jeudi 19 janvier 2017

Hubble's Slice of Sagittarius

NASA - Hubble Space Telescope patch.

Jan. 19, 2017

This stunning image, captured by the NASA/ESA Hubble Space Telescope’s Advanced Camera for Surveys (ACS), shows part of the sky in the constellation of Sagittarius (The Archer). The region is rendered in exquisite detail — deep red and bright blue stars are scattered across the frame, set against a background of thousands of more distant stars and galaxies. Two features are particularly striking: the colors of the stars, and the dramatic crosses that burst from the centers of the brightest bodies.

While some of the colors in this frame have been enhanced and tweaked during the process of creating the image from the observational data, different stars do indeed glow in different colors. Stars differ in color according to their surface temperature: very hot stars are blue or white, while cooler stars are redder. They may be cooler because they are smaller, or because they are very old and have entered the red giant phase, when an old star expands and cools dramatically as its core collapses.

The crosses are nothing to do with the stars themselves, and, because Hubble orbits above Earth’s atmosphere, nor are they due to any kind of atmospheric disturbance. They are actually known as diffraction spikes, and are caused by the structure of the telescope itself.

Like all big modern telescopes, Hubble uses mirrors to capture light and form images. Its secondary mirror is supported by struts, called telescope spiders, arranged in a cross formation, and they diffract the incoming light. Diffraction is the slight bending of light as it passes near the edge of an object. Every cross in this image is due to a single set of struts within Hubble itself! Whilst the spikes are technically an inaccuracy, many astrophotographers choose to emphasize and celebrate them as a beautiful feature of their images.

For images and more information about Hubble, visit:

Image, Text,  Credits: ESA/Hubble & NASA/Text Ccredits: European Space Agency/NASA/Karl Hille.

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Daphnis Up Close

NASA - Cassini International logo.

Jan. 19, 2017

The wavemaker moon, Daphnis, is featured in this view, taken as NASA's Cassini spacecraft made one of its ring-grazing passes over the outer edges of Saturn's rings on Jan. 16, 2017. This is the closest view of the small moon obtained yet.

Daphnis (5 miles or 8 kilometers across) orbits within the 42-kilometer (26-mile) wide Keeler Gap. Cassini's viewing angle causes the gap to appear narrower than it actually is, due to foreshortening.

The little moon's gravity raises waves in the edges of the gap in both the horizontal and vertical directions. Cassini was able to observe the vertical structures in 2009, around the time of Saturn's equinox (see PIA11654).

Like a couple of Saturn's other small ring moons, Atlas and Pan, Daphnis appears to have a narrow ridge around its equator and a fairly smooth mantle of material on its surface -- likely an accumulation of fine particles from the rings. A few craters are obvious at this resolution. An additional ridge can be seen further north that runs parallel to the equatorial band.

Fine details in the rings are also on display in this image. In particular, a grainy texture is seen in several wide lanes which hints at structures where particles are clumping together. In comparison to the otherwise sharp edges of the Keeler Gap, the wave peak in the gap edge at left has a softened appearance. This is possibly due to the movement of fine ring particles being spread out into the gap following Daphnis' last close approach to that edge on a previous orbit.

A faint, narrow tendril of ring material follows just behind Daphnis (to its left). This may have resulted from a moment when Daphnis drew a packet of material out of the ring, and now that packet is spreading itself out.

The image was taken in visible (green) light with the Cassini spacecraft narrow-angle camera. The view was acquired at a distance of approximately 17,000 miles (28,000 kilometers) from Daphnis and at a Sun-Daphnis-spacecraft, or phase, angle of 71 degrees. Image scale is 551 feet (168 meters) per pixel.

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

Related link:


For more information about the Cassini-Huygens mission visit and The Cassini imaging team homepage is at and

Image, Text,  Credits: NASA/JPL-Caltech/Space Science Institute/Tony Greicius.

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Bedrock Exhumed from the Deep

NASA - Mars Reconnaissance Orbiter (MRO) logo.

Jan. 19, 2017

Roadside bedrock outcrops are all too familiar for many who have taken a long road trip through mountainous areas on Earth. Martian craters provide what tectonic mountain building and man's TNT cannot: crater-exposed bedrock outcrops.

