Tiny balls of melanin could someday paint the rainbow. They’re one of the key ingredients in a new way to craft a spectrum of structural colors — hues created when light interacts with special nanostructures.

Structural colors are a longer-lasting alternative to chemical pigments, which lose all pizazz when they break down. Examples of durable hues abound in nature. For instance, many bird feathers and butterfly wings get their brilliant colors in part from nanoscale texturing (SN: 6/11/16, p. 32). But finding a simple way to generate these complex structural colors — a technique that can be scaled up and used to create many different hues — has been a tricky task.
In the new study, researchers made nano-sized balls of melanin aggregate into clusters called supraballs. Melanin, the pigment that darkens skin, appears black in the individual nanoparticles. But altering the spacing of the nanoparticles in the ball affects how the particles scatter light, generating a spectrum of structural colors, says study coauthor Ali Dhinojwala, a polymer scientist at the University of Akron in Ohio. So he and colleagues added a thin silica coating to the outside of the melanin nanoparticles. The coating acts like a bumper, limiting how close the particles can pack together.

Varying the diameter of the melanin core and the thickness of the silica shell creates supraballs in a range of colors, including olive, orange-red and navy blue, the researchers report September 15 in Science Advances.

This recipe is simpler than other ways of making structural colors in the lab, Dhinojwala says. The nanoparticles cluster into supraballs at room temperature in a mixture of water and an alcohol called octanol, and are easy to extract as a powder. Plus, nanoparticles with different dimensions can be mixed in one supraball to create any shade imaginable.

People in the United States who wear contact lenses share an eye-opening characteristic. Roughly 85 percent report regularly taking at least one risk when wearing or cleaning their lenses. In the Aug. 18 Morbidity and Mortality Weekly Report, researchers at the U.S. Centers for Disease Control and Prevention describe results from a 2016 national survey of more than 6,000 people.

Contrary to previous studies, teens did better in some categories than adults. The no-no’s below can lead to serious eye infections, mainly by introducing microorganisms into the eye. Even water that’s safe to drink or swim in can bug up lenses.

Ripples in spacetime travel at the speed of light. That fact, confirmed by the recent detection of a pair of colliding stellar corpses, kills a whole category of theories that mess with the laws of gravity to explain why the universe is expanding as fast as it is.

On October 16, physicists announced that the Advanced Laser Interferometer Gravitational-Wave Observatory, LIGO, had detected gravitational waves from a neutron star merger (SN Online: 10/16/17). Also, the neutron stars emitted high-energy light shortly after merging. The Fermi space telescope spotted that light coming from the same region of the sky 1.7 seconds after the gravitational wave detection. That observation showed for the first time that gravitational waves, the shivers in spacetime set off when massive bodies move, travel at the speed of light to within a tenth of a trillionth of a percent.
Within a day, five papers were posted at arXiv.org mourning hundreds of expanding universe theories that predicted gravitational waves should travel faster than light — an impossibility without changes to Einstein’s laws of gravity. These theories “are very, very dead,” says the coauthor of one of the papers, cosmologist Miguel Zumalacárregui of the Nordic Institute for Theoretical Physics, or NORDITA, in Stockholm. “We need to go back to our blackboards and start thinking of other alternatives.”

In the 1990s, observations of exploding stars showed that more distant explosions were dimmer than existing theories predicted. That suggested that the universe is expanding at an ever-increasing rate (SN: 10/22/11, p. 13). Cosmologists have struggled ever since to explain why.

The most popular explanation for the speedup is that spacetime is filled with a peculiar entity dubbed dark energy. “You can think of it like a mysterious fluid that pushes everything apart and counteracts gravity,” says cosmologist Jeremy Sakstein of the University of Pennsylvania, coauthor of another new paper.
In the simplest version of this theory, the density of this dark energy has not changed over the history of the universe, so physicists call it a cosmological constant. This doesn’t require any changes to gravity — which is good, because gravity has been well-tested inside the solar system.

The cosmological constant idea matches observations of the wider universe, but it has some theoretical difficulties. Dark energy is about 120 orders of magnitude weaker than theorists calculate it should be (SN Online: 11/18/13), a mismatch that makes scientists uncomfortable.

