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1 Nov

New Property of Flames Sparks Advances in Technology

Chemists at UCL have discovered a new property of flames, which allows them to control reactions at a solid surface in a flame and opens up a whole new field of chemical innovation. Published in the journal Angewandte Chemie, authors of the new study have discovered their previous understanding of how flames interact with a solid surface was mistaken. For the first time, they have demonstrated that a particular type of chemistry, called redox chemistry, can be accurately controlled at the surface. This finding has wide implications for future technology, for example in detection of chemicals in the air, and in developing our understanding of the chemistry of lightning. It also opens up the possibility of being able to perform nitrogen oxide and carbon dioxide electrolysis at the source for the management of green house gases. Results of the study show that depending on the chemical make-up of the flame, scientists can record a distinctive electrical fingerprint. The fingerprint is a consequence of the behaviour of specific chemical species at the surface of a solid conducting surface, where electrons can exchange at a very precise voltage. Dr Daren Caruana, from the UCL Department of Chemistry, said: "Flames can be modelled to allow us to construct efficient burners and combustion engines. But the presence of charged species or ions and electrons in flames gives them a unique electrical property." Dr Caruana added: "By considering the gaseous flame plasma as an electrolyte, we show that it is possible to control redox reactions at the solid/gas interface." The team developed an electrode system which can be used to probe the chemical make-up of flames. By adding chemical species to the flame they were able to pick up current signals at specific voltages giving a unique electrochemical finger print, called a voltammogram. The voltammograms for three different metal oxides -- tungsten oxide, molybdenum oxide and vanadium oxide -- are all unique. Furthermore, the team also demonstrated that the size of the current signatures depend on the amount of the oxide in the flame. Whilst this is possible and routinely done in liquids, this is the first time to be shown in the gas phase. UCL chemists have shown that there are significant differences between solid/gas reactions and their liquid phase equivalents. Liquid free electrochemistry presents access to a vast number of redox reactions, current voltage signatures that lie outside potential limits defined by the liquid. The prospect of new redox chemistries will enable new technological applications such as electrodeposition, electroanalysis and electrolysis, which will have significant economic and environmental benefits. Dr Caruana said: "The mystique surrounding the properties of fire has always captivated our imagination. However, there are still some very significant technical and scientific questions that remain regarding fire and flame. "
1 Nov

On the Origin of Music by Means of Natural Selection

Do away with the DJ and scrap the composer. A computer program powered by Darwinian natural selection and the musical tastes of 7,000 website users may be on the way to creating a perfect pop tune, according to new research published June 18 in the journal Proceedings of the National Academy of Sciences (PNAS). Scientists from Imperial College London have devised a way of producing music from noises without a composer. They programmed a computer to produce loops of random sounds and analyse the opinions of musical consumers, who decided which ones they liked. The result is music filled with many of the sophisticated chords and rhythms familiar from modern songs. The results could also help explain why popular musical trends continuously evolve and why traditional musical forms can persist for thousands of years. The scientists set out to test a theory that cultural changes in language, art and music evolve through Darwinian natural selection, in a similar way to how living things evolve. They simulated this cultural evolution by harnessing the power of a 7,000 strong internet audience in an experiment that was designed to answer several questions. Can music exist without being the product of a conscious, creative act? If so, what would that music sound like? Does everyone's ideal tune sound the same? Armand Leroi, co-author of the research and Professor of Evolutionary Developmental Biology from the Department of Life Sciences at Imperial College London, said: "Everyone 'knows' that music is made by traditions of musical geniuses. Bach handed the torch to Beethoven who gave it to Brahms; Lennon and McCartney gave it to the Gallaghers who gave it to Chris Martin. But is that really what drives musical evolution? We wondered whether consumer choice is the real force behind the relentless march of pop. Every time someone downloads one track rather than another they are exercising a choice, and a million choices is a million creative acts. After all, that's how natural selection created all of life on earth, and if blind variation and selection can do that, then we reckoned it should be able to make a pop tune. So we set up an experiment to explain it." The computer algorithm behind the study, called DarwinTunes, maintains a population of 100 loops of music, each eight seconds long. Listeners scored loops in batches of 20 on a five-point scale from 'I can't stand it!' to 'I love it!'. DarwinTunes then 'mates' the top ten loops, pairing them up as 'parents' and mingling musical elements of each pair, to create twenty new loops. These replace the original parents and the less pleasing non-parents. This process represents one 'generation' of musical evolution. At the time of publication, DarwinTunes had evolved through 2,513 generations. The scientists then tested the like-ability of loops from different generations by asking listeners to rate them in a separate experiment. Without knowing the generational age of the loops, the volunteers consistently ranked the more evolved music as more appealing, thus independently validating the assertion that the music was improving over time. Dr Bob MacCallum, another co-author and a mosquito genomics bioinformatician in the Department of Life Sciences at Imperial College London, said: "We knew our evolutionary music engine could make pretty good music in the hands of one user, but what we really wanted to know was if it could do so in a more Darwinian setting, with hundreds of listeners providing their feedback. Thanks to our students' and the general public's valuable input, we can confidently say it does." Members of the public can continue to help the music evolve, by taking part in the DarwinTunes experiment at http://darwintunes.org. Individual loops can also be downloaded and used as ringtones or for offline music making.
1 Nov

