Exercise may not erase old memories, as some studies in animals have previously suggested.
Running on an exercise wheel doesn’t make rats forget previous trips through an underwater maze, Ashok Shetty and colleagues report August 2 in the Journal of Neuroscience. Exercise or not, four weeks after learning how to find a hidden platform, rats seem to remember the location just fine, the team found.
The results conflict with two earlier papers that show that running triggers memory loss in some rodents by boosting the birth of new brain cells. Making new brain cells rejiggers memory circuits, and that can make it hard for animals to remember what they’ve learned, says Paul Frankland, a neuroscientist at the Hospital for Sick Children in Toronto. He has reported this phenomenon in mice, guinea pigs and degus (SN: 6/14/14, p. 7). Maybe rats are the exception, he says, “but I’m not convinced.”
In 2014, Frankland and colleagues reported that brain cell genesis clears out fearful memories in three different kinds of rodents. Two years later, Frankland’s team found similar results with spatial memories. After exercising, mice had trouble remembering the location of a hidden platform in a water maze, the team reported in February in Nature Communications. Again, Frankland and colleagues pinned the memory wipeout on brain cell creation — like a chalkboard eraser that brushes away old information. The wipe seemed to clear the way for new memories to form.
Shetty, a neuroscientist at Texas A&M Health Science Center in Temple, wondered if the results held true in rats, too. “Rats are quite different from mice,” he says. “Their biology is similar to humans.” Using a water maze similar to Frankland’s, Shetty’s team taught two groups of rats how to find a hidden platform in eight training sessions over eight days. Then rats in just one of the groups exercised on a running wheel. Four weeks later, rats in both groups performed the same in the maze test — despite the fact that running rats had 1.5 to 2 times more newly born brain cells in the hippocampus, a skinny strip of tissue that’s thought to help form new memories. These results and other memory tests “clearly showed that exercise did not interfere with memory recall,” Shetty says. And it’s likely that exercise doesn’t harm human memories either, he says.
Frankland says it’s possible that Shetty’s rats just learned the water maze too well. Shetty’s team trained their rodents for longer than Frankland’s team did, perhaps etching memories more deeply in the brain.
“The stronger the memory is, the harder it is going to be to erase it,” Frankland says.
But he points out that erasing memories isn’t necessarily a bad thing. “People get hung up on this idea,” he says, but actually, clearing out old info from the brain — forgetting — is important. Without some sort of clearance process, “your memory is going to be full of junk.”
Rainfall shifts caused by climate change plus the escalating water demands of a growing world population threaten society’s ability to meet its mounting needs. By 2025, the United Nations predicts, 2.4 billion people will live in regions of intense water scarcity, which may force as many as 700 million people from their homes in search of water by 2030.
Those water woes have people thirstily eyeing the more than one sextillion liters of water in Earth’s oceans and some underground aquifers with high salt content. For drinking or irrigation, the salt must come out of all those liters. And while desalination has been implemented in some areas — such as Israel and drought-stricken California — for much of the world, salt-removal is a prohibitively expensive energy drain. Scientists and engineers, however, aren’t giving up on the quest for desalination solutions. The technology underlying modern desalination has been around for decades, “but we have not driven it in such a way as to be ubiquitous,” says UCLA chemical engineer Yoram Cohen. “That’s what we need to figure out: how to make desalination better, cheaper and more accessible.”
Recent innovations could bring costs down and make the technology more accessible. A new wonder material may make desalination plants more efficient. Solar-powered disks could also serve up freshwater with no need for electricity. Once freshwater is on tap, coastal floating farms could supply food to Earth’s most parched places, one scientist proposes.
Watering holes Taking the salt out of water is hardly a new idea. In the fourth century B.C., Aristotle noted that Greek sailors would evaporate impure water, leaving the salt behind, and then condense the vapor to make drinkable water. In the 1800s, the advent of steam-powered travel and the subsequent need for water without corrosive salt for boilers prompted the first desalination patent, in England.
Most modern desalination plants use a technique that differs from these earlier efforts. Instead of evaporating water, pumps force pressurized saltwater from the ocean or salty underground aquifers through special sheets. These membranes contain molecule-sized holes that act like club bouncers, allowing water to pass through while blocking salt and other contaminants.
The membranes are rolled like rugs and stuffed into meter-long tubes with additional layers that direct water flow and provide structural support. A large desalination plant uses tens of thousands of membranes that fill a warehouse. This process is known as reverse osmosis and the result is salt-free water plus a salty brine waste product that is typically pumped underground or diluted with seawater and released back into the ocean. It takes about 2.5 liters of seawater to make 1 liter of freshwater.
