Posted on by Fraser Cain

Spaceships Made from Plastic?

Artist’s concept of humans set off to Mars. Image credit: NASA Click to enlarge
After reading this article, you might never look at trash bags the same way again.

We all use plastic trash bags; they’re so common that we hardly give them a second thought. So who would have guessed that a lowly trash bag might hold the key to sending humans to Mars?

Most household trash bags are made of a polymer called polyethylene. Variants of that molecule turn out to be excellent at shielding the most dangerous forms of space radiation. Scientists have long known this. The trouble has been trying to build a spaceship out of the flimsy stuff.

But now NASA scientists have invented a groundbreaking, polyethylene-based material called RXF1 that’s even stronger and lighter than aluminum. “This new material is a first in the sense that it combines superior structural properties with superior shielding properties,” says Nasser Barghouty, Project Scientist for NASA’s Space Radiation Shielding Project at the Marshall Space Flight Center.

To Mars in a plastic spaceship? As daft as it may sound, it could be the safest way to go.

Less is more

Protecting astronauts from deep-space radiation is a major unsolved problem. Consider a manned mission to Mars: The round-trip could last as long as 30 months, and would require leaving the protective bubble of Earth’s magnetic field. Some scientists believe that materials such as aluminum, which provide adequate shielding in Earth orbit or for short trips to the Moon, would be inadequate for the trip to Mars.

Barghouty is one of the skeptics: “Going to Mars now with an aluminum spaceship is undoable,” he believes.

Plastic is an appealing alternative: Compared to aluminum, polyethylene is 50% better at shielding solar flares and 15% better for cosmic rays.

The advantage of plastic-like materials is that they produce far less “secondary radiation” than heavier materials like aluminum or lead. Secondary radiation comes from the shielding material itself. When particles of space radiation smash into atoms within the shield, they trigger tiny nuclear reactions. Those reactions produce a shower of nuclear byproducts — neutrons and other particles — that enter the spacecraft. It’s a bit like trying to protect yourself from a flying bowling ball by erecting a wall of pins. You avoid the ball but get pelted by pins. “Secondaries” can be worse for astronauts’ health than the original space radiation!

Ironically, heavier elements like lead, which people often assume to be the best radiation shielding, produce much more secondary radiation than lighter elements like carbon and hydrogen. That’s why polyethylene makes good shielding: it is composed entirely of lightweight carbon and hydrogen atoms, which minimizes secondaries.

These lighter elements can’t completely stop space radiation. But they can fragment the incoming radiation particles, greatly reducing the harmful effects. Imagine hiding behind a chain-link fence to protect yourself in a snowball fight: You’ll still get some snow on you as tiny bits of snowball burst through the fence, but you won’t feel the sting of a direct hit from a hard-packed whopper. Polyethylene is like that chain link fence.

“That’s what we can do. Fragmenting — without producing a lot of secondary radiation — is actually where the battle is won or lost,” Barghouty says.

Made to order

Despite their shielding power, ordinary trash bags obviously won’t do for building a spaceship. So Barghouty and his colleagues have been trying to beef-up polyethylene for aerospace work.

That’s how Shielding Project researcher Raj Kaul, working together with Barghouty, came to invent RXF1. RXF1 is remarkably strong and light: it has 3 times the tensile strength of aluminum, yet is 2.6 times lighter — impressive even by aerospace standards.

“Since it is a ballistic shield, it also deflects micrometeorites,” says Kaul, who had previously worked with similar materials in developing helicopter armor. “Since it’s a fabric, it can be draped around molds and shaped into specific spacecraft components.” And because it’s derived from polyethylene, it’s an excellent radiation shield as well.

The specifics of how RXF1 is made are secret because a patent on the material is pending.

Strength is only one of the traits that the walls of a spaceship must have, Barghouty notes. Flammability and temperature tolerance are also important: It doesn’t matter how strong a spaceship’s walls are if they melt in direct sunlight or catch fire easily. Pure polyethylene is very flammable. More work is needed to customize RXF1 even further to make it flame and temperature resistant as well, Barghouty says.

