High-performance simulation, neutrons uncover three classes of protein motion

ScienceDaily (Oct. 2, 2011) — Molecular motion in proteins comes in three distinct classes, according to a collaboration by researchers at the Department of Energy's Oak Ridge National Laboratory and the University of Tennessee, in research reported in Physical Review Letters.

The research team, directed by ORNL-UT Governor's Chairs Jeremy Smith and Alexei Sokolov, combined high-performance computer simulation with neutron scattering experiments to understand atomic-level motions that underpin the operations of proteins.

"The analysis and interpretation of neutron scattering spectra are always difficult for complex molecules such as proteins," said Smith, who directs ORNL's Center for Molecular Biophysics. "We've performed experiments and then shown that simulation can provide a clear view of them. It allows us to see through the complexity and find out what motions are going on."

Defining the motions present -- localized diffusion, methyl group rotations and jumps -- is important as it allows scientists to think about how the motions determine the functions of proteins that are critical to all life.

"First, we found that experiment and simulation agreed perfectly with each other, which is remarkable," Smith said. "Second, the simulations told us that this type of neutron scattering can be interpreted in a very simple way."

Although the team performed its research on a particular protein called lysozyme, a natural antibacterial enzyme found in tears, saliva and egg whites, the researchers anticipate the technique will have a much broader impact in the neutron scattering community, aiding research in areas such as biofuel design or environmental remediation.

The combined simulation and neutron scattering approach should also be of use in the characterization of non-biological materials such as polymers. Smith notes that approximately half the neutron scattering experiments at ORNL's Spallation Neutron Source involve the study of motions in materials.

"These methods are of general applicability," Smith said. "Many experimentalists can now come to the ORNL's Spallation Neutron Source, measure a spectrum of whatever sample they have, and then apply this analysis in terms of three classes of motion to interpret their results."

The research was primarily conducted by ORNL's Liang Hong, with the support of Benjamin Lindner and Nikolai Smolin from ORNL. They performed neutron scattering experiments at ORNL's Spallation Neutron Source on the BASIS instrument and at the National Institute of Standards and Technology Center for Neutron Research.

The simulation component of the work was supported by ORNL's Laboratory Directed Research and Development program, while the neutron scattering component was supported by an Experimental Program to Stimulate Competitive Research (EPSCOR) grant to the University of Tennessee from the DOE Office of Science.

ORNL is managed by UT-Battelle for the Department of Energy's Office of Science.

Recommend this story on Facebook, Twitter,
and Google +1:

Other bookmarking and sharing tools:

Story Source:

The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by DOE/Oak Ridge National Laboratory.

Journal Reference:

Liang Hong, Nikolai Smolin, Benjamin Lindner, Alexei P. Sokolov, Jeremy C. Smith. Three classes of motion in the dynamic neutron-scattering susceptibility of a globular protein. Physical Review Letters, 2011; (accepted)

Note: If no author is given, the source is cited instead.

Disclaimer: Views expressed in this article do not necessarily reflect those of ScienceDaily or its staff.

View the original article here

Scientists release most accurate simulation of the universe to date

ScienceDaily (Sep. 30, 2011) — The Bolshoi supercomputer simulation, the most accurate and detailed large cosmological simulation run to date, gives physicists and astronomers a powerful new tool for understanding such cosmic mysteries as galaxy formation, dark matter, and dark energy.

The simulation traces the evolution of the large-scale structure of the universe, including the evolution and distribution of the dark matter halos in which galaxies coalesced and grew. Initial studies show good agreement between the simulation's predictions and astronomers' observations.

"In one sense, you might think the initial results are a little boring, because they basically show that our standard cosmological model works," said Joel Primack, distinguished professor of physics at the University of California, Santa Cruz. "What's exciting is that we now have this highly accurate simulation that will provide the basis for lots of important new studies in the months and years to come."

