Melissa Omand’s clever tech follows the fate of ocean carbon

As chief scientist for a voyage of the research vessel Endeavor, oceanographer Melissa Omand oversaw everything from the deployment of robotic submarines to crew-member bunk assignments. The November 2015 expedition 150 kilometers off Rhode Island’s coast was collecting data for Omand’s ongoing investigations of the fate of carbon dioxide soaked up by the ocean.

But Omand, an assistant professor at the University of Rhode Island’s campus in Narragansett, wasn’t on the ship. Instead of riding the waves with her crew, she was working, sometimes 16-hour days, inside a dark room at the university’s Inner Space Center — staring at computer monitors in a sort of NASA mission control for oceanographers. When she submitted the trip proposal a year earlier, she hadn’t foreseen that she’d be eight months pregnant with her first child when the ship set sail.
Still, missing the trip was unthinkable, she says. The Inner Space Center, she realized, offered a way to direct the mission from shore via satellite. After proposing the solution to her higher-ups, and a lot of meetings that followed, she got permission to be the first chief scientist to remotely lead an Endeavor cruise.

“She doesn’t let many obstacles get in her way,” says Colleen Durkin, an oceanographer at Moss Landing Marine Laboratories in California, who participated in the cruise. “That’s one of the fun things about working with her. She’s willing to try new things.”
Her commitment to her science and her drive to find creative solutions are helping Omand tackle a big problem in oceanography. For a decade, she has been studying the mechanisms — such as currents and the dining and dying of microorganisms — that move carbon and nutrients through the ocean. In a breakout paper, published last year in Science, she reported the discovery that eddies can pull carbon from phytoplankton deep into the ocean, a previously undescribed phenomenon. Studying the fate of that carbon isn’t just interesting, she says, it’s vital to predicting the fate of our climate. “The ocean has a huge capacity to absorb excess carbon dioxide in our atmosphere,” Omand says. But as the planet warms, atmosphere and ocean might interact differently. Scientists need all the information they can get to figure out how to adapt to those changing conditions and mitigate the effects of climate change.

Omand, 36, first got her feet wet on the rivers and lakes surrounding her hometown of Toronto. In her teens, she worked as a canoe guide, exploring the region’s waterways. “That was absolutely the root of my interest in earth science and environmental issues,” she says. “I’m essentially doing the same thing now, just on a much bigger boat.”

After starting off as a premed student at the University of Guelph in Canada, she was ultimately drawn to the university’s physics program. “I found it very satisfying that all these problems boiled down to a few underlying rules and equations,” she says. During her undergraduate studies, her focus was millions and millions of kilometers away from Earth’s oceans. She coded software used to help calibrate X-ray instruments on NASA’s Mars Exploration Rovers, which identified the makeup of Martian rocks.
While considering areas of physics for her graduate studies, Omand received an email that altered her heading. Chris Garrett, a professor (now emeritus) at Canada’s University of Victoria, introduced her to physical oceanography. “He showed me demonstrations of what happens to dye in a rotating water tank,” she recalls. “I was hooked by that.” The churning of water appealed to Omand for the same reason the field of physics did: Whether in tanks or oceans, the water’s movements can be expressed by a set of specific equations, called the Navier-Stokes equations.

Omand has applied these equations in much of her work. During a Ph.D. at the Scripps Institution of Oceanography in La Jolla, Calif., she and colleagues studied the origins of a red tide off California’s coast. The team found that the red tide, fertilized by a layer of nutrients, had been festering under the ocean surface for a week before being drawn upward. Omand and her colleagues used a Jet Ski modified with a GPS system and scientific instruments to collect data. Later, as a postdoctoral researcher at Woods Hole Oceanographic Institution in Massachusetts, she and mentor Amala Mahadevan investigated mechanisms to explain how nitrogen, an important nutrient for phytoplankton, moves around below the sunlit layer of the sea.

During her time at Woods Hole, Omand also started tracking the journey of CO2 taken in by springtime algae blooms in the North Atlantic.
When the phytoplankton in these colossal blooms, which can stretch hundreds of kilometers across, die or are digested by other marine life, particles containing organic carbon are released into the water. The heavier of these particles sink, quarantining the carbon from the atmosphere. About 30 percent of all CO2 emitted by human activities has ended up in the oceans, thanks in part to these sinking particles.