The Bottom Line

The big question, of course, is the bottom line: Can RXF1 carry humans safely to Mars? At this point, no one knows for sure.

Some “galactic cosmic rays are so energetic that no reasonable amount of shielding can stop them,” cautions Frank Cucinotta, NASA’s Chief Radiation Health Officer. “All materials have this problem, including polyethylene.”

Cucinotta and colleagues have done computer simulations to compare the cancer risk of going to Mars in an aluminum ship vs. a polyethylene ship. Surprisingly, “there was no significant difference,” he says. This conclusion depends on a biological model which estimates how human tissue is affected by space radiation–and therein lies the rub. After decades of spaceflight, scientists still don’t fully understand how the human body reacts to cosmic rays. If their model is correct, however, there could be little practical benefit to the extra shielding polyethylene provides. This is a matter of ongoing research.

Because of the many uncertainties, dose limits for astronauts on a Mars mission have not been set, notes Barghouty. But assuming that those dose limits are similar to limits set for Shuttle and Space Station flights, he believes RXF1 could hypothetically provide adequate shielding for a 30 month mission to Mars.

Today, to the dump. Tomorrow, to the stars? Polyethylene might take you farther than you ever imagined.

Original Source: NASA News Release

Posted on by Fraser Cain

Astronomers Looking for Help with Cataclysmic Variable Star

GALEX , one of the telescopes that will study AE Aqr. Image credit: NASA Click to enlarge
Amateur astronomers are being asked to help a constellation of observatories unravel the mysteries of a puzzling binary star system.

On August 30-August 31, 2005 two space-based and four professional ground-based observatories are scheduled to observe the cataclysmic variable star AE Aqr. Each of the observatories covers a different wavelength of light and amateur astronomers have been asked to help cover the visible-light portion.

“This observing campaign will take place over nearly a full day, and since no single ground-based observatory can observe AE Aqr for that long due to Earth’s rotation, amateur astronomers can make a unique and invaluable contribution to this campaign,” said Dr. Christopher Mauche of Lawrence Livermore National Laboratory, the principal investigator of the project.

Because they are spaced all across the globe, amateur astronomers can observe this star and other celestial objects unhindered by nightfall or weather.

The Chandra and GALEX space telescopes will be working with the HESS, MAGIC, VLT, and VLA ground-based telescopes. Combined, they will provide coverage of AE Aqr from high-energy gamma-rays to low-energy radio waves. Such simultaneous multiwavelength coverage is required to provide the clearest picture of the locations, mass motions, energetics, and inter-relationships of the various emission regions in the star.

AE Aqr is an intermediate polar, a type of cataclysmic variable star. It actually consists of two stars – a red dwarf and rapidly spinning magnetic white dwarf. Material drawn off the red dwarf falls toward the white dwarf, but instead of landing on the white dwarf surface, it is flung out of the system by the white dwarf’s rapidly spinning magnetic field. This mechanism, which is uncommon but not unique to AE Aqr, is referred to as a magnetic propeller.

“Amateurs astronomers have been observing AE Aqr since 1944. Since then, they have recorded over 28,815 measurements of the star, most of them made with just a telescope and their eyes. This type of historical data is immensely valuable in studying variable stars and only amateurs can provide it,” Dr. Arne Henden, Director of the American Association of Variable Star Observers (AAVSO), said.

Amateur astronomers are being asked to observe AE Aqr every night possible until September 3. Those with CCD cameras on their telescopes are requested to make scientific brightness measurements, known as photometry, of the system as well. For information on how to measure the brightness of AE Aqr and submit results to professionals, visit the AAVSO web site at http://www.aavso.org/alertnotice .

The AAVSO is the world’s preeminent professional-amateur astronomical association. Specializing in the study of variable stars, the AAVSO’s International Database has over 11 million observations of variable stars dating back over 100 years. Founded in 1911 as part of the Harvard College Observatory, the AAVSO became independent in 1954 and currently has over 3,000 members and observers in over 40 countries.