Primack and Anatoly Klypin, professor of astronomy at New Mexico State University, lead the team that produced the Bolshoi simulation. Klypin wrote the computer code for the simulation, which was run on the Pleiades supercomputer at NASA Ames Research Center. "These huge cosmological simulations are essential for interpreting the results of ongoing astronomical observations and for planning the new large surveys of the universe that are expected to help determine the nature of the mysterious dark energy," Klypin said.

Primack, who directs the University of California High-Performance Astrocomputing Center (UC-HIPACC), said the initial release of data from the Bolshoi simulation began in early September. "We've released a lot of the data so that other astrophysicists can start to use it," he said. "So far it's less than one percent of the actual output, because the total output is so huge, but there will be additional releases in the future."

The previous benchmark for large-scale cosmological simulations, known as the Millennium Run, has been the basis for some 400 papers since 2005. But the fundamental parameters used as the input for the Millennium Run are now known to be inaccurate. Produced by the Virgo Consortium of mostly European scientists, the Millennium simulation used cosmological parameters based on the first release of data from NASA's Wilkinson Microwave Anisotropy Probe (WMAP). WMAP provided a detailed map of subtle variations in the cosmic microwave background radiation, the primordial radiation left over from the Big Bang. But the initial WMAP1 parameters have been superseded by subsequent releases: WMAP5 (five-year results released in 2008) and WMAP7 (seven-year results released in 2010).

The Bolshoi simulation is based on WMAP5 parameters, which are consistent with the later WMAP7 results. "The WMAP1 cosmological parameters on which the Millennium simulation is based are now known to be wrong," Primack said. "Moreover, advances in supercomputer technology allow us to do a much better simulation with higher resolution by almost an order of magnitude. So I expect the Bolshoi simulation will have a big impact on the field."

The standard explanation for how the universe evolved after the Big Bang is known as the Lambda Cold Dark Matter model, and it is the theoretical basis for the Bolshoi simulation. According to this model, gravity acted initially on slight density fluctuations present shortly after the Big Bang to pull together the first clumps of dark matter. These grew into larger and larger clumps through the hierarchical merging of smaller progenitors. Although the nature of dark matter remains a mystery, it accounts for about 82 percent of the matter in the universe. As a result, the evolution of structure in the universe has been driven by the gravitational interactions of dark matter. The ordinary matter that forms stars and planets has fallen into the "gravitational wells" created by clumps of dark matter, giving rise to galaxies in the centers of dark matter halos.

A principal purpose of the Bolshoi simulation is to compute and model the evolution of dark matter halos. The characteristics of the halos and subhalos in the Bolshoi simulation are presented in a paper that has been accepted for publication in the Astrophysical Journal and is now available online. The authors are Klypin, NMSU graduate student Sebastian Trujillo-Gomez, and Primack.

A second paper, also accepted for publication in the Astrophysical Journal and available online, presents the abundance and properties of galaxies predicted by the Bolshoi simulation of dark matter. The authors are Klypin, Trujillo-Gomez, Primack, and UCSC postdoctoral researcher Aaron Romanowsky. A comparison of the Bolshoi predictions with galaxy observations from the Sloan Digital Sky Survey showed very good agreement, according to Primack.

The Bolshoi simulation focused on a representative section of the universe, computing the evolution of a cubic volume measuring about one billion light-years on a side and following the interactions of 8.6 billion particles of dark matter. It took 6 million CPU-hours to run the full computation on the Pleiades supercomputer, recently ranked as the seventh fastest supercomputer in the world.

A variant of the Bolshoi simulation, known as BigBolshoi or MultiDark, was run on the same supercomputer with the same number of particles, but this time in a volume 64 times larger. BigBolshoi was run to predict the properties and distribution of galaxy clusters and other very large structures in the universe, as well as to help with dark energy projects such as the Baryon Oscillation Spectroscopic Survey (BOSS).

Another variant, called MiniBolshoi, is currently being run on the Pleiades supercomputer. MiniBolshoi focuses on a smaller portion of the universe and provides even higher resolution than Bolshoi. The Bolshoi simulation and its two variants will be made publicly available to astrophysical researchers worldwide in phases via the MultiDark Database, hosted by the Potsdam Astrophysics Institute in Germany and supported by grants from Spain and Germany.

