Archive for June 2011
Discovery Adds Mystery to Earth’s Genesis
Earth and the other rocky planets aren’t made out of the solar system’s original starting material, two new studies reveal.
Scientists examined solar particles snagged in space by NASA’s Genesis probe, whose return capsule crash-landed on Earth in 2004. These salvaged samples show that the sun’s basic building blocks differ significantly from those of Earth, the moon and other denizens of the inner solar system, researchers said.
Nearly 4.6 billion years ago, the results suggest, some process altered many of the tiny pieces that eventually coalesced into the rocky planets, after the sun had already formed.
“From any kind of consensus view, or longer historical view, this is a surprising result,” said Kevin McKeegan of UCLA, lead author of one of the studies. “And it’s just one more example of how the Earth is not the center of everything.”
Salvaging the samples
The Genesis spacecraft launched in 2001 and set up shop about 900,000 miles (1.5 million kilometers) from Earth. It spent more than two years grabbing bits of the solar wind, the million-mph stream of charged particles blowing from the sun.
The idea was to give scientists an in-depth look at the sun’s composition, which in turn could help them better understand the formation and evolution of the solar system.
To that end, Genesis sent its sample-loaded return capsule back to Earth in September 2004. But things didn’t go well; the capsule’s parachute failed to deploy, and it smashed into the Utah dirt at 190 mph (306 kph).
While some of Genesis’ samples were destroyed in the crash, others were salvageable, as the two new studies show. Two different research teams looked at the solar wind particles’ oxygen and nitrogen — the most abundant elements found in Earth’s crust and atmosphere, respectively.
And they did so with a great deal of care, knowing that the crash had limited their supplies of pristine solar material.
“The stakes were raised on the samples that did survive well,” McKeegan told SPACE.com. “There wasn’t as much to go around.”
The Genesis return capsule slammed into the Utah dirt at nearly 200 mph on Sept. 8, 2004 when its parachute failed to deploy.
CREDIT: NASA/JPL
Analzying oxygen
McKeegan and his team measured the abundance of solar wind oxygen isotopes. Isotopes are versions of an element that have different numbers of neutrons in their atomic nuclei. Oxygen has three stable isotopes: oxygen-16 (eight neutrons), oxygen-17 (nine neutrons) and oxygen-18 (ten neutrons).
The researchers found that the sun has significantly more oxygen-16, relative to the other two isotopes, than Earth. Some process enriched the stuff that formed our planet — and the other rocky bodies in the inner solar system — with oxygen-17 and oxygen-18 by about 7 percent.
While scientists don’t yet know for sure how this happened, they have some ideas. The leading contender, McKeegan said, may be a process called “isotopic self-shielding.”
About 4.6 billion years ago, the planets had not yet coalesced out of the solar nebula, a thick cloud of dust and gas. Much of the oxygen in this cloud was probably bound up in gaseous carbon monoxide (CO) molecules.
But the oxygen didn’t stay bound up forever. High-energy ultraviolet light from the newly formed sun (or nearby stars) blasted into the cloud, breaking apart the CO. The liberated oxygen quickly glommed onto other atoms, forming molecues that eventually became the rocky building blocks of planets.
Photons of slightly different energy were required to chop up the CO molecules, depending on which oxygen isotope they contained. Oxygen-16 is far more common than either of the other two, so there would have been much more of this substance throughout the solar nebula, researchers said.
The result, the self-shielding theory goes, is that many of the photons needed to break up the oxygen-16 CO were “used up,” or absorbed, on the edges of the solar nebula, leaving much of the stuff in the cloud’s interior intact.
By contrast, relatively more of the photons that could strip out oxygen-17 and oxygen-18 got through to the inner parts of the cloud, freeing these isotopes, which were eventually incorporated into the rocky planets. And that, according to the theory, is why the sun and Earth’s oxygen isotope abundances are so different.
“The result that we’re publishing this week gives support to the self-shielding idea,” McKeegan said. “But we don’t know the answer yet.”
Nitrogen, too
In a separate study, another research team led by Bernard Marty of Nancy University in France analyzed the nitrogen isotopes in Genesis’ samples. (Nitrogen has two stable isotopes: nitrogen-14, which has seven neutrons, and nitrogen-15, which has eight.)
