One hundred and ninety-two atoms have tied the knot.

Chains of carbon, hydrogen, oxygen and nitrogen atoms, woven together in a triple braid, form the most complex molecular knot ever described, chemists from the University of Manchester in England report in the Jan. 13 Science.

Learning how to tie such knots could one day help researchers weave molecular fabrics with all sorts of snazzy properties. “We might get the strength of Kevlar with a lighter and more flexible material,” says study coauthor David Leigh.
That’s still a long way away, but molecular knot tying has an appeal that’s purely intellectual, too, says University of Cambridge chemist Jeremy Sanders. “It’s like the answer to why you climb Everest,” he says. “It’s a challenge.”

Mathematicians know of more than six billion types of prime knots, which, like prime numbers, cannot be broken down into simpler components. “Prime knots can’t be built up by sticking other knots together,” Leigh explains. For years, chemists were able to synthesize just one type of prime knot out of small molecules. “We thought that was pretty ridiculous,” says Leigh.

That molecular knot was a trefoil, like a three-leaf clover. Jean-Pierre Sauvage and colleagues wove it from chemical strands in 1989. Sauvage won a Nobel Prize in 2016 for earlier work that used the same principles explored in his knots (SN: 10/29/16, p. 6).

In the decades since Sauvage’s trefoil, chemists have tried to synthesize other types of molecular knots, but “they’ve always found it incredibly difficult,” says chemist Sophie Jackson, also at the University of Cambridge.

Persuading nanoscale strands to interlock together in an orderly fashion isn’t simple. “You can’t just grab the ends and tie them like you would a shoelace,” Leigh says. Instead, scientists choose molecular ingredients that assemble themselves.
In 2012, Leigh and colleagues used the self-assembly technique to make a molecular pentafoil knot, a star-shaped structure made up of 160 atoms and with strands that cross five times (SN: 1/28/12, p. 12). This latest knot, with eight crossing points, is even more intricate.

Leigh’s team mixed together building blocks containing carbon, hydrogen, oxygen and nitrogen atoms with iron ions and chloride ions. “You dump them all in, heat them all up and they self-assemble,” he says. Sticky metal ions hold the building blocks in the correct position, and a single chloride ion sitting in the middle of the structure anchors it all together. Then, a chemical catalyst links the building blocks, forming the completed knot. The new knot is the tightest ever created, Leigh says, with just 24 atoms between each crossing point.

It’s beautiful, Sanders says. “It’s a string of atoms rolled up in a spherical shape, with an astonishing amount of symmetry.” Sanders is reluctant to speculate how such a knot might be used, but it’s round and very dense, he says. That could give it some interesting materials properties.

Leigh suspects that different molecular knots might behave differently, like the various knots used by fishermen and sailors. “We want to make specific knots, see what they do and then figure out how to best exploit that,” he says.

Gold’s glimmer is not the only reason the element is so captivating. For decades, scientists have puzzled over why theoretical predictions of gold’s properties don’t match up with experiments. Now, highly detailed calculations have erased the discrepancy, according to a paper published in the Jan. 13 Physical Review Letters.

At issue was the energy required to remove an electron from a gold atom, or ionize it. Theoretical calculations of this ionization energy differed from scientists’ measurements. Likewise, the energy released when adding an electron — a quantity known as the electron affinity — was also off the mark. How easily an atom gives up or accepts electrons is important for understanding how elements react with other substances.
“It was well known that gold is a difficult system,” says chemist Sourav Pal of the Indian Institute of Technology Bombay, who was not involved with the study. Even gold’s most obvious feature can’t be explained without calling Einstein’s special theory of relativity into play: The theory accounts for gold’s yellowish color. (Special relativity shifts around the energy levels of electrons in gold atoms, causing the metal to absorb blue light, and thereby making reflected light appear more yellow.)

With this new study, scientists have finally resolved the lingering questions about the energy involved in removing or adding an electron to the atom. “That is the main significance of this paper,” Pal says.