Also, different methods for measuring the rate of expansion come up with slightly different numbers (SN: 8/6/16, p. 10). Measurements based on exploding stars suggest that distant galaxies are speeding away from each other at 73 kilometers per second for each megaparsec (about 3.3 million light-years) of space between them. But observations based on the cosmic microwave background, ancient light that encodes information about the conditions of the early universe, found that the expansion rate is 67 km/s per megaparsec. The disagreement suggests that either one of the measurements is wrong, or the theory behind dark energy needs a tweak.

So instead of invoking a substance to counteract gravity, theorists tried to explain the expanding universe by weakening gravity itself. Any modifications to gravity need to leave the solar system intact. “It’s quite hard to build a theory that accelerates the universe and also doesn’t mess up the solar system,” says cosmologist Tessa Baker of the University of Oxford, coauthor of still another paper.

These theories take hundreds of forms. “This field of modified gravity theories is a zoo,” says Baker. Some suggest that gravity leaks out into extra dimensions of space and time. Many others account for the universe’s speedy spreading by adding a different mysterious entity — some unknown particle perhaps — that drains gravity’s strength as the universe evolves.

But the new entity would have another crucial effect: It could slow the speed of light waves, similar to the way light travels more slowly through water than through air. That means that the best alternatives to dark energy required gravitational waves to travel faster than light — which they don’t.

Justin Khoury, a theoretical physicist at the University of Pennsylvania who has worked on several of the alternative gravity theories but was not involved in the new papers, was surprised that one gravitational-wave observation ruled out so many theories at once. He’s hardly disappointed, though.

“The fact that we’re learning something about dark energy because of this measurement is incredibly exciting,” he says.

Observing gravitational waves and light waves at the same time offers a third, independent way to measure how fast the universe is expanding. For now, that rate lies frustratingly right between the two clashing measurements scientists already had, at 70 km/s per megaparsec. But it’s still imprecise. Once LIGO and other observatories have seen 10 or 20 more neutron star collisions, researchers should be able to tell which measurement is correct and figure out whether dark energy needs an update, Zumalacárregui says.

“Gravitational waves may kill these models, but eventually they have the potential to tell us if this discrepancy is for real,” he says. “That’s something that is in itself very beautiful.”

Orangutans living in forested foothills on the Indonesian island of Sumatra represent a previously unknown species, researchers say.

Skeletal and genetic evidence puts these apes on a separate evolutionary trajectory from other orangutans in Sumatra (Pongo abelii) and Bornean orangutans (Pongo pygmaeus), says a team led by evolutionary anthropologist Michael Krützen of the University of Zurich. The researchers named the new species Pongo tapanuliensis, or the Tapanuli orangutan. Krützen’s team reports its findings online November 2 in Current Biology.
The name P. tapanuliensis refers to three north Sumatran districts — North, Central and South Tapanuli — where no more than 800 of these orangutans inhabit several forested areas. Tapanuli orangutans live on the brink of extinction due to road construction, illegal forest clearing and killings by villagers and hunters, the scientists say. Estimates vary, but the World Wildlife Fund puts the total number of living orangutans at nearly 120,000.

Researchers observed Tapanuli orangutans in their hilly habitat as early as the 1930s. Yet these apes have long been overlooked in favor of Sumatran orangutans that live in swampy forests north of the Tapanuli population. Bornean orangutans also live in swampy forests.

A chance to explore Tapanuli orangutans’ biology came in 2013. Krützen’s team gained permission to study the museum-held skeleton of an adult male Tapanuli orangutan that had been killed by villagers. Comparisons with skeletons of 33 Sumatran and Bornean male orangutans revealed a range of differences in the skull and teeth of the Tapanuli ape, including a distinctively narrow palate and a relatively short jaw joint.