Marty and his colleagues found an even more dramatic difference than McKeegan’s group did: The solar wind has about 40 percent less nitrogen-15 (compared to nitrogen-14) than do samples taken from Earth’s atmosphere.
Previous studies had hinted that the sun’s nitrogen might be very different from that of Earth, Mars and other rocky bodies in the inner solar system, Marty said. But the new study establishes this firmly.
“Before Genesis and the present measurement of the N isotopic composition of the solar wind and by extension of the sun, it was not possible to understand the logic of such variations,” Marty told SPACE.com in an email interview. “Now we understand that the starting composition, the solar nebula, was poor in 15N, so that variations among solar system objects are the result of mixing with a 15N-rich end-member.”
As to how this enrichment of nitrogen-15 could have happened, Marty as well suggests some type of self-shielding as a possible mechanism. But it’s not a certainty.
“This is a scenario that is consistent with present-day observations,” he said. “We cannot eliminate yet the possibility that these 15N-rich compounds were imported from outer space as dust in the solar system.”
The new results also suggest that most nanodiamonds — tiny carbon specks that are a major component of stardust — likely formed in our own solar system, because they share similar nitrogen isotope ratios with the sun. Some scientists have regarded nanodiamonds as being primarily presolar, thinking they were ejected from other stellar systems by supernova explosions.
Both studies appear in the June 23 issue of the journal Science.
Genesis’ legacy
The two new studies should help scientists get a better understanding of the solar system’s early days, researchers said.
And the results should help rehabilitate the reputation of the $264 million Genesis mission, showing that the capsule crash didn’t render it a failure, McKeegan said.
“We managed to accomplish all the science that we set out to do, all the important stuff,” he said. “The enduring image in everybody’s mind — the picture of the crashed spacecraft in the desert — will be more of a footnote instead of the primary thing that people remember. That’s my hope, anyway.”
Via Space
Solstice Sun Storm May Spark Dazzling Northern Lights Today
Norwegian photographer and skywatcher Terje Sorgjerd created an amazing video of the March 2011 auroras, or northern lights, which appear in this still from his project, entitiled “The Aurora.” CREDIT: Terje Sorgjerd
A wave of sun particles unleashed during a strong solar flare this week is arriving at Earth today (June 24) and could touch off a dazzling northern lights display, NASA officials say.
The solar storm occurred Tuesday, June 21, during Earth’s solstice, which marked the first day of summer in the Northern Hemisphere and the start of winter in the Southern Hemisphere.
The storm triggered a powerful explosion on the sun, called a coronal mass ejection, which sent a vast wave of solar particles directly at Earth at a speed of about 1.4 million mph (2.3 million kph). Those particles are now buffeting Earth’s magnetic field in interactions that could amplify the planet’s polar auroras, also known as the northern and southern lights.
“High-latitude sky watchers should be alert for auroras,” officials with NASA’s Goddard Space Center said in an update today.
The SOHO sun observatory caught this view of a large solar flare and coronal mass ejection (top of sun) erupting from the sun’s surface early June, 21, 2011. CREDIT: SOHO/NASA/ESA
Supercharged auroras
Auroras occur when solar wind particles collide with atoms of oxygen and nitrogen in Earth’s upper atmosphere. The interaction excites the atoms, which then emit light (the aurora) as they return to their normal energy level.
Tuesday’s solar flare registered as a class C7.7 flare (C-class flares are the weakest types of flares), but lasted for several hours. There are three classes of solar flares. M-class solar flares are medium-strength flares, while the most intense solar storms register as X-class flares.
There is a 30 percent to 35 percent chance of a minor geomagnetic storm in Earth’s atmosphere today from this week’s storm, NASA officials said.
A broadly widening cloud of particles, observed by SOHO’s C3 coronagraph, rushed away from the Sun as a coronal mass ejection (CME) erupted over about 12 hours (June 14, 2011). Data from the Solar Dynamics Observatory shows an eruptive prominence breaking away from the Sun about where the event originated. While the originating event did not appear to be substantial, the particle cloud was pretty impressive. The bright circle with an extending horizontal line (above and left of the blue occulting disk) is a distortion caused by the brightness of planet Mercury. CREDIT: SOHO (ESA & NASA)
The active sun
This week’s solar flare was detected by the space-based Solar and Heliospheric Observatory (SOHO) operated by NASA and the European Space Agency. It came just weeks after another strong solar flare on June 7, which unleashed a massive coronal mass ejection that stunned astronomers with its intensity.
