samedi 1 juin 2013

Mars Express - 10 years, 12,000 revolutions around Mars












ESA - Mars Express Mission patch.

June 1, 2013

 Mars Express

Designed for one Martian year, or two Earth years, the European Mars Express Sunday celebrates its 10th anniversary in space. The initial mission has been extended four times, and its operations are now funded until the end of 2014.

"This is a scientific success and experience on board continue to function perfectly," says the German Aerospace Center (DLR) on its website. Mars Express was launched June 2, 2003 from Baikonur in Kazakhstan by a Soyuz-Fregat rocket.

The main objective was to investigate the presence of water, a necessary condition for the emergence of life in its various states.

video
Mars Express 10 years

The mission of the European Space Agency (ESA) originally consisted of an orbiter carrying seven instruments and remote sensing observations and a lander, Beagle 2. It was equipped with a drill designed to collect, two meters deep, samples of Martian soil.

Beagle 2 capsule separation from Mars Express

The first signal from Mars Express was received on 25 December 2003, meaning that the probe entered successfully into orbit around the Red Planet. "It now counts more than 12,000 revolutions around Mars," said Astrium, the contractor, in a statement.

However, attempts to communicate with Beagle 2, which was also to land on Mars on Christmas Day in 2003, have failed. The Beagle 2 mission was declared permanently lost 6 February 2004.

Artist's view of Beagle 2 capsule deployed on Mars (probably crashed on Mars)

Volcanic rocks

Mars Express began its scientific observations as planned in January 2004, studying the Martian atmosphere, the structure of the planet and its geology.

video
 Mars mineral globe

Analysis of data from one of the instruments on board the infrared spectrometer Omega has helped to establish the presence of minerals that form only after prolonged volcanic rocks exposure to water. Another instrument, the Marsis radar sensor is located him in the form of water ice deposits underground.


Image above: Perspective view of Melas Chasma. On 2 May 2004, the High-Resolution Stereo Camera (HRSC) on board the ESA Mars Express spacecraft obtained images from the central area of the Mars canyon called Valles Marineris. The images were taken at a resolution of approximately 16 metres per pixel.

Stereo camera

The images of high resolution stereo camera (HRSC) developed by Astrium for the German agency representing 40% of the data transmitted from March. "So far, the camera has recorded nearly 90% of the surface of the planet," said Astrium.

The probe also flew Phobos, the small moon of Mars, providing scientists with highly accurate images. According to these observations, Phobos is gradually approaching Mars and collide with it in 10 to 20 million Martian years.

Phobos by Mars Express

Future mission

Mars Express one of three orbiters around Mars present, with U.S. Mars Odyssey and Mars Reconnaissance Orbiter (MRO). As the U.S. robot Curiosity, which landed on the planet in August, he made a decade ago to his second day drill to sample rock.

Experts do not exclude that the Mars Express probe is still operational when ESA will send its future Mars mission, ExoMars, in partnership with the Russian Space Agency Roscosmos. A key objective of ExoMars is to determine if a form of life ever existed on the Red Planet.

ExoMars Mission logo

The program plans to launch two missions on Mars in 2016, an orbiter and a lander demo, and in 2018 a robotic module.

For more information about Mars Express, visit: http://www.esa.int/Our_Activities/Space_Science/Mars_Express

Images, Video, Text, Credits: ESA / DLR / FU (G. Neukum) / Orbiter.ch Aerospace / Video Mars Mineral Globe: Hydrated mineral map: ESA / CNES / CNRS / IAS / Université Paris-Sud, Orsay; NASA / JPL / JHUAPL; Olivine, pyroxone, ferric dust & dust maps: ESA / CNES / CNRS / IAS / Université Paris-Sud, Orsay Orsay; Video production: ESA.

Best regards, Orbiter.ch

vendredi 31 mai 2013

Another American High Frontier First: 3-D Manufacturing in Space










NASA logo.

May 31, 2013

In preparation for a future where parts and tools can be printed on demand in space, NASA and Made in Space Inc. of Mountain View, Calif., have joined to launch equipment for the first 3-D microgravity printing experiment to the International Space Station.

If successful, the 3-D Printing in Zero G Experiment (3-D Print) will be the first device to manufacture parts in space. 3-D Print will use extrusion additive manufacturing, which builds objects, layer by layer, out of polymers and other materials. The 3-D Print hardware is scheduled to be certified and ready for launch to the space station next year.


Image above: In August of 2011, Made In Space started its initial testing of the effects of microgravity on 3D printing. Image credit: Made in Space.

"As NASA ventures further into space, whether redirecting an asteroid or sending humans to Mars, we'll need transformative technology to reduce cargo weight and volume," NASA Administrator Charles Bolden said during a recent tour of the agency's Ames Research Center at Moffett Field, Calif. "In the future, perhaps astronauts will be able to print the tools or components they need while in space."

NASA is a government leader in 3-D printing for engineering applications. The technology holds tremendous potential for future space exploration. One day, 3-D printing may allow an entire spacecraft to be manufactured in space, eliminating design constraints caused by the challenges and mass constraints of launching from Earth. This same technology may help revolutionize American manufacturing and benefit U.S. industries.

"The president's Advanced Manufacturing Initiative cites additive manufacturing, or '3-D printing,' as one of the key technologies that will keep U.S. companies competitive and maintain world leadership in our new global technology economy," said Michael Gazarik, NASA's associate administrator for space technology in Washington. "We're taking that technology to new heights, by working with Made in Space to test 3-D printing aboard the space station. Taking advantage of our orbiting national laboratory, we'll be able to test new manufacturing techniques that benefit our astronauts and America's technology development pipeline."


Image above: Under a contract with NASA’s Marshall Space Flight Center (MSFC), Made In Space is building the first 3D printer for space. The 3D Printing in Zero-G Experiment will fly to the International Space Station (ISS) in 2014. Image credit: Made in Space.

In addition to manufacturing spacecraft designs in orbit, 3-D printers also could work with robotic systems to create tools and habitats needed for human missions to Mars and other planetary destinations. Housing and laboratories could be fabricated by robots using printed building blocks that take advantage of in-situ resources, such as soil or minerals. Astronauts on long-duration space missions also could print and recycle tools as they are needed, saving mass, volume and resources.

"The 3-D Print experiment with NASA is a step towards the future," said Aaron Kemmer, CEO of Made in Space. "The ability to 3-D print parts and tools on demand greatly increases the reliability and safety of space missions while also dropping the cost by orders of magnitude. The first printers will start by building test items, such as computer component boards, and will then build a broad range of parts, such as tools and science equipment."

Made in Space previously partnered with NASA through the agency's Flight Opportunities Program to test its prototype 3-D Print additive manufacturing equipment on suborbital simulated microgravity flights. NASA's Flight Opportunities Program offers businesses and researchers the ability to fly new technologies to the edge of space and back for testing before launching them into the harsh space environment.