Early calculations, performed in the 1990s, differed from the predicted energies by more than a percent, and improved calculations since then still didn’t match the measured value. “Every time I went to a conference, people discussed that and asked, ‘What the hell is going on?’” says study coauthor Peter Schwerdtfeger, a chemist at Massey University Auckland in New Zealand.

The solution required a more complete consideration of the complex interplay among gold’s 79 electrons. Using advanced supercomputers to calculate the interactions of up to five of gold’s electrons at a time, the scientists resolved the discrepancy. Previous calculations had considered up to three electrons at a time. Also essential to include in the calculation were the effects of special relativity and the theory of quantum electrodynamics, which describes the quantum physics of particles like electrons.

The result indicates that gold indeed adheres to expectations — when calculations are detailed enough. “Quantum theory works perfectly well, and that makes me extremely happy,” says Schwerdtfeger.

WASHINGTON — Before astronomers could discover the expansion of the universe, they had to expand their minds.

When the 20th century began, astronomers not only didn’t know the universe was expanding, they didn’t even care.

“Astronomers in the late 19th century and the very start of the 20th century were very little interested in what we would call the broader universe or its history,” says historian of science Robert Smith of the University of Alberta in Canada.

Some astronomers were interested in the structure of the Milky Way galaxy, the vast collection of stars in which the sun, Earth and known planets reside. “But astronomers played next to no part in the debates at the end of the 19th century about the wider nature of the cosmos,” Smith said in a talk January 28 at a meeting of the American Physical Society. In fact, many scientists believed there was no wider cosmos. Majority opinion held that the Milky Way galaxy, more or less, constituted the entire universe.

“As far as almost all astronomers were concerned, the universe beyond our own limited system of stars was the realm of metaphysics, and working astronomers did not engage in metaphysics,” Smith said.

Astronomers left others to do the wondering.

“The infinite universe beyond our stellar system was territory that professional astronomers really were very happy to leave to mathematicians, physicists, philosophers and some popularizers,” Smith said.

Even among those groups, pre-20th century consensus limited the universe to the Milky Way and its immediate environs. Clues to the contrary were mostly dismissed. Most prominent among those clues was the existence of “spiral nebulae,” fuzzy patches of light clearly distinct from the pointlike stars. Photos of the spiral-shaped blobs suggested that they were solar systems in the making within or around the Milky Way; many people believed the galaxy was home to countless populated planets. Very few people believed that the nebulae were distant replicas of the Milky Way, galaxies in their own right.
In a book published in 1890, for instance, astronomer and respected science popularizer Agnes Clerke wrote that “no competent thinker” believed that nebulae could be galaxies. She retained that view in a later edition published in 1905, Smith said.

But after around 1905, he said, the modern conception of the cosmos began to emerge. Philanthropic contributions in support of new, large telescopes, particularly in the American West, led to observations that slowly transformed the restricted view of a one-galaxy universe into the current commodious cosmos, with billions and billions (technically, gazillions) of galaxies.
At Lick Observatory in California, for instance, James Keeler undertook the task of counting the spiral nebulae. At the time, astronomers knew of a few dozen. Keeler found hundreds of thousands.

“So the spiral nebulae are elevated in importance by Keeler,” Smith said.

By 1912, Vesto Slipher, at Lowell Observatory in Arizona, began reporting measurements of the light emanating from the nebulae, determining how far colors were shifted to the red end of the spectrum, a way to measure how fast the nebulae were flying away from the Earth.

“He would actually start arguing that the spiral nebulae were distant galaxies,” Smith said.

By the 1920s, more and more astronomers took the idea of distant galaxies seriously. Finally Edwin Hubble, at the Mount Wilson Observatory in Southern California, provided the deathblow to the one-galaxy universe. In 1923, his observations of the Andromeda nebula turned up a couple of Cepheid variable stars. Because Cepheids varied in brightness on a regular schedule that depended on their intrinsic brightness, they provided surefire clues to Andromeda’s distance from Earth. Andromeda resided 900,000 light-years away, vastly farther than even the most exaggerated estimates of the Milky Way’s diameter.