An analysis of DNA from 37 living orangutans, including two Tapanuli animals, indicated that Tapanuli and Sumatran orangutans diverged from a common ancestor around 3.4 million years ago. Shared gene variants pointed to interbreeding between the two species after their evolutionary split. Cross-species hookups declined sharply around 100,000 years ago and then stopped between 10,000 and 20,000 years ago, the scientists say. Sumatran and Bornean orangutans separated around 674,000 years ago, the team estimates.
Only Tapanuli orangutans appear to be direct descendants of the first mainland Asian orangutan ancestors to reach Sumatra, the investigators find. Later migrations of mainland animals may have led to the evolution of Sumatran and Bornean orangutans

Scenarios in which closely related ape species interbred after evolving into distinctive biological populations probably occurred frequently, Krützen says. DNA studies suggest ancient chimpanzees and bonobos interbred, as did Homo sapiens and Neandertals (SN: 10/15/16, p. 22). Such evidence has fueled a long-standing debate over how to define the term “species” (SN: 11/11/17, p. 22).

Krützen’s team makes a good case for a third orangutan species that interbred for a long time with a closely related species, says biological anthropologist Rebecca Ackermann of the University of Cape Town in South Africa. “I’d go out on a limb and say not only that [interbreeding] played an important role in the evolution of all living apes, but that it shaped the evolution of extinct ones as well.”

Male mammoths really had to watch their steps. More than two-thirds of woolly mammoth specimens recovered from several types of natural traps in Siberia came from males, researchers report November 2 in Current Biology.

Paleogenomicist Patrícia Pečnerová of the Swedish Museum of Natural History in Stockholm and her colleagues examined genomic data recovered from 98 mammoth bone, tooth, tusk and hair shaft specimens and found that 69 percent of their owners were male. Sex biases in fossil preservation are rare, and the sexes were almost certainly balanced at birth. So the researchers considered whether social and behavioral patterns might have meant that male mammoths more often died in such a way that their remains were buried and preserved, such as becoming trapped in a bog or falling through thin ice.

In modern elephants, herds of females and young live together, led by an experienced female, whereas males are more likely to live in bachelor groups or alone. That could result in more risk-taking behavior for those males. Woolly mammoths, the distant cousins of modern elephants, may have had the same social structures, the researchers suggest.

The study, the authors say, highlights how fossil genomic data can help illuminate the past social structures and behavior of extinct animals — and how existing fossils may not fully represent the original population.

Sickness makes some corals lose their glow.

Disease reduces a coral’s overall fluorescence even before any sign of the infection is visible to the naked eye, a new study finds. An imaging technique that illuminates the change could help with efforts to better monitor coral health, researchers report November 6 in Scientific Reports.

Many corals naturally produce fluorescent proteins that glow in a wavelength of light that human eyes can’t see in natural light. Previous studies have shown that heat stress and wounding, among others stressors, can affect coral fluorescence, but the new study is the first to look at the relationship between fluorescence and infectious disease.
Jamie Caldwell, a disease ecologist now at Stanford University, and colleagues used a technique called live-imaging laser scanning confocal microscopy to compare fluorescence in living fragments of healthy and diseased Montipora capitata coral. The reef coral, common in Hawaii, fluoresces in red and cyan, and can contract a bacterial infection called Montipora white syndrome, which causes coral lesions and tissue loss.

The diseased bits looked healthy at the macroscopic level, but under the researchers’ microscope, the sick coral’s pallid complexion was pronounced. Computer analyses of the microscopy images quantified the lost glow (red is the total area of fluorescence, black regions are where fluorescence was lost, and white lines indicate edges between the two zones). Among the samples studied, healthy coral had on average 1.2 times as much fluorescence area as diseased fragments. Diseased coral had disorganized and fragmented patterns of fluorescence — similar to a forest that has been logged extensively, the researchers found.
Such research “is transformative in our struggle to visualize the dance between pathogen attack and host response in the initial attack,” says Drew Harvell, a disease ecologist at Cornell University.
Many coral diseases appear to be increasing around the world, even when accounting for increased research effort, Caldwell says. Along with bleaching events and pollution, disease is considered one of the major contributors to reef declines globally. The new technique could be used for other coral species and diseases, she says.

THE WOODLANDS, Texas — It’s been six months since NASA’s Cassini spacecraft plunged to its doom in the atmosphere of Saturn, but scientists didn’t spend much time mourning. They got busy, analyzing the spacecraft’s final data.

