Cambridge academics shed new light on the Sun

New insights into solar activity have been revealed thanks to research from a group of Cambridge academics.

The work comes from the Atomic Astrophysics Group (AAG) at the University’s Department of Applied Mathematics and Theoretical Physics, who have been collaborating on an international solar mission, the Hinode project, with a number of space agencies.

Their research involves detailed analyses of regions of intense activity in the Sun’s atmosphere, the corona. Through examination of the ultraviolet radiation given off by these areas, known as active regions, they have found a variety of dynamic activities, including jets and flows of gas with speeds of up to 150 kilometres per second.

Temperatures within the corona are extremely high (in excess of one million degrees), whereas the solar surface is much cooler at about 6000 degrees. AAG has been seeking to understand why the corona is so hot and what the linkages are between the solar surface and atmosphere.

For the first time, the team have been able to measure physical characteristics, such as the density and temperature of features of the solar atmosphere in great detail. They found strong connections between changes in the magnetic field of the solar surface and events in the overlying active regions.

These new insights have been made possible through the Hinode spacecraft, which has provided unprecedented views of the Sun. The AAG team work mainly with the EUV Imaging Spectrometer (EIS), led by the UK.

Cristina Chifor, a graduate student with AAG, said: “Since its launch, Hinode has been returning exciting new results. Last year, I had the opportunity to go out to Japan, visit the institute where Hinode is operated, and carry out the daily planning of Hinode/EIS observations.

“It was great fun to be able to 'drive' an instrument so far away in space and to see the data coming down from the spacecraft shortly after. It was a fantastic experience, and Japan is a wonderful place to visit.”

Their results will further our understanding of solar phenomena which can affect the Earth’s environment. Active regions on the Sun can produce huge explosions of gas, which can damage satellites and cause aurora (as seen, for example, in the Northern Lights). They will also increase our knowledge of stars in general.

Dr Helen Mason, group leader for AAG, said: “The Hinode satellite is providing us with some stunning new observations. We can see the Sun in far more detail than we were previously able to. The more detail we see, the more challenging it is to explain! I am so pleased that a younger generation of solar researchers have the opportunity to experience the excitement of working on new solar space observations.”

AAG has 'swept the board' with their results, having four papers published in a special issue of Astronomy and Astrophysics (Vol 481) and one of their images (from C. Chifor et al.) on the front cover.

The Hinode spacecraft was launched in September 2006, as a joint UK, European, US and Japanese mission. The mission is operated by Institute of Space and Astronautical Science and Japan Aerospace Exploration Agency in collaboration with NASA, European Space Agency, Science and Technology Facilities Council and Norwegian Space Centre.

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A Giant of Astronomy and a Quantum of Solace

Cerro Paranal, the 2600m high mountain in the Chilean Atacama Desert that hosts ESO's Very Large Telescope, will be the stage for scenes in the next James Bond movie, "Quantum of Solace".
Looking akin to Mars, with its red sand and lack of vegetation, the Atacama Desert is thought to be the driest place on Earth. Cerro Paranal is home to ESO's Very Large Telescope (VLT), which, with its array of four giant 8.2-m individual telescopes, is the world's most advanced optical observatory. The high-altitude site and extreme dryness make excellent conditions for astronomical observations.

"We needed a unique site for a unique set of telescopes, and we found it at Paranal," said Andreas Kaufer, ESO's Paranal Director. "We are very excited that the Bond production team have also chosen this location."

The excellent astronomical conditions at Paranal come at a price, however. In this forbidding desert environment, virtually nothing can grow outside. The humidity drops below 10%, there are intense ultraviolet rays from the sun, and the high altitude leaves people short of breath. Living in this extremely isolated place feels like visiting another planet.

To make it possible for people to live and work here, a hotel or "Residencia" was built in the base camp, allowing them to escape from the arid outside environment. Here, returning from long shifts at the VLT and other installations on the mountain, they can breathe moist air and relax, sheltered from the harsh conditions outside. The Residencia's award-winning design, including an enclosed tropical garden and pool under a futuristic domed roof, gives its interior a feeling of open space within the protective walls - this is a true "haven in the desert".

It is this unique building that serves as the backdrop for the James Bond filming.

QUANTUM OF SOLACE producer, Michael G. Wilson said: "The Residencia of Paranal Observatory caught the attention of our director, Marc Forster and production designer, Dennis Gassner, both for its exceptional design and its remote location in the Atacama desert. It is a true oasis and the perfect hide-out for Dominic Greene, our villain, whom 007 is tracking in our new James Bond film."

In addition to the shooting at the Residencia, further action will take place at the Paranal airstrip.

The film crew present on Paranal includes Englishman Daniel Craig, taking again the role of James Bond, French actor Mathieu Amalric, leading lady Olga Kurylenko, from the Ukraine, as well as acclaimed Mexican actors, Joaquin Cosio and Jesus Ochoa. This cast from across Europe and Latin America mirrors the international staff that works for ESO at Paranal.

After leaving Paranal at the end of the week, the film crew will shoot in other locations close to Antofagasta. Other sequences have been filmed in Panama and, following the Chilean locations, the unit will be travelling to Italy and Austria before returning to Pinewood Studios near London in May.

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NASA Satellite Detects Record Gamma Ray Burst Explosion Halfway Across Universe

A powerful stellar explosion detected March 19 by NASA's Swift satellite has shattered the record for the most distant object that could be seen with the naked eye.

The explosion was a gamma ray burst. Most gamma ray bursts occur when massive stars run out of nuclear fuel. Their cores collapse to form black holes or neutron stars, releasing an intense burst of high-energy gamma rays and ejecting particle jets that rip through space at nearly the speed of light like turbocharged cosmic blowtorches. When the jets plow into surrounding interstellar clouds, they heat the gas, often generating bright afterglows. Gamma ray bursts are the most luminous explosions in the universe since the big bang.

"This burst was a whopper," said Swift principal investigator Neil Gehrels of NASA's Goddard Space Flight Center in Greenbelt, Md. "It blows away every gamma ray burst we've seen so far."

Swift's Burst Alert Telescope picked up the burst at 2:12 a.m. EDT, March 19, and pinpointed the coordinates in the constellation Boötes. Telescopes in space and on the ground quickly moved to observe the afterglow. The burst is named GRB 080319B, because it was the second gamma ray burst detected that day.

Swift's other two instruments, the X-ray Telescope and the Ultraviolet/Optical Telescope, also observed brilliant afterglows. Several ground-based telescopes saw the afterglow brighten to visual magnitudes between 5 and 6 in the logarithmic magnitude scale used by astronomers. The brighter an object is, the lower its magnitude number. From a dark location in the countryside, people with normal vision can see stars slightly fainter than magnitude 6. That means the afterglow would have been dim, but visible to the naked eye.

Later that evening, the Very Large Telescope in Chile and the Hobby-Eberly Telescope in Texas measured the burst's redshift at 0.94. A redshift is a measure of the distance to an object. A redshift of 0.94 translates into a distance of 7.5 billion light years, meaning the explosion took place 7.5 billion years ago, a time when the universe was less than half its current age and Earth had yet to form. This is more than halfway across the visible universe.

"No other known object or type of explosion could be seen by the naked eye at such an immense distance," said Swift science team member Stephen Holland of Goddard. "If someone just happened to be looking at the right place at the right time, they saw the most distant object ever seen by human eyes without optical aid."

GRB 080319B's optical afterglow was 2.5 million times more luminous than the most luminous supernova ever recorded, making it the most intrinsically bright object ever observed by humans in the universe. The most distant previous object that could have been seen by the naked eye is the nearby galaxy M33, a relatively short 2.9 million light-years from Earth.