Hubble’s use of Cepheids depended on the earlier pioneering work of Henrietta Swan Leavitt at the Harvard observatory. “Her discovery of the period-luminosity relationship in Cepheid variable stars is absolutely fundamental in transforming people’s ideas about first, our own galactic system and second, providing the means to demonstrate that galaxies do in fact exist,” Smith said.

By the end of the 1920s Hubble, combining his distance measurements with velocity measurement made by astronomer Milton Humason, had demonstrated that the farther a nebula was from Earth, the faster it appeared to fly away. That relationship formed the observational basis for the expanding universe. Hubble suggested as much in 1929. Others also realized that the new view of the cosmos implied an expanding universe; one, Georges Lemaître, proposed something very much like today’s Big Bang theory of the universe’s origin.

It took a while, though, for the idea of the universe as the expanding aftermath of a big explosion to open everybody’s mind. In 1935, for instance, the astronomer J.S. Plaskett called Lemaître’s ideas “speculation run wild without a shred of evidence.” Even Hubble was not entirely sure of his own discovery. In 1938, Smith pointed out, Hubble assessed the evidence as consistent with a static universe, while acknowledging that expansion could not be ruled out.

Today’s claims that other big bangs may have happened many times, creating a multitude of cosmic spacetime bubbles known as the multiverse, face similar objections. It’s true that the evidence for a multiverse is not conclusive, just as evidence in the 19th century was not conclusive that spiral nebulae were distant galaxies or “island universes” of their own. But given the historical precedent, it would be silly to say that “no competent thinker” would believe in the possibility of multiple universes today.

Abnormal is the new normal in mental health.

A small, poorly understood segment of the population stays mentally healthy from age 11 to 38, a new study of New Zealanders finds. Everyone else encounters either temporary or long-lasting mental disorders.

Only 171 of 988 participants, or 17 percent, experienced no anxiety disorders, depression or other mental ailments from late childhood to middle age, researchers report in the February Journal of Abnormal Psychology. Of the rest, half experienced a transient mental disorder, typically just a single bout of depression, anxiety or substance abuse by middle age.
“For many, an episode of mental disorder is like influenza, bronchitis, kidney stones, a broken bone or other highly prevalent conditions,” says study coauthor Jonathan Schaefer, a psychologist at Duke University. “Sufferers experience impaired functioning, many seek medical care, but most recover.”

The remaining 408 individuals (41 percent) experienced one or more mental disorders that lasted several years or more. Their diagnoses included more severe conditions such as bipolar and psychotic disorders.

Researchers analyzed data for individuals born between April 1972 and March 1973 in Dunedin, New Zealand. Each participant’s general health and behavior were assessed 13 times from birth to age 38. Eight mental health assessments occurred from age 11 to 38.
Surprisingly, those who experienced lasting mental health did not display several characteristics previously linked to a lower likelihood of developing mental disorders. Those attributes consist of growing up in unusually affluent families, enjoying especially sound physical health and scoring exceptionally high on intelligence tests.
Instead, mentally healthy participants tended to possess advantageous personality traits starting in childhood, Schaefer and colleagues found. These participants rarely expressed strongly negative emotions, had lots of friends and displayed superior self-control. Kiwis with rock-solid mental health also had fewer first- and second-degree relatives with mental disorders compared with their peers.

As adults, participants with enduring mental health reported, on average, more education, better jobs, higher-quality relationships and more satisfaction with their lives than their peers did. But lasting mental health doesn’t guarantee an exceptional sense of well-being, Schaefer says. Nearly one-quarter of never-diagnosed individuals scored below the entire sample’s average score for life satisfaction.