Scientists had believed that smaller particles would remain near the surface. But with robotic submarines called gliders that cruised up and down the water column sensing light scattered by the particles, Omand and colleagues found a surprisingly large amount of small carbon particles. These particles were around 100 to 350 meters deep, in the ocean’s “twilight zone,” where phytoplankton rarely live.
Omand combined measurements such as temperature and salinity from several gliders to explain how the particles got pulled so far down. By analyzing those measurements alongside computer simulations and satellite data — an innovative mix of sources that provided finer details and the bigger picture — she showed that the carbon-rich particles were carried down by spiraling ocean currents called eddies. Water escaping these bowl-shaped depressions can become sandwiched between deeper ocean layers, remaining trapped along with any particles even once an eddy subsides.

The accompanying carbon drain cools the Earth, says Eric D’Asaro, an oceanographer at the University of Washington in Seattle who collaborated with Omand on the research. Though the finding doesn’t change the total amount of carbon known to be taken in, the study identifies a new mechanism that could account for as much as half of all carbon known to be pulled into the deep North Atlantic during spring. The mechanism could also play a role elsewhere in the world’s oceans, D’Asaro, Omand and colleagues reported in April 2015 in Science.

“Her work sets the table for the next decade in terms of understanding the interaction between the turbulence of the ocean and how carbon is injected down to depth,” says David Siegel, an oceanographer from the University of California, Santa Barbara. “She’s going to be one of the new leaders of this field.”

Now a mother — her daughter was born a few weeks after the cruise — and an assistant professor at the University of Rhode Island, Omand continues her creative problem-solving, often by calling on unexpected technology. On a research trip in June (she was on the ship this time), Omand used an iPhone in a waterproof case to automatically snap pictures every half hour of particles raining down from the ocean’s top layer. Scientists previously measured the rates of sinking particles with traps that provided no information about how the rates changed throughout the day. Omand got the idea to affix her old iPhone to the traps after being offered only $40 for the used phone. “There’s got to be something really amazing I can do with this,” she thought.

Next spring, Omand will harness the same telepresence software she used for the 2015 Endeavor trip to virtually take undergraduate students on board. Omand’s ability to harness technology to solve tricky scientific challenges is a big reason why she can identify new truths about our oceans, says Mahadevan. “Every problem she touches,” Mahadevan says, “something beautiful comes out.”

Mercury’s surface still changing

Mercury has gotten some new wrinkles in its old age. The innermost planet shows signs of relatively recent tectonic activity, a new study suggests.

Tiny cliffs on the surface — just tens of meters high and a few kilometers long — resemble breaks in the planet’s crust, researchers report online September 26 in Nature Geoscience. The diminutive sizes of the cliffs, their sharp edges and lack of large overlapping craters imply that the faults are geologically young — less than 50 million years old. That’s much younger than Mercury’s larger, eroded scarps seen elsewhere, which probably arose more than 3.5 billion years ago. The small scarps indicate that the surface still fractures as Mercury cools and contracts, the researchers suggest, though other explanations are possible.
Thomas Watters, a geologist at the Smithsonian Institution in Washington, D.C., and colleagues discovered the young escarpments in images taken by NASA’s MESSENGER spacecraft, which orbited Mercury from 2011 to 2015. During the last 18 months of the mission, the spacecraft inched closer to the surface of Mercury, revealing new details such as these small scarps. The mission ended with an intentional crash landing on April 30, 2015 (SN Online: 4/30/15).

Mercury’s continued contraction isn’t surprising, says Sean Solomon, a planetary scientist at Columbia University. “It’s demanded by physics,” he says. Mercury has gradually cooled over its 4.6-billion-year history. As it cools, it shrinks. Sometimes that shrinkage cracks the surface. All of the other rocky planets shrivel over time as well, but their atmospheres have erased much of the evidence. Only on Mercury and the moon — both airless — is the history of contraction preserved because of limited erosion.

It’s not clear, though, if these new faults are related to that shrinking. “In and of themselves, they don’t tell us very much,” says Paul Byrne, a planetary geologist at North Carolina State University in Raleigh. Without an analysis of how the small, young scarps relate to the large, old scarps, he says, it’s hard to draw conclusions. The new arrivals could just as well be produced by shifting rubble or shock waves from run-ins with asteroids, and if so would not be a sign of continuing tectonic activity.