Brothers in Arms: Commensal Bacteria Help Fight Viruses

  Healthy humans harbor an enormous and diverse group of bacteria and other bugs that live within their intestines. These microbial partners provide beneficial aid in multiple ways -- from helping digest food to the development of a healthy immune system. In a new study published online in the journal Immunity, David Artis, PhD, associate professor of Microbiology, and Michael Abt, PhD, a postdoctoral researcher in the Artis lab, Perelman School of Medicine, University of Pennsylvania, show that commensal bacteria are also essential to fight off viral infections. "From our studies in mice, we found that signals derived from these beneficial microbes are essential for optimal immune responses to experimental viral infections," says Artis. "In one way we could consider these microbes as our 'brothers in arms' in the fight against infectious diseases." Artis is also an associate professor of Pathobiology in the Penn School of Veterinary Medicine. Signals from commensal bacteria influence immune-cell development and susceptibility to infectious or inflammatory diseases. Commensal microbial communities colonize barrier surfaces of the skin, vaginal, upper respiratory, and gastrointestinal tracts of mammals and consist of bacteria, fungi, protozoa, and viruses. The largest and most diverse microbial communities live in the intestine. Previous studies in patients have associated alterations in bacterial communities with susceptibility to diabetes, obesity, cancer, inflammatory bowel disease, allergy, and other disorders. Despite knowing all of this, exactly how commensal bacteria regulate immunity after being exposed to pathogens is not well understood. To get a better picture of how these live-in bacteria are beneficial, the Artis lab used several lines of investigation. First, they demonstrated that mice -- treated with antibiotics to reduce numbers of commensal bacteria -- exhibit an impaired antiviral immune response and a substantially delayed clearance of a systemic virus or influenza virus that infects the airways. What's more, the treated mice had severely damaged airways and increased rate of death after the experimental influenza virus infection, demonstrating that alterations in commensal bacterial communities can have a negative impact on immunity against viruses. Next, they profiled the genes that were expressed in immune cells called macrophages isolated from the antibiotic-treated mice. These data revealed a decreased expression of genes associated with antiviral immunity. In addition, macrophages from antibiotic-treated mice showed defective responses to interferons, proteins made and released in response to viruses, bacteria, parasites, or tumor cells. Under normal circumstances, interferons facilitate communication between cells to trigger the immune cells that attack pathogens or tumors. The antibiotic-treated mice also had an impaired capacity to limit viral replication. However, when mice were treated with a compound that restored interferon responsiveness, protective antiviral immunity was re-established. "It is remarkable that signals derived from one type of microbe, in this case bacteria, can have such a profound effect on immune responses to viruses that are a very different type of microbe," says first author Abt. "Just like we would set a thermostat to regulate when a heater should come on, our studies indicate that signals derived from commensal bacteria are required to set the activation threshold of the immune system." Taken together, these lines of evidence indicate that signals from commensal bacteria beneficially stimulate immune cells in a way that is optimal for antiviral immunity. "Although more work needs to be done, these findings could illuminate new ways to promote better immunity to potentially life-threatening viral infections," adds Artis. This research is supported by the National Institutes of Health National Institute of Allergy and Infectious Disease(grants AI061570, AI087990, AI074878, AI095608, AI091759, AI095466, AI071309, AI078897, AI095608, AI083022, AI077098, HHSN266200500030C, T32-AI05528, T32-AI007532, T32-RR007063, K08-DK093784, T32-AI007324); the Irvington Institute Postdoctoral Fellowship of the Cancer Research Institute; the Burroughs Wellcome Fund, the National Institute of Diabetes and Digestive and Kidney Disease Center for the Molecular Studies in Digestive and Liver Disease and the Molecular Pathology and Imaging Core.  
1 Nov