The Cassini mission ended September 15, 2017, after more than 13 years orbiting Saturn (SN Online: 9/15/17). The spacecraft’s final 22 orbits, dubbed the Grand Finale, sent Cassini into the potentially dangerous region between the gas giant and its rings, and its final orbit sent it directly into Saturn’s atmosphere.
That perspective helped solve mysteries about the planet and its moons that could not be tackled any other way, scientists said March 19 at the Lunar and Planetary Science Conference in The Woodlands, Texas.

“In so many ways, the Grand Finale orbits provided information that was totally unexpected,” said Cassini project scientist Linda Spilker of NASA’s Jet Propulsion Laboratory in Pasadena, Calif. “So many of our models were not correct.”

Here are five things we now know and a few outstanding mysteries.

1. Saturn’s clouds go deep
   Those final daredevil orbits allowed Cassini to measure the gravity of Saturn and its rings independent of one another. Looking at the planet’s gravity field alone revealed that the swirling bands of clouds penetrate much deeper into the planet than expected.

Astronomers this month announced a similar discovery for an even larger gas giant, reporting that the Juno spacecraft, which is orbiting Jupiter, had found that the planet’s rotating cloud belts reach roughly 3,000 kilometers below the top of the atmosphere.

Saturn’s clouds reach a few times deeper than that. “This was an astonishing result,” Spilker said.

“People used to think that maybe Saturn was just a slightly smaller version of Jupiter, but it’s evident that that’s not the case,” says planetary scientist Paul Schenk of the Lunar and Planetary Institute in Houston, who was not involved in the gravity measurements. The difference speaks to how diverse planets are, he says. “Every place you look, everywhere we’ve been to, it’s just been so dramatically different and unique.”

2. Ring rain is eroding the innermost ring
   Grains of ice from the rings are raining down into Saturn’s atmosphere, Cassini’s final orbits confirmed. This “ring rain” idea has been suggested since the 1980s, but only by tasting the atmosphere and directly sampling the space between Saturn and the rings could Cassini confirm the rains are real.

In its last five full orbits, Cassini found a zoo of organic molecules in and just above Saturn’s atmosphere, said planetary scientist Kelly Miller of the Southwest Research Institute in San Antonio. The spacecraft found a lot of water, which wasn’t surprising — water makes up about 90 percent of the rings. But there were also a lot of hydrocarbons similar to propane, plus some methane and sulfur-bearing molecules.

The types of molecules became less well-mixed as the spacecraft looked deeper into Saturn’s atmosphere, which is what would happen if the particles came from the rings and sank at different speeds. The researchers think this material is especially raining from Saturn’s D ring, the thin innermost ring. Other Cassini data suggest this ring is losing mass.

“The D ring is slowly being eroded away and going into the planet,” Spilker said.

3. Organics could explain mysterious ring hues
   The organics in the ring rain could solve a debate about why Saturn’s rings appear reddish in some spots.

“We’ve had this debate going on for a couple of years now — are they red because of good old-fashioned rust like Mars, or because of the same kinds of organic materials … that make carrots and tomatoes and watermelon red?” said planetary scientist Jeff Cuzzi of NASA’s Ames Research Center in Moffett Field, Calif. “To me, this answers the question of what makes the rings red: It’s organics.”

It’s still not clear where the organics come from, though. They could be created within the rings, or they could come from cosmic dust from the tails of comets. Miller and her colleagues are comparing the ring rain molecules with data on comet 67P, which the Rosetta spacecraft observed, to see how well they match up (SN: 11/11/17, p. 32).

4. Titan’s “magic islands” aren’t islands, or bubbles
   Mysterious disappearing features in the lakes of Saturn’s moon Titan are caused by sunlight reflecting off giant waves, said planetary scientist Alexander Hayes of Cornell University.
   These features were named “magic islands” when they were first spotted in 2014. As recently as April 2017, planetary scientists thought they had the islands solved: They seemed to be the result of champagnelike bubbles of nitrogen burbling through the moon’s methane and ethane seas (SN Online: 4/18/17).

But Hayes presented newly analyzed data from August 2014, when Cassini looked at Kraken Mare, the moon’s largest northern sea, in radar and infrared wavelengths within two hours of each other. The radar images showed a magic island, and the infrared ones showed a peak in brightness at the same spot.