In 2015, more than 18,000 desalination plants worldwide had the annual capacity to produce 31.6 trillion liters of freshwater across 150 countries. While still less than 1 percent of worldwide freshwater usage, desalination production is two-thirds higher than it was in 2008. Driving the boom is a decades-long drop in energy requirements thanks to innovations such as energy-efficient water pumps, improved membranes and plant configurations that use outbound water to help pressurize incoming water. Seawater desalination in the 1970s consumed as much as 20 kilowatt-hours of energy per cubic meter of produced fresh-water; modern plants typically require just over three kilowatt-hours.
Water, water, everywhere Desalination plants supply water to more than 300 million people worldwide and experts expect that number to grow. Blue dots in this map represent the more than 500 large desalination plants currently in operation. Each plant produces more than 20 million liters of freshwater daily from seawater and salty groundwater. The number of smaller plants, such as those that provide freshwater on ships or for personal use, is unclear.
Source: DesalData/Global Water Intelligence, the International Desalination Association
There’s a limit, however, to the energy savings. Theoretically, separating a cubic meter of freshwater from two cubic meters of seawater requires a minimum of about 1.06 kilowatt-hours of energy. Desalination is typically only viable when it’s cheaper than the next alternative water source, says Brent Haddad, a water management expert at the University of California, Santa Cruz. Alternatives, such as reducing usage or piping freshwater in from afar, can help, but these methods don’t create more H2O. While other hurdles remain for desalination, such as environmentally friendly wastewater disposal, cost is the main obstacle.
The upfront cost of each desalination membrane is minimal. For decades, most membranes have been made from polyamide, a synthetic polymer prized for its low manufacturing cost — around $1 per square foot. “That’s very, very cheap,” says MIT materials scientist Shreya Dave. “You can’t even buy decent flooring at Home Depot for a dollar a square foot.”
But polyamide comes with additional costs. It degrades quickly when exposed to chlorine, so when the source water contains chlorine, plant workers have to add two steps: remove chlorine before desalination, then add it back later, since drinking water requires chlorine as a disinfectant. To make matters worse, in the absence of chlorine, the membranes are susceptible to growing biological matter that can clog up the works.
With these problems in mind, researchers are turning to other membrane materials. One alternative, graphene oxide, may knock polyamide out of the water.
Membrane maze Since its discovery in 2004, graphene has been touted as a supermaterial, with proposed applications ranging from superconductors to preventing blood clots (SN: 10/3/15, p. 7; SN Online: 2/11/14). Each graphene sheet is a single-atom-thick layer of carbon atoms arranged in a honeycomb grid. As a hypothetical desalination membrane, graphene would be sturdy and put up little resistance to passing water, reducing energy demands, says MIT materials scientist Jeff Grossman. Pure graphene is astronomically expensive and difficult to make in large sheets. So Grossman, Dave and colleagues turned to a cheaper alternative, graphene oxide. The carbon atoms in graphene oxide are bordered by oxygen and hydrogen atoms.
Those extra atoms make graphene oxide “messy,” eliminating many of the material’s unique electromagnetic properties. “But for a membrane, we don’t care,” Grossman says. “We’re not trying to run an electric current through it, we’re not trying to use its optical properties — we’re just trying to make a thin piece of material we can poke holes into.”
The researchers start with graphene flakes peeled from hunks of graphite, the form of carbon found in pencil lead. Researchers suspend the graphene oxide flakes, which are easy and cheap to make, in liquid. As a vacuum sucks the liquid out of the container, the flakes form a sheet. The researchers bind the flakes together by adding chains of carbon and oxygen atoms. Those chains latch on to and connect the graphene oxide flakes, forming a maze of interconnected layers. The length of these chains is fine-tuned so that the gaps between flakes are just wide enough for water molecules, but not larger salt molecules, to pass through.
The team can fashion paperlike graphene oxide sheets a couple of centimeters across, though the technique should easily scale up to the roughly 40-square-meter size currently packed into each desalination tube, Dave says. Furthermore, the sheets hold up under pressure. “We are not the only research group using vacuum filtration to assemble membranes from graphene oxide,” she says, “but our membranes don’t fall apart when exposed to water, which is a pretty important thing for water filtration.”
The slimness of the graphene oxide membranes makes it much easier for water molecules to pass through compared with the bulkier poly-amide, reducing the energy needed to pump water through them. Grossman, Dave and colleagues estimated the cost savings of such highly permeable membranes in 2014 in a paper in Energy & Environmental Science. Desalination of ground-water would require 46 percent less energy; processing of saltier seawater would use 15 percent less, though the energy demands of the new proto-types haven’t yet been tested.