Analysis of GRB 080319B is just getting underway, so astronomers don't know why this burst and its afterglow were so bright. One possibility is the burst was more energetic than others, perhaps because of the mass, spin, or magnetic field of the progenitor star or its jet. Or perhaps it concentrated its energy in a narrow jet that was aimed directly at Earth.

GRB 080319B was one of four bursts that Swift detected, a Swift record for one day. "Coincidentally, the passing of Arthur C. Clarke seems to have set the universe ablaze with gamma ray bursts," said Swift science team member Judith Racusin of Penn State University in University Park, Pa.

Swift is managed by Goddard. It was built and is being operated in collaboration with Penn State, the Los Alamos National Laboratory, and General Dynamics in the U.S.; the University of Leicester and Mullard Space Sciences Laboratory in the United Kingdom; Brera Observatory and the Italian Space Agency in Italy; plus partners in Germany and Japan.

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New discovery at Jupiter could help protect Earth-orbit satellites

Radio waves accelerate electrons within Jupiter's magnetic field in the same way as they do on Earth

Radio waves accelerate electrons within Jupiter’s magnetic field in the same way as they do on Earth, according to new research published in Nature Physics this week. The discovery overturns a theory that has held sway for more than a generation and has important implications for protecting Earth-orbiting satellites.

Using data collected at Jupiter by the Galileo spacecraft, Dr Richard Horne of British Antarctic Survey (BAS) and colleagues from the University of California, Los Angeles, and the University of Iowa found that a special type of very low frequency radio wave is strong enough to accelerate electrons up to very high energies inside Jupiter’s magnetic field.

According to lead author, Dr Richard Horne,

“We’ve shown before that very low frequency radio waves can accelerate electrons in the Earth’s magnetic field, but we have now shown that exactly the same theory works on Jupiter, where the magnetic field is 20,000 times stronger than the Earth’s and the composition of the atmosphere is very different. This is the ultimate test of our theory.”

“On Jupiter, the waves are powered by energy from volcanoes on the moon Io, combined with the planet’s rapid rotation – once every 10 hours. Volcanic gasses are ionized and flung out away from the planet by centrifugal force. This material is replaced by an inward flow of particles that excite the waves that in turn accelerate the electrons.”

Understanding how electrons are accelerated will help scientists make better predictions of when satellites are at risk of damage by high-energy charged particles. These particles encircle the Earth in the Van Allen radiation belts and can damage satellites by causing malfunctions and degrading electronic components. However, the number of particles in the radiation belts can change dramatically within a few minutes, which is why more accurate forecasting is needed.

The discovery also has other scientific implications for Jupiter – it overturns a theory that has held sway for more than 30 years. According to Dr Horne,

“For more than 30 years it was thought that the electrons are accelerated as a result of transport towards Jupiter, but now we show that gyro-resonant wave acceleration is a very important step that acts in concert. Once the electrons are accelerated, they are transported closer to the planet and emit intense synchrotron radiation out into interplanetary space. Our theory provides the missing step to explain this high intensity radiation from Jupiter, which was first detected on Earth more than 50 years ago.

Via

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Light echoes whisper the distance to a star

Astronomers calibrate the distance scale of the Universe

Taking advantage of the presence of light echoes, a team of astronomers have used an ESO telescope to measure, at the 1% precision level, the distance of a Cepheid - a class of variable stars that constitutes one of the first steps in the cosmic distance ladder.

"Our measurements with ESO's New Technology Telescope at La Silla allow us to obtain the most accurate distance to a Cepheid," says Pierre Kervella, lead-author of the paper reporting the result.

Cepheids [1] are pulsating stars that have been used as distance indicators since almost a hundred years. The new accurate measurement is important as, contrary to many others, it is purely geometrical and does not rely on hypotheses about the physics at play in the stars themselves.

The team of astronomers studied RS Pup, a bright Cepheid star located towards the constellation of Puppis ('the Stern') and easily visible with binoculars. RS Pup varies in brightness by almost a factor of five every 41.4 days. It is 10 times more massive than the Sun, 200 times larger, and on average 15 000 times more luminous.

RS Pup is the only Cepheid to be embedded in a large nebula [2], which is made of very fine dust that reflects some of the light emitted by the star.

Because the luminosity of the star changes in a very distinctive pattern, the presence of the nebula allows the astronomers to see light echoes and use them to measure the distance of the star.

"The light that travelled from the star to a dust grain and then to the telescope arrives a bit later than the light that comes directly from the star to the telescope," explains Kervella. "As a consequence, if we measure the brightness of a particular, isolated dust blob in the nebula, we will obtain a brightness curve that has the same shape as the variation of the Cepheid, but shifted in time."

This delay is called a 'light echo', by analogy with the more traditional echo, the reflection of sound by, for example, the bottom of a well.

By monitoring the evolution of the brightness of the blobs in the nebula, the astronomers can derive their distance from the star: it is simply the measured delay in time, multiplied by the velocity of light (300 000 km/s). Knowing this distance and the apparent separation on the sky between the star and the blob, one can compute the distance of RS Pup.

From the observations of the echoes on several nebular features, the distance of RS Pup was found to be 6500 light years, plus or minus 90 light years.

"Knowing the distance to a Cepheid star with such an accuracy proves crucial to the calibration of the period-luminosity relation of this class of stars," says Kervella. "This relation is indeed at the basis of the distance determination of galaxies using Cepheids."

RS Pup is thus distant by about a quarter of the distance between the Sun and the Centre of the Milky Way. RS Pup is located within the Galactic plane, in a very populated region of our Galaxy.

Notes

[1]: Cepheids are rare and very luminous pulsating stars whose luminosity varies in a very regular way. They are named after the star Delta Cephei in the constellation of Cepheus, the first known variable star of this particular type and bright enough to be easily seen with the unaided eye. Almost a century ago, in 1912, American astronomer Henrietta Leavitt published a relation between the intrinsic brightness and the pulsation period of Cepheids, the longer periods corresponding to the brighter stars. This relation still plays today a central role in the extragalactic distance scale.

[2]: The nebula around RS Pup was discovered in 1961 by Swedish astronomer Bengt Westerlund, who later became ESO Director in Chile (1970-74).

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WMAP Reveals Neutrinos, End of Dark Ages, First Second of Universe

NASA released this week five years of data collected by the Wilkinson Microwave Anisotropy Probe (WMAP) that refines our understanding of the universe and its development. It is a treasure trove of information, including at least three major findings:

New evidence that a sea of cosmic neutrinos permeates the universe

Clear evidence the first stars took more than a half-billion years to create a cosmic fog

Tight new constraints on the burst of expansion in the universe's first trillionth of a second

"We are living in an extraordinary time," said Gary Hinshaw of NASA's Goddard Space Flight Center in Greenbelt, Md. "Ours is the first generation in human history to make such detailed and far-reaching measurements of our universe."

WMAP measures a remnant of the early universe - its oldest light. The conditions of the early times are imprinted on this light. It is the result of what happened earlier, and a backlight for the later development of the universe. This light lost energy as the universe expanded over 13.7 billion years, so WMAP now sees the light as microwaves. By making accurate measurements of microwave patterns, WMAP has answered many longstanding questions about the universe's age, composition and development.

The universe is awash in a sea of cosmic neutrinos. These almost weightless sub-atomic particles zip around at nearly the speed of light. Millions of cosmic neutrinos pass through you every second.