A closer inspection of Mercury will have to wait until the European spacecraft BepiColombo, scheduled to launch in 2018, arrives in late 2024. While its altitude will be similar to MESSENGER’s, BepiColombo will get a better look at Mercury’s southern hemisphere, which should allow researchers to get a more global view of how all these wrinkles in the surface tie together.

Maps show genetic diversity in mammals, amphibians around the world

Maps have long been used to show the animal kingdom’s range, regional mix, populations at risk and more. Now a new set of maps reveals the global distribution of genetic diversity.

“Without genetic diversity, species can’t evolve into new species,” says Andreia Miraldo, a population geneticist at the Natural History Museum of Denmark in Copenhagen. “It also plays a fundamental role in allowing species populations to adapt to changes in their environment.”
Miraldo and her colleagues gathered geographical coordinates for more than 92,000 records of mitochondrial DNA from 4,675 species of land mammals and amphibians. The researchers compared changes in cytochrome b, a gene often used to measure genetic diversity within a species, and then mapped the average genetic diversity for all species within roughly 150,000 square-kilometer areas.
For both mammals and amphibians, the tropical Andes and the Amazon have high genetic diversity, shown in dark blue. The same is true for mammal species in subtropical regions of South Africa and amphibian species in eastern North America, Miraldo and colleagues report in the Sept. 30 Science.
Areas affected by people, such as cities and croplands, show lower genetic diversity. The maps are a snapshot and so can’t quantify humans’ impact on this key marker, Miraldo notes. But she hopes the work provides a baseline to monitor how human activity and changes in climate affect the distribution of genetic diversity around the globe.

Ocean plastic emits chemical that may trick seabirds into eating trash

Plastic smells like supper for some seabirds. When the ubiquitous material ends up in the ocean, it gives off a chemical that petrels, prions and shearwaters often use to locate food, researchers report November 9 in Science Advances. That might lead the birds to ingest harmful junk instead of a real meal.

Researchers at the University of California, Davis let small beads of three common plastics linger off the coast of California. After a few weeks, the once-clean plastic accumulated grit, grime and bacteria that gave off an odiferous gas called dimethyl sulfide (SN: 2/20/16, p. 20). Phytoplankton give off the same gas, and certain seabirds use the odor as a cue that dinner is nearby. Birds that rely more heavily on dimethyl sulfide as a beacon for a nearby meal are more likely to ingest plastic than birds that don’t, the team found. Other marine animals that use the cue could also be fooled.

Number of teens who report doing drugs falls in 2016

Fewer teenagers in the United States used drugs in 2016 than in previous decades. The positive news comes from an annual survey of almost 45,500 U.S. students in grades eight, 10 and 12.

“There’s a lot of good news here,” says pediatrician Sharon Levy of Boston Children’s Hospital. Public health messages from pediatricians, educators and others seem to be sinking in, she says. “I think that’s fabulous. Substance use is one of the most important — yet modifiable — behavioral health issues of adolescents.”
Adolescents’ use of many of the substances, including alcohol and cigarettes, hit an all-time low since the survey, known as the Monitoring the Future study, began collecting data 42 years ago. Heroin, methamphetamines, inhalants and stimulants also hit lows this year.

E-cigarettes have been particularly concerning as more adolescents gave the new devices a try, reaching a high in 2015 (SN: 5/28/16, p. 4). For the first time, the number of students who vape is declining, the survey found. In 2015, 16.3 percent of 12th-graders reported vaping in the last 30 days. In 2016, that fell to 12.5. Similar declines were evident among eighth- and 10th-graders.
In a happy surprise, misuse of prescription opioid use decreased in the last five years among 12th–graders. The drop was “a big surprise,” particularly against a backdrop of a much wider opioid epidemic in the general population (SN: 9/3/16, p. 14), Nora Volkow, the director of the National Institute on Drug Abuse in Bethesda, Md., said December 13 at a news briefing.
The news isn’t all good, though. Marijuana bucked the declining trends, at least for 12th-graders. In 2016, about 6 percent of 12th-graders said they use marijuana daily — a number that hasn’t changed much in the last five years.

Researchers don’t yet know why the rates for many drugs are down, but one idea is that the drop in illegal drugs may stem in part from reductions in alcohol and tobacco use. “There is a connection there,” Lloyd Johnston, a social psychologist at the University of Michigan in Ann Arbor who led the survey, said in the news briefing.