Although crater and valley walls offer us roadside-like outcrops from just below the Martian surface, their geometry is not always conducive to orbital views. On the other hand, a crater central peak -- a collection of mountainous rocks that have been brought up from depth, but also rotated and jumbled during the cratering process -- produce some of the most spectacular views of bedrock from orbit.

This color composite cutout shows an example of such bedrock that may originate from as deep as 2 miles beneath the surface. The bedrock at this scale is does not appear to be layered or made up of grains, but has a massive appearance riddled with cross-cutting fractures, some of which have been filled by dark materials and rock fragments (impact melt and breccias) generated by the impact event. A close inspection of the image shows that these light-toned bedrock blocks are partially to fully covered by sand dunes and coated with impact melt bearing breccia flows.

This is a stereo pair with

The University of Arizona, Tucson, operates HiRISE, which was built by Ball Aerospace & Technologies Corp., Boulder, Colo. NASA's Jet Propulsion Laboratory, a division of Caltech in Pasadena, California, manages the Mars Reconnaissance Orbiter Project for NASA's Science Mission Directorate, Washington.

Mars Reconnaissance Orbiter (MRO):

Image, Text, Credits: NASA/HiRISE/Tony Greicius.


mercredi 18 janvier 2017

BASE precisely measures antiproton’s magnetic moment

CERN - European Organization for Nuclear Research logo.

Jan. 18, 2017

In a paper published today in the journal Nature Communications, the BASE collaboration at CERN reports the most precise measurement ever made of the magnetic moment of the antiproton, allowing a fundamental comparison between matter and antimatter. The BASE measurement shows that the magnetic moments of the proton and antiproton are identical, apart from their opposite signs, within the experimental uncertainty of 0.8 parts per million. The result improves the precision of the previous best measurement by the ATRAP collaboration in 2013, also at CERN, by a factor of 6.

At the scale of elementary particles, an almost perfect symmetry between matter and antimatter exists. On cosmological scales, however, the amount of matter outweighs that of antimatter. Understanding this profound contradiction demands that physicists compare the fundamental properties of particles and their antiparticles with high precision.

BASE uses antiprotons from CERN’s unique antimatter factory, the Antiproton Decelerator (AD), and is designed specifically to perform precision measurements of the antimatter counterparts of normal matter particles. The magnetic moment, which determines how a particle behaves when immersed in a magnetic field, is one of the most studied intrinsic characteristics of a particle. Although different particles have different magnetic behaviour, the magnetic moments of protons and antiprotons are supposed to differ only in their sign as a consequence of so-called charge-parity-time symmetry. Any difference in their magnitudes would challenge the Standard Model of particle physics and would offer a glimpse of new physics.

Image above: The BASE collaboration at CERN reports the most precise measurement ever made of the magnetic moment of the antiproton, allowing a fundamental comparison between matter and antimatter (Image: Maximilien Brice/CERN).

To perform the experiments, the BASE collaboration cools down antiprotons to the extremely low temperature of about 1 degree above absolute zero, and traps them using sophisticated electromagnetic containers so that they do not come into contact with matter and annihilate (thanks to such devices, BASE has recently managed to store a bunch of antiprotons for more than one year). From here, antiprotons are fed one-by-one to further traps where their behaviour under magnetic fields allows researchers to determine their intrinsic magnetic moment. Similar techniques have already been successfully applied in the past to electrons and their antimatter partners, positrons, but antiprotons present a much bigger challenge because their magnetic moments are considerably weaker. The new BASE measurement required a specially designed magnetic “bottle” that is more than 1000 times stronger than that used in electron/positron experiments.

“This measurement is so far the culmination point of 10 years of hard work by the BASE team,” said Stefan Ulmer, spokesperson of the BASE collaboration. “Together with other AD experiments, we are really making rapid progress in our understanding of antimatter.”

BASE now plans to measure the antiproton magnetic moment using a new trapping technique that should enable a precision at the level of a few parts per billion – i.e. a factor of 200 to 800 improvement. “The implementation of this method is much more challenging than the method which was used here and will require several additional iteration steps,” says first author Hiroki Nagahama.


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

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

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

Related articles:

ATRAP experiment makes world’s most precise measurement of antiproton magnetic moment

The BASE antiprotons celebrate their first birthday

Related links:

Nature Communications:


Antiproton Decelerator (AD):

Elementary particles:


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

Image (mentioned), Text, Credits: CERN/Harriet Kim Jarlett.