Primack, Klypin, and their collaborators are continuing to analyze the results of the Bolshoi simulation and submit papers for publication. Among their findings are results showing that the simulation correctly predicts the number of galaxies as bright as the Milky Way that have satellite galaxies as bright as the Milky Way's major satellites, the Large and Small Magellanic Clouds.

"A lot more papers are on the way," Primack said.

This research was funded by grants from NASA and the National Science Foundation.

Recommend this story on Facebook, Twitter,
and Google +1:

Other bookmarking and sharing tools:

Story Source:

The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by University of California - Santa Cruz.

Note: If no author is given, the source is cited instead.

Disclaimer: Views expressed in this article do not necessarily reflect those of ScienceDaily or its staff.

View the original article here

Scientists release most accurate simulation of the universe to date

ScienceDaily (Sep. 30, 2011) — The Bolshoi supercomputer simulation, the most accurate and detailed large cosmological simulation run to date, gives physicists and astronomers a powerful new tool for understanding such cosmic mysteries as galaxy formation, dark matter, and dark energy.

The simulation traces the evolution of the large-scale structure of the universe, including the evolution and distribution of the dark matter halos in which galaxies coalesced and grew. Initial studies show good agreement between the simulation's predictions and astronomers' observations.

"In one sense, you might think the initial results are a little boring, because they basically show that our standard cosmological model works," said Joel Primack, distinguished professor of physics at the University of California, Santa Cruz. "What's exciting is that we now have this highly accurate simulation that will provide the basis for lots of important new studies in the months and years to come."

Primack and Anatoly Klypin, professor of astronomy at New Mexico State University, lead the team that produced the Bolshoi simulation. Klypin wrote the computer code for the simulation, which was run on the Pleiades supercomputer at NASA Ames Research Center. "These huge cosmological simulations are essential for interpreting the results of ongoing astronomical observations and for planning the new large surveys of the universe that are expected to help determine the nature of the mysterious dark energy," Klypin said.

Primack, who directs the University of California High-Performance Astrocomputing Center (UC-HIPACC), said the initial release of data from the Bolshoi simulation began in early September. "We've released a lot of the data so that other astrophysicists can start to use it," he said. "So far it's less than one percent of the actual output, because the total output is so huge, but there will be additional releases in the future."

The previous benchmark for large-scale cosmological simulations, known as the Millennium Run, has been the basis for some 400 papers since 2005. But the fundamental parameters used as the input for the Millennium Run are now known to be inaccurate. Produced by the Virgo Consortium of mostly European scientists, the Millennium simulation used cosmological parameters based on the first release of data from NASA's Wilkinson Microwave Anisotropy Probe (WMAP). WMAP provided a detailed map of subtle variations in the cosmic microwave background radiation, the primordial radiation left over from the Big Bang. But the initial WMAP1 parameters have been superseded by subsequent releases: WMAP5 (five-year results released in 2008) and WMAP7 (seven-year results released in 2010).

The Bolshoi simulation is based on WMAP5 parameters, which are consistent with the later WMAP7 results. "The WMAP1 cosmological parameters on which the Millennium simulation is based are now known to be wrong," Primack said. "Moreover, advances in supercomputer technology allow us to do a much better simulation with higher resolution by almost an order of magnitude. So I expect the Bolshoi simulation will have a big impact on the field."

The standard explanation for how the universe evolved after the Big Bang is known as the Lambda Cold Dark Matter model, and it is the theoretical basis for the Bolshoi simulation. According to this model, gravity acted initially on slight density fluctuations present shortly after the Big Bang to pull together the first clumps of dark matter. These grew into larger and larger clumps through the hierarchical merging of smaller progenitors. Although the nature of dark matter remains a mystery, it accounts for about 82 percent of the matter in the universe. As a result, the evolution of structure in the universe has been driven by the gravitational interactions of dark matter. The ordinary matter that forms stars and planets has fallen into the "gravitational wells" created by clumps of dark matter, giving rise to galaxies in the centers of dark matter halos.