The June 7 event kicked up a wave of plasma that rained back down on the sun over an area 75 times the width of Earth. The leading edge of the particles that erupted from the sun were traveling at about 3.5 million mph (5.7 million kph), SOHO officials have said.
Another coronal mass ejection on June 14 unleashed an eerie wave of material that formed a partial halo as it expanded into space.
The most severe solar storms, when aimed at Earth, can pose a danger to astronauts in space, satellites and even ground-based communications and power systems. This week’s solar flare, however, is not powerful enough to pose a serious risk, NASA officials said.
The sun is currently in an active period of its 11-year solar cycle. NASA and other space and weather agencies are keeping a close watch on the sun using space-based observatories, satellites and ground-based monitoring systems.
Via Space
Ice spray shooting out of Saturn moon points to a giant ocean lurking beneath its surface
Scientists have collected the strongest evidence yet that Saturn moon Enceladus has a large saltwater ocean lurking beneath its surface.
Samples of ice spray shooting out of the moon have been collected by the Nasa’s Cassini spacecraft during one of its frequent Saturn fly-bys.
The plumes shooting water vapor and tiny grains of ice into space were originally discovered emanating from Enceladus – one of 19 known moons of Saturn – by the Cassini spacecraft in 2005.
Samples of ice spray shooting out of Saturn moon Enceladus have been collected by Nasa’s Cassini spacecraft. Scientists believe it is the strongest evidence yet that Enceladus has a large saltwater ocean lurking beneath its surface
They were originating from the so-called ‘tiger stripe’ surface fractures at the moon’s south pole and apparently have created the material for the faint E Ring that traces the orbit of Enceladus around Saturn.
During three of Cassini’s passes through the plume in 2008 and 2009, the Cosmic Dust Analyser (CDA) on board measured the composition of freshly ejected plume grains.
The icy particles hit the detector’s target at speeds of up to 11miles-per-second, instantly vaporising them. The CDA separated the constituents of the resulting vapor clouds, allowing scientists to analyse them.
The ice grains found further out from Enceladus are relatively small and mostly ice-poor, closely matching the composition of the E Ring. Closer to the moon, however, the Cassini observations indicate that relatively large, salt-rich grains dominate.
Lead researcher Frank Postberg, of the University of Heidelberg in Germany, said: ‘There currently is no plausible way to produce a steady outflow of salt-rich grains from solid ice across all the tiger stripes other than the salt water under Enceladus’ icy surface.’
Plumes, both large and small, spray water ice from multiple locations along the ‘tiger stripes’ near the south pole of Enceladus.
Co-author Sascha Kempf, of the University of Colorado Boulder, added: ‘The study indicates that “salt-poor” particles are being ejected from the underground ocean through cracks in the moon at a much higher speed than the larger, salt-rich particles.
‘The E Ring is made up predominately of such salt-poor grains, although we discovered that 99 per cent of the mass of the particles ejected by the plumes was made up of salt-rich grains, which was an unexpected finding.
‘Since the salt-rich particles were ejected at a lower speed than the salt-poor particles, they fell back onto the moon’s icy surface rather than making it to the E Ring.’
According to the researchers, the salt-rich particles have an ‘ocean-like’ composition that indicates most, if not all, of the expelled ice comes from the evaporation of liquid salt water rather than from the icy surface of the moon.
When salt water freezes slowly the salt is ‘squeezed out’, leaving pure water ice behind. If the plumes were coming from the surface ice, there should be very little salt in them, which was not the case, according to the research team.
Dwarfed: Enceladus can be seen near Saturn’s south pole at the bottom of this image
The scientists believe that perhaps 50 miles beneath the surface crust of Enceladus a layer of water exists between the rocky core and the icy mantle that is kept in a liquid state by gravitationally driven tidal forces created by Saturn and several neighboring moons, as well as by heat generated by radioactive decay.
It is thought that roughly 440lbs of water vapor are lost every second from the plumes, along with smaller amounts of ice grains.
Calculations show the liquid ocean must have a sizable evaporating surface or it would easily freeze over, halting the formation of the plumes.
‘This study implies that nearly all of the matter in the Enceladus plumes originates from a saltwater ocean that has a very large evaporating surface,’ said Dr Kempf.
