Muons, electrons’ heftier cousins, rain down through the Earth’s atmosphere in numbers higher than physicists expect. The discrepancy could simply point to a gap in physicists’ understanding of the nitty-gritty physics of particle interactions, or perhaps something unexpected is going on, such as the creation of a new state of matter.
When cosmic rays — spacefaring protons or atomic nuclei — smash into the atmosphere at ultrahigh energies, they launch a cascade of many other types of particles, including muons. New observations made at the Pierre Auger Observatory detect about 30 percent more muons than simulations predict, scientists report October 31 in Physical Review Letters. The Auger observatory, located in Argentina, uses telescopes to observe faint light from particle showers in the atmosphere, and detects particles that reach the ground using tanks of water. By comparing simulated particle showers to real data, and allowing for possible miscalibration of their detectors, the scientists concluded that the predicted numbers of muons don’t match up with reality. Hints of the muon excess have been popping up since the ’90s, says physicist Thomas Gaisser of the University of Delaware. But the new measurement is “a better job, which confirms the excess compared to what’s predicted by the models.”
The ultrahigh energy cosmic rays that the researchers analyzed probe physics at energies 10 times those reached at the world’s most powerful particle accelerator, the Large Hadron Collider, potentially allowing scientists to detect new phenomena. But, says Spencer Klein of the Lawrence Berkeley National Laboratory in California, “it’s premature to say that this is something really interesting.” He suggests that the discrepancy could simply be due to an incomplete grasp of the physics of how protons and neutrons inside a nucleus behave when nuclei collide. The complexities of that behavior could result in particles that eventually decay into more muons than scientists naïvely expected, thus explaining the glut.
But, says Auger physicist Glennys Farrar of New York University, scientists have unsuccessfully tried to explain the muon surplus using standard physics for many years. “That’s in a way the most convincing reason to think that there may be new physics.” An explanation Farrar favors is a phenomenon in which a new state of matter appears at high energies. In such a state, large numbers of gluons — particles that transmit the strong nuclear force — may behave collectively, like photons in sync in a laser. If enough energy is pumped in by the cosmic rays, the gluons could “start to develop a life of their own,” Farrar says. The gluons might then gang up into hypothetical particles called glueballs, which could decay into particles that produce more muons.
Editor’s Note: After this article was published, Horbatsch and colleagues discovered an error in their analysis, which weakened the conclusions. The new calculation of the proton radius falls in between the two previous estimates, and therefore does not add much additional support for the smaller proton.
A spat over the size of the proton just got a bit more complicated.
Measurements of the proton’s radius disagree, with one group of scientists saying it’s smaller than the accepted estimate. Now, a new analysis of old data bolsters the case for a small proton. But the result may dash hopes that the discrepancy could point the way to new physics. Scientists at York University in Toronto and the Autonomous University of Barcelona reanalyzed data from a 2010 electron scattering experiment at the Mainz Microtron in Germany, in which physicists bombarded protons with electrons and observed how the electrons ricocheted. That scattering, under the influence of the protons’ spheres of positive charge, allows scientists to tease out the size of a proton. The updated estimate came up small, the scientists report November 1 on arXiv.org.
“I think it’s not going to be easy for the proponents of a relatively large proton radius to just discuss this away,” says physicist Randolf Pohl of the Max Planck Institute of Quantum Optics in Garching, Germany. “But I’m not convinced that people will accept it.”
Until several years ago, scientists’ various techniques for sizing up the proton were in agreement. Electron scattering studies like the Mainz experiment implied the same size proton as a second technique, which involves studying the energy levels of hydrogen atoms. These estimates indicated that the proton’s radius was about 0.88 quadrillionths of a meter. But in 2010, a new technique caused a kerfuffle. Measurements of the proton radius using muonic hydrogen — a hydrogen atom with its electron replaced by a heavier relative called a muon — pegged the proton to a size 4 percent smaller than the other estimates (SN: 7/31/10, p. 7).
