A 13-sided shape known as “the hat” has mathematicians tipping their caps.

It’s the first true example of an “einstein,” a single shape that forms a special tiling of a plane: Like bathroom floor tile, it can cover an entire surface with no gaps or overlaps but only with a pattern that never repeats.

“Everybody is astonished and is delighted, both,” says mathematician Marjorie Senechal of Smith College in Northampton, Mass., who was not involved with the discovery. Mathematicians had been searching for such a shape for half a century. “It wasn’t even clear that such a thing could exist,” Senechal says.

Although the name “einstein” conjures up the iconic physicist, it comes from the German ein Stein, meaning “one stone,” referring to the single tile. The einstein sits in a weird purgatory between order and disorder. Though the tiles fit neatly together and can cover an infinite plane, they are aperiodic, meaning they can’t form a pattern that repeats.

With a periodic pattern, it’s possible to shift the tiles over and have them match up perfectly with their previous arrangement. An infinite checkerboard, for example, looks just the same if you slide the rows over by two. While it’s possible to arrange other single tiles in patterns that are not periodic, the hat is special because there’s no way it can create a periodic pattern.
Identified by David Smith, a nonprofessional mathematician who describes himself as an “imaginative tinkerer of shapes,” and reported in a paper posted online March 20 at arXiv.org, the hat is a polykite — a bunch of smaller kite shapes stuck together. That’s a type of shape that hadn’t been studied closely in the search for einsteins, says Chaim Goodman-Strauss of the National Museum of Mathematics in New York City, one of a group of trained mathematicians and computer scientists Smith teamed up with to study the hat.

It’s a surprisingly simple polygon. Before this work, if you’d asked what an einstein would look like, Goodman-Strauss says, “I would’ve drawn some crazy, squiggly, nasty thing.”

Mathematicians previously knew of nonrepeating tilings that involved multiple tiles of different shapes. In the 1970s, mathematician Roger Penrose discovered that just two different shapes formed a tiling that isn’t periodic (SN: 3/1/07). From there, “It was natural to wonder, could there be a single tile that does this?” says mathematician Casey Mann of the University of Washington Bothell, who was not involved with the research. That one has finally been found, “it’s huge.”
Other shapes have come close. Taylor-Socolar tiles are aperiodic, but they are a jumble of multiple disconnected pieces — not what most people think of as a single tile. “This is the first solution without asterisks,” says mathematician Michaël Rao of CNRS and École Normale Supérieure de Lyon in France.

Smith and colleagues proved that the tile was an einstein in two ways. One came from noticing that the hats arrange themselves into larger clusters, called metatiles. Those metatiles then arrange into even larger supertiles, and so on indefinitely, in a type of hierarchical structure that is common for tilings that aren’t periodic. This approach revealed that the hat tiling could fill an entire infinite plane, and that its pattern would not repeat.

The second proof relied on the fact that the hat is part of a continuum of shapes: By gradually changing the relative lengths of the sides of the hat, the mathematicians were able to form a family of tiles that can take on the same nonrepeating pattern. By considering the relative sizes and shapes of the tiles at the extremes of that family — one shaped like a chevron and the other reminiscent of a comet — the team was able to show that the hat couldn’t be arranged in a periodic pattern.
While the paper has yet to be peer-reviewed, the experts interviewed for this article agree that the result seems likely to hold up to detailed scrutiny.

Nonrepeating patterns can have real-world connections. Materials scientist Dan Shechtman won the 2011 Nobel Prize in chemistry for his discovery of quasicrystals, materials with atoms arranged in an orderly structure that never repeats, often described as analogs to Penrose’s tilings (SN: 10/5/11). The new aperiodic tile could spark further investigations in materials science, Senechal says.

Similar tilings have inspired artists, and the hat appears to be no exception. Already the tiling has been rendered artistically as smiling turtles and a jumble of shirts and hats. Presumably it’s only a matter of time before someone puts hat tiles on a hat.

The new aperiodic monotile discovered by Dave Smith, Joseph Myers, Craig Kaplan, and Chaim Goodman-Strauss, rendered as shirts and hats. The hat tiles are mirrored relative to the shirt tiles. pic.twitter.com/BwuLUPVT5a

— Robert Fathauer (@RobFathauerArt) March 21, 2023
And the hat isn’t the end. Researchers should continue the hunt for additional einsteins, says computer scientist Craig Kaplan of the University of Waterloo in Canada, a coauthor of the study. “Now that we’ve unlocked the door, hopefully other new shapes will come along.”

The ghost catfish transforms from glassy to glam when white light passes through its mostly transparent body. Now, scientists know why.

The fish’s iridescence comes from light bending as it travels through microscopic striped structures in the animal’s muscles, researchers report March 13 in the Proceedings of the National Academy of Sciences.

Many fishes with iridescent flair have tiny crystals in their skin or scales that reflect light (SN: 4/6/21). But the ghost catfish (Kryptopterus vitreolus) and other transparent aquatic species, like eel larvae and icefishes, lack such structures to explain their luster.