The team’s study is published in the journal Nature.
Via DailyMail
Biological gems found in Philippines
Click through a slideshow featuring the new species.
“The Philippines is one of the hottest of the hotspots for diverse and threatened life on Earth,” Terrence Gosliner, dean of science and research collections at the California Academy of Sciences and leader of the 2011 Philippine Biodiversity Expedition, said today in a news release about the findings. “Despite this designation, however, the biodiversity here is still relatively unknown, and we found new species during nearly every dive and hike as we surveyed the country’s reefs, rainforests, and the ocean floor.”
The 42-day expedition was launched in late April and focused on Luzon, the largest island in the Philippine archipelago, as well as the surrounding waters. In cooperation with more than two dozen colleagues from the Philippines, the academy’s scientists surveyed a wide range of ecosystems and shared their findings with local communities and conservationists.
Among the suspected new species are dozens of types of insects and spiders, deep-sea corals, sea pens, sea urchins and more than 50 kinds of sea slugs. Scientists say they came across a new kind of cicada that makes a distinctive “laughing” call, a starfish that eats only sunken driftwood, and a deep-sea swell shark that sucks water into its stomach to bulk up and scare off predators.
When the expedition ended, the scientists combined their data and identified their top conservation priorities — expansion of marine protected areas, plus reforestation to reduce sedimentation damage to coral reefs. The academy said reduction of plastic waste was also a priority, because plastic litter was pervasive throughout the marine environment, even on the ocean floor at depths of more than 6,000 feet.
Over the coming months, the expedition’s scientists will be analyzing their specimens with the aid of microscopes and DNA sequencing equipment to confirm their discoveries.
The academy’s expedition is one of many efforts around the globe to document and safeguard biodiversity — in part because yet-to-be-discovered species may point the way to commercially useful drugs or technologies, in part because they may turn out to be key to an ecosystem’s health, and in part because they’re beautiful, exotic or just plain odd.
“The species lists and distribution maps that we created during this expedition will help to inform future conservation decisions and ensure that this remarkable biodiversity is afforded the best possible chance of survival,” Gosliner said.
Via MSNBC/Alan Boyle
Fusion Experiment Faces New Hurdles
The world’s most-ambitious nuclear experiments have escalated at Lawrence Livermore National Laboratory.
Federal researchers there are seeking to fuse some of the lightest atoms in the universe to study — and hopefully harness — the type of energy produced by hydrogen bombs and the sun.
The tests were delayed six months while safety devices were installed to protect workers from radiation at the National Ignition Facility, a stadium-sized laboratory that contains 192 lasers trained on a target the size of a BB. The goal is to generate temperatures of more than 100 million degrees to fuse hydrogen atoms and release nuclear energy.
Scientists describe this process, which they hope to achieve next year, as the creation of a miniature star on earth.
But the $3.5 billion ignition facility, derided by some critics as taxpayer-financed science fiction, is running into new challenges that may further delay and perhaps scuttle its goal.
Among those challenges is the unanticipated presence of particles that clog filters designed to prevent the escape of radioactive material. Officials have proposed bypassing the filters for some experiments and venting radioactive particles directly into the air.
Officials say the radiation risks to people living in the surrounding area and to Lawrence Livermore researchers not involved with the experiments will be negligible. But according to a worst-case scenario outlined in a draft environmental report, an average of one worker involved in the experiments could die every 18 years from cancer caused by radiation exposure.
Tri-Valley CAREs, a watchdog group that monitors Lawrence Livermore, argues that the National Nuclear Security Agency, which financed construction of the facility, should not allow an increase in the amount of radiation produced by the fusion project.
“There is no safe level of exposure,” said Marylia Kelley, the group’s executive director.
The ignition facility was designed to help the United States government monitor the safety of nuclear weapons without having to test them. One of its primary missions is to help improve the United States’ weapons arsenal, but officials also describe the facility as an effort to revolutionize nuclear power.
If researchers can fuse atoms and control the energy that is released, an era of abundant carbon-free power could dawn. The technology would minimize the waste and storage issues faced by fission-based nuclear power plants, which split heavy atoms into smaller ones.
The tipping point for nuclear fusion is “ignition,” the moment when the lasers release the same amount of energy that is required to power them.
But that goal has remained elusive.
