Tuesday, 30 August 2011
Monday, 8 August 2011
How is Infinera Different?
Carriers have told us that they want the benefits of digital networks for their optical layer. They want the service flexibility that comes from digital add/drop of any optical service at any network node. They want to simplify network engineering and operations through regular digital cleanup of analog optical impairments, digital grooming and multiplexing, and advanced digital coding. And they want these benefits in a network that costs less than the traditional "analog optical" alternative. In short, these carriers have created an alternative vision for the optical layer that we call the Digital Optical Network.
Digital Optical Networking is the antithesis of the way that most other optical networking vendors have chosen to evolve their network architectures. These vendors have chosen the "all-optical route" with all the drawbacks that this entails.
Infinera took a different approach. We began with the assumption that "digital is good". After all, the vast majority of data being carried over optical networks today is created in digital form. In addition, anything to do with administering or fault-finding the services that carry this data is also digital, and any attempts to mimic these OAM or performance management capabilities in the analog domain tend to be somewhat ineffective.
We decided we had to find a way to make "digital" work. To make it scale, and to make it economical to deploy and operate. The key was to allow economical Optical-Electrical-Optical (OEO) conversions.
OEO conversions are uneconomical in conventional networks because they involve a number of discrete optical components for each wavelength, multiplied by the number of wavelengths that DWDM allows us to transmit in a single fiber.
For example, to create a signal for an individual wavelength we typically need:
- A source of light - such as a laser
- A way to put a digital signal onto that light - known as a modulator
- A means to ensure that the laser stays on the correct wavelength
- Components that control the output power of the laser
A number of optical component companies have developed small scale PICs that combine a number of these components into the same chip package. Sometimes these PICs are built on the same semiconductor substrate, while sometimes they're simply combined together in the same package (see monolithic photonic integration vs co-packaging).
Infinera has pioneered the technique of large scale photonic integration. Our PICs integrate the components needed for ten different wavelengths onto a single chip. At the moment that means over fifty discrete optical components on a single transmit PIC, and we'll continue to drive integration of additional components and functions.
Unique Space Image of Alabama Tornado Tracks
Unique Space Image of Alabama Tornado Tracks
May 16, 2011: NASA has released a unique satellite image tracing the damage of a monster EF-4 tornado that tore through Tuscaloosa, Alabama, on April 27th. It combines visible and infrared data to reveal damage unseen in conventional photographs.
"This is the first time we've used the ASTER instrument to track the wake of a super-outbreak of tornadoes," says NASA meteorologist Gary Jedlovec of the Marshall Space Flight Center in Huntsville, AL.
An ASTER visible-IR image of tornado damage near Tuscaloosa, AL. [larger image]
In the picture, captured just days after the storm, pink represents vegetation and aqua is the absence of vegetation. The tornado ripped up everything in its path, scouring the Earth's surface with its terrible force. The "tearing up" of vegetation makes the tornado's track stand out as a wide swath of aqua.
"This image and others like it are helping us study the torn landscape to determine just how huge and powerful these twisters were and to assess the damage they inflicted," says Jedlovec.
ASTER, short for Advanced Spaceborne Thermal Emission and Reflection Radiometer, orbits Earth onboard NASA's Terra spacecraft. Its data products include digital elevation maps from stereo images; surface temperatures; vegetation maps; cloud and sea ice data; and more. Last spring the instrument helped track the movement of the oil spill in the Gulf of Mexico.
Ground survey teams have a lot to contend with. [Youtube video]
To detect the scars left by the twisters, ASTER senses the visible and infrared energy reflected from the planet's surface. Destruction like crushed houses, torn and snapped trees, and uprooted crops are evident in the multi-wavelength images.
"A demolished house, debris and soil scattered on vegetated surfaces, and damaged trees and crops all change the pattern of reflected radiation measured by the satellite," explains Jedlovec. "We can analyze these patterns to help storm survey teams evaluate the damage."
