The researchers found evidence of at least one and possibly two or three additional planets orbiting the star, which is about 22 light years from Earth.

The team includes UC Santa Cruz astronomers Steven Vogt and Eugenio Rivera and was led by Guillem Anglada-Escude and Paul Butler of the Carnegie Institution for Science. Their work will be published by Astrophysical Journal Letters, and the manuscript will be posted online at arxiv.org/archive/astro-ph.

The host star is a member of a triple-star system and has a different makeup than our sun, with a much lower abundance of elements heavier than helium, such as iron, carbon, and silicon. This discovery indicates that potentially habitable planets can occur in a greater variety of environments than previously believed.

The researchers used public data from the European Southern Observatory and analyzed it with a novel data-analysis method. They also incorporated new measurements from the W. M. Keck Observatory's High Resolution Echelle Spectrograph and the new Carnegie Planet Finder Spectrograph at the Magellan II Telescope. Their planet-finding technique involved measuring the small wobbles in a star's motion caused by the gravitational tug of a planet.

The host star, called GJ 667C, is an M-class dwarf star. The other two stars in the triple-star system (GJ 667AB) are a pair of orange K dwarfs, with a concentration of heavy elements only 25 percent that of our sun's. Such elements are the building blocks of terrestrial planets, so it was thought to be less likely for metal-depleted star systems to have an abundance of low-mass planets.

"This was expected to be a rather unlikely star to host planets. Yet there they are, around a very nearby, metal-poor example of the most common type of star in our galaxy," said Vogt, a professor of astronomy and astrophysics at UCSC.

"The detection of this planet, this nearby and this soon, implies that our galaxy must be teeming with billions of potentially habitable rocky planets."

GJ 667C had previously been observed to have a super-Earth (GJ 667Cb) with a period of 7.2 days, although this finding was never published. This planet orbits so close to the star that it would be too hot for liquid water. The new study started with the aim of obtaining the orbital parameters of this super-Earth.

But in addition to this first candidate, the research team found the clear signal of a new planet (GJ 667Cc) with an orbital period of 28.15 days and a minimum mass of 4.5 times that of Earth. The new planet receives 90 percent of the light that Earth receives.

However, because most of its incoming light is in the infrared, a higher percentage of this incoming energy should be absorbed by the planet. When both these effects are taken into account, the planet is expected to absorb about the same amount of energy from its star that the Earth absorbs from the sun.

"This planet is the new best candidate to support liquid water and, perhaps, life as we know it," Anglada-Escude said.

The team found that the system might also contain a gas-giant planet and an additional super-Earth with an orbital period of 75 days. However, further observations are needed to confirm these two possibilities.

"With the advent of a new generation of instruments, researchers will be able to survey many M dwarf stars for similar planets and eventually look for spectroscopic signatures of life in one of these worlds," said Anglada-Escude, who was with Carnegie when he conducted the research, but has since moved on to the University of Gottingen.

]]> Thu, 09 FEB 2012 08:59:10 AEST Moffet Field CA (NASA) Feb 06, 2012 - Trace elements in stars may influence the evolution of habitable zones around them where life as we know it might dwell, scientists now find.

Stars are made nearly entirely from hydrogen and helium gas. Still, traces of heavier elements - which astronomers call metals, even if they are not what one normally think of as metals - can be found in stars as well, either inherited from the remains of older stars or forged via nuclear fusion.

Scientists can detect what elements a star possesses by looking at its light, which comes in a wide variety of wavelengths, some visible, many invisible.

The wavelengths of light that matter emits often comes in specific clumps or lines, which can act like a fingerprint, revealing the identity of the material in question.

By looking at the wavelengths or spectra of light from nearby dwarf stars as part of searches for alien worlds, or exoplanets, researchers have with high precision determined the abundance of certain elements for more than a hundred of these stars, with more to come. Now researchers suggest variations in the compositions of these stars could impact the habitable zones around them.

What scientists call the habitable zone of a star is defined by whether liquid water can survive on a planet's surface, given that life exists virtually wherever there is liquid water on Earth.

Too far from a star, and the lack of light makes a world too cold, freezing all its water; too close to a star, and all that blazing heat makes a world too hot, with its water eventually all boiling off.

Normally scientists figure out the habitable zones of stars by seeing how hot the stars are. This involves looking at their brightness and color. Computer models now suggest that variations in a star's elemental composition might alter its long-term behavior, significantly affecting the location and lifetime of its habitable zone.

