Could Betelgeuse Fry Earth?

Source and Credit: Astrobiology Magazine

When stars go pop, a murderous torrent of energy is released. Life on Earth may have been partly extinguished by just such a violent outburst, but there's little hard evidence yet to justify such a claim. A new study plans to fill in the forensic details.

"We are trying to get a better estimate of how dangerous a particular event will be," says Brian Thomas of Washburn University in Topeka, Kansas.

Thomas and his colleagues will be studying the wide-range of astrophysical phenomena that could fling high energy radiation across interstellar space to Earth's doorstep [as occured in a colossal blast detected in 2004]. The team also will radiate different types of phytoplankton to understand how life would be affected by a stellar blast, since life around the globe is highly dependent on these microscopic plants.

The danger from stellar explosions has been considered before, but this will be the first comprehensive study. "We are building on previous work by broadening it to a wide range of astrophysical events and by making the biological modeling more precise," Thomas says. The project is part of NASA's Exobiology and Evolutionary Biology Program.

The usual suspects

Stars are generally too far away to be a concern for life on our planet. But certain stellar eruptions have the potential to reach across tens or even thousands of light-years.

The most familiar of these is a supernova, which is the curtain call of a massive star with eight or more times the mass of our sun. When the nuclear fuel runs out for such a behemoth, the collapsing core generates an explosion that outshines an entire galaxy-worth of stars while it lasts.

A couple supernovae go off in our galaxy every century. But for one of these to haveserious consequences for Earth, we would need to be roughly within a 10 light-year radius of the blast.

Certain star explosions, called hypernovae, have much greater reach. Ten times more powerful than typical supernovae, hypernovae are the source for long-duration gamma ray bursts (GRBs), which are high-energy beams emitted along the dying star's axis. A GRB could travel 6,500 light-years and still inflict terrific damage on Earth, Thomas says.

The number of GRBs is much less than the number of supernovae, but the exact rate in our galaxy is still a matter of debate. A few years ago, a group of astronomers calculated that the likelihood of a GRB going off near us was very low, due to the fact that GRBs tend to arise in young galaxies with less heavy elements than the Milky Way.

But Thomas says that subsequent analyses have called this calculation into question, partly because our galaxy has merged in the past with smaller, younger galaxies that could have brought GRB-ticking-time-bombs in with them. "Our likelihood for hosting a GRB could vary with time," Thomas says.

He speculates that on average a GRB lights up our galaxy about once every 10 million years.

Other possible culprits

Long-duration GRBs and supernovae may be the best-understood, but they are not the only super-stellar calamities.

Short-duration GRBs do not arise from massive star deaths, but instead are believed to mainly be the merger of two neutron stars. Although less energy is released than in a long-duration GRB, the fraction of high-energy gamma rays is higher. Moreover, short-duration GRBs are more likely to occur in mature galaxies like ours, where neutron stars are more common.

Soft gamma-ray repeaters also originate from neutron stars – supposedly when the super-dense surface cracks. If one of these happened 10 light-years away, the effects could be dramatic. Indeed, on Dec. 27, 2004, the radiation from a soft gamma-ray repeater disrupted radio wave transmissions on Earth. Nothing was damaged, but the source object was an amazing 50,000 light-years away.

Thomas and his colleagues will be pulling together recent data from the Swift satellite and the Fermi Gamma-Ray Space Telescope to better estimate the rates and radiation output of soft gamma-ray repeaters, GRBs and supernovae.

Although there's no evidence that one of these went off recently in our neighborhood, it's important to note that our sun migrates around the galaxy and therefore could have brushed next to a star having a high-energy fit.

Worldwide ozone hole

The other half of the study will look at the possible biological aftermath of an astrophysical firework going off nearby.

Gamma rays and X-rays cannot penetrate very far into the Earth's atmosphere, but they still can have a long-lasting impact. The high-energy radiation breaks apart nitrogen and oxygen molecules in the Earth's stratosphere, allowing them to reform as nitric oxide (NO). This molecule destroys ozone in the same way that chlorofluorocarbons (CFCs) do.

"The effect is like the current ozone hole, but spread over the globe," Thomas says.

Ozone protects life on Earth from the sun's ultraviolet rays. By shattering this atmospheric shield, an astrophysical blast could lead to higher rates of DNA and protein damage in organisms from greater sunlight exposure.

Thomas' group has previously determined that a relatively close GRB could destroy 75 percent of the ozone in certain regions, with a globally averaged depletion of around 35 to 40 percent. In contrast, the ozone hole that currently hovers over Antarctica is at most 60 percent depleted but only accounts for a globally-averaged depletion of 3 to 5 percent.

Thomas says that the ozone destruction would begin as soon as the radiation hits, and would continue for several years. It may take more than a decade for the Earth's ozone shield to return to full strength.

Fried plankton

The loss of ozone would have serious effects on life across the planet. One of the most susceptible organisms would be phytoplankton. These single-celled organisms live at the top of the water column, where UV light is able to reach. They also reproduce quickly, so DNA damage would accumulate over several generations.

If phytoplankton began dying off, the effects would ripple throughout the ocean, since these photosynthetic microbes are the base of the marine food chain. They also produce at least half of the world's oxygen.

The team has selected a couple representative species of phytoplankton to irradiate at different levels, and see how their productivity levels change. The results of the study should give astrobiologists a better sense of how likely it is that our planet or another planet in our galaxy was zapped by a stellar eruption.

Possible signs of such astrophysical foul play are seen in the Ordovician extinction, which occurred 450 million years ago and resulted in the loss of 60 percent of marine invertebrates. The fossil record shows that organisms near the top of the water column and at mid-latitudes were hardest hit, as one would expect from a sudden loss of ozone.

Ancient Martian Lake

Image Credit: G. Di Achille, University of Colorado

Source and Credit: University of Colorado at Boulder

A University of Colorado at Boulder research team has discovered the first definitive evidence of shorelines on Mars, an indication of a deep, ancient lake there and a finding with implications for the discovery of past life on the Red Planet.