So far, the new membranes are especially durable, Grossman says. “Unlike polyamide, graphene oxide membranes are resilient to important cleaning chemicals like chlorine, and they hold up in harsh chemical environments and at high temperatures.” With lower energy requirements and no need to remove and replace chlorine from source water, the new membranes could be one solution to many desalination challenges. In large quantities, the graphene oxide membranes may be economically viable, Dave predicts. At scale, she estimates that manufacturing graphene oxide membranes will cost around $4 to $5 per square foot — not drastically more expensive than polyamide, considering its other benefits. Existing plants could swap in graphene oxide membranes when older polyamide membranes need replacing, spreading out the cost of the upgrade over about 10 years, Dave says. The team is currently patenting its membrane–making methodology, though the researchers think it will take a few more years before the technology is commercially viable.
“We are at a point where we need a quantum leap, and that can be achieved by new membrane structures,” says Nikolay Voutchkov, executive director of Water Globe Consulting, a company that advises industries and municipalities on desalination projects. The work on graphene oxide “is one way to do it.”
Other materials are also vying to be poly-amide’s successor. Researchers are testing carbon nanotubes, tiny cylindrical carbon structures, as a desalination membrane. Which material wins “will come down to cost,” Voutchkov says. Even if graphene oxide or other membranes save money in the long run, high upfront costs would make them less appealing.
Plus, those new membranes won’t solve the problems of desalination in less-developed areas. The costs of building a large plant and pumping freshwater over long distances make desalination a hard sell in rural Africa and other water-starved places. For hard-to-reach locales, scientists are thinking small.
A portable approach In remote Africa, electricity is hard to come by. Materials scientist Jia Zhu of Nanjing University in China and colleagues are hoping to bring drinkable water to unpowered, parched places by turning to an old-school desalination technique: evaporating and condensing water.
Their system runs on sunshine, something that is both free and abundant in Earth’s hotter regions. Using the sun’s rays to desalinate water is hardly new, but most existing systems are inefficient. Only about 30 to 45 percent of incoming sunlight typically goes into evaporating water, which means a big footprint is needed to create sizable amounts of freshwater. Zhu and colleagues hope to boost efficiency with a more light-absorbing material.
The material’s fabrication starts with a base sheet made of aluminum oxide speckled with 300-nanometer-wide holes. The researchers then coat this sheet with a thin layer of aluminum particles.
When light hits aluminum particles inside one of the holes, the added energy makes electrons in the aluminum start to oscillate and ripple. These electrons can transfer some of that energy to their surroundings, heating and evaporating nearby water without the need for boiling (SN Online: 4/8/16). The researchers have produced 2.5-centimeter-wide disks of the new material so far, which are light enough to float. The black disks absorb more than 96 percent of incoming sunlight and about 90 percent of the absorbed energy is used in evaporating water, the researchers reported in the June Nature Photonics.
The evaporated water condenses and collects in a transparent box containing stainless steel. In laboratory tests, the researchers successfully desalinated water from China’s Bohai Sea to levels low enough to meet drinking water standards. The researchers reckon that they can produce around five liters of fresh-water per hour for every square meter of material under intense light. In early tests, the disks held up after multiple uses without dropping in performance.
Aluminum is cheap and the material’s fabrication process can easily scale, Zhu says. While the disks can’t produce as much drinkable water as quickly as big desalination plants, the new method may serve a different need, since it’s more affordable and more portable, he says. “We are developing a personalized water solution without big infrastructure, without extra energy consumption and with a minimum carbon footprint.” The researchers hope that their new desalination technique will find use in developing countries and remote areas where conventional desalination plants aren’t feasible.
The disks are worth pursuing, says Haddad at UC Santa Cruz. “I say let’s try it out. Let’s work with some villages and see how well the tech works and get their feedback. That to me is a good next step to take.”
Desalinating water by evaporation has a downside, though, Voutchkov says. Unlike most methods for removing salt, evaporation produces pure distilled water without any important dissolved minerals such as calcium and magnesium. Drinking water without those minerals can cause health issues over time, he warns. “It’s OK for a few weeks, but you can’t drink it forever.” Minerals would need to be added back in to the water, which is hard to do in remote places, he says.
Freshwater isn’t just for filling water bottles, though. With a nearly endless supply of salt-free water at hand, desalination could bring agriculture to new places.
Coastal crops When Khaled Moustafa looks at a beach, he doesn’t just see a place for sunning and surfing. The biologist at the National Conservatory of Arts and Crafts in Paris sees the future of farming.
In the April issue of Trends in Biotechnology, Moustafa proposed that desalination could supply irrigation water to colossal floating farms. Self-sufficient floating farms could bring agriculture to arid coastal regions previously inhospitable to crops. The idea, while radical, isn’t too farfetched, given recent technological advancements, Moustafa says.
