Thirsty zebra finches “drink” their body fat. The songbirds are the first birds shown to get through a day without water by breaking down adipose tissue to stay hydrated, says evolutionary physiologist Ulf Bauchinger.

Two earlier tests of deprived birds summoning water from their tissues report that birds rely on protein. But zebra finches (Taeniopygia guttata) coped with one-day droughts in the lab not by breaking down such tissues as muscle but with the safer choice of metabolizing fat, say Bauchinger, Joanna Rutkowska and their colleagues at Jagiellonian University in Kraków, Poland. In comfortable temperatures and humidity, the little birds (averaging 13.5 grams in weight) produced about 0.444 grams of water metabolically. That boost would have taken large amounts of fleshy moist protein, equivalent to one-third the mass of their flight muscles or three times the mass of their hearts, the researchers say online August 31 in the Journal of Experimental Biology.
“Exciting,” says Alexander Gerson of the University of Massachusetts Amherst, whose own work has shown birds taking the protein route. Gerson’s interest in animals deriving water by metabolizing body parts traces to research on migratory birds surviving several thousand kilometers of flight across the Sahara. His wind-tunnel tests of five-hour flights in dry air suggested that birds were fueling their flight with energy from fat reserves but were supplementing with water produced by breaking down protein.

What deprived birds do when they’re not migrating, however, might involve different trade-offs. But Gerson’s work with house sparrows kept from water still showed evidence of metabolizing proteins.

Unlike house sparrows, zebra finches have an evolutionary history of life in dry places, such as arid Australia. To see their water-management techniques, the researchers in Poland created total food and/or water shortages for lab birds just doing mundane finch things in cages instead of crossing a desert.

All the birds reached the end of their bad day without signs of dehydration, the researchers found. But 12 birds deprived of food and water showed more total fat loss than another 12 birds allowed to drink but not eat. Parched finches had 42 percent less fat than birds that had access to drinking water. Measures of lost lean tissue, including protein-rich muscle, barely differed.

Other bird species might respond to water shortages in the same way, Rutkowska speculates. Her test method differs a bit from the sparrow work. Gerson muses that zebra finches, with arid lands in their native range, might have different thresholds for metabolizing fat versus protein than house sparrows do.

For humans, Rutkowska says she gets asked about implications for dieting. Her answer: Sorry, no evidence of miracle shortcuts here.

Few people today could recite the scientific accomplishments of 19th century physician Julius Petri. But almost everybody has heard of his dish.

For more than a century, microbiologists have studied bacteria by isolating, growing and observing them in a petri dish. That palm-sized plate has revealed the microbial universe — but only a fraction, the easy stuff, the scientific equivalent of looking for keys under the lamppost.

But in the light — that is, the greenhouse-like conditions of a laboratory — most bacteria won’t grow. By one estimate, a staggering 99 percent of all microbial species on Earth have yet to be discovered, remaining in the shadows. They’re known as “microbial dark matter,” a reference to astronomers’ description of the vast invisible matter in space that makes up most of the mass in the cosmos.
In the last decade or so, though, scientists have developed new tools for growing bacteria and collecting genetic data, allowing faster and better identifications of microbes without ever removing them from natural conditions. A device called the iChip, for instance, encourages bacteria to grow in their home turf. (That device led to the discovery of a potential new antibiotic, in a time when infections are fast outwitting all the old drugs.) Recent genetic explorations of land, water and the human body have raised the prospect of finding hundreds of thousands of new bacterial species.

Already, the detection of these newfound organisms is challenging what scientists thought they knew about the chemical processes of biology, the tree of life and the manner in which microbes live and grow. The secrets of microbial dark matter may redefine how life evolved and exists, and even improve the understanding of, and treatments, for many diseases.

“Everything is changing,” says Kelly Wrighton, a microbiologist at Ohio State University in Columbus. “The whole field is full of enthusiasm and discovery.”
Counter culture
Microbiologists have in the past discovered new organisms without petri dishes, but those experiments were slow going. In one of her first projects, Tanja Woyke analyzed the bacterial community huddled inside a worm that lives in the Mediterranean Sea. Woyke, a microbiologist at the U.S. Department of Energy’s Joint Genome Institute in Walnut Creek, Calif., and colleagues published the report in Nature in 2006. It was two years in the making.

They relied on metagenomics, which involves gathering a sample of DNA from the environment — in soil, water or, in this case, worm insides. After extracting the genetic material of every microbe the worm contained, Woyke and colleagues determined the order, or sequences, of all the DNA units, or bases. Analyzing that sequence data allowed the researchers to infer the existence of four previously unknown microbes. It was a bit like obtaining boxes of jigsaw puzzle pieces that need assembly without knowing what the pictures look like or how many different puzzles they belong to, she says. The project involved 300 million bases and cost more than $100,000, using the time-consuming methods available at the time.
Just as Woyke was wrapping up the worm endeavor, new technology came online that gave genetic analysis a turbo boost. Sequencing a genome — the entirety of an organism’s DNA — became faster and cheaper than most scientists ever predicted. With next-generation sequencing, Woyke can analyze more than 100 billion bases in the time it takes to turn around an Amazon order, she says, and for just a few thousand dollars. By scooping up random environmental samples and searching for DNA with next-generation sequencing, scientists have turned up entirely new phyla of bacteria in practically every place they look. In 2013 in Nature, Woyke and her colleagues described more than 200 members of almost 30 previously unknown phyla. Finding so many phyla, the first big groupings within a kingdom, tells biologists that there’s a mind-boggling amount of uncharted diversity.

