X-ray emission.

The lower-mass companion star in Delta Ori Aa has a very weak wind and is very faint in X-rays.  Astronomers can use Chandra to watch as the companion star blocks out various parts of the wind of the more massive star. This allows scientists to better see what happens to the X-ray emitting gas surrounding the primary star, helping to answer the long-standing question of where in the stellar wind the X-ray emitting gas is formed.  The data show that most of the X-ray emission comes from the wind of the giant star, and is likely produced by shocks resulting from collisions between rapidly-moving clumps of gas embedded within the wind.

The researchers also found that the X-ray emission from certain atoms in the wind of Delta Ori Aa changes as the stars in the binary move around. This may be caused by collisions between winds from the two stars, or from a collision of the wind from the primary star with the surface of the secondary star. This interaction, in turn, obstructs some of the wind from the brighter star.

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

Parallel optical data from the Canadian Space Agency’s Microvariability and Oscillation of Stars Telescope (MOST) revealed evidence for oscillations of the primary star produced by tidal interactions between the primary and companion star as the stars travel in their orbits.  Measurements of the changes of brightness in optical light plus detailed analysis of optical and ultraviolet spectra were used to refine the parameters of the two stars. The researchers were also able to resolve some previously claimed inconsistencies between the stellar parameters and models of how the stars are expected to evolve with time.

These results were published in four coordinated papers that were recently published in The Astrophysical Journal led by Michael Corcoran (NASA’s Goddard Space Flight Center & Universities Space Research Association), Joy Nichols (Harvard-Smithsonian Center for Astrophysics), Herbert Pablo (University of Montreal), and Tomer Shenar (University of Potsdam). 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/Marshall Space Flight Center/Molly Porter/Lee Mohon.


Fermi Satellite Detects First Gamma-ray Pulsar in Another Galaxy

NASA - Fermi Gamma-ray Space Telescope logo.

Nov. 12, 2015

Researchers using NASA's Fermi Gamma-ray Space Telescope have discovered the first gamma-ray pulsar in a galaxy other than our own. The object sets a new record for the most luminous gamma-ray pulsar known.


Fermi Detects First Gamma-ray Pulsar in Another Galaxy

Video above: Explore Fermi's discovery of the first gamma-ray pulsar detected in a galaxy other than our own. Video Credits: NASA's Goddard Space Flight Center.

The pulsar lies in the outskirts of the Tarantula Nebula in the Large Magellanic Cloud, a small galaxy that orbits our Milky Way and is located 163,000 light-years away. The Tarantula Nebula is the largest, most active and most complex star-formation region in our galactic neighborhood. It was identified as a bright source of gamma rays, the highest-energy form of light, early in the Fermi mission. Astronomers initially attributed this glow to collisions of subatomic particles accelerated in the shock waves produced by supernova explosions.  

"It's now clear that a single pulsar, PSR J0540-6919, is responsible for roughly half of the gamma-ray brightness we originally thought came from the nebula," said lead scientist Pierrick Martin, an astrophysicist at the National Center for Scientific Research (CNRS) and the Research Institute in Astrophysics and Planetology in Toulouse, France. "That is a genuine surprise."

Image above: NASA's Fermi Gamma-ray Space Telescope has detected the first extragalactic gamma-ray pulsar, PSR J0540-6919, near the Tarantula Nebula (top center) star-forming region in the Large Magellanic Cloud, a satellite galaxy that orbits our own Milky Way. Fermi detects a second pulsar (right) as well but not its pulses. PSR J0540-6919 now holds the record as the highest-luminosity gamma-ray pulsar. The angular distance between the pulsars corresponds to about half the apparent size of a full moon. Background: An image of the Tarantula Nebula and its surroundings in visible light. Image Credits: NASA's Goddard Space Flight Center; background: ESO/R. Fosbury (ST-ECF).

When a massive star explodes as a supernova, the star's core may survive as a neutron star, where the mass of half a million Earths is crushed into a magnetized ball no larger than Washington, D.C. A young isolated neutron star spins tens of times each second, and its rapidly spinning magnetic field powers beams of radio waves, visible light, X-rays and gamma rays. If the beams sweep past Earth, astronomers observe a regular pulse of emission and the object is classified as a pulsar.

The Tarantula Nebula was known to host two pulsars, PSR J0540-6919 (J0540 for short) and PSR J0537−6910 (J0537), which were discovered with the help of NASA's Einstein and Rossi X-ray Timing Explorer (RXTE) satellites, respectively. J0540 spins just under 20 times a second, while J0537 whirls at nearly 62 times a second -- the fastest-known rotation period for a young pulsar.