"I was expecting some subtle changes in our stellar evolution models in terms of the surface temperature and brightness - I was not looking for such a dramatic change in the lifetimes of the stars," said study lead author Patrick Young, a theoretical astrophysicist and astrobiologist at Arizona State University.

Scientists typically measure the abundance of heavy elements in a star relative to the iron content in its atmosphere, as iron is a common element and its spectrum is relatively easy to measure. Past research found that abundances of various heavy elements could vary by more than a factor of two given otherwise similar star types.

Young and his colleagues generated computer models for how variations in levels of eight elements - carbon, oxygen, sodium, aluminum, magnesium, silicon, calcium and titanium - might affect the behavior of F, G and K stars, those most similar to our sun. Metals in a star can alter its evolution by affecting how opaque its plasma is.

"The persistence of stars as stable objects relies on the heating of plasma in the star by nuclear fusion to produce pressure that counteracts the inward force of gravity," Young explained. "A higher opacity traps the energy of fusion more efficiently and results in a larger radius, cooler star. More efficient use of energy also means that nuclear burning can proceed more slowly, resulting in a longer lifetime for the star."

The scientists found that calcium, sodium, magnesium, aluminum and silicon had small but significant effects on a star's evolution. Higher levels of these elements resulted in cooler, redder stars.

Oxygen also proved especially important because it could dramatically alter the lifetime of a star's habitable zone. "The habitable lifetime of an orbit the size of Earth's around a one-solar-mass star is only 3.5 billion years for oxygen-depleted compositions but 8.5 billion years for oxygen-rich stars," Young said.

"For comparison, we expect the Earth to remain habitable for another billion years or so, for about 5.5 billion years total, before the Sun becomes too luminous. Complex life on Earth arose some 3.9 billion years after its formation, so if Earth is at all representative, low-oxygen stars are perhaps less than ideal targets."

Moreover, the presence of oxygen was linked with ultraviolet radiation, which is known to damage cells. "A star that is otherwise like the Sun in iron abundance and mass but relatively scarce in oxygen could produce twice as much of the cell-damaging radiation that causes skin cancer and is sometimes used for sterilization," Young said.

Young did note that habitable zones are a rather nebulous concept, since they depend on the atmosphere and geological evolution of a planet, making it tricky to draw any conclusions about the lifetime or extent of habitable zones.

"This is why we concentrate on the stellar modeling," Young said. "We can provide input to any climate model other researchers wish to use. For illustrative purposes we have chosen a simple, conservative prescription, not too optimistic or pessimistic."

A better knowledge of where a star's habitable zone really lies could influence which exoplanets astrobiologists end up studying more and which they end up ignoring because they lie outside habitable zones.

"Kepler has already detected worlds in the current habitable zones of their stars and planets smaller than Earth, and there are dozens more candidates that await confirmation," Young said.

"Detecting a planet with life will be a difficult proposition at best, requiring too many resources to observe indiscriminately. With this information we can narrow down our search to planets that are not only currently in their habitable zones, but have been and will remain there for long enough to potentially develop complex life."

The composition of a star can also influence the composition of its planets. Two important considerations are the carbon-oxygen and magnesium-silicon ratios of stars, which can affect whether a planet has certain magnesium- or silicon-loaded clay minerals such as magnesium silicate (MgSiO3), silicon dioxide (SiO2), magnesium orthosilicate (Mg2SiO4), and magnesium oxide (MgO). Clay minerals seem to be a good surface to create key components of life, such as the lipid membranes of cells.

"This is why one of the targets of the Mars Science Laboratory will be phyllosilicate clays in Gale Crater," Young said. "Some clays are better than others, and the magnesium-silicon ratio in part determines the type of clay formed."

Variations in the compositions of stars could also lead to planets that have different elemental combinations dominating, such as a planet with mostly carbon-based rock as opposed to our silicon-based Earth. "We'd expect tectonics and volcanism to be very different on a planet whose crust is dominated by graphite and silicon carbide than on Earth."

Certain elements within a star also strongly line up with the abundance of radioactive elements such as uranium and thorium, which are key in determining how molten the interior of planets are, Young said. Molten planetary interiors are key to plate tectonics, which in turn may be important to the evolution of life on Earth.

