Science Forums - Science News

NASA's Wise Gets Ready to Survey the Whole Sky

C1ay — Thu, 19 Nov 2009 11:04:46 GMT

NASA's Wide-field Infrared Survey Explorer, or Wise, is chilled out, sporting a sunshade and getting ready to roll. NASA's newest spacecraft is scheduled to roll to the pad on Friday, Nov. 20, its last stop before launching into space to survey the entire sky in infrared light.

Wise is scheduled to launch no earlier than 6:09 a.m. PST (9:09 a.m. EST) on Dec. 9 from Vandenberg Air Force Base in California. It will circle Earth over the poles, scanning the entire sky one-and-a-half times in nine months. The mission will uncover hidden cosmic objects, including the coolest stars, dark asteroids and the most luminous galaxies.

"The eyes of Wise are a vast improvement over those of past infrared surveys," said Edward "Ned" Wright, the principal investigator for the mission at UCLA. "We will find millions of objects that have never been seen before."

The mission will map the entire sky at four infrared wavelengths with sensitivity hundreds to hundreds of thousands of times greater than its predecessors, cataloging hundreds of millions of objects. The data will serve as navigation charts for other missions, pointing them to the most interesting targets. NASA's Hubble and Spitzer Space Telescopes, the European Space Agency's Herschel Space Observatory, and NASA's upcoming Sofia and James Webb Space Telescope will follow up on Wise finds.

"This is an exciting time for space telescopes," said Jon Morse, NASA's Astrophysics Division director at NASA Headquarters in Washington. "Many of the telescopes will work together, each contributing different pieces to some of the most intriguing puzzles in our universe."

Visible light is just one slice of the universe's electromagnetic rainbow. Infrared light, which humans can't see, has longer wavelengths and is good for seeing objects that are cold, dusty or far away. In our solar system, Wise is expected to find hundreds of thousands of cool asteroids, including hundreds that pass relatively close to Earth's path. Wise's infrared measurements will provide better estimates of asteroid sizes and compositions -- important information for understanding more about potentially hazardous impacts on Earth.

"With infrared, we can find the dark asteroids other surveys have missed and learn about the whole population. Are they mostly big, small, fluffy or hard?" said Peter Eisenhardt, the Wise project scientist at NASA's Jet Propulsion Laboratory in Pasadena, Calif.

Wise also will find the coolest of the "failed" stars, or brown dwarfs. Scientists speculate it is possible that a cool star lurks right under our noses, closer to us than our nearest known star, Proxima Centauri, which is four light-years away. If so, Wise will easily pick up its glow. The mission also will spot dusty nests of stars and swirling planet-forming disks, and may find the most luminous galaxy in the universe.

To sense the infrared glow of stars and galaxies, the Wise spacecraft cannot give off any detectable infrared light of its own. This is accomplished by chilling the telescope and detectors to ultra-cold temperatures. The coldest of Wise's detectors will operate at below 8 Kelvin, or minus 445 degrees Fahrenheit.

"Wise is chilled out," said William Irace, the project manager at JPL. "We've finished freezing the hydrogen that fills two tanks surrounding the science instrument. We're ready to explore the universe in infrared."

JPL manages Wise for NASA's Science Mission Directorate in Washington. The mission was competitively selected under NASA's Explorers Program managed by the Goddard Space Flight Center in Greenbelt, Md. The science instrument was built by the Space Dynamics Laboratory in Logan, Utah, and the spacecraft was built by Ball Aerospace & Technologies Corp. in Boulder, Colo. Science operations and data processing take place at the Infrared Processing and Analysis Center at the California Institute of Technology in Pasadena. Caltech manages JPL for NASA.

More information about Wise is available online at NASA - WISE and http://wise.astro.ucla.edu .

Source: NASA

"Homegrown" hybrid solar cell aims for low-cost power

C1ay — Mon, 16 Nov 2009 12:36:02 GMT

Scientists at the U.S. Department of Energy�s (DOE) Argonne National Laboratory have refined a technique to manufacture solar cells by creating tubes of semiconducting material and then "growing" polymers directly inside them. The method has the potential to be significantly cheaper than the process used to make today�s commercial solar cells.

Because the production costs of today's generation of solar cells prevent them from competing economically with fossil fuels, Argonne researchers are working to re-imagine the solar cell's basic design. Most current solar cells use crystalline silicon or cadmium telluride, but growing a high-purity crystal is energy- and labor-intensive, making the cells expensive.