Estimated to be more than 3 billion years old, the lake appears to have covered as much as 80 square miles and was up to 1,500 feet deep -- roughly the equivalent of Lake Champlain bordering the United States and Canada, said CU-Boulder Research Associate Gaetano Di Achille, who led the study. The shoreline evidence, found along a broad delta, included a series of alternating ridges and troughs thought to be surviving remnants of beach deposits.

"This is the first unambiguous evidence of shorelines on the surface of Mars," said Di Achille. "The identification of the shorelines and accompanying geological evidence allows us to calculate the size and volume of the lake, which appears to have formed about 3.4 billion years ago."

A paper on the subject by Di Achille, CU-Boulder Assistant Professor Brian Hynek and CU-Boulder Research Associate Mindi Searls, all of the Laboratory for Atmospheric and Space Physics, is in press in Geophysical Research Letters, a publication of the American Geophysical Union.

Images used for the study were taken by a high-powered camera known as the High Resolution Imaging Science Experiment, or HiRISE. Riding on NASA's Mars Reconnaissance Orbiter, HiRISE can resolve features on the surface down to one meter in size from its orbit 200 miles above Mars.

An analysis of the HiRISE images indicate that water carved a 30-mile-long canyon that opened up into a valley, depositing sediment that formed a large delta. This delta and others surrounding the basin imply the existence of a large, long-lived lake, said Hynek, also an assistant professor in CU-Boulder's geological sciences department. The lake bed is located within a much larger valley known as the Shalbatana Vallis.

"Finding shorelines is a Holy Grail of sorts to us," said Hynek.

In addition, the evidence shows the lake existed during a time when Mars is generally believed to have been cold and dry, which is at odds with current theories proposed by many planetary scientists, he said. "Not only does this research prove there was a long-lived lake system on Mars, but we can see that the lake formed after the warm, wet period is thought to have dissipated."

Planetary scientists think the oldest surfaces on Mars formed during the wet and warm Noachan epoch from about 4.1 billion to 3.7 billion years ago that featured a bombardment of large meteors and extensive flooding. The newly discovered lake is believed to have formed during the Hesperian epoch and postdates the end of the warm and wet period on Mars by 300 million years, according to the study.

The deltas adjacent to the lake are of high interest to planetary scientists because deltas on Earth rapidly bury organic carbon and other biomarkers of life, according to Hynek. Most astrobiologists believe any present indications of life on Mars will be discovered in the form of subterranean microorganisms.

But in the past, lakes on Mars would have provided cozy surface habitats rich in nutrients for such microbes, Hynek said.

The retreat of the lake apparently was rapid enough to prevent the formation of additional, lower shorelines, said Di Achille. The lake probably either evaporated or froze over with the ice slowly turning to water vapor and disappearing during a period of abrupt climate change, according to the study.

Di Achille said the newly discovered pristine lake bed and delta deposits would be a prime target for a future landing mission to Mars in search of evidence of past life.

"On Earth, deltas and lakes are excellent collectors and preservers of signs of past life," said Di Achille. "If life ever arose on Mars, deltas may be the key to unlocking Mars' biological past."

Seeing Water On Exoplanets

Earth as seen from Deep Impact spacecraft (NASA). Yes, that's the Moon also.

Source and Credit: University of Washington

Since the early 1990s astronomers have discovered more than 300 planets orbiting stars other than our sun, nearly all of them gas giants like Jupiter. Powerful space telescopes, such as the one that is central to NASA's recently launched Kepler Mission, will make it easier to spot much smaller rocky extrasolar planets, or exoplanets, more similar to Earth.

But seen from dozens of light years away, an Earth-like exoplanet will appear in telescopes as little more than a "pale blue dot," the term coined by the late astronomer Carl Sagan to describe how Earth appeared in a 1990 photograph taken by the Voyager spacecraft from near the edge of the solar system.

Using instruments aboard the Deep Impact spacecraft, a team of astronomers and astrobiologists has devised a technique to tell whether such a planet harbors liquid water, which in turn could tell whether it might be able to support life.

"Liquid water on the surface of a planet is the gold standard that people are looking for," said Nicolas Cowan, a University of Washington doctoral student in astronomy and lead author of a paper explaining the new technique that has been accepted for publication in Astrophysical Journal.

As part of NASA's Extrasolar Planet Observation and Characterization mission, the scientists obtained two separate 24-hour observations of light intensity from Earth in seven bands of visible light, from shorter wavelengths near ultraviolet to longer wavelengths near infrared. Earth appears gray at most wavelengths because of cloud cover, but it appears blue at short wavelengths because of the same atmospheric phenomenon that makes the sky look blue to people on the surface.

The researchers studied small deviations from the average color caused by surface features like clouds and oceans rotating in and out of view. They found two dominant colors, one reflective at long, or red, wavelengths and the other at short, or blue, wavelengths. They interpreted the red as land masses and the blue as oceans.

The analysis was undertaken "as if we were aliens looking at Earth with the tools we might have in 10 years" and did not already know Earth's composition, Cowan said. "You sum up the brightness into a single pixel in the telescope's camera, so it truly is a pale blue dot."

Since Earth's colors changed throughout the 24-hour-long observations, the scientists made maps of the planet in the dominant red and blue colors and then compared their interpretations with the actual location of the planet's continents and oceans.

"You could tell that there were liquid oceans on the planet," Cowan said. "The idea is that to have liquid water the planet would have to be in its system's habitable zone, but being in the habitable zone doesn't guarantee having liquid water."

The observations on March 18 and June 4, 2008 were made when the spacecraft was between 17 million and 33 million miles from Earth, and while it was directly above the equator. Observations from above a polar region likely would show up as white, Cowan said.

It will be some years before the launch of space telescopes capable of making similar observations for Earth-sized exoplanets, but devising this technique now could guide the construction of those instruments, he said. And while those planets will be much farther away, the technique still will be applicable.