Robots Get a Feel for the World: Touch More Sensitve Than a Human’s

What does a robot feel when it touches something? Little or nothing until now. But with the right sensors, actuators and software, robots can be given the sense of feel -- or at least the ability to identify different materials by touch. Researchers at the University of Southern California's Viterbi School of Engineering published a study June 18 in Frontiers in Neurorobotics showing that a specially designed robot can outperform humans in identifying a wide range of natural materials according to their textures, paving the way for advancements in prostheses, personal assistive robots and consumer product testing. The robot was equipped with a new type of tactile sensor built to mimic the human fingertip. It also used a newly designed algorithm to make decisions about how to explore the outside world by imitating human strategies. Capable of other human sensations, the sensor can also tell where and in which direction forces are applied to the fingertip and even the thermal properties of an object being touched. Like the human finger, the group's BioTacĀ® sensor has a soft, flexible skin over a liquid filling. The skin even has fingerprints on its surface, greatly enhancing its sensitivity to vibration. As the finger slides over a textured surface, the skin vibrates in characteristic ways. These vibrations are detected by a hydrophone inside the bone-like core of the finger. The human finger uses similar vibrations to identify textures, but the robot finger is even more sensitive. When humans try to identify an object by touch, they use a wide range of exploratory movements based on their prior experience with similar objects. A famous theorem by 18th century mathematician Thomas Bayes describes how decisions might be made from the information obtained during these movements. Until now, however, there was no way to decide which exploratory movement to make next. The article, authored by Professor of Biomedical Engineering Gerald Loeb and recently graduated doctoral student Jeremy Fishel, describes their new theorem for solving this general problem as "Bayesian Exploration." Built by Fishel, the specialized robot was trained on 117 common materials gathered from fabric, stationery and hardware stores. When confronted with one material at random, the robot could correctly identify the material 95% of the time, after intelligently selecting and making an average of five exploratory movements. It was only rarely confused by pairs of similar textures that human subjects making their own exploratory movements could not distinguish at all. So, is touch another task that humans will outsource to robots? Fishel and Loeb point out that while their robot is very good at identifying which textures are similar to each other, it has no way to tell what textures people will prefer. Instead, they say this robot touch technology could be used in human prostheses or to assist companies who employ experts to assess the feel of consumer products and even human skin. Loeb and Fishel are partners in SynTouch LLC, which develops and manufactures tactile sensors for mechatronic systems that mimic the human hand. Founded in 2008 by researchers from USC's Medical Device Development Facility, the start-up is now selling their BioTac sensors to other researchers and manufacturers of industrial robots and prosthetic hands.
1 Nov