The next generation, called hybrid solar cells, uses a blend of cheaper organic and inorganic materials. To combine these materials effectively, Argonne researchers created a new technique to grow organic polymers directly inside inorganic nanotubes.

At its most basic level, solar cell technology relies on a series of processes initiated when photons, or particles of light, strike semiconducting material. When a photon hits the cell, it excites one electron out of its initial state, leaving behind a "hole" of positive charge.

Hybrid solar cells contain two separate types of semiconducting material: one conducts electrons, the other holes. At the junction between the two semiconductors, the electron-hole pair gets pulled apart, creating a current.

In the study, Argonne nanoscientist Seth Darling and colleagues at Argonne and the University of Chicago had to rethink the geometry of the two materials. If the two semiconductors are placed too far apart, the electron-hole pair will die in transit. However, if they're packed too closely, the separated charges won�t make it out of the cell.

In designing an alternative, scientists paired an electron-donating conjugated polymer with the electron acceptor titanium dioxide (TiO2).

Titanium dioxide readily forms miniscule tubes just tens of nanometers across�10,000 times smaller than a human hair. Rows of tiny, uniform nanotubes sprout across a film of titanium that has been submerged in an electrochemical bath.

The next step required the researchers to fill the nanotubes with the organic polymer�a frustrating process.

"Filling nanotubes with polymer is like trying to stuff wet spaghetti into a table full of tiny holes," Darling said. "The polymer ends up bending and twisting, which leads to inefficiencies both because it traps pockets of air as it goes and because twisted polymers don�t conduct charges as well.

"In addition, this polymer doesn�t like titanium dioxide," Darling added. "So it pulls away from the interface whenever it can."

Trying to sidestep this problem, the team hit on the idea of growing the polymer directly inside the tubes. They filled the tubes with a polymer precursor, turned on ultraviolet light, and let the polymers grow within the tubes.

Grown this way, the polymer doesn�t shy away from the TiO2. In fact, tests suggest the two materials actually mingle at the molecular level; together they are able to capture light at wavelengths inaccessible to either of the two materials alone. This "homegrown" method is potentially much less expensive than the energy-intensive process that produces the silicon crystals used in today�s solar cells.

These devices dramatically outperform those fabricated by filling the nanotubes with pre-grown polymer, producing about 10 times more electricity from absorbed sunlight. The solar cells produced by this technique, however, do not currently harness as much of the available energy from sunlight as silicon cells can. Darling hopes that further experiments will improve the cells' efficiency.

The paper, entitled "Improved Hybrid Solar Cells via in situ UV Polymerization", was published in the journal Small and is available online.

Funding for this research was provided by the Department of Energy�s Office of Basic Energy Sciences and by the NSF-Materials Research Science and Engineering Center at the University of Chicago.

Argonne National Laboratory seeks solutions to pressing national problems in science and technology. The nation's first national laboratory, Argonne conducts leading-edge basic and applied scientific research in virtually every scientific discipline. Argonne researchers work closely with researchers from hundreds of companies, universities, and federal, state and municipal agencies to help them solve their specific problems, advance America 's scientific leadership and prepare the nation for a better future. With employees from more than 60 nations, Argonne is managed by UChicago Argonne, LLC for the U.S. Department of Energy's Office of Science.

Source: Argonne National Laboratory

Exoplanets Clue to Sun's Curious Chemistry

C1ay — Fri, 13 Nov 2009 12:42:09 GMT

A ground-breaking census of 500 stars, 70 of which are known to host planets, has successfully linked the long-standing �lithium mystery� observed in the Sun to the presence of planetary systems. Using ESO�s successful HARPS spectrograph, a team of astronomers has found that Sun-like stars that host planets have destroyed their lithium much more efficiently than �planet-free� stars. This finding does not only shed light on the lack of lithium in our star, but also provides astronomers with a very efficient way of finding stars with planetary systems.

"For almost 10 years we have tried to find out what distinguishes stars with planetary systems from their barren cousins," says Garik Israelian, lead author of a paper appearing this week in the journal Nature. "We have now found that the amount of lithium in Sun-like stars depends on whether or not they have planets."

Low levels of this chemical element have been noticed for decades in the Sun, as compared to other solar-like stars, and astronomers have been unable to explain the anomaly. The discovery of a trend among planet-bearing stars provides a natural explanation to this long-standing mystery. "The explanation of this 60 year-long puzzle is for us rather simple," adds Israelian. "The Sun lacks lithium because it has planets."