A principal purpose of the Bolshoi simulation is to compute and model the evolution of dark matter halos. The characteristics of the halos and subhalos in the Bolshoi simulation are presented in a paper that has been accepted for publication in the Astrophysical Journal and is now available online. The authors are Klypin, NMSU graduate student Sebastian Trujillo-Gomez, and Primack.

A second paper, also accepted for publication in the Astrophysical Journal and available online, presents the abundance and properties of galaxies predicted by the Bolshoi simulation of dark matter. The authors are Klypin, Trujillo-Gomez, Primack, and UCSC postdoctoral researcher Aaron Romanowsky. A comparison of the Bolshoi predictions with galaxy observations from the Sloan Digital Sky Survey showed very good agreement, according to Primack.

The Bolshoi simulation focused on a representative section of the universe, computing the evolution of a cubic volume measuring about one billion light-years on a side and following the interactions of 8.6 billion particles of dark matter. It took 6 million CPU-hours to run the full computation on the Pleiades supercomputer, recently ranked as the seventh fastest supercomputer in the world.

A variant of the Bolshoi simulation, known as BigBolshoi or MultiDark, was run on the same supercomputer with the same number of particles, but this time in a volume 64 times larger. BigBolshoi was run to predict the properties and distribution of galaxy clusters and other very large structures in the universe, as well as to help with dark energy projects such as the Baryon Oscillation Spectroscopic Survey (BOSS).

Another variant, called MiniBolshoi, is currently being run on the Pleiades supercomputer. MiniBolshoi focuses on a smaller portion of the universe and provides even higher resolution than Bolshoi. The Bolshoi simulation and its two variants will be made publicly available to astrophysical researchers worldwide in phases via the MultiDark Database, hosted by the Potsdam Astrophysics Institute in Germany and supported by grants from Spain and Germany.

Primack, Klypin, and their collaborators are continuing to analyze the results of the Bolshoi simulation and submit papers for publication. Among their findings are results showing that the simulation correctly predicts the number of galaxies as bright as the Milky Way that have satellite galaxies as bright as the Milky Way's major satellites, the Large and Small Magellanic Clouds.

"A lot more papers are on the way," Primack said.

This research was funded by grants from NASA and the National Science Foundation.

Recommend this story on Facebook, Twitter,
and Google +1:

Other bookmarking and sharing tools:

Story Source:

The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by University of California - Santa Cruz.

Note: If no author is given, the source is cited instead.

Disclaimer: Views expressed in this article do not necessarily reflect those of ScienceDaily or its staff.

View the original article here

High-performance simulation, neutrons uncover three classes of protein motion

ScienceDaily (Oct. 2, 2011) — Molecular motion in proteins comes in three distinct classes, according to a collaboration by researchers at the Department of Energy's Oak Ridge National Laboratory and the University of Tennessee, in research reported in Physical Review Letters.

The research team, directed by ORNL-UT Governor's Chairs Jeremy Smith and Alexei Sokolov, combined high-performance computer simulation with neutron scattering experiments to understand atomic-level motions that underpin the operations of proteins.

"The analysis and interpretation of neutron scattering spectra are always difficult for complex molecules such as proteins," said Smith, who directs ORNL's Center for Molecular Biophysics. "We've performed experiments and then shown that simulation can provide a clear view of them. It allows us to see through the complexity and find out what motions are going on."

Defining the motions present -- localized diffusion, methyl group rotations and jumps -- is important as it allows scientists to think about how the motions determine the functions of proteins that are critical to all life.

"First, we found that experiment and simulation agreed perfectly with each other, which is remarkable," Smith said. "Second, the simulations told us that this type of neutron scattering can be interpreted in a very simple way."

Although the team performed its research on a particular protein called lysozyme, a natural antibacterial enzyme found in tears, saliva and egg whites, the researchers anticipate the technique will have a much broader impact in the neutron scattering community, aiding research in areas such as biofuel design or environmental remediation.