Dating Evidence: Relics Could Be of John the Baptist

New dating evidence supports claims that bones found under a church floor in Bulgaria may be of John the Baptist, who is described in the Bible as a leading prophet and relative of Jesus Christ. A team from the Oxford Radiocarbon Accelerator Unit at Oxford University dated a knucklebone from the right hand to the 1st century AD, a date which fits with the widely held view of when he would have lived. The researchers say they were surprised when they discovered the very early age of the remains adding, however, that dating evidence alone cannot prove the bones to be of John the Baptist. The bones were originally discovered in 2010 by archaeologist Kazimir Popkonstantinov, excavating under an ancient church on an island in Bulgaria known as Sveti Ivan, which translates into English as St John. The knucklebone was one of six human bones, including a tooth and the face part of a cranium, found in small marble sarcophagus under the floor near the altar. Three animal bones were also inside the sarcophagus. Oxford professors Thomas Higham and Christopher Ramsey attempted to radiocarbon date four human bones, but only one of them contained a sufficient amount of collagen to be dated successfully. Professor Higham said: "We were surprised when the radiocarbon dating produced this very early age. We had suspected that the bones may have been more recent than this, perhaps from the third or fourth centuries. However, the result from the metacarpal hand bone is clearly consistent with someone who lived in the early first century AD. Whether that person is John the Baptist is a question that we cannot yet definitely answer and probably never will." Former Oxford student Dr Hannes Schroeder and Professor Eske Willerslev, both from the University of Copenhagen, also reconstructed the complete mitochondrial DNA genome sequence from three of the human bones to establish that the bones were all from the same individual. Significantly, they identified a family group of genes (mtDNA haplotype) as being a group most commonly found in the Near East, which is better known as the Middle East today -- the region where John the Baptist would have originated from. They also established that the bones were probably of a male individual after an analysis of the nuclear DNA from samples. Dr Schroeder said: "Our worry was that the remains might have been contaminated with modern DNA. However, the DNA we found in the samples showed damage patterns that are characteristic of ancient DNA, which gave us confidence in the results. Further, it seems somewhat unlikely that all three samples would yield the same sequence considering that they had probably been handled by different people. Both of these facts suggest that the DNA we sequenced was actually authentic. Of course, this does not prove that these were the remains of John the Baptist but nor does it refute that theory as the sequences we got fit with a Near Eastern origin." The Bulgarian archaeologists, who excavated the bones, also found a small tuff box (made of hardened volcanic ash) close to the sarcophagus. The tuff box bears inscriptions in ancient Greek that directly mention John the Baptist and his feast day, and text asking God to 'help your servant Thomas'. One theory is that the person referred to as Thomas had been given the task of bringing the relics to the island. An analysis of the box has shown that the tuff box has a high waterproof quality and is likely to have originated from Cappadocia, a region of modern-day Turkey. The Bulgarian researchers believe that the bones probably came to Bulgaria via Antioch, an ancient Turkish city, where the right hand of St John was kept until the tenth century. In a separate study, another Oxford researcher Dr Georges Kazan has used historical documents to show that in the latter part of the fourth century, monks had taken relics of John the Baptist out of Jerusalem and these included portions of skull. These relics were soon summoned to Constantinople by the Roman Emperor who built a church to house them there. Further research by Dr Kazan suggests that the reliquary used to contain them may have resembled the sarcophagus-shaped casket discovered at Sveti Ivan. Archaeological and written records suggest that these reliquaries were first developed and used at Constantinople by the city's ruling elite at around the time that the relics of John the Baptist are said to have arrived there. Dr Kazan said: "My research suggests that during the fifth or early sixth century, the monastery of Sveti Ivan may well have received a significant portion of St John the Baptist's relics, as well as a prestige reliquary in the shape of a sarcophagus, from a member of Constantinople's elite. This gift could have been to dedicate or rededicate the church and the monastery to St John, which the patron or patrons may have supported financially." The scientific analysis of the relics undertaken by Tom Higham and Christopher Ramsey at Oxford, and their colleagues in Copenhagen was supported by the National Geographic Society. The documentary 'Head of John the Baptist', featuring the scientists' work was shown on the National Geographic Channel on 17 June 2012.
1 Nov