Woyke has shifted from these broad genetic fishing expeditions to working on individual bacterial cells. Gently breaking them open, she catalogs the DNA inside. Many of the organisms she has found defy previous rules of biological chemistry. Two genomes taken from a hydrothermal vent in the Pacific Ocean, for example, contained the code UGA, which stands for the bases uracil, guanine and adenine in a strand of RNA. UGA normally separates the genes that code for different proteins, acting like a period at the end of a sentence. In most other known species of animal or microbe, UGA means “stop.” But in these organisms, and one found about the same time in a human mouth, instead of “stop,” the sequence codes for the amino acid glycine. “That was something we had never seen before,” Woyke says. “The genetic code is not as rigid as we thought.”

Other recent finds also defy long-held notions of how life works. This year in the ISME Journal, Ohio State’s Wrighton reported a study of the enzyme RubisCO taken from a new microbial species that had never been grown in a laboratory. RubisCO, considered the most abundant protein on Earth, is key to photosynthesis; it helps convert carbon from the atmosphere into a form useful to living things. Because the majority of life on the planet would not exist without it, RubisCO is a familiar molecule — so familiar that most scientists thought they had found all the forms it could take. Yet, Wrighton says, “we found so many new versions of this protein that were entirely different from anything we had seen before.”

The list of oddities goes on. Some newly discovered organisms are so small that they barely qualify as bacteria at all. Jillian Banfield, a microbiologist at the University of California, Berkeley, has long studied the microorganisms in the groundwater pumped out of an aquifer in Rifle, Colo. To filter this water, she and her colleagues used a mesh with openings 0.2 micrometers wide — tiny enough that the water coming out the other side is considered bacteria-free. Out of curiosity, Banfield’s team decided to use next-generation sequencing to identify cells that might have slipped through. Sure enough, the water contained extremely minuscule sets of genes.
“We realized these genomes were really, really tiny,” Banfield says. “So we speculated if something has a tiny genome, the cells are probably pretty tiny, too.” And she has pictures to prove it. Last year in Nature Communications, she and her team published the first images (taken with an electron microscope) and detailed description of these ultrasmall microbes (see, right). They are probably difficult to isolate in a petri dish, Banfield says, because they are slow-growing and must scavenge many of the essential nutrients they need from the environment around them. Part of the price of a minigenome is that you don’t have room for the DNA to make everything you need to live.

Relationship status: It’s complicated
Banfield predicts that an “unimaginably large number” of species await in every cranny of the globe — soil, rocks, air, water, plants and animals. The human microbiome alone is probably teeming with unfamiliar microbial swarms. As a collection of organisms that live on and in the body, the human microbiome affects health in ways that science is just beginning to comprehend (SN: 2/6/16, p. 6).

Scientists from UCLA, the University of Washington in Seattle and colleagues recently offered the most detailed descriptions yet of a human mouth bacterium belonging to a new phylum: TM7. (TM stands for “Torf, mittlere Schicht,” German for a middle layer of peat; organisms in this phylum were first detected in the mid-1990s in a bog in northern Germany.) German scientists found TM7 by sifting through soil samples, using a test that’s specific for the genetic information in bacteria. In the last decade, TM7 species have been found throughout the human body. An overabundance of TM7 appears to be correlated with inflammatory bowel disease and gum disease, plus other conditions.

Until recently, members of TM7 have stubbornly resisted scientists’ efforts to study them. In 2015, Jeff McLean, a microbiologist at the University of Washington, and his collaborators finally isolated a TM7 species in a lab and deciphered its full genome. To do so, the team combined the best of old and new technology: First the researchers figured out how to grow most known oral bacteria together, and then they gradually thinned down the population until only two species remained: TM7 and a larger organism.

“The really remarkable thing is we finally found out how it lives,” McLean says, and why it wouldn’t grow in the lab. They discovered that this species of TM7, like the miniature bacteria in Colorado groundwater, doesn’t have the cellular machinery to get by on its own. Even more unusual, these bacteria pilfer missing amino acids and whatever else they need by latching on, like parasites, to a larger bacterium. Eventually they can kill their host. “We think this is the first example of a bacterium that lives in this manner,” McLean says.

He expects to see more unusual relationships among microbes as the dark matter comes to light. Many have evaded detection, he suspects, because of their small size (sometimes perhaps mistaken for bacterial debris) and dependence on other organisms for survival. In 2013 in the Proceedings of the National Academy of Sciences, McLean and colleagues were the first to describe a member of another uncultivated phylum, TM6. They found this group growing in the slime in a hospital sink drain. Later studies determined that the organism lives by tucking itself inside an amoeba.
One of the greatest hopes for microbial dark matter exploration is that newly found microbes might provide desperately needed antibiotics. From the 1940s to the 1960s, scientists discovered 10 new classes of drugs by testing chemicals found in soil and elsewhere for action against common infections. But only two classes of medically important antibiotics have been discovered in the last 30 years, and none since 1997. Some major infections are at the brink of being unstoppable because they’ve become resistant to most existing drugs (SN Online: 5/27/16). Many experts think that natural sources of antibiotics have been exhausted.

