Never underestimate the value of a disposable mucus house.

Filmy, see-through envelopes of mucus, called “houses,” get discarded daily by the largest of the sea creatures that exude them. The old houses, often more than a meter across, sink toward the ocean bottom carrying with them plankton and other biological tidbits snagged in their goo.

Now, scientists have finally caught the biggest of these soft and fragile houses in action, filtering particles out of seawater for the animal to eat. The observations, courtesy of a new deepwater laser-and-camera system, could start to clarify a missing piece of biological roles in sequestering carbon in the deep ocean, researchers say May 3 in Science Advances.
The houses come from sea animals called larvaceans, not exactly a household name. Their bodies are diaphanous commas afloat in the oceans: a blob of a head attached to a long tail that swishes water through its house. From millimeter-scale dots in surface waters to relative giants in the depths, larvaceans have jellyfish-translucent bodies but a cordlike structure (called a notochord) reminiscent of very ancient ancestors of vertebrates. “They’re more closely related to us than to jellyfish,” says bioengineer Kakani Katija of the Monterey Bay Aquarium Research Institute in Moss Landing, Calif.

The giants among larvaceans, with bodies in the size range of candy bars, don’t form their larger, enveloping houses when brought into the lab. So Katija and colleagues took a standard engineering strategy of tracking particle movement to measure flow rates in fluids and reengineered equipment to watch giant houses at work deep in the ocean.
Getting the hardware right was challenging, and so was deploying it remotely from a research ship at the surface of the Monterey Bay. “This is a 1-millimeter-thick laser sheet bisecting an animal that’s about 2 centimeters wide that is 400 meters below the surface vessel,” Katija says.
The rig managed to capture measurements of water flow through houses of larvaceans belonging to two Bathochordaeus species. The top rate for B. mcnutti, more than 20 milliliters per second, broke the record (previously held by salps) for fastest recorded filtration rates from a zooplankton. If the maximum population of giant larvaceans in Monterey Bay pumped water that fast, they would clean all the particles out of their home depth in about 13 days.
Larvacean feeding rates matter because the sea creatures send organic matter, including carbon, to the deep ocean in two ways, explains biological oceanographer Stephanie Wilson of Bangor University in Wales. Larvaceans discard houses that become clogged with particles pumped in. (Small species can secrete a replacement in minutes though giants take longer. “Imagine that you have a head full of snot, and you sneeze your house,” Wilson says.)

Larvaceans also send carbon to the seafloor in football-shaped excrement. That’s an American football, Wilson clarifies. The tiny plankton that larvaceans near the surface eat wouldn’t sink far on their own, but once an animal ingests them and excretes a dense pellet, the carbon in the meal sinks better.

If carbon-containing fallout from the upper ocean falls fast enough, it bypasses diversions by other creatures and reaches depths where nothing much happens to it for a long time, says Sari Giering of the National Oceanography Centre in Southampton, England, where she studies oceanic carbon. “The faster a particle sinks, the more likely its carbon will be stored in the ocean for centuries,” she says.

Giering enthusiastically welcomes the new laser-and-camera system. She points out that researchers thought giant larvaceans could be important in sequestering carbon. But the fragile houses have been hard to study in action until now.

One of the most pressing and perplexing questions parents have to answer is what to do about screen time for little ones. Even scientists and doctors are stumped. That’s because no one knows how digital media such as smartphones, iPads and other screens affect children.

The American Academy of Pediatrics recently put out guidelines, but that advice was based on a frustratingly slim body of scientific evidence, as I’ve covered. Scientists are just scratching the surface of how screen time might influence growing bodies and minds. Two recent studies point out how hard these answers are to get. But the studies also hint that the answers might be important.

In the first study, Julia Ma at the University of Toronto and colleagues found that, in children younger than 2, the more time spent with a handheld screen, such as a smartphone or tablet, the more likely the child was to show signs of a speech delay. Ma presented the work May 6 at the 2017 Pediatric Academic Societies Meeting in San Francisco.