The flaw among the three techniques might seem likely to lie with the one outlier, the muon experiment. But “there’s actually quite a bit of certainty about those results,” says physicist Marko Horbatsch of York University, a coauthor of the new paper. So Horbatsch and colleagues decided to revisit electron scattering instead, using a subset of the data from the Mainz experiment. Horbatsch’s team focused on glancing collisions where the electron altered its course only slightly. Those collisions are the most essential for determining the proton radius. Then the researchers used theoretical calculations to account for effects that occur in more extreme collisions. Their analysis revealed a slightly scaled-down proton.
If the result is reinforced by future electron scattering measurements, the hydrogen atom data that resulted in the larger-sized proton would still require explanation. But it would also mean that the discrepancy won’t lead to new insights about the universe. Under the standard model of particle physics, muons and electrons should be identical except for mass. Physicists had hoped that the black sheep status of the muonic hydrogen experiment indicated something was different about muons. Agreement of the electron scattering and muonic hydrogen experiments eliminates that possible explanation. The new analysis is “undoubtedly sensible,” says physicist Judith McGovern of the University of Manchester. “I’m a bit surprised no one has done it before. In fact, I’m a bit surprised I haven’t done it before.”
But that doesn’t mean scientists are fully convinced. MIT physicist Jan Bernauer, one of the authors of the original electron scattering result, says he doesn’t think the puzzle will be solved by reanalysis of existing data. “I’m positive that new data are needed.”
A hunter’s gaze betrays its strategy. And looking at what an animal looks at when it’s hunting for prey has revealed foraging patterns in humans, other primates — and now, birds.
Suzanne Amador Kane of Haverford College in Pennsylvania and her colleagues watched archival footage of three raptor species hunting: northern goshawks (Accipiter gentilis), Cooper’s hawks (A. cooperii) and red-tailed hawks (Buteo jamaicensis). They also mounted a video camera to the head of a goshawk to record the bird’s perspective (a technique that’s proved useful in previous studies of attack behavior). The team noted how long birds spent fixating on specific points before giving up, moving their head and, thus, shifting their gaze.
When searching for prey, raptors don’t turn their heads in a predictable pattern. Instead, they appear to scan and fixate randomly based on what they see in their environment, Kane and her colleagues report November 16 in The Auk. In primates, a buildup of sensory information drives foraging animals to move their eyes in similar patterns.
Though the new study only examines three species and focuses on head tracking rather than eye tracking, Kane and her colleagues suggest that the same basic neural processes may drive search decisions of human and hawk hunters.
A 130-million-year-old bird holds a clue to ancient color that has never before been shown in a fossil.
Eoconfuciusornis’ feathers contain not only microscopic pigment pods called melanosomes, but also evidence of beta-keratin, a protein in the stringy matrix that surrounds melanosomes, Mary Schweitzer and colleagues report November 21 in the Proceedings of the National Academy of Sciences.
Together, these clues could strengthen the case for inferring color from dinosaur fossils, a subject of debate for years (SN: 11/26/16, p. 24). Schweitzer, a paleontologist at North Carolina State University in Raleigh, has long pointed out that the microscopic orbs that some scientists claim are melanosomes may actually be microbes. The two look similar, but they have some key differences. Microbes aren’t enmeshed in keratin, for one.
In Eoconfuciusornis’ feathers, Schweitzer and colleagues found round, 3-D structures visible with the aid of an electron microscope. And a molecular analysis revealed bundles of skinny fibers, like the filaments of beta-keratin in modern feathers. The authors don’t speculate on the bird’s color, but they do offer a new way to support claims for ancient pigments.
“Identifying keratin is key to ruling out a microbial source for microbodies identified in fossils,” they write.
Weight from massive deposits of frozen nitrogen, methane and carbon monoxide, built up billions of years ago, could have carved out the left half of the dwarf planet’s heart-shaped landscape, researchers report online November 30 in Nature.