"You will still have all the spectral information, and more importantly to us you'll still have the information so that you can see how the brightness of that speck is changing over time, Cowan said."

Co-authors are Eric Agol, Victoria Meadows and Tyler Robinson of the UW, Timothy Livengood and Drake Deming of the NASA Goddard Space Flight Center, Carey Lisse of Johns Hopkins University, Michael A'Hearn and Dennis Wellnitz of the University of Maryland, Sara Seager of the Massachusetts Institute of Technology and David Charbonneau of the Harvard-Smithsonian Center for Astrophysics. The work was funded by the Natural Sciences and Engineering Research Council of Canada, the National Science Foundation and the NASA Discovery Program.

Cowan notes that some non-habitable planets, such as Neptune, also can appear to be blue, but the color is constant and, in the case of Neptune, likely caused by methane in the atmosphere.

"It looks blue from every angle, the same blue all the way around. If you had an ocean planet it might look like that, but you can do other tests to determine that," he said. "For Earth, the blue varies from one place to another, which indicates that it's not something in the atmosphere."

Habitable Zones Smaller Than Thought?

Image Credit: ESO

Source and Credit: University of Washington

A number of planets have been discovered orbiting red dwarf stars, which make up about three-quarters of the stars close to our solar system. Potentially habitable planets must orbit close to those stars -- perhaps one-fiftieth the distance of Earth to the sun -- since those stars are smaller and generate less heat than our sun.

But new calculations indicate that, with planets so close, tidal forces exerted on planets by the parent star's gravity could limit what is regarded as a star's habitable zone and change the criteria for planets where life could potentially take root.

Scientists believe liquid water is essential for life. But a planet also must have plate tectonics to pull excess carbon from its atmosphere and confine it in rocks to prevent runaway greenhouse warming. Tectonics, or the movement of the plates that make up a planet's surface, typically is driven by radioactive decay in the planet's core, but a star's gravity can cause tides in the planet, which creates more energy to drive plate tectonics.

"If you have plate tectonics, then you can have long-term climate stability, which we think is a prerequisite for life," said Rory Barnes, a University of Washington postdoctoral researcher in astronomy.

However, tectonic forces cannot be so severe that geologic events quickly repave a planet's surface and destroy life that might have gotten a foothold, he said. The planet must be at a distance where tugging from the star's gravitational field generates tectonics without setting off extreme volcanic activity that resurfaces the planet in too short a time for life to prosper.

Barnes is lead author of a paper to be published by The Astrophysical Journal Letters that uses new calculations from computer modeling to define a "tidal habitable zone." Co-authors are Brian Jackson and Richard Greenberg from the University of Arizonaand Sean Raymond from the University of Colorado. The research was funded by NASA.

"Overall, the effect of this work is to reduce the number of habitable environments in the universe, or at least what we have thought of as habitable environments," Barnes said. "The best places to look for habitability are where this new definition and the old definition overlap."

The new calculations have implications for planets previously considered too small for habitability. An example is Mars, which used to experience tectonics but that activity ceased as heat from the planet's decaying inner core dissipated.

But as planets get closer to their suns, the gravitational pull gets stronger, tidal forces increase and more energy is released. If Mars were to move closer to the sun, the sun's tidal tugs could possibly restart the tectonics, releasing gases from the core to provide more atmosphere. If Mars harbors liquid water, at that point it could be habitable for life as we know it.

Various moons of Jupiter have long been considered as potentially harboring life. But one of them, Io, has so much volcanic activity, the result of tidal forces from Jupiter, that it is not regarded as a good candidate. Tectonic activity remakes Io's surface in less than 1 million years.

"If that were to happen on Earth, it would be hard to imagine how life would develop," Barnes said.

A potential Earth-like planet, but eight times more massive, called Gliese 581d was discovered in 2007 about 20 light years away in the constellation Libra. At first it was thought the planet was too far from its sun, Gliese 581, to have liquid water, but recent observations have determined the orbit is within the habitable zone for liquid water. However, the planet is outside the habitable zone for its sun's tidal forces, which the authors believe drastically limits the possibility of life.

"Our model predicts that tides may contribute only one-quarter of the heating required to make the planet habitable, so a lot of heat from decay of radioactive isotopes may be required to make up the difference," Jackson said.

Barnes added, "The bottom line is that tidal forcing is an important factor that we are going to have to consider when looking for habitable planets."

Planetary Disaster In Offing?

From the Bad Astronomical News of the Week department:

More here from New Scientist.

Is This What An Alien Looks Like?

Source and Credit: Society for General Microbiology

A novel bacterium that has been trapped more than three kilometres under glacial ice in Greenland for over 120 000 years, may hold clues as to what life forms might exist on other planets.

Dr Jennifer Loveland-Curtze and a team of scientists from Pennsylvania State University report finding the novel microbe, which they have called Herminiimonas glaciei, in the current issue of the International Journal of Systematic and Evolutionary Microbiology. The team showed great patience in coaxing the dormant microbe back to life; first incubating their samples at 2˚C for seven months and then at 5˚C for a further four and a half months, after which colonies of very small purple-brown bacteria were seen.

H. glaciei is small even by bacterial standards – it is 10 to 50 times smaller than E. coli. Its small size probably helped it to survive in the liquid veins among ice crystals and the thin liquid film on their surfaces. Small cell size is considered to be advantageous for more efficient nutrient uptake, protection against predators and occupation of micro-niches and it has been shown that ultramicrobacteria are dominant in many soil and marine environments.

Most life on our planet has always consisted of microorganisms, so it is reasonable to consider that this might be true on other planets as well. Studying microorganisms living under extreme conditions on Earth may provide insight into what sorts of life forms could survive elsewhere in the solar system.

"These extremely cold environments are the best analogues of possible extraterrestrial habitats", said Dr Loveland-Curtze, "The exceptionally low temperatures can preserve cells and nucleic acids for even millions of years. H. glaciei is one of just a handful of officially described ultra-small species and the only one so far from the Greenland ice sheet; studying these bacteria can provide insights into how cells can survive and even grow under extremely harsh conditions, such as temperatures down to -56˚C, little oxygen, low nutrients, high pressure and limited space."