Young noted that some of the elements they would like to look at are very difficult to observe. For instance, "we want to find trace elements that are important to terrestrial-style life like molybdenum and phosphorus," he said.

"I am conducting other research to find abundant elements that we could use as proxies for finding enhancements in those trace elements because they are produced in the same conditions inside stars or stellar explosions."

The researchers are now analyzing the elemental abundances seen in 600 stars that are targets of exoplanet searches. They are also producing a much larger set of stellar evolution models for different mass stars and compositions.

"We will be producing a list of what we consider the best 100 targets for habitable planet searches based on a number of criteria including those presented in this work," Young said.

Young and his colleagues detailed their findings Jan. 11 at the annual meeting of the American Astronomical Society in Austin, Texas.

]]> Thu, 09 FEB 2012 08:59:10 AEST Washington (AFP) Feb 2, 2012 - International astronomers said on Thursday they have found the fourth potentially habitable planet outside our solar system with temperatures that could support water and life about 22 light-years from Earth.

The team analyzed data from the European Southern Observatory about a star known as GJ 667C, which is known as an M-class dwarf star and puts out much less heat than our Sun.

However, at least three planets are orbiting close to the star, and one of them appears to be close enough that it likely absorbs about as much incoming light and energy as Earth, has similar surface temperatures and perhaps water.

The new rocky planet, GJ 667Cc, orbits its star every 28.15 days -- meaning its year equals about one Earth month -- and has a mass at least 4.5 times that of Earth, according to the research published in Astrophysical Journal Letters.

"This planet is the new best candidate to support liquid water and, perhaps, life as we know it," said Guillem Anglada-Escude who was with the Carnegie Institution for Science when he conducted the research but has since moved on to the University of Gottingen in Germany.

The theory about water, however, cannot be confirmed until astronomers learn more about the planets atmosphere.

Other planets circling the same star -- which is part of a three-star system -- could include a gas-giant and an additional super-Earth with an orbital period of 75 days, but more observations are needed to confirm that.

Some experts have been skeptical that M-class dwarf stars could have planets that support life because they are too dim and tend to have lots of solar flare activity which could send off lethal radiation to nearby planets.

And even though this star, GJ 667C, has a much lower abundance of elements heavier than helium, such as iron, carbon, and silicon -- the building blocks of terrestrial planets -- than our Sun, astronomers are intrigued by the possibilities.

"This was expected to be a rather unlikely star to host planets. Yet there they are, around a very nearby, metal-poor example of the most common type of star in our galaxy," said co-author Steven Vogt, a professor of astronomy and astrophysics at University of California Santa Cruz.

"The detection of this planet, this nearby and this soon, implies that our galaxy must be teeming with billions of potentially habitable rocky planets."

French astronomers in May last year confirmed the first exoplanet, Gliese 581d, to meet key requirements for sustaining life. It is a rocky planet about 20 light-years away.

Swiss astronomers reported in August that another planet, HD 85512 b, about 36 light-years away seemed to be in the habitable zone of its star.

The US space agency NASA confirmed its first such planet late last year, Kepler 22b, about 600 light-years away.

]]> Thu, 09 FEB 2012 08:59:10 AEST Tel Aviv, Israel (SPX) Feb 03, 2012 - In the last two decades, the study of extrasolar planets - those that lie outside our own solar system - has become one of the most important fields of astrophysics.

Now a National Aeronautics and Space Administration (NASA) team that includes Prof. Tsevi Mazeh of Tel Aviv University's Department of Astronomy and Astrophysics and the Director of the Wise Observatory has discovered two new planets, named Kepler-34 and Kepler-35, each of which revolves around its own double suns. Together with Kepler-16, discovered a few months ago, there are now three such known systems in the galaxy.

According to Prof. Mazeh, these discoveries indicate that planets revolving around binary suns (suns that are formed as a pair) are a common phenomenon. Double stars or suns are typical in the universe, and now we know that planets can orbit around these intriguing phenomena, he says.

The team discovered the planets, which are 5,000 light years from Earth in the Cygnus constellation, by measuring the light emitted by the double suns. The data was collected by NASA's Kepler satellite, and the results recently published in the journal Nature.

It takes two
Most suns in the universe exist in pairs, explains Prof. Mazeh. These partnerships closely mimic human relationships - if two suns are formed together, they stay together, unless a third star comes too close to the pair and breaks the bond between the two.