The ghost catfish’s see-through body caught the eye of physicist Qibin Zhao when he was in an aquarium store. The roughly 5-centimeter-long freshwater fish is a popular ornamental species. “I was standing in front of the tank and staring at the fish,” says Zhao, of Shanghai Jiao Tong University. “And then I saw the iridescence.”

To investigate the fish’s colorful properties, Zhao and colleagues first examined the fish under different lighting conditions. The researchers determined its iridescence arose from light passing through the fish rather than reflecting off it. By using a white light laser to illuminate the animal’s muscles and skin separately, the team found that the muscles generated the multicolored sheen.
The researchers then characterized the muscles’ properties by analyzing how X-rays scatter when traveling through the tissue and by looking at it with an electron microscope. The team identified sarcomeres — regularly spaced, banded structures, each roughly 2 micrometers long, that run along the length of muscle fibers — as the source of the iridescence.

The sarcomeres’ repeating bands, comprised of proteins that overlap by varying amounts, bend white light in a way that separates and enhances its different wavelengths. The collective diffraction of light produces an array of colors. When the fish contracts and relaxes its muscles to swim, the sarcomeres slightly change in length, causing a shifting rainbow effect.
The purpose of the ghost catfish’s iridescence is a little unclear, says Heok Hee Ng, an independent ichthyologist in Singapore who was not involved in the new study. Ghost catfish live in murky water and seldom rely on sight, he says. But the iridescence might help them visually coordinate movements when traveling in schools, or it could help them blend in with shimmering water to hide from land predators, like some birds, he adds.

Regardless of function, Ng is excited to see scientists exploring the ghost catfish’s unusual characteristics.

“Fishes actually have quite a number of these interesting structures that serve them in many ways,” he says. “And a lot of these structures are very poorly studied.”

Tiny particles of plastic have been found everywhere — from the deepest place on the planet, the Mariana Trench, to the top of Mount Everest. And now more and more studies are finding that microplastics, defined as plastic pieces less than 5 millimeters across, are also in our bodies.

“What we are looking at is the biggest oil spill ever,” says Maria Westerbos, founder of the Plastic Soup Foundation, an Amsterdam-based nonprofit advocacy organization that works to reduce plastic pollution around the world. Nearly all plastics are made from fossil fuel sources. And microplastics are “everywhere,” she adds, “even in our bodies.”
In recent years, microplastics have been documented in all parts of the human lung, in maternal and fetal placental tissues, in human breast milk and in human blood. Microplastics scientist Heather Leslie, formerly of Vrije Universiteit Amsterdam, and colleagues found microplastics in blood samples from 17 of 22 healthy adult volunteers in the Netherlands. The finding, published last year in Environment International, confirms what many scientists have long suspected: These tiny bits can get absorbed into the human bloodstream.

“We went from expecting plastic particles to be absorbable and present in the human bloodstream to knowing that they are,” Leslie says.
The findings aren’t entirely surprising; plastics are all around us. Durable, versatile and cheap to manufacture, they are in our clothes, cosmetics, electronics, tires, packaging and so many more items of daily use. And the types of plastic materials on the market continues to increase. “There were around 3,000 [plastic materials] when I started researching microplastics over a decade ago,” Leslie says. “Now there are over 9,600. That’s a huge number, each with its own chemical makeup and potential toxicity.”

Though durable, plastics do degrade, by weathering from water, wind, sunlight or heat — as in ocean environments or in landfills — or by friction, in the case of car tires, which releases plastic particles along roadways during motion and braking.

In addition to studying microplastic particles, researchers are also trying to get a handle on nanoplastics, particles which are less than 1 micrometer in length. “The large plastic objects in the environment will break down into micro- and nanoplastics, constantly raising particle numbers,” says toxicologist Dick Vethaak of the Institute for Risk Assessment Sciences at Utrecht University in the Netherlands, who collaborated with Leslie on the study finding microplastics in human blood.

Nearly two decades ago, marine biologists began drawing attention to the accumulation of microplastics in the ocean and their potential to interfere with organism and ecosystem health (SN: 2/20/16, p. 20). But only in recent years have scientists started focusing on microplastics in people’s food and drinking water — as well as in indoor air.

Plastic particles are also intentionally added to cosmetics like lipstick, lip gloss and eye makeup to improve their feel and finish, and to personal care products, such as face scrubs, toothpastes and shower gels, for the cleansing and exfoliating properties. When washed off, these microplastics enter the sewage system. They can end up in the sewage sludge from wastewater treatment plants, which is used to fertilize agricultural lands, or even in treated water released into waterways.

What if any damage microplastics may do when they get into our bodies is not clear, but a growing community of researchers investigating these questions thinks there is reason for concern. Inhaled particles might irritate and damage the lungs, akin to the damage caused by other particulate matter. And although the composition of plastic particles varies, some contain chemicals that are known to interfere with the body’s hormones.

Currently there are huge knowledge gaps in our understanding of how these particles are processed by the human body.