The roughly 1,000-kilometer-wide frozen basin dubbed Sputnik Planitia was on display when the New Horizons spacecraft tore past in July 2015 (SN: 12/26/15, p. 16). Previous studies have proposed that the region could be a scar left by an impact with interplanetary debris (SN: 12/12/15, p. 10).
Sputnik Planitia sits in a cold zone, a prime location for ice to build up, planetary scientist Douglas Hamilton of the University of Maryland in College Park and colleagues calculate. Excess ice deposited early in the planet’s history would have led to a surplus of mass. Gravitational interactions between Pluto and its largest moon, Charon, slowed the planet’s rotation until that mass faced in the opposite direction from Charon. Once Charon became synced to Pluto’s rotation — it’s always over the same spot on Pluto — gravity would have held Sputnik Planitia in Pluto’s cold zone, attracting even more ice. As the ice cap grew, the weight could have depressed Pluto’s surface, creating the basin that exists today.
For clues to Parkinson’s brain symptoms, a gut check is in order.
Intestinal microbes send signals that set off the disease’s characteristic brain inflammation and motor problems in mice, researchers report December 1 in Cell. Doctors might someday be able to treat Parkinson’s by fixing this bacterial imbalance.
“It’s quite an exciting piece of work,” says John Cryan, a neuroscientist at University College Cork in Ireland who wasn’t involved in the study. “The relationship between the brain and gut for Parkinson’s has been bubbling up for many years.” The new research, he says, “brings the microbiome really into the forefront for the first time.” Parkinson’s affects more than 10 million people worldwide, and roughly 70 percent of those patients also have gastrointestinal issues like constipation. Sometimes the GI symptoms show up years before the muscle weakness and other neurological problems. Several recent studies in humans have suggested a link between gut microbes and Parkinson’s. But it wasn’t clear whether intestinal microbes were actually causing the disease, says study coauthor Sarkis Mazmanian, a microbiologist at Caltech. “What our study adds is a functional, mechanistic role for the microbiome.”
Mazmanian’s team studied mice that produced too much alpha-synuclein, the protein that’s believed to cause Parkinson’s when it clumps in the brain. Mice with extra alpha-synuclein acted like they had Parkinson’s: They traversed a narrow beam more slowly, they couldn’t grip as well to a pole and they struggled to pull stickers off their noses. Their brains showed signs of inflammation, too. But when the researchers raised the same type of mice to be germ-free —that is, to not have any gut microbes — the animals acted less sick.
Those mice were still producing boatloads of alpha-synuclein, but the protein wasn’t clumping in their brains. And without the clumps, the mice didn’t have the unsteady gait and muscle weakness typical of Parkinson’s.
In another experiment, the researchers transferred gut microbes from Parkinson’s patients into germ-free mice making too much alpha-synuclein. Those mice developed motor problems when tested 6 or 7 weeks after the transfer, but mice who got microbes from healthy humans were fine.
“Even though the mice that received the healthy microbiota received hundreds of bacteria, they didn’t get the disease,” says Mazmanian. That suggests it’s not the presence or absence of bacteria that triggers Parkinson’s, but the specific composition of the microbial cocktail. Alpha-synuclein clumps can move from the gut to the brain, a recent study showed. Now, it seems that gut bacteria themselves are also sending important signals.
Researchers are now trying to figure out which signals — and which microbes —are throwing off the balance.
Fecal samples from the mice implanted with bacteria from Parkinson’s patients had higher than normal levels of certain intestinal bacteria. That could be sparking symptoms, says Caltech microbiologist Tim Sampson, who also worked on the study. “I’m interested in trying to understand if there are potential pathogenic microbes that might be individually driving the disease,” he says. “Once we’ve figured that out we’ll be able to understand whether we can remove that group of organisms or block them.”