"H. glaciei isn't a pathogen and is not harmful to humans", Dr Loveland-Curtze added, "but it can pass through a 0.2 micron filter, which is the filter pore size commonly used in sterilization of fluids in laboratories and hospitals. If there are other ultra-small bacteria that are pathogens, then they could be present in solutions presumed to be sterile. In a clear solution very tiny cells might grow but not create the density sufficient to make the solution cloudy".

Robots That Read Human Intent

Source and Credit: ICT Results

European researchers in robotics, psychology and cognitive sciences have developed a robot that can predict the intentions of its human partner. This ability to anticipate (or question) actions could make human-robot interactions more natural.

The walking, talking, thinking robots of science fiction are far removed from the automated machines of today. Even today's most intelligent robots are little more than slaves – programmed to do our bidding.

Many research groups are trying to build robots that could be less like workers and more like companions. But to play this role, they must be able to interact with people in natural ways, and play a pro-active part in joint tasks and decision-making. We need robots that can ask questions, discuss and explore possibilities, assess their companion's ideas and anticipate what their partners might do next.

The EU-funded JAST project brings a multidisciplinary team together to do just this. The project explores ways by which a robot can anticipate/predict the actions and intentions of a human partner as they work collaboratively on a task.

Who knows best?

You cannot make human-robot interaction more natural unless you understand what 'natural' actually means. But few studies have investigated the cognitive mechanisms that are the basis of joint activity (i.e. where two people are working together to achieve a common goal).

A major element of the JAST project, therefore, was to conduct studies of human-human collaboration. These experiments and observations could feed into the development of more natural robotic behaviour.

The researchers participating in JAST are at the forefront of their discipline and have made some significant discoveries about the cognitive processes involved in joint action and decision-making. Most importantly, they scrutinised the ways in which observation plays an important part in joint activity.

Scientists have already shown that a set of 'mirror neurons' are activated when people observe an activity. These neurons resonate as if they were mimicking the activity; the brain learns about an activity by effectively copying what is going on. In the JAST project, a similar resonance was discovered during joint tasks: people observe their partners and the brain copies their action to try and make sense of it.

In other words, the brain processes the observed actions (and errors, it turns out) as if it is doing them itself. The brain mirrors what the other person is doing either for motor-simulation purposes or to select the most adequate complementary action.

Resonant robotics

The JAST robotics partners have built a system that incorporates this capacity for observation and mirroring (resonance).

“In our experiments the robot is not observing to learn a task,” explains Wolfram Erlhagen from the University of Minho and one of the project consortium's research partners. “The JAST robots already know the task, but they observe behaviour, map it against the task, and quickly learn to anticipate [partner actions] or spot errors when the partner does not follow the correct or expected procedure.”

The robot was tested in a variety of settings. In one scenario, the robot was the 'teacher' – guiding and collaborating with human partners to build a complicated model toy. In another test, the robot and the human were on equal terms. “Our tests were to see whether the human and robot could coordinate their work,” Erlhagen continues. “Would the robot know what to do next without being told?”

By observing how its human partner grasped a tool or model part, for example, the robot was able to predict how its partner intended to use it. Clues like these helped the robot to anticipate what its partner might need next. “Anticipation permits fluid interaction,” says Erlhagen. “The robot does not have to see the outcome of the action before it is able to select the next item.”

The robots were also programmed to deal with suspected errors and seek clarification when their partners’ intentions were ambiguous. For example, if one piece could be used to build three different structures, the robot had to ask which object its partner had in mind.

From JAST to Jeeves

But how is the JAST system different to other experimental robots?

“Our robot has a neural architecture that mimics the resonance processing that our human studies showed take place during joint actions,” says Erlhagen. “The link between the human psychology, experimentation and the robotics is very close. Joint action has not been addressed by other robotics projects, which may have developed ways to predict motor movements, but not decisions or intentions. JAST deals with prediction at a much hig

Before robots like this one can be let loose around humans, however, they will have to learn some manners. Humans know how to behave according to the context they are in. This is subtle and would be difficult for a robot to understand.

Nevertheless, by refining this ability to anticipate, it should be possible to produce robots that are proactive in what they do.

Not waiting to be asked, perhaps one day a robot may use the JAST approach to take initiative and ask: “Would you care for a cup of tea?”

Search For E.T. Just Got Easier

Image Credit: Gabriel Perez Diaz, SMM, Instituto de Astrofisica de Canarias (IAC)

Source and Credit: Science & Technology Facilities Council

Astronomers using the Science and Technology Facilities Council’s (STFC) William Herschel Telescope (WHT) on La Palma have confirmed an effective way to search the atmospheres of planets for signs of life, vastly improving our chances of finding alien life outside our solar system.

The team from the Instituto de Astrofisica de Canarias (IAC) used the WHT and the Nordic Optical Telescope (NOT) to take the first transmission spectrum of the Earth - information about the chemical composition of the Earth’s atmosphere from sunlight that has passed through it. The research is published today (11th June) in Nature.

When a planet passes in front of its parent star, part of the starlight passes through the planet’s atmosphere and contains information about the constituents of the atmosphere, providing vital information about the planet itself. This is called a transmission spectrum and even though astronomers can’t use exactly the same method to look at the Earth’s atmosphere, they were able to gain a spectrum of our planet by observing light reflected from the Moon towards the Earth during a lunar eclipse. This is the first time the transmission spectrum of the Earth has been measured.

The spectrum not only contained signs of life but these signs were unmistakably strong. It also contained unexpected molecular bands and the signature of the earth ionosphere.

Enric Palle, lead author of the paper, from the Instituto de Astrofisica de Canarias, said, “Now we know what the transmission spectrum of a inhabited planet looks like, we have a much better idea of how to find and recognize Earth like planets outside our solar system where life may be thriving. The information in this spectrum shows us that this is a very effective way to gather information about the biological processes that may be taking place on a planet.”