The combined simulation and neutron scattering approach should also be of use in the characterization of non-biological materials such as polymers. Smith notes that approximately half the neutron scattering experiments at ORNL's Spallation Neutron Source involve the study of motions in materials.

"These methods are of general applicability," Smith said. "Many experimentalists can now come to the ORNL's Spallation Neutron Source, measure a spectrum of whatever sample they have, and then apply this analysis in terms of three classes of motion to interpret their results."

The research was primarily conducted by ORNL's Liang Hong, with the support of Benjamin Lindner and Nikolai Smolin from ORNL. They performed neutron scattering experiments at ORNL's Spallation Neutron Source on the BASIS instrument and at the National Institute of Standards and Technology Center for Neutron Research.

The simulation component of the work was supported by ORNL's Laboratory Directed Research and Development program, while the neutron scattering component was supported by an Experimental Program to Stimulate Competitive Research (EPSCOR) grant to the University of Tennessee from the DOE Office of Science.

ORNL is managed by UT-Battelle for the Department of Energy's Office of Science.

Recommend this story on Facebook, Twitter,
and Google +1:

Other bookmarking and sharing tools:

Story Source:

The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by DOE/Oak Ridge National Laboratory.

Journal Reference:

Liang Hong, Nikolai Smolin, Benjamin Lindner, Alexei P. Sokolov, Jeremy C. Smith. Three classes of motion in the dynamic neutron-scattering susceptibility of a globular protein. Physical Review Letters, 2011; (accepted)

Note: If no author is given, the source is cited instead.

Disclaimer: Views expressed in this article do not necessarily reflect those of ScienceDaily or its staff.

View the original article here

First habitable exoplanet? Climate simulation reveals new candidate that could support Earth-like life

ScienceDaily (May 16, 2011) — The planetary system around the red dwarf Gliese 581, one of the closest stars to the Sun in the galaxy, has been the subject of several studies aiming to detect the first potentially habitable exoplanet. Two candidates have already been discarded, but a third planet, Gliese 581d, can be considered the first confirmed exoplanet that could support Earth-like life. This is the conclusion of a team of scientists from the Institut Pierre Simon Laplace (CNRS, UPMC, ENS Paris, Ecole Polytechnique) in Paris, France, whose study is published in The Astrophysical Journal Letters.

Are there other planets inhabited like Earth, or at least habitable? The discovery of the first habitable planet has become a quest for many astrophysicists who look for rocky planets in the "habitable zone" around stars, the range of distances in which planets are neither too cold nor too hot for life to flourish.

In this quest, the red dwarf star Gliese 581 has already received a huge amount of attention. In 2007, scientists reported the detection of two planets orbiting not far from the inner and outer edge of its habitable zone. While the more distant planet, Gliese 581d, was initially judged to be too cold for life, the closer-in planet was thought to be potentially habitable by its discoverers. However, later analysis by atmospheric experts showed that if it had liquid oceans like Earth, they would rapidly evaporate in a 'runaway greenhouse' effect similar to that which gave Venus the hot, inhospitable climate it has today. A new possibility emerged late in 2010, when a team of observers led by Steven Vogt at the University of California, Santa Cruz, announced that they had discovered a new planet, which they dubbed Gliese 581g, or 'Zarmina's World'. This planet, they claimed, had a mass similar to that of Earth and was close to the centre of the habitable zone. For several months, the discovery of the first potential Earth twin outside the Solar System seemed to have been achieved. Unfortunately, later analysis by independent teams has raised serious doubts on this extremely difficult detection. Many now believe that Gliese 581g may not exist at all. Instead, it may simply be a result of noise in the ultra-fine measurements of stellar 'wobble' needed to detect exoplanets in this system.