Original Source: AAVSO News Release

Posted on by Fraser Cain

Our Collision With Andromeda Will Look Like This

NGC 520. Image credit: Gemini Click to enlarge
In the constellation of Pisces, some 100 million light-years from Earth, two galaxies are seen to collide – providing an eerie insight into the ultimate fate of our own planet when the Milky Way fatally merges with our neighbouring galaxy of Andromeda.

The image of the intertwined galaxies was captured on the night of 13-14th July 2005 by the Gemini Multi-Object Spectrograph [GMOS] instrument fitted to the 8-metre class Gemini North Observatory, sited on Mauna Kea, Hawaii.

Prof. Ian Robson, Director of the UK Astronomy Technology Centre which built GMOS in collaboration with other partners said,” This is quite scary. Since GMOS was installed on the telescope back in 2001 it has taken some amazing astronomical images of very faint, distant galaxies and star forming regions, providing a wealth of scientific data, but this one sends shivers down my spine. Our saving grace is that we have about 5 billion years left before we get swallowed up by Andromeda. Nevertheless, it’s amazing to see so far in advance how planet Earth and our own galaxy will ultimately end. Glad to say I won’t be around when the fireball happens”.

The image of the combined galaxies, which are known as NGC 520, may be fairly early in their galactic dance of death and it is likely that the situation has changed dramatically in the time it has taken for their light to reach Earth*.

Prof. Robson added, “Hints of new star formation taking place can be seen in the faint red glowing areas above and beneath the middle of the image. Perhaps even now the galaxies have totally combined to form a whole new galaxy with a brand new set of stars and associated planets – and maybe new life on one of those planets!”

The unique shape of NGC 520 is the result of the two galaxies colliding. One galaxy’s dust lane can be seen easily in the foreground and a distant tail is visible at the bottom centre. These features are the result of the gravitational interactions that have robbed both galaxies of their original shapes.

Original Source: PPARC News Release

Posted on by Fraser Cain

Titan’s Bright Side

Natural color view of Titan. Image credit: NASA/JPL/SSI Click to enlarge
As Cassini approached Titan on Aug. 21, 2005, it captured this natural color view of the moon’s orange, global smog. Titan’s hazy atmosphere was frustrating to NASA Voyager scientists during the first tantalizing Titan flybys 25 years ago, but now Titan’s surface is being revealed by Cassini with startling clarity (see Titan Mosaic — East of Xanadu ).
Images taken with the wide-angle camera using red, green and blue spectral filters were combined to create this color view. The images were acquired at a distance of approximately 213,000 kilometers (132,000 miles) from Titan and at a Sun-Titan-spacecraft, or phase, angle of 55 degrees. Resolution in the image is about 13 kilometers (8 miles) per pixel.

The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. The Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the mission for NASA’s Science Mission Directorate, Washington, D.C. The Cassini orbiter and its two onboard cameras were designed, developed and assembled at JPL. The imaging operations center is based at the Space Science Institute in Boulder, Colo.

For more information about the Cassini-Huygens mission visit http://saturn.jpl.nasa.gov . The Cassini imaging team homepage is at http://ciclops.org .

Original Source: NASA/JPL/SSI News Release

Posted on by Mark Mortimer

Book Review: Dying Planet

Mars holds a special place in the history of humankind. Bright, coloured and oh, so close, this planet tugs at our dreams. Responding to these dreams, some of our brighter denizens took action. The astronomer Percival Lowell perceived lines. From them, he deduced that Martians survived only by building canals to channel water from polar to temperate regions. At about the same time, the author H.G. Wells wrote of Martians who needed to escape their dying planet and thus targeted Earth with all powerful war machines. Better equipment and other knowledgeable people expanded or contradicted these ideas for many years. Even after the desolate images from the Mariner and Viking missions showed a harsh planet, the government agency NASA promoted a need to counter anthropocentric thinking. Adjoining these more recent investigations, the author Kim Stanley Robinson, in three works, placed people on Mars where he mixed issues of today’s society with those of an imaginary space faring race hundreds of years in the future. In reviewing the actions associated with these and others it seems that each new tidbit concerning Mars promoted a new relation to our current and future conditions on Earth.