Nevertheless, it took more than six years of observations by Fermi's Large Area Telescope (LAT), as well as a complete reanalysis of all LAT data in a process called Pass 8, to detect gamma-ray pulsations from J0540. The Fermi data establish upper limits for gamma-ray pulses from J0537 but do not yet detect them.

Martin and his colleagues present these findings in a paper to be published in the Nov. 13 edition of the journal Science.

"The gamma-ray pulses from J0540 have 20 times the intensity of the previous record-holder, the pulsar in the famous Crab Nebula, yet they have roughly similar levels of radio, optical and X-ray emission," said coauthor Lucas Guillemot, at the Laboratory for Physics and Chemistry of Environment and Space, operated by CNRS and the University of Orléans in France. "Accounting for these differences will guide us to a better understanding of the extreme physics at work in young pulsars."

Image above: A gamma-ray view of the same region shown above in visible wavelengths. Lighter colors indicate greater numbers of gamma rays with energies between 2 and 200 billion electron volts. For comparison, visible light ranges between 2 and 3 electron volts. The two pulsars, PSR J0540−6919 (left) and PSR J0537−6910, clearly stand out. Image Credits: NASA/DOE/Fermi LAT Collaboration.

J0540 is a rare find, with an age of roughly 1,700 years, about twice that of the Crab Nebula pulsar. By contrast, most of the more than 2,500 known pulsars are from 10,000 to hundreds of millions of years old.

Despite J0540's luminosity, too few gamma rays reach the LAT to detect pulsations without knowing the period in advance. This information comes from a long-term X-ray monitoring campaign using RXTE, which recorded both pulsars from the start of the Fermi mission to the end of 2011, when RXTE operations ceased.

"This campaign began as a search for a pulsar created by SN 1987A, the closest supernova seen since the invention of the telescope," said co-author Francis Marshall, an astrophysicist at NASA's Goddard Space Flight Center in Greenbelt, Maryland. "That search failed, but it discovered J0537."

Prior to the launch of Fermi in 2008, only seven gamma-ray pulsars were known. To date, the mission has found more than 160.

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

Related links:

Rossi X-ray Timing Explorer (RXTE) satellite:

NASA's Einstein satellite:

Fermi Gamma-Ray Space Telescope:


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


Rosetta and Philae: one year since landing on a comet

ESA - Rosetta Mission patch.

12 November 2015

One year since Philae made its historic landing on a comet, mission teams remain hopeful for renewed contact with the lander, while also looking ahead to next year’s grand finale: making a controlled impact of the Rosetta orbiter on the comet.

Rosetta arrived at Comet 67P/Churyumov–Gerasimenko on 6 August 2014, and after an initial survey and selection of a landing site, Philae was delivered to the surface on 12 November.

Reconstructing Philae’s flight

After touching down in the Agilkia region as planned, Philae did not secure itself to the comet, and it bounced to a new location in Abydos. Its flight across the surface is depicted in a new animation, using data collected by Rosetta and Philae to reconstruct the lander’s rotation and attitude.

In the year since landing, a thorough analysis has also now been performed on why Philae bounced.

There were three methods to secure it after landing: ice screws, harpoons and a small thruster. The ice screws were designed with relatively soft material in mind, but Agilkia turned out to be very hard and they did not penetrate the surface.

The harpoons were capable of working in both softer and harder material. They were supposed to fire on contact and lock Philae to the surface, while a thruster on top of the lander was meant to push it down to counteract the recoil from the harpoon.

Agilkia mosaic, labelled

Attempts to arm the thruster the night before failed: it is thought that a seal did not open, although a sensor failure cannot be excluded.

Then, on landing, the harpoons themselves did not fire. “It seems that the problem was either with the four ‘bridge wires’ taking current to ignite the explosive that triggers the harpoons, or the explosive itself, which may have degraded over time,” explains Stephan Ulamec, Philae lander manager at the DLR German Aerospace Center.

“In any case, if we can regain contact with Philae, we might consider an attempt to retry the firing.”

The reason is scientific: the harpoons contain sensors that could measure the temperature below the surface.

Despite the unplanned bouncing, Philae completed 80% of its planned first science sequence before falling into hibernation in the early hours of 15 November when the primary battery was exhausted. There was not enough sunlight in Philae’s final location at Abydos to charge the secondary batteries and continue science measurements.