Pilar Montañes-Rodriguez, from the Instituto de Astrofisica de Canarias, added, “Many discoveries of Earth-size planets are expected in the next decades and some will orbit in the habitable zone of their parent stars. Obtaining their atmospheric properties will be highly challenging; the greatest reward will happen when one of those planets shows a spectrum like that of our Earth.”

The past two decades have witnessed the discovery of hundreds of exoplanets (planets beyond our solar system). Ambitious missions, ground and space based, are already being planned for the next decades, and the discovery of Earth-like planets is only a matter of time. Once these planets are found, techniques like transmission spectra will be invaluable to their further exploration.

Professor Keith Mason, Chief Executive of the Science and Technology Facilities Council (STFC), said, “This new transmission spectrum is good news for future upcoming ground and space based missions dedicated to the search for life in the universe. The UK is committed to cutting edge science and UK owned facilities like the WHT are helping to make many groundbreaking discoveries and expand our knowledge of the Universe. Not only do these results improve our knowledge of our own planet but we now have an effective way to search for life on the increasing number of exoplanets being found by astronomers.”

Earth's Billion-Year Reprieve

Source and Credit: Caltech

Roughly a billion years from now, the ever-increasing radiation from the sun will have heated Earth into inhabitability; the carbon dioxide in the atmosphere that serves as food for plant life will disappear, pulled out by the weathering of rocks; the oceans will evaporate; and all living things will disappear.

Or maybe not quite so soon, say researchers from the California Institute of Technology (Caltech), who have come up with a mechanism that doubles the future lifespan of the biosphere—while also increasing the chance that advanced life will be found elsewhere in the universe.

Earth maintains its surface temperatures through the greenhouse effect. Although the planet's greenhouse gases—chiefly water vapor, carbon dioxide, and methane-have become the villain in global warming scenarios, they're crucial for a habitable world, because they act as an insulating blanket in the atmosphere that absorbs and radiates thermal radiation, keeping the surface comfortably warm.

As the sun has matured over the past 4.5 billion years, it has become both brighter and hotter, increasing the amount of solar radiation received by Earth, along with surface temperatures. Earth has coped by reducing the amount of carbon dioxide in the atmosphere, thus reducing the warming effect. (Despite current concerns about rising carbon dioxide levels triggering detrimental climate change, the pressure of carbon dioxide in the atmosphere has dropped some 2,000-fold over the past 3.5 billion years; modern, man-made increases in atmospheric carbon dioxide offset a fraction of this overall decrease.)

The problem, says Joseph L. Kirschvink, the Nico and Marilyn Van Wingen Professor of Geobiology at Caltech and a coauthor of the PNAS paper, is that "we're nearing the point where there's not enough carbon dioxide left to regulate temperatures following the same procedures."

Kirschvink and his collaborators Yuk L. Yung, a Caltech professor of planetary science, and graduate students King-Fai Li and Kaveh Pahlevan, say that the solution is to reduce substantially the total pressure of the atmosphere itself, by removing massive amounts of molecular nitrogen, the largely nonreactive gas that makes up about 78 percent of the atmosphere. This would regulate the surface temperatures and allow carbon dioxide to remain in the atmosphere, to support life, and could tack an additional 1.3 billion years onto Earth's expected lifespan.

In the "blanket" analogy for greenhouse gases, carbon dioxide would be represented by the cotton fibers making up the blanket. "The cotton weave may have holes, which allow heat to leak out," explains Li, the lead author of the paper.

"The size of the holes is controlled by pressure," Yung says. "Squeeze the blanket," by increasing the atmospheric pressure, "and the holes become smaller, so less heat can escape. With less pressure, the holes become larger, and more heat can escape," he says, helping the planet to shed the extra heat generated by a more luminous sun.

Strikingly, no external influence would be necessary to take nitrogen out of the air, the scientists say. Instead, the biosphere itself would accomplish this, because nitrogen is incorporated into the cells of organisms as they grow, and is buried with them when they die.

In fact, "this reduction of nitrogen is something that may already be happening," says Pahlevan, and that has occurred over the course of Earth's history. This suggests that Earth's atmospheric pressure may be lower now than it was earlier in the planet's history.

Proof of this hypothesis may come from other research groups that are examining the gas bubbles formed in ancient lavas to determine past atmospheric pressure: the maximum size of a forming bubble is constrained by the amount of atmospheric pressure, with higher pressures producing smaller bubbles, and vice versa.

If true, the mechanism also would potentially occur on any extrasolar planet with an atmosphere and a biosphere.

"Hopefully, in the future we will not only detect earth-like planets around other stars but learn something about their atmospheres and the ambient pressures," Pahlevan says. "And if it turns out that older planets tend to have thinner atmospheres, it would be an indication that this process has some universality.

Adds Yung: "We can't wait for the experiment to occur on Earth. It would take too long. But if we study exoplanets, maybe we will see it. Maybe the experiment has already been done."

Increasing the lifespan of our biosphere—from roughly 1 billion to 2.3 billion years—has intriguing implications for the search for life elsewhere in the universe. The length of the existence of advanced life is a variable in the Drake equation, astronomer Frank Drake's famous formula for estimating the number of intelligent extraterrestrial civilizations in the galaxy. Doubling the duration of Earth's biosphere effectively doubles the odds that intelligent life will be found elsewhere in the galaxy.

"It didn't take very long to produce life on the planet, but it takes a very long time to develop advanced life," says Yung. On Earth, this process took four billion years. "Adding an additional billion years gives us more time to develop, and more time to encounter advanced civilizations, whose own existence might be prolonged by this mechanism. It gives us a chance to meet."

The work described in the paper, "Atmospheric Pressure as a Natural Regulator of the Climate of a Terrestrial Planet with Biosphere," was funded by NASA and the Virtual Planetary Laboratory at Caltech.