Extremely Thin Perfect Nanotube Could Be Grown One Meter Long

At the right temperature, with the right catalyst, there's no reason a perfect single-walled carbon nanotube 1/50,000th the thickness of a human hair can't be grown a meter long. That calculation is one result of a study by collaborators at Rice, Hong Kong Polytechnic and Tsinghua universities who explored the self-healing mechanism that could make such extraordinary growth possible. That's important to scientists who see high-quality carbon nanotubes as critical to advanced materials and, if they can be woven into long cables, power distribution over the grid of the future. The report published online by Physical Review Letters is by Rice theoretical physicist Boris Yakobson; Feng Ding, an adjunct assistant professor at Rice and an assistant professor at Hong Kong Polytechnic; lead author Qinghong Yuan, a postdoctoral researcher at Hong Kong Polytechnic; and Zhiping Xu, a professor of engineering mechanics at Tsinghua and former postdoctoral researcher at Rice. They determined that iron is the best and quickest among common catalysts at healing topological defects -- rings with too many or too few atoms -- that inevitably bubble up during the formation of nanotubes and affect their valuable electronic and physical properties. The right combination of factors, primarily temperature, leads to kinetic healing in which carbon atoms gone astray are redirected to form the energetically favorable hexagons that make up nanotubes and their flat cousin, graphene. The team employed density functional theory to analyze the energies necessary for the transformation. "It is surprising that the healing of all potential defects -- pentagons, heptagons and their pairs -- during carbon nanotube growth is quite easy," said Ding, who was a research scientist in Yakobson's Rice lab from 2005 to 2009. "Only less than one-10 billionth may survive an optimum condition of growth. The rate of defect healing is amazing. If we take hexagons as good guys and others as bad guys, there would be only one bad guy on Earth." The energies associated with each carbon atom determine how it finds its place in the chicken-wire-like form of a nanotube, said Yakobson, Rice's Karl F. Hasselmann Chair in Engineering and a professor of materials science and mechanical engineering and of chemistry. But there has been a long debate among scientists over what actually happens at the interface between the catalyst and a growing tube. "There have been two hypotheses," Yakobson said. "A popular one was that defects are being created quite frequently and get into the wall of the tube, but then later they anneal. There's some kind of fixing process. Another hypothesis is that they basically don't form at all, which sounds quite unreasonable. "This was all just talk; there was no quantitative analysis. And that's where this work makes an important contribution. It evaluates quantitatively, based on state-of-the-art computations, specifically how fast this annealing can take place, depending on location," he said. A nanotube grows in a furnace as carbon atoms are added, one by one, at the catalyst. It's like building the peak of a skyscraper first and adding bricks to the bottom. But because those bricks are being added at a furious rate -- millions in a matter of minutes -- mistakes can happen, altering the structure. In theory, if one ring has five or seven atoms instead of six, it would skew the way all subsequent atoms in the chain orient themselves; an isolated pentagon would turn the nanotube into a cone, and a heptagon would turn it into a horn, Yakobson said. But calculations also showed such isolated defects cannot exist in a nanotube wall; they would always appear in 5/7 pairs. That makes a quick fix easier: If one atom can be prompted to move from the heptagon to the pentagon, both rings come up sixes. The researchers found that very transition happens best when carbon nanotubes are grown at temperatures around 930 kelvins (1,214 degrees Fahrenheit). That is the optimum for healing with an iron catalyst, which the researchers found has the lowest energy barrier and reaction energy among the three common catalysts considered, including nickel and cobalt. Once a 5/7 forms at the interface between the catalyst and the growing nanotube, healing must happen very quickly. The further new atoms push the defect into the nanotube wall, the less likely it is to be healed, they determined; more than four atoms away from the catalyst, the defect is locked in. Tight control of the conditions under which nanotubes grow can help them self-correct on the fly. Errors in atom placement are caught and fixed in a fraction of a millisecond, before they become part of the nanotube wall. The researchers also determined through simulations that the slower the growth, the longer a perfect nanotube could be. A nanotube growing about 1 micrometer a second at 700 kelvins could potentially reach the meter milestone, they found. The work at Rice University was initially supported by the National Science Foundation and at a later stage by an Office of Naval Research grant.
1 Nov