The sound of Philae hammering

The hope was that as the comet moved nearer to the Sun, heading towards closest approach in August, there would be enough energy to reactivate Philae. Indeed, contact was made with the lander on 13 June but only eight intermittent contacts were made up to 9 July.

The problem was that the increasing sunlight also led to increased activity on the comet, forcing Rosetta to retreat to several hundred kilometres for safety, well out of range with Philae.

However, over the past few weeks, with the comet’s activity now subsiding, Rosetta has started to approach again. This week it reached 200 km, the limit for making good contact with Philae, and today it dips to within 170 km.

In the meantime, the lander teams have continued their analysis of the data returned during the contacts in June and July, hoping to understand the status of Philae when it first woke up from hibernation.

“We had already determined that one of Philae’s two receivers and one of the two transmitters were likely no longer working,” says Koen Geurts, Philae’s technical manager at DLR’s Lander Control Centre in Cologne, Germany, “and it now seems that the other transmitter is suffering problems. Sometimes it did not switch on as expected, or it switched off too early, meaning that we likely missed possible contacts.”

Philae's descent: The director's cut

The team is taking this new information into account to determine the most promising strategy to regain regular contact.

But it’s a race against time: with the comet now heading out beyond the orbit of Mars, temperatures are falling.

“We think we have until the end of January before the lander’s internal temperature gets too cold to operate: it cannot work below –51ºC,” adds Koen.

Meanwhile, Rosetta continues to return unique data with its suite of instruments, analysing changes to the comet’s surface, atmosphere and plasma environment in incredible detail.

“We recently celebrated our first year at the comet and we are looking forward to the scientific discoveries the next year will bring,” says Matt Taylor, ESA’s Rosetta project scientist.

“Next year, we plan to do another far excursion, this time through the comet’s tail and out to 2000 km. To complement that, we hope to make some very close flybys towards the end of the mission, as we prepare to put the orbiter down on the comet.”

Comet on 31 October 2015 – NavCam

The plan is to end the mission with a ‘controlled impact’ of Rosetta on the surface. This idea emerged around six months ago, when an extension of operations from December 2015 to September 2016 was announced.

The solar-powered Rosetta will no longer receive enough sunlight to operate as the comet recedes from the Sun, out beyond the orbit of Jupiter on its 6.5-year circuit. It will travel even further out than during the previous 31 months of deep-space hibernation that ended in January 2014.

In addition, as seen from Earth next September, Rosetta and the comet will look very close to the Sun, making the relay of both scientific data and operational commands very difficult.

The Rosetta teams are now investigating the manoeuvres needed for operating close to the comet in the weeks leading up to the dramatic mission finale.

“We are still discussing exactly what the final end of mission scenario will involve,” says Sylvain Lodiot, ESA’s Rosetta spacecraft operations manager. “It is very complex and challenging, even more so even than the lander delivery trajectory our flight dynamics teams had to plan for delivering Philae.

“The schedule we’re looking at would first involve a move into highly elliptical orbits – perhaps as low as 1 km – in August, before moving out to a more distant point for a final approach that will set Rosetta on a slow collision course with the comet at the end of September.”

It is expected that science observations would continue throughout and up to almost the end of mission, allowing Rosetta’s instruments to gather unique data at unprecedentedly close distances.

“We’ll control Rosetta all the way down to the end, but once on the surface it will be highly improbable that we’ll be able to ‘speak’ to it anymore,” adds Sylvain.

“Landing Rosetta on a comet will be a fitting ending to this incredible mission,” says Patrick Martin, ESA’s Rosetta mission manager.

Further information:

Background information regarding landing Rosetta on the comet: From one comet landing to another: planning Rosetta’s grand finale:

More about the new animation: Reconstructing Philae's flight across the comet:

More about the SESAME-CASSE experiment that 'listened' to MUPUS hammer the surface of the comet: The sound of Philae conducting science:

About Rosetta:

Rosetta is an ESA mission with contributions from its Member States and NASA. Rosetta’s Philae lander was provided by a consortium led by DLR, MPS, CNES and ASI.