Our solar system, which revolves around one sun, is more unusual, though we can't dismiss the possibility that our sun has an undiscovered distant companion, he says. And while the phenomenon of binary stars has been well known for centuries, the recent discoveries prove that binary suns can also support planets.

Each sun in these systems revolves around its mate in a regular, cyclical pattern. During sunsets on Kepler-34 and Kepler-35, one sun will descend first, followed by a twilight period. Afterwards, the second sun will set and night will fall.

In Hebrew, the word for twilight means "between the suns," explains Prof. Mazeh, saying that the translation is an accurate description of what twilight is like on these newly discovered planets. Kepler-34 revolves around its double sun every 289 days, Kepler-35 every 131 days.

This discovery provides a unique opportunity to learn about solar systems that are very different from our own, says Prof. Mazeh. In the future, more research will be done on the planets themselves, including their possible atmospheres and the rotation of the planets.

A limitless universe
An expert in extrasolar planets and recent recipient of the Weizmann Prize for Excellence in Science, Prof. Mazeh is grateful to be working with the Kepler team. When he began his work in the early 1980s, it was widely believed that all planets and suns must be similar to the ones within our own solar system. And this simply isn't the case, he says.

"We shouldn't limit our search by assuming that all the planets are like those in our solar system. Some of them are very different from what we have here, and every time we find a new planet, we're explorers landing on unknown territory.

"The sky is not the limit," he smiles.

]]> Thu, 09 FEB 2012 08:59:10 AEST Moscow, Russia (RIA Novosti) Feb 03, 2012 - Russian astronomers are planning to start their own search for planets outside the Solar System using ground-based telescopes, head of the Institute for Space Research Lev Zelyony said on Wednesday.

"Scientists from the Pulkovo Observatory are planning to use ground-based instruments to study the transit of planets around their parent stars," Zelyony said at a roundtable meeting at RIA Novosti headquarters in Moscow.

The search for extrasolar planets or exoplanets is one of the fastest developing areas of astronomy. A total of 755 such planets have been identified since 1989 when observations suggested that a planet orbits the star Gamma Cephei in the constellation of Cepheus.

The U.S. Kepler and France's CoRoT space telescopes proved to be very successful in identifying exoplanets but ground-based projects could also be effective, Zelyony said citing the example of the Hungarian Automated Telescope Network (HATNet) which so far has discovered 29 exoplanets.

The transit method of detection, which the Russian astronomers are planning to use, is based on the observation of a star's small drop in brightness that occurs when the orbit of a planet passes in front of the star.

"It is an interesting research, which should be pursued," Zelyony said. "It will also help us look at our Solar System from a different perspective."

]]> Thu, 09 FEB 2012 08:59:10 AEST Livermore CA (SPX) Feb 03, 2012 - Using models similar to those used in weapons research, scientists may soon know more about exoplanets, those objects beyond the realm of our solar system. In a new study, Lawrence Livermore National Laboratory scientists and collaborators came up with new methods for deriving and testing the equation of state (EOS) of matter in exoplanets and figured out the mass-radius and mass-pressure relations for materials relevant to planetary interiors.

Astronomers started detecting exoplanets 18 years ago and more than 700 have been found so far, the vast majority within the last two years. Interest is now growing in the structure and atmospheres of these worlds.

New equation-of-state work helps interpret the structure of exoplanets. As there is a minimal amount of data in each exoplanet observation, interpretation of their composition and structure depends largely on comparing their mass and radius with the composition expected given the distance from their parent star. The makeup implies a mass-radius relation, which relies heavily on EOS calculated from electronic structure theory and measured experimentally on Earth.

In the new research, lead Laboratory scientist Damian Swift, along with LLNL colleagues Jon Eggert, Damien Hicks, Sebastien Hamel, Kyle Caspersen, Eric Schwegler and Rip Collins, compared their modeling results with the observed masses and radii of exoplanets. Their results broadly support recent assumptions about the structures of exoplanets but can now take advantage of the accurate EOS models and data produced at Livermore.

"Current theoretical techniques for calculating electronic structures can predict EOS relevant to planetary interiors," Swift said. "But we still need experimental validation of these calculations; something that can now be done at the National Ignition Facility (NIF)."

LLNL's National Ignition Facility is the world's largest laser designed to perform research on national security, fusion experimentation and basic science, such as astrophysics.

The team made specific predictions for notable exoplanets having earth-like, rocky, icy compositions, with planetary center pressures ranging from 8 to 19,000 Mbar (8 million to 1.9 billion atmospheres of pressure).