Markley uses this promotion in his review of literature about Mars. That is, he assesses the state of the art in the science of Mars for a given time. He compiles and assesses both popular and learned views. In particular, his perception of the bickering and antagonism between scientists gives some poignant insight into the scientific process. After these, he repeats the review process for science fiction literature. For the most part, he shows how the latest science data and conclusions shape the literature though not necessarily drive it. In his view, the literature predominantly uses Mars as an analogue to an eco-apocalypse on Earth, hence the title of Dying Planet.

Given Markley is an English professor, I was pleasantly surprised at the equally detailed and impressive reviews for both the science and literature. Though neither are exhaustive, they have depth and copious references. As well, the references are usually from source or highly rated topical publications hence their validity is assured. The book is well delineated with topics and subjects in unique sections. Sometimes though this makes the book seem like a collection of essays rather than a continuous piece. Because of this, even though the presentation is chronological, the flow of Markely’s argument gets lost. That is, though Markley provides an excellent review of both the literature and the science of Mars, it is not very clear as to if there is an over-arching purpose.

Further, the writing style varies. Most of the scientific passages would be readily comprehensible to the every day person on the street. On occasion the literary critiques get phrased in the parlance of the ivory tower as in, ‘In contrast to later dystopian novels…Red Start depicts freedom as the shared fulfilment of a revolutionary future, a sociocultural transcendence of bourgeois individualism, capital exploitation and the false sciences of compartmentalization.’ The introduction is particularly of this flavour and may turn off some who would likely find the remainder of the text very rewarding.

Given this, the overall impression is of a literary professor with a life long interest in science fiction and space science, who wrote a personal review. As such, it is a great review. However, it is lacking in direction; that is, I could not discern the target audience. Markley pushes the idea of science fiction as being a literary thought experiment much as Einstein had his own practical thought experiments. This is laudable yet Einstein and the referenced science fiction authors had a requirement to convey new ideas to colleagues and the general public. Markley needs a similar argument to really make this review purposeful.

The planet Mars acted as a beacon for many civilizations. Even today, whether as an analogue or a veritable pinnacle of scientific research, it shines forth with questions and queries. Robert Markley in his book Dying Planet reviews the previous hundred years of scientific discovery surrounding Mars and its related science fiction literature. He compiles a compact, well detailed synopsis of the science and a insightful critique of the literature to provide an in-depth resource for understand how Mars impinges on our human psyche.

Review by Mark Mortimer

Read more reviews online, or purchase a copy from Amazon.com.

Posted on by Fraser Cain

NASA Says Liquid Water Made Martian Gullies

Alcove, channel, and debris apron of recent gullies on Mars. Image credit: NASA Click to enlarge
NASA scientists say liquid water formed recent gullies on Mars.

A NASA-led team will present its Mars gully findings at the American Astronomical Society’s Division for Planetary Sciences annual meeting in Cambridge, England, Sept. 5, 2005.

“The gullies may be sites of near-surface water on present-day Mars and should be considered as prime astrobiological target sites for future exploration,” ventured National Research Council scientist Jennifer Heldmann, principal author of the study who works at NASA Ames Research Center in California’s Silicon Valley.

“The gully sites may also be of prime importance for human exploration of Mars because they may represent locations of relatively near surface liquid water, which can be accessed by crews drilling on the red planet,” she added.

“If liquid water pops out onto Mars’ surface, it can create short gullies about 550-yards (500-meters) long,” Heldmann said. “We used a computer to simulate the flow of liquid water within gully channels,” Heldmann explained.