Ground teams conducting field surveys of tornado damage must try to pinpoint where the twisters touched down, how long they stayed on the ground, and the force of their winds. But doing this from ground level can be tricky. Some places are nearly impossible to reach by foot or car. Also, in remote areas, damage often goes unreported, so survey teams don't know to look there.
This is where satellites can help.
"To get an accurate picture survey teams need to look everywhere that sustained damage – even unreported areas. Satellite sensors detect damage in rural areas, wilderness areas, and other unpopulated areas. Only with that knowledge can surveyors determine the true track of a tornado."
Otherwise, says Jedlovec, a twister could have flattened a single dwelling in a remote location, killing everyone inside, and no one would know.
Another sample of ASTER tornado data showing three nearly-parallel tracks of destruction. [large image] [annotated composite image]
Less critical but still important are home owners' insurance issues. To evaluate claims submitted by storm victims, insurance companies rely on National Weather Service storm reports based on the field surveys.
"Let's say you live in a remote area," says Jedlovec. "If there's no record of a storm passing over your area, you could be out of luck."
Jedlovec and colleagues are working now to produce satellite images of other areas ravaged by the historic outbreak of tornadoes.
"We want to help the storm victims any way we can."
May 16, 2011: NASA has released a unique satellite image tracing the damage of a monster EF-4 tornado that tore through Tuscaloosa, Alabama, on April 27th. It combines visible and infrared data to reveal damage unseen in conventional photographs.
"This is the first time we've used the ASTER instrument to track the wake of a super-outbreak of tornadoes," says NASA meteorologist Gary Jedlovec of the Marshall Space Flight Center in Huntsville, AL.
An ASTER visible-IR image of tornado damage near Tuscaloosa, AL. [larger image]
In the picture, captured just days after the storm, pink represents vegetation and aqua is the absence of vegetation. The tornado ripped up everything in its path, scouring the Earth's surface with its terrible force. The "tearing up" of vegetation makes the tornado's track stand out as a wide swath of aqua.
"This image and others like it are helping us study the torn landscape to determine just how huge and powerful these twisters were and to assess the damage they inflicted," says Jedlovec.
ASTER, short for Advanced Spaceborne Thermal Emission and Reflection Radiometer, orbits Earth onboard NASA's Terra spacecraft. Its data products include digital elevation maps from stereo images; surface temperatures; vegetation maps; cloud and sea ice data; and more. Last spring the instrument helped track the movement of the oil spill in the Gulf of Mexico.
Ground survey teams have a lot to contend with. [Youtube video]
To detect the scars left by the twisters, ASTER senses the visible and infrared energy reflected from the planet's surface. Destruction like crushed houses, torn and snapped trees, and uprooted crops are evident in the multi-wavelength images.
"A demolished house, debris and soil scattered on vegetated surfaces, and damaged trees and crops all change the pattern of reflected radiation measured by the satellite," explains Jedlovec. "We can analyze these patterns to help storm survey teams evaluate the damage."
Ground teams conducting field surveys of tornado damage must try to pinpoint where the twisters touched down, how long they stayed on the ground, and the force of their winds. But doing this from ground level can be tricky. Some places are nearly impossible to reach by foot or car. Also, in remote areas, damage often goes unreported, so survey teams don't know to look there.
This is where satellites can help.
"To get an accurate picture survey teams need to look everywhere that sustained damage – even unreported areas. Satellite sensors detect damage in rural areas, wilderness areas, and other unpopulated areas. Only with that knowledge can surveyors determine the true track of a tornado."
Otherwise, says Jedlovec, a twister could have flattened a single dwelling in a remote location, killing everyone inside, and no one would know.
Another sample of ASTER tornado data showing three nearly-parallel tracks of destruction. [large image] [annotated composite image]
Less critical but still important are home owners' insurance issues. To evaluate claims submitted by storm victims, insurance companies rely on National Weather Service storm reports based on the field surveys.
"Let's say you live in a remote area," says Jedlovec. "If there's no record of a storm passing over your area, you could be out of luck."
Jedlovec and colleagues are working now to produce satellite images of other areas ravaged by the historic outbreak of tornadoes.
"We want to help the storm victims any way we can."
