- Saturn’s Moon Made Mountains Out of Moonlets
- It May Not Be Too Late for Polar Bears
- Iron Age Copper Reveals Earth’s Stronger, Faster Magnetic Field
- Video: Physics Getting Freaky on Bed of Nails
- Clusterwink Snails Defend Themselves With Superfast Flashing Shells
- The Tenuous Future of Water in the Desert Southwest
Posted: 15 Dec 2010 02:25 PM PST
Iapetus's spiky belt, which stretches all the way around the moon's equator, has baffled astronomers for decades.
The ridge's mountains stretch up to 12 miles high, more than twice as high as Mount Everest. The mountain range is "ramrod straight, and sits exactly on the equator," Dombard said. "There's nothing like this anywhere else in the solar system."
The usual ways rocky worlds form mountains don't work for Iapetus, he says. If tectonic plates crunched together and folded the landscape above them, the way mountain ranges like the Rockies and Himalayas formed on Earth, then Iapetus should have other mountains north and south of the equator.
Some have suggested the ridge could have come from a ring, much like Saturn's famous rings, that collapsed onto the moon's surface. If that were true, though, other icy moons like Rhea and Jupiter's moon Callisto should also have spiked collars, but they don't. Iapetus also probably lacks the gravitational oomph to pull material from Saturn's rings to form its own.
But the rings could have come from inside Iapetus itself. In a talk at the AGU meeting, Dombard suggested that Iapetus could have once had a sub-moon knocked from its surface by a colossal impact. The Earth's own moon and Pluto's moon Charon are thought to have formed the same way.
Depending on its mass and distance from Iapetus, the sub-moon could have orbited comfortably for 100,000 to millions of years, Dombard said. But the sub-moon would slowly lose energy and spiral in toward Iapetus. Eventually, tidal forces from the larger moon would shred the sub-moon into hundreds of tiny moonlets.
Those chunks of ice and rock would briefly orbit Iapetus's equator as a ring, then rain down on the moon's surface to build the mountain range.
"This is the best explanation so far," said planetary scientist Cynthia Phillips of the SETI Institute in Mountain View, California, who was not involved in the new work. "It seems like a very strange case, but it's a very strange feature."
A similar idea was recently proposed to explain the origin of Saturn's rings: Saturn may once have had a big icy moon that broke up into the gas giant's famous rings and several smaller moons.
"It's a complimentary idea," Dombard said.
Dombard and colleagues haven't done rigorous simulations to prove their idea right, though they hope to soon. But Saturn's moon Rhea provides some supporting evidence. Earlier this year, planetary scientist Paul Schenk of the Lunar and Planetary Institute in Houston and colleagues found that Rhea has a line of splotchy blue streaks around its equator, which they suggest was formed by a collapsing ring. (Schenk also made the movie of flying over Iapetus's ridge, above, using data from the Cassini orbiter.)
"The same process happened on Iapetus, but taken to its ridiculous extreme," Dombard said.
The similarity to Rhea convinced Schenk that Dombard's model is believable. "I became a convert," he said.
Video: Paul Schenk, Lunar and Planetary Institute, Houston
Posted: 15 Dec 2010 01:44 PM PST
Cutting greenhouse gas emissions enough over the next few decades may stabilize the rapidly shrinking Arctic sea ice sufficiently to provide a sustainable habitat for polar bears, a paper in the Dec. 16 Nature reports. And if emissions do keep rising, another new study finds, the only species that has officially been declared threatened by the U.S. government due to global warming may still be able to hang on for a while in a few pockets of the northern Arctic.
Polar bears need sea ice to hunt their prey, but the frozen skin that floats atop the Arctic Ocean has been thinning and shrinking in recent decades as global temperatures rise. Between 1979 and 2010, Arctic sea ice cover at the end of the summer melt season dropped an average of 11.5 percent per decade. Many researchers think that end-summer Arctic ice could be almost entirely gone by the middle of this century.
In 2007, the U.S. Geological Survey reported that two-thirds of the world's 25,000 polar bears could disappear within 50 years if greenhouse gas emissions continued unabated. The following year, interior secretary Dirk Kempthorne relied on that report when putting the bear, Ursus maritimus, on the government's list of threatened species.