"A block of lead the size of our entire solar system wouldn't even come close to stopping a cosmic neutrino," said science team member Eiichiro Komatsu of the University of Texas at Austin.

WMAP has found evidence for this so-called "cosmic neutrino background" from the early universe. Neutrinos made up a much larger part of the early universe than they do today.

Microwave light seen by WMAP from when the universe was only 380,000 years old, shows that, at the time, neutrinos made up 10% of the universe, atoms 12%, dark matter 63%, photons 15%, and dark energy was negligible. In contrast, estimates from WMAP data show the current universe consists of 4.6% percent atoms, 23% dark matter, 72% dark energy and less than 1 percent neutrinos.

Cosmic neutrinos existed in such huge numbers they affected the universe's early development. That, in turn, influenced the microwaves that WMAP observes. WMAP data suggest, with greater than 99.5% confidence, the existence of the cosmic neutrino background - the first time this evidence has been gleaned from the cosmic microwaves.

Much of what WMAP reveals about the universe is because of the patterns in its sky maps. The patterns arise from sound waves in the early universe. As with the sound from a plucked guitar string, there is a primary note and a series of harmonics, or overtones. The third overtone, now clearly captured by WMAP, helps to provide the evidence for the neutrinos.

The hot and dense young universe was a nuclear reactor that produced helium. Theories based on the amount of helium seen today predict a sea of neutrinos should have been present when helium was made. The new WMAP data agree with that prediction, along with precise measurements of neutrino properties made by Earth-bound particle colliders.

Another breakthrough derived from WMAP data is clear evidence the first stars took more than a half-billion years to create a cosmic fog. The data provide crucial new insights into the end of the "dark ages," when the first generation of stars began to shine. The glow from these stars created a thin fog of electrons in the surrounding gas that scatters microwaves, in much the same way fog scatters the beams from a car's headlights.

"We now have evidence that the creation of this fog was a drawn-out process, starting when the universe was about 400 million years old and lasting for half a billion years," said WMAP team member Joanna Dunkley of the University of Oxford in the U.K. and Princeton University in Princeton, N.J. "These measurements are currently possible only with WMAP."

A third major finding arising from the new WMAP data places tight constraints on the astonishing burst of growth in the first trillionth of a second of the universe, called "inflation", when ripples in the very fabric of space may have been created. Some versions of the inflation theory now are eliminated. Others have picked up new support.

"The new WMAP data rule out many mainstream ideas that seek to describe the growth burst in the early universe," said WMAP principal investigator, Charles Bennett, of The Johns Hopkins University in Baltimore, Md. "It is astonishing that bold predictions of events in the first moments of the universe now can be confronted with solid measurements."

The five-year WMAP data were released this week, and results were issued in a set of seven scientific papers submitted to the Astrophysical Journal. For further information, see

http://wmap.gsfc.nasa.gov

Prior to the release of the new five-year data, WMAP already had made a pair of landmark finds. In 2003, the probe's determination that there is a large percentage of dark energy in the universe erased remaining doubts about dark energy's very existence. That same year, WMAP also pinpointed the 13.7 billion year age of the universe.

Additional WMAP science team institutions are: the Canadian Institute for Theoretical Astrophysics, Columbia University, University of British Columbia, ADNET Systems, University of Chicago, Brown University, and UCLA.

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NASA Know-How Helps Athletes Rocket Through Water

When a swimsuit manufacturer wanted to create a better fabric for competitive swimmers, it sought out some unlikely experts -- aerospace engineers at NASA's Langley Research Center in Hampton.

NASA has decades of experience in fluid dynamics and drag reduction. However, aerospace engineers usually concentrate on the element through which airplanes and spacecraft fly, not the liquid through which swimmers travel. Still, some of the science is similar.

"Air and water are both what are referred to as Newtonian fluids," said Steve Wilkinson, a researcher at Langley's Fluid Physics and Control Branch. "Air has different fluid properties than water, including lower density and viscosity, but it still obeys the same physical laws of motion."

That fact led Warnaco Inc. of New York, the U.S. licensee of the Speedo swimwear brand, to seek use of a NASA wind tunnel at Langley to test swimsuit fabrics that may be used by athletes in international competitions.

"We evaluated the surface roughness effects of nearly 60 fabrics or patterns in our small low-speed tunnel, which is perfect for this purpose," Wilkinson said. "We were assessing which fabrics and weaves had the lowest drag."

Reducing drag helps planes fly more efficiently, and reducing drag helps swimmers go faster. Studies indicate viscous drag, or skin friction, is about one-third of the total restraining force on a swimmer. Wind tunnel tests measure the drag on the surface of the fabrics.

Wilkinson and other NASA researchers usually spend their time studying drag reduction for airplanes. They even have worked on drag reduction technology for boats, including an America's Cup winner in the 1980s. This expertise is one reason Speedo chose to work with NASA.

"This is the first time I've tested a fabric and there were some challenges involved," said Wilkinson. "I think we've done a really good job with the help of Speedo in coming up with a protocol that enables us to test these fabrics with ease and precision."

The materials tested come in the form of tubes. Wilkinson stretches the tubes over a smooth, flat aluminum plate and then secures the edges with smooth metal rails and tape to form a precise rectangular model shape. Wilkinson runs the material through a number of wind speeds and, with the help of sensors, measures drag on the surface. Under a reimbursable agreement, NASA turns the wind tunnel data over to Speedo for their use.

"It turns out to simulate a swimmer in the water at about two meters per second, we need to run the wind tunnel at about 28 meters per second, which is well within its capability," Wilkinson added. "The tests generally have shown the smoother the fabric, the lower the drag."

Speedo International's research and development team, Aqualab, took those results and used them to help create a new swimsuit the company says is its most hydro-dynamically advanced to date.

SOURCE

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Columbus module heads to the space station

Europe’s Columbus laboratory has been successfully launched into space towards its eventual home on the International Space Station (ISS). The 10-tonne Columbus module took off on board the space shuttle Atlantis as it lifted off from the Kennedy Space Center in Cape Canaveral, Florida at about 14:50 EST (19:50 GMT) today. American and European astronauts will spend the next 11 days connecting the module to the space station, in what will be the single largest contribution by the European Space Agency (ESA) to this international effort.

Columbus is a 4.5–metre–wide cylindrical space capsule that has room for 14 separate science experiments. The lab will primarily study how reduced gravity affects a range of medical and physical phenomena.

“I think it is very important for Europe to have a permanent laboratory up there,” says Martin Zell, ESA’s head of research operations in human spaceflight, microgravity and exploration.

The €700 m laboratory is a user facility, containing 10 telephone-booth-sized racks that can accommodate a wide range of experiments over Columbus’s proposed 10-year lifetime. “A satellite mission is fixed from the beginning, whereas in Columbus the facilities host experiments that can change,” says Zell. Five of the racks have been pre-installed in Columbus before launch with experiments to study fluid science, biology and physiology.

The shuttle Atlantis also contains two separate payloads — a suite of solar observation equipment and a material testing platform — that astronauts will hook up to two of Columbus’ four external mountings that are exposed to outer space. “Columbus is more than a science laboratory; it is a technology test bed that will give Europe experience in living in space,” Zell says.

Physics experiments

Several physics experiments take place in the Fluid Science Laboratory (FSL), which includes various interferometers and high-speed cameras for studying user-provided liquids, emulsions and aqueous foams in the station’s microgravity. The first FSL experiment is Geoflow, which will model the dynamic flow in the Earth’s liquid mantle by trapping silicon oil between two concentric spherical shells. Simulating the mantle is extremely difficult on the Earth’s surface because gravity overwhelms the other forces that are of interest. “Columbus provides us the opportunity to study the influences of temperature and rotation on convective flow when gravity is no longer there,” says Geoflow team member Birgit Futterer of Brandenburg Technical University in Cottbus, Germany.