Super Storm on Saturn
Super Storm on Saturn
May 19, 2011: NASA's Cassini spacecraft and a European Southern Observatory ground-based telescope are tracking the growth of a giant early-spring storm in Saturn's northern hemisphere so powerful that it stretches around the entire planet. The rare storm has been wreaking havoc for months and shooting plumes of gas high into the planet's atmosphere.
This false-color infrared image shows clouds of large ammonia ice particles dredged up by the powerful storm. Credit: Cassini. [more]
"Nothing on Earth comes close to this powerful storm," says Leigh Fletcher, a Cassini team scientist at the University of Oxford in the United Kingdom, and lead author of a study that appeared in this week's edition of Science Magazine. "A storm like this is rare. This is only the sixth one to be recorded since 1876, and the last was way back in 1990."
Cassini's radio and plasma wave science instrument first detected the large disturbance in December 2010, and amateur astronomers have been watching it ever since through backyard telescopes. As it rapidly expanded, the storm's core developed into a giant, powerful thunderstorm, producing a 3,000-mile-wide (5,000-kilometer-wide) dark vortex possibly similar to Jupiter's Great Red Spot.
This is the first major storm on Saturn observed by an orbiting spacecraft and studied at thermal infrared wavelengths. Infrared observations are key because heat tells researchers a great deal about conditions inside the storm, including temperatures, winds, and atmospheric composition. Temperature data were provided by the Very Large Telescope (VLT) on Cerro Paranal in Chile and Cassini's composite infrared spectrometer (CIRS), operated by NASA's Goddard Space Flight Center in Greenbelt, Md.
"Our new observations show that the storm had a major effect on the atmosphere, transporting energy and material over great distances -- creating meandering jet streams and forming giant vortices -- and disrupting Saturn's seasonal [weather patterns]," said Glenn Orton, a paper co-author, based at NASA's Jet Propulsion Laboratory in Pasadena, Calif.
The violence of the storm -- the strongest disturbances ever detected in Saturn's stratosphere -- took researchers by surprise. What started as an ordinary disturbance deep in Saturn's atmosphere punched through the planet's serene cloud cover to roil the high layer known as the stratosphere.
Thermal infrared images of Saturn from the Very Large Telescope Imager and Spectrometer for the mid-Infrared (VISIR) instrument on the European Southern Observatory's Very Large Telescope, on Cerro Paranal, Chile, appear at center and on the right. An amateur visible-light image from Trevor Barry, of Broken Hill, Australia, appears on the left. The images were obtained on Jan. 19, 2011. [more]
"On Earth, the lower stratosphere is where commercial airplanes generally fly to avoid storms which can cause turbulence," says Brigette Hesman, a scientist at the University of Maryland in College Park who works on the CIRS team at Goddard and is the second author on the paper. "If you were flying in an airplane on Saturn, this storm would reach so high up, it would probably be impossible to avoid it."
A separate analysis using Cassini's visual and infrared mapping spectrometer, led by Kevin Baines of JPL, confirmed the storm is very violent, dredging up deep material in volumes several times larger than previous storms. Other Cassini scientists are studying the evolving storm and, they say, a more extensive picture will emerge soon.
May 19, 2011: NASA's Cassini spacecraft and a European Southern Observatory ground-based telescope are tracking the growth of a giant early-spring storm in Saturn's northern hemisphere so powerful that it stretches around the entire planet. The rare storm has been wreaking havoc for months and shooting plumes of gas high into the planet's atmosphere.
This false-color infrared image shows clouds of large ammonia ice particles dredged up by the powerful storm. Credit: Cassini. [more]
"Nothing on Earth comes close to this powerful storm," says Leigh Fletcher, a Cassini team scientist at the University of Oxford in the United Kingdom, and lead author of a study that appeared in this week's edition of Science Magazine. "A storm like this is rare. This is only the sixth one to be recorded since 1876, and the last was way back in 1990."