The team used information gleaned from nearly 900 children’s 18-month checkups. Parents answered a questionnaire about their child’s mobile media use and then filled out a checklist designed to identify heightened risk of speech problems. This checklist is a screening tool that picks up potential signs of trouble; it doesn’t offer a diagnosis of a language delay, points out study coauthor Catherine Birken, a pediatrician at The Hospital for Sick Children in Toronto.

Going into the study, the researchers didn’t have expectations about how many of these toddlers were using handheld screens. “We had very little clues, because there is almost no literature on the topic,” Birken says. “There’s just really not a lot there.”

It turns out that about 1 in 5 of the toddlers used handheld screens, and those kids had an average daily usage of about a half hour. Handheld screen time was associated with potential delays in expressive language, the team found. For every half hour of mobile media use, a child’s risk of language delay increased by about 50 percent.

“The relationship is not that strong,” Birken says, and those numbers come with big variations. Still, a link exists. And finding that association means there’s a lot more work to do, Birken says. In this study, researchers looked only at time spent with handheld screens. Future studies could investigate whether parents watching along with a child, the type of content or even time of day might change the calculation.

A different study, published April 13 in Scientific Reports, looked at handheld digital device use among young children and its relationship to sleep. As a group, kids from ages 6 months to 3 years who spent more time using mobile touch screen devices got less sleep at night.
Parent surveys filled out online indicated that each hour of touch screen use was linked to 26.4 fewer minutes of night sleep and 10.8 minutes more sleep during the day. Extra napping time “may go some way to offset the disturbed nighttime sleep, but the total sleep time of high users is still less than low users,” says study coauthor Tim Smith, a cognitive psychologist at Birkbeck, University of London. Each additional hour of touch screen use is linked to about 15 minutes less sleep over 24 hours.

By analyzing 20 independent studies, an earlier study found a similar link between portable screen use and less sleep among older children. The new results offer “a consistent message that the findings from older children translate into those younger,” says Ben Carter of King’s College London, who was a coauthor on the study of older children.

So the numbers are in. Daily doses of Daniel Tiger’s Neighborhood on a mobile device equals 7.5 minutes less sleep and a 50 percent greater risk of expressive language delay for your toddler, right? Well, no. It’s tempting to grab onto these numbers, but the science is too preliminary. In both cases, the results show that the two things go together, not that one caused the other.

It may be a long time before scientists have answers about how digital technology affects children. In the meantime, you can follow the American Academy of Pediatrics’ recently updated guidelines, which discourage screens (except for video chatting) before 18 months of age and for all children during meals or in bedrooms.

We now live in a world where smartphones are ever-present companions, a saturation that normalizes the sight of small screens in tiny hands. But I think we should give that new norm some extra scrutiny. The role of mobile devices in our kids’ lives — and our own — is something worth thinking about, hard.

The juice saga continues. The American Academy of Pediatrics updated their official ruling on fruit juice, recommending none of the sweet stuff before age 1. Published in the June Pediatrics, the recommendation is more restrictive than the previous one, which advised no juice before age 6 months.

The move comes from the recognition that whole fruits — not just the sweet, fiberless liquid contained within — are the most nutritious form of the food. Babies under 1 year old should be getting breast milk or formula until they’re ready to try solid foods. After their first birthdays, any extra liquids they drink should be water or milk. (These updated guidelines may not apply to babies who might need fruit juice to help with constipation.)

Whole fruits — or, mashed up clumps of them — have more fiber and protein than juice. The only benefit that juice has over its former whole form is that it’s way easier for a kid to slurp down.

The potential risks of cavities and obesity in part prompted the updated guidelines. It’s worth saying that neither of these outcomes are guaranteed with juice drinking. In fact, a recent study failed to find a link between juice drinking and excessive weight gain in children. Still, juice offers no nutritional advantage over whole fruits, so the reasoning of the AAP seems to be, “Why risk it?”