Maybe not. In 2015, a research team led by scientists from Northeastern University in Boston captured headlines after describing in Nature a new chemical extracted from a ground-dwelling bacterium in Maine. The scientists isolated the organism using the iChip, a thumb-sized tool that contains almost 400 separate wells, each large enough to hold only an individual bacterial cell plus a smidgen of its home dirt. The bacteria grow on this scaffold in part because they never leave their natural surroundings. In lauding the discovery, Francis Collins, director of the National Institutes of Health, called the iChip “an ingenious approach that enhances our ability to search one of nature’s richest sources of potential antibiotics: soil.” So far, the research team has discovered about 50,000 new strains of bacteria.

One strain held an antibiotic, named teixobactin (SN: 2/7/15, p. 10). In laboratory experiments, it killed two major pathogens in a way that did not appear easily vulnerable to the development of resistance. Most antibiotics work by disrupting a microbe’s survival mechanism. Over time, the bacteria genetically adapt, find a work-around and overcome the threat. This new antibiotic, however, prevents a microbe from assembling the molecules it needs to form an outer wall. Since the antibiotic interrupts a mechanical process and not just a specific chemical reaction, “there’s no obvious molecular target” for resistance, says Kim Lewis, a microbiologist at Northeastern.
Everything is illuminated
Some microbiologists feel like astronomers who, after years of staring up into the dark, were just handed the Hubble Space Telescope. Billions of galaxies are coming into view. Banfield expects this new microbial universe to be mapped over the next few years. Then, she says, an even more exciting era begins, as science explores how these dark matter bacteria make a living. “They are doing a lot of things, and we have no idea what,” she says.

Part of the excitement comes from knowing that microbes have a history of granting unexpected solutions to problems that scientists never expected to solve. Consider that the enzyme that makes the laboratory technique PCR possible came from organisms that live inside the thermal vents at Yellowstone National Park. PCR, which works like a photocopier to make multiple copies of DNA segments, is now used across a range of situations, from diagnosing cancer to paternity testing. CRISPR, a powerful gene-editing technology, relies on “molecular scissors” that were found in bacteria (SN: 9/3/16, p. 22).

Banfield estimates that 30 to 50 percent of newly discovered organisms contain proteins that never met a petri dish. Their function in the chemistry of life is an obscure mystery. Since microbes are the world’s most abundant organism, Banfield says, “the vast majority of life consists of biochemistry we don’t understand.” But once we do, the future could be very bright.

In a recent poll, more than four-fifths of U.S. adults could not name a living scientist. Of those who could, the plurality (40 percent) named Stephen Hawking. (The next highest response was Neil deGrasse Tyson, followed by Jane Goodall.) No offense to the rightfully famous Hawking, but at Science News we would like to change these results. Why aren’t more scientists, particularly those who are young and accomplished, household names? Where, we want to know, are the Taylor Swifts of science?

You’ll find some of them below. For the second year in a row, Science News is highlighting 10 early- and mid-career scientists on their way to widespread acclaim. The SN 10: Scientists to Watch includes a laser physicist with laserlike focus, a materials scientist challenging what it means to be alive and a computational biologist willing to get personal with his microbiome, among many others who are making important advances in their chosen fields.

Though none of these scientists have recorded hit singles — at least not that our reporting uncovered — all were nominated by a Nobel laureate or recently elected member of the National Academy of Sciences. And all were age 40 or younger at the time of nomination.

These remarkable individuals have diverse personalities and talents: They are tenacious and creative, practical-minded and dreamers. They are lab animals and data heads. Some seek simplicity, others complexity. If there is one unifying trait, though, it would have to be their passion — a quality so cliché among successful scientists that it has to be true. As Marie Curie famously wrote in a letter to her sister, “Sometimes my courage fails me and I think I ought to stop working…. But I am held by a thousand bonds.” She did not know, she confessed, whether she could live without the laboratory.

After a year caring for patients at the heart of Brazil’s Zika epidemic, pediatric neurologist Vanessa van der Linden has seen some of the worst cases.

She was one of the first researchers to link Zika virus to microcephaly, a now well-known birth defect marked by a small, misshapen head and, sometimes, a forehead that slopes backward. Babies with the defect can have other symptoms, too: Van der Linden has seen 24-hour crying bouts, spasms, extreme irritability and difficulty swallowing.
But microcephaly is just the tip of the Zika iceberg, she said September 22 at a workshop hosted by the National Institutes of Health in North Bethesda, Md. That’s something public health officials have been warning about for months. Now, scientists have begun to describe a head-to-toe assortment of health problems linked to Zika virus infection in utero; they’re calling it congenital Zika syndrome.

Still, the full scope of the problem, including the threat of more subtle neurologic disorders such as learning disabilities or developmental delays, remains murky, says Peter Hotez, a pediatrician and microbiologist at Baylor College of Medicine in Houston.

“That’s the big unknown: There’s probably a spectrum of illness,” similar to autism, he says. And it could take years for scientists to sort it all out.

It’s a problem that Brazil is facing now, and one that Puerto Rico has just begun grappling with.