Related links:

Rosetta Mission:

Rosetta at Astrium:

Rosetta at DLR:

Ground-based comet observation campaign:

ESA Rosetta blog:

Images, Text, Credits: ESA/Rosetta/NavCam/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA/Philae/SESAME/DLR (CC BY-SA IGO 3.0)/The video was prepared with inputs from the ROMAP, RPC-MAG, OSIRIS, ROLIS, CIVA CONSERT, SESAME and MUPUS instrument teams, and with lander house keeping data from the Lander Control Centre at DLR/Original descent sequence images: ESA/Rosetta/Philae/ROLIS/DLR, Stefano Mottola - Sequence interpolation and editing: Jakub Knapik, Platige Image - Music: “Saline” (instrumental version), from “Experiments in Mass Appeal”, Frost*/Jem Godfrey - Overall movie editing: Sarah Poletti and Marc Thiebaut (ATG/medialab for ESA).

Best regards,

mercredi 11 novembre 2015

UN agrees new global flight tracking procedures

UN - United Nations logo.

Nov. 11, 2015

UN agrees new global flight tracking procedures. Video Credit: Euronews

Identify aircraft around the world in 2017, it is the objective of the agreement sealed Wednesday in the UN.

The experts meeting at the World Radiocommunication Conference in Geneva (Switzerland) decided to allocate spectrum to satellites that can receive signals from aircraft. Today 70% of the land surface (oceans, deserts, mountains) does not allow this monitoring.

Concretely, experts gathered in Geneva decided to allocate the frequency band 1 087.7 ​​to 1 092.3 MHz to the aeronautical mobile-satellite (Earth-to-space) for receiving satellite space stations by signal emissions called ADS-B (automatic dependent surveillance broadcast) from aircraft transmitters, the ITU (International Telecommunications Union) said in a statement. The information is then automatically sent to ground stations in charge of air traffic control.

Image above: ADS-B (automatic dependent surveillance broadcast) Air Traffic Management by satellites. Image Credit: ESA.

The agreement will be in place by the International Civil Aviation Organization (ICAO).

After the still unsolved disappearance of Malaysia Airlines Flight MH370, civil aviation authorities were under further pressure to adopt new tracking guidelines. These will include aircraft sending their position at least every 15 minutes, or more in case of emergency.

Related links:

ADS-B Technologies Website:

(PDF file) Automatic Dependent Surveillance Broadcast (ADS-B):

Image (mentioned), Video (mentioned), Text, Credits: AFP/Euronews/Translation: Aerospace.


Secondhand Spacecraft Has Firsthand Asteroid Experience

NASA - NEO WISE Mission logo.

Nov. 11, 2015

Since it began operations in December 2009, NASA’s NEOWISE mission has observed 158,000 asteroids and discovered more than 35,000.

The NEOWISE mission hunts for near-Earth objects (NEOs) using the Wide-field Infrared Survey Explorer (WISE) spacecraft. Funded by NASA’s NEO Observations Program, the NEOWISE mission uses images taken by the spacecraft to look for asteroids and comets, providing a rich source of measurements of solar system objects at infrared wavelengths. These measurements include wavelengths that are difficult or impossible to detect directly from the ground.

NEOWISE is one of 54 ongoing projects supported by the NEO Observations Program in fiscal year 2015. NASA-funded survey projects have found 98 percent of the known catalogue of more than 13,000 NEOs. NASA-funded surveys are currently finding NEOs at a rate of about 1,500 per year.

Wide-field Infrared Survey Explorer (WISE) spacecraft. Image Credit: NASA

The NEOWISE mission uses a repurposed NASA spacecraft to find and characterize asteroids. Launched in December 2009, WISE was tasked with documenting in infrared light some of the most remote objects in not only our galaxy, but our universe. Less than two years later, WISE had done just that, scanning the entire sky not once, but twice. From galaxies, to stars, to black holes, WISE collected data on over 750 million celestial targets of interest. With its mission a complete success after a year of operations, WISE was put into hibernation. In December 2014, the space telescope was revived with an updated mission and a new name. Its job was to find and collect the infrared signatures on some of our closest celestial neighbors – asteroids, comets and near-Earth objects. Now led by Principal Investigator Amy Mainzer of NASA's Jet Propulsion Laboratory in Pasadena, Calif., the mission was named Near-Earth Object WISE, or NEOWISE.

As an infrared telescope, NEOWISE sees the heat emitted from celestial bodies. Although it’s common to think of objects in space as very cold, our sun warms the surfaces of asteroids, making them glow brightly in NEOWISE images. Even asteroids as dark as black ink, which can be difficult to see against the darkness of space in visible wavelengths, can be spotted by NEOWISE's camera.