How do microplastics get into our bodies?
Research points to two main entry routes into the human body: We swallow them and we breathe them in.

Evidence is growing that our food and water is contaminated with microplastics. A study in Italy, reported in 2020, found microplastics in everyday fruits and vegetables. Wheat and lettuce plants have been observed taking up microplastic particles in the lab; uptake from soil containing the particles is probably how they get into our produce in the first place.

Sewage sludge can contain microplastics not only from personal care products, but also from washing machines. One study looking at sludge from a wastewater treatment plant in southwest England found that if all the treated sludge produced there were used to fertilize soils, a volume of microplastic particles equivalent to what is found in more than 20,000 plastic credit cards could potentially be released into the environment each month.

On top of that, fertilizers are coated with plastic for controlled release, plastic mulch film is used as a protective layer for crops and water containing microplastics is used for irrigation, says Sophie Vonk, a researcher at the Plastic Soup Foundation.

“Agricultural fields in Europe and North America are estimated to receive far higher quantities of microplastics than global oceans,” Vonk says.
A recent pilot study commissioned by the Plastic Soup Foundation found microplastics in all blood samples collected from pigs and cows on Dutch farms, showing livestock are capable of absorbing some of the plastic particles from their feed, water or air. Of the beef and pork samples collected from farms and supermarkets as part of the same study, 75 percent showed the presence of microplastics. Multiple studies document that microplastic particles are also in fish muscle, not just the gut, and so are likely to be consumed when people eat seafood.

Microplastics are in our drinking water, whether it’s from the tap or bottled. The particles may enter the water at the source, during treatment and distribution, or, in the case of bottled water, from its packaging.

Results from studies attempting to quantify levels of human ingestion vary dramatically, but they suggest people might be consuming on the order of tens of thousands of microplastic particles per person per year. These estimates may change as more data come in, and they will likely vary depending on people’s diets and where they live. Plus, it is not yet clear how these particles are absorbed, distributed, metabolized and excreted by the human body, and if not excreted immediately, how long they might stick around.

Babies might face particularly high exposures. A small study of six infants and 10 adults found that the infants had more microplastic particles in their feces than the adults did. Research suggests microplastics can enter the fetus via the placenta, and babies could also ingest the particles via breast milk. The use of plastic feeding bottles and teething toys adds to children’s microplastics exposure.

Microplastic particles are also floating in the air. Research conducted in Paris to document microplastic levels in indoor air found concentrations ranging from three to 15 particles per cubic meter of air. Outdoor concentrations were much lower.

Airborne particles may turn out to be more of a concern than those in food. One study reported in 2018 compared the amount of microplastics present within mussels harvested off Scotland’s coasts with the amount of microplastics present in indoor air. Exposure to microplastic fibers from the air during the meal was far higher than the risk of ingesting microplastics from the mussels themselves.

Extrapolating from this research, immunologist Nienke Vrisekoop of the University Medical Center Utrecht says, “If I keep a piece of fish on the table for an hour, it has probably gathered more microplastics from the ambient air than it has from the ocean.”
What’s more, a study of human lung tissue reported last year offers solid evidence that we are breathing in plastic particles. Microplastics showed up in 11 of 13 samples, including those from the upper, middle and lower lobes, researchers in England reported.

Perhaps good news: Microplastics seem unable to penetrate the skin. “The epidermis holds off quite a lot of stuff from the outside world, including [nano]particles,” Leslie says. “Particles can go deep into your skin, but so far we haven’t observed them passing the barrier, unless the skin is damaged.”

What do we know about the potential health risks?
Studies in mice suggest microplastics are not benign. Research in these test animals shows that lab exposure to microplastics can disrupt the gut microbiome, lead to inflammation, lower sperm quality and testosterone levels, and negatively affect learning and memory.

But some of these studies used concentrations that may not be relevant to real-world scenarios. Studies on the health effects of exposure in humans are just getting under way, so it could be years before scientists understand the actual impact in people.

Immunologist Barbro Melgert of the University of Groningen in the Netherlands has studied the effects of nylon microfibers on human tissue grown to resemble lungs. Exposure to nylon fibers reduced both the number and size of airways that formed in these tissues by 67 percent and 50 percent, respectively. “We found that the cause was not the microfibers themselves but rather the chemicals released from them,” Melgert says.

“Microplastics could be considered a form of air pollution,” she says. “We know air pollution particles tend to induce stress in our lungs, and it will probably be the same for microplastics.”

Vrisekoop is studying how the human immune system responds to microplastics. Her unpublished lab experiments suggest immune cells don’t recognize microplastic particles unless they have blood proteins, viruses, bacteria or other contaminants attached. But it is likely that such bits will attach to microplastic particles out in the environment and inside the body.