As of September 23, the U.S. territory had reported 22,358 confirmed cases of Zika infection. Of these cases, 1,871 are pregnant women. Carmen Zorrilla, an obstetrician-gynecologist at the University of Puerto Rico’s Maternal-Infant Studies Center who has examined some of these women and their babies, emphasizes the importance of following up on all babies exposed to Zika in the womb — even those without apparent birth defects.
“Even if they are born normal,” she said, “it doesn’t mean they’ll be OK.”

Insidious problems
At the workshop, Zorrilla described the case of one of the first Puerto Rican babies born to a mother diagnosed with Zika. The baby didn’t have microcephaly, but she did have another unusual problem: She couldn’t open her eyes. A bad case of conjunctivitis (pinkeye) left her needing help opening her eyelids every morning — even 27 days after birth.
Zorrilla can’t say for sure whether the problem was related to Zika, but “it really concerned me,” she said. “This is the first baby I’ve seen with conjunctivitis that lasted for so long.”

The case may be another clue that Zika’s assaults on the body are widespread. And Zorrilla can expect to see more cases soon. Ultrasound examinations of 228 women in Puerto Rico with confirmed Zika infection have spotted brain abnormalities in 13 fetuses, including one with microcephaly.

Another observation could hint at problems yet to come: Most of the Zika-exposed fetuses tended to have slightly smaller heads than average, although “still within the normal limits,” Zorrilla said. But measurements of leg bones and stomach size indicate that the rest of the body is growing normally. Implications remain unclear, but the findings — preliminary results from Alberto de la Vega, also an obstetrician-gynecologist at the University of Puerto Rico — are the latest in a litany of anomalies linked to Zika.

Long-term problems aren’t unusual in babies infected with a different kind of virus that causes microcephaly. Like Zika, cytomegalovirus can infect babies in the womb. Most CMV-infected babies don’t have any obvious symptoms, but asymptomatic kids may have problems as they grow, including intellectual disabilities, hearing loss or cerebral palsy, researchers suggested in the October Brain and Development.

Beyond microcephaly, scientists have recently described other symptoms linked to Zika infection. In some babies, for example, Zika seems to damage hearing. Of 70 Zika-exposed infants born with microcephaly, 10 percent had some hearing loss, researchers noted in a Sept. 2 report published by the U.S. Centers for Disease Control and Prevention.
Zika can leave a mark on the eyes, too. More than a third of 29 babies with microcephaly had some sort of eye oddity, including mottled pigmenting and withered tissue, researchers reported in May in JAMA Ophthalmology.

Van der Linden has also observed a link between Zika and a deformity called arthrogryposis, where a child’s joints can be stuck in contorted positions — even in babies without microcephaly. The condition might stem from problems with infected babies’ motor neurons, the nerve cells that relay messages from the brain to the muscles, van der Linden and colleagues suggested August 9 in BMJ.

She has even seen babies born with normal head circumferences who later develop microcephaly or other brain defects. One mother, she says, came in five months after giving birth because she thought her baby wasn’t developing normally. Like children with congenital Zika syndrome, the baby’s head scans revealed “the same pattern of brain damage,” van der Linden says. This pattern includes a malformed cerebral cortex, the wrinkled outer layer of the brain, and calcifications, strange lumps of calcium deposited within the tissue.

Infiltrating the brain
Scientists still don’t know exactly how Zika damages the brain, but they have some ideas.

One recent report found that the virus can infiltrate and kill both neuroepithelial stem cells, which give rise to all sorts of brain cells, and radial glial cells, which can generate newborn neurons and help guide them to their proper place in the brain.

Zika also hinders these cells’ ability to split into new cells, Yale University neuroscientist Marco Onorati and colleagues reported September 6 in Cell Reports.
Stem cells at work in the fetal brain eventually give rise to structures responsible for thought and memory and learning, raising concerns of a cascade of problems down the road. “This is a virus that blocks the development of the fetal brain,” Hotez says. “That’s about the worst thing you can possibly imagine.”

And fetuses might not be the only ones at risk, he points out. “Kids in the first years of life also have growing, developing brains,” he says. “What if they get infected with Zika?”

It’s not an easy question to answer. But another disease could offer clues.

Malaria, for example, can cause severe neurological problems. In children, a condition called cerebral malaria may be linked to mental health disorders such as attention-deficit/hyperactivity disorder, antisocial behavior and depression, researchers reported in March in Malaria Journal.

Researchers will also need to watch out for long-term troubles in Zika-exposed babies born with no obvious symptoms, says the CDC’s Sonja Rasmussen. “We don’t want to make families too scared,” she says. “But we do recognize the possibility of later-on seizures or developmental delay.”

Since most people don’t show signs of Zika infection, pinpointing the total number of pregnant women (and babies) exposed to the virus may be impossible.

In the Americas, at least, the number is probably enormous. Tens of thousands of children may eventually suffer some sort of neurologic or psychiatric illness triggered by Zika, Hotez predicted in a paper published in JAMA Pediatrics in August.

Van der Linden can’t say whether the babies she has seen have learning disabilities or psychiatric illnesses, or other more subtle cognitive problems — most of her patients are between 9 months and 1 year old.

But she plans to follow these patients, and the babies who appeared normal at birth, for years. “We need time to better understand the disease,” she says.

Hotez agrees: “It’s going to take a generation of pediatric neurologists and infectious disease experts to figure this out.”