Cassini's radio and plasma wave science instrument first detected the large disturbance in December 2010, and amateur astronomers have been watching it ever since through backyard telescopes. As it rapidly expanded, the storm's core developed into a giant, powerful thunderstorm, producing a 3,000-mile-wide (5,000-kilometer-wide) dark vortex possibly similar to Jupiter's Great Red Spot.
This is the first major storm on Saturn observed by an orbiting spacecraft and studied at thermal infrared wavelengths. Infrared observations are key because heat tells researchers a great deal about conditions inside the storm, including temperatures, winds, and atmospheric composition. Temperature data were provided by the Very Large Telescope (VLT) on Cerro Paranal in Chile and Cassini's composite infrared spectrometer (CIRS), operated by NASA's Goddard Space Flight Center in Greenbelt, Md.
"Our new observations show that the storm had a major effect on the atmosphere, transporting energy and material over great distances -- creating meandering jet streams and forming giant vortices -- and disrupting Saturn's seasonal [weather patterns]," said Glenn Orton, a paper co-author, based at NASA's Jet Propulsion Laboratory in Pasadena, Calif.
The violence of the storm -- the strongest disturbances ever detected in Saturn's stratosphere -- took researchers by surprise. What started as an ordinary disturbance deep in Saturn's atmosphere punched through the planet's serene cloud cover to roil the high layer known as the stratosphere.
Thermal infrared images of Saturn from the Very Large Telescope Imager and Spectrometer for the mid-Infrared (VISIR) instrument on the European Southern Observatory's Very Large Telescope, on Cerro Paranal, Chile, appear at center and on the right. An amateur visible-light image from Trevor Barry, of Broken Hill, Australia, appears on the left. The images were obtained on Jan. 19, 2011. [more]
"On Earth, the lower stratosphere is where commercial airplanes generally fly to avoid storms which can cause turbulence," says Brigette Hesman, a scientist at the University of Maryland in College Park who works on the CIRS team at Goddard and is the second author on the paper. "If you were flying in an airplane on Saturn, this storm would reach so high up, it would probably be impossible to avoid it."
A separate analysis using Cassini's visual and infrared mapping spectrometer, led by Kevin Baines of JPL, confirmed the storm is very violent, dredging up deep material in volumes several times larger than previous storms. Other Cassini scientists are studying the evolving storm and, they say, a more extensive picture will emerge soon.
NASA's Galaxy Evolution Explorer Helps Confirm Nature of Dark Energy
PASADENA, Calif. -- A five-year survey of 200,000 galaxies, stretching back seven billion years in cosmic time, has led to one of the best independent confirmations that dark energy is driving our universe apart at accelerating speeds. The survey used data from NASA's space-based Galaxy Evolution Explorer and the Anglo-Australian Telescope on Siding Spring Mountain in Australia.
The findings offer new support for the favored theory of how dark energy works -- as a constant force, uniformly affecting the universe and propelling its runaway expansion. They contradict an alternate theory, where gravity, not dark energy, is the force pushing space apart. According to this alternate theory, with which the new survey results are not consistent, Albert Einstein's concept of gravity is wrong, and gravity becomes repulsive instead of attractive when acting at great distances.
"The action of dark energy is as if you threw a ball up in the air, and it kept speeding upward into the sky faster and faster," said Chris Blake of the Swinburne University of Technology in Melbourne, Australia. Blake is lead author of two papers describing the results that appeared in recent issues of the Monthly Notices of the Royal Astronomical Society. "The results tell us that dark energy is a cosmological constant, as Einstein proposed. If gravity were the culprit, then we wouldn't be seeing these constant effects of dark energy throughout time."
Dark energy is thought to dominate our universe, making up about 74 percent of it. Dark matter, a slightly less mysterious substance, accounts for 22 percent. So-called normal matter, anything with atoms, or the stuff that makes up living creatures, planets and stars, is only approximately four percent of the cosmos.
The idea of dark energy was proposed during the previous decade, based on studies of distant exploding stars called supernovae. Supernovae emit constant, measurable light, making them so-called "standard candles," which allows calculation of their distance from Earth. Observations revealed dark energy was flinging the objects out at accelerating speeds.