“If the microplastics are not clean … the immune cells [engulf] the particle and die faster because of it,” Vrisekoop says. “More immune cells then rush in.” This marks the start of an immune response to the particle, which could potentially trigger a strong inflammatory reaction or possibly aggravate existing inflammatory diseases of the lungs or gastrointestinal tract.
Some of the chemicals added to make plastic suitable for particular uses are also known to cause problems for humans: Bisphenol A, or BPA, is used to harden plastic and is a known endocrine disruptor that has been linked to developmental effects in children and problems with reproductive systems and metabolism in adults (SN: 7/18/09, p. 5). Phthalates, used to make plastic soft and flexible, are associated with adverse effects on fetal development and reproductive problems in adults along with insulin resistance and obesity. And flame retardants that make electronics less flammable are associated with endocrine, reproductive and behavioral effects.

“Some of these chemical products that I worked on in the past [like the polybrominated diphenyl ethers used as flame retardants] have been phased out or are prohibited to use in new products now [in the European Union and the United States] because of their neurotoxic or disrupting effects,” Leslie says.
What are the open questions?
The first step in determining the risk of microplastics to human health is to better understand and quantify human exposure. Polyrisk — one of five large-scale research projects under CUSP, a multidisciplinary group of researchers and experts from 75 organizations across 21 European countries studying micro- and nanoplastics — is doing exactly that.

Immunotoxicologist Raymond Pieters, of the Institute for Risk Assessment Sciences at Utrecht University and coordinator of Polyrisk, and colleagues are studying people’s inhalation exposure in a number of real-life scenarios: near a traffic light, for example, where cars are likely to be braking, versus a highway, where vehicles are continuously moving. Other scenarios under study include an indoor sports stadium, as well as occupational scenarios like the textile and rubber industry.

Melgert wants to know how much microplastic is in our houses, what the particle sizes are and how much we breathe in. “There are very few studies looking at indoor levels [of microplastics],” she says. “We all have stuff in our houses — carpets, insulation made of plastic materials, curtains, clothes — that all give off fibers.”

Vethaak, who co-coordinates MOMENTUM, a consortium of 27 research and industry partners from the Netherlands and seven other countries studying microplastics’ potential effects on human health, is quick to point out that “any measurement of the degree of exposure to plastic particles is likely an underestimation.” In addition to research on the impact of microplastics, the group is also looking at nanoplastics. Studying and analyzing these smallest of plastics in the environment and in our bodies is extremely challenging. “The analytical tools and techniques required for this are still being developed,” Vethaak says.

Vethaak also wants to understand whether microplastic particles coated with bacteria and viruses found in the environment could spread these pathogens and increase infection rates in people. Studies have suggested that microplastics in the ocean can serve as safe havens for germs.

Alongside knowing people’s level of exposure to microplastics, the second big question scientists want to understand is what if any level of real-world exposure is harmful. “This work is confounded by the multitude of different plastic particle types, given their variations in size, shape and chemical composition, which can affect uptake and toxicity,” Leslie says. “In the case of microplastics, it will take several more years to determine what the threshold dose for toxicity is.”

Several countries have banned the use of microbeads in specific categories of products, including rinse-off cosmetics and toothpastes. But there are no regulations or policies anywhere in the world that address the release or concentrations of other microplastics — and there are very few consistent monitoring efforts. California has recently taken a step toward monitoring by approving the world’s first requirements for testing microplastics in drinking water sources. The testing will happen over the next several years.

Pieters is very pragmatic in his outlook: “We know ‘a’ and ‘b,’” he says. “So we can expect ‘c,’ and ‘c’ would [imply] a risk for human health.”

He is inclined to find ways to protect people now even if there is limited or uncertain scientific knowledge. “Why not take a stand for the precautionary principle?” he asks.

For people who want to follow Pieters’ lead, there are ways to reduce exposure.

“Ventilate, ventilate, ventilate,” Melgert says. She recommends not only proper ventilation, including opening your windows at home, but also regular vacuum cleaning and air purification. That can remove dust, which often contains microplastics, from surfaces and the air.

Consumers can also choose to avoid cosmetics and personal care products containing microbeads. Buying clothes made from natural fabrics like cotton, linen and hemp, instead of from synthetic materials like acrylic and polyester, helps reduce the shedding of microplastics during wear and during the washing process.

Specialized microplastics-removal devices, including laundry balls, laundry bags and filters that attach to washing machines, are designed to reduce the number of microfibers making it into waterways.

Vethaak recommends not heating plastic containers in the microwave, even if they claim to be food grade, and not leaving plastic water bottles in the sun.

Perhaps the biggest thing people can do is rely on plastics less. Reducing overall consumption will reduce plastic pollution, and so reduce microplastics sloughing into the air and water.

Leslie recommends functional substitution: “Before you purchase something, think if you really need it, and if it needs to be plastic.”

Westerbos remains hopeful that researchers and scientists from around the world can come together to find a solution. “We need all the brainpower we have to connect and work together to find a substitute to plastic that is not toxic and doesn’t last [in the environment] as long as plastic does,” she says.

A thick sphere of icy debris known as the Oort cloud shrouds the solar system. Other star systems may harbor similar icy reservoirs, and those clouds may be visible in the universe’s oldest light, researchers report.