Less surprising was the 83 percent overall prevalence rate for mental disorders. That coincides with recent estimates from four other long-term projects. In those investigations — two in the United States, one in Switzerland and another in New Zealand — between 61 percent and 85 percent of participants developed mental disorders over 12- to 30-year spans.

Comparably high rates of emotional disorders were reported in 1962 for randomly selected Manhattan residents. Many researchers doubted those findings, which relied on a diagnostic system that was less strict than the three versions of psychiatry’s diagnostic manual that were introduced and used to evaluate New Zealand participants as they got older, says psychiatric epidemiologist William Eaton of Johns Hopkins Bloomberg School of Public Health. But the Manhattan study appears to have been on the right track, Eaton says.

Increased awareness that most people will eventually develop a mental disorder (SN: 10/10/09, p. 5), at least briefly, can reduce stigma attached to these conditions (SN Online: 10/13/16), he suspects.

Psychiatric epidemiologist Ronald Kessler suspects the numbers of people experiencing a mental disorder may be even higher than reported. Many participants deemed to have enduring mental health likely developed brief mental disorders that got overlooked, such as a couple of weeks of serious depression after a romantic breakup, says Kessler of Harvard Medical School, who directs U.S. surveys of mental disorders. Rather than focusing on rare cases of lasting mental health, “the more interesting thing is to compare people with persistent mental illness to those with temporary disorders,” he says.

Hydras, petite pond polyps known for their seemingly eternal youth, exemplify the art of bouncing back (SN: 7/23/16, p. 26). The animals’ cellular scaffolding, or cytoskeleton, can regrow from a slice of tissue that’s just 2 percent of the original hydra’s full body size. Researchers thought that molecular signals told cells where and how to rebuild, but new evidence suggests there are other forces at play.

Physicist Anton Livshits and colleagues at the Technion-Israel Institute of Technology in Haifa genetically engineered Hydra vulgaris specimens so that stretchy protein fibers called actins, which form the cytoskeleton, lit up under a microscope. Then, the team sliced and diced to look for mechanical patterns in the regeneration process.
Actin fibers in pieces of hydra exert mechanical force that lines up new cells and guides the growth of the animal’s head and tentacles, the researchers found. Turning off motor proteins that move actin stopped regeneration, and physically manipulating actin fiber alignment resulted in hydras with multiple heads. Providing hydras with further structural stability encouraged tissue slices to grow normally. Both mechanical and molecular forces may mold hydras in regeneration, the researchers report in the Feb. 7 Cell Reports.
When researchers anchored rings of hydra tissue to a wire (right), they found that the added mechanical stability made a hydra grow normally along one body axis, and thus grow one head. Without this stability, the actin scaffolding was more disrupted and the animal grew two heads (left).

WASHINGTON — A nasty stomach virus that can linger on fruits and veggies may have met its match in cold plasma.

In experiments, the ionized gas, created by filtering room-temperature air through an electric field, virtually eliminated norovirus from lettuce, researchers reported February 7 at the American Society for Microbiology Biothreats meeting.

Norovirus is the leading cause of foodborne illness in the United States, infecting more than 20 million people every year. Sterilizing food with heat is one way to kill the virus, but that approach doesn’t work for fresh produce. Cold plasma could be a way to sterilize fruits and vegetables without damaging them, said Hamada Aboubakr, a food microbiologist at the University of Minnesota in St. Paul.
Aboubakr and colleagues used a cold plasma device to blast contaminated romaine lettuce leaves and stainless steel surfaces. After five minutes, the plasma wiped out about 99 percent of norovirus particles.

The researchers are testing the device on other foodborne viruses such as hepatitis A, which sickened more than 140 people last year after they ate contaminated strawberries. Unpublished experiments have shown that cold plasma also can destroy drug-resistant bacteria on chicken breasts and leafy greens. Aboubakr hopes to adapt the technology for use in restaurants, on cruise ships and in the produce aisles of grocery stores.