Dark energy is in a tug-of-war contest with gravity. In the early universe, gravity took the lead, dominating dark energy. At about 8 billion years after the Big Bang, as space expanded and matter became diluted, gravitational attractions weakened and dark energy gained the upper hand. Billions of years from now, dark energy will be even more dominant. Astronomers predict our universe will be a cosmic wasteland, with galaxies spread apart so far that any intelligent beings living inside them wouldn't be able to see other galaxies.
The new survey provides two separate methods for independently checking the supernovae results. This is the first time astronomers performed these checks across the whole cosmic timespan dominated by dark energy. The team began by assembling the largest three-dimensional map of galaxies in the distant universe, spotted by the Galaxy Evolution Explorer. The ultraviolet-sensing telescope has scanned about three-quarters of the sky, observing hundreds of millions of galaxies.
"The Galaxy Evolution Explorer helped identify bright, young galaxies, which are ideal for this type of study," said Christopher Martin, principal investigator for the mission at the California Institute of Technology in Pasadena. "It provided the scaffolding for this enormous 3-D map."
The astronomers acquired detailed information about the light for each galaxy using the Anglo-Australian Telescope and studied the pattern of distance between them. Sound waves from the very early universe left imprints in the patterns of galaxies, causing pairs of galaxies to be separated by approximately 500 million light-years.
This "standard ruler" was used to determine the distance from the galaxy pairs to Earth -- the closer a galaxy pair is to us, the farther apart the galaxies will appear from each other on the sky. As with the supernovae studies, this distance data were combined with information about the speeds at which the pairs are moving away from us, revealing, yet again, the fabric of space is stretching apart faster and faster.
The team also used the galaxy map to study how clusters of galaxies grow over time like cities, eventually containing many thousands of galaxies. The clusters attract new galaxies through gravity, but dark energy tugs the clusters apart. It slows down the process, allowing scientists to measure dark energy's repulsive force.
"Observations by astronomers over the last 15 years have produced one of the most startling discoveries in physical science; the expansion of the universe, triggered by the Big Bang, is speeding up," said Jon Morse, astrophysics division director at NASA Headquarters in Washington. "Using entirely independent methods, data from the Galaxy Evolution Explorer have helped increase our confidence in the existence of dark energy."
Caltech leads the Galaxy Evolution Explorer mission and is responsible for science operations and data analysis. NASA's Jet Propulsion Laboratory in Pasadena, manages the mission and built the science instrument. The mission was developed under NASA's Explorers Program managed by the Goddard Space Flight Center, Greenbelt, Md. Researchers sponsored by Yonsei University in South Korea and the Centre National d'Etudes Spatiales (CNES) in France collaborated on this mission. Caltech manages JPL for NASA
The findings offer new support for the favored theory of how dark energy works -- as a constant force, uniformly affecting the universe and propelling its runaway expansion. They contradict an alternate theory, where gravity, not dark energy, is the force pushing space apart. According to this alternate theory, with which the new survey results are not consistent, Albert Einstein's concept of gravity is wrong, and gravity becomes repulsive instead of attractive when acting at great distances.
"The action of dark energy is as if you threw a ball up in the air, and it kept speeding upward into the sky faster and faster," said Chris Blake of the Swinburne University of Technology in Melbourne, Australia. Blake is lead author of two papers describing the results that appeared in recent issues of the Monthly Notices of the Royal Astronomical Society. "The results tell us that dark energy is a cosmological constant, as Einstein proposed. If gravity were the culprit, then we wouldn't be seeing these constant effects of dark energy throughout time."
Dark energy is thought to dominate our universe, making up about 74 percent of it. Dark matter, a slightly less mysterious substance, accounts for 22 percent. So-called normal matter, anything with atoms, or the stuff that makes up living creatures, planets and stars, is only approximately four percent of the cosmos.
The idea of dark energy was proposed during the previous decade, based on studies of distant exploding stars called supernovae. Supernovae emit constant, measurable light, making them so-called "standard candles," which allows calculation of their distance from Earth. Observations revealed dark energy was flinging the objects out at accelerating speeds.