“If it was easy, we would have done it 50 years ago,” said Doug Eddy, a senior nuclear security agency operations manager working on the project.
Mr. Eddy said the ignition facility was engaged in a “tuning campaign,” raising the amount of fuel used and the amount of energy generated by the lasers.
“You keep bringing it up a bit more and more and more,” he said. “You don’t want to go big-time straight off the bat.”
Researchers have discovered that more power will be needed for some tests than first thought, Mr. Eddy said. They propose nearly tripling the amount of laser power to 120 megajoules, roughly the equivalent amount of energy produced by 50 pounds of TNT, which will increase radiation levels.
The types of hydrogen that will be fused are called deuterium and tritium. Tritium is radioactive, and fine molecular filters are installed at the facility to prevent it from escaping.
But the tritium is proving difficult to manage. The molecules are so small that other tiny atoms are also captured in the filters. Workers frequently enter the experiment chamber to change the clogged filters.
To solve that problem, officials propose allowing more tritium to accumulate before the filters are removed and sent to Nevada as low-level radioactive waste.
More controversially, the officials have proposed bypassing the filters during some experiments and venting tritium through an exhaust system into the air.
Tritium dissolves in water, persists for decades in the environment and can cause cancer.
“It will bind to DNA, so it gets pretty much everywhere in the body once it’s been absorbed,” said Mark Little, a senior scientist at the National Cancer Institute who has published papers dealing with tritium’s hazards. “With large quantities, damage can be done. As long as the releases are kept within mandatory limits, I would imagine the risks are small.”
Officials at the Department of Energy say the tritium releases at Lawrence Livermore would remain below safety limits set by the Environmental Protection Agency. But Tri-Valley CAREs points to a long list of tritium accidents and airborne releases from Livermore facilities, which have caused radioactive material to accumulate in Livermore’s water, food, honey and wine.
“When tritium gets into the environment and it’s on top of radiation being released from other parts of the laboratory, it potentially increases the dose and potentially increases the risk,” Ms. Kelley said.
And tritium is not her organization’s only concern, she added.
When tritium and deuterium fuse to create helium, a neutron is squeezed out and radiation is released. The neutrons can seep out of the building and rise into the atmosphere, where they cause additional radiation called skyshine to rain back down.
“If it’s high-enough energy, it can scatter and go up to the atmosphere, scatter in the atmosphere and bounce back down,” Mr. Eddy said. “Where it will scatter down is mostly around the site, but there’s no guarantee.”
Officials said that they would determine an area around the Livermore building where radiation might exceed federal safety standards and that Livermore personnel not involved with the research would be evacuated from those areas. Employees will be warned not to enter the area until after the experiment.
Despite several delays, Mr. Eddy said he was confident that ignition would occur next year. But some scientists question whether ignition will ever be possible.
“It’s a tough job, and some of the peer review questioned whether it would work,” said Frank von Hippel, a Princeton University physics professor and former science adviser to President Bill Clinton. “I think there are still skeptics out there.”
Via NYTimes
Sci-fi master turns into film character
The latest movie based on Philip K. Dick’s offbeat science-fiction stories features one especially offbeat character … named Philip K. Dick.
“Radio Free Albemuth,” an indie film that is getting a sneak-preview screening tonight at the Experience Music Project and Science Fiction Museum in Seattle, incorporates some of the wilder parts of Dick’s biography — including his belief that he was getting information from a superintelligent, extraterrestrial entity called VALIS (Vast Active Living Intelligence System).
“Dick was very skeptical of these experiences,” John Alan Simon, the screenwriter, director and producer for “Radio Free Albemuth,” told me this week. “Some people think he was crazy. But if he was, he was a very lucid, skeptical kind of crazy.”
Simon will participate in a Q&A at the Seattle screening, which kicks off a weekend celebration for new inductees in the Science Fiction Hall of Fame. Dick, who passed away in 1982, is already in that Hall of Fame — in part because his works have been such a fertile ground for sci-fi film adaptations such as “Blade Runner,” “Minority Report,” “Total Recall,” ” A Scanner Darkly” and “The Adjustment Bureau.”