NASA C-9B Zero-G aircraft. Image credit: NASA

For this mission, Made in Space was awarded a Phase III small business innovation and research contract from NASA's Marshall Space Flight Center in Huntsville, Ala. After flight certification, NASA plans to ship 3-D Print to the space station aboard an American commercial resupply mission. NASA is working with American industry to develop commercially-provided U.S. spacecraft and launch vehicles for delivery of cargo -- and eventually crew -- to the International Space Station.

For more information about Made in Space, visit: http://www.madeinspace.us

NASA's Space Technology Mission Directorate leads the agency's participation in the president's National Network for Manufacturing Innovation. The directorate's Game Changing Development program leads the agency's efforts in 3-D printing. For more information about the directorate, which is innovating, developing, testing and flying hardware for use in NASA's future missions, visit: http://www.nasa.gov/spacetech

Images (mentioned), Text, Credit: NASA.

Greetings, Orbiter.ch

jeudi 30 mai 2013

NASA's GRAIL Mission Solves Mystery of Moon's Surface Gravity











NASA - GRAIL Mission patch.

May 30, 2013

NASA's Gravity Recovery and Interior Laboratory (GRAIL) mission has uncovered the origin of massive invisible regions that make the moon's gravity uneven, a phenomenon that affects the operations of lunar-orbiting spacecraft.

Because of GRAIL's findings, spacecraft on missions to other celestial bodies can navigate with greater precision in the future.

GRAIL's twin spacecraft studied the internal structure and composition of the moon in unprecedented detail for nine months. They pinpointed the locations of large, dense regions called mass concentrations, or mascons, which are characterized by strong gravitational pull. Mascons lurk beneath the lunar surface and cannot be seen by normal optical cameras.

GRAIL scientists found the mascons by combining the gravity data from GRAIL with sophisticated computer models of large asteroid impacts and known detail about the geologic evolution of the impact craters. The findings are published in the May 30 edition of the journal Science.


Image above: Using a precision formation-flying technique, the twin GRAIL spacecraft mapped the moon's gravity field, as depicted in this artist's rendering. detail. Image credit: NASA/JPL-Caltech.

"GRAIL data confirm that lunar mascons were generated when large asteroids or comets impacted the ancient moon, when its interior was much hotter than it is now," said Jay Melosh, a GRAIL co-investigator at Purdue University in West Lafayette, Ind., and lead author of the paper. "We believe the data from GRAIL show how the moon's light crust and dense mantle combined with the shock of a large impact to create the distinctive pattern of density anomalies that we recognize as mascons."

The origin of lunar mascons has been a mystery in planetary science since their discovery in 1968 by a team at NASA's Jet Propulsion Laboratory in Pasadena, Calif. Researchers generally agree mascons resulted from ancient impacts billions of years ago. It was not clear until now how much of the unseen excess mass resulted from lava filling the crater or iron-rich mantle upwelling to the crust.

On a map of the moon's gravity field, a mascon appears in a target pattern. The bulls-eye has a gravity surplus. It is surrounded by a ring with a gravity deficit. A ring with a gravity surplus surrounds the bulls-eye and the inner ring. This pattern arises as a natural consequence of crater excavation, collapse and cooling following an impact. The increase in density and gravitational pull at a mascon's bulls-eye is caused by lunar material melted from the heat of a long-ago asteroid impact.

"Knowing about mascons means we finally are beginning to understand the geologic consequences of large impacts," Melosh said. "Our planet suffered similar impacts in its distant past, and understanding mascons may teach us more about the ancient Earth, perhaps about how plate tectonics got started and what created the first ore deposits."

This new understanding of lunar mascons also is expected to influence knowledge of planetary geology well beyond that of Earth and our nearest celestial neighbor.

"Mascons also have been identified in association with impact basins on Mars and Mercury," said GRAIL principal investigator Maria Zuber of the Massachusetts Institute of Technology in Cambridge. "Understanding them on the moon tells us how the largest impacts modified early planetary crusts."

Mapping Lunar Highlands

Image above: This graphic depicting the bulk density of the lunar highlands on the near and far sides of the moon was generated using gravity data from NASA's GRAIL mission and topography data from NASA's Lunar Reconnaissance Orbiter. Red corresponds to higher than average densities and blue corresponds to lower than average densities. The average bulk density of the lunar highlands crust is 2,550 kilograms per meter cubed, which is 12 percent lower than generally assumed. White denotes regions that contain mare basalts (thin lines) and that were not analyzed. Solid circles correspond to prominent impact basins. The largest basin on the moon's far side hemisphere, the South Pole-Aitken basin, has a higher than average density that reflects its atypical iron-rich surface composition. Data are presented in two Lambert azimuthal equal-area projections centered over the near (left) and far side (right) hemispheres, with each image covering 75 percent of the lunar surface. Image Credit: NASA/JPL-Caltech/ IPGP.

Launched as GRAIL A and GRAIL B in September 2011, the probes, renamed Ebb and Flow, operated in a nearly circular orbit near the poles of the moon at an altitude of about 34 miles (55 kilometers) until their mission ended in December 2012. The distance between the twin probes changed slightly as they flew over areas of greater and lesser gravity caused by visible features, such as mountains and craters, and by masses hidden beneath the lunar surface.

JPL, a division of the California Institute of Technology in Pasadena, Calif. managed GRAIL for NASA's Science Mission Directorate in Washington. The mission was part of the Discovery Program managed at NASA's Marshall Space Flight Center in Huntsville, Ala. NASA's Goddard Space Flight Center, in Greenbelt, Md., manages the Lunar Reconnaissance Orbiter. Operations of the spacecraft's laser altimeter, which provided supporting data used in this investigation, is led by the Massachusetts Institute of Technology in Cambridge. Lockheed Martin Space Systems in Denver built GRAIL.

For more information about GRAIL, visit http://www.nasa.gov/grail and http://grail.nasa.gov

Images (mentioned), Text, Credits: NASA / Dwayne Brown / JPL / DC Agle / Purdue University / Elizabeth Gardner / Massachusetts Institute of Technology / Jennifer Chu.

Greetings, Orbiter.ch

Study: Asteroids Provide Sustainable Resource












NASA patch.

May 30, 2013

The prospects of a robotic manufacturing base operating off the Earth is not as far-fetched as it used to be according to a study published by a team of NASA researchers led by a Kennedy Space Center physicist.

Because asteroids are loaded with minerals that are rare on Earth, near-Earth asteroids and the asteroid belt could become the mining centers for remotely operated excavators and processing machinery. In 20 years, an industry barely imagined now could be sending refined materials, rare metals and even free, clean energy to the Earth from asteroids and other bodies.