Today, it is finally Gliese 581g's big brother -- the larger and more distant Gliese 581d -- which has been shown to be the confirmed potentially habitable exoplanet by Robin Wordsworth, François Forget and co-workers from Laboratoire de Météorologie Dynamique (CNRS, UPMC, ENS Paris, Ecole Polytechnique) at the Institute Pierre Simon Laplace in Paris. Although it is likely to be a rocky planet, it has a mass at least seven times that of Earth, and is estimated to be about twice its size. At first glance, Gliese 581d is a pretty poor candidate in the hunt for life: it receives less than a third of the stellar energy Earth does and may be tidally locked, with a permanent day and night side. After its discovery, it was generally believed that any atmosphere thick enough to keep the planet warm would become cold enough on the night side to freeze out entirely, ruining any prospects for a habitable climate.

To test whether this intuition was correct, Wordsworth and colleagues developed a new kind of computer model capable of accurately simulating possible exoplanet climates. The model simulates a planet's atmosphere and surface in three dimensions, rather like those used to study climate change on Earth. However, it is based on more fundamental physical principles, allowing the simulation of a much wider range of conditions than would otherwise be possible, including any atmospheric cocktail of gases, clouds and aerosols.

To their surprise, they found that with a dense carbon dioxide atmosphere -- a likely scenario on such a large planet -- the climate of Gliese 581d is not only stable against collapse, but warm enough to have oceans, clouds and rainfall. One of the key factors in their results was Rayleigh scattering, the phenomenon that makes the sky blue on Earth. In the Solar System, Rayleigh scattering limits the amount of sunlight a thick atmosphere can absorb, because a large portion of the scattered blue light is immediately reflected back to space. However, as the starlight from Gliese 581 is red, it is almost unaffected. This means that it can penetrate much deeper into the atmosphere, where it heats the planet effectively due to the greenhouse effect of the CO2 atmosphere, combined with that of the carbon dioxide ice clouds predicted to form at high altitudes. Furthermore, the 3D circulation simulations showed that the daylight heating was efficiently redistributed across the planet by the atmosphere, preventing atmospheric collapse on the night side or at the poles.

Scientists are particularly excited by the fact that at 20 light years from Earth, Gliese 581d is one of our closest galactic neighbours. For now, this is of limited use for budding interstellar colonists -- the furthest-travelled human-made spacecraft, Voyager 1, would still take over 300,000 years to arrive there. However, it does mean that in the future telescopes will be able to detect the planet's atmosphere directly. While Gliese 581d may be habitable there are other possibilities; it could have kept some atmospheric hydrogen, like Uranus and Neptune, or the fierce wind from its star during its infancy could even have torn its atmosphere away entirely. To distinguish between these different scenarios, Wordsworth and co-workers came up with several simple tests that observers will be able to perform in future with a sufficiently powerful telescope.

If Gliese 581d does turn out to be habitable, it would still be a pretty strange place to visit -- the denser air and thick clouds would keep the surface in a perpetual murky red twilight, and its large mass means that surface gravity would be around double that on Earth. But the diversity of planetary climates in the galaxy is likely to be far wider than the few examples we are used to from the Solar System. In the long run, the most important implication of these results may be the idea that life-supporting planets do not in fact need to be particularly like Earth at all.

Story Source:

The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by CNRS (Délégation Paris Michel-Ange).

Journal Reference:

Robin D. Wordsworth, François Forget, Franck Selsis, Ehouarn Millour, Benjamin Charnay, Jean-Baptiste Madeleine. Gliese 581d is the first discovered terrestrial-mass exoplanet in the habitable zone. The Astrophysical Journal, 2011; 733 (2): L48 DOI: 10.1088/2041-8205/733/2/L48

Note: If no author is given, the source is cited instead.

Disclaimer: Views expressed in this article do not necessarily reflect those of ScienceDaily or its staff.

View the original article here

First habitable exoplanet? Climate simulation reveals new candidate that could support Earth-like life

ScienceDaily (May 16, 2011) — The planetary system around the red dwarf Gliese 581, one of the closest stars to the Sun in the galaxy, has been the subject of several studies aiming to detect the first potentially habitable exoplanet. Two candidates have already been discarded, but a third planet, Gliese 581d, can be considered the first confirmed exoplanet that could support Earth-like life. This is the conclusion of a team of scientists from the Institut Pierre Simon Laplace (CNRS, UPMC, ENS Paris, Ecole Polytechnique) in Paris, France, whose study is published in The Astrophysical Journal Letters.