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Chandra Images Show That Geometry Solves a Pulsar Puzzle

NASA - Chandra X-ray Observatory patch.

Jan. 18, 2017

NASA's Chandra X-ray Observatory has taken deep exposures of two nearby energetic pulsars flying through the Milky Way galaxy. The shape of their X-ray emission suggests there is a geometrical explanation for puzzling differences in behavior shown by some pulsars.

Pulsars − rapidly rotating, highly magnetized, neutron stars born in supernova explosions triggered by the collapse of massive stars − were discovered 50 years ago via their pulsed, highly regular, radio emission.  Pulsars produce a lighthouse-like beam of radiation that astronomers detect as pulses as the pulsar's rotation sweeps the beam across the sky.

Since their discovery, thousands of pulsars have been discovered, many of which produce beams of radio waves and gamma rays. Some pulsars show only radio pulses and others show only gamma-ray pulses. Chandra observations have revealed steadier X-ray emission from extensive clouds of high-energy particles, called pulsar wind nebulas, associated with both types of pulsars. New Chandra data on pulsar wind nebulas may explain the presence or absence of radio and gamma-ray pulses.

Image credits: Geminga image: NASA/CXC/PSU/B. Posselt et al; Infrared: NASA/JPL-Caltech; B0355+54: X-ray: NASA/CXC/GWU/N. Klingler et al; Infrared: NASA/JPL-Caltech; Illustrations: Nahks TrEhnl.

This four-panel graphic shows the two pulsars observed by Chandra. Geminga is in the upper left and B0355+54 is in the upper right. In both of these images, Chandra’s X-rays, colored blue and purple, are combined with infrared data from NASA’s Spitzer Space Telescope that shows stars in the field of view. Below each data image, an artist’s illustration depicts more details of what astronomers think the structure of each pulsar wind nebula looks like.

For Geminga, a deep Chandra observation totaling nearly eight days over several years was analyzed to show sweeping, arced trails spanning half a light year and a narrow structure directly behind the pulsar. A five-day Chandra observation of the second pulsar, B0355+54, showed a cap of emission followed by a narrow double trail extending almost five light years.

The underlying pulsars are quite similar, both rotating about five times per second and both aged about half a million years. However, Geminga shows gamma-ray pulses with no bright radio emission, while B0355+54 is one of the brightest radio pulsars known yet not seen in gamma rays.

A likely interpretation of the Chandra images is that the long narrow trails to the side of Geminga and the double tail of B0355+54 represent narrow jets emanating from the pulsar’s spin poles. Both pulsars also contain a torus of emission spreading from the pulsar’s spin equator. These disk-shaped structures and the jets are crushed and swept back as the pulsars fly through the Galaxy at supersonic speeds

In the case of Geminga, the view of the torus is close to edge-on, while the jets point out to the sides.  B0355+54 has a similar structure, but with the torus viewed nearly face-on and the jets pointing nearly directly towards and away from Earth. In B0355+54, the swept-back jets appear to lie almost on top of each other, giving a doubled tail.

Both pulsars have magnetic poles quite close to their spin poles, as is the case for the Earth’s magnetic field. These magnetic poles are the site of pulsar radio emission so astronomers expect the radio beams to point in a similar direction as the jets. By contrast the gamma-ray emission is mainly produced along the spin equator and so aligns with the torus.

For Geminga, astronomers view the bright gamma-ray pulses along the edge of the torus, but the radio beams near the jets point off to the sides and remain unseen. For B0355+54, a jet points almost along our line of sight towards the pulsar. This means astronomers see the bright radio pulses, while the torus and its associated gamma-ray emission are directed in a perpendicular direction to our line of sight, missing the Earth.

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

These two deep Chandra images have, therefore, exposed the spin orientation of these pulsars, helping to explain the presence, and absence, of the radio and gamma-ray pulses.

The Chandra observations of Geminga and B0355+54 are part of a large campaign, led by Roger Romani of Stanford University, to study six pulsars that have been seen to emit gamma-rays. The survey sample covers a range of ages, spin-down properties and expected inclinations, making it a powerful test of pulsar emission models.