"Using visible wavelengths of light, it is difficult to tell if an asteroid is big and dark, or bright and small, because both combinations reflect the same amount of light," said Carrie Nugent, a NEOWISE scientist at the Infrared Processing and Analysis Center at California Institute of Technology, in Pasadena. "But when you look at an asteroid in the infrared with NEOWISE, the amount of infrared light corresponds with how big the asteroid is, and with some thermal models on a computer, you can figure out how big the asteroids are."

With these thermal models, the NEOWISE team has measured the size and brightness of about 20 percent of the known asteroid population. In the first year since reactivation, Nugent and the NEOWISE team have made these measurements for almost 8,000 asteroids, including 201 near-Earth asteroids.

"When WISE rolled off the assembly line, it was like a shiny new car with all the latest technology," said Nugent. "Now it's like that first car you get out of school -- more vintage than new and with a lot of miles on the odometer. But NEOWISE is giving us great data and experience behind the wheel and reminding us every day how powerful infrared space telescopes are for finding and studying asteroids."

NEOWISE snaps an infrared image of the sky every 11 seconds from its orbit around Earth. Outside of Earth's atmosphere, it always has a clear view of the night sky. NEOWISE's orbit was designed so that the telescope never sees the sun. Although a person may not like the idea of living in darkness, this is perfect for NEOWISE, since too much light would damage its sensitive sensors.

Although NEOWISE has been a reliable workhorse operating long past its planned lifetime, its mission will eventually come to an end. The spacecraft's orbit is changing, and sometime in 2017, engineers estimate it will move into too much sunlight to function. However, the team is eyeing a new space telescope, one with a little more muscle. NEOWISE Principal Investigator Amy Mainzer led a proposal for a new asteroid-hunting spacecraft, the Near-Earth Object Camera (NEOCam). Unlike NEOWISE, NEOCam is specifically designed to hunt asteroids. NEOCam is one of five Discovery-class proposals funded for further study this year by NASA.

"There's so much left to discover when it comes to asteroids," said Nugent. "And the NEOWISE mission is a great asset for learning more about our closest extraterrestrial neighbors."

More information about the NEOWISE mission is at:

More information about the NEOCam proposal is at:

Image (mentioned), Text, Credits: NASA/JPL/DC Agle/Tony Greicius.


Curiosity - Upgrade Helps NASA Study Mineral Veins on Mars

NASA - Mars Science Laboratory (MSL) logo.

Nov. 11, 2015

Image above: Looking Up at Mars Rover Curiosity in 'Buckskin' Selfie. Image Credits: NASA/JPL-Caltech/MSSS.

Scientists now have a better understanding about a site with the most chemically diverse mineral veins NASA's Curiosity rover has examined on Mars, thanks in part to a valuable new resource scientists used in analyzing data from the rover.

Image above: This March 27, 2015, view from the Mast Camera (Mastcam) on NASA's Curiosity Mars rover shows a site with a network of prominent mineral veins below a cap rock ridge on lower Mount Sharp. At this "Garden City" site, the veins have been more resistant to erosion than the surrounding host rock. Image Credits: NASA/JPL-Caltech/MSSS.

Curiosity examined bright and dark mineral veins in March 2015 at a site called "Garden City," where some veins protrude as high as two finger widths above the eroding bedrock in which they formed.

The diverse composition of the crisscrossing veins points to multiple episodes of water moving through fractures in the bedrock when it was buried. During some wet periods, water carried different dissolved substances than during other wet periods. When conditions dried, fluids left clues behind that scientists are now analyzing for insights into how ancient environmental conditions changed over time.

Image above: Prominent mineral veins at the "Garden City" site examined by NASA's Curiosity Mars rover vary in thickness and brightness, as seen in this image from Curiosity's Mast Camera (Mastcam). The image covers and area roughly 2 feet across. Image Credits: NASA/JPL-Caltech/MSSS.

"These fluids could be from different sources at different times," said Diana Blaney, a Curiosity science team member at NASA's Jet Propulsion Laboratory, Pasadena, California. "We see crosscutting veins with such diverse chemistry at this localized site. This could be the result of distinct fluids migrating through from a distance, carrying chemical signatures from where they'd been."

Researchers used Curiosity's laser-firing Chemistry and Camera (ChemCam) instrument to record the spectra of sparks generated by zapping 17 Garden City targets with the laser. The unusually diverse chemistry detected at Garden City includes calcium sulfate in some veins and magnesium sulfate in others. Additional veins were found to be rich in fluorine or varying levels of iron.