Floating farms would lay anchor along coastlines and suck up seawater, he proposes. A solar panel–powered water desalination system would provide freshwater to rows of cucumbers, tomatoes or strawberries stacked like a big city high-rise inside a “blue house” (that is, a floating greenhouse). Each floating farm would stretch 300 meters long by 100 meters wide, providing about 1 square kilometer of cultivable surface over only three-hundredths of a square kilometer of ocean, Moustafa says. The farms could even be mobile, cruising around the ocean to transport crops and escape bad weather.
Such a portable and self-contained farming solution would be most appealing in dry coastal regions that get plenty of sunshine, such as the Arabian Gulf, North Africa and Australia.
“I wouldn’t say it’s a silly idea,” Voutchkov says. “But it’s an idea that can’t get a practical implementation in the short term. In the long term, I do believe it’s a visionary idea.”
Floating farms may come with a large price tag, Moustafa admits. Still, expanding agriculture should “be more of a priority than building costly football stadiums or indoor ski parks in the desert,” he argues.
Whether or not farming will ever take to the seas, new desalination technologies will transform the way society quenches its thirst. More than 300 million people rely on desalination for at least some of their daily water, and that number will only grow as needs rise and new materials and techniques improve the process.
“Desalination can sometimes get a rap for being energy intensive,” Dave says. “But the immediate benefits of having access to water that would not otherwise be there are so large that desalination is a technology that we will be seeing for a long time into the future.”
This article appears in the August 20, 2016, Science News with the headline, “Quenching society’s thirst: Desalination may soon turn a corner, from rare to routine.”
Manchester, England, is not the birthplace of graphene — the atom-thin, honeycomb-like layer of carbon known for its wondrous properties and seemingly limitless applications. But the city is the material’s main booster and, according to the University of Manchester, the official Home of Graphene. That’s because it was there that Andre Geim and Kostya Novoselov figured out that you could isolate the elusive material from graphite (the “lead” in pencils) with repeated dabs of sticky tape. The two-dimensional material also proved to be a peerless electrical conductor and superstrong, earning the two Manchester scientists the 2010 Nobel Prize in physics. So when the city played host to the EuroScience Open Forum conference late last month, it made sense that Geim, graphene and the material’s many evolving applications took center stage. At the local science museum’s new exhibit about graphene, I learned that Geim is the only Nobelist who has also been honored with an Ig Nobel (which has fun celebrating seemingly useless research in science). He contends many are more familiar with his Ig Nobel–winning device to levitate a tiny frog than with his work on graphene.
Notably, graphene comes up in both of the feature stories in this issue, adding some heft, perhaps, to Mancunian claims. In Thomas Sumner’s cover story “Quenching society’s thirst,” about the growing interest in desalination to meet the globe’s escalating need for freshwater, graphene oxide has a potentially starring role. New membranes made from this material may help increase the efficiency of separating salt from water. Cost and efficiency, Sumner reports, remain the biggest obstacles to the widespread use of desalination.
Graphene can serve as analogy and inspiration in physicists’ efforts to create solid metallic hydrogen, another theorized wonder material, which Emily Conover describes in “Chasing a devious metal.” “It’s a high-stakes, high-passion pursuit that sparks dreams of a coveted new material that could unlock enormous technological advances in electronics,” Conover writes. Solid hydrogen, which has been made, takes on a graphenelike structure when squeezed to high pressures. Solid metal hydrogen might be a superconductor at room temperature, an exciting prospect. Despite significant progress, so far no one has been able to create it.
Local celebrity or not, graphene did share the spotlight with other science superstars at the EuroScience meeting. The gene-editing tool CRISPR got lots of attention. In a review of the historic detection of gravitational waves, Sheila Rowan of the University of Glasgow offered a bevy of questions that gravitational astronomy might be able to answer in the coming years: Where and when do black holes form? What does that tell you about the large-scale formation of galaxies? Is general relativity still valid when gravity is very strong (such as near supermassive black holes)? A session on the human microbiome generated even more questions, as scientists described efforts to use microbial species as telltale signs of diseases such as cancer. And a debate about how to prevent food allergies left most agreeing that more data are needed. As answers come in on all of these and many more fascinating topics, you can be sure that Science News will be there to report on them.
COLUMBIA, Mo. — Human babies born via cesarean section miss out on an opportunity to pick up beneficial microbes that other babies get when they take a trip through mom’s vagina. And even though the scientific jury’s still out on whether this is a good idea, some parents have been wiping their C-section babies down with vaginal fluid in the hopes that their newborns might get some of those microbial benefits, Laura Sanders reported earlier this yearover at the Growth Curve blog.