Astronomer Eric Baxter of the University of Pennsylvania and colleagues looked for evidence of such exo-Oort clouds in maps of the cosmic microwave background, the cool cosmic glow of the first light released after the Big Bang, roughly 13.8 billion years ago. No exo-Oort clouds have been spotted yet, but the technique looks promising, the team reports November 2 in the Astronomical Journal. Finding exo-Oort clouds could help shed light on how other solar systems — and perhaps even our own — formed and evolved.
The Oort cloud is thought to be a planetary graveyard stretching between about 1,000 and 100,000 times as far from the sun as Earth. Scientist think that this reservoir of trillions of icy objects formed early in the solar system’s history, when violent movements of the giant planets as they took shape tossed smaller objects outward. Every so often, one of those frozen planetary fossils dives back in toward the sun and is visible as a comet (SN: 11/16/13, p. 14).

But it’s difficult to observe the Oort cloud directly from within it. Despite a lot of circumstantial evidence for the Oort cloud’s existence, no one has ever seen it.

Ironically, exo-Oort clouds might be easier to spot, Baxter and colleagues thought. The objects in an exo-Oort cloud wouldn’t reflect enough starlight to be seen directly, but they would absorb starlight and radiate it back out into space as heat. For the sun’s Oort cloud, that heat signal would be smeared evenly across the entire sky from Earth’s perspective. But an exo-Oort cloud’s warmth would be limited to a tiny region around its star.

Baxter and colleagues calculated that the expected temperature of an exo-Oort cloud should be about –265° Celsius, or 10 kelvins. That’s right in range for experiments that detect the cosmic microwave background, or CMB, which is about 3 kelvins.
The team used data from the CMB-mapping Planck satellite to search for areas across the sky with the right temperature (SN Online: 7/24/18). Then, the researchers compared the results with the Gaia space telescope’s ultraprecise stellar map to see if those regions surrounded stars (SN: 5/26/18, p. 5).

Although the astronomers found some intriguing signals around several bright, nearby stars, it wasn’t enough to declare victory. “That’s pretty interesting, but we can’t definitively say that it’s from an Oort cloud or not,” Baxter says.

Other ongoing CMB experiments with higher resolution, like those with the South Pole Telescope and the Atacama Cosmology Telescope in the Chilean Andes, could confirm if those hints of exo-Oort clouds are real.

“It’s a super clever observational idea,” says astronomer Nicolas Cowan of McGill University in Montreal who was not involved in the new work. “Looking for exo-Oort clouds is looking for a signature of these violent histories in other solar systems.”

Cowan has suggested that the cosmic microwave background could also be used to search for a hypothetical Planet Nine in the sun’s Oort cloud (SN: 7/23/16, p. 7). “The very coolest thing would be if we could get measurements of the exo-Oort clouds and find planets in those systems,” he says.

DNA from a 9,000-year-old baby tooth from Alaska, the oldest natural mummy in North America and remains of ancient Brazilians is helping researchers trace the steps of ancient people as they settled the Americas. Two new studies give a more detailed and complicated picture of the peopling of the Americas than ever before presented.

People from North America moved into South America in at least three migration waves, researchers report online November 8 in Cell. The first migrants, who reached South America by at least 11,000 years ago, were genetically related to a 12,600-year-old toddler from Montana known as Anzick-1 (SN: 3/22/14, p. 6). The child’s skeleton was found with artifacts from the Clovis people, who researchers used to think were the first people in the Americas, although that idea has fallen out of favor. Scientists also previously thought these were the only ancient migrants to South America.
But DNA analysis of samples from 49 ancient people suggests a second wave of settlers replaced the Clovis group in South America about 9,000 years ago. And a third group related to ancient people from California’s Channel Islands spread over the Central Andes about 4,200 years ago, geneticist Nathan Nakatsuka of Harvard University and colleagues found.
People who settled the Americas were also much more genetically diverse than previously thought. At least one group of ancient Brazilians shared DNA with modern indigenous Australians, a different group of researchers reports online November 8 in Science.
Early Americans moved into prehistoric South America in at least three migratory waves, a study proposes. Ancestral people who crossed from Siberia into Alaska first gave rise to groups that settled North America (gray arrows). The first wave of North Americans (blue) were related to Clovis people, represented by a 12,600-year-old toddler from Montana called Anzick-1. They moved into South America at least 11,000 years ago, followed by a second wave (green) whose descendants contributed most of the indigenous ancestry among South Americans today. A third migration wave (yellow) from a group that lived near California’s Channel Island moved into the Central Andes about 4,200 years ago. Dotted areas indicate that people there today still have that genetic ancestry.
Genetically related, but distinct groups of people came into the Americas and spread quickly and unevenly across the continents, says Eske Willerslev, a geneticist at the Natural History Museum of Denmark in Copenhagen and a coauthor of the Science study. “People were spreading like a fire across the landscape and very quickly adapted to the different environments they were encountering.”