This conclusion is based on the analysis of 500 stars, including 70 planet-hosting stars. Most of these stars were monitored for several years with ESO�s High Accuracy Radial Velocity Planet Searcher. This spectrograph, better known as HARPS, is attached to ESO's 3.6-metre telescope and is the world�s foremost exoplanet hunter. "This is the best possible sample available to date to understand what makes planet-bearing stars unique," says co-author Michel Mayor.

The astronomers looked in particular at Sun-like stars, almost a quarter of the whole sample. They found that the majority of stars hosting planets possess less than 1% of the amount of lithium shown by most of the other stars. "Like our Sun, these stars have been very efficient at destroying the lithium they inherited at birth," says team member Nuno Santos. "Using our unique, large sample, we can also prove that the reason for this lithium reduction is not related to any other property of the star, such as its age."

Unlike most other elements lighter than iron, the light nuclei of lithium, beryllium and boron are not produced in significant amounts in stars. Instead, it is thought that lithium, composed of just three protons and four neutrons, was mainly produced just after the Big Bang, 13.7 billion years ago. Most stars will thus have the same amount of lithium, unless this element has been destroyed inside the star.

This result also provides the astronomers with a new, cost-effective way to search for planetary systems: by checking the amount of lithium present in a star astronomers can decide which stars are worthy of further significant observing efforts.

Now that a link between the presence of planets and curiously low levels of lithium has been established, the physical mechanism behind it has to be investigated. "There are several ways in which a planet can disturb the internal motions of matter in its host star, thereby rearrange the distribution of the various chemical elements and possibly cause the destruction of lithium. It is now up to the theoreticians to figure out which one is the most likely to happen," concludes Mayor.

Source: ESO

What happened to Mars?

C1ay — Tue, 10 Nov 2009 13:28:27 GMT

Once upon a time - roughly four billion years ago - Mars was warm and wet, much like Earth. Liquid water flowed on the Martian surface in long rivers that emptied into shallow seas. A thick atmosphere blanketed the planet and kept it warm. Living microbes might have even arisen, some scientists believe, starting Mars down the path toward becoming a second life-filled planet next door to our own.

But that's not how things turned out.

Mars today is bitter cold and bone dry. The rivers and seas are long gone. Its atmosphere is thin and wispy, and if Martian microbes still exist, they're probably eking out a meager existence somewhere beneath the dusty Martian soil.

What happened? Why did Mars dry up and freeze over? These haunting questions have long puzzled scientists. A few years from now we might finally know the answer, thanks to a new orbiter NASA will send to Mars called MAVEN (short for Mars Atmosphere and Volatile Evolution).

"The goal of MAVEN is to figure out what processes were responsible for those changes in the climate," says Bruce Jakosky, Principal Investigator for MAVEN at the University of Colorado at Boulder.

One way or another, scientists believe, Mars must have lost its most precious asset: its thick atmosphere of carbon dioxide. CO₂ in Mars's atmosphere is a greenhouse gas, just as it is in our own atmosphere. A thick blanket of CO₂ and other greenhouse gases would have provided the warmer temperatures and greater atmospheric pressure required to keep liquid water from freezing solid or boiling away.

Over the last four billion years, Mars somehow lost most of that blanket. Scientists have proposed various theories for how that loss happened. Perhaps an asteroid impact blew most of the atmosphere into space in one catastrophic event. Or maybe erosion by the solar wind - a stream of charged particles emanating from the sun - could have slowly stripped the atmosphere away over eons. The planet's surface might also have absorbed the CO₂ and locked it up in minerals such as carbonate. [video]

Ultimately, nobody knows for sure where all the missing CO₂ went.

MAVEN will be the first mission to Mars specifically designed to help scientists understand the ongoing escape of CO₂ and other gases into space. The probe will orbit Mars for at least one Earth-year. At the elliptical orbit's low point, MAVEN will be 125 km above the surface; its high point will take it more than 6000 km out into space. This wide range of altitudes will enable MAVEN to sample Mars's atmosphere more thoroughly than ever before.

As it orbits, MAVEN's instruments will track ions and molecules in this broad cross-section of the Martian atmosphere, thoroughly documenting the flow of CO₂ and other molecules into space for the first time.

Once Jakosky and his colleagues know how quickly Mars is losing CO₂ right now, they can extrapolate backward in time to estimate the total amount lost to space during the last four billion years. "MAVEN will determine if [loss to space] was the most important player," Jakosky says.

But just as important as "how much?" is the question of "how?"