Images above: These images and overlay bar charts from the Chemistry and Camera (ChemCam) instrument on NASA's Curiosity Mars rover indicate where some high-potassium material is localized within mineral veins at "Garden City." Images Credits: NASA/JPL Caltech/LANL/CNES/IRAP/LPGNantes/CNRS/IAS.

As researchers analyzed Curiosity's observations of the veins, the ChemCam team was completing the most extensive upgrade to its data-analysis toolkit since Curiosity reached Mars in August 2012. They more than tripled -- to about 350 -- the number of Earth-rock geochemical samples examined with a test version of ChemCam. This enabled an improvement in their data interpretation, making it more sensitive to a wider range of possible composition of Martian rocks.

Blaney said, "The chemistry at Garden City would have been very enigmatic if we didn't have this recalibration."

The Garden City site is just uphill from a mudstone outcrop called "Pahrump Hills," which Curiosity investigated for about six months after reaching the base of multi-layered Mount Sharp in September 2014. The mission is examining ancient environments that offered favorable conditions for microbial life, if Mars has ever hosted any, and the changes from those environments to drier conditions that have prevailed on Mars for more than 3 billion years. Curiosity has found evidence that base layers of Mount Sharp were deposited in lakes and rivers. The wet conditions recorded by the Garden City veins existed in later eras, after the mud deposited in lakes had hardened into rock and cracked.

Image above: This view from the Mars Hand Lens Imager (MAHLI) on the arm of NASA's Curiosity Mars rover shows texture within a light-toned vein at a site called "Garden City" on lower Mount Sharp. Image Credits: NASA/JPL-Caltech/MSSS.

Eye-catching geometry revealed in images of the veins offers additional clues. Younger veins continue uninterrupted across intersections with veins that formed earlier, indicating relative ages.

ChemCam provides the capability of making distinct composition readings of multiple laser targets close together on different veins, rather than lumping the information together. The chemistry of these veins is also related to mineral alteration observed at other places on and near Mount Sharp. What researchers learned here can be used to help understand a very complex fluid chemical history in the region. Since leaving Garden City, Curiosity has climbed to higher, younger layers of Mount Sharp.

Image above: This view from the Mars Hand Lens Imager (MAHLI) on the arm of NASA's Curiosity Mars rover shows a combination of dark and light material within a mineral vein at a site called "Garden City" on lower Mount Sharp. The image was taken on April 4, 2015, and covers an area roughly 1 inch wide. Image Credits: NASA/JPL-Caltech/MSSS.

Today, Blaney presented findings from ChemCam's Garden City investigations at the annual meeting of the American Astronomical Society's Division for Planetary Science, in National Harbor, Maryland.

Image above: Light material emplaced within darker vein material is seen in this view of a mineral vein at the "Garden City" site on lower Mount Sharp, Mars. The Mars Hand Lens Imager (MAHLI) on the arm of NASA's Curiosity Mars Rover took the image on April 4, 2015. The area shown is roughly 0.4 inch wide. Image Credits: NASA/JPL-Caltech/MSSS.

The U.S. Department of Energy's Los Alamos National Laboratory in Los Alamos, New Mexico, developed ChemCam in partnership with scientists and engineers funded by the French national space agency. More information is available at:

NASA's Jet Propulsion Laboratory built Curiosity and manages the project for NASA's Science Mission Directorate in Washington. For more the mission, visit:

You can follow the mission on Facebook and Twitter at:

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

Best regards,

Cassini Finds Monstrous Ice Cloud in Titan’s South Polar Region

NASA / ESA - Cassini-Huygens Mission to Saturn & Titan patch.

Nov. 11, 2015

New observations made near the south pole of Titan by NASA’s Cassini spacecraft add to the evidence that winter comes in like a lion on this moon of Saturn.

Scientists have detected a monstrous new cloud of frozen compounds in the moon’s low- to mid-stratosphere – a stable atmospheric region above the troposphere, or active weather layer.

Image above: As winter sets in at Titan’s south pole, a cloud system called the south polar vortex (small, bright “button”) has been forming, as seen in this 2013 image. Image Credits: NASA/JPL-Caltech/Space Science Institute.

Cassini’s camera had already imaged an impressive cloud hovering over Titan’s south pole at an altitude of about 186 miles (300 kilometers). However, that cloud, first seen in 2012, turned out to be just the tip of the iceberg. A much more massive ice cloud system has now been found lower in the stratosphere, peaking at an altitude of about 124 miles (200 kilometers).