"We have a project to measure material properties up to billions of atmospheres on NIF. We will eventually exceed the highest pressures investigated in the very small number of previous experiments using underground nuclear tests, which reached far above pressures that can be explored with other techniques currently available," Swift said.

Placing constraints on the structure of exoplanets requires accurate information about the compressibility of relevant compositions of matter, including iron alloys, silicates, and ices, under extreme conditions of pressure and temperature.

"This sets the record straight and presents a survey of exoplanet structure information using material properties generated for, and validated using, experimental capabilities at the national labs," Swift said.

Other collaborators include the University of Rostock and the University of Edinburgh. The research recently appeared in The Astrophysical Journal (APJ, 744:59, 2012).

The research was funded by LLNL's Laboratory Research and Development program. LDRD is used to fund creative basic and applied research activities in areas aligned with the Lab's principal missions.

]]> Thu, 09 FEB 2012 08:59:10 AEST Princeton, N.J. (UPI) Jan 30, 2012 - A possible planet outside our solar system captured by the Hubble space telescope has failed to show up in subsequent searches, U.S. astronomers say.

An image taken by Hubble in 2008 of a pinpoint of light orbiting a star called Fomalhaut about 25 light-years from Earth was hailed as the first actual picture of an exoplanet.

Now scientists using the Spitzer Space Telescope say they suspect the dot of light in the Hubble image isn't a planet at all because it doesn't radiate at the infrared wavelengths expected of an exoplanet, ScienceNews.org reported.

The Spitzer data was reported by a team led by Markus Janson of Princeton University.

The object dubbed Fomalhaut b still puzzles astronomers, since it's proved invisible to ground-based infrared telescopes and is following an unexpected path around its star.

Explanations for the pinpoint of light range from a background star to light scattered by a dust cloud that surrounds the star Fomalhaut.

That dust cloud bears an elliptical shape that could be the handiwork of a giant planetary shepherd, a planet that just hasn't been detected yet, researchers said.

"The 'real' Fomalhaut b still hides in the system," they said in their published study.

]]> Thu, 09 FEB 2012 08:59:10 AEST Moffett Field CA (SPX) Jan 30, 2012 - NASA's Kepler mission has discovered 11 new planetary systems hosting 26 confirmed planets. These discoveries nearly double the number of verified Kepler planets and triple the number of stars known to have more than one planet that transits, or passes in front of, its host star. Such systems will help astronomers better understand how planets form.

The planets orbit close to their host stars and range in size from 1.5 times the radius of Earth to larger than Jupiter. Fifteen of them are between Earth and Neptune in size, and further observations will be required to determine which are rocky like Earth and which have thick gaseous atmospheres like Neptune.

The planets orbit their host star once every six to 143 days. All are closer to their host star than Venus is to our sun.

"Prior to the Kepler mission, we knew of perhaps 500 exoplanets across the whole sky," said Doug Hudgins, Kepler program scientist at NASA Headquarters in Washington.

"Now, in just two years staring at a patch of sky not much bigger than your fist, Kepler has discovered more than 60 planets and more than 2,300 planet candidates. This tells us that our galaxy is positively loaded with planets of all sizes and orbits."

Kepler identifies planet candidates by repeatedly measuring the change in brightness of more than 150,000 stars to detect when a planet passes in front of the star. That passage casts a small shadow toward Earth and the Kepler spacecraft.

"Confirming that the small decrease in the star's brightness is due to a planet requires additional observations and time-consuming analysis," said Eric Ford, associate professor of astronomy at the University of Florida and lead author of the paper confirming Kepler-23 and Kepler-24.

"We verified these planets using new techniques that dramatically accelerated their discovery."

Each of the new confirmed planetary systems contains two to five closely spaced transiting planets. In tightly packed planetary systems, the gravitational pull of the planets among themselves causes one planet to accelerate and another planet to decelerate along its orbit.

The acceleration causes the orbital period of each planet to change. Kepler detects this effect by measuring the changes, or so-called Transit Timing Variations (TTVs).

Planetary systems with TTVs can be verified without requiring extensive ground-based observations, accelerating confirmation of planet candidates. The TTV detection technique also increases Kepler's ability to confirm planetary systems around fainter and more distant stars.