A paper on Geminga led by Bettina Posselt of Penn State University was accepted for publication in The Astrophysical Journal and is available online. A paper on B0355+54 led by Noel Klingler of the George Washington University was published in the December 20th, 2016 issue of The Astrophysical Journal and is available online. 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.

The Astrophysical Journal:

Read More from NASA's Chandra X-ray Observatory:

For more Chandra images, multimedia and related materials, visit:

Images & Illustations (mentioned), Text, Credits: NASA/Lee Mohon.


Galileo: Swiss components have broken down

ESA - GALILEO Programme logo.

Jan. 18, 2017

New glitch for the "European GPS": several of the atomic clocks on board its satellites no longer work.

"This does not affect for the moment" the navigation system that has just started its services, according to the European Space Agency (ESA). "This is a sensitive issue", as atomic clocks are "very important" elements for the smooth operation of the satellite navigation system, which is a competitor to the US GPS, ESA Director General Jan Woerner said, A press conference in Paris.

Galileo satellites

However, in his view, we can not speak of "a new setback" for Galileo, which has experienced many delays and problems since the launch of the program in 1999. Its total cost is about ten billion euros .

So far 18 satellites have been launched. The constellation must count 30 operational satellites and two reserve ones by 2020. "The system is not questioned, not at all", Galileo "continues" but "we want to be transparent," said the official.

Four on each satellite

The atomic clocks of Galileo are supposed to ensure to the European system a very high precision. That is why each satellite carefully carries with it four atomic clocks of two types ("passive hydrogen masers" and rubidium atomic clocks). In order for each satellite to work well on this plane, at least one of the four clocks must be in good working order.

Passive hydrogen masers (atomic clock) by Argotec

Currently 9 out of 72 clocks are down (6 passive hydrogen masers, 3 rubidium atomic clocks), said Woerner, pointing out that "on every satellite there are at least two clocks that work."

"To date, thanks to this redundancy of clocks, none of the satellites in the constellation is out of order," he said.

Swiss Clocks

ESA is investigating the causes of the problem and has successfully restarted one of these clocks when previously it thought to have ten broken down. The satellites concerned have been launched at various times and the last ones, in orbit since November, are also concerned.

"We must learn the behavior of these atomic clocks and how to use them," Woerner said. They are manufactured by SpectraTime, based in Neuchâtel, with partners. SpectraTime confirmed to the ats that its experts are involved in research to identify the causes of the outage.

Rubidium atomic clock by SpectraTime

In this context, should the launch of four new Galileo satellites be delayed by an Ariane 5 rocket planned for the second half of 2017? "It's a sensitive issue," said Woerner. "If we wait and have other failures, we risk reducing the capacity of the system. But if we launch new satellites, they risk taking atomic clocks with problems. "

Do not delay the program

"Personally, I am in favor of not delaying the deployment of the constellation," he added. On 15 December, Europe launched the first services of its Galileo system, with the promise of a more precise location, reserved at present for the few possessors of compatible equipment.

Only a handful of privileged, possessors of the few smartphones compatible with Galileo (the first, the Aquaris X5 Plus of the Spanish manufacturer BQ, has been on the market since the autumn) can for now pick up the new signal.

These pioneers will be able to use the European system free of charge to find a pharmacy, the best route to go on holiday or settle their stride in the marathon. But for a mass arrival of products compatible with Galileo, we will have to be a little patient.

To the nearest centimeter

The European service aims to be more efficient with, in particular, a positioning of a precision, of the order of one meter, greater than that of its competitors. In addition, a paid service will allow a location within a few centimeters.

Galileo constellation

Moreover, the European signal will be dated to a few billionths of a second, a useful service for banks, insurance companies and energy suppliers.

Passive hydrogen masers must precisely ensure a stability of the nanosecond (one billionth of a second) per 24 hours, which is equivalent to losing or gaining a second every 2.7 million years. Rubidium clocks offer an accuracy of 10 nanoseconds per day.

As Galileo is compatible with GPS, the user can access both systems simultaneously and improve the quality and reliability of his position.

What is Galileo?:

ESA GALILEO / Navigation:



Images, Text, Credits: ATS/ESA/Argotec/SpectraTime/ Aerospace/Roland Berga.

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NASA, NOAA Data Show 2016 Warmest Year on Record Globally

NASA Goddard Institute for Space Studies logo.