Unlike those tales, “Radio Free Albemuth” is set in an alternate-reality past rather than the future: a past in which a Nixon-like president burns the Watergate tapes and creates a conspiracy theory aimed at keeping him in office. Meanwhile, VALIS transmits messages down to a resistance movement. Philip K. Dick (played by Shea Whigham in the movie) is among those who are drawn into the resistance, along with the story’s protagonist (Nicholas Brady, played by Jonathan Scarfe) and a singer whose songs are encoded with subliminal messages.
The singer’s role is filled by Alanis Morissette, the Canadian-American singer/actress who just happened to play God in the 1999 film “Dogma.” Whigham is best-known for his role in the HBO series “Boardwalk Empire,” while Scarfe has appeared in a number of TV series including “E.R.” and “CSI: Miami.” Most of the actors have had meaty roles in films and on TV, but Simon said “Radio Free Albemuth” is more about Dick’s vision rather than about big-name movie stars.
“The movie asks a lot of very, very interesting questions about ‘What is religion,’ and ‘What is God,’ and ‘What do you do if God begins sending messages to you?'” he told me. “What if God were an alien, and what if all the great religious movements of all time were inspired by the same over-intelligence in the universe? I found that a very intriguing notion. … The movie is skeptical of answers, the same way Philip K. Dick was skeptical of religion.”
Another theme in the film is sparked by the conflict between the government and the resistance. “It’s the message of ‘1984,’ the message of Huxley’s ‘Brave New World,’ which is the importance of the individual over the supremacy of the state,” Simon said. “That’s a timeless message.”
But the director also emphasized that the film wasn’t just a philosophical treatise. “It is, at the end of the day, an exciting science-fiction thriller. … not that dissimilar from ‘The Da Vinci Code,'” Simon said.
“Radio Free Albemuth” has been making its way through the film-festival circuit, and so far it’s gotten awards as well as accolades for staying true to the spirit of Dick’s work, even if that means the movie gets a little talky at times.
“While watching ‘Radio Free Albemuth’ has made me wonder whether stage or radio may be a better platform for a Dick adaptation, I came away from the film with that unique Dickian sense of unease, insignificance and wonder, and it’s good to see his work reproduced so faithfully on the big screen, flawed or not,”Quiet Earth’s” Ben Austwick wrote.
Simon said he hopes “Radio Free Albemuth” will build on the same sort of grass-roots interest that turned “What the Bleep Do We Know” into such a phenomenon seven years ago.
The movie seems certain to win over the sci-fi master’s hard-core fans, who call themselves “Dick-heads.” But will the wider public dial in to “Radio Free Albemuth” as well? Stay tuned. …
Via MSNBC
Asteroid Heading Near Earth
NASA, which is not as busy scheduling space launches anymore, is focusing a great deal of energy on an asteroid about the size of a tour bus that is expected to make an extremely close pass by the Earth on Monday.
On June 27 the asteroid should fly 7,500 miles above the Earth’s surface. The asteroid, named 2011 MD, was discovered last Wednesday by a pair of roboti telescopes in New Mexico that constantly scan the skies. NASA estimates that an object this size comes this close to Earth on an average of every six years.
NASA said for several hours prior to its closest approach, 2011 MD will be visible in moderately large amateur telescopes.
Of the thousands of objects discovered by NASA, approximately 827 are asteroids with a diameter of approximately a half-mile or larger. They’re classified as Potential Hazardous Asteroid. NASA is planning to launch a probe to visit one of the dangerous objects before the asteroid makes its way near the Earth.
Via BoiseWeekly
Acoustic ‘cloaking device’ shields objects from sound
Scientists have shown off a “cloaking device” that makes objects invisible – to sound waves.
Such acoustic cloaking was proposed theoretically in 2008 but has only this year been put into practice.
Described in Physical Review Letters, the approach borrows many ideas from attempts to “cloak” objects from light.
It uses simple plastic sheets with arrays of holes, and could be put to use in making ships invisible to sonar or in acoustic design of concert halls.
Much research has been undertaken toward creating Harry Potter-style “invisibility cloaks” since the feasibility of the idea was first put forward in 2006.
Those approaches are mostly based on so-called metamaterials, man-made materials with properties that do not occur in nature. The metamaterials are designed such that they force light waves to travel around an object; to an observer, it is as if the object were not there.
But researchers quickly found out that the mathematics behind bending these light waves, called transformation optics, could also be applied to sound waves.
“Fundamentally, in terms of hiding objects, it’s the same – how anything is sensed is with some kind of wave and you either hear or see the effect of it,” said Steven Cummer of Duke University. “But when it comes to building the materials, things are very different between acoustics and electromagnetics.