The AAP gave additional, more nuanced advice for parents who do decide to give juice to children age 1 and older:

Don’t give kids juice in bottles or sippy cups, especially at bedtime. That ease of drinkability would encourage kids to drink juice for long periods of time, prolonging sugar baths for teeth.

Look out for unpasteurized juice. Harmful forms of E. coli bacteria can appear in unpasteurized apple cider, for instance, posing a particular risk for young people.

Give 1- to 3-year-old kids no more than 4 ounces of juice a day. That recommendation drops 2 ounces from earlier guidance that limited juice to between 4 and 6 ounces daily. Children ages 4 to 6 years old get those extra 2 ounces back, with a daily limit of between 4 and 6 ounces.

Make sure kids are drinking 100 percent juice, not those sneaky “cocktails” or “drinks.” Those are often nutritional wastelands, packed with even more sugar and devoid of other nutrients.
Though the guidelines don’t mention habit formation, I suspect this also came into play in the AAP’s encouragement of whole fruits over juice. Children’s taste preferences get shaped early. Really early, actually. Fetuses learn to love flavors their mothers ate while pregnant. So babies who grow accustomed to sweet juice might be less impressed with water or milk. And while that might not be a problem in the early years of life, years or decades of drinking sweet liquids will catch up with them eventually.

Anyone who’s dragged roller luggage knows it’s liable to fishtail. To most people, this is a nuisance. To a few scientists, it’s a physics problem. Researchers detail the precise interplay of forces that set suitcases shimmying in a study published online June 21 in Proceedings of the Royal Society A.

The researchers simulated and observed the motion of a toy model suitcase on a treadmill. They found that the suitcase’s side-to-side motion at any given moment is related to its tilt and distance off-center from the line of travel.
For instance, imagine a suitcase rolling straight ahead, but then hitting a bump or cutting a corner that causes the right wheel to lift. The suitcase’s tilt makes the left wheel steer the suitcase rightward. When the right wheel falls back to the ground and the left wheel lifts off, the suitcase — now positioned and tilted to the right — banks left. Switch wheels, swing, repeat.

“It’s a pretty good analysis of the system,” says Andy Ruina, a physicist at Cornell University who was not involved in the research.

This swaying motion is “a bit funny and counterintuitive,” says study coauthor Sylvain Courrech du Pont. It actually gets smaller when the suitcase rolls faster. Lowering the angle of the suitcase can get the rocking to stop altogether, he says.

Understanding the physics of this system could be useful for more than designing stable suitcases, because it also applies to other two-wheel carriers — like car-pulled trailers. “In the near future, maybe we will have a car without a driver,” says Courrech du Pont, a physicist at Paris Diderot University. “It would be a good thing if the car knows how to stop this kind of motion.”

When it comes to smelling pretty, petunias are pretty pushy.

Instead of just letting scent compounds waft into the air, the plants use a particular molecule called a transporter protein to help move the compounds along, a new study found. The results, published June 30 in Science, could help researchers genetically engineer many kinds of plants both to attract pollinators and to repel pests and plant eaters.

“These researchers have been pursuing this transporter protein for a while,” says David Clark, an expert in horticultural biotechnology and genetics at the University of Florida in Gainesville. “Now they’ve got it. And the implications could be big.”
Plants use scents to communicate (SN: 7/27/02, p. 56). The scent compounds can attract insects and other organisms that spread pollen and help plants reproduce, or can repel pests and plant-eating animals. The proteins found in the new study could be used to dial the amount of scent up or down so that plants can attract more pollinators or better protect themselves. Currently unscented plants could be engineered to smell, too, giving them a better shot at reproduction and survival, Clark says.
Plants get their scents from volatile organic compounds, which easily turn into gases at ambient temperatures. Petunias get their sweet smell from a mix of benzaldehyde, the same compound that gives cherries and almonds their fruity, nutty scent, and phenylpropanoids, often used in perfumes.