Dark energy is in a tug-of-war contest with gravity. In the early universe, gravity took the lead, dominating dark energy. At about 8 billion years after the Big Bang, as space expanded and matter became diluted, gravitational attractions weakened and dark energy gained the upper hand. Billions of years from now, dark energy will be even more dominant. Astronomers predict our universe will be a cosmic wasteland, with galaxies spread apart so far that any intelligent beings living inside them wouldn't be able to see other galaxies.
The new survey provides two separate methods for independently checking the supernovae results. This is the first time astronomers performed these checks across the whole cosmic timespan dominated by dark energy. The team began by assembling the largest three-dimensional map of galaxies in the distant universe, spotted by the Galaxy Evolution Explorer. The ultraviolet-sensing telescope has scanned about three-quarters of the sky, observing hundreds of millions of galaxies.
"The Galaxy Evolution Explorer helped identify bright, young galaxies, which are ideal for this type of study," said Christopher Martin, principal investigator for the mission at the California Institute of Technology in Pasadena. "It provided the scaffolding for this enormous 3-D map."
The astronomers acquired detailed information about the light for each galaxy using the Anglo-Australian Telescope and studied the pattern of distance between them. Sound waves from the very early universe left imprints in the patterns of galaxies, causing pairs of galaxies to be separated by approximately 500 million light-years.
This "standard ruler" was used to determine the distance from the galaxy pairs to Earth -- the closer a galaxy pair is to us, the farther apart the galaxies will appear from each other on the sky. As with the supernovae studies, this distance data were combined with information about the speeds at which the pairs are moving away from us, revealing, yet again, the fabric of space is stretching apart faster and faster.
The team also used the galaxy map to study how clusters of galaxies grow over time like cities, eventually containing many thousands of galaxies. The clusters attract new galaxies through gravity, but dark energy tugs the clusters apart. It slows down the process, allowing scientists to measure dark energy's repulsive force.
"Observations by astronomers over the last 15 years have produced one of the most startling discoveries in physical science; the expansion of the universe, triggered by the Big Bang, is speeding up," said Jon Morse, astrophysics division director at NASA Headquarters in Washington. "Using entirely independent methods, data from the Galaxy Evolution Explorer have helped increase our confidence in the existence of dark energy."
Caltech leads the Galaxy Evolution Explorer mission and is responsible for science operations and data analysis. NASA's Jet Propulsion Laboratory in Pasadena, manages the mission and built the science instrument. The mission was developed under NASA's Explorers Program managed by the Goddard Space Flight Center, Greenbelt, Md. Researchers sponsored by Yonsei University in South Korea and the Centre National d'Etudes Spatiales (CNES) in France collaborated on this mission. Caltech manages JPL for NASA
Gliese 581d: A Habitable Exoplanet?
Gliese 581d: A Habitable Exoplanet?
Source: CNRS press release
Alien Life
Posted: 05/20/11
Summary: A new computer model that simulates possible exoplanet climates indicates that the planet Gliese 581d might be warm enough to have oceans, clouds and rainfall. Gliese 581d is likely to be a rocky planet with a mass at least seven times that of Earth.
Schematic of the global climate model used to study Gliese 581d. Red / blue shading indicate hot / cold surface temperatures, while the arrows show wind velocities at 2 km height in the atmosphere. © LMD/CNRS Are there other planets inhabited like the 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 (Gliese 581d and Gliese 581c). While the more distant planet, Gliese 581d, was initially judged to be too cold for life, the closer-in planet, Gliese 581c, 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.
Surface temperature maps for simulations of Gliese 581d assuming an atmosphere of 20 bars of CO2 and varying rotation rates. It is currently unknown whether the planet rotates slowly or has permanent day and night sides. In all cases, the temperatures allow for the presence of liquid water on the surface. © LMD/CNRS It is 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/Ecole Polytechnique) at the Institute Pierre Simon Laplace in Paris, in collaboration with a researcher from the Laboratoire d'astrophysique de Bordeaux (CNRS/Université Bordeaux 1). 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.