Image above: The asteroid Eros was studied by NASA's NEAR mission in the early 2000s. Researchers want to find out whether asteroids such as this contain minerals and other resources that can be mined and used on Earth or for space-based industries. Photo credit: NASA.

In their paper called "Affordable, Rapid Bootstrapping of the Space Industry and Solar System Civilization," published in the Journal of Aerospace Engineering, Phil Metzger, Anthony Muscatello, Robert Mueller and James Mantovani detail an intriguing path toward developing a self-sustaining, space-based industry that would use resources from asteroids and other heavenly bodies to meet the needs of humanity.

The result would provide the most profound societal changes since the Industrial Revolution introduced large-scale machinery and manufacturing techniques in the late 18th and early 19th centuries, said Metzger the Kennedy-based physicist who led the evaluation.

"We're predicting that we are on the verge of the next revolution in human civilization," Metzger said.

Two fundamental developments make this prospect possible: robotics and the discovery of fundamental elements to make plastic and rubber and metals existing throughout space.

"Now that we know we can get carbon in space, the basic elements that we need for industry are all within reach," Metzger said. "That was game-changing for us. The asteroid belt has a billion times more platinum than is found on Earth. There is literally a billion times the metal that is on the Earth, and all the water you could ever need."

Another critical technology also is coming in at just the right time: additive manufacturing in the form of 3D printers that can turn out individual pieces that can be assembled into ever-more-complex machinery and increasingly capable robots.

"The idea is you start with resources out of Earth's gravity well in the vicinity of the Earth," Metzger said. "But what we argued is that you can establish industry in space for a surprisingly low cost, much less than anybody previously thought."

The finished minerals could be returned to Earth or used in space to build new machinery or as supplies for astronauts as they explore the solar system.

So where to start?

The closer to Earth, the better -- at least at first.

NASA is searching for an asteroid of about 500 tons that can be moved into a path within the moon's orbit so astronauts can visit it as early as 2021 to take samples of the space rock.

"When we wrote this paper we were focused on the moon as a source of near-Earth resources, but near Earth asteroids work equally well and offer several additional advantages," Metzger said. "It takes less fuel to bring resources away from the lower gravity of an asteroid, and since the ultimate goal is to move the industry to the asteroid main belt starting with asteroids first will help develop the correct technologies."

But all asteroids are not created equal, and each one is likely to offer a unique fingerprint of substances created when the solar system formed billions of years ago.

"There are some types of asteroids that would be fantastic for space resources," Metzger said. "It's primordial solar system material. You can make plastics and you can make rubber by combining the carbon and the hydrogen."

A near-Earth asteroid or other nearby body presumably will contain enough material to allow a robotic system to mine the materials and refine them into usable metal or other substances. Those materials would be formed into pieces and assembled into another robot system that would itself build similar models and advance the design.


Image above: Robotically concept capture a small near-Earth asteroid and redirect it safely to a stable orbit in the Earth-moon system where astronauts can visit and explore it.  Image credit: NASA/JPL-Caltech.

"The first generation only makes the simplest materials, it can include metal and therefore you can make structure out of metal and then you can send robots that will attach electronics and wiring onto the metal," Metzger said. "So by making the easiest thing, you've reduced the largest amount of mass that you have to launch."

The first generation of machinery would be akin to the simple mechanical devices of the 1700s, with each new generation advancing quickly to the modern vanguard of abilities. They would start with gas production and the creation of solar cells, vital for providing a power source.

Each new robot could add improvements to each successive model and quickly advance the mining and manufacturing capabilities. It would not take long for the miners to produce more material than they need for themselves and they could start shipping precious metals back to Earth, riding on heat shields made of the leftover soil that doesn't contain any precious material.

Kennedy researchers already have tested heat shield samples made from soil.

Bodies near Earth also were recently revealed to contain water ice, which gives planners the chemicals needed to produce fuel and air. With those resources available, the robotic miners would be able to propel themselves farther out into the solar system, mainly to the resource-rich asteroid belt between Mars and Jupiter. There they could set up more manufacturing and refining facilities.

Perhaps the most unusual aspect of the whole endeavor is that it would not take many launches from Earth to achieve. Launch costs, which now run at best $1,000 per pound, would be saved because robots building themselves in space from material gathered there wouldn't need anything produced by people. Very quickly, only the computer chips, electronics boards and wiring would need to come from Earth.

"We took it through six generations of robotic development and you can achieve full closure and make everything in space," Metzger said. "We showed you can get it down to launching 12 tons of hardware, which is incredibly small."

For comparison, that would be less than half the weight of the Apollo command and service modules flown on a moon mission.

This enterprise would take years to establish, but not as long as one might think. And the payoff for Earth would be felt when the first shipments of materials began arriving from space. A sudden influx of rare metals, for instance, would drive down the price of those materials on Earth and allow a similar drastic reduction in manufacturing costs for products made with the materials.

There are numerous examples of such revolutions taking place over and over again on Earth, including the discovery after the Civil War of a process for refining bauxite into aluminum that made the metal go from being as valuable as gold to something soda cans are made of. Does that mean soda cans would be made from platinum? Maybe not, but the changes could be just as dramatic.

"You could grow an industry that is a million times bigger than the United States' in the main asteroid belt," Metzger said. "Then you really are capable of terraforming planets and doing all the other great things because it wouldn't cost you anything" in terms of labor, resources or materials.

video
Asteroid Initiative Animation

NASA's FY2014 budget proposal includes a plan to robotically capture a small near-Earth asteroid and redirect it safely to a stable orbit in the Earth-moon system where astronauts can visit and explore it.

Performing these elements for the proposed asteroid initiative integrates the best of NASA's science, technology and human exploration capabilities and draws on the innovation of America's brightest scientists and engineers. It uses current and developing capabilities to find both large asteroids that pose a hazard to Earth and small asteroids that could be candidates for the initiative, accelerates our technology development activities in high-powered solar electric propulsion and takes advantage of our hard work on the Space Launch System rocket and Orion spacecraft, helping to keep NASA on target to reach the President's goal of sending humans to Mars in the 2030s.

When astronauts don their spacesuits and venture out for a spacewalk on the surface of an asteroid, how they move and take samples of it will be based on years of knowledge built by NASA scientists and engineers who have assembled and operated the International Space Station, evaluated exploration mission concepts, sent scientific spacecraft to characterize near-Earth objects and performed ground-based analog missions.

Related link:

The Long and Storied Path to Human Asteroid Exploration: http://www.nasa.gov/topics/history/features/asteroids.html

Images (mentioned), Video, Text, Credits: NASA / Kennedy Space Center / Steven Siceloff.

Greetings, Orbiter.ch

Pebbly Rocks Testify to Old Streambed on Mars












NASA - Mars Science Laboratory (MSL) patch.

May 30, 2013

Detailed analysis and review have borne out researchers' initial interpretation of pebble-containing slabs that NASA's Mars rover Curiosity investigated last year: They are part of an ancient streambed.