But nice smells have a trade-off: If these volatile compounds build up inside a plant, they can damage the plant’s cells.
About two years ago, study coauthor Joshua Widhalm, a horticulturist at Purdue University in West Lafayette, Ind., and colleagues used computer simulations to look at the way petunias’ scent compounds moved. The results showed that the compounds can’t move out of cells fast enough on their own to avoid damaging the plant. So the researchers hypothesized that something must be shuttling the compounds out.

In the new study, led by Purdue biochemist Natalia Dudareva, the team looked for genetic changes as the plant developed from its budding stage, which had the lowest levels of volatile organic compounds, to its flower-opening stage, with the highest levels. As flowers opened and scent levels peaked, the gene PhABCG1 went into overdrive; levels of the protein that it makes jumped to more than 100 times higher than during the budding stage, the researchers report.

The team then genetically engineered petunias to produce 70 to 80 percent less of the PhABCG1 protein. Compared with regular petunias, the engineered ones released around half as much of the scent compounds, with levels inside the plant’s cells building to double or more the normal levels. Images of the cells show that the accumulation led to deterioration of cell membranes.

A lot of work has been done to identify the genes and proteins that generate scent compounds, says Clark. But this appears to be the first study to have identified a transporter protein to shuttle those compounds out of the cell. “That’s a big deal,” he says.

Humpback whales, those innovative foodies, have discovered their own pop-up restaurants.

Migrant humpbacks returning to southeastern Alaska in spring are the first of their kind known to make routine visits to fish hatcheries releasing young salmon into the sea, says marine ecologist Ellen Chenoweth.

The whales are “40 feet long and they’re feeding on fish that are the size of my finger,” says Chenoweth, of the Juneau fisheries center of University of Alaska Fairbanks. For tiny prey to be worthwhile to humpbacks, it’s good to find crowds — such as young salmon streaming out of hatchery nets.

Six years of systematic observations of whales at five hatcheries at Baranof Island reveal a pattern of humpbacks visiting during springtime releases, Chenoweth and her colleagues report June 12 in Royal Society Open Science.

Whale visits to the salmon buffet enhance humpbacks’ reputation for innovation in feeding, Chenoweth says. And since the water is relatively shallow, visits also make it easier to film humpback lunge feeding. More often, studying whale food dives means watching animals surface from the depths to catch their breath before the next exciting plunge. “It’s like going to a basketball game but you can only really watch players on the bench,” Chenoweth says.

Underwater, a humpback opens its jaws and rushes into the mass of prey as its throat balloons out “like a parachute opening,” she says. The toothless whale then filters the mouthful, swooshing it out through dangling fringes of baleen, which snag what’s worth swallowing. In one lunge, a humpback can take in about 27,600 liters of seawater — about 28 metric tons — roughly doubling the whale’s weight.

An unlikely hero has emerged in the quest to fight HIV: the cow. In a first for any animal, including humans, four cows injected with a type of HIV protein rapidly produced powerful antibodies against the virus, researchers report. Learning how to induce similar antibodies in humans may be key to a successful HIV vaccine.

The antibodies, called broadly neutralizing antibodies, can stop infection from a variety of HIV types. The cows generated these antibodies as soon as 42 days after immunization, the researchers report online July 20 in Nature. For the small percentage of people estimated to develop these antibodies after a natural infection, it can take several years.
The work identifies “a new and much more efficient method to generate broadly active antibodies against HIV,” says immunologist Justin Bailey of Johns Hopkins University School of Medicine, who was not involved in the study.

Making an HIV vaccine has proved difficult because the virus changes all the time. Different strains exist throughout the world, and the virus even mutates within an infected person’s body. Most often, people develop antibodies that are specific to one strain but ineffective against others. HIV vaccines tested so far have not led to the production of broadly neutralizing antibodies.