Steven Amstrup, an Anchorage-based senior scientist with Polar Bears International in Bozeman, Mont., who was a coauthor on the 2007 USGS report, decided to look at whether cutting emissions could preserve enough of the Arctic sea ice to save polar bears from extinction.
In the Nature paper, his team studied five scenarios for how much atmospheric levels of greenhouse gases would rise over the next century.
Using a widely accepted climate model, the researchers analyzed potential futures for several measures of sea ice habitability — such as the amount of sea ice extending over continental shelves, the number of months each year those shelves are free of ice and the distance between that ice and the more northerly pack ice that bears also use to hunt.
The results don't support the idea that Arctic sea ice is headed for a catastrophic "tipping point" beyond which the ice disintegrates completely, Amstrup says. Instead, if greenhouse gas emissions and hence temperatures can be stabilized, the sea ice stabilizes too.
"If we act, it isn't too late to save the polar bear," Amstrup says.
As it thins, sea ice reaches a point where it becomes more responsive to the water temperature below and is better able to regrow in the winter , says Marika Holland, a sea ice specialist at the National Center for Atmospheric Research in Boulder, Colo. This enhanced growth helps stabilize the shrinking ice.
Still, the more people can limit greenhouse gas emissions, the less melting will happen in the first place, says Amstrup.
Even if emissions keep rising, sea ice will stick around in certain areas of the Arctic longer than others, Stephanie Pfirman, an Arctic specialist at Barnard College in New York and the nearby Lamont-Doherty Earth Observatory, and her colleagues will report in San Francisco December 16 at the annual meeting of the American Geophysical Union. The work meshes nicely with the new Nature paper, she said: "They're asking what happens if we act to mitigate. We're looking at the base case: What if we don't act?"
Winds and ocean circulation regularly pile ice up in the Canadian Arctic archipelago and north of Greenland, Pfirman said. Sea ice is thick there today and may persist long after it has melted elsewhere, the researchers propose.
Polar bears aren't the only creatures that may depend on those last remnants of ice cover, Pfirman noted. An entire ecosystem, including seals and walruses, depends on sea ice. On December 3, the National Oceanic and Atmospheric Administration proposed listing four subspecies of ringed seal and two populations of bearded seal as threatened because of shrinking ice. It is the first such proposal since the polar bear based solely on the threat of climate change.
By 2100 only the northern fringes of Canada and Greenland — the same areas Pfirman's group identified in its polar bear study — will have snow deep enough to shelter ringed seal pups, suggests research presented at the AGU meeting by Brendan Kelly, a marine-mammal specialist at NOAA's National Marine Laboratory in Juneau, Alaska, and Cecilia Bitz, a sea ice physicist at the University of Washington in Seattle. Each spring, these seals make snow caves atop the ice to shelter their newborn pups; to do so, they need snow at least 50 centimeters deep.
But in a greenhouse world, these high Arctic pockets will last only so long, says Robert Newton, an oceanographer at Lamont-Doherty.
"This [refuge] is not expected to last forever," Newton says. "As the planet keeps warming, it will eventually be lost."
Posted: 15 Dec 2010 12:32 PM PST
"This is a very challenging result," said geomagnetist Luis Silva of the University of Leeds, who was not involved in the new work. "It's completely outside of anything we thought could be happening in the core."
The Earth's magnetic field comes from the movement of molten iron in the core. The field's strength and structure are constantly changing. But paleomagnetists (scientists who study the history of the Earth's magnetic field) thought the changes were usually small and slow, fluctuating by about 16 percent over the course of a century.
But a new study of ancient copper mines in southern Israel found that the strength of the magnetic field could double and then fall back down in less than 20 years.
"The magnetic field reached an intensity that was much higher than anyone had ever thought before, two and a half times the present field," said graduate student Ron Shaar of the Hebrew University of Jerusalem, lead author of the new study. "And you can have dramatic changes in the intensity of the field in periods of less than decades." Shaar presented his results in a poster here at the American Geophysical Union meeting Dec. 14, and in a paper to appear in Earth and Planetary Science Letters.