The launch, originally planned for early December last year, was twice called off due to a glitch in a now-repaired fuel gauge sensor. This final hold-up capped a 16-year delay, as the Columbus lab was due to lift-off in 1992 to commemorate the 500th anniversary of its namesake’s voyage to America. However, it was not until 1995 that ESA decided on the lab’s full development and not until 2002 that much of the construction was completed in Italy and Germany. The Columbia shuttle disaster in 2003, in which seven astronauts died, put all plans on hold.

Geoflow had been scheduled to start just as soon as Columbus was secured to the station, but with the two-month delay, mission planners have moved ahead some biology experiments that are more time-sensitive. After such a long wait, both European and American scientists are anxious for Columbus to get going. “It is a huge enhancement in the research capabilities of the space station,” says Zell.

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Scientists propose test of string theory

Ancient light absorbed by neutral hydrogen atoms could be used to test certain predictions of string theory, say cosmologists at the University of Illinois. Making the measurements, however, would require a gigantic array of radio telescopes to be built on Earth, in space or on the moon.

String theory – a theory whose fundamental building blocks are tiny one-dimensional filaments called strings – is the leading contender for a “theory of everything.” Such a theory would unify all four fundamental forces of nature (the strong and weak nuclear forces, electromagnetism, and gravity). But finding ways to test string theory has been difficult.

Now, cosmologists at the U. of I. say absorption features in the 21-centimeter spectrum of neutral hydrogen atoms could be used for such a test.

“High-redshift, 21-centimeter observations provide a rare observational window in which to test string theory, constrain its parameters and show whether or not it makes sense to embed a type of inflation – called brane inflation – into string theory,” said Benjamin Wandelt, a professor of physics and of astronomy at the U. of I.

“If we embed brane inflation into string theory, a network of cosmic strings is predicted to form,” Wandelt said. “We can test this prediction by looking for the impact this cosmic string network would have on the density of neutral hydrogen in the universe.”

Wandelt and graduate student Rishi Khatri describe their proposed test in a paper accepted for publication in the journal Physical Review Letters.

About 400,000 years after the Big Bang, the universe consisted of a thick shell of neutral hydrogen atoms (each composed of a single proton orbited by a single electron) illuminated by what became known as the cosmic microwave background.

Because neutral hydrogen atoms readily absorb electromagnetic radiation with a wavelength of 21 centimeters, the cosmic microwave background carries a signature of density perturbations in the hydrogen shell, which should be observable today, Wandelt said.

Cosmic strings are filaments of infinite length. Their composition can be loosely compared to the boundaries of ice crystals in frozen water.

When water in a bowl begins to freeze, ice crystals will grow at different points in the bowl, with random orientations. When the ice crystals meet, they usually will not be aligned to one another. The boundary between two such misaligned crystals is called a discontinuity or a defect.

Cosmic strings are defects in space. A network of strings is predicted by string theory (and also by other supersymmetric theories known as Grand Unified Theories, which aspire to unify all known forces of nature except gravity) to have been produced in the early universe, but has not been detected so far. Cosmic strings produce characteristic fluctuations in the gas density through which they move, a signature of which will be imprinted on the 21-centimeter radiation.

The cosmic string network predicted to occur with brane inflation could be tested by looking for the corresponding fluctuations in the 21-centimeter radiation.

Like the cosmic microwave background, the cosmological 21-centimeter radiation has been stretched as the universe has expanded. Today, this relic radiation has a wavelength closer to 21 meters, putting it in the long-wavelength radio portion of the electromagnetic spectrum.

To precisely measure perturbations in the spectra would require an array of radio telescopes with a collective area of more than 1,000 square kilometers. Such an array could be built using current technology, Wandelt said, but would be prohibitively expensive.

If such an enormous array were eventually constructed, measurements of perturbations in the density of neutral hydrogen atoms could also reveal the value of string tension, a fundamental parameter in string theory, Wandelt said. “And that would tell us about the energy scale at which quantum gravity begins to become important.”

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Ice clouds put Mars in the shade

Until now, Mars has generally been regarded as a desert world, where a visiting astronaut would be surprised to see clouds scudding across the orange sky. However, new results show that the arid planet possesses high-level clouds that are sufficiently dense to cast a shadow on the surface.

The results were obtained by the OMEGA Visible and Infrared Mineralogical Mapping Spectrometer instrument on board ESA’s Mars Express.

Mars is not entirely a haven for Sun worshippers. Clouds of water ice particles do occur, for example on the flanks of the giant Martian volcanoes. There have also been hints of much higher, wispy clouds made up of carbon dioxide (CO₂) ice crystals. This is not too surprising, since the thin Martian atmosphere is mostly made of carbon dioxide, and temperatures on the fourth planet from the Sun often plunge well below the ‘freezing point’ of carbon dioxide.

Now, a team of French scientists has shown that such clouds of dry ice do, indeed, exist. Furthermore, they are sometimes so large and dense that they throw quite dark shadows on the dusty surface.

“This is the first time that carbon dioxide ice clouds on Mars have been imaged and identified from above,” said Franck Montmessin of the Service d’Aeronomie, University of Versailles (UVSQ), lead author of the paper in the Journal of Geophysical Research. “This is important because the images tell us not only about their shape, but also their size and density.

“Previously, we had to rely on indirect information – for example, from the SPICAM instrument on board Mars Express - to find out what the clouds are made of. However, it is very difficult to separate the signals coming from the clouds, the atmosphere and the surface.”

Data from the SPICAM Ultraviolet and Infrared Atmospheric Spectrometer indicated that any high altitude clouds are not very thick and made up of much smaller particles, but the CO₂ clouds detected by OMEGA are very different. Not only are they surprisingly high – more than 80 km above the surface – but they can be several hundred kilometres across. They are also much thicker than expected. Instead of looking like the wispy ice clouds seen on Earth, they resemble tall convectional clouds that grow as the result of rising columns of warm air.

Even more surprising is the fact that the CO₂ ice clouds are made of quite large particles - more than a micron (one thousandth of a millimetre) across – and they are sufficiently dense to noticeably dim the Sun. Normally, particles of this size would not be expected to form in the upper atmosphere or to stay aloft for very long before falling back towards the surface.

“The clouds imaged by OMEGA can reduce the Sun’s apparent brightness by up to 40 per cent,” said Montmessin. “This means that they cast quite a dense shadow and this has a noticeable effect on the local ground temperature. Temperatures in the shadow can be up to 10°C cooler than their surroundings, and this in turn modifies the local weather, particularly the winds.”

Since the CO₂ clouds are mostly seen in equatorial regions, the OMEGA team believes that the unexpected shape of the clouds and large size of their ice crystals can be explained by the extreme variations in daily temperature that occur near the equator.

“The cold temperatures at night and relatively high day-time temperatures cause large diurnal waves in the atmosphere,” explained Montmessin. “This means there is a potential for large-scale convection, particularly as the morning Sun warms the ground.”

Bubbles of warm gas rise above the surface and when they reach high levels they become cold enough for CO₂ to condense. This process releases latent heat, which causes the gas and the ice particles to rise even further.