Jan. 18, 2017

Global temperatures 2012-2016

Earth’s 2016 surface temperatures were the warmest since modern recordkeeping began in 1880, according to independent analyses by NASA and the National Oceanic and Atmospheric Administration (NOAA).

Globally-averaged temperatures in 2016 were 1.78 degrees Fahrenheit (0.99 degrees Celsius) warmer than the mid-20th century mean. This makes 2016 the third year in a row to set a new record for global average surface temperatures.

The 2016 temperatures continue a long-term warming trend, according to analyses by scientists at NASA’s Goddard Institute for Space Studies (GISS) in New York. NOAA scientists concur with the finding that 2016 was the warmest year on record based on separate, independent analyses of the data.

Animated graphic above: The planet’s long-term warming trend is seen in this chart of every year’s annual temperature cycle from 1880 to the present, compared to the average temperature from 1880 to 2015. Record warm years are listed in the column on the right.
Graphic Credits: NASA/Joshua Stevens, Earth Observatory.

Because weather station locations and measurement practices change over time, there are uncertainties in the interpretation of specific year-to-year global mean temperature differences. However, even taking this into account, NASA estimates 2016 was the warmest year with greater than 95 percent certainty.

“2016 is remarkably the third record year in a row in this series,” said GISS Director Gavin Schmidt. “We don’t expect record years every year, but the ongoing long-term warming trend is clear.”

The planet’s average surface temperature has risen about 2.0 degrees Fahrenheit (1.1 degrees Celsius) since the late 19th century, a change driven largely by increased carbon dioxide and other human-made emissions into the atmosphere.

Most of the warming occurred in the past 35 years, with 16 of the 17 warmest years on record occurring since 2001. Not only was 2016 the warmest year on record, but eight of the 12 months that make up the year – from January through September, with the exception of June – were the warmest on record for those respective months. October, November, and December of 2016 were the second warmest of those months on record – in all three cases, behind records set in 2015.

Phenomena such as El Niño or La Niña, which warm or cool the upper tropical Pacific Ocean and cause corresponding variations in global wind and weather patterns, contribute to short-term variations in global average temperature. A warming El Niño event was in effect for most of 2015 and the first third of 2016. Researchers estimate the direct impact of the natural El Niño warming in the tropical Pacific increased the annual global temperature anomaly for 2016 by 0.2 degrees Fahrenheit (0.12 degrees Celsius). 

NASA's Analysis of 2016 Global Temperature

Video above: Animation of global temperatures since 1880. Video Credits: NASA/Scientific Visualization Studio.

Weather dynamics often affect regional temperatures, so not every region on Earth experienced record average temperatures last year. For example, both NASA and NOAA found the 2016 annual mean temperature for the contiguous 48 United States was the second warmest on record. In contrast, the Arctic experienced its warmest year ever, consistent with record low sea ice found in that region for most of the year.

NASA’s analyses incorporate surface temperature measurements from 6,300 weather stations, ship- and buoy-based observations of sea surface temperatures, and temperature measurements from Antarctic research stations. These raw measurements are analyzed using an algorithm that considers the varied spacing of temperature stations around the globe and urban heating effects that could skew the conclusions. The result of these calculations is an estimate of the global average temperature difference from a baseline period of 1951 to 1980.

NOAA scientists used much of the same raw temperature data, but with a different baseline period, and different methods to analyze Earth’s polar regions and global temperatures.

GISS is a laboratory within the Earth Sciences Division of NASA’s Goddard Space Flight Center in Greenbelt, Maryland. The laboratory is affiliated with Columbia University’s Earth Institute and School of Engineering and Applied Science in New York.

NASA monitors Earth's vital signs from land, air and space with a fleet of satellites, as well as airborne and ground-based observation campaigns. The agency develops new ways to observe and study Earth's interconnected natural systems with long-term data records and computer analysis tools to better see how our planet is changing. NASA shares this unique knowledge with the global community and works with institutions in the United States and around the world that contribute to understanding and protecting our home planet.

The full 2016 surface temperature data set and the complete methodology used to make the temperature calculation are available at:

The slides for the Jan. 18, news conference are available at:

For more information about NASA's Earth science programs, visit:

Image, Graphic (mentioned), Video (mentioned), Text, Credits: NASA/Sean Potter/Karen Northon/Goddard Institute for Space Studies/Michael Cabbage/Leslie McCarthy.