"By precisely timing when each planet transits its star, Kepler detected the gravitational tug of the planets on each other, clinching the case for ten of the newly announced planetary systems," said Dan Fabrycky, Hubble Fellow at the University of California, Santa Cruz and lead author for a paper confirming Kepler-29, 30, 31 and 32."

Five of the systems (Kepler-25, Kepler-27, Kepler-30, Kepler-31 and Kepler-33) contain a pair of planets where the inner planet orbits the star twice during each orbit of the outer planet.

Four of the systems (Kepler-23, Kepler-24, Kepler-28 and Kepler-32) contain a pairing where the outer planet circles the star twice for every three times the inner planet orbits its star.

"These configurations help to amplify the gravitational interactions between the planets, similar to how my sons kick their legs on a swing at the right time to go higher," said Jason Steffen, the Brinson postdoctoral fellow at Fermilab Center for Particle Astrophysics in Batavia, Ill., and lead author of a paper confirming Kepler-25, 26, 27 and 28.

The system with the most planets among these discoveries is Kepler-33, a star that is older and more massive than our sun. Kepler-33 hosts five planets, ranging in size from 1.5 to 5 times that of Earth and all located closer to their star than any planet is to the sun.

The properties of a star provide clues for planet detection. The decrease in the star's brightness and duration of a planet transit combined with the properties of its host star present a recognizable signature.

When astronomers detect planet candidates that exhibit similar signatures around the same star the likelihood of any of these planet candidates being a false positive is very low.

"The approach that was used to verify the Kepler-33 planets shows that the overall reliability of Kepler's candidate multiple transiting systems is quite high," said Jack Lissauer, planetary scientist at NASA Ames Research Center at Moffett Field, Calif., and lead author of the paper confirming Kepler-33. "This is a validation by multiplicity."

These discoveries are published in the Astrophysical Journal and the Monthly Notices of the Royal Astronomical Society.

]]> Thu, 09 FEB 2012 08:59:10 AEST Washington (AFP) Jan 26, 2012 - The US space agency said Thursday its Kepler space telescope mission has confirmed 26 new planets outside our solar system, all of them orbiting too close to their host stars to sustain life.

Scattered across 11 planetary systems, their temperatures would be too hot for survival, as they all circle their stars closer than Venus, the second planet from the Sun, which has a surface temperature of 464 Celsius (867 F).

But NASA scientists were still pleased with the findings, which nearly double the number of confirmed planets that Kepler has found since 2009.

"Prior to the Kepler mission, we knew of perhaps 500 exoplanets across the whole sky," said Doug Hudgins, Kepler program scientist at NASA headquarters.

"Now, in just two years staring at a patch of sky not much bigger than your fist, Kepler has discovered more than 60 planets and more than 2,300 planet candidates," he added.

"This tells us that our galaxy is positively loaded with planets of all sizes and orbits."

The discoveries are described in four different papers in the Astrophysical Journal and the Monthly Notices of the Royal Astronomical Society, NASA said in a statement.

Kepler is NASA's first mission in search of Earth-like planets orbiting stars similar to our Sun.

It launched in March 2009, equipped with the largest camera ever sent into space -- a 95-megapixel array of charge-coupled devices -- and is expected to continue its science operations until at least November 2012.

In December last year, NASA announced Kepler had confirmed its first-ever planet in a habitable zone outside our solar system, Kepler 22b, though it remained unclear whether the surface was rocky or gaseous.

Such planets have the right distance from their star to support water, plus a suitable temperature and atmosphere to support life.

Spinning around its star some 600 light years away, Kepler 22b is 2.4 times the size of the Earth and orbits its Sun-like star every 290 days.

The 26 planets that Kepler confirmed on Thursday orbit their stars between every six and 143 days.

]]> Thu, 09 FEB 2012 08:59:10 AEST Moffett Field CA (SPX) Jan 24, 2012 - Two astronomers from Spain are trying to determine how brightly Earth would shine in the age of the dinosaurs. Their results not only reveal how Earth would look to a distant observer, but could also help astronomers determine the layout of landforms on faraway planets.

Rather than relying on climate models, the pair analyzed the relationship between cloud cover and landforms to calculate how clouds would gather over different regions.

"When you look at the planet...it has a given distribution of continents and clouds," said Enric Palle, of the Astrophysical Institute of the Canary Islands (IAC).

"But it has not always been the same."