“Our model indicates that these fluvially-carved gullies were formed in the low temperature and low pressure conditions of present-day Mars by the action of relatively pure liquid water,” said Heldmann.

The science team found that the maximum length of gullies simulated in the computer models were comparable to the martian gullies studied. “We find that the short length of the gully features implies they did form under conditions similar to those on present-day Mars, with simultaneous freezing and rapid evaporation of nearly pure liquid water,” Heldmann said.

In addition, images taken by the Mars Global Surveyor spacecraft show ‘geologically young’ small-scale features on the red planet that resemble terrestrial water-carved gullies, according to scientists.

“The young geologic age of these gullies is often thought to be a paradox, because liquid water is unstable at the martian surface,” Heldmann said. At present martian air pressure and temperature, water will boil and freeze at very rapid rates, the scientists reported.

Team scientists noticed that images of some of Mars’ gullies show that they taper off into very small debris fields ? or no debris fields at all ? suggesting that water rushing through the gullies rapidly froze and/or evaporated.

“In the martian case, fluid well above the boiling point (which is a very low temperature at Mars’ low atmospheric pressure and air temperature) is suddenly exposed to the atmosphere,” said Heldmann. “The difference between the vapor and ambient pressures relative to the ambient pressure is large, and flash boiling can occur, leading to a violent loss of fluid.”

Scientists believe that ice probably would not accumulate in the gullies, because of the rapid evaporation of water and relatively high flow velocities, but in some cases, some ice could be carried downstream. The researchers studied computer simulations of both scenarios.

“We tested our model using known flow parameters and environmental conditions of perennial saline springs in the Mars analog environment of the Canadian High Arctic,” Heldmann noted.

In addition to Heldmann, Chris McKay, also of NASA Ames; Brian Toon, Michael Mellon and John Pitlick, of the University of Colorado, Boulder; Wayne Pollard, of McGill University, Montreal, Canada; and Dale Andersen, of the SETI Institute, Mountain View, Calif., are study co-authors.

Original Source: NASA News Release

Posted on by Fraser Cain

Earth’s Climate During the Permian Extinction

Western Hemisphere. Image credit: NASA Click to enlarge
Scientists at the National Center for Atmospheric Research (NCAR) have created a computer simulation showing Earth’s climate in unprecedented detail at the time of the greatest mass extinction in the planet’s history. The work gives support to a theory that an abrupt and dramatic rise in atmospheric levels of carbon dioxide triggered the massive die-off 251 million years ago. The research appears in the September issue of Geology.

“The results demonstrate how rapidly rising temperatures in the atmosphere can affect ocean circulation, cutting off oxygen to lower depths and extinguishing most life,” says NCAR scientist Jeffrey Kiehl, the lead author.

Kiehl and coauthor Christine Shields focused on the dramatic events at the end of the Permian Era, when an estimated 90 to 95% of all marine species, as well as about 70% of all terrestrial species, became extinct. At the time of the event, higher-latitude temperatures were

18 to 54 degrees Fahrenheit (10 to 30 degrees Celsius) higher than today, and extensive volcanic activity had released large amounts of carbon dioxide and sulfur dioxide into the atmosphere over a 700,000-year period.

To solve the puzzle of how those conditions may have affected climate and life around the globe, the researchers turned to the Community Climate System Model (CCSM). One of the world’s premier climate research tools, the model can integrate changes in atmospheric temperatures with ocean temperatures and currents. Research teams had previously studied the Permian extinction with more limited computer models that focused on a single component of Earth’s climate system, such as the ocean.

The CCSM indicated that ocean waters warmed significantly at higher latitudes because of rising atmospheric levels of carbon dioxide (CO2), a greenhouse gas. The warming reached a depth of about 10,000 feet (4,000 meters), interfering with the normal circulation process in which colder surface water descends, taking oxygen and nutrients deep into the ocean.

As a result, ocean waters became stratified with little oxygen, a condition that proved deadly to marine life. This in turn accelerated the warming, since marine organisms were no longer removing carbon dioxide from the atmosphere.