BOSTON — For a lawn that helps the environment — and doesn’t need to be mowed — look to the ocean. Meadows of underwater seagrass plants might lower levels of harmful bacteria in nearby ocean waters, researchers reported February 16 during a news conference at the annual meeting of the American Association for the Advancement of Science. That could make the whole ecosystem — from corals to fish to humans — healthier.

Not truly a grass, seagrasses are flowering plants with long, narrow leaves. They grow in shallow ocean water, spreading into vast underwater lawns. Seagrasses are “a marine powerhouse, almost equal to the rainforest. They’re one of the largest stores of carbon in the ocean,” says study coauthor Joleah Lamb, an ecologist at Cornell University. “But they don’t get a lot of attention.”
It’s no secret that seagrasses improve water quality, says James Fourqurean, a biologist at Florida International University in Miami who wasn’t involved in the research, which appears in the Feb. 17 Science. The plants are great at removing excess nitrogen and phosphorus from coastal waters. But now, it seems, they might take away harmful bacteria, too.

A few years ago, Lamb’s colleagues became ill with amoebic dysentery while studying coral reefs in Indonesia, an archipelagic nation that straddles the Indian and Pacific oceans. When a city or village on one of the country’s thousands of islands dumps raw sewage into the ocean, shoreline bacteria populations can spike to dangerous levels.
Water sampled close to the shores of four small and densely populated Indonesian islands had 10 times the U.S. Environmental Protection Agency’s recommended exposure limit of Enterococcusbacteria, which can cause illness in humans and often signals the presence of other pathogens. But water collected from offshore tidal flats and coral reefs with seagrass beds had lower levels of the bacteria compared with similar sites without the plants less than 20 meters away. The water had lower levels of numerous bacterial species that can make fish and marine invertebrates sick, too. And field surveys of more than 8,000 coral heads showed that those growing adjacent to or within seagrass beds had fewer diseases than those growing farther away.
It’s unclear how far from seagrass beds this cleaner water extends, but the benefits can ripple through the entire ecosystem, Lamb said at the news conference. Healthier corals help protect the islands from erosion. And fish less contaminated with bacteria make a better source of food for people.

Lamb is planning follow-up studies to figure out exactly how the seagrasses clean the water. Like a shag carpet, seagrasses trap small particulates drifting through the ocean and prevent them from flowing on. The plants might ensnare bacteria in the same way, building up biofilms on their blades. Or, she suggests, the leaves could be giving off antimicrobial compounds that directly kill the bacteria.

The findings are one more reason to conserve seagrasses, study coauthor Jeroen van de Water, an ecologist at the Scientific Center of Monaco, said at the news conference. Worldwide, seagrass beds are declining by 7 percent each year, thanks to pollution and habitat loss. And while restoration efforts are underway in some areas, “it’s better to stop what we’re doing to the meadows than to try to replant them,” Lamb added. “Seagrasses are quite particular in the depth they want to be at and the environment they want to have. It’s hard to start doing restoration projects if the environment isn’t exactly what the seagrass prefers.”

A big coconut crab snaps its outsized left claw as hard as a lion can bite, new measurements suggest. So what does a land crab the size of a small house cat do with all that pinch power?

