- Study Blames Plasma Flow for Spotless Sun
- Hagfish May Absorb Carcasses With Their Skin, Gills
- Sight Gets Repurposed in Brains of the Blind
- Tiny Spheres Turn Regular Microscopes Into Nanoscopes
- NASA’s Messenger Spacecraft Zeroes In on Mercury
Posted: 02 Mar 2011 10:07 AM PST
A new computer model suggests the shifting speeds of plasma inside the sun could have shut off sunspots at the end of the most recent solar cycle.
The model, described in the March 3 Nature, attempts to explain why the most recent lull in solar activity was so long and so quiet. The sun's magnetic activity ramps up and calms down on a fairly regular 11-year cycle. The highs are full of sunspots, dark splotches that mark where knots of magnetic field have risen from the solar interior to pop up at the surface like a cork. During the lows, some days have no sunspots at all.
The last solar cycle peaked in 2001 and was supposed to end in 2008. But the sun stayed asleep, displaying a weak magnetic field and an unusually high number of sunspotless days, for an extra 15 months beyond what astronomers expected.
Now, Dibyendu Nandy of the Indian Institute of Science Education and Research and colleagues offer an explanation: A "conveyor belt" of plasma inside the sun ran quickly at first and then slowed down.
Nandy and colleagues at the University of Montana and the Harvard-Smithsonian Center for Astrophysics ran a computer simulation of magnetic flow inside the sun for 210 sunspot cycles. They randomly varied the speed of plasma flow around a loop called the meridional circulation, which carries magnetic fields from the sun's interior to its surface and from the equator to the poles.
Observations suggest that the fastest flow runs around 22 meters per second (49 miles per hour). Nandy's model looked at speeds between 15 and 30 meters per second (33 to 67 miles per hour).
The model found that a fast flow followed by a slow flow reproduced both the weak magnetic field and the dearth of sunspots observed in the last solar minimum.
"This is the first paper that is able to provide a rationale and reproduce two of the main characteristics of the extended solar minimum," said NASA solar physicist Madhulika Guhathakurta, who was not involved in the new work. "For something as complicated as the solar dynamo and solar cycle, this relatively simple model has produced remarkable results."
The model makes physical sense, Nandy says. The seeds of sunspots form when the magnetic field is strong in a region Nandy calls the "creation zone," about a third of the way down into the sun. A faster meridional flow means magnetic plasma spends less time in the creation zone, making a weaker magnetic field and fewer sunspots.
"What you're doing by having a very fast flow early on in the cycle is you're producing a sunspot cycle which is not very strong," he said. "It runs out of steam before the next cycle can start."
A slower flow in the second half delays the onset of the next solar maximum, leaving a sunspot-free gap between the two cycles.
Unfortunately, observations of the sun's surface seem to directly contradict the new model.
"We're in this quandary, this clash between theory and observations," said NASA astronomer David Hathaway, who analyzed 13 years of data from the Solar and Heliospheric Observatory (SOHO) that tracked the movement of charged material near the surface of the sun.
Hathaway agrees that a fast flow can cause weak magnetic fields and fewer sunspots. But his observations, published March 12, 2010 in Science, suggest that the meridional flow was slow in the first half of the last solar cycle, from about 1996 to 2000. Only after the solar maximum did the flow speed up.
"That's where there's a problem," Hathaway said. "We see one thing, they want the opposite to explain the observations."
Nandy and colleagues point out that the SOHO observations only see plasma moving at the surface of the sun, not in the deep interior where sunspots are born. The surface flows might not reflect what's going on underneath, he says.
"In an analogy that you might be able to relate to, one could ask, do ripples on the surface of the sea indicate how ocean currents determine the migration of aquatic animals deeper inside?" Nandy said.
Hathaway argues that changes in the surface should be transmitted to the interior at the speed of sound, and should reach the creation zone in half an hour or less. The disagreement between theory and data means there must be a problem with the models, he says.
"Since 1999, I was a huge champion of these models. They so nicely explained why the sunspot zones drift toward the equator at the speeds they do," he said. "But I'm worried now. I'm really worried."
More observations, especially with NASA's fairly new Solar Dynamics Observatory, should clear things up.
"The sun will ultimately tell us how to resolve this conflict because only it knows what the next cycle will bring," Guhathakurta said.
Image: 1) A spotless sun in September 2008. Credit: SOHO/ESA/NASA. 2) William T. Bridgman (NASA/GSFC), Dibyendu Nandy (IISER Kolkata), Andrés Muñoz-Jaramillo (Harvard Smithsonian Center for Astrophysics) and Petrus C.H. Martens (Montana State University).