The survey and the information it produces is “extremely important,” Levy says, “but it’s not everything.” Other measures of kids’ drug use, such as rates of substance use disorders, will offer a fuller view of how adolescents interact with drugs, she says.

A message to rock climbers: Be kind to nature

For the millions of people who have taken up the sport of rock climbing, a cliff face is a challenge, a vertical puzzle solved only with the proper placement of hands and feet. Look closely, though, and those crevices and cracks that provide hand- and footholds also provide homes for a variety of plants, invertebrates and other easily overlooked species.

People who participate in outdoor sports like rock climbing may not think about the environmental impact of what they’re doing. After all, how big of an impact can one person really have on a rock? But there is a potential for harm, notes ecologist Andrea Holzschuh of the University of Würzburg in Germany. Finding evidence of that harm, though, is a challenge — the features that make some cliffs fun to climb, or not, also make for complicated research.

Holzschuh became interested in the effects that climbers are having on the environment in part because she is a climber herself, partial to tackling rocks in the Frankenjura region of Germany, which is noted for having some of the best climbing in Europe. The plants, animals and other species that make the cliffs their home, she notes, are often specialists that have found ways to adapt and even thrive in the extreme conditions found on the rock face. They may be rare or completely absent from nearby spots, and they often are slow-growing and their numbers grow only in spurts.

And then come the climbers, who may trample what grows at the bottom of a cliff, dig out whatever is growing in a crevice to gain a better handhold, spread species not native to the area or taint the rock face with chalk, altering pH or nutrient conditions for whatever is growing there. Rock climbing isn’t quite as impact-free as some might assume.

But scientists haven’t really been able to adequately assess that impact. Holzschuh went looking for research on this topic and found only 22 studies that tested how rock climbing might affect plants or animals. She tossed out six of those studies because they failed to make comparisons with unclimbed areas or had other major design problems that made it impossible to tease out effects. The remaining 16 studies found a variety of impacts on organisms ranging from lichens to snails to cedar trees. Holzschuh’s review appears in the December Biological Conservation.

But what the review really highlights is just how difficult it is to study rock climbing’s potential impacts. Holzschuh says a big challenge is in finding appropriate unclimbed cliff faces to compare to those that rock climbers frequent — ones that share traits such as slope and how much sunlight the face gets. “Often, all cliffs in a regions that are attractive for climbers are climbed and only cliffs that do not resemble the climbed cliffs in all abiotic traits remain unclimbed,” she notes. “Then no reliable study can be conducted.”

And then, of course, there’s the inaccessibility of many cliffs and the difficulty in studying even the accessible ones. “How many people have these skills and the flexibility to work on these projects?” says Michael Tessler of the American Museum of Natural History and Fordham University. Plus, he notes that a subset of rock climbing called bouldering — in which climbers tackle boulders or short cliff faces measuring less than 3.5 meters high, without using safety ropes — is especially popular with younger people. “Professors inherently aren’t always young,” he notes.
Tessler and colleague Theresa Clark of the University of Nevada, Las Vegas published the first ever analysis attempting to quantify the impact of bouldering on the environment. This type of climbing has similar potential for ecosystem damage as roped rock climbing, they note, plus a couple of additional ones: Boulderers often clear the ground below of rocks and logs so that they can place crash pads in case of falls, and they may be more likely to trample anything at the top of a boulder or cliff, rather than coming directly down.

Tessler and Clark tried to measure the impact of climbers at bouldering routes in the Shawangunk Ridge, a popular climbing site in New York where Tessler climbs. They compared transects in climbed boulder routes with transects along nearby unclimbed sections of rock and found differences in lichen, moss and woody plants. None of this added up to a major threat, but conservation managers might want to monitor these activities in remote sites and shut down certain routes that are proving too popular — and potentially too harmful to whatever is growing there, Tessler and Clark suggest in the December Biological Conservation.

While we still can’t really say how much impact climbers might be having on the rocky environments they climb, there is a definite need for more scientists to strap on their climbing shoes and tackle the questions of climbing’s impact. (Try it! It’s lots of fun!) But climbers, too, can do their part, Holzschuh and Tessler say.