Conventional wisdom holds that Mars's atmosphere is vulnerable because the planet lacks a global magnetic field. Earth's magnetic field stretches far out into space and envelopes the whole planet in a protective bubble that deflects the solar wind. Mars has only regional, patchy magnetic fields that cover relatively small areas of the planet, mostly in the southern hemisphere. The rest of the atmosphere is fully exposed to the solar wind. So the loss could be caused by the slow erosion of the atmosphere in these exposed areas.

David Brain of UC Berkeley has proposed another, seemingly contrary possibility. These small magnetic fields might actually hasten the loss of Mars's atmosphere, Brain suggests.

The solar wind might buffet those magnetic field lines, occasionally pinching off a "bubble" of field lines that then drifts off into space - carrying a large chunk of the atmosphere with it. If so, having a partial magnetic field might be worse than having none at all. This possibility was described in a 2008 Science@NASA story, "Solar Wind Rips Up Martian Atmosphere."

Some evidence from NASA's Mars Global Surveyor spacecraft supports Brain's theory, but decisive measurements will have to wait for MAVEN, currently scheduled to launch in 2013.

The mission will be a big step toward understanding what happened to Mars - how it ended up so cold and dry after such a warm and watery beginning. After all these years, MAVEN could write the final chapter in a haunting tale of planetary woe.

Source: NASA

New Synthetic Molecules Trigger Immune Response

C1ay — Fri, 06 Nov 2009 12:28:35 GMT

Researchers at Yale University have developed synthetic molecules capable of enhancing the body�s immune response to HIV and HIV-infected cells, as well as to prostate cancer cells. Their findings, published online in the Journal of the American Chemical Society, could lead to novel therapeutic approaches for these diseases.

The molecules � called �antibody-recruiting molecule targeting HIV� (ARM-H) and �antibody-recruiting molecule targeting prostate cancer� (ARM-P) � work by binding simultaneously to an antibody already present in the bloodstream and to proteins on HIV, HIV-infected cells or cancer cells. By coating these pathogens in antibodies, the molecules flag them as a threat and trigger the body�s own immune response. In the case of ARM-H, by binding to proteins on the outside of the virus, they also prevent healthy human cells from being infected.

�Instead of trying to kill the pathogens directly, these molecules manipulate our immune system to do something it wouldn�t ordinarily do,� said David Spiegel, Ph.D., M.D., assistant professor of chemistry and the corresponding author of both papers.

Because both HIV and cancer have methods for evading the body�s immune system, treatments and vaccinations for the two diseases have proven difficult. Current treatment options for HIV and prostate cancer � including antiviral drugs, radiation and chemotherapy � involve severe side effects and are often ineffective against advanced cases. While there are some antibody drugs available, they are difficult to produce in large quantities and are costly. They also must be injected and are accompanied by severe side effects of their own.

By contrast, the ARM-H and ARM-P molecules, which the team has begun testing in mice, are structurally simple, inexpensive to produce, and could in theory be taken in pill form, Spiegel said. And because they are unlikely to target essential biological processes in the body, the side effects could be smaller, he noted.

�This is an entirely new approach to treating these two diseases, which are extraordinarily important in terms of their impact on human health,� Spiegel said.

HIV is a global pandemic that affects 33 million people worldwide, while prostate cancer is the second leading cause of cancer-related death among American men, with one out of every six American men expected to develop the disease.

Funding for this research was provided by the National Institutes of Health.

Source: Yale University

[News] Quantum gas microscope offers glimpse of quirky ultracold atoms

Tormod — Thu, 05 Nov 2009 10:11:34 GMT

Physicists at Harvard University have created a quantum gas microscope that can be used to observe single atoms at temperatures so low the particles follow the rules of quantum mechanics, behaving in bizarre ways.

The work, published this week in the journal Nature, represents the first time scientists have detected single atoms in a crystalline structure made solely of light, called a Bose Hubbard optical lattice. It's part of scientists' efforts to use ultracold quantum gases to understand and develop novel quantum materials.

"Ultracold atoms in optical lattices can be used as a model to help understand the physics behind superconductivity or quantum magnetism, for example," says senior author Markus Greiner, an assistant professor of physics at Harvard and an affiliate of the Harvard-MIT Center for Ultracold Atoms. "We expect that our technique, which bridges the gap between earlier microscopic and macroscopic approaches to the study of quantum systems, will help in quantum simulations of condensed matter systems, and also find applications in quantum information processing."

The quantum gas microscope developed by Greiner and his colleagues is a high-resolution device capable of viewing single atoms -- in this case, atoms of rubidium -- occupying individual, closely spaced lattice sites. The rubidium atoms are cooled to just 5 billionths of a degree above absolute zero (-273 degrees Celsius).