“The implication of our study is that elevated CO2 is sufficient to lead to inhospitable conditions for marine life and excessively high temperatures over land would contribute to the demise of terrestrial life,” the authors concluded in the article.

The CCSM’s simulations showed that ocean circulation was even more stagnant than previously thought. In addition, the research demonstrated the extent to which computer models can successfully simulate past climate events. The CCSM appeared to correctly capture key details of the late Permian, including increased ocean salinity and sea surface temperatures in the high latitudes that paleontologists believe were 14 degrees Fahrenheit (8 degrees Celsius) higher than present.

The modeling presented unique challenges because of limited data and significant geographic differences between the Permian and present-day Earth. The researchers had to estimate such variables as the chemical composition of the atmosphere, the amount of sunlight reflected by Earth’s surface back into the atmosphere, and the movement of heat and salinity in the oceans at a time when all the continents were consolidated into the giant land mass known as Pangaea.

“These results demonstrate the importance of treating Earth’s climate as a system involving physical, chemical , and biological processes in the atmosphere, oceans, and land surface, all acting in an interactive manner,” says Jay Fein, director of NSF’s climate dynamics program, which funded the research. “Other studies have reached similar conclusions. What’s new here is the application of a detailed version of one of the world’s premier climate system models, the CCSM, to understand how rising levels of atmospheric carbon dioxide affected conditions in the world’s oceans and land surfaces enough to trigger a massive extinction hundreds of millions of years ago.”

Original Source: NCAR News Release

Posted on by Fraser Cain

Supernova in Galaxy NGC 1559

Supernova 2005dh and NGC 1559. Image credit: ESO Click to enlarge
The southern Reticulum constellation certainly isn’t a big hit for amateur astronomers. This tiny, bleak and diamond-shaped constellation, not far on the sky from the Large Magellanic Cloud, is often overlooked. But recently, astronomers had a closer look at a galaxy situated inside it. And more precisely at an exploding star hosted by the spiral galaxy NGC 1559.

On the night of August 4, 2005, Australian amateur astronomer Reverend Robert Evans discovered a supernova just North of the galaxy with his 0.31-m telescope. The supernova – the explosion of a star – was of magnitude 13.8, that is, only 20 times fainter than the entire host galaxy. Being the 104th supernova discovered in 2005, it received the name SN 2005df. Noticeably, Evans had already discovered 2 other supernovae in the same galaxy: in 1984 (SN 1984J) and in 1986 (SN 1986L).

The following night, astronomer Marilena Salvo and her Australian colleagues classified the supernova as a somewhat unusual type Ia supernova, caught probably 10 days before it reached its maximum brightness. Such a supernova is thought to be the result of the explosion of a small and dense star – a white dwarf – inside a binary system. As its companion was continuously spilling matter onto the white dwarf, the white dwarf reached a critical mass, leading to a fatal instability and the supernova.

These are exactly a kind of supernovae in which Dietrich Baade, Ferdinando Patat (ESO), Lifan Wang (Lawrence Berkeley National Laboratory, USA), and their colleagues are interested. In particular, they study the polarization properties of this kind of supernova in order to learn more about their asphericity, which holds important clues to the detailed physics that governs this terminal catastrophe in the life of such stars.

Having an accepted observing programme that uses the FORS1 multi-mode instrument on Kueyen, one of the four Unit Telescopes of ESO’s 8.2m Very Large Telescope at Cerro Paranal, they triggered a Target of Opportunity request so that on-duty astronomers at the VLT could observe this supernova, which was done on August 6.

From a very first analysis of their data, Wang and his colleagues found that SN 2005df resembles closely another supernova they had studied before, SN 2001el, whose explosion they showed was significantly asymmetric.