“The thing you need to engineer into the materials is very different behaviour in different directions that the wave travels through it,” he told BBC News.
In 2008, Dr Cummer first described the theory of acoustic cloaking in an article in Physical Review Letters, and earlier this year a group from the University of Illinois Urbana-Champaign demonstrated the first practical use of the theory in an article in the same journal.
That work showed acoustic invisibility in a shallow layer of water, at ultrasound frequencies above those we can hear.
Now, Dr Cummer and his colleagues have shown off an acoustic cloaking technique that works in air, for audible frequencies between one and four kilohertz – corresponding to two octaves on the higher half of a piano.
It works by using stacked sheets of plastic with regular arrays of holes through them. The exact size and placement of the holes on each sheet, and the spacing between the sheets, has a predictable effect on incoming sound waves.
When placed on a flat surface, the stack redirects the waves such that reflected waves are exactly as they would be if the stack were not there at all.
That means that an object under the stack – in the team’s experiments, a block of wood about 10cm long – would not “hear” the sound, and any attempts to locate the object using sound waves would not find it.
“How the sound reflects off this reflecting surface with this composite object on it – which is pretty big and has a cloaking shell on it – really reflects… just like a flat surface does,” Dr Cummer said.
Hole poking
Ortwin Hess, a director of Imperial College London’s Centre for Plasmonics and Metamaterials, called the work “a really remarkable experimental demonstration”.
“It shows very nicely that although acoustic and electromagnetic waves are very different in nature, the powers of transformation optics and transformation acoustics are [similar] – I’m quite pleased that there’s activity on both ends.”
Professor Hess pointed out that the demonstration was for very directed sound waves, and only in two dimensions, but the most notable aspect of the approach was its simplicity.
“It’s almost like someone could take a pencil and poke holes in a particular way in the plastic,” he told BBC News.
“It’s a bit more challenging for three dimensions. I don’t see any reason why it shouldn’t be possible but it won’t be just an afternoon’s work.”
The work shows that an object can be hidden from sonar, and protected from incoming sound, but the same principles could be applied in the other direction – that is, containing or directing the sound within a space, for instance in soundproofing a studio or fine-tuning the acoustics of a concert hall.
Via BBC News
Mercury’s origins may differ from sister planets
Mercury’s origins may be very different from its sister planets, including Earth, based on early findings that show surprisingly rich deposits of sulfur on the ground, scientists said on Thursday.
Early findings from the first spacecraft to orbit Mercury is forcing scientists to rethink how the planet closest to the sun formed and what has happened to it over the past 4 billion years.
NASA’s Mercury Surface, Space Environment, Geochemistry and Ranging spacecraft — nicknamed Messenger — is three months into a planned year-long mission. It has also uncovered evidence of a lopsided magnetic field and regular bursts of electrons jetting through the magnetosphere.
“It’s almost a new planet because we’ve never had this kind of observatory before,” said lead researcher Sean Solomon of the Carnegie Institution of Washington, D.C.
Volcanoes appear to have played a rather large role in shaping Mercury, providing fresh material to fill its cratered face, but also possibly providing an unexpected supply of sulfur to the surface, a finding that suggests Mercury may have had different building blocks than Venus, Earth and Mars.
Scientists expected that Mercury, which is believed to have formed in the hottest, densest part of the original solar nebula, wouldn’t have had the right temperatures to hang on to lighter-weight materials like sulfur.
“Elements like that are usually lost in space,” Solomon said. “The fact that we see sulfur from the surface points strongly that we had sulfur gases coming out.
“All of our simple ideas … a hot planet, easily depleted of volatiles … are not turning out to be the simple story we thought,” Solomon added.
New images from Messenger reveal a massive plain of ancient lava flow, the largest of which spans 400 million square kilometers, about half the size of the continental United States.
Another surprise was the planet’s lopsided magnetic field, which is stronger in the north than the south. Scientists can’t yet account for the asymmetry, but one theory is that the planet’s magnetic field is in the processing of flipping.