"At such low temperatures, atoms follow the rules of quantum mechanics, causing them to behave in very unexpected ways," explains first author Waseem S. Bakr, a graduate student in Harvard's Department of Physics. "Quantum mechanics allows atoms to quickly tunnel around within the lattice, move around with no resistance, and even be 'delocalized' over the entire lattice. With our microscope we can individually observe tens of thousands of atoms working together to perform these amazing feats."

In their paper, Bakr, Greiner, and colleagues present images of single rubidium atoms confined to an optical lattice created through projections of a laser-generated holographic pattern. The neighboring rubidium atoms are just 640 nanometers apart, allowing them to quickly tunnel their way through the lattice.

Confining a quantum gas -- such as a Bose�Einstein condensate -- in such an optically generated lattice creates a system that can be used to model complex phenomena in condensed-matter physics, such as superfluidity. Until now, only the bulk properties of such systems could be studied, but the new microscope's ability to detect arrays of thousands of single atoms gives scientists what amounts to a new workshop for tinkering with the fundamental properties of matter, making it possible to study these simulated systems in much more detail, and possibly also forming the basis of a single-site readout system for quantum computation.

"There are many unsolved questions regarding quantum materials, such as high-temperature superconductors that lose all electrical resistance if they are cooled to moderate temperatures," Greiner says. "We hope this ultracold atom model system can provide answers to some of these important questions, paving the way for creating novel quantum materials with as-yet unknown properties."

Source

There�s a Speed Limit to the Pace of Evolution

C1ay — Tue, 03 Nov 2009 12:54:09 GMT

Researchers at the University of Pennsylvania have developed a theoretical model that informs the understanding of evolution and determines how quickly an organism will evolve using a catalogue of �evolutionary speed limits.� The model provides quantitative predictions for the speed of evolution on various �fitness landscapes,� the dynamic and varied conditions under which bacteria, viruses and even humans adapt.

A major conclusion of the work is that for some organisms, possibly including humans, continued evolution will not translate into ever-increasing fitness. Moreover, a population may accrue mutations at a constant rate �- a pattern long considered the hallmark of �neutral� or non-Darwinian evolution -� even when the mutations experience Darwinian selection.

While much is known about the qualitative aspects of evolutionary theory � that organisms mutate and these mutations are selected by the environment and are gradually absorbed by the entire population, very little is known about how, or how quickly, this is accomplished. Information on evolution between consecutive generations is hard to come by, and the lack of understanding has real-world implications. Public-health officials would have an easier time preparing targeted vaccinations, or combating drug resistance, if they understood the evolutionary speed limits on viruses and bacteria such as influenza and M. tuberculosis.

Penn researchers presented a theory of how the fitness of a population will increase over time, for a total of 14 types of underlying landscapes or �speed limits� that describe the consequences of available genetic mutations. These categories determine the speed and pattern of evolution, predicting how a population�s overall fitness, and the number of accumulated beneficial mutations, are expected to increase over time.

Researchers compared the theory to the data from a two-decades study of E. coli to investigate how the bacterium evolves. Organisms of that simplicity and size reproduce more rapidly than larger species, providing 40,000 generations of data to study.

�We asked, quantitatively, how a population�s fitness will increase over time as beneficial mutations accrue,� said Joshua B. Plotkin, principal investigator and an assistant professor in the Department of Biology in Penn�s School of Arts and Sciences. His research focuses on evolution at the molecular scale.

�This was an attempt to provide a theoretical framework for studying rates of molecular evolution,� said first-author Sergey Kryazhimskiy, also of the Department of Biology. �We applied this theory to infer the underlying fitness landscape of bacteria, using data from a long-term bacterial experiment.�.

In some theoretically conceivable landscapes, fitness levels are expected to increase exponentially forever because of an inexhaustible supply of beneficial mutations. But in more realistic landscapes the rate of adaptive substitutions (mutations that improve an organism�s fitness) eventually lose steam, resulting in sub-linear fitness growth. In some of these landscapes, the fitness eventually levels out and the organism ceases to adapt, even though mutations may continue to accrue.

E. coli, for example, has been observed to increase its rate of cellular division by roughly 40 percent during the course of 40,000 generations. Initially, the bacterial fitness increased rapidly, but eventually the fitness leveled out. These data have allowed the research team to infer that early mutations, while conferring large beneficial effects, also diminish the beneficial effects of subsequent mutations.