The new cloud was detected by Cassini’s infrared instrument – the Composite Infrared Spectrometer, or CIRS – which obtains profiles of the atmosphere at invisible thermal wavelengths. The cloud has a low density, similar to Earth’s fog but likely flat on top.

For the past few years, Cassini has been catching glimpses of the transition from fall to winter at Titan’s south pole – the first time any spacecraft has seen the onset of a Titan winter. Because each Titan season lasts about 7-1/2 years on Earth’s calendar, the south pole will still be enveloped in winter when the Cassini mission ends in 2017.

“When we looked at the infrared data, this ice cloud stood out like nothing we’ve ever seen before,” said Carrie Anderson of NASA’s Goddard Space Flight Center in Greenbelt, Maryland. “It practically smacked us in the face.”

Image above: This 2012 close-up offers an early snapshot of the changes taking place at Titan’s south pole. Cassini’s camera spotted this impressive cloud hovering at an altitude of about 186 miles (300 kilometers). Cassini’s thermal infrared instrument has now detected a massive ice cloud below it. Image Credits: NASA/JPL-Caltech/Space Science Institute.

Anderson is presenting the findings at the annual Meeting of the Division of Planetary Sciences of the American Astronomical Society at National Harbor, Maryland, on Nov. 11.

The ice clouds at Titan’s pole don’t form in the same way as Earth’s familiar rain clouds.

For rain clouds, water evaporates from the surface and encounters cooler temperatures as it rises through the troposphere. Clouds form when the water vapor reaches an altitude where the combination of temperature and air pressure is right for condensation. The methane clouds in Titan’s troposphere form in a similar way.

However, Titan’s polar clouds form higher in the atmosphere by a different process. Circulation in the atmosphere transports gases from the pole in the warm hemisphere to the pole in the cold hemisphere. At the cold pole, the warm air sinks, almost like water draining out of a bathtub, in a process known as subsidence.

The sinking gases – a mixture of smog-like hydrocarbons and nitrogen-bearing chemicals called nitriles – encounter colder and colder temperatures on the way down. Different gases will condense at different temperatures, resulting in a layering of clouds over a range of altitudes.

Cassini arrived at Saturn in 2004 – mid-winter at Titan’s north pole. As the north pole has been transitioning into springtime, the ice clouds there have been disappearing. Meanwhile, new clouds have been forming at the south pole. The build-up of these southern clouds indicates that the direction of Titan’s global circulation is changing.

“Titan's seasonal changes continue to excite and surprise," said Scott Edgington, Cassini deputy project scientist at NASA's Jet Propulsion Laboratory (JPL) in Pasadena, California. "Cassini, with its very capable suite of instruments, will continue to periodically study how changes occur on Titan until its Solstice mission ends in 2017.”

The size, altitude and composition of the polar ice clouds help scientists understand the nature and severity of Titan’s winter. From the ice cloud seen earlier by Cassini’s camera, scientists determined that temperatures at the south pole must get down to at least -238 degrees Fahrenheit (-150 degrees Celsius).

Image above: Artist's interpretation of Cassini spacecraft transmitting data to Earth after Titan flyby. Image Credit: NASA/ /JPL-Caltech.

The new cloud was found in the lower stratosphere, where temperatures are even colder. The ice particles are made up of a variety of compounds containing hydrogen, carbon and nitrogen.

Anderson and her colleagues had found the same signature in CIRS data from the north pole, but in that case, the signal was much weaker. The very strong signature of the south polar cloud supports the idea that the onset of winter is much harsher than the end.

“The opportunity to see the early stages of winter on Titan is very exciting,” said Robert Samuelson, a Goddard researcher working with Anderson. “Everything we are finding at the south pole tells us that the onset of southern winter is much more severe than the late stages of Titan’s northern winter.”

The Cassini-Huygens mission is a cooperative project of NASA, ESA (European Space Agency) and the Italian Space Agency. JPL manages the mission for NASA's Science Mission Directorate in Washington. The CIRS team is based at Goddard.

For more information about Cassini, visit:

Images (mentioned), Text, Credits: NASA’s Goddard Space Flight Center/Elizabeth Zubritsky/JPL/Preston Dyches/Ashley Morrow.


The Glowing Halo of a Zombie Star

ESO - European Southern Observatory logo.

11 November 2015

VLT maps out remains of white dwarf’s meal

Artist’s impression of the glowing disc of material around the white dwarf SDSS J1228+1040

The remains of a fatal interaction between a dead star and its asteroid supper have been studied in detail for the first time by an international team of astronomers using the Very Large Telescope at ESO’s Paranal Observatory in Chile. This gives a glimpse of the far-future fate of the Solar System.