Both studies offer details that help fill out an oversimplified narrative of the prehistoric Americas, says Jennifer Raff, an anthropological geneticist at the University of Kansas in Lawrence who was not involved in the work. “We’re learning some interesting, surprising things,” she says.

For instance, Willerslev’s group did detailed DNA analysis of 15 ancient Americans different from those analyzed by Nakatsuka and colleagues. A tooth from Trail Creek in Alaska was from a baby related to a group called the ancient Beringians, who occupied the temporary land mass between Alaska and Siberia called Beringia. Sometimes called the Bering land bridge, the land mass was above water before the glaciers receded at the end of the last ice age. The ancient Beringians stayed on the land bridge and were genetically distinct from the people who later gave rise to Native Americans, Willerslev and colleagues found.

The link between Australia and ancient Amazonians also hints that several genetically distinct groups may have come across Beringia into the Americas.

The Australian signature was first found in modern-day indigenous South Americans by Pontus Skoglund and colleagues (SN: 8/22/15, p. 6). No one was sure why indigenous Australians and South Americans shared DNA since the groups didn’t have any recent contact. One possibility, says Skoglund, a geneticist at the Francis Crick Institute in London and a coauthor of the Cell paper, was that the signature was very old and inherited from long-lost ancestors of both groups.

So Skoglund, Nakatsuka and colleagues tested DNA from a group of ancient Brazilians, but didn’t find the signature. Willerslev’s group, however, examined DNA from 10,400-year-old remains from Lagoa Santa, Brazil, and found the signature, supporting the idea that modern people could have inherited it from much older groups. And Skoglund is thrilled. “It’s amazing to see it confirmed,” he says.

How that genetic signature got to Brazil in the first place is still a mystery, though. Researchers don’t think early Australians paddled across the Pacific Ocean to South America. “None of us really think there was some sort of Pacific migration going on here,” Skoglund says.

That leaves an overland route through Beringia. There’s only one problem: Researchers didn’t find the Australian signature in any of the ancient remains tested from North or Central America. And no modern-day indigenous North or Central Americans tested have the signature either.

Still, Raff thinks it likely that an ancestral group of people from Asia split off into two groups, with one heading to Australia and the other crossing the land bridge into the Americas. The group that entered the Americas didn’t leave living descendants in the north. Or, because not many ancient remains have been studied, it’s possible that scientists have just missed finding evidence of this particular migration.

If Raff is right, that could mean that multiple groups of genetically distinct people made the Berigian crossing, or that one group crossed but was far more genetically diverse than researchers have realized.

The studies may also finally help lay to rest a persistent idea that some ancient remains in the Americas are not related to Native Americans today.

The Lagoa Santans from Brazil and a 10,700-year-old mummy from a place called Spirit Cave in Nevada had been grouped as “Paleoamericans” because they both had narrow skulls with low faces and protruding jaw lines, different from other Native American skull shapes. Some researchers have suggested that Paleoamericans — including the so-called Kennewick Man, whose 8,500-year-old remains were found in the state of Washington (SN: 12/26/15, p. 30) — weren’t Native Americans, but a separate group that didn’t have modern descendants.

But previous studies of Paleoamericans and Willerslev’s analysis of the Spirit Cave mummy’s DNA provide evidence that, despite their skull shapes, the Paleoamericans were not different from other Native Americans of their time. And the ancient people are more closely related to present-day Native Americans than any other group.

Willerslev presented the results about the Spirit Cave mummy to the Fallon Paiute-Shoshone tribe when the data became available. Based on the genetic results, the tribe was able to claim the mummy as an ancestor and rebury the remains.

What do you get when you flip a fossilized “jellyfish” upside down? The answer, it turns out, might be an anemone.

Fossil blobs once thought to be ancient jellyfish were actually a type of burrowing sea anemone, scientists propose March 8 in Papers in Palaeontology.

From a certain angle, the fossils’ features include what appears to be a smooth bell shape, perhaps with tentacles hanging beneath — like a jellyfish. And for more than 50 years, that’s what many scientists thought the animals were.
But for paleontologist Roy Plotnick, something about the fossils’ supposed identity seemed fishy. “It’s always kind of bothered me,” says Plotnick, of the University of Illinois Chicago. Previous scientists had interpreted one fossil feature as a curtain that hung around the jellies’ tentacles. But that didn’t make much sense, Plotnick says. “No jellyfish has that,” he says. “How would it swim?”

One day, looking over specimens at the Field Museum in Chicago, something in Plotnick’s mind clicked. What if the bell belonged on the bottom, not the top? He turned to a colleague and said, “I think this is an anemone.”

Rotated 180 degrees, Plotnick realized, the fossils’ shape — which looks kind of like an elongated pineapple with a stumpy crown — resembles some modern anemones. “It was one of those aha moments,” he says. The “jellyfish” bell might be the anemone’s lower body. And the purported tentacles? Perhaps the anemone’s upper section, a tough, textured barrel protruding from the seafloor.