Planets Common Around Binary Stars?

Image Credit: David A. Aguilar (CfA)

Source and Credit: Astrobiology Magazine (NASA/JPL)

Astronomers have announced that a sequence of images collected with the Smithsonian’sSubmillimeter Array (SMA) radio telescope system clearly reveals the presence of a rotating, molecular disk orbiting the young binary star system V4046 Sagittarii.

The SMA images of V4046 Sagittarii, which were presented by UCLA graduate student David Rodriguez in a press conference at the American Astronomical Society meeting in Pasadena, Calif., provide an unusually vivid snapshot of the process offormation of giant planets, comets, and Pluto-like bodies. The results also confirm that such objects may just as easily form around double stars as around single stars like our sun.

“It’s a case of seeing is believing,” says Joel Kastner of Rochester (NY) Institute of Technology, the lead scientist on the study. “We had the first evidence for this rotating disk in radio telescope observations of V4046 Sagittarii that we made last summer. But at that point, all we had were molecular spectra, and there are different ways to interpret the spectra. Once we saw the image data from the SMA, there was no doubt that we have a rotating disk here.”

According to Rodriguez, the images clearly demonstrate that the molecular disk orbiting the V4046 Sagittarii binary system extends from within the approximate radius of Neptune’s orbit out to about 10 times that orbit. This region corresponds to the zone where the solar system’s giant planets, as well as its Pluto-like Kuiper Belt objects, may have formed.

We believe that V4046 Sagittarii provides one of the clearest examples yet discovered of a Keplerian, planet-forming disk orbiting a young star system,” Wilner says. “This particular system is made that much more remarkable by the fact that it consists of a pair of roughly solar-mass stars that are approximately 12 million years old and are separated by a mere 5 solar diameters.”

“This could be the oldest known orbiting protoplanetary molecular disk and it shows that, at least for some stars, formation of Jovian-mass planets may continue well after the few million years, which astronomers have deduced is characteristic of the formation time for most such planets,” Zuckerman says.

Findings of the SMA imaging study build on previous work published in the December 2008 issue of Astronomy and Astrophysics in which Kastner and his team first suggested that the case of V4046 Sagittarii well illustrates how planets may easily form around certain types of binary stars.

“We thought the molecular gas around these two stars almost literally represented ‘smoking gun’ evidence of recent or possibly ongoing ‘giant,’ Jupiter-like planet formation around the binary star system, Kastner says. “The SMA images showing an orbiting disk certainly support that idea.”

The evidence for a molecular disk orbiting these twin young suns in the constellation Sagittarius suggested to the scientists that many such binary systems should also host as-yet undetected planets.

“The most successful technique used so far for discovery of extrasolar planets -- that of measurement of precision radial velocities – is exceedingly difficult for close binary stars such as V4046 Sagittarii. So these radio observations are probing a new region of discovery space for extrasolar planets,” says Rodriguez.

“At a distance of only 240 light-years from the solar system, the V4046 Sagittarii binary is at least two times closer to Earth than almost all known planet-forming star systems, which gives us a good shot at imaging any planets that have already formed and are now orbiting the stars,” he continued.

Kastner and collaborators had previously used the 30-meter radio telescope operated by the Institut de Radio Astronomie Millimetrique (IRAM) to study radio molecular spectra emitted from the vicinity of the twin stars. The scientists used these data to identify the raw materials for planet formation around V4046 Sagittarii -- circumstellar carbon monoxide and hydrogen cyanide -- in the noxious circumstellar molecular gas cloud.

“In this case the stars are so close together, and the profile of the gas -- in terms of the types ofmolecules that are there -- is so much like the types of gaseous disks that we see around single stars, that we now have a direct link between planets forming around single stars and planets forming around double stars,” Kastner says.

Domestic Robots

More here from New Scientist.

Did Meteors Make Life Possible?

Image Credit: NASA/JPL

Source and Credit: Imperial College of London

Large bombardments of meteorites approximately four billion years ago could have helped to make the early Earth and Mars more habitable for life by modifying their atmospheres, suggests the results of a paper published today in the journal Geochimica et Cosmochima Acta.

When a meteorite enters a planet’s atmosphere, extreme heat causes some of the minerals and organic matter on its outer crust to be released as water and carbon dioxide before it breaks up and hits the ground.

Researchers suggest the delivery of this water could have made Earth’s and Mars’ atmospheres wetter. The release of the greenhouse gas carbon dioxide could have trapped more energy from sunlight to make Earth and Mars warm enough to sustain liquid oceans.

In the new study, researchers from Imperial College London analysed the remaining mineral and organic content of fifteen fragments of ancient meteorites that had crashed around the world to see how much water vapour and carbon dioxide they would release when subjected to very high temperatures like those that they would experience upon entering the Earth’s atmosphere.

The researchers used a new technique called pyrolysis-FTIR, which uses electricity to rapidly heat the fragments at a rate of 20,000 degrees Celsius per second, and they then measured the gases released.

They found that on average, each meteorite was capable of releasing up to 12 percent of its mass as water vapour and 6 percent of its mass as carbon dioxide when entering an atmosphere. They concluded that contributions from individual meteorites were small and were unlikely to have a significant impact on the atmospheres of planets on their own.

The researchers then analysed data from an ancient meteorite shower called the Late Heavy Bombardment (LHB), which occurred 4 billion years ago, where millions of rocks crashed to Earth and Mars over a period of 20 million years.

Using published models of meteoritic impact rates during the LHB, the researchers calculated that 10 billion tonnes of carbon dioxide and 10 billion tonnes of water vapour could have been delivered to the atmospheres of Earth and Mars each year.

This suggests that the LHB could have delivered enough carbon dioxide and water vapour to turn the atmospheres of the two planets into warmer and wetter environments that were more habitable for life, say the researchers.