About 1 percent of HIV-infected people eventually generate broadly neutralizing antibodies that are especially potent and effective against many types of HIV. The development of these antibodies doesn’t seem to help infected people. But when given to monkeys before exposure to a virus similar to HIV, the antibodies prevent infection.

Broadly neutralizing antibodies specific to HIV have a few quirky features, one of which is the presence of a long stretch of amino acids that sticks out from the antibody surface. This protruding part of the antibody binds to a viral site that remains the same between strains, because the virus needs it to gain entry to a cell. HIV’s thick coat of surface sugars makes the viral binding site difficult to access. A longer stretch of amino acids seems to be able to pierce through “and reach in, almost like the long arm of the law,” says Vaughn Smider, a molecular immunologist at the Scripps Research Institute in La Jolla, Calif.

In people infected with HIV who develop broadly neutralizing antibodies, this antibody region — called HCDR3 — has about 30 amino acids, about twice as long as what is usual for human antibodies. Although on the long side for a human, “that’s actually kind of short for a cow,” Smider says.
And so the idea to immunize cows was born. Since cows naturally make longer HCDR3s, Smider explains, perhaps they’d have this sought-after response to HIV.

Smider and colleagues took serum — blood with the cells removed, leaving antibodies behind — from four immunized cows and tested it against different types of HIV virus in a test tube. All of the cows developed broadly neutralizing antibodies. The researchers then tested one cow’s antibodies on an even larger number of virus types. After 381 days, this cow’s antibodies prevented 96 percent of the 117 HIV types from infecting cells in a lab dish. The researchers also isolated an antibody from this cow that had a long HCDR3 of 60 amino acids and stopped infection by 72 percent of the HIV types.

If researchers could induce antibodies with long HCDR3s in humans, “then that could be the basis of getting a vaccine to work,” Smider says. “You need a step before the immunization that helps expand the rare antibodies.” Since cows are so good at making broadly neutralizing antibodies, it also might be possible to turn the cow’s handiwork into drugs for HIV treatment, if bovine antibodies are effective at stopping the virus in other animals, he says.

Galaxies may grow by swiping gas from their neighbors.

New simulations suggest that nearly half the matter in the Milky Way may have been siphoned from the gas of other galaxies. That gas provides the raw material that galaxies use to build their bulk. The finding, scheduled to appear in the Monthly Notices of the Royal Astronomical Society, reveals a new, unexpected way for galaxies to acquire matter and could give clues to how they evolve.
“These simulations show a huge amount of interaction among galaxies, a huge dance that’s going on,” says astronomer Romeel Davé of the University of Edinburgh. That dance, and the subsequent exchange of atoms, could be what establishes a galaxy’s character — whether it’s small or big, elliptical or spiral, quiet or bursting with star formation. If the simulation results are confirmed with observations, it could be a major advancement in understanding galaxy formation, Davé says.

It makes sense that much of the material in one galaxy actually came from other galaxies, says study coauthor Claude-André Faucher-Giguère, a theoretical astrophysicist at Northwestern University in Evanston, Ill. “Still, the result was really unexpected,” he says.

Astronomers thought galaxies got their matter in two main ways. First, atoms clumped together to form stars and then galaxies, not long after the Big Bang about 13.8 billion years ago. Then some of those atoms were eventually ejected by supernovas but rained back onto the same galaxy, recycling the gas again and again.

The new simulations showed a third way galaxies could score gas. Powerful supernova explosions would eject atoms, in the form of gas, far from their home galaxies into intergalactic space. Those atoms would then travel through space, pushed toward other galaxies by galactic winds that move at several hundred kilometers per second. When the particles neared a galaxy’s gravitational pull, they would get sucked in, where they would serve as the basis for stars, planets, dust and other material in their new galactic home. Still, this exchange of atoms is extremely difficult to spot in space because the gas atoms, don’t give off light like stars do.
Faucher-Giguère and colleagues spotted the exchange in computer simulations that show how galaxies formed just after the Big Bang and how they have evolved over time. The team tracked gas atoms as they moved through the model universe, formed stars and then were ejected from galaxies as those stars exploded.