Plotnick and his colleagues examined thousands of the fossilized animals, dubbed Essexella asherae, unearthing more clues. Bands running through the fossils match the shape of some modern anemones’ musculature. And some specimens’ pointy protrusions resemble an anemone’s contracted tentacles.
“It’s totally possible that these are anemones,” says Estefanía Rodríguez, an anemone expert at the American Museum of Natural History in New York City who was not involved with the work. The shape of the fossils, the comparison with modern-day anemones — it all lines up, she says, though it’s not easy to know for sure.

Paleontologist Thomas Clements agrees. Specimens like Essexella “are some of the most notoriously difficult fossils to identify,” he says. “Jellyfish and anemones are like bags of water. There’s hardly any tissue to them,” meaning there’s little left to fossilize.
Still, it’s plausible that the blobs are indeed fossilized anemones, says Clements, of Friedrich-Alexander-Universität Erlangen-Nürnberg in Germany. He was not part of the new study but has spent several field seasons at Mazon Creek, the Illinois site where Essexella lived some 310 million years ago. Back then, the area was near the shoreline, Clements says, with nearby rivers dumping sediment into the environment – just the kind of place ancient burrowing anemones may have once called home.

Disinfection of public drinking water is one of the great public health success stories of the 20th century. In 1900, outbreaks of cholera and typhoid, both caused by waterborne bacteria, were common in American cities. In 1908, Jersey City, N.J., became the first U.S. city to routinely disinfect community water. Other cities and towns quickly followed, and by 1920, the typhoid rate in the United States had dropped by 66 percent.

But that battle isn’t over. Around the world, more than 2 billion people lack reliable access to safe water (SN: 8/18/18, p. 14), and half a million people die each year from diarrhea caused by contaminated water, according to the World Health Organization.
And in the United States, challenges remain. The management failures that caused the 2014 lead contamination crisis in Flint, Mich., were a wake-up call (SN: 3/19/16, p. 8), but Flint is hardly alone. Systems in other big cities are also falling short. In October, officials in Newark, N.J., scrambled to hand out home water filters after it became clear that efforts to prevent lead from leaching into drinking water were not getting the job done. In the first six months of 2017, more than 22 percent of water samples in that city exceeded federal limits for lead, according to news reports.

If big cities are struggling, small towns with skimpy budgets as well as the many people who get their water from private wells often have it harder, lacking access to the infrastructure or technology to make water reliably safe. But science can help.

In this issue, Science News staff writer Laurel Hamers digs into the latest research on water treatment technology and finds a focus on efforts to invent affordable, scalable solutions. There’s a lot of engineering and chemistry involved, not surprisingly, and also physics — it’s hard to move water efficiently through a filter while also catching the bad stuff. Her story is a testament to researcher ingenuity, and a helpful primer on how a typical municipal water treatment plant works.

As I read Hamers’ story, I realized that I didn’t know how our water is treated here in Washington, D.C., even though I live barely a mile from one of the city’s two treatment plants. (I at least get credit for knowing the water comes from the Potomac River.) So I Googled it and found a description of how that process works. Plus I found data on potential contaminants such as Giardia and Cryptosporidium, as well as information on how residents can get their water tested for lead, which can leach from pipes or fixtures.
I also learned that each spring, the Washington Aqueduct briefly switches disinfectants from chloramine to chlorine while the agency cleans the water pipes. That might explain the short-lived swimming pool smell in the tap water.

For me, this became a double win; I learned a lot about advances in water treatment technology from Hamers’ reporting, and I was motivated to seek out information about my local water supply.

If other readers feel inspired by our work to learn more, count me as a happy journalist.

A newly designed airplane prototype does away with noisy propellers and turbines.

Instead, it’s powered by ionic wind: charged molecules, or ions, flowing in one direction and pushing the plane in the other. That setup makes the aircraft nearly silent. Such stealth planes could be useful for monitoring environmental conditions or capturing aerial imagery without disturbing natural habitats below.

The aircraft is the first of its kind to be propelled in this way, researchers report in the Nov. 22 Nature. In 10 indoor test flights the small plane, which weighs about as much as a Chihuahua, traveled 40 to 45 meters for almost 10 seconds at a steady height, even gaining about half a meter of altitude over the course of a flight.
Most planes rely on spinning parts to move forward. In some, an engine turns a propeller that pushes the plane forward. Or a turbine sucks in air with a spinning fan, and then shoots out jets of gas that propel the plane forward.