“I think climbers can easily minimize their impact on the cliff vegetation if they do not willingly remove vegetation from the cliff to ‘clean’ hand- and footholds in the climbing route. Climbers should not access the cliff plateau [and should] leave this cliff part completely undisturbed,” Holzschuh says. “At the cliff base, bags and gear should be laid down within a small area to reduce the effects of trampling.”

Tessler also has advice. “Boulderers should be aware that even infrequent climbing leaves some impression on rock-associated vegetation,” he says. “They should remove as little vegetation and soil when climbing and establishing climbs. Also, if a climb is wet, dirty or covered in vegetation, maybe go to another one. This is an easy way to ensure that some rock faces can stay more natural.”

And if climbing is restricted because, say, rare birds are breeding there, rock climbers should obey the restriction and go climb somewhere else, Holzschuh says. There are plenty of other cliffs to be conquered.

New claim staked for metallic hydrogen

A team of scientists may have given hydrogen a squeeze strong enough to turn it into a metal. But critics vigorously dispute the claim.

Researchers from Harvard University report that under extremely high pressures hydrogen became reflective — one of the key properties of a metal. The feat required compressing hydrogen to 4.9 million times atmospheric pressure, the scientists report online January 26 in Science.

If correct, the result would be the culmination of a decades-long search for a material that could have unusual properties such as superconductivity — the ability to conduct electricity without resistance.
But physicist Eugene Gregoryanz of the University of Edinburgh, who works on similar experiments, decries the study’s publication as a failure of the journal’s review process. Given the evidence presented in the paper, Gregoryanz is skeptical that the claimed pressures were actually reached and notes that the researchers presented results from only one experiment. “How is it possible to do only one experiment and claim such a big thing?” he says.

Physicist Alexander Goncharov of the Carnegie Institution for Science in Washington, D.C., also takes issue with the researchers’ conclusions. “It’s not shown whether they have hydrogen at all at high pressure,” Goncharov says.

Not everyone is so skeptical. “I think there’s a good chance that it’s correct,” says theoretical physicist David Ceperley of the University of Illinois at Urbana-Champaign. The pressure at which the hydrogen became reflective is about where theoretical physicists have calculated that a metal should form, Ceperley says.

Theorists’ calculations also indicate that metallic hydrogen could be a high-temperature superconductor (SN: 8/20/16, p. 18). Most superconductors work only in extreme cold, but metallic hydrogen might function even at room temperature — higher than any other known superconductor. If so, its discovery would raise hopes that superconducting metallic hydrogen could be used in power lines, making transmission of electricity vastly more efficient.

To put the pressure on hydrogen, scientists capture it as a gas between the tips of two diamonds and squeeze them together. It’s no easy task. “The problem in making metallic hydrogen has been that the predicted pressures have been very high,” says physicist Isaac Silvera of Harvard University, a coauthor of the study. “Diamonds always break before you can obtain those pressures.”
To stave off breakage, the scientists smoothed the surface of the diamonds to remove any defects and covered the gems in a thin layer of aluminum oxide to prevent hydrogen from diffusing inside and creating cracks. The researchers also cooled the setup to temperatures of 83 kelvins (−190° Celsius) or below. As the scientists ratcheted up the pressure, the hydrogen first turned black, indicating a possible semiconducting phase, then became reflective, indicating a metal. The metallic hydrogen could be either a solid or a liquid, Silvera says.

But such experiments are tricky — only a few teams of researchers in the world are capable of performing them. One of the pitfalls can be that the hydrogen escapes from the chamber without the scientists realizing it. However, Silvera says, “We’re sure we have hydrogen in there.”

Some previous metallic hydrogen experiments have monitored hydrogen as the pressure is ramped up to help ensure that the hydrogen hasn’t escaped and to study its evolution. To do so, scientists use a technique called Raman spectroscopy, which involves shining a laser through the diamonds and observing the scattered light. But at pressures this high, lasers could cause the diamonds to break, Silvera says. So the researchers used lasers only after the sample had reached the metallic state.

Silvera’s group is not the first to announce the discovery of metallic hydrogen. Earlier claims of finding the metal have been overturned (SN: 12/17/11, p. 9). “It’s not the last word,” says Ceperley. “It should encourage all the other groups to come out and try to reproduce it.”

Pinhead-sized sea creature was a bag with a mouth

A roughly 540-million-year-old creature that may have once skimmed shorelines was a real oddball.