According to the study, a population�s fitness and substitution trajectories �t he mutations acquired to achieve higher fitness � depend not on the full distribution of fitness effects of available mutations but rather on the expected fixation probability and the expected fitness increment of mutations. This mathematical observation greatly simplifies the possible trajectories of evolution into 14 distinct categories.

Researchers demonstrated that linear substitution trajectories that signify a constant rate of accruing mutations, long considered the hallmark of neutral evolution, can arise even when mutations are strongly beneficial. The results provide a basis for understanding the dynamics of adaptation and for inferring properties of an organism�s fitness landscape from long-term experimental data. Applying these methods to data from bacterial experiments allowed the researchers to characterize the evolutionary relationships among beneficial mutations in the E. coli genome.

The study, appearing in the current issue of the journal Proceedings of the National Academy of Sciences, was performed by Plotkin and Kryazhimskiy along with Ga�per Tkacik of the Department of Physics and Astronomy at Penn.

The study was funded by the Burroughs Wellcome Fund, the David and Lucille Packard Foundation, the James S. McDonnell Foundation, the Alfred P. Sloan Foundation, a Defense Advanced Research Projects Agency grant and the National Science Foundation.

Source: University of Pennsylvania

The Sun's Sneaky Variability

C1ay — Mon, 02 Nov 2009 12:53:12 GMT

Every 11 years, the sun undergoes a furious upheaval. Dark sunspots burst forth from beneath the sun's surface. Explosions as powerful as a billion atomic bombs spark intense flares of high-energy radiation. Clouds of gas big enough to swallow planets break away from the sun and billow into space. It's a flamboyant display of stellar power.

So why can't we see any of it?

Almost none of the drama of Solar Maximum is visible to the human eye. Look at the sun in the noontime sky and--ho-hum--it's the same old bland ball of bright light.

"The problem is, human eyes are tuned to the wrong wavelength," explains Tom Woods, a solar physicist at the University of Colorado in Boulder. "If you want to get a good look at solar activity, you need to look in the EUV."

EUV is short for "extreme ultraviolet," a high-energy form of ultraviolet radiation with wavelengths between 1 and 120 nanometers. EUV photons are much more energetic and dangerous than the ordinary UV rays that cause sunburns. Fortunately for humans, Earth's atmosphere blocks solar EUV; otherwise a day at the beach could be fatal.

When the sun is active, intense solar EUV emissions can rise and fall by factors of thousands in just a matter of minutes. These surges heat Earth's upper atmosphere, puffing it up and increasing the drag on satellites. EUV photons also break apart atoms and molecules, creating a layer of ions in the upper atmosphere that can severely disturb radio signals.

To monitor these energetic photons, NASA is going to launch a sensor named "EVE," short for EUV Variability Experiment, onboard the Solar Dynamics Observatory as early as this winter.

"EVE gives us the highest time resolution (10 sec) and the highest spectral resolution (< 0.1 nm) that we've ever had for measuring the sun, and we'll have it 24/7," says Woods, the lead scientist for EVE. "This is a huge improvement over past missions."

Although EVE is designed to study solar activity, its first order of business is to study solar inactivity. SDO is going to launch during the deepest solar minimum in almost 100 years. Sunspots, flares and CMEs are at low ebb. That's okay with Woods. He considers solar minimum just as interesting as solar maximum.

"Solar minimum is a quiet time when we can establish a baseline for evaluating long-term trends," he explains. "All stars are variable at some level, and the sun is no exception. We want to compare the sun's brightness now to its brightness during previous minima and ask ourselves, is the sun getting brighter or dimmer?"

Lately, the answer seems to be dimmer. Measurements by a variety of spacecraft indicate a 12-year lessening of the sun's "irradiance" by about 0.02% at visible wavelengths and 6% at EUV wavelengths. These results, which compare the solar minimum of 2008-09 to the previous minimum of 1996, are still very preliminary. EVE will improve confidence in the trend by pinning down the EUV spectrum with unprecedented accuracy.

The sun's intrinsic variability and its potential for future changes are not fully understood - hence the need for EVE. "The EUV portion of the sun's spectrum is what changes most during a solar cycle," says Woods, "and that is the part of the spectrum we will be observing."

Woods gazes out his office window at the Colorado sun. It looks the same as usual. EVE, he knows, will have a different story to tell.

Source: NASA

Colourful Cosmic Jewel Box

C1ay — Thu, 29 Oct 2009 12:01:24 GMT

The combination of images taken by three exceptional telescopes, the ESO Very Large Telescope on Cerro Paranal , the MPG/ESO 2.2-metre telescope at ESO�s La Silla observatory and the NASA/ESA Hubble Space Telescope, has allowed the stunning Jewel Box star cluster to be seen in a whole new light.