Because the observations were taken two hours apart, the island probably couldn’t have been due to bubbles, Hayes said — bubbles would pop or disperse too quickly. Instead, he thinks the brightening could be the glint of sunlight reflecting directly off of giant waves on the lake, like how the ocean ripples with gold at sunset. Simulations of Titan’s atmosphere suggest these waves could be raised by winds as slow as 0.5 meters per second, which would barely move a wind vane on Earth.

5. Enceladus’ plumes may brighten by the pull of another moon
   Saturn’s tiny moon Enceladus has plumes that may be driven by nudges from another moon.

The spurts of liquid water were discovered in 2006. Over the next six years, scientists noticed that the plumes varied in brightness (a proxy for how much material is gushing from the moon) on a daily cycle, probably driven by Saturn’s different positions in Enceladus’ sky.

Then, in 2015 some researchers noted that the plumes’ overall brightness had been decreasing since the beginning of the Cassini mission.

One possible explanation was that the plumes changed with Saturn’s seasons. Another was that ice built up in the vents, clogging them and decreasing the flow. But looking at the full 13-year dataset, planetary scientist Francis Nimmo found that the plumes grow brighter in a regular cycle every four and 11 years. The pattern is too coherent to be explained by clogged vents, said Nimmo, of the University of California, Santa Cruz. Oddly, the plume grew brighter in 2017, so the seasonal explanation doesn’t fit either.

The variations could be explained by a neighboring moon, Dione. Every time Dione and Enceladus line up, their gravitational stress on each other could force Enceladus’ vents open a bit more, causing the plumes to grow brighter.

Unsolved enigmas
So far, analyzing data from Cassini hasn’t answered all of scientists’ questions. Is Enceladus the only moon with plumes? Dione showed signs of activity, too, but Cassini wasn’t able to confirm it. How thick is Enceladus’ ice sheet? Why are Titan’s smaller lakes full of clear, pure methane, when scientists expected the lakes to be clogged with hydrocarbon silt?

Even though the spacecraft is gone, it left decades’ worth of data to sift through in search of answers. “Cassini is going to keep on giving as long as we keep looking,” Hayes said.

Editors’ note: This story was updated on March 21, 2018, to include the affiliations of Jeff Cuzzi and Francis Nimmo.

BOSTON — Conflicting results on whether brain stimulation helps or hinders memory may be explained by the electrodes’ precise location: whether they’re tickling white matter or gray matter.

New research on epilepsy patients suggests that stimulating a particular stretch of the brain’s white matter — tissue that transfers nerve signals around the brain — improves performance on memory tests. But stimulating the same region’s gray matter, which contains the brain’s nerve cells, seems to impair memory, Nanthia Suthana, a cognitive neuroscientist at UCLA, reported March 25 at a meeting of the Cognitive Neuroscience Society.
A groundbreaking study by Suthana and colleagues, published in 2012 the New England Journal of Medicine, found that people performed better on a memory task if their entorhinal cortex — a brain hub for memory and navigation — was given a low jolt of electricity during the task. But subsequent studies stimulating that area have had conflicting results. Follow-up work by Suthana suggests that activating the entorhinal cortex isn’t enough: Targeting a particular path of nerve fibers matters.

“It’s a critical few millimeters that can make all the difference,” said Suthana.

The research underscores the complexity of investigations of and potential treatments for memory loss, said Youssef Ezzyat, a neuroscientist at the University of Pennsylvania. Many variables seem to matter. Recent work by Ezzyat and colleagues found that the kind of brain activity during stimulation is also important, as is the precise timing of the stimulation (SN: 3/31/2018, p.16).

Suthana and her colleagues worked with 25 people with epilepsy who had electrodes already implanted in the brain for controlling seizures. Some people’s electrodes were in the entorhinal cortex’s gray matter, and some were in its white matter fibers, which extend to the hippocampus, an area known for its role in memory. Study participants received a low current of electricity while performing a memory task such as learning lists of words, names of objects (for example, “chair” or “cat”) or recognizing particular faces. Participants were then distracted with another task and then had to recall what they had learned previously.
People whose electrodes were stimulating white matter did better on the memory tasks, the researchers discovered. Stimulating gray matter seemed to have a detrimental effect, though there were too few participants to determine whether or not the impairment results were a fluke.