Led by Christopher Manser, a PhD student at the University of Warwick in the United Kingdom, the team used data from ESO’s Very Large Telescope (VLT) and other observatories to study the shattered remains of an asteroid around a stellar remnant — a white dwarf called SDSS J1228+1040 [1].

Artist’s impression comparing the disc of material around SDSS J1228+1040 and Saturn

Using several instruments, including the Ultraviolet and Visual Echelle Spectrograph (UVES) and X-shooter, both attached to the VLT, the team obtained detailed observations of the light coming from the white dwarf and its surrounding material over an unprecedented period of twelve years between 2003 and 2015. Observations over periods of years were needed to probe the system from multiple viewpoints [2].

“The image we get from the processed data shows us that these systems are truly disc-like, and reveals many structures that we cannot detect in a single snapshot,” explained lead author Christopher Manser.

The team used a technique called Doppler tomography — similar in principle to medical tomographic scans of the human body — which allowed them to map out in detail the structure of the glowing gaseous remains of the dead star’s meal orbiting J1228+1040 for the first time.

The motions of the material around the white dwarf SDSS J1228+1040

While large stars — those more massive than around ten times the mass of the Sun — suffer a spectacularly violent climax as a supernova explosion at the ends of their lives, smaller stars are spared such dramatic fates. When stars like the Sun come to the ends of their lives they exhaust their fuel, expand as red giants and later expel their outer layers into space. The hot and very dense core of the former star — a white dwarf — is all that remains.

But would the planets, asteroids and other bodies in such a system survive this trial by fire? What would be left? The new observations help to answer these questions.

It is rare for white dwarfs to be surrounded by orbiting discs of gaseous material — only seven have ever been found. The team concluded that an asteroid had strayed dangerously close to the dead star and been ripped apart by the immense tidal forces it experienced to form the disc of material that is now visible.

The orbiting disc was formed in similar ways to the photogenic rings seen around planets closer to home, such as Saturn. However, while J1228+1040 is more than seven times smaller in diameter than the ringed planet, it has a mass over 2500 times greater. The team learned that the distance between the white dwarf and its disc is also quite different — Saturn and its rings could comfortably sit in the gap between them [3].

Artist’s impression of the glowing disc of material around the white dwarf SDSS J1228+1040

The new long-term study with the VLT has now allowed the team to watch the disc precess under the influence of the very strong gravitational field of the white dwarf. They also find that the disc is somewhat lopsided and has not yet become circular.

“When we discovered this debris disc orbiting the white dwarf back in 2006, we could not have imagined the exquisite details that are now visible in this image, constructed from twelve years of data — it was definitely worth the wait,” added Boris Gänsicke, a co-author of the study.

Remnants such as J1228+1040 can provide key clues to understanding the environments that exist as stars reach the ends of their lives. This can help astronomers to understand the processes that occur in exoplanetary systems and even forecast the fate of the Solar System when the Sun meets its demise in about seven billion years.


[1] The white dwarf’s full designation is SDSS J122859.93+104032.9.

[2] The team identified the unmistakable trident-like spectral signature from ionised calcium, called the calcium (Ca II) triplet. The difference between the observed and known wavelengths of these three lines can determine the velocity of the gas with considerable precision.

[3] Although the disc around this white dwarf is much bigger than Saturn’s ring system in the Solar System, it is tiny compared to the debris discs that form planets around young stars.

More information:

This research was presented in a paper entitled “Doppler-imaging of the planetary debris disc at the white dwarf SDSS J122859.93+104032.9”, by C. Manser et al., to appear in the Monthly Notices of the Royal Astronomical Society.

The team is composed of Christopher Manser (University of Warwick, UK), Boris Gaensicke (University of Warwick), Tom Marsh (University of Warwick), Dimitri Veras (University of Warwick, UK), Detlev Koester (University of Kiel, Germany), Elmé Breedt (University of Warwick), Anna Pala (University of Warwick), Steven Parsons (Universidad de Valparaiso, Chile) and John Southworth (Keele University, UK).

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”.


Link to Research Paper:

Photos of the Very Large Telescope:

Images, Text, Credits: ESO/Mark Garlick ( and University of Warwick/NASA/Cassini/University of Warwick/C. Manser/Video: ESO/Mark Garlick ( and University of Warwick.

Best regards,