In the simulations, up to half of the atoms in large galaxies were pulled in from other galaxies. Because more massive galaxies have more gravity, they tended to pull atoms from the ejected material of small galaxies. The exchange appears to take billions of years as atoms travel the vast space between galaxies, the team notes.

“It’s that not surprising to see a galaxy kick out matter, which is then pulled in by other galaxies,” Davé says. What is surprising, he says, is the amount of material that’s transferred. Before seeing the simulations, he would have guessed that about 5 percent of gas was transferred among galaxies this way. “To see that it is up to 50 percent is pretty remarkable,” he says.

Already, astronomers are searching for evidence of this material-swapping behavior among galaxies. Faucher-Giguère and colleagues, working with researchers using the Hubble Space Telescope, hope to observe intergalactic transfer of gas among galaxies soon.

Single-celled microbes may have taught plants and animals how to pack their genetic baggage.

Archaea, a type of single-celled life-form similar to bacteria, keep their DNA wrapped around proteins much in the same way as more complex organisms, researchers report in the Aug. 11 Science. This finding provides new insight into the evolutionary origins of the DNA-packing process and the secret to archaea’s hardiness, which enables some to live in acid, boiling water or other extreme environments.
All eukaryotes, including plants and animals, store their genetic material in cell compartments called nuclei. Such organisms cram meters of genetic material into the tiny nuclei by wrapping strands of DNA around clusters of proteins called histones (SN: 1/10/15, p. 32). “It doesn’t really matter which eukaryote you look at, whether it’s amoebas or plants or humans or fish or insects or anything,” says coauthor John Reeve, a microbiologist at Ohio State University. “They all have exactly the same structure.”

Unlike bacteria, some archaea also contain histones, but researchers weren’t sure whether these microbes spool DNA around the protein bobbins the way eukaryotes do. So Reeve and colleagues used a method called X-ray crystallography to discern, for the first time, the precise shape of archaea DNA bound to histones.

The researchers saw that archaea DNA coils around the histones, similar to the way it does in eukaryotes. “It’s a big deal actually seeing this,” says Steven Henikoff, a molecular biologist at the Fred Hutchinson Cancer Research Center in Seattle who was not involved in the work. The resemblance between archaea and eukaryote DNA wrapping means that the first organism that used this storage scheme was an ancestor of both modern eukaryotes and archaea, the researchers conclude.

But the way archaea DNA twists around histones isn’t identical to the coils of DNA seen in eukaryotes. In eukaryotes, a strand of DNA loops twice around a cluster of eight histones to create what’s called a nucleosome, and connects many of these nucleosomes like beads on a string. Archaea DNA string together bundles of proteins, too. But while eukaryotes always tether eight-protein clumps, archaea DNA can spiral around stacks of many more histones to create rod-shaped structures of various lengths. “So it’s not as uniform as in eukaryotes,” says coauthor Karolin Luger, a biophysicist and Howard Hughes Medical Institute investigator at the University of Colorado Boulder.

Researchers tested the importance of that rodlike architecture by tampering with the histone-DNA structures of some archaea and then observing how these mutant archaea fared in different conditions. “We tried to mimic some real-life situations that some of these organisms could get into,” Luger says.
For instance, some archaea that live in volcanic vents that emit sulfurous gases sometimes get spewed out and have to survive sans sulfur. Archaea with normal histone-DNA shapes can handle that kind of midlife crisis. But when researchers cut their mutant microbes off sulfur, the microorganisms’ growth was stunted. These microbes may not have been able to adapt to sulfur deprivation as well as their wild counterparts “because they can’t unpackage their DNA as readily if the structure has been changed,” Reeve says.