For starters, it protests having its claw-force measured, says Shin-ichiro Oka of the Okinawa Churashima Foundation in Motobu, Japan. “The coconut crab is very shy,” he says. It doesn’t attack people unprovoked. But wrangling 29 wild Birgus latro crabs on Okinawa and getting them to grip a measurement probe inspired much snapping at scientists. Oka’s hand got pinched twice (no broken bones). “Although it was just a few minutes,” he says, “I felt eternal hell.”
The strongest claw grip the researchers measured squeezed with a force of about 1,765 newtons, worse than crushing a toe under the force of the full weight of a fridge. For comparison, a lion’s canines bite with 1,315 newtons and some of its molars can crunch with 2,024 newtons, a 2007 study calculated. Because grip strength increases with body size, crabs bigger than those measured in the study might surpass the bite force of most land predators, Oka and colleagues proposed last year in PLOS ONE.
Coconut crabs, however, start life about as scary as a soggy grain of rice. Fertilized eggs hatch in seawater and bob around planktonlike in the western Pacific and Indian oceans. The crabs eventually return to land, where they spend most of their long lives, up to 50 (or maybe 100) years, as landlubbers that will drown if forced back into water for too long. Yet females have to risk the ocean’s edge each time they lay the next generation of eggs.
Both moms and dads grow a powerful left claw, handy for dismembering whatever the omnivorous scavengers find: roadkill and other dead stuff, innards of palm trees and nuts. The crabs can break open coconuts, but the job “takes hours,” says Jakob Krieger of the University of Greifswald in Germany. Cracking open a red crab, however, takes seconds.

Coconut crabs not only scavenge red crabs but also hunt them on Christmas Island in the Indian Ocean, Krieger says. Only the strictest vegetarian would ignore the 44 million or so red crabs scuttling around, and even small coconut crabs get a taste. Krieger watched an underpowered coconut crab grab hold of and wrestle its prey. The red crab abandoned its trapped limb and fled. But the little coconut crab scored a crab-leg dinner.

The planning for our supernova special issue began months ago. In one early meeting, astronomy writer Christopher Crockett lit up as he told the story of the night supernova 1987A was discovered. The account has all the ingredients of a blockbuster. There’s a struggle (with an observatory door), the element of surprise (an unexpected burst on a photographic plate), disbelief (by our protagonist and a collaborator), a scramble (to figure out how to report the discovery of the supernova), and an action scene that seems impossibly quaint: A driver races to the nearest town 100 kilometers away to send a telegram and alert the world that 166,000 light-years away, a star has exploded.

That story opens Crockett’s feature article commemorating the 30th anniversary of the supernova’s discovery. And we’ve brought it to life in video form as well. Ian Shelton, the telescope operator who spotted 1987A on a three-hour exposure he took of the Large Magellanic Cloud, was kind enough to consult with us for the video. He stars in it in clay form, and his voice makes a few guest appearances too.
Our anniversary coverage of 1987A offers a great summary of the importance of the discoveries that came from the stellar explosion. But Science News has been telling the story of SN 1987A for years. In fact, we began telling its story just days after the discovery. News of the explosion reached the International Astronomical Union on a Tuesday; on Wednesday, the day we went to press, Science News editors slipped a mention of it into that week’s issue. The following week’s issue carried a full story. Dozens more followed. We’ve pulled many of those together in the timeline below, which includes links to PDFs of the original magazine articles. Happy reading!

Volcanoes that belch hydrogen could bump up the number of potentially habitable planets in the universe.

Ramses Ramirez and Lisa Kaltenegger, both of Cornell University, modeled the atmospheres of planets blemished with hydrogen-spewing volcanoes. These gaseous eruptions could warm planets and ultimately widen a star’s habitable zone, the region where liquid water can exist on a planet’s surface, by about 30 to 60 percent, researchers report in the March 1 Astrophysical Journal Letters. That would be like extending the outer edge of the sun’s habitable zone from about 254 million kilometers — just beyond Mars’ orbit — to 359 million kilometers, or roughly to the asteroid belt between Mars and Jupiter.

Exoplanets that astronomers had previously thought too cold to support life might, in fact, be ripe for habitability if they have hydrogen volcanoes, the researchers say. One example is TRAPPIST-1h, the farthest-out planet identified in an odd system of seven Earth-sized planets 39 light-years from Earth (SN Online: 2/22/17). That world is thought to be icy like Jupiter’s moon Europa.

Adding planets to a star’s habitable zone means more exotic worlds could be targets in the search for signatures of life beyond our solar system. Astronomers plan to search for these signatures with the James Webb Space Telescope, slated to launch in 2018, and later with the European Extremely Large Telescope, scheduled to begin operations in 2024.