What are the particles around which the CO₂ ice condenses? On Earth, cloud droplets form around tiny nuclei – often particles of dust or salt. On Mars, the answer remains uncertain. One possibility is that Martian dust is carried to high altitudes. Another potential source of condensation nuclei is particles left behind by micrometeorites entering the upper atmosphere. Or the nuclei may simply be tiny crystals of water ice carried aloft on the thermal updraughts.

“This discovery is important when we come to consider the past climate of Mars,” said Montmessin. “The planet seems to have been much warmer billions of years ago, and one theory suggests that Mars was then blanketed with CO₂ clouds. We can use our studies of present-day conditions to understand the role that such high level clouds could have played in the global warming of Mars.”

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Hubble Finds Double Einstein Ring

NASA's Hubble Space Telescope has revealed a never-before-seen optical alignment in space: a pair of glowing rings, one nestled inside the other like a bull's-eye pattern. The double-ring pattern is caused by the complex bending of light from two distant galaxies strung directly behind a foreground massive galaxy, like three beads on a string.

More than just a novelty, this very rare phenomenon can offer insight into dark matter, dark energy, the nature of distant galaxies, and even the curvature of the universe.

The ring was found by an international team of astronomers led by Raphael Gavazzi and Tommaso Treu of the University of California, Santa Barbara. The discovery is part of the ongoing Sloan Lens Advanced Camera for Surveys (SLACS) program. The team is reporting its results at the 211th meeting of the American Astronomical Society in Austin, Texas. A paper has been submitted to The Astrophysical Journal.

The phenomenon, called gravitational lensing, occurs when a massive galaxy in the foreground bends the light rays from a distant galaxy behind it, in much the same way as a magnifying glass would. When both galaxies are exactly lined up, the light forms a circle, called an "Einstein ring," around the foreground galaxy. If another background galaxy lies precisely on the same sightline, a second, larger ring will appear.

Because the odds of seeing such a special alignment are estimated to be 1 in 10,000, Tommaso says that they "hit the jackpot." The odds of seeing this phenomenon are less than winning two consecutive bets on a single number at Roulette.

"Such stunning cosmic coincidences reveal so much about nature. Dark matter is not hidden to lensing," added Leonidas Moustakas of the Jet Propulsion Laboratory in Pasadena, Calif. "The elegance of this lens is trumped only by the secrets of nature that it reveals."

The massive foreground galaxy is almost perfectly aligned in the sky with two background galaxies at different distances. The foreground galaxy is 3 billion light-years away. The inner ring and outer ring are comprised of multiple images of two galaxies at a distance of 6 billion and approximately 11 billion light-years.

SLACS team member Adam Bolton of the University of Hawaii's Institute for Astronomy in Honolulu first identified the lens in the Sloan Digital Sky Survey (SDSS). "The original signature that led us to this discovery was a mere 500 photons (particles of light) hidden among 500,000 other photons in the SDSS spectrum of the foreground galaxy," commented Bolton.

"The twin rings were clearly visible in the Hubble image, added Tommaso. "When I first saw it I said 'wow, this is insane!' I could not believe it!"

The distribution of dark matter in the foreground galaxies that is warping space to create the gravitational lens can be precisely mapped. Tommaso finds that the fall-off in density of the dark matter is similar to what is seen in spiral galaxies (as measured by the speed of a galaxy's rotation, which yields a value for the amount of dark matter pulling on it), though he emphasizes there is no physical reason to explain this relationship.

In addition, the geometry of the two Einstein rings allowed the team to measure the mass of the middle galaxy precisely to be a value of 1 billion solar masses. The team reports that this is the first measurement of the mass of a dwarf galaxy at cosmological distance (redshift of z=0.6).

A sample of several dozen double rings such as this one would offer a purely independent measure. The comparative radius of the rings could also be used to provide an independent measure of the curvature of space by gravity. This would help in determining the matter content of the universe and the properties of dark energy.

Observations of the cosmic microwave background (a relic from the Big Bang) favor flat geometry. A sample of 50 suitable double Einstein rings would be sufficient to measure the dark matter content of the universe and the equation of state of the dark energy (a measure of its pressure) to 10 percent precision. Other double Einstein rings could be found with wide-field space telescope sky surveys that are being proposed for the Joint Dark Energy Mission (JDEM) and recently recommended by the National Research Council.
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Mysterious X-ray source in nearby galaxy

Astronomers studying a nearby galaxy have spied a rare type of star system -- one that contains a black hole that suddenly began glowing brightly with X-rays.

Though this type of star system is supposed to be rare, it's the second such system discovered in that galaxy, called Centaurus A.

The discovery suggests that astronomers have more to learn about the lives and deaths of massive stars in galaxies such as our own.

Normally when astronomers study Centaurus A, it's the giant X-ray jets emanating from the heart of the galaxy that steal the show, explained Gregory Sivakoff, a postdoctoral researcher in astronomy at Ohio State University. The jets extend from the galaxy for 13,000 light years in different directions.

But when his team studied Centaurus A with NASA's Chandra X-ray Observatory starting in March 2007, they saw a new X-ray source -- much smaller than the X-ray jets, but still glowing brightly. The source wasn't there during the last survey of the galaxy in 2003, but it shined throughout the time of the new observations, from March to May of 2007.

Because it hadn't been seen before, the astronomers classified the object as a “transient” X-ray source, meaning that the object had been there before 2007, but had only recently brightened enough to stand out.

Sivakoff discussed the results in a press briefing Wednesday, January 9, 2008 at the American Astronomical Society meeting in Austin, Texas.

The newly bright object, dubbed CXOU J132518.2-430304, is most likely a binary star system, the researchers concluded. The two stars likely formed at the same time, with one much more massive than the other. The more massive star evolved more quickly, and collapsed to form a black hole. It is now slowly devouring its companion. Such binary systems are thought to be extremely rare.

But this is the second bright, transient X-ray binary system discovered in Centaurus A -- and that's the problem, Sivakoff said.

“When we look at other galaxies like Centaurus A, we don't see these bright, transient X-ray binaries,” he said. “But now we've found two such objects in Centaurus A, and the implication is that we may not understand these objects as well as we thought we did.”

“So right now, our discovery is actually pointing to a puzzle rather than a solution.”

Because Centaurus A is near to our galaxy, astronomers have long hoped to use it as a Rosetta stone for studying other galaxies with black holes.

As astronomers piece together an explanation for the existence of the newly-discovered binary system, they may gain a better understanding of how black holes form from massive stars and how binary systems evolve.

“These binary systems are signposts of the massive stars that once existed in galaxies like Centaurus A. To understand the massive stars, we must first know how to read the signs,” he said.

Sivakoff and Ralph Kraft of the Harvard-Smithsonian Center for Astrophysics led the study; their collaborators were from NASA Goddard Space Flight Center, Oak Ridge Associated Universities, University of Hertfordshire, University of Virginia, University of Bristol, McMaster University, and the University of
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The £80m black hole

"Total disaster"; "crazy"; "catastrophic"; "scientific vandalism"; "savage"; and "bombshell". These were some of the words used by physicists and astronomers last month to describe the potential impact of an £80m funding shortfall in the budget of the UK's Science and Technology Facilities Council (STFC). Rumours of a deficit had been circulating for several months, and researchers' worst fears were confirmed when the government announced how much it will spend on science over the next three years

On the face of it, the science budget is not at all disappointing — it will rise by an average of just under 6% a year from £3.38bn in 2007/08 to £3.97bn in 2010/11. But the lion's share of the increases will go to the Medical Research Council, while the STFC will have to make do with an average rise of just 4.5% a year during that period. That is an above-inflation increase, but the STFC not only has to allocate research grants in particle physics and astronomy, but also has to pay for subscriptions to international labs like CERN as well as build and maintain large facilities.