Henikoff calls it “a pretty cool experiment.” It showed that the archaea’s particular DNA-histone architecture was “biologically relevant, not just a novelty,” he says.

A total solar eclipse shines a light on the sun’s elusive atmosphere. When the moon blocks the sun, it’s finally possible to see how this diffuse cloud of plasma, called the corona, is magnetically sculpted into beautiful loops. The material there is about a trillionth the density of the solar surface. From its delicate and diaphanous appearance, you might expect the corona to be where the sun goes to cool off.

That couldn’t be more wrong. The corona is a mysteriously sizzling inferno where the temperature jumps from a mere few thousand degrees to several million degrees. Why?
“It’s one of the longest unanswered questions in all of solar physics,” says Paul Bryans of the High Altitude Observatory at the National Center for Atmospheric Research in Boulder, Colo. “There are a bunch of different ideas about what’s going on there, but it’s still highly debated.” Data collected during the Aug. 21 solar eclipse may bring scientists closer to settling that debate.

The sun simmers at about 5,500° Celsius at its visible surface, the photosphere. But the gas just above the photosphere is heated to about 10,000° C. Then in the corona, the temperature makes an abrupt jump to several million degrees.

“It’s counterintuitive that as you move away from a heat source, it gets warmer,” Bryans says. The corona’s diffuseness makes its heat even stranger — the most basic ways to heat a material rely on particles crashing into each other, but the corona is too tenuous for that to work.

An eclipse first brought this abnormal arrangement to light. German astronomer Walter Grotrian observed spectral lines — the fingerprints of elements that show up when light is split into its component wavelengths — emitted by the corona during a total solar eclipse in 1869.

Astronomers at first assumed those lines were due to a new element they dubbed coronium. But Grotrian realized that iron atoms stripped of several of their electrons by the heat were responsible. These iron lines in the corona are still used to measure its temperature: The more electrons lost, the hotter the material in the corona (SN Online: 6/16/17).
Such extreme temperatures have something to do with the corona’s magnetic field, which is probably where all that energy is stored. Once the energy is there, the corona has a hard time radiating it away, so it builds up. Most of the ways that materials release energy — stripping electrons from atoms, accelerating those electrons so they release X-rays and ultraviolet particles of light — are already maxed out in the corona.
“We know there’s energy coming in, and it’s hard to get it out unless you get very hot,” says Amir Caspi of the Southwest Research Institute in Boulder, Colo. “What we don’t understand is how that energy gets into the corona in the first place.”

Physicists have several ideas. Maybe loops of magnetic field lines in the corona vibrate like guitar strings, heating things up, sort of like how a microwave oven heats food. Maybe the magnetic anchors of those loops on the sun’s surface braid and twist the magnetic field above them, dumping in energy that is then continually radiated away like the heating element in a toaster.

Or maybe tiny explosions called nanoflares or jets called spicules carry energy away from the photosphere and into the corona. The formation of new coronal loops that connect to existing ones could dump in enough extra energy to heat the plasma up.

During the solar eclipse, dozens of groups of scientists across the country will deploy telescopes equipped with filters to pick out polarized light, infrared light or those electron-deprived iron atoms in search of answers. Bryans and his colleagues will be on a mountaintop near Casper, Wyo., in the path of totality. There, the team will take images at a fast clip in both visual and infrared wavelengths to map how the corona changes as the moon moves across the sun. (I will be in Wyoming with this team on the day of the eclipse and will be sharing more about how the experiments went.)

“We can look at how things change as we move from the surface up into the atmosphere,” Bryans says. “How that changes is tied to understanding how the corona is heated.”

Probably all of those mechanisms scientists have thought up contribute to the corona’s extreme heat. It’s difficult to declare just one the most important. But ultimately, the solar eclipse is the best chance scientists have to test them. It’s the only time the corona is the star of the solar show.