The rocks are the first ever found on Mars that contain streambed gravels. The sizes and shapes of the gravels embedded in these conglomerate rocks -- from the size of sand particles to the size of golf balls -- enabled researchers to calculate the depth and speed of the water that once flowed at this location.


Image above: NASA's Curiosity rover found evidence for an ancient, flowing stream on Mars at a few sites, including the rock outcrop pictured here, which the science team has named "Hottah" after Hottah Lake in Canada's Northwest Territories. Image credit: NASA/JPL-Caltech/MSSS.

"We completed more rigorous quantification of the outcrops to characterize the size distribution and roundness of the pebbles and sand that make up these conglomerates," said Rebecca Williams of the Planetary Science Institute, Tucson, Ariz., lead author of a report about them in the journal Science this week. "We ended up with a calculation in the same range as our initial estimate last fall. At a minimum, the stream was flowing at a speed equivalent to a walking pace -- a meter, or three feet, per second -- and it was ankle-deep to hip-deep."

Three pavement-like rocks examined with the telephoto capability of Curiosity's Mast Camera (Mastcam) during the rover's first 40 days on Mars are the basis for the new report. One, "Goulburn," is immediately adjacent to the rover's "Bradbury Landing" touchdown site. The other two, "Link" and "Hottah," are about 165 and 330 feet (50 and 100 meters) to the southeast. Researchers also used the rover's laser-shooting Chemistry and Camera (ChemCam) instrument to investigate the Link rock.


This stereo view from NASA's Mars rover Curiosity shows a rock called "Link," which bears rounded pebbles that provide evidence about vigorous flow of water in a stream on ancient Mars. Image credit: NASA/JPL-Caltech/MSSS.

"These conglomerates look amazingly like streambed deposits on Earth," Williams said. "Most people are familiar with rounded river pebbles. Maybe you've picked up a smoothed, round rock to skip across the water. Seeing something so familiar on another world is exciting and also gratifying."

The larger pebbles are not distributed evenly in the conglomerate rocks. In Hottah, researchers detected alternating pebble-rich layers and sand layers. This is common in streambed deposits on Earth and provides additional evidence for stream flow on Mars. In addition, many of the pebbles are touching each other, a sign that they rolled along the bed of a stream.


This set of images compares the Link outcrop of rocks on Mars (left) with similar rocks seen on Earth (right). Image credit: NASA/JPL-Caltech/MSSS and PSI.

"Our analysis of the amount of rounding of the pebbles provided further information," said Sanjeev Gupta of Imperial College, London, a co-author of the new report. "The rounding indicates sustained flow. It occurs as pebbles hit each other multiple times. This wasn't a one-off flow. It was sustained, certainly more than weeks or months, though we can't say exactly how long."

The stream carried the gravels at least a few miles, or kilometers, the researchers estimated.


This image from NASA's Curiosity Rover shows a high-resolution view of an area that is known as Goulburn Scour, a set of rocks blasted by the engines of Curiosity's descent stage on Mars. Image credit: NASA/JPL-Caltech/MSSS.

The atmosphere of modern Mars is too thin to make a sustained stream flow of water possible, though the planet holds large quantities of water ice. Several types of evidence have indicated that ancient Mars had diverse environments with liquid water. However, none but these rocks found by Curiosity could provide the type of stream flow information published this week. Curiosity's images of conglomerate rocks indicate that atmospheric conditions at Gale Crater once enabled the flow of liquid water on the Martian surface.

Curiosity self portrait. Image credit: NASA/JPL-Caltech

During a two-year prime mission, researchers are using Curiosity's 10 science instruments to assess the environmental history in Gale Crater on Mars, where the rover has found evidence of ancient environmental conditions favorable for microbial life.

More information about Curiosity is online at: http://www.nasa.gov/msl and http://mars.jpl.nasa.gov/msl/ .

You can follow the mission on Facebook at: http://www.facebook.com/marscuriosity and on Twitter at http://www.twitter.com/marscuriosity

Images (mentioned), Text, Credits: NASA / JLP / Guy Webster.

Cheers, Orbiter.ch

NASA Radar Reveals Asteroid Has Its Own Moon











Asteroid Watch.

May 30, 2013


First radar images of asteroid 1998 QE2 were obtained when the asteroid was about 3.75 million miles (6 million kilometers) from Earth. Image credit: NASA/JPL-Caltech/GSSR.

A sequence of radar images of asteroid 1998 QE2 was obtained on the evening of May 29, 2013, by NASA scientists using the 230-foot (70-meter) Deep Space Network antenna at Goldstone, Calif., when the asteroid was about 3.75 million miles (6 million kilometers) from Earth, which is 15.6 lunar distances.

The radar imagery revealed that 1998 QE2 is a binary asteroid. In the near-Earth population, about 16 percent of asteroids that are about 655 feet (200 meters) or larger are binary or triple systems. Radar images suggest that the main body, or primary, is approximately 1.7 miles (2.7 kilometers) in diameter and has a rotation period of less than four hours. Also revealed in the radar imagery of 1998 QE2 are several dark surface features that suggest large concavities. The preliminary estimate for the size of the asteroid's satellite, or moon, is approximately 2,000 feet (600 meters) wide. The radar collage covers a little bit more than two hours.

The radar observations were led by scientist Marina Brozovic of NASA's Jet Propulsion Laboratory, Pasadena, Calif.


Image above: The closest approach of the asteroid occurs on May 31 at 1:59 p.m. Pacific (4:59 p.m. Eastern / 20:59 UTC), when the asteroid will get no closer than about 3.6 million miles (5.8 million kilometers), or about 15 times the distance between Earth and the moon. This is the closest approach the asteroid will make to Earth for at least the next two centuries. Asteroid 1998 QE2 was discovered on Aug. 19, 1998, by the Massachusetts Institute of Technology Lincoln Near Earth Asteroid Research (LINEAR) program near Socorro, N.M.

The resolution of these initial images of 1998 QE2 is approximately 250 feet (75 meters) per pixel. Resolution is expected to increase in the coming days as more data become available. Between May 30 and June 9, radar astronomers using NASA's 230-foot-wide (70 meter) Deep Space Network antenna at Goldstone, Calif., and the Arecibo Observatory in Puerto Rico, will perform an extensive campaign of observations on asteroid 1998 QE2. The two telescopes have complementary imaging capabilities that will enable astronomers to learn as much as possible about the asteroid during its brief visit near Earth.

Radar is a powerful technique for studying an asteroid's size, shape, rotation state, surface features and surface roughness, and for improving the calculation of asteroid orbits. Radar measurements of asteroid distances and velocities often enable computation of asteroid orbits much further into the future than if radar observations weren't available.

video
Revealing Asteroids with Radar

Video above: When Asteroid 1998 QE2 makes its closest approach to Earth on May 31, 2013, it promises to be a bonanza for radar science. Credits: NASA/JPL-Caltech.