Given the damaging shortfall, the STFC has decided to give priority to exploiting new facilities, while — seemingly with little consultation — choosing to pull the country out of cutting-edge projects like the International Linear Collider (ILC) and the Gemini telescopes, and axing support for certain fields like high-energy gamma-ray astronomy. It is also being forced to slash research grants in particle physics and astronomy by up to 25%, which will hit university departments that carry out significant research in those areas. Job losses are almost certain.

Quite why a shortfall has arisen is unclear. The STFC told Physics World that its programmes have been cut partly to pay for the operating costs of the new Diamond synchrotron near Oxford. Indeed, the House of Commons publicaccounts select committee recently reported that Diamond's running costs are expected to overrun by 89%. However, Diamond bosses dispute this figure, saying its costs "have been known for a long time and have not changed".

It sounds like a mess that the STFC should — and could — have avoided when negotiating its budget with the government and civil servants. The president of the Royal Society has referred diplomatically to "sub-optimal planning"; the rest of us would call it a cock-up. Physicists are particularly perplexed because the UK government has given generous increases to science over the last 10 years — and now, for the want of just £80m, the STFC is forcing researchers to pull out of key projects.

Scientists are also angry because former science minister Malcolm Wicks assured them that they would not be affected when the STFC was created last year from a merger between the Particle Physics and Astronomy Research Council and the Council for the Central Laboratory of the Research Councils. The withdrawal from the ILC is particularly embarrassing internationally: in November the research councils had only just identified the ILC as "the highest priority for a major new accelerator", while several high-profile researchers had also been attracted to the UK to help plan it. The cuts also send out the wrong signals to young people who are considering studying physics at university.

Ministers have promised a review of physics funding. Unfortunately, it is expected to take six to nine months, while the STFC wants to make savings now. Unless the cuts are reversed immediately, UK physics could be irreparably damaged.

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Instrument to make detailed measurements of sun activity

For five years, Stanford research physicist Phil Scherrer and his team have raised a sophisticated space telescope with the attention a parent gives to a child, preparing it for the day when it flies away on a satellite to study the weather on the sun—and maybe save an astronaut from dying of radiation sickness.

A couple of weeks ago, Scherrer's Helioseismic and Magnetic Imager (HMI) left home. A FedEx truck carried it nonstop across the country to NASA's Goddard Space Flight Center in Maryland, where it will be mounted next to other instruments on NASA's Solar Dynamics Observatory. The entire satellite will be subjected to rigorous testing (sometimes known as "shake and bake") to ensure it can withstand the vibration and heat of a launch into space.

A year from now, when an Atlas V missile finally lofts the HMI into geosynchronous orbit 22,500 miles above Earth, it will, with total disregard for the usual parental advice, stare directly into the sun. For several years it will record, in unprecedented detail, the behavior of powerful magnetic fields in the sun and the subtle surface undulations that surrender information about crucial activity deep within. Every two seconds, for at least five years, HMI will snap a high-resolution image and download it to a radio link in New Mexico.

"That's an awful lot of data,'' Scherrer said.

The ultimate mission of HMI (designed in partnership with Lockheed-Martin's Solar and Astrophysics Lab and built at the Lockheed-Martin lab in Palo Alto) and the other two instruments aboard NASA's Solar Dynamics Observatory satellite is to hasten the day when accurate weather forecasts for the sun will be readily available. Space travelers, airline pilots, communication satellites, electric lines, pipelines, telephones and radios all can be harmed when events on the sun send unusually high amounts of solar particles streaming toward Earth.

The sun offers up a smorgasbord of these disruptive events. There are sunspots, operating on their 11-year cycle, solar flares, "coronal mass ejections" and the solar wind.

Astronauts without proper shielding could be killed by high-energy particle radiation produced in the sun's corona during a flare. "It's just like being in a reactor," Scherrer said. NASA's plans for a moon colony or a human expedition to Mars are greatly complicated by the threat of solar storms. A two-year Mars mission would be much safer if there were a two-year solar weather forecast predicting the planetary equivalent of clear skies.

The central question for Scherrer is the origin of variations in the sun's magnetic fields. Convection flows of hot material rise to the surface of the sun, like bubbles the size of California rising in a pot of boiling water, and create magnetic fields by their movement.

Variation in those fields can lead to instability, a key to solar events. HMI's continuous recording of the magnetic fields will provide a deeper understanding of their role.

To understand the other major aspect of the HMI mission, think of the sun as an acoustic instrument with sound waves continuously rebounding around inside, the way seismic waves reverberate inside Earth. (Or, as Scherrer says, "The sun is just a big ball of gas filled up with sound waves bouncing around in all directions.")

These sound waves, generated by hot, bubbling gases, cause small bulges on the sun's surface. To find them, HMI's instruments will measure the sun at 12 million different points. The speed and other characteristics of the waves will offer indications of the flows beneath the surface, possibly identifying precursor events that could provide advance warning of dangerous storms.

The science is known as helioseismology, and it is no small task. "It's like deducing the interior structure of a piano by listening to it fall down a flight of stairs," Scherrer said. The wave motion can even be used to calculate the presence of sunspots on the far side of the sun, which takes about 27 days to spin on its axis. As a result, sunspots can be, in effect, heard before they are seen.

To some extent, this has been done before, by HMI's predecessor on the SOHO (Solar and Heliospheric Observatory) satellite. But while SOHO could see only a portion of the sun at any given time, HMI will provide a "full-disc" view at all times. HMI will be able to follow a developing solar event for the full 13 days it is visible, before the sun's rotation takes it from view. SOHO's view was limited to two days.

HMI will conduct both of its crucial measurements—of the magnetic field and the seismic waves—by looking at a very narrow frequency of light in the visible outer layer of the sun, a spectral line that corresponds to the presence of iron.

A slight shift in the color of the light (the Doppler effect) indicates that a portion of the sun's surface is moving slightly toward or away from the satellite, in time with the sun's internal reverberations. The same color line, when photographed with polarizing lenses, measures the magnetic vector field. Some of the calcite crystals involved in these devices cannot be manufactured, Scherrer said—they grow in caves.

Making these precise measurements of motion on the sun's surface from Earth orbit, 93 million miles away, is not easy. "We have to subtract the motion of the spacecraft," Scherrer said. "The spacecraft is going around the Earth at a speed of 3 kilometers per second; the sun itself is rotating at 2 kilometers per second at the equator. And the surface is bouncing up and down from these waves at 500 meters per second. So we have to sort it all out. It's serious computing."

The great value of the satellite he has nurtured, Scherrer said, will be its ability to see the entire sun, in high-definition, almost all the time, giving science a better understanding of the evolution of solar events.

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Polarization technique focuses limelight

An international team of astronomers, led by Professor Svetlana Berdyugina of ETH Zurich’s Institute of Astronomy, has for the first time ever been able to detect and monitor the visible light that is scattered in the atmosphere of an exoplanet. Employing techniques similar to how Polaroid sunglasses filter away reflected sunlight to reduce glare, the team of scientists were able to extract polarized light to enhance the faint reflected starlight ‘glare’ from an exoplanet. As a result, the scientists could infer the size of its swollen atmosphere. They also directly traced the orbit of the planet, a feat of visualization not possible using indirect methods.