When babies are ready for solid foods, the meal usually arrives on a spoon. Parents scoop up pureed carrots, liquefied banana or soupy rice cereal and deliver it straight to their baby’s mouth (or forehead). But a different way of introducing solids is gaining ground. Called baby-led weaning, the approach is based on letting the baby feed herself whole foods such as a soft pear or a spear of cooked broccoli — no spoon required.

Advocates say that by having control over what goes in their mouths, babies learn to regulate their food intake, refine motor skills and perhaps even become more adventurous eaters. But critics fret that inexperienced eaters may be more likely to choke on solid foods that they feed themselves. A new study of about 200 Australian babies has some reassuring news: Provided that certain risky foods were avoided, babies who fed themselves solid foods were no more likely to choke than spoon-fed babies.

Half of the babies started solid food the traditional way, with parents spoon-feeding them purees and other mushy foods. The other half were given solid foods on their trays and encouraged to feed themselves. Parents were told that babies ought to be sitting up and in the presence of a caregiver while eating. And parents also received a list of risky foods to avoid: hard crackers, diced or hard meat, raw vegetables and popcorn made the list. (A general rule of thumb for checking whether the food is safe: If you can squish the food against the roof of your mouth, then it’s probably OK for your baby to try.)

Spoon-fed babies choked just as much as babies who fed themselves, the researchers report in the September Pediatrics. At 6 months of age, about 22 percent of spoon-fed babies had choked at least once. In the baby-led weaning group, about 18 percent of babies had choked at least once. Choking rates between the two groups were on par as the babies grew older.

There’s an important distinction here between gagging and true choking. Gagging is common among babies as their mouths learn to handle new textures and flavors. The throat slams shut and the mouth tries to get the offending food out. A gagging baby may have watery eyes, push his tongue out of his mouth and make retching movements. He may even puke. This can be hard for parents to watch, but gagging isn’t dangerous.

True choking is. This is when the airway becomes partially or fully blocked. The baby may cough or sputter in an attempt to dislodge the food. He may make a raspy, squeaky whisper as he tries to communicate distress. Or he may go silent. It’s always good to be up on infant CPR, particularly if you’ve got a new eater.

The babies who fed themselves seemed to quickly hone their skills. Initially, self-feeding babies gagged more often than spoon-fed babies at 6 months of age. But by 8 months old, self-feeders had become experts, gagging less than spoon-fed babies.
Although the news seems good for parents who want to try baby-led weaning, the research also turned up something concerning: Lots of babies were given risky foods, regardless of feeding style. At seven months of age, just over half of babies were given something from the no-feed list. By 12 months, almost all the babies had been given riskier foods that can lead to choking. Hard crackers, meat and whole grapes topped the list.

The results suggest that whether you feed your baby or you let your baby feed herself, it’s still important to pay attention to the type of food that’s going into her cute little mouth.

Scientists have lost their latest round of hide-and-seek with dark matter, but they’re not out of the game.

Despite overwhelming evidence that an exotic form of matter lurks unseen in the cosmos, decades of searches have failed to definitively detect a single particle of dark matter. While some scientists continue down the road of increasingly larger detectors designed to catch the particles, others are beginning to consider a broader landscape of possibilities for what dark matter might be.

“We’ve been looking where our best guess told us to look for all these years, and we’re starting to wonder if we maybe guessed wrong,” says theoretical astrophysicist Dan Hooper of Fermilab in Batavia, Ill. “People are just opening their minds to a wider range of options.”

Dark matter permeates the cosmos: The material keeps galaxies from flying apart and has left its imprints in the oldest light in the universe, the cosmic microwave background, which dates back to just 380,000 years after the Big Bang. Indirect evidence from dark matter’s gravitational influences shows that it makes up the bulk of the mass in the universe. But scientists can’t pin down what dark matter is without detecting it directly.
In new results published in August and September, three teams of scientists have come up empty-handed, finding no hints of dark matter. The trio of experiments searched for one particular variety of dark matter — hypothetical particles known as WIMPs, or weakly interacting massive particles, with a range of possible masses that starts at several times that of a proton. WIMPs, despite their name, are dark matter bigwigs — they have long been the favorite explanation for the universe’s missing mass. WIMPs are thought to interact with normal matter only via the weak nuclear force and gravity.

Part of WIMPs’ appeal comes from a prominent but unverified theory, supersymmetry, which independently predicts such particles. Supersymmetry posits that each known elementary particle has a heavier partner; the lightest partner particle could be a dark matter WIMP. But evidence for supersymmetry hasn’t materialized in particle collisions at the Large Hadron Collider in Geneva, so supersymmetry’s favored status is eroding (SN: 10/1/16, p. 12). Supersymmetry arguments for WIMPs are thus becoming shakier — especially since WIMPs aren’t showing up in detectors.

Scientists typically search for WIMPs by looking for interactions with normal matter inside a detector. Several current experiments use tanks of liquefied xenon, an element found in trace amounts in Earth’s atmosphere, in hopes of detecting the tiny amounts of light and electric charge that would be released when a WIMP strikes a xenon nucleus and causes it to recoil.