Professor Mark Sephton, from Imperial’s Department of Earth Science and Engineering believes the study provides important clues about Earth’s ancient past:

“For a long time, scientists have been trying to understand why Earth is so water rich compared to other planets in our solar system. The LHB may provide a clue. This may have been a pivotal moment in our early history where Earth’s gaseous envelope finally had enough of the right ingredients to nurture life on our planet.”

Lead- author of the study, Dr Richard Court from Imperial’s Department of Earth Science and Engineering, adds:

“Because of their chemistry, ancient meteorites have been suggested as a way of furnishing the early Earth with its liquid water. Now we have data that reveals just how much water and carbon dioxide was directly injected into the atmosphere by meteorites. These gases could have got to work immediately, boosting the water cycle and warming the planet.”

However, researchers say Mars’ good fortune did not last. Unlike Earth, Mars doesn’t have a magnetic field to act as a protective shield from the Sun’s solar wind. As a consequence, Mars was stripped of most of its atmosphere. A reduction in volcanic activity also cooled the planet. This caused its liquid oceans to retreat to the poles where they became ice.

Climate Change: We're So Screwed

From the Bad News of the Week Department (via an MIT press release):

Climate change odds much worse than thought

New analysis shows warming could be double previous estimates

The most comprehensive modeling yet carried out on the likelihood of how much hotter the Earth's climate will get in this century shows that without rapid and massive action, the problem will be about twice as severe as previously estimated six years ago - and could be even worse than that.

The study uses the MIT Integrated Global Systems Model, a detailed computer simulation of global economic activity and climate processes that has been developed and refined by the Joint Program on the Science and Policy of Global Change since the early 1990s. The new research involved 400 runs of the model with each run using slight variations in input parameters, selected so that each run has about an equal probability of being correct based on present observations and knowledge. Other research groups have estimated the probabilities of various outcomes, based on variations in the physical response of the climate system itself. But the MIT model is the only one that interactively includes detailed treatment of possible changes in human activities as well - such as the degree of economic growth, with its associated energy use, in different countries.

Study co-author Ronald Prinn, the co-director of the Joint Program and director of MIT's Center for Global Change Science, says that, regarding global warming, it is important "to base our opinions and policies on the peer-reviewed science," he says. And in the peer-reviewed literature, the MIT model, unlike any other, looks in great detail at the effects of economic activity coupled with the effects of atmospheric, oceanic and biological systems. "In that sense, our work is unique," he says.

The new projections, published this month in the American Meteorological Society's Journal of Climate, indicate a median probability of surface warming of 5.2 degrees Celsius by 2100, with a 90% probability range of 3.5 to 7.4 degrees. This can be compared to a median projected increase in the 2003 study of just 2.4 degrees. The difference is caused by several factors rather than any single big change. Among these are improved economic modeling and newer economic data showing less chance of low emissions than had been projected in the earlier scenarios. Other changes include accounting for the past masking of underlying warming by the cooling induced by 20th century volcanoes, and for emissions of soot, which can add to the warming effect. In addition, measurements of deep ocean temperature rises, which enable estimates of how fast heat and carbon dioxide are removed from the atmosphere and transferred to the ocean depths, imply lower transfer rates than previously estimated.

Prinn says these and a variety of other changes based on new measurements and new analyses changed the odds on what could be expected in this century in the "no policy" scenarios - that is, where there are no policies in place that specifically induce reductions in greenhouse gas emissions. Overall, the changes "unfortunately largely summed up all in the same direction," he says. "Overall, they stacked up so they caused more projected global warming."

While the outcomes in the "no policy" projections now look much worse than before, there is less change from previous work in the projected outcomes if strong policies are put in place now to drastically curb greenhouse gas emissions. Without action, "there is significantly more risk than we previously estimated," Prinn says. "This increases the urgency for significant policy action."

Get the rest of the Bad News here.

Super-Bolide!

From SpaceWeather.com:

On May 31st, evening sky watchers in northern Poland were temporarily blinded by a sudden flash of light brighter than the full Moon. An automated camera in the town of Gniewowo captured this snapshot of the "un-night" sky:

What happened? A meteoroid of unknown origin hit Earth's atmosphere and exploded. "It was a huge fireball, probably brighter than magnitude -13," reports Gniewowo resident Przemyslaw Zoladek. "The explosion occured at 20:48 UT and was observed by many casual witnesses and at least two Polish Fireball Network video stations." No one knows if fragments of the object reached the ground. Click here for updates.

Those Damn Romulans . . .

and their infernal cloaking devices.

From a Purdue University press release:

Researchers have created a new type of invisibility cloak that is simpler than previous designs and works for all colors of the visible spectrum, making it possible to cloak larger objects than before and possibly leading to practical applications in "transformation optics."

Whereas previous cloaking designs have used exotic "metamaterials," which require complex nanofabrication, the new design is a far simpler device based on a "tapered optical waveguide," said Vladimir Shalaev, Purdue University's Robert and Anne Burnett Professor of Electrical and Computer Engineering.

Waveguides represent established technology - including fiber optics - used in communications and other commercial applications.

The research team used their specially tapered waveguide to cloak an area 100 times larger than the wavelengths of light shined by a laser into the device, an unprecedented achievement. Previous experiments with metamaterials have been limited to cloaking regions only a few times larger than the wavelengths of visible light.

Because the new method enabled the researchers to dramatically increase the cloaked area, the technology offers hope of cloaking larger objects, Shalaev said.

Findings are detailed in a research paper appearing May 29 in the journal Physical Review Letters. The paper was written by Igor I. Smolyaninov, a principal electronic engineer at BAE Systems in Washington, D.C.; Vera N. Smolyaninova, an assistant professor of physics at Towson University in Maryland; Alexander Kildishev, a principal research scientist at Purdue's Birck Nanotechnology Center; and Shalaev.

"All previous attempts at optical cloaking have involved very complicated nanofabrication of metamaterials containing many elements, which makes it very difficult to cloak large objects," Shalaev said. "Here, we showed that if a waveguide is tapered properly it acts like a sophisticated nanostructured material."