With the relationship in hand, they looked back in time to measure how much the brightness of the planet would vary as the continents of Earth shifted 90, 230, 340, and 500 million years ago, when the planet had a different layout.

Studying the changes in the light reflected from the Sun (the albedo) could help astronomers figure out what might lay under the clouds of extrasolar planets.

When life tries to hide
Palle and lead author Esther Sanroma, also of the IAC, used 23 years worth of data on the global distribution of clouds over various landforms from the International Satellite Cloud Climatology Project. Detailed landform models from paleogeologist Ron Blakely provided them with a layout of the Earth over four different time periods.

They wanted to look farther back, but the atmosphere has only had a similar temperature and composition for the last half billion years.

They found that for much of Earth's history, the daily variations were minimal. Such small shifts would be a challenge to measure from a distance.

However, 500 million years ago, there were huge swings in the light as the planet rotated each day. The variations were four times as large as changes in other periods.

The authors attribute this to two causes.

First, the land masses were closer together, rather than spread out, leaving wider expanses of oceans. These result in a wildly different cloud distribution.

Second, the land half a billion years ago was all desert, completely bare of all life.

"Five hundred million years ago is the time in which life evolved from oceans to land," Palle said.

As plants began to cover the land, the cloud arrangement shifted. Deserts have few clouds, because there is very little water vapor in the air. Thus, the advent of life brought changes that would have made Earth more difficult to examine from space.

"We camouflaged ourselves, and made it more difficult for a distant observer to characterize the Earth," Palle said.

The process could work in reverse - a light curve with small changes could potentially indicate vegetation on another planet.

Of course, astronomers studying an exoplanet would need more information before they could definitively reach such a conclusion.

The link between land and clouds

Watching your local weather, it might seem as though the movement and behavior of clouds are random, but in fact they are not. Wider trends emerge when you look at the planet on a global scale.

"There are some spots on Earth that are always cloudy, like over the Amazon rainforest, and there's other spots like the Sahara desert which are always clear," said planetary scientist Sara Seager, of the Massachusetts Institute of Technology. Seager, who was not involved in this research, models the atmospheres of exoplanets.

Rather than relying on climate modeling to predict how clouds would behave, Palle and Sanroma decided to take advantage of these trends.

Their model assumes that such patterns would continue in the past, with clouds behaving the same way over oceans and deserts as they do today.

"Big cloud patterns, on a global scale, are tied to the continental distribution and ocean circulation," Palle said.

By applying this pattern to other time frames, they were able to calculate how widely the brightness of Earth would change over the course of its daily rotation.

"This is a different way of looking at the problem," Seager said.

According to Palle, a new approach was necessary to look so far back in time. He points out that we have about 30 global models predicting the cloud formation in a hundred years in the future. Though they agree that the temperature will change in response to an increase in carbon dioxide, they provide a range of responses to how the clouds will react - and no one knows which one might be correct.

By focusing on the patterns of clouds over land and ocean, Sanroma and Palle hope to overcome the uncertainties that crop up in climate modeling.

The search for planets
So how long before we can identify the continents of distant planets?

"It might be feasible with the next generation of space telescopes," Palle said.

At the present, nothing is planned that would be able to detect such variations, but perhaps in the near future. "The TPF (Terrestrial Planet Finder) would have been able to take this kind of observations for a close planet," he said.

NASA's Terrestrial Planet Finder, or TPF, had a proposed goal of studying all aspects of exoplanets, but, after being proposed several times, it was canceled in 2011.

"We hope that our TPF concept will be resurrected and will launch sometime in the future," Seager said.

As astronomers study extrasolar planets, they can determine much of its composition from the changes in brightness. Rocky planets with no atmosphere, icy planets, and planets with permanent cloud cover would all have almost no variations.

But, according to Palle, "if it has an atmosphere with broken clouds, we will see it in variability."

The scattered cloud cover would imply oceans on the surface, which could be potential habitats for the development of life. The type of liquid would depend on how close the planet lay to its sun.

"If it has water clouds, it has water oceans," Seager said.

Palle agrees. "Any water raining down will eventually create an ocean. Maybe smaller than we have on Earth, but still, an ocean."

]]> Thu, 09 FEB 2012 08:59:10 AEST Subscribe to our daily selection of space, military, environment and energy newsletters responseText http://visitor.constantcontact.com/manage/optin/ea?v=0016gbbKsaiGSpQFojVO8ZoHw%3D%3D