Microbial transfer from mom to offspring happens in a lot of species, but researchers are more familiar with how species that give live birth do this than those that lay eggs, biologist Stacey Weiss of the University of Puget Sound in Tacoma, Wash., noted August 1 at the 53rd Annual Conference of the Animal Behavior Society. Researchers have found that moms can transfer microbes right into the egg itself before it is laid or onto or near the egg after laying.
But Weiss thinks that such microbial transfer might happen through another route — as eggs travel through a female animal’s cloaca. (The cloaca is a combination of genital tract and end of the digestive system found in many invertebrates and most vertebrates, except most mammals.) She and her colleagues have been studying whether striped plateau lizard moms transfer microbes that protect their eggs from pathogens.
“Pathogenic infection is one of the leading causes of egg mortality,” she said. And some studies have proposed that microbes might be able to protect against those infections. None have yet proposed that the source of the microbes could be the cloaca, but this might be a common source since “all vertebrate eggs go through cloacas, and all cloacas have microbes,” she said.
Weiss latched onto the idea that microbes from the cloaca might be important after noticing that when she obtained eggs through dissection, they tended to have a lower survival rate than eggs that were laid. The dissected eggs often succumbed to fungal infections, while the laid eggs did not.
She and her team started by comparing the microbiomes of male and female lizards’ cloacas. “Females are different than males,” she said. Males had more diverse microbial communities in their cloacas. Females were missing whole categories of microbes found in males and had one type that is known to have antifungal activity.
The researchers then compared the microbiomes of eggs that were laid with those that had been dissected out. The team is still waiting on the results of DNA tests that will tell them exactly what kinds of microbes are found on the eggs, but initial results showed that the laid eggs are more likely to have any bacteria at all. “There’s something about going through the cloaca that is increasing bacterial load on these eggshells,” Weiss said. Fungi, though, showed up only on eggs that had been obtained through dissection. Weiss, her colleagues and some high school students then performed tests in which fungus was applied directly to eggs. They found that laid eggs were able to inhibit fungal growth while dissected eggs were not. So it appears that the mom’s cloaca microbiome may indeed be providing some protection for her offspring.
Weiss said that these results, while still preliminary, may help expand what parental protection of offspring means. In species without direct parental care, transfer of microbes might be an important way that moms and dads help to keep their offspring safe.
Going for walks, playing fetch and now participating in genetic research are just a few things people and their dogs can do together.
Darwin’s Dogs, a citizen science project headquartered at the University of Massachusetts Medical School in Worcester, is looking for good — and bad — dogs to donate DNA. The project aims to uncover genes that govern behavior, including those involved in mental illness in both people and pets.
Looking to dogs for clues about mental illness isn’t as strange as it may seem. Certain breeds are plagued by some of the same diseases and mental health issues that afflict people. Researchers have learned about the genetics of narcolepsy and obsessive compulsive disorder, as well as cancer, blindness and many other ailments from studying purebred dogs. Studies of purebreds are mainly useful when the problem is caused by mutations in a single gene. But most behaviors are the product of interactions between many genes and the environment. A search for those genes can’t be done with a small number of genetically similar dogs. So, Darwin’s Dogs hopes to gather data on a large number of canines, including many breeds and genetically diverse mutts. Finding behavior-related genes, such as ones that lead dogs to chew up shoes or engage in marathon fetch sessions, may give clues to genes that affect human behavior. “It seemed to me that if we could understand how [changes in DNA] make a dog so excited about chasing a ball, we could learn something about how our brains work and what goes wrong in psychiatric disease,” says project leader Elinor Karlsson.
Karlsson and colleagues launched darwinsdogs.org, inviting people to answer questions about their dogs’ behavior and share their pets’ DNA. More than 7,000 dog owners have already signed up, and the researchers are still recruiting new volunteers.
The process is simple and can be done alone with your dog, or even as a family activity. First, take an online quiz about your canine companion. The quiz is divided into multiple sections. Some sections gather basic information about your dog’s appearance, exercise and eating habits; others ask about simple behaviors, such as whether your dog crosses its front paws when lying down or tilts its head. (Some questions are philosophical puzzles like whether your dog knows it is a dog.) Each question has a comment box in case you want to explain an answer. Plan to spend at least half an hour completing the questionnaire.
Once the questions are answered and the dog is registered, researchers send you a DNA sampling kit that comes with written instructions and an easy-to-follow picture guide. The kit contains a large sterile cotton swab for collecting DNA from your dog’s mouth. (It’s an easy procedure for the human involved, and Sally, the 14-year-old Irish setter “volunteer” Science News sampled, was rather stoic.) Also included is a tape measure for recording your dog’s height, length, nose and collar size. When you’re done, just seal the sample, measurement sheet and consent form inside the return mailer and drop it in a mailbox.