NASA places a high priority on tracking asteroids and protecting our home planet from them. In fact, the United States has the most robust and productive survey and detection program for discovering near-Earth objects. To date, U.S. assets have discovered more than 98 percent of the known Near-Earth Objects.

In 2012, the Near-Earth Object budget was increased from $6 million to $20 million. Literally dozens of people are involved with some aspect of near-Earth object research across NASA and its centers. Moreover, there are many more people involved in researching and understanding the nature of asteroids and comets, including those objects that come close to Earth, plus those who are trying to find and track them in the first place.

In addition to the resources NASA puts into understanding asteroids, it also partners with other U.S. government agencies, university-based astronomers, and space science institutes across the country that are working to track and better understand these objects, often with grants, interagency transfers and other contracts from NASA.

NASA's Near-Earth Object Program at NASA Headquarters, Washington, manages and funds the search, study, and monitoring of asteroids and comets whose orbits periodically bring them close to Earth. JPL manages the Near-Earth Object Program Office for NASA's Science Mission Directorate in Washington. JPL is a division of the California Institute of Technology in Pasadena.

video
Asteroid 1998 QE2

Video above: Radar data of asteroid 1998 QE2 obtained on May 29, 2013. Credits: NASA/JPL-Caltech.

In 2016, NASA will launch a robotic probe to one of the most potentially hazardous of the known Near-Earth Objects. The OSIRIS-REx mission to asteroid (101955) Bennu will be a pathfinder for future spacecraft designed to perform reconnaissance on any newly-discovered threatening objects. Aside from monitoring potential threats, the study of asteroids and comets enables a valuable opportunity to learn more about the origins of our solar system, the source of water on Earth, and even the origin of organic molecules that lead to the development of life.

NASA recently announced development of a first-ever mission to identify, capture and relocate an asteroid for human exploration. Using game-changing technologies this mission would mark an unprecedented technological achievement that raises the bar of what humans can do in space. Capturing and redirecting an asteroid will integrate the best of NASA's science, technology and human exploration capabilities and draw on the innovation of America's brightest scientists and engineers.

More information about asteroids and near-Earth objects is available at: http://neo.jpl.nasa.gov/ , http://www.jpl.nasa.gov/asteroidwatch and via Twitter at http://www.twitter.com/asteroidwatch .

More information about asteroid radar research is at: http://echo.jpl.nasa.gov/

More information about the Deep Space Network is at: http://deepspace.jpl.nasa.gov/dsn .

Images (mentioned), Videos (mentioned), Text, Credits: NASA / JPL / DC Agle.

Greetings, Orbiter.ch

Data from NASA Rover's Voyage to Mars Aids Planning












NASA - Mars Science Laboratory (MSL) patch.

May 30, 2013

Measurements taken by NASA's Mars Science Laboratory mission as it delivered the Curiosity rover to Mars in 2012 are providing NASA the information it needs to design systems to protect human explorers from radiation exposure on deep-space expeditions in the future.

Curiosity's Radiation Assessment Detector (RAD) is the first instrument to measure the radiation environment during a Mars cruise mission from inside a spacecraft that is similar to potential human exploration spacecraft. The findings reduce uncertainty about the effectiveness of radiation shielding and provide vital information to space mission designers who will need to build in protection for spacecraft occupants in the future.


This set of artist's concepts shows NASA's Mars Science Laboratory cruise capsule and NASA's Orion spacecraft, which is being built now at NASA's Johnson Space Center and will one day send astronauts to Mars. Image credit: NASA/JPL-Caltech/JSC.

"As this nation strives to reach an asteroid and Mars in our lifetimes, we're working to solve every puzzle nature poses to keep astronauts safe so they can explore the unknown and return home," said William Gerstenmaier, NASA's associate administrator for human exploration and operations in Washington. "We learn more about the human body's ability to adapt to space every day aboard the International Space Station. As we build the Orion spacecraft and Space Launch System rocket to carry and shelter us in deep space, we'll continue to make the advances we need in life sciences to reduce risks for our explorers. Curiosity's RAD instrument is giving us critical data we need so that we humans, like the rover, can dare mighty things to reach the Red Planet."

The findings, which are published in the May 31 edition of the journal Science, indicate radiation exposure for human explorers could exceed NASA's career limit for astronauts if current propulsion systems are used.


This graphic compares the radiation dose equivalent for several types of experiences, including a calculation for a trip from Earth to Mars based on measurements made by the Radiation Assessment Detector instrument shielded inside NASA's Mars Science Laboratory spacecraft during the flight from Earth to Mars in 2011 and 2012. Image credit: NASA/JPL-Caltech/SwRI.

Two forms of radiation pose potential health risks to astronauts in deep space. One is galactic cosmic rays (GCRs), particles caused by supernova explosions and other high-energy events outside the solar system. The other is solar energetic particles (SEPs) associated with solar flares and coronal mass ejections from the sun.

Radiation exposure is measured in units of Sievert (Sv) or milliSievert (one one-thousandth Sv). Long-term population studies have shown exposure to radiation increases a person's lifetime cancer risk. Exposure to a dose of 1 Sv, accumulated over time, is associated with a five percent increase in risk for developing fatal cancer.


This instrument, shown prior to its September 2010 installation onto NASA's Mars rover Curiosity, will aid future human missions to Mars by providing information about the radiation environment on Mars and on the way to Mars. Image credit: NASA/JPL-Caltech/SwRI.

NASA has established a three percent increased risk of fatal cancer as an acceptable career limit for its astronauts currently operating in low-Earth orbit. The RAD data showed the Curiosity rover was exposed to an average of 1.8 milliSieverts of GCR per day on its journey to Mars. Only about three percent of the radiation dose was associated with solar particles because of a relatively quiet solar cycle and the shielding provided by the spacecraft.

The RAD data will help inform current discussions in the United States' medical community, which is working to establish exposure limits for deep-space explorers in the future.

"In terms of accumulated dose, it's like getting a whole-body CT scan once every five or six days," said Cary Zeitlin, a principal scientist at the Southwest Research Institute (SwRI) in San Antonio and lead author of the paper on the findings. "Understanding the radiation environment inside a spacecraft carrying humans to Mars or other deep space destinations is critical for planning future crewed missions."


The Radiation Assessment Detector (RAD) on NASA's Curiosity Mars rover monitors high-energy atomic and subatomic particles coming from the sun, distant supernovae and other sources. Image credit: NASA/JPL-Caltech/SwRI.

Current spacecraft shield much more effectively against SEPs than GCRs. To protect against the comparatively low energy of typical SEPs, astronauts might need to move into havens with extra shielding on a spacecraft or on the Martian surface, or employ other countermeasures. GCRs tend to be highly energetic, highly penetrating particles that are not stopped by the modest shielding provided by a typical spacecraft.