Particle Physics: BaBar Data Hint at Cracks in the Standard Model

Recently analyzed data from the BaBar experiment may suggest possible flaws in the Standard Model of particle physics, the reigning description of how the universe works on subatomic scales. The data from BaBar, a high-energy physics experiment based at the U.S. Department of Energy's (DOE) SLAC National Accelerator Laboratory, show that a particular type of particle decay called "B to D-star-tau-nu" happens more often than the Standard Model says it should. In this type of decay, a particle called the B-bar meson decays into a D meson, an antineutrino and a tau lepton. While the level of certainty of the excess (3.4 sigma in statistical language) is not enough to claim a break from the Standard Model, the results are a potential sign of something amiss and are likely to impact existing theories, including those attempting to deduce the properties of Higgs bosons. "The excess over the Standard Model prediction is exciting," said BaBar spokesperson Michael Roney, professor at the University of Victoria in Canada. The results are significantly more sensitive than previously published studies of these decays, said Roney. "But before we can claim an actual discovery, other experiments have to replicate it and rule out the possibility this isn't just an unlikely statistical fluctuation." The BaBar experiment, which collected particle collision data from 1999 to 2008, was designed to explore various mysteries of particle physics, including why the universe contains matter, but no antimatter. The collaboration's data helped confirm a matter-antimatter theory for which two researchers won the 2008 Nobel Prize in Physics. Researchers continue to apply BaBar data to a variety of questions in particle physics. The data, for instance, has raised more questions about Higgs bosons, which arise from the mechanism thought to give fundamental particles their mass. Higgs bosons are predicted to interact more strongly with heavier particles -- such as the B mesons, D mesons and tau leptons in the BaBar study -- than with lighter ones, but the Higgs posited by the Standard Model can't be involved in this decay. "If the excess decays shown are confirmed, it will be exciting to figure out what is causing it," said BaBar physics coordinator Abner Soffer, associate professor at Tel Aviv University. Other theories involving new physics are waiting in the wings, but the BaBar results already rule out one important model called the "Two Higgs Doublet Model." "We hope our results will stimulate theoretical discussion about just what the data are telling us about new physics," added Soffer. The researchers also hope their colleagues in the Belle collaboration, which studies the same types of particle collisions, see something similar, said Roney. "If they do, the combined significance could be compelling enough to suggest how we can finally move beyond the Standard Model." The results have been presented at the 10th annual Flavor Physics and Charge-Parity Violation Conference in Hefei, China, and submitted for publication in the journal Physical Review Letters. The paper is available on arXiv in preprint form. This work is supported by DOE and NSF (USA), STFC (United Kingdom), NSERC (Canada), CEA and CNRS-IN2P3 (France), BMBF and DFG (Germany), INFN (Italy), FOM (The Netherlands), NFR (Norway), MES (Russia), and MICIIN (Spain), as well as support from Israel and India. Individuals have received funding from the Marie Curie EIF (European Union) and the A.P. Sloan Foundation (USA).
1 Nov

Black Holes as Particle Detectors

Finding new particles usually requires high energies -- that is why huge accelerators have been built, which can accelerate particles to almost the speed of light. But there are other creative ways of finding new particles: At the Vienna University of Technology, scientists presented a method to prove the existence of hypothetical "axions." These axions could accumulate around a black hole and extract energy from it. This process could emit gravity waves, which could then be measured. Axions are hypothetical particles with a very low mass. According to Einstein, mass is directly related to energy, and therefore very little energy is required to produce axions. "The existence of axions is not proven, but it is considered to be quite likely," says Daniel Grumiller. Together with Gabriela Mocanu he calculated at the Vienna University of Technology (Institute for Theoretical Physics), how axions could be detected. Astronomically Large Particles In quantum physics, every particle is described as a wave. The wavelength corresponds to the particle's energy. Heavy particles have small wavelengths, but the low-energy axions can have wavelengths of many kilometers. The results of Grumiller and Mocanu, based on works by Asmina Arvanitaki and Sergei Dubovsky (USA/Russia), show that axions can circle a black hole, similar to electrons circling the nucleus of an atom. Instead of the electromagnetic force, which ties the electrons and the nucleus together, it is the gravitational force which acts between the axions and the black hole. The Boson-Cloud However, there is a very important difference between electrons in an atom and axions around a black hole: Electrons are fermions -- which means that two of them can never be in the same state. Axions on the other hand are bosons, many of them can occupy the same quantum state at the same time. They can create a "boson-cloud" surrounding the black hole. This cloud continuously sucks energy from the black hole and the number of axions in the cloud increases. Sudden Collapse Such a cloud is not necessarily stable. "Just like a loose pile of sand, which can suddenly slide, triggered by one single additional grain of sand, this boson cloud can suddenly collapse," says Daniel Grumiller. The exciting thing about such a collapse is that this "bose-nova" could be measured. This event would make space and time vibrate and emit gravity waves. Detectors for gravity waves have already been developed, in 2016 they are expected to reach an accuracy at which gravity waves should be unambiguously detected. The new calculations in Vienna show that these gravity waves can not only provide us with new insights about astronomy, they can also tell us more about new kinds of particles.
 