Dog owners don’t need to pay a fee to participate, but they do need patience, Karlsson says. It takes time to analyze DNA, and the researchers can’t say exactly how long it will be before owners (and Science News) learn their dogs’ results. These results will include the dog’s raw genetic data as well as information about the dog’s possible ancestry. Knowing ancestry or particular mutations a dog carries may help veterinarians personalize a dog’s care. Dog trainers are being enlisted to give owners feedback on their dogs’ personalities and to suggest activities the dogs may enjoy. Karlsson hopes to create a way for impatient owners who are willing to donate money to the project to get their reports back faster.
If you’d like to vacation at the newly found planet orbiting Proxima Centauri, you might want to reconsider. It’s nearby astronomically — a mere 4.2 light-years away — but still too far away for any plausible transportation technology to reach within the current millennium.
In fact, it’s a pretty safe bet the Chicago Cubs will win the World Series before any human steps foot on Earth’s nearest exoplanetary neighbor (known as Proxima b). Unless P. Centaurian aliens arrive soon with a “To Serve Man” cookbook, your chances of visiting Proxima b before you die are about the same as sainthood for Ted Bundy. By the time anybody from here goes there, years will have five digits.
It took NASA’s New Horizons probe — the fastest spacecraft humans have ever launched — over nine years just to get to Pluto. At its top speed of 16 kilometers per second, New Horizons would need almost 80,000 years to get to Proxima Centauri.
Solar sail propulsion — in which lightweight craft could be accelerated by pressure from sunlight — would be a little be faster, but not by much, taking (by one estimate) 66,000 years to make the Proxima Centauri run.
Novel propulsion schemes have been proposed that could reduce that time substantially. A sail driven by alpha particle recoil, for instance, provides some serious advantages over solar sails, as Wenwu Zhang and colleagues point out in the August issue of Applied Radiation and Isotopes.
Ordinary rocket speed is limited by how fast the combusted fuel can eject exhaust; NASA has investigated a plasma engine design that can attain exhaust speeds of 50 km/s. But that approach requires huge energy input and high voltage, Zhang and colleagues point out (and so would be prohibitively expensive). Alpha particles emitted by radioactive substances, on the other hand, can speed away about 300 times faster. Therefore, Zhang and coauthors assert, “alpha decay particles … may be a potential solution for long-time acceleration in space.”
Usually, of course, a chunk of radioactive matter would emit alpha particles in all directions. So your craft would need a shield on one side to absorb the particles before they got very far. The rest would stream away in the opposite direction, pushing the craft forward (by virtue of the law of conservation of momentum). True, alpha particles are tiny and the effect of their recoil would be small. But it would add up. Shot into space with standard technology (thereby achieving a 16 km/s start-up speed), an alpha recoil spacecraft could eventually reach a speed in the range of 200–300 km/s or so. It helps to choose the right alpha-emitting material. Uranium-232 would be ideal. It has a long enough half-life (almost 70 years) to last for an extended voyage, but it also decays into daughter nuclei that emit alpha particles more frequently, boosting the recoil effect. (You won’t find any U-232 in uranium mines, though — it would need to be produced in nuclear transmutation factories.)
Assuming a suitably light and thin absorption material, Zhang and colleagues envision an alpha-powered interstellar sail about 24 meters across. They calculate a travel time to Proxima Centauri between about 4,000 and 9,000 years (depending on the ratio of fuel mass to total spacecraft mass). That would easily win the race against a solar sail, but would far exceed most people’s available vacation time. “Interstellar travel definitely asks for even better propulsion technologies,” Zhang and colleagues understate. And surely within 4,000 years somebody will invent a faster technology that could pass the alpha-decay craft and get to Proxima b first.
Other people already have ideas, as Science News astronomy writer Christopher Crockett noted in his story on the discovery of Proxima b. Philanthropist Yuri Milner recently announced a research project to explore the prospects of sending numerous nanocraft to Proxima Centauri’s neighborhood — the Alpha Centauri triple star system. (Proxima is the third star, presumably in orbit around Alpha Centauri A and B.) That plan envisions wafers weighing about a gram or so carried along by similar-mass light sails propelled by a powerful laser beam. If current technological dreams come true, tiny cameras and lasers on the wafer could capture and transmit information about Proxima b back to Earth.
Supposedly such nanocraft could reach 20 percent of the speed of light, allowing them to reach Proxima Centauri by maybe 20 years after launch. So there’s an outside chance of getting a message back from Proxima b before the Cubs win a World Series. But there’s no hope of hitching a ride on such a wafer, unless, perhaps, you’re a tardigrade.