Abnormally low levels of other bacteria could also factor in. The analyses aren’t large enough to firmly conclude which microbes are particularly important players. But if scientists can figure out what those missing beneficial bacteria are, Mazmanian says, targeted probiotic therapy might be a treatment option in the future.
Aging-associated diseases like Parkinson’s are tricky to study in mice, cautions Stanford University microbiologist Justin Sonnenburg. “They’re typically the result of decades of accumulations of problems,” whereas the mice in the current study were just a couple months old. So the findings will need to be validated in human studies before influencing treatments. Still, he says, “it’s a really important contribution to the growing list of ways that gut microbes can alter our health.”
Graphene-infused Silly Putty forms an electrical sensor that is sensitive enough to detect the gentle caresses of spider feet walking across it.
Mixing graphene, or atom-thick sheets of carbon, and polysilicone, the substance found in the children’s toy Silly Putty, made it conduct electricity. Its electrical resistance was highly sensitive to pressure: Squishing the putty caused the graphene sheets within to shift and disconnect, impeding the flow of electricity.
When placed on a person’s neck over the carotid artery, the putty could monitor pulse and blood pressure via changes in the material’s resistance. The putty could also detect breathing and finger motions. To illustrate just how sensitive the sensor was, scientists coaxed a small spider to walk over the putty; the sensor registered the spider’s footfalls, researchers report December 9 in Science.
The decades-long dwindling of glaciers is “categorical evidence of climate change,” a new study affirms.
The link between global warming and glacial retreat had previously garnered only a “likely,” or at least 66 percent probability, rating from the Intergovernmental Panel on Climate Change. Comparing the long-term decline of 37 glaciers, researchers estimate that all but one are “very likely” – or with at least 90 percent probability – the result of climate change.
Natural variability and complex dynamics make sussing out climate change’s role in glacial retreat difficult. Earth system scientist Gerard Roe of the University of Washington in Seattle and colleagues calculated the natural ups and downs of well-documented glaciers from around the world. The researchers then noted how far the glaciers have drifted from that natural variability and compared that trend with changes in the nearby climate.
For 21 out of the 37 glaciers, the researchers say it is “virtually certain” that climate change caused the glaciers’ retreat, the researchers report December 12 in Nature Geoscience. Glaciers hold about 75 percent of Earth’s freshwater and their decline serves as a canary in the coal mine for climate change.
A Brazilian mother cradles her baby girl under a bruised purple sky. The baby’s face is scrunched up, mouth open wide — like any other crying child. But her head is smaller than normal, as if her skull has collapsed above her eyebrows.
A week earlier, not far away, a doctor wrapped a measuring tape around the forehead of a 1-month-old boy, held in the arms of his grandmother. This baby too has a shrunken head, a birth defect whose name — microcephaly — has now become seared into the public consciousness. These images and many more told a harrowing story that case reports alone couldn’t convey: A little-known mosquito-borne virus called Zika appeared to be taking a terrible toll on women and babies, and their families. The world got a gut-wrenching view of microcephaly in 2016, along with a mountain of evidence convincing scientists that Zika bears much of the blame for the dramatic increase in cases.
“Once you’ve seen those pictures from Brazil, you realize what a huge impact this kind of outbreak can have,” says Sonja Rasmussen, a pediatrician at the U.S. Centers for Disease Control and Prevention in Atlanta. Brazil logged its first cases of Zika in 2015, but infections there peaked this spring with perhaps up to 8,000 new infections per week. The virus crept northward and infiltrated many more countries including Panama, Haiti and Mexico. Now, the threat has come to the United States: Cases have been reported in every state except Alaska. They stem mostly from travelers infected abroad, but the virus has staked out new territory in Puerto Rico, the U.S. Virgin Islands, American Samoa and Florida.