The three xenon experiments are the Large Underground Xenon, or LUX, experiment, located in the Sanford Underground Research Facility in Lead, S.D.; the PandaX-II experiment, located in China’s JinPing underground laboratory in Sichuan; and the XENON100 experiment, located in the Gran Sasso National Laboratory in Italy. Teams of scientists at the three locations each reported no signs of dark matter particles. The experiments are most sensitive to particles with masses around 40 or 50 times that of a proton. Scientists can’t completely rule out WIMPs of these masses, but the interactions would have to be exceedingly rare.
In initial searches, proponents of WIMPs expected that the particles would be easy to find. “It was thought to be like, ‘OK, we’ll run the detector for five minutes, discover dark matter, and we’re all done,’” says physicist Matthew Szydagis of the University at Albany in New York, a member of LUX. That has turned into decades of hard work. As WIMPs keep failing to turn up, some scientists are beginning to become less enamored with the particles and are considering other possibilities more closely.

One alternative dark matter contender now attracting more attention is the axion. This particle was originally proposed decades ago as part of the solution to a particle physics quandary known as the strong CP problem — the question of why the strong nuclear force, which holds particles together inside the nucleus, treats matter and antimatter equally. If dark matter consists of axions, the particle could therefore solve two problems at once.

Axions are small fry as dark matter goes — they can be as tiny as a millionth of a billionth the mass of a WIMP. The particles interact so feebly that they are extremely difficult to detect. If axions are dark matter, “you’re sitting in an enormous, dense sea of axions and you don’t even notice them,” says physicist Leslie Rosenberg of the University of Washington in Seattle, the leader of the Axion Dark Matter eXperiment. After a recent upgrade to the experiment, ADMX scientists are searching for dark matter axions using a magnetic field and special equipment to coax the particles to convert into photons, which can then be detected.
Although WIMPs and axions remain the front-runners, scientists are beginning to move beyond these two possibilities. In between the featherweight axions and hulking WIMPs lies a broad range of masses that hasn’t been well explored. Scientists’ favorite theories don’t predict dark matter particles with such intermediate masses, says theoretical physicist Kathryn Zurek of Lawrence Berkeley National Laboratory in California, but that doesn’t mean that dark matter couldn’t be found there. Zurek advocates a diverse search over a broad range of masses, instead of focusing on one particular theory. “Dark matter direct detection is not one-size-fits-all,” she says.
In two papers published in Physical Review Letters on January 7 and September 14, Zurek and colleagues proposed using superconductors — materials that allow electricity to flow without resistance — and superfluids, which allow fluids to flow without friction, to detect light dark matter particles. “We are trying to broaden as much as possible the tools to search for dark matter,” says Zurek. Likewise, scientists with the upcoming Super Cryogenic Dark Matter Search SNOLAB experiment, to be located in an underground lab in Sudbury, Canada, will use detectors made of germanium and silicon to search for dark matter with smaller masses than the xenon experiments can.

Scientists have not given up on xenon WIMP experiments. Soon some of those experiments will be scaling up — going from hundreds of kilograms of liquid xenon to tons — to improve their chances of catching a dark matter particle on the fly. The next version of XENON100, the XENON1T experiment (pronounced “XENON one ton”) is nearly ready to begin taking data. LUX’s next generation experiment, known as LUX-ZEPLIN or LZ, is scheduled to begin in 2020. PandaX-II scientists are also planning a sequel. Physicists are still optimistic that these detectors will finally find the elusive particles. “Maybe we will have some opportunity to see something nobody has seen,” says Xiangdong Ji of Shanghai Jiao Tong University, the leader of PandaX-II. “That’s what’s so exciting.”

In the sea of nondetections of dark matter, there is one glaring exception. For years, scientists with the DAMA/LIBRA experiment at Gran Sasso have claimed to see signs of dark matter, using crystals of sodium iodide. But other experiments have found no signs of DAMA’s dark matter. Many scientists believe that DAMA has been debunked. “I don’t know what generates the weird signal that DAMA sees,” says Hooper. “That being said, I don’t think it’s likely that it’s dark matter.”

But other experiments have not used the same technology as DAMA, says theoretical astrophysicist Katherine Freese of the University of Michigan in Ann Arbor. “There is no alternative explanation that anybody can think of, so that is why it is actually still very interesting.” Three upcoming experiments should soon close the door on the mystery, by searching for dark matter using sodium iodide, as DAMA does: the ANAIS experiment in the Canfranc Underground Laboratory in Spain, the COSINE-100 experiment at YangYang Underground Laboratory in South Korea, and the SABRE experiment, planned for the Stawell Underground Physics Laboratory in Australia.

Scientists’ efforts could still end up being for naught; dark matter may not be directly detectable at all. “It’s possible that gravity is the only lens with which we can view dark matter,” says Szydagis. Dark matter could interact only via gravity, not via the weak force or any other force. Or it could live in its own “hidden sector” of particles that interact among themselves, but mostly shun normal matter.

Even if no particles are detected anytime soon, most scientists remain convinced that an unseen form of matter exists. No alternative theory can explain all of scientists’ cosmological observations. “The human being is not going to give up for a long, long time to try to search for dark matter, because it’s such a big problem for us,” says Ji.

In empty space, quantum particles flit in and out of existence, electromagnetic fields permeate the vacuum, and space itself trembles with gravitational waves. What may seem like nothingness paradoxically teems with activity.