Even if some futuristic technology permitted building a real ship, say the size of the space shuttle, that could fly 20 percent of the speed of light, it might not be a good idea. Such a ship could, in the wrong hands, become the most devastating weapon ever imagined. Flying 20 percent of light speed, a space shuttle would possess a kinetic energy roughly the equivalent of 1,000 hydrogen bombs (or millions of Hiroshima-sized bombs). Of course, it would be an expensive ship and probably nobody would want to crash it. Unless the people who took it to Proxima Centauri got really mad at the people back on Earth.
As of today, antibacterial soaps have a short shelf life. The U.S. Food and Drug Administration has banned soap products containing 19 active ingredients, including the notorious chemical triclosan, marketed as antiseptics.
While the term “antibacterial” suggests to consumers that such soaps prevent the spread of germs, evidence suggests otherwise. After asking companies to submit data on the safety and efficacy of their products back in 2013, the FDA noted in its September 2 final ruling that manufacturers failed to prove that these products were safe to use every day or that they were more effective than plain old soap and water at cutting infectious microbes.
“In fact, some data suggests that antibacterial ingredients may do more harm than good over the long-term,” Janet Woodcock, director of the FDA’s Center for Drug Evaluation and Research, said in a statement.
Triclosan, in particular, has a pretty bad rap. Found in many household products, the chemical ends up everywhere from vegetables to our snot. It’s been associated with exposure to toxic compounds, risk of staph infections and mucking up sewage treatment. Over a decade of damning data had already prompted some companies to remove triclosan from their products. Others will have a year to remove it and other newly banned ingredients from their recipes.
The FDA ban does not include antibacterial hand sanitizers, which the agency is evaluating separately. In the meantime, the FDA recommends using hand sanitizers that are at least 60 percent alcohol, or washing with old-school soap and water.
Live long and prosper In Science News’ special report on aging (SN: 7/23/16, p. 16), writers Laura Sanders, Tina Hesman Saey and Susan Milius explored the latest research — from the evolution of aging in the animal kingdom to scientists’ quest to delay the process in humans’ bodies and minds.
“I would very much like to know how research into aging may benefit people who are middle-aged or elderly now?” asked leftysrule200 in a Reddit Ask Me Anything about the special report. “Is there any research that can result in treatments in the very near future, or are the real-world applications only going to be visible in the distant future?” Middle-aged and elderly people will be the first to benefit from aging research, Saey says. “A clinical trial using the diabetes drug metformin as an antiaging therapy will begin soon. That drug will be tested on healthy people aged 60 and older,” she says.
Sanders cautions that most antiaging treatments are still a long way off. But various studies in rodents and humans provide potential clues to aging’s secrets. Blood from young rats, for instance, has been shown to rejuvenate the bodies and brains of old rats. Based on those findings, a clinical study in humans is now under way that is looking at the effects of plasma from young donors on the brains of people with Alzheimer’s. “If scientists could pinpoint the compounds that give young blood its power, then they could presumably develop drugs that mimic that process,” Sanders says. In the meantime, people may be able to slow the effects of aging by leading a healthy lifestyle. Sanders points to a long-term study of middle-aged women in Australia. Women who were more physically active had sharper memories 20 years later, the researchers found. Until proven antiaging treatments are available, “it seems that keeping the body physically active and strong is one of the best ways to keep your brain sharp as you age,” she says. Dino spills its guts Tiny tracks discovered in the blackened stomach contents of a 77-million-year-old duck-billed dinosaur fossil suggest gut parasites infected dinosaurs, Meghan Rosen reported in “Parasites wormed way into dino’s gut” (SN: 7/23/16, p. 14).
Online reader Jim Stangle Dvm thought the worms may not have been parasites at all. “It is more likely that the tunnels were formed by a scavenger worm [after the dino had died]. Still I think the findings are way cool!” he wrote.
It’s hard to say definitively whether the burrows were made by parasites or not, says paleontologist Justin Tweet. Scavenger worms could have tunneled through the gut after the dino’s death, but his team found only one type of worm burrow “which suggests that either only one kind of scavenger had access to the carcass,” or “that these burrows were an inside job,” Tweet says.
That’s no moon! A recently discovered asteroid appears to orbit Earth, but that’s just an illusion. The asteroid orbits the sun, but its constant proximity to Earth makes it the planet’s only known quasisatellite, Christopher Crockett reported in “Say What? Quasisatellite” (SN: 7/23/16, p. 5).
Reader Mike Lieber wondered if the moon could also be a quasisatellite. “The gravitational attraction of the sun on the moon is twice that of the Earth,” he wrote. “It seems that the apparent looping of the moon around the Earth is also illusory.”