"Scientists need to validate theories and models with actual measurements, which RAD is now providing," said Donald M. Hassler, a program director at SwRI and principal investigator of the RAD investigation. "These measurements will be used to better understand how radiation travels through deep space and how it is affected and changed by the spacecraft structure itself. The spacecraft protects somewhat against lower energy particles, but others can propagate through the structure unchanged or break down into secondary particles."

After Curiosity landed on Mars in August, the RAD instrument continued operating, measuring the radiation environment on the planet's surface. RAD data collected during Curiosity's science mission will continue to inform plans to protect astronauts as NASA designs future missions to Mars in the coming decades.

video
Will Radiation Kill Mars Astronauts?

Video above: Astronauts on long interplanetary trips will face at least two kinds of radiation hazards. The Mars Science Lab's Radiation Assessment Detector (RAD) has quantified the risk. Crews could get much more than the current accepted career dose. Credit: Space Now.

SwRI, together with Christian Albrechts University in Kiel, Germany, built RAD with funding from NASA's Human Exploration and Operations Mission Directorate and Germany's national aerospace research center, Deutsches Zentrum für Luft- und Raumfahrt.

NASA's Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, Calif., manages the Mars Science Laboratory Project and the project's Curiosity rover. The NASA Science Mission Directorate at NASA Headquarters in Washington manages the Mars Exploration Program.

For more information about the mission, visit: http://www.nasa.gov/msl and http://mars.jpl.nasa.gov/msl . To follow the mission on Facebook and Twitter visit: http://www.facebook.com/marscuriosity and http://www.twitter.com/marscuriosity

For more information about NASA human spaceflight and exploration, visit: http://www.nasa.gov/exploration .

Images (mentioned), Video (mentioned), Text, Credits: NASA / Trent Perrotto / JPL / Guy Webster / Southwest Research Institute / Deb Schmid.

Best regards, Orbiter.ch

mercredi 29 mai 2013

Cassini Finds Hints of Activity at Saturn Moon Dione










NASA / ESA - Cassini Mission logo.

May 29, 2013

From a distance, most of the Saturnian moon Dione resembles a bland cueball. Thanks to close-up images of a 500-mile-long (800-kilometer-long) mountain on the moon from NASA's Cassini spacecraft, scientists have found more evidence for the idea that Dione was likely active in the past. It could still be active now.

"A picture is emerging that suggests Dione could be a fossil of the wondrous activity Cassini discovered spraying from Saturn's geyser moon Enceladus or perhaps a weaker copycat Enceladus," said Bonnie Buratti of NASA's Jet Propulsion Laboratory in Pasadena, Calif., who leads the Cassini science team that studies icy satellites. "There may turn out to be many more active worlds with water out there than we previously thought."


Image above: The Cassini spacecraft looks down, almost directly at the north pole of Dione. Image credit: NASA/JPL-Caltech/Space Science Institute.

Other bodies in the solar system thought to have a subsurface ocean – including Saturn's moons Enceladus and Titan and Jupiter's moon Europa – are among the most geologically active worlds in our solar system. They have been intriguing targets for geologists and scientists looking for the building blocks of life elsewhere in the solar system. The presence of a subsurface ocean at Dione would boost the astrobiological potential of this once-boring iceball.

Hints of Dione's activity have recently come from Cassini, which has been exploring the Saturn system since 2004. The spacecraft’s magnetometer has detected a faint particle stream coming from the moon, and images showed evidence for a possible liquid or slushy layer under its rock-hard ice crust. Other Cassini images have also revealed ancient, inactive fractures at Dione similar to those seen at Enceladus that currently spray water ice and organic particles.


Image above: The Cassini spacecraft swooped in for a close-up of the cratered, fractured surface of Saturn's moon Dione in this image taken during the spacecraft's Jan. 27, 2010, non-targeted flyby. Image credit: NASA/JPL-Caltech/Space Science Institute.

The mountain examined in the latest paper -- published in March in the journal Icarus -- is called Janiculum Dorsa and ranges in height from about 0.6 to 1.2 miles (1 to 2 kilometers). The moon's crust appears to pucker under this mountain as much as about 0.3 mile (0.5 kilometer).

"The bending of the crust under Janiculum Dorsa suggests the icy crust was warm, and the best way to get that heat is if Dione had a subsurface ocean when the ridge formed,” said Noah Hammond, the paper's lead author, who is based at Brown University, Providence, R.I.

Dione gets heated up by being stretched and squeezed as it gets closer to and farther from Saturn in its orbit. With an icy crust that can slide around independently of the moon's core, the gravitational pulls of Saturn get exaggerated and create 10 times more heat, Hammond explained. Other possible explanations, such as a local hotspot or a wild orbit, seemed unlikely.


This image, which is composed of data obtained by NASA's Cassini spacecraft, shows the topography of a mountain known as Janiculum Dorsa on the Saturnian moon Dione. Image credit: NASA/JPL-Caltech/SSI/Brown.

Scientists are still trying to figure out why Enceladus became so active while Dione just seems to have sputtered along. Perhaps the tidal forces were stronger on Enceladus, or maybe the larger fraction of rock in the core of Enceladus provided more radioactive heating from heavy elements. In any case, liquid subsurface oceans seem to be common on these once-boring icy satellites, fueling the hope that other icy worlds soon to be explored – like the dwarf planets Ceres and Pluto – could have oceans underneath their crusts. NASA's Dawn and New Horizons missions reach those dwarf planets in 2015.

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

Hammond's work was funded through a NASA Outer Planets Research grant.

For more information about Cassini, visit: http://www.nasa.gov/cassini and http://saturn.jpl.nasa.gov and  http://www.esa.int/Our_Activities/Space_Science/Cassini-Huygens

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

Best regards, Orbiter.ch

NASA'S WISE Mission Finds Lost Asteroid Family Members









NASA - WISE Mission patch.

May 29, 2013

Data from NASA's Wide-field Infrared Survey Explorer (WISE) have led to a new and improved family tree for asteroids in the main belt between Mars and Jupiter.

Astronomers used millions of infrared snapshots from the asteroid-hunting portion of the WISE all-sky survey, called NEOWISE, to identify 28 new asteroid families. The snapshots also helped place thousands of previously hidden and uncategorized asteroids into families for the first time. The findings are a critical step in understanding the origins of asteroid families, and the collisions thought to have created these rocky clans.


This artist's conception shows how families of asteroids are created. Over the history of our solar system, catastrophic collisions between asteroids located in the belt between Mars and Jupiter have formed families of objects on similar orbits around the sun. Image credit: NASA/JPL-Caltech.

"NEOWISE has given us the data for a much more detailed look at the evolution of asteroids throughout the solar system," said Lindley Johnson, the program executive for the Near-Earth Object Observation Program at NASA Headquarters in Washington. "This will help us trace the NEOs back to their sources and understand how some of them have migrated to orbits hazardous to the Earth."