Star clusters are among the most visually alluring and astrophysically fascinating objects in the sky. One of the most spectacular nestles deep in the southern skies near the Southern Cross in the constellation of Crux.

The Kappa Crucis Cluster, also known as NGC 4755 or simply the �Jewel Box� is just bright enough to be seen with the unaided eye. It was given its nickname by the English astronomer John Herschel in the 1830s because the striking colour contrasts of its pale blue and orange stars seen through a telescope reminded Herschel of a piece of exotic jewelery.

Open clusters such as NGC 4755 typically contain anything from a few to thousands of stars that are loosely bound together by gravity. Because the stars all formed together from the same cloud of gas and dust their ages and chemical makeup are similar, which makes them ideal laboratories for studying how stars evolve.

The position of the cluster amongst the rich star fields and dust clouds of the southern Milky Way is shown in the very wide field view generated from the Digitized Sky Survey 2 data. This image also includes one of the stars of the Southern Cross as well as part of the huge dark cloud of the Coal Sack.

A new image taken with the Wide Field Imager (WFI) on the MPG/ESO 2.2-metre telescope at ESO�s La Silla Observatory in Chile shows the cluster and its rich surroundings in all their multicoloured glory. The large field of view of the WFI shows a vast number of stars. Many are located behind the dusty clouds of the Milky Way and therefore appear red.

The FORS1 instrument on the ESO Very Large Telescope (VLT) allows a much closer look at the cluster itself. The telescope�s huge mirror and exquisite image quality have resulted in a brand-new, very sharp view despite a total exposure time of just 5 seconds. This new image is one of the best ever taken of this cluster from the ground.

The Jewel Box may be visually colourful in images taken on Earth, but observing from space allows the NASA/ESA Hubble Space Telescope to capture light of shorter wavelengths than can not be seen by telescopes on the ground. This new Hubble image of the core of the cluster represents the first comprehensive far ultraviolet to near-infrared image of an open galactic cluster. It was created from images taken through seven filters, allowing viewers to see details never seen before. It was taken near the end of the long life of the Wide Field Planetary Camera 2 ― Hubble�s workhorse camera up until the recent Servicing Mission, when it was removed and brought back to Earth. Several very bright, pale blue supergiant stars, a solitary ruby-red supergiant and a variety of other brilliantly coloured stars are visible in the Hubble image, as well as many much fainter ones. The intriguing colours of many of the stars result from their differing intensities at different ultraviolet wavelengths.

The huge variety in brightness of the stars in the cluster exists because the brighter stars are 15 to 20 times the mass of the Sun, while the dimmest stars in the Hubble image are less than half the mass of the Sun. More massive stars shine much more brilliantly. They also age faster and make the transition to giant stars much more quickly than their faint, less-massive siblings.

The Jewel Box cluster is about 6400 light-years away and is approximately 16 million years old.

Source: ESO

Scientists Model Origins of the Unseen Universe

C1ay — Tue, 27 Oct 2009 12:35:00 GMT

Understanding dark energy is the number one issue in explaining the universe, according to Salman Habib, of the Laboratory�s Nuclear and Particle Physics, Astrophysics and Cosmology group.

�Because the universe is expanding and at the same time accelerating, either there is a huge gap in our understanding of physics, or there is a strange new form of matter that dominates the universe � 'dark energy' � making up about 70 percent of it,� said Habib. �In addition, there is five times more of an unknown �dark matter� than there is ordinary matter in the universe, and we know it�s there from many different observations, most spectacularly, we�ve seen it bend light in pictures from the Hubble Space Telescope, but its origin is also not understood.�

Even though it�s looking at only a small segment of the �accessible� universe, Habib�s �Roadrunner Universe� model requires a petascale computer because, like the universe, it�s mind-bendingly large. The model�s basic unit is a particle with a mass of approximately one billion suns (in order to sample galaxies with masses of about a trillion suns), and it includes 64 billion and more of those particles.

The model is one of the largest simulations of the distribution of matter in the universe, and aims to look at galaxy-scale mass concentrations above and beyond quantities seen in state-of-the-art sky surveys.