As of December 1, Puerto Rico had reported more than 34,000 people with Zika infections. More than 2,700 are pregnant women. And elsewhere in the United States, the CDC has reported well over 4,000 laboratory-confirmed cases of Zika. In these places and others, the images from Brazil have filled expectant mothers (and anyone considering having kids) with uncertainty and fear. “It’s really scary to be pregnant right now,” Rasmussen says. “We don’t know what to tell women.” The threat to unborn babies wasn’t clear when Zika first hit Brazil, or in earlier, smaller outbreaks on Yap Island in the western Pacific and in French Polynesia. In fact, before 2016, not much was known about the virus at all. The majority of people infected don’t show any symptoms. But in the last year, scientists have thrown themselves at Zika, publishing more than 1,500 papers on different facets of the virus, from what species of mosquito it hides in to what cells it invades.
“We’re learning something new every day,” says obstetrician/gynecologist Catherine Spong, deputy director of the National Institute of Child Health and Human Development in Bethesda, Md.
The studies have scrubbed away some of Zika’s mystery — in particular, what the virus does in the womb. Scientists have found traces of Zika in the brains of human fetuses and confirmed that the virus can infect and kill brain cells in the lab. “This is the year that people became convinced that this mosquito-borne virus could cause birth defects,” Rasmussen says.
Though there was no smoking gun — no single piece of evidence that clinched Zika as the culprit — little clues began adding up, beginning with the conspicuous timing of Brazil’s microcephaly upsurge (SN: 4/2/16, p. 26). In January the CDC first issued a warning to pregnant women to postpone travel to Zika-affected regions. On April 13, a day that may be forever etched into Rasmussen’s memory, she and colleagues reported “a causal relationship” between Zika and microcephaly, along with other birth defects, in a study published online in the New England Journal of Medicine. Since then, Rasmussen says, “The data have become absolutely overwhelming.” In May, a mouse study offered the first direct proof in animals that in utero Zika infection can lead to microcephaly (SN Online: 5/11/16). In September, researchers reported that a pregnant pigtailed macaque infected with Zika in the third trimester then gave birth to a baby whose brain had stopped growing. In human babies, the range of disorders linked to Zika has ballooned to include problems with the eyes, ears and joints, as well as seizures and extreme irritability (SN: 10/29/16, p. 14). At a workshop in North Bethesda, Md., this fall, a room crowded with doctors and scientists watched videos of inconsolable infants jerking erratically, arms and legs unnaturally stiff. “Heartbreaking,” Rasmussen says.
In December, researchers reported a surge in babies with microcephaly in Colombia (SN Online: 12/9/16), further evidence for Zika’s role in birth defects.
Zika isn’t the first virus to harm babies in the womb. Cytomegalovirus can also cause microcephaly, for example, and rubella, known as “German measles,” can leave babies with hearing, vision and heart problems. Even among these viruses, though, Zika stands out. “It’s such a precedent-setting thing,” Rasmussen says. “Never before has there been a mosquito-borne virus known to cause birth defects.”
Despite what scientists have learned in 2016, there’s little consolation for families already affected by microcephaly. And huge questions remain for expectant mothers. In particular, says Spong, it’s not clear just how risky Zika infection during pregnancy really is. One study published in the New England Journal of Medicine in July estimated that the risk of bearing a child with microcephaly increases to somewhere between 1 and 13 percent for women infected in their first trimester.
Spong hopes that a new study will clarify things. It’s called the Zika in Infants and Pregnancy Cohort Study, or ZIP, and the plan is to enroll 10,000 women in their first trimester. They’ll come from Puerto Rico, as well as Brazil and other countries, Spong says, and include both infected and uninfected women.
Tracking these women through pregnancy, birth and their baby’s first year of life could fill in some answers, like whether an infected pregnant woman who doesn’t have symptoms is better off than one who does. It’s also possible that some type of cofactor, like environmental toxins or other infections, is working with Zika to cause birth defects.
“You’re supposed to avoid stress when you’re pregnant,” Rasmussen says. “How do you avoid stress when you’re thinking that your baby could have these problems related to Zika?”