The main asteroid belt is a major source of near-Earth objects (NEOs), which are those asteroids and comets that come within 28 million miles (45 million kilometers) of Earth's path around the sun. Some near-Earth objects start out in stable orbits in the main asteroid belt, until a collision or gravitational disturbance flings them inward like flippers in a game of pinball.

The NEOWISE team looked at about 120,000 main belt asteroids out of the approximately 600,000 known. They found that about 38,000 of these objects, roughly one third of the observed population, could be assigned to 76 families, 28 of which are new. In addition, some asteroids thought to belong to a particular family were reclassified.

An asteroid family is formed when a collision breaks apart a large parent body into fragments of various sizes. Some collisions leave giant craters. For example, the asteroid Vesta's southern hemisphere was excavated by two large impacts. Other smash-ups are catastrophic, shattering an object into numerous fragments, as was the case with the Eos asteroid family. The cast-off pieces move together in packs, traveling on the same path around the sun, but over time the pieces become more and more spread out.

NASA's Wide-field Infrared Survey Explorer (WISE) in orbit. Image credit: NASA/JPL-Caltech

Previous knowledge of asteroid family lineages comes from observations of their orbits. NEOWISE also looked at the asteroids' reflectivity to identify family members.

Asteroids in the same family generally have similar mineral composition and reflect similar amounts of light. Some families consist of darker-colored, or duller, asteroids, while others are made up of lighter-colored, or shinier, rocks. It is difficult to distinguish between dark and light asteroids in visible light. A large, dull asteroid can appear the same as a small, shiny one. The dark asteroid reflects less light but has more total surface area, so it appears brighter.

NEOWISE could distinguish between the dark and light asteroids because it could detct infrared light, which reveals the heat of an object. The larger the object, the more heat it gives off. When the size of an asteroid can be measured, its true reflective properties can be determined, and a group of asteroids once thought to belong to a single family circling the sun in a similar orbit can be sorted into distinct families.

"We're separating zebras from the gazelles," said Joseph Masiero of NASA's Jet Propulsion Laboratory in Pasadena, Calif., who is lead author of a report on the new study that appears in the Astrophysical Journal. "Before, family members were harder to tell apart because they were traveling in nearby packs. But now we have a better idea of which asteroid belongs to which family."

The next step for the team is to learn more about the original parent bodies that spawned the families.

"It's as if you have shards from a broken vase, and you want to put it back together to find out what happened," said Amy Mainzer, the NEOWISE principal investigator at JPL. "Why did the asteroid belt form in the first place and fail to become a planet? We are piecing together our asteroids' history."

JPL, a division of the California Institute of Technology in Pasadena, managed and operated WISE for NASA's Science Mission Directorate. The spacecraft was put into hibernation mode in 2011, after completing its main objectives of scanning the entire sky twice.

More information about the mission is online at: http://www.nasa.gov/wise .

Images (mentioned), Text, Credit: NASA / JPL / Whitney Clavin.

Greetings, Orbiter.ch

NASA's Swift Reveals New Phenomenon in a Neutron Star












NASA - Swift Mission patch.

May 29, 2013

Astronomers using NASA's Swift X-ray Telescope have observed a spinning neutron star suddenly slowing down, yielding clues they can use to understand these extremely dense objects.

A neutron star is the crushed core of a massive star that ran out of fuel, collapsed under its own weight, and exploded as a supernova. A neutron star can spin as fast as 43,000 times per minute and boast a magnetic field a trillion times stronger than Earth's. Matter within a neutron star is so dense a teaspoonful would weigh about a billion tons on Earth.


An artist's rendering of an outburst on an ultra-magnetic neutron star, also called a magnetar. Credit: NASA's Goddard Space Flight Center.

This neutron star, 1E 2259+586, is located about 10,000 light-years away toward the constellation Cassiopeia. It is one of about two dozen neutron stars called magnetars, which have very powerful magnetic fields and occasionally produce high-energy explosions or pulses.

Observations of X-ray pulses from 1E 2259+586 from July 2011 through mid-April 2012 indicated the magnetar's rotation was gradually slowing from once every seven seconds, or about eight revolutions per minute. On April 28, 2012, data showed the spin rate had decreased abruptly, by 2.2 millionths of a second, and the magnetar was spinning down at a faster rate.


The magnetar 1E 2259+586 shines a brilliant blue-white in this false-color X-ray image of the CTB 109 supernova remnant, which lies about 10,000 light-years away toward the constellation Cassiopeia. CTB 109 is only one of three supernova remnants in our galaxy known to harbor a magnetar. X-rays at low, medium and high energies are respectively shown in red, green, and blue in this image created from observations acquired by the European Space Agency's XMM-Newton satellite in 2002. Credit: ESA/XMM-Newton/M. Sasaki et al.

"Astronomers have witnessed hundreds of events, called glitches, associated with sudden increases in the spin of neutron stars, but this sudden spin-down caught us off guard," said Victoria Kaspi, a professor of physics at McGill University in Montreal. She leads a team that uses Swift to monitor magnetars routinely.

Astronomers dubbed the event an "anti-glitch," said co-author Neil Gehrels, principal investigator of the Swift mission at NASA's Goddard Space Flight Center in Greenbelt, Md. "It affected the magnetar in exactly the opposite manner of every other clearly identified glitch seen in neutron stars."

The discovery has important implications for understanding the extreme physical conditions present within neutron stars, where matter becomes squeezed to densities several times greater than an atomic nucleus. No laboratory on Earth can duplicate these conditions.

A report on the findings appears in the May 30 edition of the journal Nature.


Image above: A neutron star is the densest object astronomers can observe directly, crushing half a million times Earth's mass into a sphere about 12 miles across, or similar in size to Manhattan Island, as shown in this illustration. Credit: NASA's Goddard Space Flight Center.

The internal structure of neutron stars is a long-standing puzzle. Current theory maintains a neutron star has a crust made up of electrons and ions; an interior containing oddities that include a neutron superfluid, which is a bizarre state of matter without friction; and a surface that accelerates streams of high-energy particles through the star's intense magnetic field.

The streaming particles drain energy from the crust. The crust spins down, but the fluid interior resists being slowed. The crust fractures under the strain. When this happens, a glitch occurs. There is an X-ray outburst and the star gets a speedup kick from the faster-spinning interior.

Processes that lead to a sudden rotational slowdown constitute a new theoretical challenge.

On April 21, 2012, just a week before Swift observed the anti-glitch, 1E 2259+586 produced a brief, but intense X-ray burst detected by the Gamma-ray Burst Monitor aboard NASA's Fermi Gamma-ray Space Telescope. The scientists think this 36-millisecond eruption of high-energy light likely signaled the changes that drove the magnetar's slowdown.