This artist's concept illustrates a young, red dwarf star surrounded by three planets. Such stars are dimmer and smaller than yellow stars like our sun. Credit: NASA/JPL-Caltech 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 man-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 the Earth at all.
Source: CNRS press release
Alien Life
Posted: 05/20/11
Summary: A new computer model that simulates possible exoplanet climates indicates that the planet Gliese 581d might be warm enough to have oceans, clouds and rainfall. Gliese 581d is likely to be a rocky planet with a mass at least seven times that of Earth.
Schematic of the global climate model used to study Gliese 581d. Red / blue shading indicate hot / cold surface temperatures, while the arrows show wind velocities at 2 km height in the atmosphere. © LMD/CNRS Are there other planets inhabited like the 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 (Gliese 581d and Gliese 581c). While the more distant planet, Gliese 581d, was initially judged to be too cold for life, the closer-in planet, Gliese 581c, 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.
Surface temperature maps for simulations of Gliese 581d assuming an atmosphere of 20 bars of CO2 and varying rotation rates. It is currently unknown whether the planet rotates slowly or has permanent day and night sides. In all cases, the temperatures allow for the presence of liquid water on the surface. © LMD/CNRS It is 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/Ecole Polytechnique) at the Institute Pierre Simon Laplace in Paris, in collaboration with a researcher from the Laboratoire d'astrophysique de Bordeaux (CNRS/Université Bordeaux 1). 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.
This artist's concept illustrates a young, red dwarf star surrounded by three planets. Such stars are dimmer and smaller than yellow stars like our sun. Credit: NASA/JPL-Caltech 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 man-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 the Earth at all.
Local Scientists Produce First Aerogel in Space
First Space-Produced Aerogel Made on Space Sciences Laboratory Rocket Flight
June 19, 1996: Aerogel is the lightest solid known to mankind, with only three times the density of air. A block the size of a human weighs less than a pound. Because of its amazing insulating properties, an inch-thick slab can safely shield the human hand from the heat of a blowtorch. A sugar-cubed size portion of the material has the internal surface area of a basketball court. As the only known transparent insulator, Aerogel is a supercritically dried gel sometimes referred to as "frozen smoke".
On April 3, 1996, the first space-produced samples of aerogels were produced by NASA on a flight of a starfire rocket. The production of such materials in space is interesting because of the strong influence of gravity on how a gel is formed. Comparison of gels manufactured in space and on the ground have shown large differences, and the production of gels in space can provide a higher-quality product with a more uniform structure.
Chemical Engineering Progress (June 1995, p 14) described "the holy grail of aerogel applications has been developing invisible insulation for use between window panes." The production of insulating and transparent windows through aerogel manufacturing in space can develop into a substantial market for residential and commercial applications. The excellent thermal properties and transparent nature of silica aerogel make it an obvious choice for super-insulating windows, skylights, solar collector covers, and specialty windows.
June 19, 1996: Aerogel is the lightest solid known to mankind, with only three times the density of air. A block the size of a human weighs less than a pound. Because of its amazing insulating properties, an inch-thick slab can safely shield the human hand from the heat of a blowtorch. A sugar-cubed size portion of the material has the internal surface area of a basketball court. As the only known transparent insulator, Aerogel is a supercritically dried gel sometimes referred to as "frozen smoke".
On April 3, 1996, the first space-produced samples of aerogels were produced by NASA on a flight of a starfire rocket. The production of such materials in space is interesting because of the strong influence of gravity on how a gel is formed. Comparison of gels manufactured in space and on the ground have shown large differences, and the production of gels in space can provide a higher-quality product with a more uniform structure.
Chemical Engineering Progress (June 1995, p 14) described "the holy grail of aerogel applications has been developing invisible insulation for use between window panes." The production of insulating and transparent windows through aerogel manufacturing in space can develop into a substantial market for residential and commercial applications. The excellent thermal properties and transparent nature of silica aerogel make it an obvious choice for super-insulating windows, skylights, solar collector covers, and specialty windows.
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