NGC 1559 is a SBc(s)-type spiral galaxy located about 50 million light-years away, that weighs the equivalent of about 10,000 million of suns, and is about 7 times smaller than our Milky Way: on the sky, it measures about 4×2 arcmin2. Receding from us at a speed of about 1,300 km/s, it is a galaxy of the Seyfert type. Such galaxies are characterized by a bright nucleus that radiates strongly in the blue and in the ultraviolet. Astronomers think that about 2 solar masses of gas per year are transformed into stars in this galaxy. Like most galaxies, NGC 1559 probably contains a black hole in its centre, which should have a mass that is equivalent to 300,000 suns.

Original Source: ESO News Release

Posted on by Fraser Cain

Future Ice Free Summers in the Arctic

Arctic ocean. Image credit: NASA/GSFC Click to enlarge
The current warming trends in the Arctic may shove the Arctic system into a seasonally ice-free state not seen for more than one million years, according to a new report. The melting is accelerating, and a team of researchers were unable to identify any natural processes that might slow the de-icing of the Arctic.

Such substantial additional melting of Arctic glaciers and ice sheets will raise sea level worldwide, flooding the coastal areas where many of the world’s people live.

Melting sea ice has already resulted in dramatic impacts for the indigenous people and animals in the Arctic, which includes parts of Alaska, Canada, Russia, Siberia, Scandinavia and Greenland.

?What really makes the Arctic different from the rest of the non-polar world is the permanent ice in the ground, in the ocean and on land,? said lead author University of Arizona geoscientist Jonathan T. Overpeck. ?We see all of that ice melting already, and we envision that it will melt back much more dramatically in the future as we move towards this more permanent ice-free state.?

The report by Overpeck and his colleagues is published in the Aug. 23 Eos, the weekly newspaper of the American Geophysical Union. A complete list of authors and their affiliations is at the end of this release.

The report is the result of weeklong meeting of a team of interdisciplinary scientists who examined how the Arctic environment and climate interact and how that system would respond as global temperatures rise. The workshop was organized by the NSF Arctic System Science Committee, which is chaired by Overpeck. The National Science Foundation funded the meeting.

The past climates in the Arctic include glacial periods, where sea ice coverage expanded and ice sheets extended into Northern America and Europe, and warmer interglacial periods during which the ice retreats, as it has during the past 10,000 years.

By studying natural data loggers such as ice cores and marine sediments, scientists have a good idea what the ?natural envelope? for Arctic climate variations has been for the past million years, Overpeck said.

The team of scientists synthesized what is currently known about the Arctic and defined key components that make up the current system. The scientists identified how the components interact, including feedback loops that involve multiple parts of the system.

?In the past, researchers have tended to look at individual components of the Arctic,? said Overpeck. ?What we did for the first time is really look at how all of those components work together.?

The team concluded that there were two major amplifying feedbacks in the Arctic system involving the interplay between sea and land ice, ocean circulation in the North Atlantic, and the amounts of precipitation and evaporation in the system.

Such feedback loops accelerate changes in the system, Overpeck said. For example, the white surface of sea ice reflects radiation from the sun. However, as sea ice melts, more solar radiation is absorbed by the dark ocean, which heats up and results in yet more sea ice melting.

While the scientists identified one feedback loop that could slow the changes, they did not see any natural mechanism that could stop the dramatic loss of ice.

?I think probably the biggest surprise of the meeting was that no one could envision any interaction between the components that would act naturally to stop the trajectory to the new system,? Overpeck said. He added that the group investigated several possible braking mechanisms that had been previously suggested.

In addition to sea and land ice melting, Overpeck warned that permafrost?the permanently frozen layer of soil that underlies much of the Arctic?will melt and eventually disappear in some areas. Such thawing could release additional greenhouse gases stored in the permafrost for thousands of years, which would amplify human-induced climate change.

Overpeck said humans could step on the brakes by reducing carbon dioxide emissions. ?The trouble is we don?t really know where the threshold is beyond which these changes are inevitable and dangerous,” Overpeck said. ?Therefore it is really important that we try hard, and as soon as we can, to dramatically reduce such emissions.?

Original Source: University of Arizona News Release