"Variations in the Sun's Meridional Flow over a Solar Cycle." David H. Hathaway and Lisa Rightmire. Science, Vol. 327 no. 5971, 12 March 2010. DOI: 10.1126/science.1181990
Posted: 02 Mar 2011 06:45 AM PST
When Pacific hagfish burrow into a carcass and eat their way out, they may be feeding directly through their gills and skin as well as their guts.
Lab tests suggest that hagfish actively take up nutrients through their outer tissues, says fish physiologist Chris M. Wood of McMaster University in Hamilton, Canada. Plenty of marine animals without backbones can feed through their skin, but no one had demonstrated the power in a species so close to fish and modern vertebrates, Wood and his colleagues say in a paper to be published in the Proceedings of the Royal Society B.
"One of the important steps in evolution was abandoning feeding through the skin and concentrating on feeding through the gut," Wood says. Skin with strong barriers against outside substances allowed animals to keep their inner chemistry more separate from the outside world, and thus move into fresh water or onto land.
Hagfishes may not quite count as true modern vertebrates, because their bony skulls don't lead to bony vertebrae making up a backbone. Instead what's called a notochord, a flexible rod of tissue, extends along hagfish backs. Wood calls hagfishes "ancient vertebrates" in honor of their status, currently under debate, as descendants of close relatives to the first fully backboned vertebrates.
The gill pouch of a Pacific hagfish (shown here removed from the fish) may be able to take up nutrients directly. Carol Bucking/Andrea Morash
To test the idea that these almost-vertebrates use skin-feeding powers during full-contact dining, Wood and his colleagues removed bits of skin or gills from the fish but provided glucose to the tissues to keep cells functioning for at least several hours. Then researchers exposed the outside of the tissues to varying solutions of two amino acids and checked the other side of the tissue to see how much of the nutrients passed through, and under what circumstances.
If nutrients were just passing through as if the tissue were a lifeless sheet, then increasing the concentrations of nutrients on one side would have increased the concentrations on the other side. Yet that's not what happened, the researchers found. Rising concentrations reached a plateau on the "inner" side of the hagfish tissue. That's a characteristic sign the tissues are actively taking up a substance, in which case the transport mechanism can get saturated, Wood explains.
Also, taking sodium away from a seawater-like soup of nutrients on the outside of the tissue disrupted passage through the gills. That blockage, Wood says, suggests the hagfish tissue is using a transport system familiar from other organisms, in which sodium needs to bind to a chemical load for the load to be ferried through a tissue.
Another longtime hagfish biologist, Frederic Martini of the University of Hawaii at Manoa, welcomes the attention to the physiology of hagfishes, but says he'd like to see what hagfish would do with other kinds of nutrients besides amino acids.
Also, "what you can show in a lab isn't always functionally relevant," he cautions. In the real world the hagfish may not be doing so much carrion-burrowing, he says, because some populations seem so big he suspects the animals prey on animals still living.
Wood says he's trying to study more natural feeding behavior. In lab tanks, though, hagfish turn out to be uncooperative, picky eaters.
Image: Linda Snook/NOAA/CBNMS
Posted: 01 Mar 2011 01:49 PM PST
In the brains of people blind from birth, structures used in sight are still put to work — but for a very different purpose. Rather than processing visual information, they appear to handle language.
Linguistic processing is a task utterly unrelated to sight, yet the visual cortex performs it well.
"It suggests a kind of plasticity that's even broader than the kinds observed before," said Marina Bedny, a cognitive neuroscientist at the Massachusetts Institute of Technology. "It's a really drastic change. It suggests there isn't a predetermined function an area can serve. It can take a wide range of possible functions."
In a study published Tuesday in the Proceedings of the National Academy of Sciences, Bedny's team monitored the brain activity of five congenitally blind individuals engaged in language-intensive tasks.
Immense neurological plasticity was suggested by research conducted in the late 1990s on "rewired" ferrets — after their optical nerves were severed and rerouted into their auditory cortices, they could still see — but such studies, already ethically troubling in animals, would be unconscionable in humans.
Instead, researchers have used brain imaging to study plasticity resulting from natural sensory deprivation in people. They've found that the visual cortices of blind people become active as they read Braille. It wasn't clear, however, whether this was a function of Braille's spatial demands, which overlap with the spatial aspects of sight, or a radical repurposing of supposedly specialized areas.
'Language is a property that emerges out of the system, rather than a magic-bullet solution from one brain area.'
In Bedny's study, the brains of blind people were analyzed as they listened to complete sentences — a relatively high-level comprehension task. Then they were given lesser linguistic challenges, from listening to lists of unrelated words to hearing sentences played backwards, or trying to comprehend grammatically structured speech containing nonsense words.