Hot Jupiter

The transiting exoplanet under study circles the dwarf star HD189733 in the constellation Vulpecula and lies more than 60 light years from the earth. Known as HD189733b, this exoplanet was discovered two years ago via Doppler spec-troscopy. HD189733b is so close to its parent star that its atmosphere expands from the heat. Until now, astronomers have never seen light reflected from an exoplanet, although they have deduced from other observations that HD189733b probably resembles a ‘hot Jupiter’ – a planet orbiting extremely closely to its parent star. Unlike Jupiter, however, HD189733b orbits its star in a couple of days rather than the 12 years it takes Jupiter to make one orbit of the sun.

Two half-moon phases

The international team, consisting of Svetlana Berdyugina, Dominique Fluri (ETH Zurich), Andrei Berdyugin and Vilppu Piirola (Tuorla Observatory, Finland), used the 60cm KVA telescope by remote control. The telescope, which belongs to the Royal Swedish Academy of Science, is located at La Palma, Spain and was modernised by scientists in Finland. The researchers obtained polarimetric measurements of the star and its planet. They discovered that polarization peaks near the moments when half of the planet is illuminated by the star as seen from the earth. Such events occur twice during the orbit, similar to half-moon phases.

The polarization indicates that the scattering atmosphere is considerably larger (>30%) than the opaque body of the planet seen during transits and most probably consists of particles smaller than half a micron, for example atoms, molecules, tiny dust grains or perhaps water vapour, which was recently sug-gested to be present in the atmosphere. Such particles effectively scatter blue light – in exactly the same scattering process that creates the blue sky of the earth’s atmosphere. The scientists were also able for the first time to recover the orientation of the planet’s orbit and trace its motion in the sky.

“The polarimetric detection of the reflected light from exoplanets opens new and vast opportunities for exploring physical conditions in their atmospheres”, Pro-fessor Svetlana Berdyugina said. “In addition, more can be learned about radii and true masses, and thus the densities of non-transiting planets.”

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How Mars Could Have Been Warm And Wet But Limestone Free

Planetary scientists have puzzled for years over an apparent contradiction on Mars. Abundant evidence points to an early warm, wet climate on the red planet, but there's no sign of the widespread carbonate rocks, such as limestone, that should have formed in such a climate.

Now, a detailed analysis in the Dec. 21 issue of Science by MIT's Maria T. Zuber and Itay Halevy and Daniel P. Schrag of Harvard University provides a possible answer to the mystery. In addition to being warmed by a greenhouse effect caused by carbon dioxide in the atmosphere, as on Earth, the early Mars may have had the greenhouse gas sulfur dioxide in its atmosphere. That would have interfered with the formation of carbonates, explaining their absence today.

It would also explain the discovery by the twin Mars rovers, Spirit and Opportunity, of sulfur-rich minerals that apparently formed in bodies of water in that early Martian environment. And it may provide clues about the Earth's history as well.

The challenge was to interpret the planet's history, based on the data gathered by the Mars rovers--and especially Opportunity's discovery of sulfate minerals--from just tiny fractions of the surface, says Zuber, who is head of MIT's Department of Earth, Atmospheric and Planetary Sciences and the E.A. Griswold Professor of Geophysics. "How do you take very detailed measurements of chemical composition at one tiny place on Mars," she says, "and put it into the context of the broad evolution of the planet?" The breakthrough, she said, was when she and her colleagues realized "we'd been after the wrong molecule."

After several years of exploring the role of carbon dioxide and the carbon cycle, she said, they realized "maybe the key is sulfur dioxide, not carbon dioxide."

It was Opportunity's discovery of the mineral jarosite, which only forms in highly acidic water, that set them thinking about how that acidic environment could have come about. Sulfur provided the answer.

The new analysis suggests that on Mars, sulfur went through a whole cycle through the atmosphere, bodies of water on the surface, and burial in the soil and crust, comparable to the well-known carbon cycle on Earth. Through most of Earth's history, carbon dioxide has been released in volcanic eruptions, then absorbed into seawater, where it fosters the formation of calcium carbonate (limestone), which gets buried in ocean sediments.

Much evidence suggests Mars may once have had an ocean that covered about a third of the planet, in its northern hemisphere. Sulfur dioxide dissolves easily in water, so after being spewed into the atmosphere by the giant volcanoes of Mars' Tharsis bulge, much of it would have ended up in the water, where it inhibited the formation of carbonate minerals but led to the formation of silicates and sulfites, such as calcium sulfite.

These minerals degrade relatively rapidly, so they would not be expected on the surface of Mars today. But they also allow formation of clays, which have been found on Mars, and which added to the puzzle since clays are usually associated with the same conditions that produce carbonates.

The new picture of a sulfur cycle helps to solve another mystery, which is how early Mars could have been warm enough to sustain liquid water on its surface. A carbon dioxide atmosphere produces some greenhouse warming, but sulfur dioxide is a much more powerful greenhouse gas. Just 10 parts per million of sulfur dioxide in the mostly carbon dioxide air would double the amount of warming and make it easier for liquid water to be stable.

The analysis may also tell us something about our own planet's past. The early Earth's environment could well have been similar to that on Mars, but most traces of that era have been erased by Earth's very dynamic climate and tectonics. "This might have been a phase that Earth went through" in its early years, Zuber says. "It's fascinating to think about whether this process may have played a role" in the evolution of the early Earth.

The work was funded by NASA, a Radcliffe fellowship, the George Merck Fund and a Harvard graduate fellowship.

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Suzaku Explains Cosmic Powerhouses

By working in synergy with a ground-based telescope array, the joint Japanese Aerospace Exploration Agency (JAXA)/NASA Suzaku X-ray observatory is shedding new light on some of the most energetic objects in our galaxy, but objects that remain shrouded in mystery.

These cosmic powerhouses pour out vast amounts of energy, and they accelerate particles to almost the speed of light. But very little is known about these sources because they were discovered only recently. "Understanding these objects is one of the most intriguing problems in astrophysics," says Takayasu Anada of the Institute for Space and Astronautical Science in Kanagawa, Japan. Anada is lead author of a paper presented last week at a Suzaku science conference in San Diego, Calif.

These mysterious objects have been discovered in just the last few years by an array of four European-built telescopes named the High Energy Stereoscopic System (H.E.S.S.), located in the African nation of Namibia. H.E.S.S. indirectly detects very-high-energy gamma rays from outer space. These gamma rays are the highest-energy form of light ever detected from beyond Earth, so H.E.S.S. and other similar arrays have opened up a new branch of astronomy.

The gamma rays themselves are absorbed by gases high up in Earth’s atmosphere. But as the gamma rays interact with air molecules, they produce subatomic particles that radiate a blue-colored light known as Cherenkov radiation. H.E.S.S. detects this blue light, whose intensity and direction reveals the energy and position of the gamma-ray source.

The H.E.S.S. observations were groundbreaking, but the array’s images aren’t sharp enough to reveal the exact location where particles are being accelerated or how the particles are being accelerated. To solve this problem, several teams aimed Suzaku in the direction of some of these H.E.S.S. sources. Any object capable of emitting high-energy gamma rays will also produce X-rays, and Suzaku is particularly sensitive to high-energy (hard) X-rays.

When Anada and his colleagues pointed Suzaku at a source known as HESS J1837-069 (the numerals express the object’s sky coordinates), the X-ray spectrum closely resembled X-ray spectra of pulsar wind nebulae — gaseous clouds that are sculpted by winds blown off by collapsed stars known as pulsars. Pulsar wind nebulae emit hard X-rays, and their X-ray output remains relatively constant over long timescales. "The origin of the gamma-ray emission from HESS J1837-069 remains unclear, but we suspect that this source is a pulsar wind nebula from the Suzaku observation," says Anada.