To measure the strength of the magnetic field, Shaar and colleagues turned to piles of waste metal left near an ancient Egyptian copper mine.
When melted iron cools rapidly, it freezes with a signature of the Earth's magnetic field at that instant. Paleomagnetists have traditionally studied the glass-like rocks thrown from volcanoes to build a picture of how the magnetic field has changed over time. Their measurements, plus theoretical models, showed that the magnetic field's strength peaked around 3,000 years ago in the middle Egypt's Iron Age.
"We don't have volcanic glass in Israel, but we do have slag," Shaar said. When the ancient Egyptians (in what is now Israel) melted ore to produce copper, they created a lot of leftover molten rock that they threw immediately on a waste heap. The rock cooled quickly, preserving a signature of the magnetic field.
"It's like a small scale lava flow," Shaar said.
To see what the magnetic field was doing 3,000 years ago, Shaar and his colleagues collected slag samples from the ancient copper mines of Timna in southern Israel. They found remnants of wheat, dates, grapes and human hair, too, which allowed them to use carbon dating to figure out how long ago the slag layers were laid down. Combined with slag from a previous study of the Khirbat en-Nahas mines to the northeast in Jordan, their samples spanned almost two centuries, from 3,050 to 2,870 years ago.
Back in the lab, the team melted and re-froze some of the slag in the presence of a known magnetic field, to make sure they could trust the rock to faithfully trap the field strength. Then they measured the field strength in the raw slag.
They found that the magnetic field abruptly spiked twice during the 180 years they studied, once around 2,990 years ago and once around 2,900 years ago. Both times, the field jumped up in strength and then fell by at least 40 percent in the space of about 20 years.
"These geomagnetic spikes are very different from what we see now or have seen before," Shaar said.
"He sees the field changing 5 to 10 times faster than anything else we have seen so far," said geomagnetist Cathy Constable of the Scripps Institute of Oceanography in San Diego, who makes global maps of the changing magnetic field but was not involved in the new work.
Constable notes that the spikes seem to happen only in the part of the Middle East that Shaar studied, not everywhere on Earth. That suggests that the spike could be caused by a small piece of especially magnetic molten iron moving through the Earth's core right under Israel.
Shaar and his colleagues plan to visit Roman mines in Cyprus to see if similar spikes happened there.
Posted: 15 Dec 2010 12:09 PM PST
As-yet-unexplained laws of physics keep popping up in the darnedest places, like, for example, this bed of nails.
Perfectly arrayed in horizontal rows, one would expect their pattern to break down when shaken. But as this stop-motion video shows, they lose pattern in a very orderly way.
The video was taken by T. Lynn MacDonald, a student in the lab of University of Toronto physicist Stephen Morris. His specialty is experimental nonlinear physics, investigating how and why patterns emerge in interacting particles. Whether the particles are water molecules, grains of sand, inch-long nails or stars is just a matter of scale.
Morris' lab received plenty of attention this year, first for research on theories of icicle formation and then for a "Supernova in a Jar." Flying under the radar was MacDonald's as-yet-unpublished work on nails, which shows them collectively transformed in a way typically seen when heat transforms crystal to liquid.
By shaking the bed of nails, "we 'melt' it," wrote Morris in an email.
The observations represent an early research stage, with fuller investigations to come. "The emergence of collective behavior is exactly the point of the experiment," wrote Morris. The experiment also hints at a non-scientific truth, articulated by mathematician Henri Poincaré and epigraphed on Morris' website:
"The scientist does not study nature because it is useful; he studies it because he delights in it, and he delights in it because it is beautiful," wrote Poincaré.
Video: T. Lynn MacDonald.
Citation: "Pattern Formation in Vertically Vibrated Nails," by T. Lynn MacDonald. Unpublished, available online (pdf).
Posted: 15 Dec 2010 11:21 AM PST
Tiny snails found on Australia's eastern coast can flicker their spiral shells like dim, blue-green light bulbs.
Some snails excrete bioluminescent trails of snot or blink their muscly foot to attract mates. But the clusterwink snail is the first discovered to use the shell-flashing trick, which seems to have evolved as a form of self-defense.