The results were twofold. Blind people's visual cortices clearly responded to language, not to space. Moreover, they were most active in response to high-level language demands, just as the brain's "traditional" language centers are.
Implications of the findings are many. Some neuroscientists have proposed that human brains are hard-wired for language, with specific regions evolved for the task. While our brains are obviously well-suited for language, its performance by visual centers suggests that more than hard-wiring is at work.
"Language is a property that emerges out of the system, rather than a magic-bullet solution from one brain area," said Bedny.
Indeed, the brains of congenitally blind people may even hint at the human brain's early state, with "visual" centers open for processing different types of information, and only later becoming involved in vision.
Bodny is now using behavioral tests to investigate in greater detail how blind people process language. "We really want to know what sort of things are blind people better at," she said. "Parsing complicated sentences, with different grammatical structure? Might they be better at resolving ambiguities? If they're listening to several things at a time, can they parse two speech streams rather than one? We don't know the answer to those questions yet."
Image: Helen Keller./Wikimedia Commons.
Citations: "Language processing in the occipital cortex of congenitally blind adults." By Marina Bedny, Alvaro Pascual-Leone, David Dodell-Feder, Evelina Fedorenko, and Rebecca Saxe. Proceedings of the National Academy of Sciences, Vol. 108 No. 9, March 1, 2011.
Posted: 01 Mar 2011 12:06 PM PST
Ordinary microscopes can see 8 times more minutely than known physical limits if miniature glass spheres are sprinkled onto samples, according to a new study.
The cheapest and most common microscopes use white light to magnify objects, but the nature of light and the limitations of our eyes mean those microscopes can't image things smaller than bacteria. Other microscopy techniques, which use lasers, metamaterials and electron beams to image microscopic and nanoscopic worlds, can exceed such limits. But they are difficult, time-consuming and expensive to use, and they can kill live samples.
Glass microspheres about the size of red blood cells, however, described March 1 in Nature Communications, act like tiny magnifying glasses and bring normally invisible structures into sight. Stitching the microspheres' images together with software could create unprecedented white-light photos.
"We have broken the theoretical limits of optical microscopy in white light," said engineer Lin Li of the University of Manchester, a co-author of the study. "The surprising thing is the simplicity. One hundred dollars buys you about 100 million microspheres. Using conventional optical microscopes, almost anyone can do this."
The microspheres may allow microscopes to image viruses in action or the insides of living cells. But the technique may not be as simple to use as the study's authors say.
An independent group of microscope experts at Purdue University, led by physicist and engineer Vladimir Shalaev, couldn't replicate similar images on their first attempt. But Shalaev said they're working with the paper's authors to be certain they did it correctly.
"It can be very hard to reproduce new experiments," Shalaev said. "I have to admit this all sounds too good to be true. But if it is true, it's going to be a huge, huge development."
Microscope resolution is limited by diffraction, or the bending and spreading of light when it encounters obstacles like glass. What we see through microscopes is also restricted by cells in the eye's retina, which can only detect light with wavelengths between 390 and 750 nanometers (between violet and red colors, respectively).
Image: Nature Publishing Group
These limitations prevent us from directly seeing objects smaller than 200 nanometers — just larger than a rabies virus or Mycoplasma, the smallest-known bacteria. Physicists and engineers have circumvented the 200-nanometer barrier with electron microscopy, laser fluorescence and nanoscale metamaterials, but they're expensive, kill live samples or are difficult to use. So Li and his colleagues sought a new method.
In one experiment with glass beads between 2 microns and 9 microns wide, they could see 50-nanometer-wide holes in gold foil, or 8 times beyond the limits of conventional microscopy (image below). They were also able to see the tiny data grooves on a Blu-Ray disc (image above).
"This is quite cheap and easy to implement, while the alternatives are far more expensive and complicated," Li said.
Physicist and engineer Igor Smolyaninov of the University of Maryland, who wasn't involved in the research, has used metamaterials to image objects as small as 70 nanometers in size. He doesn't think the new results are unreliable or untrue, but does see some limitations to the technique.
"They looked at artificial structures. Metal lines, holes and such. These are not a virus or bacteria, which are much, much more difficult to see because they move around," Smolyaninov said. "I tried to do this before but couldn't convince myself it was real. If they can pull it off, I'll be extremely happy."