An artist's rendering of an outburst on an ultra-magnetic neutron star, also called a magnetar, showing magnetic field lines. Credit: NASA's Goddard Space Flight Center.

"What is really remarkable about this event is the combination of the magnetar's abrupt slowdown, the X-ray outburst, and the fact we now observe the star spinning down at a faster rate than before," said lead author Robert Archibald, a graduate student at McGill.

Goddard manages Swift, which was launched in November 2004. The telescope is operated in collaboration with Pennsylvania State University in University Park, Pa., the Los Alamos National Laboratory in New Mexico and Orbital Sciences Corp. in Dulles, Va. International collaborators are in the United Kingdom and Italy, and the mission includes contributions from Germany and Japan.

Related Links:

Download additional graphics from NASA Goddard's Scientific Visualization Studio: http://svs.gsfc.nasa.gov/goto?11260

Penn State press release: http://www.science.psu.edu/news-and-events/2013-news/Kennea5-2013

"New NASA Explorer Mission to Uncover Physics of Neutron Stars and Demonstrate Game-Changing Navigation Technology" (04.05.13): http://www.nasa.gov/centers/goddard/news/releases/2013/13-022.html

"NASA's Chandra Finds Superfluid in Neutron Star's Core" (02.23.11): http://www.nasa.gov/mission_pages/chandra/news/casa2011.html

"Eclipsing Pulsar Promises Clues to Crushed Matter" (08.17.10): http://www.nasa.gov/topics/universe/features/eclipsing-pulsar.html

The McGill Pulsar Group's Magnetar Catalog: http://www.physics.mcgill.ca/~pulsar/magnetar/main.html

NASA's Swift mission: http://www.nasa.gov/swift

NASA's Fermi Gamma-ray Space Telescope: http://www.nasa.gov/fermi

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

Best regards, Orbiter.ch

Low Sodium Diet Key to Old Age for Stars












ESO - European Southern Observatory logo.

29 May 2013

New VLT observations create major headache for stellar theories

The globular star cluster NGC 6752

Astronomers expect that stars like the Sun will blow off much of their atmospheres into space near the ends of their lives. But new observations of a huge star cluster made using ESO’s Very Large Telescope have shown — against all expectations — that a majority of the stars studied simply did not get to this stage in their lives at all. The international team found that the amount of sodium in the stars was a very strong predictor of how they ended their lives.

The way in which stars evolve and end their lives was for many years considered to be well understood. Detailed computer models predicted that stars of a similar mass to the Sun would have a period towards the ends of their lives — called the asymptotic giant branch, or AGB [1] — when they undergo a final burst of nuclear burning and puff off a lot of their mass in the form of gas and dust.

The globular star cluster NGC 6752 in the constellation of Pavo

This expelled material [2] goes on to form the next generations of stars and this cycle of mass loss and rebirth is vital to explain the evolving chemistry of the Universe. This process is also what provides the material required for the formation of planets — and indeed even the ingredients for organic life.

video
Zooming in on the globular star cluster NGC 6752

But when Australian stellar theory expert Simon Campbell of the Monash University Centre for Astrophysics, Melbourne, scoured old papers he found tantalising suggestions that some stars may somehow not follow the rules and might skip the AGB phase entirely. He takes up the story:

“For a stellar modelling scientist this suggestion was crazy! All stars go through the AGB phase according to our models. I double-checked all the old studies but found that this had not been properly investigated. I decided to investigate myself, despite having little observational experience.”

Campbell and his team used ESO’s Very Large Telescope (VLT) to very carefully study the light coming from stars in the globular star cluster NGC 6752 in the southern constellation of Pavo (The Peacock). This vast ball of ancient stars contains both a first generation of stars and a second that formed somewhat later [3]. The two generations can be distinguished by the amount of sodium they contain — something that the very high-quality VLT data can be used to measure.

“FLAMES, the multi-object high-resolution spectrograph on the VLT, was the only instrument that could allow us to get really high-quality data for 130 stars at a time. And it allowed us to observe a large part of the globular cluster in one go,” adds Campbell.

video
A close look at the globular star cluster NGC 6752

The results were a surprise — all of the AGB stars in the study were first generation stars with low levels of sodium and none of the higher-sodium second generation stars had become AGB stars at all. As many as 70% of the stars were not undergoing the final nuclear burning and mass-loss phase [4] [5].

“It seems stars need to have a low-sodium “diet” to reach the AGB phase in their old age. This observation is important for several reasons. These stars are the brightest stars in globular clusters — so there will be 70% fewer of the brightest stars than theory predicts. It also means our computer models of stars are incomplete and must be fixed!” concludes Campbell.

The team expects that similar results will be found for other star clusters and further observations are planned.

Notes:

[1] AGB stars get their odd name because of their position on the Hertzsprung Russell diagram, a plot of the brightnesses of stars against their colours.

[2] For a short period of time this ejected material is lit up by the strong ultraviolet radiation from the star and creates a planetary nebula (see for instance eso1317).

[3] Although the stars in a globular cluster all formed at about the same time, it is now well established that these systems are not as simple as they once thought to be. They usually contain two or more populations of stars with different amounts of light chemical elements such as carbon, nitrogen and — crucially for this new study — sodium.

[4] It is thought that stars which skip the AGB phase will evolve directly into helium white dwarf stars and gradually cool down over many billions of years.

[5] It is not thought that the sodium itself is the cause of the different behaviour, but must be strongly linked to the underlying cause — which remains mysterious.

More information:

This research was presented in a paper entitled “Sodium content as a predictor of the advanced evolution of globular cluster stars” by Simon Campbell et al., to appear online in the journal Nature on 29 May 2013.

The team is composed of Simon W. Campbell (Monash University, Melbourne, Australia), Valentina D’Orazi (Macquarie University, Sydney, Australia; Monash University), David Yong (Australian National University, Canberra, Australia [ANU]), Thomas N. Constantino (Monash University), John C. Lattanzio (Monash University), Richard J. Stancliffe (ANU; Universität Bonn, Germany), George C. Angelou (Monash University), Elizabeth C. Wylie-de Boer (ANU), Frank Grundahl (Aarhus University, Denmark).

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 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 the 39-metre European Extremely Large optical/near-infrared Telescope, the E-ELT, which will become “the world’s biggest eye on the sky”.

Links:

Research paper: http://www.eso.org/public/archives/releases/sciencepapers/eso1323/eso1323a.pdf

Photos of the VLT: http://www.eso.org/public/images/archive/category/paranal/

ESO images of planetary nebulae: http://www.eso.org/public/images/archive/search/?category=324

Images, Text, Credits: ESO, IAU and Sky & Telescope / Videos: ESO/Nick Risinger (skysurvey.org)/Steve Crouch, Music: movetwo.

Greetings, Orbiter.ch