Are there other planets inhabited like Earth, or at least habitable? The discovery of the first habitable planet has become a quest for many astrophysicists who look for rocky planets in the "habitable zone" around stars, the range of distances in which planets are neither too cold nor too hot for life to flourish.

In this quest, the red dwarf star Gliese 581 has already received a huge amount of attention. In 2007, scientists reported the detection of two planets orbiting not far from the inner and outer edge of its habitable zone. While the more distant planet, Gliese 581d, was initially judged to be too cold for life, the closer-in planet was thought to be potentially habitable by its discoverers. However, later analysis by atmospheric experts showed that if it had liquid oceans like Earth, they would rapidly evaporate in a 'runaway greenhouse' effect similar to that which gave Venus the hot, inhospitable climate it has today. A new possibility emerged late in 2010, when a team of observers led by Steven Vogt at the University of California, Santa Cruz, announced that they had discovered a new planet, which they dubbed Gliese 581g, or 'Zarmina's World'. This planet, they claimed, had a mass similar to that of Earth and was close to the centre of the habitable zone. For several months, the discovery of the first potential Earth twin outside the Solar System seemed to have been achieved. Unfortunately, later analysis by independent teams has raised serious doubts on this extremely difficult detection. Many now believe that Gliese 581g may not exist at all. Instead, it may simply be a result of noise in the ultra-fine measurements of stellar 'wobble' needed to detect exoplanets in this system.

Today, it is finally Gliese 581g's big brother -- the larger and more distant Gliese 581d -- which has been shown to be the confirmed potentially habitable exoplanet by Robin Wordsworth, François Forget and co-workers from Laboratoire de Météorologie Dynamique (CNRS, UPMC, ENS Paris, Ecole Polytechnique) at the Institute Pierre Simon Laplace in Paris. Although it is likely to be a rocky planet, it has a mass at least seven times that of Earth, and is estimated to be about twice its size. At first glance, Gliese 581d is a pretty poor candidate in the hunt for life: it receives less than a third of the stellar energy Earth does and may be tidally locked, with a permanent day and night side. After its discovery, it was generally believed that any atmosphere thick enough to keep the planet warm would become cold enough on the night side to freeze out entirely, ruining any prospects for a habitable climate.

To test whether this intuition was correct, Wordsworth and colleagues developed a new kind of computer model capable of accurately simulating possible exoplanet climates. The model simulates a planet's atmosphere and surface in three dimensions, rather like those used to study climate change on Earth. However, it is based on more fundamental physical principles, allowing the simulation of a much wider range of conditions than would otherwise be possible, including any atmospheric cocktail of gases, clouds and aerosols.

To their surprise, they found that with a dense carbon dioxide atmosphere -- a likely scenario on such a large planet -- the climate of Gliese 581d is not only stable against collapse, but warm enough to have oceans, clouds and rainfall. One of the key factors in their results was Rayleigh scattering, the phenomenon that makes the sky blue on Earth. In the Solar System, Rayleigh scattering limits the amount of sunlight a thick atmosphere can absorb, because a large portion of the scattered blue light is immediately reflected back to space. However, as the starlight from Gliese 581 is red, it is almost unaffected. This means that it can penetrate much deeper into the atmosphere, where it heats the planet effectively due to the greenhouse effect of the CO2 atmosphere, combined with that of the carbon dioxide ice clouds predicted to form at high altitudes. Furthermore, the 3D circulation simulations showed that the daylight heating was efficiently redistributed across the planet by the atmosphere, preventing atmospheric collapse on the night side or at the poles.