Mercury is the only terrestrial body besides Earth that has a magnetic field and one of the prime goals of the Messenger mission is to figure out how Mercury, which sports a massive iron core, was assembled. Scientists believe Mercury’s core, like Earth’s, is responsible for generating its magnetic field
Messenger also has been monitoring regular outbursts of electrons in Mercury’s magnetosphere. Hints of the phenomenon were first detected by NASA’s Mariner 10 probe, which flew past Mercury in 1974.
“We’re seeing these seeing these very dynamic phenomena in the magnetosphere. It’s very surprising and energetic,” Solomon said.
Still to come: measurements to reveal if Mercury hides ice insides its permanently shadowed craters.
Via DiscoveryOn
Cassini finally catches Helene
The Cassini team has had a wretched time trying to get pictures of Helene in the past, but their streak of bad luck is over. Helene is one of the four “co-orbital” moons in the Saturn system, which occupy meta-stable spots in the leading and trailing Lagrangian points on the orbits of Tethys and Dione.
It’s the biggest of the four, but that’s not saying much; it’s only about 36 by 32 by 30 kilometers across, so it’s in the same general size range as Phobos.
It’s proven challenging to predict where it’s going to be with enough accuracy to make sure Cassini can capture it in its camera field of view, with the result that nearly every imaging sequence that Cassini has been commanded to take of Helene has seen the moon wander out of the field of view at one time or another.
Well, Cassini has finally achieved gorgeous global imaging of Helene with a spectacular flyby on Saturday, in which they absolutely nailed the spacecraft’s pointing and got Helene to pose prettily for the camera from beginning to end of the encounter. And what a wacky, wacky world Cassini has revealed Helene to be!!
Helene in enhanced color |
We saw these gullies on the previous close flyby but this is a much better view. There are two things that are very strange about these gullies. One is to see them at all. Features like this, if seen on Earth or even Mars, would be assumed to have something to do with water, but there is no possibility of liquid water on Helene (though it is likely made mostly of rock-hard water ice). These gullies must form by a dry process in which material — likely very powdery dusty stuff — cascades toward local topographic lows.
The other thing that is very strange is the strong difference in color between the higher-standing stuff and the smooth gully slide areas in between them. Others of Saturn’s moons have some color variations across their surfaces, but really I don’t know of one other than Iapetus where there are such sharp boundaries between one color of material and another. The color differences are most obvious on the right side of the image, where the Sun hits Helene directly and there aren’t many cast shadows; color differences fade as you get toward the lower and lower light near the terminator at the left side of the image. Those color differences are what make this movie version of the flyby images appear to “beat” — every time an image is shot through a short-wavelength ultraviolet filter, the inter-gully ridge areas darken substantially.
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Cassini’s June 2011 Helene flyby (bounces 3 times) The surface appears to “beat” with contrast changes because Cassini was cycling through different filters to take the images. In short-wavelength filters, the areas between gullies are darker than the smooth gully floors, while there is less contrast between them in the longer-wavelength filters. To generate this animation, I aligned the frames and rotated them 180 degrees to place north up. Then I used the Photoshop “dust and scratches” filter to remove most of the cosmic ray hits. This also removed a bit of detail from gully areas, unfortunately, but it saved me a lot of time and effort. I cleaned up the worst remaining cosmic ray hits using the clone tool. I adjusted the contrast to push black space to completely black and to bring out some more detail in shadowed areas. As you watch the animation, try focusing on different areas. Like the massive crater in the north that is partially illuminated in the opening of the animation. Or the faceted shape of the moon, which suddenly brings a huge sunlit face into view. Also try to see if you can see the shadows move across Helene’s face as it rotates; most of the apparent motion is due to Cassini’s motion, but some is Helene rotating on its axis. Credit: NASA / JPL / SSI / animation by Emily Lakdawalla |
There are a couple of dozen little tiny bowl-shaped impact craters scattered across the image, and there are eroded features that are almost certainly older, larger impact craters, but really there are not very many craters considering Helene’s location in the shooting gallery of the Saturn system, so whatever process makes these gullies has also very likely been active recently and has wiped away past smaller craters. This inference becomes even more interesting when you look at the opposite face of Helene, the one that faces out from Saturn, which is heavily cratered as you might expect. Ian Regan put together a really nice comparison of Cassini’s various views of Helene’s two faces:
Cassini’s views of Helene through March 2010 |
Why are Helene’s two sides so different? It’s just one of many mysteries that Cassini’s science team still has to solve.
Via Planetary
Teperdexrian 