In Void: The Strange Physics of Nothing, physicist and philosopher James Owen Weatherall explores how physicists’ beliefs about nothingness have changed over several revolutionary periods. The void, Weatherall argues, is physics distilled to its bare essence. If physicists can’t agree on the properties of empty space, they won’t be able to explain the physics of planets or particles either.
Scientists have argued over nothingness since the early days of physics. Vacant space was unthinkable to Aristotle, and Descartes so abhorred the idea of a vacuum that he posited that an invisible “plenum” suffused the gaps between objects. But Isaac Newton upended this view, arguing that space was just a barren container into which matter is placed.

Since then, physicists have continued to flip-flop on this issue. The discovery in the mid-1800s that light is an electromagnetic wave led scientists to conclude that a vibrating medium, an “ether,” filled space. Just as sound waves vibrate the air, physicists thought there must be some medium for light waves to ripple. Albert Einstein tore down that idea with his special theory of relativity. Since the speed of light was the same for all observers, no matter their relative speeds, he reasoned, light could not be traveling through some absolute, stationary medium. But he later predicted, as part of his general theory of relativity, that space itself can ripple with gravitational waves (SN: 3/5/16, p. 6) — suggesting that the void is not quite empty.

Under the modern view of quantum physics, various fields pervade all of space, and particles are simply excitations, or waves, in these fields. Even in a vacuum, experiments show, fluctuating fields produce a background of transient particles and antiparticles. Does a space pulsating with gravitational waves and bubbling with particles really qualify as empty? It depends on the scientific definition of “nothing,” Weatherall argues, which may not conform to intuition.

Weatherall serves readers a fairly typical buffet of physics theories, dishing up Newtonian mechanics, relativity, quantum mechanics and a small helping of string theory. But he does this through a lens that highlights connections between those theories in a novel way. Weatherall contends, for instance, that differing notions of nothingness between theories of general relativity and quantum mechanics could help explain why scientists are still struggling to unite the two ideas into one theory of quantum gravity.

Exploring the physics of nothing demands quite a bit of wading through the physics of something, and it’s not always clear how the threads Weatherall is following will lead back to the void. When he finally makes these connections, though, they often reveal insights that are missed in the typical focus on things of substance.

The new record-holder for fastest flying animal isn’t a bat out of hell. It’s a bat from Brazil, a new study claims. Brazilian free-tailed bats (Tadarida brasiliensis) can reach ground speeds of 160 kilometers per hour.

It’s unclear why they need that kind of speed to zoom through the night sky, but Brazilian bats appear to flap their wings in a similar fashion to ultrafast birds, an international group of researchers report November 9 in Royal Society Open Science. A sleek body, narrow wings and a wingspan longer than most other bats’ doesn’t hurt either.

Radio transmitters attached to the backs of seven bats allowed the team, led by evolutionary biologist Gary McCracken of the University of Tennessee, Knoxville, to track the flight path and speed of the bats after they emerged from a cave in southwestern Texas. All seven reached almost 100 km/hr when flying horizontally; one bat hit about 160 km/hr.

Until now, common swifts held the record of fastest fliers, soaring at up to 112 km/hr, often with help from wind and gravity. The Brazilian bats, however, reached their higher speeds with no assist. Since bat flight is rarely studied, there may be even faster bats out there, the researchers speculate.

An oddball superconductor is the first of its kind — and if scientists are lucky, its discovery may lead to others.

At a frigid temperature 5 ten-thousandths of a degree above absolute zero, bismuth becomes a superconductor — a material that conducts electricity without resistance — physicists from the Tata Institute of Fundamental Research in Mumbai, India, report online December 1 in Science.

Bismuth, a semimetallic element, conducts electricity less efficiently than an ordinary metal. It is unlike most other known superconductors in that it has very few mobile electrons. Consequently, the prevailing theory of superconductivity doesn’t apply.
The result is “quite important,” says theoretical physicist Marvin Cohen of the University of California, Berkeley. New ideas — either a different theory or a tweak to the standard one — are needed to explain bismuth’s superconductivity. “It might lead us to a better theory of superconductivity with more details,” Cohen says.

An improved theoretical understanding might lead scientists to other superconductors, potentially ones that work at more practical temperatures, says Srinivasan Ramakrishnan, a coauthor of the paper. “It opens a new path for discovering new superconducting materials.”

Physicists’ ultimate goal is to find a superconductor that operates at room temperature. Such a material could be used to replace standard metals in wires and electronics, providing massive energy savings and technological leaps, from advanced supercomputers to magnetically levitating trains.

To confirm that bismuth was superconducting, Ramakrishnan and collaborators chilled ultrapure crystals of bismuth, while shielding the crystals from magnetic fields. Below 0.00053 kelvins (about –273° Celsius), the researchers observed a hallmark of superconductivity known as the Meissner effect, in which the superconductor expunges magnetic fields from within itself.

In the standard theory of superconductivity, electrons partner up in a fashion that removes resistance to their flow, thanks to the electrons’ interactions with ions in the material. But the theory, known as the Bardeen-Cooper-Schrieffer, or BCS, theory, works only for materials with many free-floating electrons. A typical superconductor has about one mobile electron for each atom in the material, while in bismuth each electron is shared by 100,000 atoms.
Bismuth has previously been made to superconduct when subjected to high pressure or when formed into nanoparticles, or when its atoms are disordered, rather than neatly arranged in a crystal. But under those conditions, bismuth behaves differently, so the BCS theory still applies. The new result is the first sign of superconducting bismuth in its normal form.