NASA’s Chandra X-ray Observatory and the European Space Agency’s XMM-Newton X-ray Observatory have revealed that other H.E.S.S. sources are also pulsar wind nebulae. These combined gamma-ray and X-ray observations are revealing that pulsar wind nebulae are more common and more energetic than astronomers had expected.

Another group, led by Hironori Matsumoto of the University of Kyoto in Japan, targeted Suzaku on HESS J1614-518. This source belongs to a class of objects known as "dark particle accelerators" because their ultrahigh energies suggest they are accelerating particles to near-light speed, turning them into cosmic rays. But what are these objects, and what kinds of particles are being accelerated?

Although the nature of these objects remains a mystery, Suzaku’s observations do reveal the identity of the particles. When electrons are accelerated to high speeds, they spiral around magnetic field lines that permeate space, generating copious X-rays. But since protons are 2,000 times more massive than electrons, they emit few X-rays. Matsumoto and his colleagues reported at the conference that HESS J1614-518 is a very weak X-ray emitter. "This result strongly suggests that high-energy protons are being produced in this object," says Matsumoto.

Suzaku also observed two other H.E.S.S. dark particle accelerators, but found no obvious X-ray counterparts at the H.E.S.S. positions. These sources must also be weak X-ray emitters, indicating they are accelerating mostly protons. As Matsumoto says, "Using the high sensitivity of the Suzaku satellite, we can find strong candidates for the origin of cosmic rays."

Launched in 2005, Suzaku is the fifth in a series of Japanese satellites devoted to studying celestial X-ray sources. Managed by JAXA, this mission is a collaborative effort between Japanese universities and institutions and NASA Goddard.

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Earliest Stage of Planet Formation Dated

UC Davis researchers have dated the earliest step in the formation of the solar system -- when microscopic interstellar dust coalesced into mountain-sized chunks of rock -- to 4,568 million years ago, within a range of about 2,080,000 years.

UC Davis postdoctoral researcher Frederic Moynier, Qing-zhu Yin, assistant professor of geology, and graduate student Benjamin Jacobsen established the dates by analyzing a particular type of meteorite, called a carbonaceous chondrite, which represents the oldest material left over from the formation of the solar system.

The physics and timing of this first stage of planet formation are not well understood, Yin said. So, putting time constraints on the process should help guide the physical models that could be used to explain it.

In the second stage, mountain-sized masses grew quickly into about 20 Mars-sized planets and, in the third and final stage, these small planets smashed into each other in a series of giant collisions that left the planets we know today. The dates of those stages are well established.

Carbonaceous chondrites are made up of globules of silica and grains of metals embedded in black, organic-rich matrix of interstellar dust. The matrix is relatively rich in the element manganese, and the globules are rich in chromium. Looking at a number of different meteorites collected on Earth, the researchers found a straight-line relationship between the ratio of the amount of manganese to that of chromium, the amount of matrix in the meteorites, and the amount of chromium-53.

These meteorites never became large enough to heat up from radioactive decay, so they have never been melted, Yin said. They are "cosmic sediments," he said.

By measuring the amount of chromium-53, Yin said, they could work out how much of the radioactive isotope manganese-53 had initially been present, giving an indication of age. They then compared the amount of manganese-53 to slightly younger igneous (molten) meteorites of known age, called angrites.

The UC Davis researchers estimate the timing of the formation of the carbonaceous chondrites at 4,568 million years ago, ranging from 910,000 years before that date to 1,170,000 years later.

"We've captured a moment in history when this material got packed together," Yin said.

The work is published in the Dec. 20 issue of Astrophysical Journal Letters, and was funded by grants from NASA.

Source=http://www.news.ucdavis.edu

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MIT to lead ambitious lunar mission

MIT will lead a $375 million mission to map the moon's interior and reconstruct its thermal history, NASA announced this week.

The Gravity Recovery and Interior Laboratory (GRAIL) mission will be led by MIT professor Maria Zuber and will be launched in 2011. It will put two separate satellites into orbit around the moon to precisely map variations in the moon's gravitational pull. These changes will reveal differences in density of the moon's crust and mantle, and can be used to answer fundamental questions about the moon's internal structure and its history of collisions with asteroids.

The detailed information about lunar gravity will also significantly facilitate any future manned or unmanned missions to land on the moon. Such data will be used to program the descent to the surface to avoid a crash landing and will also help target desirable landing sites. Moreover, the mission's novel technology could eventually be used to explore other interesting worlds such as Mars.

"After the three-month mission is completed, we will know the lunar gravitational field better than we know Earth's," says Zuber, who is head of MIT's Department of Earth, Atmospheric and Planetary Sciences and the E.A. Griswold Professor of Geophysics. She will be the principal investigator for the GRAIL mission.

Former astronaut Sally Ride, the first U.S. woman in space, will lead the project's educational outreach phase, which will include five live MoonKam cameras on each satellite that will be targeted by young students--especially middle-school girls--in their classrooms to get close-up still and video views of the moon's surface.

So far, even such fundamental questions as whether or not the moon has a separate, differentiated core, as Earth does, are unknown, Zuber says. In addition to answering that question, the new mission should reveal details about lunar history, including the relative timing and effects of the myriads of huge impacts that created the craters and basins seen on the surface today. The moon, with its airless, un-eroded surface, serves as a kind of Rosetta Stone for understanding the history of all the solar system's inner planets--Mercury, Venus, Earth and Mars--so the mission should also help to unlock secrets of the evolution of all these planets.

"The moon has the best-preserved record of the solar system's early history," Zuber says, while on other planets much of that record has been lost through erosion and other surface changes.

The technology used in the mission is a direct spinoff from the highly successful Gravity Recovery and Climate Experiment (GRACE) mission, which has been mapping Earth's gravitational field since 2002. Using that technology made this a "low risk" mission for NASA because the necessary instruments had already been developed and tested.

As with that mission, GRAIL measurements of the gravitational field will come from very precise monitoring of changes in the distance between the two satellites. The resulting measurements will map the moon's gravitational field up to 1,000 times more accurately than any previous mapping.

The main new technology needed to make GRAIL possible was a way to calibrate the timing of the satellites accurately. The Earth-orbiting GRACE satellites use the GPS satellite navigation system, but there is no such system at the moon. Instead, the team adapted a technique that involves precise monitoring of radio signals originally designed for a different purpose for another planetary mission in development, named Juno.

The same technology could be applied to future missions to map the gravitational fields of other interesting worlds such as Mars, where it could reveal the exchange of carbon dioxide between the polar caps and atmosphere or the movement of flowing subsurface water, Zuber says. "We could learn amazing things" from such follow-up missions, she says. "Since we solved the GPS problem for the moon, we could propose this with little modification for other planets."

NASA selected the MIT-led mission from among two dozen original proposals. NASA Associate Administrator for Science Alan Stern noted that "GRAIL's revolutionary capabilities stood out in this Discovery mission competition owing to its unsurpassed combination of high scientific value and low technical and programmatic risk."

The GRAIL satellites will be built and operated by Lockheed Martin Space Systems of Denver, Colo. NASA's Jet Propulsion Laboratory (JPL) in Pasadena, Calif., will handle project management and development of the communications and navigation systems.

The mission's science team also includes David E. Smith of NASA Goddard Space Flight Center (GSFC), who will be the deputy principal investigator, and other researchers from JPL, GSFC, the Carnegie Institution of Washington, the University of Arizona, the University of Paris and the Southwest Research Institute.

Source:http://web.mit.edu

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