1 Nov

Mars Weather Report: Size of Particles in Martian Clouds of Carbon Dioxide Snow Calculated

In the dead of a Martian winter, clouds of snow blanket the Red Planet's poles -- but unlike our water-based snow, the particles on Mars are frozen crystals of carbon dioxide. Most of the Martian atmosphere is composed of carbon dioxide, and in the winter, the poles get so cold -- cold enough to freeze alcohol -- that the gas condenses, forming tiny particles of snow. Now researchers at MIT have calculated the size of snow particles in clouds at both Martian poles from data gathered by orbiting spacecraft. From their calculations, the group found snow particles in the south are slightly smaller than snow in the north -- but particles at both poles are about the size of a red blood cell. "These are very fine particles, not big flakes," says Kerri Cahoy, the Boeing Career Development Assistant Professor of Aeronautics and Astronautics at MIT. If the carbon dioxide particles were eventually to fall and settle on the Martian surface, "you would probably see it as a fog, because they're so small." Cahoy and graduate student Renyu Hu worked with Maria Zuber, the E.A. Griswold Professor of Geophysics at MIT, to analyze vast libraries of data gathered from instruments onboard the Mars Global Surveyor (MGS) and Mars Reconnaissance Orbiter (MRO). From the data, they determined the size of carbon dioxide snow particles in clouds, using measurements of the maximum buildup of surface snow at both poles. The buildup is about 50 percent larger at Mars' south pole than its north pole. Over the course of a Martian year (a protracted 687 days, versus Earth's 365), the researchers observed that as it gets colder and darker from fall to winter, snow clouds expand from the planet's poles toward its equator. The snow reaches halfway to the equator before shrinking back toward the poles as winter turns to spring, much like on Earth. "For the first time, using only spacecraft data, we really revealed this phenomenon on Mars," says Hu, lead author of a paper published in the Journal of Geophysical Research, which details the group's results. Diving through data To get an accurate picture of carbon dioxide condensation on Mars, Hu analyzed an immense amount of data, including temperature and pressure profiles taken by the MRO every 30 seconds over the course of five Martian years (more than nine years on Earth). The researchers looked through the data to see where and when conditions would allow carbon dioxide cloud particles to form. The team also sifted through measurements from the MGS' laser altimeter, which measured the topography of the planet by sending laser pulses to the surface, then timing how long it took for the beams to bounce back. Every once in a while, the instrument picked up a strange signal when the beam bounced back faster than anticipated, reflecting off an anomalously high point above the planet's surface. Scientists figured these laser beams had encountered clouds in the atmosphere. Hu analyzed these cloud returns, looking for additional evidence to confirm carbon dioxide condensation. He looked at every case where a cloud was detected, then tried to match the laser altimeter data with concurrent data on local temperature and pressure. In 11 instances, the laser altimeter detected clouds when temperature and pressure conditions were ripe for carbon dioxide to condense. Hu then analyzed the opacity of each cloud -- the amount of light reflected -- and through calculations, determined the density of carbon dioxide in each cloud. To estimate the total mass of carbon dioxide snow deposited at both poles, Hu used earlier measurements of seasonal variations in the Martian gravitational field done by Zuber's group: As snow piles up at Mars' poles each winter, the planet's gravitational field changes by a tiny amount. By analyzing the gravitational difference through the seasons, the researchers determined the total mass of snow at the north and south poles. Using the total mass, Hu figured out the number of snow particles in a given volume of snow cover, and from that, determined the size of the particles. In the north, molecules of condensed carbon dioxide ranged from 8 to 22 microns, while particles in the south were a smaller 4 to 13 microns. "It's neat to think that we've had spacecraft on or around Mars for over 10 years, and we have all these great datasets," Cahoy says. "If you put different pieces of them together, you can learn something new just from the data." What can the size of snow tell us? Hu says knowing the size of carbon dioxide snow cloud particles on Mars may help researchers understand the properties and behavior of dust in the planet's atmosphere. For snow to form, carbon dioxide requires something around which to condense -- for instance, a small silicate or dust particle. "What kinds of dust do you need to have this kind of condensation?" Hu asks. "Do you need tiny dust particles? Do you need a water coating around that dust to facilitate cloud formation?" Just as snow on Earth affects the way heat is distributed around the planet, Hu says snow particles on Mars may have a similar effect, reflecting sunlight in various ways, depending on the size of each particle. "They could be completely different in their contribution to the energy budget of the planet," Hu says. "These datasets could be used to study many problems." This research was funded by the Radio Science Gravity investigation of the NASA Mars Reconnaissance Orbiter mission.
1 Nov