Deep brain stimulation has been heralded as a possible treatment for ills from obesity to obsessive-compulsive disorder to traumatic brain injury. But studies often rely on patients who have electrodes implanted for something other than memory so it can take years and collaborations among several institutions to collect enough data to see something meaningful. The size of electrode, its exact location, the amount of current delivered and other factors may matter more than researchers have recognized. But the devil may be in these details, which need to be noted as research unfolds, Suthana said.

“This is an opportunity as a field for us to adopt common guidelines and methods of reporting so we can better understand what’s happening,” she said.

Nearly 2,000 years ago, Pliny the Elder reported that hippopotamuses find relief from overeating by piercing their skin in a hippo version of bloodletting. Eventually, scientists learned that the oozing red stuff Pliny described isn’t even blood but a secretion that may have antibacterial and sun-blocking properties. While chasing down the truth for herself, Lucy Cooke scooped the goo from a hippo and smeared it on her own skin — if nothing else, her hand was “noticeably silkier,” she writes in The Truth About Animals.
Cooke, a zoologist and documentary filmmaker, has a storehouse of such tales of animal adventure. She’s also the founder of the Sloth Appreciation Society, whose motto is “Being fast is overrated.” That motto gives a glimpse into her sense of humor, which shines through page after page, and her affinity for misunderstood creatures. Cooke battles the notion that sloths are lazy or stupid just because they’re slow-moving. In her book, she set out to, as she writes, “create my very own menagerie of the misunderstood.”

And quite a menagerie it is. Each chapter takes on a different animal — bats, storks, vultures and pandas, among others — long shrouded in myth or misconception. Some, like bats, are unfairly maligned; others are adored despite shocking behavior, such as Adélie penguins, whose sex lives were considered so depraved that, in 1915, London’s Natural History Museum boldly marked a paper about the birds’ mating behavior as “Not for Publication.”

In many cases, science created or perpetuated myths before eventually debunking them. Among the ludicrous ideas once taken as fact: Beavers escape hunters by chewing off their own testicles and dropping them as a distraction. To explain where birds disappear in winter, Aristotle once posited that they transform into different species.
Even hard-core animal lovers will find surprises in these histories. I knew, for instance, that the long-running mystery over European and American eels’ spawning sites eventually led to the North Atlantic’s Sargasso Sea (SN Online: 4/13/17). But I had no idea that Sigmund Freud was among the many who tried to solve another eel conundrum: where the fish hide their gonads. After disemboweling hundreds of eels to find their testes, Freud threw up his hands and eventually moved on to study the human psyche, perhaps slippery enough.

In the end, the history of zoology reveals as much about our human foibles as about the animals we study. And this book will leave readers more enlightened about both.

PHOENIX — High-tech attire that would give users the sensation of being pushed, pinched or poked could someday make virtual realities feel as real as they look.

Today’s VR systems rely heavily on goggle-generated visual displays to transport users to simulated worlds. But superthin, shape-shifting sheets worn as sleeves or built into other garments could provide gamers with tactile feedback that makes virtual realities more immersive.

The new device, described April 5 at the Materials Research Society spring meeting, contains a grid of tiny, inflatable bubbles, sandwiched between two soft, stretchy silicone films. When one of these bubble wrap–like sheets is placed against a user’s skin, inflating different air pockets by different amounts at different speeds can make a gamer feel like she’s been grabbed around the wrist or patted on the back.
Some previously developed hand- or finger-worn devices have allowed wearers to feel or manipulate virtual objects. But clothing embedded with smart silicone skins could make VR gaming more of a full-body experience.

Each air pocket on the sheet is coated with a liquid metal sensor that tracks how much that bubble is distended, which helps regulate the device’s shape-shifting. Those sensors also detect indentations in the bubbles, so these sleeves could work as touch pad game controllers, too, says study coauthor Matthew Robertson, a roboticist at École Polytechnique Fédérale de Lausanne in Switzerland.

Currently, plastic tubes feed air into the device from an external pump. “Our ultimate goal is to get rid of all the tubes,” Robertson says. He imagines future versions of these VR sleeves fitted with tiny tanks of compressed gas to inflate the air bubbles.