Scientists are particularly excited by the fact that at 20 light years from Earth, Gliese 581d is one of our closest galactic neighbours. For now, this is of limited use for budding interstellar colonists -- the furthest-travelled human-made spacecraft, Voyager 1, would still take over 300,000 years to arrive there. However, it does mean that in the future telescopes will be able to detect the planet's atmosphere directly. While Gliese 581d may be habitable there are other possibilities; it could have kept some atmospheric hydrogen, like Uranus and Neptune, or the fierce wind from its star during its infancy could even have torn its atmosphere away entirely. To distinguish between these different scenarios, Wordsworth and co-workers came up with several simple tests that observers will be able to perform in future with a sufficiently powerful telescope.

If Gliese 581d does turn out to be habitable, it would still be a pretty strange place to visit -- the denser air and thick clouds would keep the surface in a perpetual murky red twilight, and its large mass means that surface gravity would be around double that on Earth. But the diversity of planetary climates in the galaxy is likely to be far wider than the few examples we are used to from the Solar System. In the long run, the most important implication of these results may be the idea that life-supporting planets do not in fact need to be particularly like Earth at all.

Story Source:

The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by CNRS (Délégation Paris Michel-Ange).

Journal Reference:

Robin D. Wordsworth, François Forget, Franck Selsis, Ehouarn Millour, Benjamin Charnay, Jean-Baptiste Madeleine. Gliese 581d is the first discovered terrestrial-mass exoplanet in the habitable zone. The Astrophysical Journal, 2011; 733 (2): L48 DOI: 10.1088/2041-8205/733/2/L48

Note: If no author is given, the source is cited instead.

Disclaimer: Views expressed in this article do not necessarily reflect those of ScienceDaily or its staff.

View the original article here

Quantum simulation with light: Frustrations between photon pairs

ScienceDaily (May 6, 2011) — Researchers from the Vienna Center for Quantum Science and Technology at the University of Vienna and the Institute of Quantum Optics and Quantum Information (IQOQI) at the Austrian Academy of Sciences used a quantum mechanical system in the laboratory to simulate complex many-body systems. This experiment, which is published in Nature Physics, promises future quantum simulators with enormous potential insights into unknown quantum phenomena.

Already the behavior of relatively small quantum systems cannot be calculated because quantum states contain much more information than their classical counter-parts. However, if another quantum system is used to simulate the quantum system of interest, then answers about the properties of the complex quantum system can be obtained.

When is a quantum system frustrated?

Currently, many international groups are focusing their research on frustrated quantum systems, which have been conjectured to explain high-temperature superconductivity. A quantum system is frustrated if competing requirements cannot be satisfied simultaneously. The Viennese research group realized for the first time an experimental quantum simulation, where the frustration regarding the "pairing" of correlations was closely investigated.

Using two pairs of entangled photons, a frustrated quantum system could be simulated that consists of four particles. "Just the recent development of our quantum technology allows us to not only rebuild other quantum systems, but also to simulate its dynamics" says Philip Walther (University of Vienna). "Now we can prepare quantum states of individual photons to gain insights into other quantum systems," explains Xiao-song Ma (Austrian Academy of Sciences).Therefore, two in polarization entangled photons exhibit in many ways the same quantum physical properties as for example electrons in matter.

Conflict over partnerships

The research team of international scientists from China, Serbia, New Zeeland and Austria prepared single photons that were facing the conflict over partnerships between each other. Each photon can establish a single bond to only one partner exclusively, but wants to get correlated with several partners -- obviously this leads to frustration. As a result, the quantum system uses "tricks" that allow quantum fluctuations that different pairings can coexist as superposition.

The work of the Viennese group underlines that quantum simulations are a very good tool for calculating quantum states of matter and are thus opening the path for the investigation of more complex systems.

Story Source:

The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by University of Vienna.

Journal Reference:

Xiao-song Ma, Borivoje Dakic, William Naylor, Anton Zeilinger, Philip Walther. Quantum simulation of the wavefunction to probe frustrated Heisenberg spin systems. Nature Physics, 2011; 7 (5): 399 DOI: 10.1038/nphys1919

Note: If no author is given, the source is cited instead.

Disclaimer: Views expressed in this article do not necessarily reflect those of ScienceDaily or its staff.

View the original article here