"The snail produces light when tapped or around animals that might eat it, even while it's hiding in its shell," said Dimitiri Deheyn, a marine biologist at the Scripps Oceanographic Institute in San Diego. Deheyn and his colleague describe the bioluminescent trick of the snail, also known as Hinea brasiliana, in an upcoming study in the journal Proceedings of the Royal Society B.
The snail's glow-in-the-dark-shell trick was noticed by scientists decades ago, but until now, nobody had any idea what chemicals are involved in generating the glow, or how the shell lights amplifies the light.
"Pinning down what particular biomechanism the snails use to glow is going to be important for the biotech industry," said marine biologist Mark Moline of California Polytechnic State University, who wasn't involved in the study.
When threatened, fingernail-sized H. brasiliana generates pulses of bioluminescent light from a single spot on its mushy body. The light pulses are variable, lasting as short as 1/50th of a second to as long as a few seconds. But the opaque shell diffuses only the blue-green color of light it generates — and no other color — like a highly selective frosted light bulb.
"I wondered, 'How is this possible?' If you put a blue-green laser up to the shell, the whole thing lights up," Deheyn said.
When Deheyn and his lab hit the shell with other colors of light, there was no glow. The same experiments performed on the shells of a sister species didn't make its shells glow using any wavelength of light.
"It's not only the diffusion that's pronounced, but also the amplification. The opaque shell is specific to one color, which shows a very close co-evolution of the bioluminescence and the shell," Deheyn said.
Flashing like a light bulb in dark water may seem like a good way to attract predators, but two different evolutionary ideas back it as an effective protective mechanism. Imagine you're a crab scuttling for some snail food in the dark, Deheyn says, and you find a delicious meal on a rock.
"Suddenly there's a bright flash that makes you go, 'what the hell was that?' It scares you away," Deheyn said. To back up the scenario, he described a recent experiment in which a brittle starfish's bioluminescent glow increased the heart rate of crabs and scared them away.
The snail's flash may attract some animals that would want to eat it. But it could also attract larger predators to eat those animals before they get to the snail.
"Basically, flashing like a light can attract the predator of your predator," Moline said. He'd also like to know if the glow is also used as a form of communication between snails.
Deheyn is eager to unravel the snail's light-making mechanism, primarily to see if it's viable for tagging DNA. Green fluorescent protein genes derived from jellyfish, for example, won their discoverer a 2008 Nobel prize for their role in highlighting genetic activity in experimental animal models.
Until the chemical reaction and the genes responsible are pinned down, however, he'd at least like to show off the snail's super-fast flashing ability in high-definition video.
"The problem there is that it's flashing is too fast," Deheyn said. "We'd need a piece of equipment called an electron-amplified low-light digital camera. It's high-def and high-speed, but it costs $50,000. It's a lot of money."
Images: Courtesy of Dimitri Deheyn. 1) A Hinea brasiliana shell in green laser light, showing the diffusion/glowing effect. 2) The same Hinea brasiliana in normal light.
Posted: 15 Dec 2010 04:27 AM PST
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The urbanization of the southwestern United States is a modern legacy of Manifest Destiny, that nation-shaping vision of an America settled from sea to shining sea. But there was one problem: Westward expansion was predicated on adequate water supplies.
That water was secured through a century of massive government dam-building and irrigation projects, diverting every major and minor water flow in the west. Those days are over. The greatest engineering project in human history has run its course.
"The systems we have built are unsustainable without fundamental change," wrote Peter Gleick, president of the Pacific Institute for Studies in Development, Environment, and Security, in a Dec. 14 Proceedings of the National Academy of Sciences article. "The 20th century approaches used to deal with water challenges are now failing, and new thinking and management approaches are needed."
Gleick's is one of eight new PNAS papers on the future of water in the southwestern United States. The region has become a giant laboratory for arid regions around the world, where limited water resources and growing populations are on a collision course.
The analysis contained in the papers is sobering, but they reinforce what experts have said for years: If people want to live in the desert, they can't avoid its environmental realities.
Image: Grand Coulee Dam./Bureau of the Interior.
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