In the best-case scenario, a Zika vaccine could still be a few years away. And though infection rates may be winding down in some places, in areas with seasonally high temperatures and rainfall, such as Puerto Rico, Zika could become a local fixture. Still, any scrap of new information might help. Results from ZIP and other studies won’t erase the damage, but they could offer a pinprick of light following a year darkened by disease.
Water ice lies just beneath the cratered surface of dwarf planet Ceres and in shadowy pockets within those craters, new studies report. Observations from NASA’s Dawn spacecraft add to the growing body of evidence that Ceres, the largest object in the asteroid belt between the orbits of Mars and Jupiter, has held on to a considerable amount of water for billions of years.
“We’ve seen ice in different contexts throughout the solar system,” says Thomas Prettyman, a planetary scientist at the Planetary Science Institute in Tucson and coauthor of one of the studies, published online December 15 in Science. “Now we see the same thing on Ceres.” Ice accumulates in craters on Mercury and the moon, an icy layer sits below the surface of Mars, and water ice slathers the landscape of several moons of the outer planets. Each new sighting of H2O contributes to the story of how the solar system formed and how water was delivered to a young Earth. A layer of ice mixed with rock sits within about one meter of the surface concentrated near the poles, Prettyman and colleagues report. And images of inside some craters around the polar regions, from spots that never see sunlight, show bright patches, at least one of which is made of water ice, a separate team reports online December 15 in Nature Astronomy.
“Ceres was always believed to contain lots of water ice,” says Michael Küppers, a planetary scientist at the European Space Astronomy Center in Madrid, who was not involved with either study. Its overall density is lower than pure rock, implying that some low-density material such as ice is mixed in. The Herschel Space Observatory has seen water vapor escaping from the dwarf planet (SN Online: 1/22/14), and the Dawn probe, in orbit around Ceres since 2015, spied a patch of water ice in Oxo crater, though the amount of direct sunlight there implies the ice has survived for only dozens of years (SN Online: 9/1/16). The spacecraft has also found minerals on the surface that formed in the presence of water.
But researchers would like to know where Ceres’ water is. Knowing whether it is blended throughout the interior or segregated from the rock could help piece together the story of where Ceres formed and how the tiny world was put together. That, in turn, could provide insight into how diverse the worlds around other stars might be.
To map the subsurface ice, Prettyman and colleagues used a neutron and gamma-ray detector onboard Dawn. As Ceres is bombarded with cosmic rays — highly energetic particles that originate outside the solar system — atoms in the dwarf planet spray out neutrons. The amount and energy of the neutrons can provide a clue to the abundance of hydrogen, presumably locked up in water molecules and hydrated minerals.
Finding patches of ice was a bit more straightforward. Planetary scientist Thomas Platz and colleagues pinpointed permanently shadowed spots on Ceres, typically in crater floors near the north and south poles. The team then scoured images of those locations for bright patches. Out of the more than 600 darkened craters they identified, the researchers found 10 with bright deposits that could be surface ice. One had a chunk sticking out into just enough sunlight for Dawn to measure the spectrum of the reflected light and detect signs of water. Water vapor escaping from inside the dwarf planet likely falls back to Ceres, where some of it gets trapped in these cold spots, says Platz, of the Max Planck Institute for Solar System Research in Göttingen, Germany.
Just because there is water doesn’t mean Ceres is a good place for life to take hold. Temperatures in the shadows don’t get above –216° Celsius. “It’s pretty cold, there’s no sunlight. We don’t think that’s a habitable environment,” Platz says. Although, he adds, “one could mine for future missions to get fuel.”
Ceres is now the third major heavily cratered body, along with Mercury and the moon, with permanently shadowed regions where ice builds up. “All the ones we’ve got info on to test this show you’ve accumulated something,” says Peter Thomas, a planetary scientist at Cornell University, who is not a part of either research team. Those details improve researchers’ understanding of how water interacts with a variety of planetary environments.