Another class of superconductors, known as high-temperature superconductors, likewise remains enigmatic (SN: 8/8/15, p. 12). Scientists have yet to reach a consensus on how they work. Though these superconductors must be cooled, they operate at relatively high temperatures, above the boiling point of liquid nitrogen (77 kelvins, or –196° Celsius).

Bismuth’s unusual behavior provides another handle with which to investigate the still-mysterious phenomenon of superconductivity. In addition to its low electron density and unexpected superconductivity, bismuth has several anomalous properties, including unusual optical and magnetic behavior. “A good global picture is missing” for explaining the abnormal element, says theoretical physicist Ganapathy Baskaran of the Institute of Mathematical Sciences in Chennai, India. “I think it’s only a tip of an iceberg.”

In a better world, it would be the big news of the year just to report that Arctic sea ice shrank to 4.14 million square kilometers this summer, well below the 1981–2010 average of 6.22 million square kilometers (SN Online: 9/19/16). But in this world of changing climate, extreme summer ice loss has become almost expected. More novel in 2016 were glimpses of the complex biological consequences of melting at the poles and the opening of Arctic passageways, talked about for at least a decade and now well under way.

With top-of-the-world trade and tourist shortcuts opening, less ice means more travel. Europe-to-Asia shipping routes will typically shorten by about 10 days by midcentury, a report in Geophysical Research Letters predicted. Hopes for Northwest Passage routes obsessed (and killed) explorers in previous centuries, but in 2016, the thousand-passenger cruise ship Crystal Serenity offered the first megascale tourist trip from Alaska to New York with fine dining, casino gambling and an escort icebreaker vessel.
Biologists are delving into consequences for organisms other than human tourists — or the much-discussed polar bear. “There’s been a marked shift in the research community,” says climate change ecologist Eric Post of the University of California, Davis. There’s new interest in considering more than just species that dwell on sea ice, with researchers looking for the less direct effects of declining ice.
In the February Global Change Biology, eight scientists issued a call for observations of what could be early signs of faunal exchange: the mingling of Atlantic and Pacific species. One possible indicator is the sighting of gray whales off the coast of Namibia and also off Israel, even though that species went extinct in the Atlantic two centuries ago. These whales feed by snouting around in soft ocean bottoms, adding another predator to the system but also creating new habitat opportunities for some creatures (SN: 1/23/16, p. 14).

Since the call was published, biodiversity scientist Seabird McKeon of Colby College in Waterville, Maine, has heard new reports, such as a sighting of an ancient murrelet off the coast of Maine. It’s not the first wrong-coast report for the bird, which typically resides in the northern Pacific, but repeat sightings could be important, too. “What I think we’re seeing is not just new species coming across, but also perhaps an increased chance of survival and reproduction if more come over,” McKeon says. He is hoping to get new data from the online Encyclopedia of Life’s upcoming Fresh Data system, which connects scientists to people reporting nature observations.
For terrestrial northerners, melting ice often means loss of mobility. Peary caribou on the 36,000 or more islands of Canada’s northern archipelago occasionally use ice bridges to travel to new territories and mix genes with other populations. Yet ice losses since 1979 have

made it some 15 percent harder

to find traveling paths, researchers reported in September inBiology Letters

(

SN: 10/29/16, p. 8

).

Even some plants such as dwarf birch probably travel by ice, scientists also reported in September in Biology Letters. Reconstructing long-ago sea ice extent and plant colonization dates suggests that seeds hitchhiked on slowly creeping frozen conveyors around northern Europe to colonize new territory at the end of the Ice Age. Losing ice roads could lead to tattered, disconnected populations as recolonization becomes less likely. Yet, there are pluses and minuses, says Post, who is helping to develop a package of scientific articles for Biology Letters on the biological effects of sea ice loss. Reseeding populations after a wipeout could be more difficult with tattered ice, but for the highly specialized and vulnerable plants very far north, the loss of sea ice could slow the arrival of invasive species that threaten the natives.

The minimum summer sea ice extent since 1979 has declined by about 87,000 square kilometers per year, equivalent to an area more than three times the size of New Jersey disappearing annually, as Post has put it. The September 2016 sea ice minimum didn’t break a record, as some had expected it might. It tied for second worst, behind the 2012 minimum, and roughly equaled the 2007 minimum. 2016 did set a new record low for winter Arctic ice extent (SN Online: 3/28/16).
Sea ice changes reverberate through the ecosystem. Ice melting cues the springtime phytoplankton blooms that feed copepods and other tiny marine grazers. The grazers feed their predators and, in turn, the predators of those predators. In years when spring warming brings an early ice retreat, the phyto-plankton bloom is not a huge, rich burst. It favors smaller grazing zooplankton that don’t fuel as much of a boom in their predators, marine ecologist Martin Renner of Homer, Alaska, and colleagues reported in a paper for the Biology Letters special collection.

Tracing the effects of shrinking ice through these grazers to fish to seabirds revealed a tangled web of ups and downs and shifting foraging grounds. In the end, Renner and colleagues predict “a very different eastern Bering Sea ecosystem and fishery than we know today.” And that may be far from the only sea change in the far north.