Image: Top row: Three blocks of lines etched into a metal surface, as seen with a scanning electron microscope, with bunched-up microspheres covering the bottom block (left). The top blocks of lines aren't visible with a light microscope, but under the microspheres they are (right). Bottom row: A gold surface with 50-nanometer holes punched in it, as seen with SEM. A microsphere covers the bottom right (left). The same mesh, with the holes visible under the microsphere with a light microscope (right). Nature Publishing Group
Image: Top row: A Blu-Ray disc's 100- and 200-nanometer grooves under a Scanning Electron Microscope (left). The same grooves are visible using microspheres with a light microscope (right). Bottom row: A 1,000-nanometer star etched into a DVD under SEM (left). The same star as seen through a microsphere (right). (Nature Publishing Group)
Citation: "Optical virtual imaging at 50 nm lateral resolution with a white-light nanoscope." Zengbo Wang, Wei Guo, Lin Li, Boris Luk' yanchuk, Ashfaq Khan, Zhu Liu, Zaichun Chen &
Posted: 01 Mar 2011 10:41 AM PST
NASA's Messenger probe will finally settle into orbit around Mercury on March 17, making it the first spacecraft ever to orbit the innermost planet.
Since its launch in August 2004, Messenger (MErcury Surface, Space ENvironment, GEochemistry and Ranging) has revolutionized the way astronomers think about the closest planet to the sun. Combined with data from the Mariner 10 mission in the '70s, astronomers have mapped 98 percent of the planet's surface. The video above, compiled from photos snapped as Messenger flew by Mercury in 2008, reveals huge impact craters and evidence of recent volcanic eruptions that were thought to be impossible on such a small, hot world. Other on-board instruments measured Mercury's magnetic field and tenuous atmosphere.
But so far, Messenger's trip has been a tease. The spacecraft has spent the last seven years careening around the inner solar system, catching just three quick glances of Mercury as it flew by. Once Messenger gets into orbit, the real work will begin.
"We'll be constantly taking data," said principal investigator Sean C. Solomon, a planetary scientist at the Carnegie Institution of Washington, in a talk Feb. 20 at the meeting of the American Association for the Advancement of Science in Washington, D.C.
One of the most exciting questions Messenger might answer is whether Mercury, like the moon, hides water ice in shadowed craters. Every part of Mercury's surface spends some time in daylight. But there are impact craters near the poles that are in permanent shadow.
"They don't see the sun for millions, probably billions of years," Solomon said. "They're very cold — cold enough to preserve water ice for geologically long periods of time."
Messenger's neutron spectrometer, an instrument that measures the concentrations of different kinds of uncharged particles that are knocked off Mercury's surface by cosmic rays, should be able to detect hydrogen in craters' dark corners, a signature of water ice.
A vent to the north of Mercury's Rachmaninoff crater is "our best example of relatively young volcanism," said principal investigator Sean C. Solomon.
Other spectrometers — one that measures gamma rays and another that measures X-rays — could help figure out what Mercury's surface is made of. The flybys showed definitively that Mercury has had active volcanoes in its recent past, but didn't show the makeup of the stuff that was erupted.
"We're building up a catalog of probable volcanic centers, many of which appear to involve explosive volcanism," Solomon said. "That is a surprise."
On Earth, Mars and the moon, volcanic eruptions are explosive only if the magma is full of volatile materials that form bubbles easily, like nitrogen, carbon dioxide and ammonia. For Mercury to have as many explosive volcanoes as it seems to, it would have to have much higher concentrations of volatile chemicals than Earth.
That's surprising because Mercury was thought to have been extremely hot when it formed, which ought to have forced all the volatiles to evaporate, Solomon said. Instead, Mercury's formation might have been more like the moon's.
"The comparison between Mercury and the moon will have a lot to tell us," Solomon said.
Planetary scientists hope to decipher the planet's inside as well as its outside. Earlier observations show that Mercury's core makes up 60 percent of the planet by mass, making the planet unusually dense. Mercury is also the only planet in our solar system other than Earth whose magnetic field is probably driven by a molten metal core that drives a dynamo. Under Messenger's continuous watch, astronomers can finally figure out what's going on inside Mercury, which can give insight into how all the rocky planets formed in the early solar system.
By the time Messenger gets into orbit, it will have traveled 4.9 billion miles and circled the sun more than 15 times. The spacecraft will end this long journey by cutting its speed by about half-a-mile per second, burning almost a third of its fuel in the process.
The final orbit will be a wide ellipse that takes the spacecraft nearly from pole to pole every 12 hours, just 124 miles from the surface at the nearest point and 9,420 miles at the farthest. This orbit avoids the worst of the scorching temperatures on Mercury's day side, which can reach 700 degrees Fahrenheit.
After it's safely in orbit, Messenger will start returning images April 4. It will stay in orbit for one full Earth year, or four of Mercury's 88-day years. An extended mission could keep Messenger in orbit for another year or two after that, if NASA's budget allows. When fuel or funding runs out, the spacecraft will crash into Mercury's surface.
Video: NASA/Sean Solomon. Images: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington
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