The moon is a true satellite, Crockett says. If the sun were to disappear, the moon would continue orbiting Earth. “The moon is within Earth’s ‘Hill sphere,’ the volume of space in which Earth’s gravity is the dominant influence,” he says. “The strength of the gravitational force isn’t as important as by how much it changes from one place to another.” Given the moon’s proximity to our planet, Earth prevails. “The moon orbits Earth and the Earth-moon system orbits the sun,” he says.
Modern rattlesnakes have pared down their weaponry stockpile from their ancestor’s massive arsenal. Today’s rattlers have irreversibly lost entire toxin-producing genes over the course of evolution, narrowing the range of toxins in their venom, scientists report September 15 in Current Biology.
“After going through all the work of evolving powerful toxins, over time, some snakes have dispensed with them,” says study coauthor Sean B. Carroll, an investigator with the Howard Hughes Medical Institute who is at the University of Wisconsin–Madison. These modern rattlesnakes produce smaller sets of toxins that might be more specialized to their prey. Carroll, an evolutionary biologist, and his colleagues focused on a family of enzymes called phospholipase A2, or PLA2. Genes in the PLA2 family are one of the main sources of toxic proteins in the deadly cocktail of rattlesnake venom. This set of genes can be shuffled around, added to and deleted from to yield different collections of toxins.
Data from the genome — the complete catalog of an organism’s genetic material — can reveal how those genetic gymnastics have played out over time. Carroll’s team looked at the relevant genome regions in three modern rattlesnake species (western diamondback, eastern diamondback and Mojave) and also measured molecules that help turn genetic instructions into proteins. That showed not just how the genes were arranged, but which genes the snakes were actually using. Then, the scientists blended that data with genetic information about other closely related rattlesnakes to construct a potential evolutionary story for the loss of PLA2 genes in one group of snakes.
The most recent common ancestor of this group probably had a large suite of PLA2 genes 22 million years ago, the scientists found. That collection of genes, which probably came about through many gene duplications, coded for toxins affecting the brain, blood and muscles of the snake’s prey. But 4 million to 7 million years ago, some rattlesnake species independently dropped different combinations of those genes to get smaller and more specialized sets of venom toxins. For instance, three closely related rattlesnake species in the group lost the genes that made their venom neurotoxic.
“The surprise is [the genes’] wholesale loss at two levels: complete disappearance from the venom and complete disappearance from the genome,” Carroll says. In other words, some of the genes are still lurking in the genome but aren’t turned on. The proteins those genes produce don’t show up in the venom in modern snakes. But other genes have left the genome entirely — a more dramatic strategy than simple changes in gene regulation.
Environmental shifts might have encouraged this offloading of evolutionary baggage, Carroll says. If a certain snake species’ main food source stopped responding to a neurotoxin, the snake would waste energy producing a protein that didn’t do anything helpful. Plus, a rattlesnake doesn’t just invest in producing venom. It also needs to produce antibodies and other proteins to protect itself from its own poison, says Todd Castoe, an evolutionary biologist at the University of Texas at Arlington who wasn’t involved in the study. As a snake’s weapon becomes more complex, its shield does too — and that protection can use up resources.
Researchers also found that venom genes might not be consistent even within a single species of rattlesnake, perhaps because snakes in different areas specialize in different prey. One western diamondback rattlesnake that Carroll’s team sampled had unexpected extra genes that the other western diamondbacks didn’t have. His lab is currently looking into these within-species differences in venom composition to see how dynamic the PLA2 genome region still is today.
As for the ancestral rattlesnake, it’s impossible to say exactly how powerful the now-extinct reptile’s venom was, Carroll says. But the wider variety of enzymes this rattlesnake could hypothetically produce would have given it more flexibility to adapt its poison to environmental curveballs — an ability that Castoe describes as “the pinnacle of nastiness.”
Your summer suntan is almost entirely locally sourced. But a smidgen of that healthy glow hails not from the sun but from the ultraviolet light of nearby stars and other galaxies: less than one-billionth of 1 percent. Even photons lingering from the Big Bang contribute some: roughly 0.001 percent.
Simon Driver, an astronomer at the University of Western Australia in Crawley, and colleagues calculated these numbers, but not because they’re interested in tanning. They were trying to decipher the extragalactic background light, or EBL, a diffuse glow that fills the universe (SN: 9/7/13, p. 22). Using galaxy observations from multiple telescopes, they assessed the number of EBL photons, from infrared to ultraviolet, that reach Earth. About half originated with the formation of galaxy cores and supermassive black holes during roughly the first 4 billion years of cosmic history, the researchers report in the Aug. 20 Astrophysical Journal. The growth of disks of stars in galaxies since that time accounts for the other half.