�We are trying to really understand how to more completely and more accurately describe the observable universe, so we can help in the design of future experiments and interpret observations from ongoing observations like the Sloan Digital Sky Survey-III. We are particularly interested in the Large Synoptic Survey Telescope (LSST) in Chile, in which LANL is an institutional member, and DOE and NASA�s Joint Dark Energy Mission (JDEM),� said Habib. �To do the science in any sort of reasonable amount of time requires a petascale machine at the least.�

The Roadrunner Universe model relies on a hierarchical grid/particle algorithm that best matches the physical aspects of the simulation to the hybrid architecture of Roadrunner. Habib and his team wrote an entirely new computer code that aggressively exploits Roadrunner's hybrid architecture and makes full use of the PowerXCell 8i computational accelerators. They also created a dedicated analysis and visualization software framework to handle the huge simulation database.

�Our effort is aimed at pushing the current state of the art by three orders of magnitude in terms of computational and scientific throughput,� said Habib. I�m confident the final database created by Roadrunner will be an essential component of dark universe science for years to come.�

Source: Los Alamos National Laboratory

Scientists Develop New Method to Quantify Climate Modeling Uncertainty

C1ay — Fri, 23 Oct 2009 12:28:45 GMT

Climate scientists recognize that climate modeling projections include a significant level of uncertainty. A team of researchers using computing facilities at Oak Ridge National Laboratory (ORNL) has identified a new method for quantifying this uncertainty.

The new approach suggests that the range of uncertainty in climate projections may be greater than previously assumed. One consequence is the possibility of greater warming and more heat waves later in the century under the Intergovernmental Panel on Climate Change's (IPCC) high fossil fuel use scenario.

The team performed an ensemble of computer "runs" using one of the most comprehensive climate models--the Community Climate System Model version 3, developed by the National Center for Atmospheric Research (NCAR)--on each of three IPCC scenarios. The first IPCC scenario, known as A1F1, assumes high global economic growth and continued heavy reliance on fossil fuels for the remainder of the century. The second scenario, known as B1, assumes a major move away from fossil fuels toward alternative and renewable energy as the century progresses. The third scenario, known as A2, is a middling scenario, with less even economic growth and some adoption of alternative and renewable energy sources as the century unfolds.

The team computed uncertainty by comparing model outcomes with historical climate data from the period 2000-2007. Models run on historical periods typically depart from the actual weather data recorded for those time spans. The team used statistical methods to develop a range of temperature variance for each of the three scenarios, based on their departure from actual historical data.

The approach's outcome is roughly similar to the National Weather Service's computer predictions of a hurricane's path, familiar to TV viewers. There is typically a dark line on the weather map showing the hurricane's predicted path over the next few days, and there is a gray or colored area to either side of the line showing how the hurricane may diverge from the predicted path, within a certain level of probability. The ORNL team developed a similar range of variance--technically known as "error bars"--for each of the scenarios.

Using resources at ORNL's Leadership Computing Facility, the team then performed ensemble runs on three decade-long periods at the beginning, middle, and end of the twenty-first century (2000-2009, 2045-2055, and 2090-2099) to get a sense of how the scenarios would unfold over the twenty-first century's hundred years.

Interestingly, when the variance or "error bars" are taken into account, there is no statistically significant difference between the projected temperatures resulting from the high fossil fuel A1F1 scenario and the middling A2 scenario up through 2050. That is, the A1F1 and A2 error bars overlap. After 2050, however, the A1F1 range of temperature projections rise above those of A2, until they begin to overlap again toward the century's end.

Typically climate scientists have understood the range of uncertainty in projections to be the variance between high and low scenarios. But when the error bars are added in the range between high and low possibilities actually widens, indicating greater uncertainty.

"We found that the uncertainties obtained when we compare model simulations with observations are significantly larger than what the ensemble bounds would appear to suggest," said ORNL's Auroop R. Ganguly, the study's lead author.

In addition, the error bars in the A1F1 scenario suggests at least the possibility of even higher temperatures and more heat waves after 2050, if fossil fuel use is not curtailed.

The team also looked at regional effects and found large geographical variability under the various scenarios. The findings reinforce the IPCC's call for greater focus on regional climate studies in an effort to understand specific impacts and develop strategies for mitigation of and adaptation to climate change.

The study was published in the Proceedings of the National Academy of Sciences. Co-authors include Marcia Branstetter, John Drake, David Erickson, Esther Parish, Nagendra Singh, and Karsten Steinhaeuser of ORNL, and Lawrence Buja of NCAR. Funding for the work was provided by ORNL's new cross-cutting initiative called Understanding Climate Change Impacts through the Laboratory Directed Research and Development program.

The paper can be accessed electronically here: http://www.pnas.org/content/106/37/15555

UT-Battelle manages Oak Ridge National Laboratory for the Department of Energy.

Source: Oak Ridge National Laboratory