Ancient Warming Greened Antarctica, Study Finds

A new university-led study with NASA participation finds ancient Antarctica was much warmer and wetter than previously suspected. The climate was suitable to support substantial vegetation -- including stunted trees -- along the edges of the frozen continent. The team of scientists involved in the study, published online June 17 in Nature Geoscience, was led by Sarah J. Feakins of the University of Southern California in Los Angeles, and included researchers from NASA's Jet Propulsion Laboratory in Pasadena, Calif., and Louisiana State University in Baton Rouge. By examining plant leaf wax remnants in sediment core samples taken from beneath the Ross Ice Shelf, the research team found summer temperatures along the Antarctic coast 15 to 20 million years ago were 20 degrees Fahrenheit (11 degrees Celsius) warmer than today, with temperatures reaching as high as 45 degrees Fahrenheit (7 degrees Celsius). Precipitation levels also were found to be several times higher than today. "The ultimate goal of the study was to better understand what the future of climate change may look like," said Feakins, an assistant professor of Earth sciences at the USC Dornsife College of Letters, Arts and Sciences. "Just as history has a lot to teach us about the future, so does past climate. This record shows us how much warmer and wetter it can get around the Antarctic ice sheet as the climate system heats up. This is some of the first evidence of just how much warmer it was." Scientists began to suspect that high-latitude temperatures during the middle Miocene epoch were warmer than previously believed when co-author Sophie Warny, assistant professor at LSU, discovered large quantities of pollen and algae in sediment cores taken around Antarctica. Fossils of plant life in Antarctica are difficult to come by because the movement of the massive ice sheets covering the landmass grinds and scrapes away the evidence. "Marine sediment cores are ideal to look for clues of past vegetation, as the fossils deposited are protected from ice sheet advances, but these are technically very difficult to acquire in the Antarctic and require international collaboration," said Warny. Tipped off by the tiny pollen samples, Feakins opted to look at the remnants of leaf wax taken from sediment cores for clues. Leaf wax acts as a record of climate change by documenting the hydrogen isotope ratios of the water the plant took up while it was alive. "Ice cores can only go back about one million years," Feakins said. "Sediment cores allow us to go into 'deep time.'" Based upon a model originally developed to analyze hydrogen isotope ratios in atmospheric water vapor data from NASA's Aura spacecraft, co-author and JPL scientist Jung-Eun Lee created experiments to find out just how much warmer and wetter climate may have been. "When the planet heats up, the biggest changes are seen toward the poles," Lee said. "The southward movement of rain bands associated with a warmer climate in the high-latitude southern hemisphere made the margins of Antarctica less like a polar desert, and more like present-day Iceland." The peak of this Antarctic greening occurred during the middle Miocene period, between 16.4 and 15.7 million years ago. This was well after the age of the dinosaurs, which became extinct 64 million years ago. During the Miocene epoch, mostly modern-looking animals roamed Earth, such as three-toed horses, deer, camel and various species of apes. Modern humans did not appear until 200,000 years ago. Warm conditions during the middle Miocene are thought to be associated with carbon dioxide levels of around 400 to 600 parts per million (ppm). In 2012, carbon dioxide levels have climbed to 393 ppm, the highest they've been in the past several million years. At the current rate of increase, atmospheric carbon dioxide levels are on track to reach middle Miocene levels by the end of this century. High carbon dioxide levels during the middle Miocene epoch have been documented in other studies through multiple lines of evidence, including the number of microscopic pores on the surface of plant leaves and geochemical evidence from soils and marine organisms. While none of these 'proxies' is as reliable as the bubbles of gas trapped in ice cores, they are the best evidence available this far back in time. While scientists do not yet know precisely why carbon dioxide was at these levels during the middle Miocene, high carbon dioxide, together with the global warmth documented from many parts of the world and now also from the Antarctic region, appear to coincide during this period in Earth's history. This research was funded by the U.S. National Science Foundation with additional support from NASA. The California Institute of Technology in Pasadena manages JPL for NASA.