The waveguide is inherently broadband, meaning it could be used to cloak the full range of the visible light spectrum. Unlike metamaterials, which contain many light-absorbing metal components, only a small portion of the new design contains metal.

Theoretical work for the design was led by Purdue, with BAE Systems leading work to fabricate the device, which is formed by two gold-coated surfaces, one a curved lens and the other a flat sheet. The researchers cloaked an object about 50 microns in diameter, or roughly the width of a human hair, in the center of the waveguide.

"Instead of being reflected as normally would happen, the light flows around the object and shows up on the other side, like water flowing around a stone," Shalaev said.

The research falls within a new field called transformation optics, which may usher in a host of radical advances, including cloaking; powerful "hyperlenses" resulting in microscopes 10 times more powerful than today's and able to see objects as small as DNA; computers and consumer electronics that use light instead of electronic signals to process information; advanced sensors; and more efficient solar collectors.

Unlike natural materials, metamaterials are able to reduce the "index of refraction" to less than one or less than zero. Refraction occurs as electromagnetic waves, including light, bend when passing from one material into another. It causes the bent-stick-in-water effect, which occurs when a stick placed in a glass of water appears bent when viewed from the outside. Each material has its own refraction index, which describes how much light will bend in that particular material and defines how much the speed of light slows down while passing through a material.

Natural materials typically have refractive indices greater than one. Metamaterials, however, can be designed to make the index of refraction vary from zero to one, which is needed for cloaking.

The precisely tapered shape of the new waveguide alters the refractive index in the same way as metamaterials, gradually increasing the index from zero to 1 along the curved surface of the lens, Shalaev said.

Previous cloaking devices have been able to cloak only a single frequency of light, meaning many nested devices would be needed to render an object invisible.

Kildishev reasoned that the same nesting effect might be mimicked with the waveguide design. Subsequent experiments and theoretical modeling proved the concept correct.

Researchers do not know of any fundamental limit to the size of objects that could be cloaked, but additional work will be needed to further develop the technique.

Recent cloaking findings reported by researchers at other institutions have concentrated on a technique that camouflages features against a background. This work, which uses metamaterials, is akin to rendering bumps on a carpet invisible by allowing them to blend in with the carpet, whereas the Purdue-based work concentrates on enabling light to flow around an object.

Finding Water On Other Earths

Source and Credit: University of Washington

Since the early 1990s astronomers have discovered more than 300 planets orbiting stars other than our sun, nearly all of them gas giants like Jupiter. Powerful space telescopes, such as the one that is central to NASA's recently launched Kepler Mission, will make it easier to spot much smaller rocky extrasolar planets, or exoplanets, more similar to Earth.

But seen from dozens of light years away, an Earth-like exoplanet will appear in telescopes as little more than a "pale blue dot," the term coined by the late astronomer Carl Sagan to describe how Earth appeared in a 1990 photograph taken by the Voyager spacecraft from near the edge of the solar system.

Using instruments aboard the Deep Impact spacecraft, a team of astronomers and astrobiologists has devised a technique to tell whether such a planet harbors liquid water, which in turn could tell whether it might be able to support life.

"Liquid water on the surface of a planet is the gold standard that people are looking for," said Nicolas Cowan, a University of Washington doctoral student in astronomy and lead author of a paper explaining the new technique that has been accepted for publication in Astrophysical Journal.

As part of NASA's Extrasolar Planet Observation and Characterization mission, the scientists obtained two separate 24-hour observations of light intensity from Earth in seven bands of visible light, from shorter wavelengths near ultraviolet to longer wavelengths near infrared. Earth appears gray at most wavelengths because of cloud cover, but it appears blue at short wavelengths because of the same atmospheric phenomenon that makes the sky look blue to people on the surface.

The researchers studied small deviations from the average color caused by surface features like clouds and oceans rotating in and out of view. They found two dominant colors, one reflective at long, or red, wavelengths and the other at short, or blue, wavelengths. They interpreted the red as land masses and the blue as oceans.

The analysis was undertaken "as if we were aliens looking at Earth with the tools we might have in 10 years" and did not already know Earth's composition, Cowan said. "You sum up the brightness into a single pixel in the telescope's camera, so it truly is a pale blue dot."

Since Earth's colors changed throughout the 24-hour-long observations, the scientists made maps of the planet in the dominant red and blue colors and then compared their interpretations with the actual location of the planet's continents and oceans.

"You could tell that there were liquid oceans on the planet," Cowan said. "The idea is that to have liquid water the planet would have to be in its system's habitable zone, but being in the habitable zone doesn't guarantee having liquid water."

The observations on March 18 and June 4, 2008 were made when the spacecraft was between 17 million and 33 million miles from Earth, and while it was directly above the equator. Observations from above a polar region likely would show up as white, Cowan said.

It will be some years before the launch of space telescopes capable of making similar observations for Earth-sized exoplanets, but devising this technique now could guide the construction of those instruments, he said. And while those planets will be much farther away, the technique still will be applicable.

"You will still have all the spectral information, and more importantly to us you'll still have the information so that you can see how the brightness of that speck is changing over time, Cowan said."

Co-authors are Eric Agol, Victoria Meadows and Tyler Robinson of the UW, Timothy Livengood and Drake Deming of the NASA Goddard Space Flight Center, Carey Lisse of Johns Hopkins University, Michael A'Hearn and Dennis Wellnitz of the University of Maryland, Sara Seager of the Massachusetts Institute of Technology and David Charbonneau of the Harvard-Smithsonian Center for Astrophysics. The work was funded by the Natural Sciences and Engineering Research Council of Canada, the National Science Foundation and the NASA Discovery Program.

Cowan notes that some non-habitable planets, such as Neptune, also can appear to be blue, but the color is constant and, in the case of Neptune, likely caused by methane in the atmosphere.

"It looks blue from every angle, the same blue all the way around. If you had an ocean planet it might look like that, but you can do other tests to determine that," he said. "For Earth, the blue varies from one place to another, which indicates that it's not something in the atmosphere."