Dozens of peculiar, roundish fossils discovered in what is now South China represent the earliest known deuterostomes, a gigantic category of creatures that includes everything from humans to sea cucumbers.

No bigger than a pinhead, the fossils have wrinkly, baglike bodies and gaping mouths that are pleated around the edges like an accordion, researchers report January 30 in Nature. Unlike most other deuterostomes, the animals don’t seem to have an anus. Instead, the ancient oddities, named Saccorhytus coronarius, may have leaked waste (and other bodily fluids like mucus and sex cells) out of tiny holes lining their sides. These holes may have later evolved into gill slits.

A tough, flexible skin would have protected Saccorhytus as it wriggled through grains of dirt, the authors suggest. The find supports previous suggestions that the earliest deuterostomes were actually a kind of water-dwelling worm.

The animal guide to finding love

Are you feeling the pressure of Valentine’s Day and in need of advice on how to find someone special? The animal world has some advice for you.

Make sure you look nice.
There’s no need to go for an entire makeover, but looking your best is usually a good idea when on the search for a partner. Male black-and-white snub-nosed monkeys appear to have taken a lesson from Revlon — they go for the rouge-lipped look during the mating season. Those with bright, red lips tend to be surrounded by females.
Learn to dance …
As anyone who has ever watched John Travolta in Saturday Night Fever knows, having the right dance moves can make finding a mate easier. For some animals, it’s essential. That’s true for male peacock spiders, which raise colorful flaps on their behinds and wave them while lifting their third legs in an adorable dance aimed at luring a mate. And if a guy doesn’t have the best moves or try hard enough, females don’t just reject him — they get aggressive.

… and how to flirt.
Even if you’re an expert dancer, you’ll probably need to do at least a little flirting. It may be a bit more subtle than torrent frogs, though, who turn flirting into a big production. A male frog will get a female’s attention by first calling out and puffing up his vocal sacs. Then he’ll shake his hands and feet and wiggle his toes. If he’s successful, the female will let him know with a special call.

Attend a party.
The best place to put all of this on display is, of course, a party! And there are parties everywhere, even at the bottom of the ocean. Scientists exploring a seamount off the Pacific coast of Panama in 2015 found an enormous party of small, red crabs swarming all over each other. Such large aggregations are common among crab species and may be linked to reproduction.

Practice, practice, practice.
Once you’ve landed a partner, you might want to serenade him or her with the perfect love song. But first you’ll need to practice, just like great reed warblers (probably) do. Males spend their entire winter vacation singing the songs they seem to use to woo the ladies come spring. All that singing cuts into time the guys could spend foraging for food or resting, but that practice might pay off because female warblers prefer males that sing more complex tunes.

Keep an eye on the competition.
You may not be the only one interested in your partner, so make like a peacock and check out your competition. Peacocks fan out their feathers to lure the ladies, but females only pay attention to what’s happening at the bottom of the show, studies have revealed. Males do likewise, keeping their gaze tuned to the bottom of the competition’s display.

Bring a gift.
You probably don’t need to worry that your partner will go cannibal, but that doesn’t mean you can’t take a hint from a species where that does happen. When approaching a female, male nursery spiders are smart to bring a gift of a big dead insect wrapped up in silk. The gift will not only keep the female busy while the male mates with her, but it can also double as a shield if she sees him as a potential meal rather than a mate.

Rare triplet of high-energy neutrinos detected from an unknown source

Three high-energy neutrinos have been spotted traveling in tandem.

The IceCube Neutrino Observatory in Antarctica detected the trio of lilliputian particles on February 17, 2016. This is the first time the experiment has seen a triplet of neutrinos that all seemed to come from the same place in the sky and within 100 seconds of one another. Researchers report the find February 20 on arXiv.org.

Physicists still don’t know where high-energy neutrinos are born. The three neutrinos’ proximity in time and space suggests the particles came from the same source, such as a flaring galaxy or an exploding star. But the scientists couldn’t rule out the possibility of a fluke — the triplet could simply have been the result of accidental alignment between unassociated neutrinos.

Eight different telescopes followed up on the neutrino triplet, checking for some sign of the particles’ origins. The telescopes, which searched for gamma rays, X-rays and other wavelengths of light, found nothing clearly associated with the particles. But scientists were able to rule out some possible explanations, like a nearby stellar explosion caused by the collapse of a dying star.