Ionic wind is instead generated by a high-voltage electric field around a positively charged wire, called an emitter. The electricity, often supplied by batteries, makes electrons in the air collide with atoms and molecules, which then release other electrons. That creates a swarm of positively charged air molecules around the emitter, which are drawn to a negatively charged wire. The movement of molecules between the two wires, the ionic wind, can push a plane forward. The current design uses four sets of these wires.
Moving ions have helped other things to fly through the air, such as tiny airborne robots. But conventional wisdom said that using the approach to move something through the air as big as an airplane wasn’t possible, because adding enough battery power to propel a plane this way would make it too heavy to stay aloft. (The ion thrusters that propel spacecraft through the vacuum of space work in a very different way and aren’t functional in air.) Attempts to build ion-propelled aircraft in the 1960s weren’t very successful.
MIT aeronautics researcher Steven Barrett thought differently. With the right aircraft design and light enough batteries, flight might be possible, his initial calculations suggested. So he and his team used mathematical equations to optimize various features of the airplane — its shape, materials, power supply — and to predict how each version would fly. Then the researchers built prototypes of promising designs and tested the planes at the MIT indoor track, launching them via a bungee system.
“The models and the reality of construction don’t always match up perfectly,” Barrett says, so finding the right design took a lot of tries. But in the new study, he and his collaborators report success: 10 flights of the aircraft, which has a 5-meter wingspan and weighs just under 2.5 kilograms.

Barrett’s team isn’t the only one who thought the ionic wind method might take off. Based on calculations done in his lab, “we were confident that this could be done,” says Franck Plouraboue of the Toulouse Fluid Mechanics Institute in France, who wasn’t part of the research. “Here they’ve done it — which is fantastic!”

It’s an example of distributed electric propulsion, says Plouraboue — spreading out the thrust-generating parts of the plane, instead of having one centralized source. That’s a hot area for aircraft research right now. NASA’s X-57 Maxwell plane, for example, bears 14 battery-operated motors along its wings. Increasing the number of propellers makes the plane go farther on the same amount of energy, says Plouraboue, but also increases the drag. With ionic wind propulsion, increasing the number of wires doesn’t increase drag very much.

The plane still needs some upgrades before it’s ready for the real world: Its longest flight was only 12 seconds. And while the aircraft can maintain steady flight for a short time once launched, it can’t actually get off the ground using ionic wind.

Even with improvements, ion-propelled aircraft won’t find their niche as passenger planes, predicts Daniel Drew, an aerodynamics researcher at the University of California, Berkeley, who was not involved in the work. (Drew has designed miniature flying bots that fly using ionic propulsion.) It’s probably not feasible to scale up to something the size of a 747 — there are efficiency trade-offs as planes get bigger, he says. But down the road, the approach might be useful for small, uncrewed planes or drones.

Devices that eavesdrop on neural activity can help paralyzed people command computer tablets to stream music, text friends, check the weather or surf the internet.

Three people with paralysis below the neck were able to navigate off-the-shelf computer tablets using an electrode array system called BrainGate2. The results, published November 21 in PLOS One, are the latest to show that neural signals can be harnessed to directly allow movement (SN: 6/16/12, p. 5).

The two men and one woman had electrode grids implanted over part of the motor cortex, an area of the brain that helps control movement. The brain implants picked up neural activity indicating that the participants were thinking about moving a cursor. Those patterns were then sent to a virtual mouse that was wirelessly paired to the tablet.
Using nothing more than their intentions to move a cursor, the three participants performed seven common digital tasks, including web browsing and sending e-mail. One participant looked up orchid care, ordered groceries online and played a digital piano. “The tablet became second nature to me, very intuitive,” she told the researchers when asked about her experience, according to the study.

Another participant enjoyed texting friends, “especially because I could interject some humor,” he told the scientists. The system even allowed two of the participants to chat with each other in real time.

For the study, the researchers used tablets with standard settings, without installing any shortcuts or features to make typing or navigation easier.

SAN DIEGO — Getting goose bumps doesn’t just make hairs stand on end; it may also help hair grow.

Nerves and muscles that raise goose bumps also stimulate stem cells in the skin to make hair follicles and grow hair. Ya-Chieh Hsu, a stem cell researcher at Harvard University, reported the unpublished findings December 9 at the joint meeting of the American Society for Cell Biology and the European Molecular Biology Organization. Getting goose bumps when it’s cold may encourage animals’ fur to grow thicker, Hsu said.
Nerves that are part of the sympathetic nervous system — which controls pupil dilation, heart rate and other automatic processes — nestle next to stem cells that will create hair follicles, Hsu and her colleagues found. Usually nerves are wrapped in a protective coating called myelin, like electrical wire sheathed in plastic. But Hsu’s group found that the nerves’ ends were naked where they meet hair follicle stem cells, like wires stripped at the tips to make contacts with electrical nodes.

The nerves secrete the hormone norepinephrine. That hormone is necessary for hair growth, the researchers found. Those findings might help explain why hair loss is a side effect of drugs known as beta-blockers, which interfere with norepinephrine’s action.

Sympathetic nerves next to hair follicles are also wrapped around tiny arrector pili muscles, which contract to make hair cells stand on end, causing goose bumps. Mice with mutations that prevented the muscles from growing also lacked the sympathetic nerves and didn’t grow hair normally. Men with male pattern baldness also lack arrector pili muscles in their scalps, Hsu said, suggesting that sympathetic nerves and goose bump–raising muscles may also be important in that type of baldness. Restoring the nerves and muscles may lead to new hair growth, she said.