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We’ve stepped into a new year, which for many people means new resolutions. And this story was supposed to tackle a big one: the best exercise people can do to be healthy.

There’s just one small problem. “There’s simply no such thing as ‘best exercise,’” says Emmanuel Stamatakis, a physical activity epidemiologist at the University of Sydney. If you see a headline like that, he says, it’s probably clickbait.

What scientists do know — from piles of studies spanning 70 years — is that regular physical activity pays off in long-term health benefits. And recent work is starting to paint a clearer picture of all the activities that can help. You don’t have to body build like Arnold Schwarzenegger or crush marathons like Tigst Assefa. And not everyone has the time, money or ability to join a gym or use special equipment. But you don’t need to, Stamatakis says. Biking to the grocery store, raking leaves, playing soccer with your kids — it all counts.

Scientists still have much to figure out, like how physical activity’s benefits cascade through the body and how to empower people to add movement to their daily lives. But at least one conclusion seems clear, says I-Min Lee, an epidemiologist at Harvard Medical School and Brigham and Women’s Hospital in Boston. “Any physical activity is better than none.”

For Lee, it comes down to finding something you enjoy. That can make the difference between getting off the couch or staying put. “The best physical activity,” she says, “is something that you will do and stick with.”

Physical activity can extend your life and offer a slew of other health benefits

The idea that physical activity is good for you might seem eye-rollingly obvious and peskily pervasive. Fitness influencers post workouts on social media, news reports tout exercise’s benefits and governments worldwide try to get citizens moving.

Still, the United States’ current physical activity guidelines, published in 2018, reported that some 80 percent of adults aren’t doing enough. Adults need at least 150 minutes of moderate physical activity or 75 minutes of vigorous activity per week, plus muscle-strengthening activities at least two days per week, the guidelines suggest. (How long should these muscle-strengthening sessions last? “We don’t really know,” Lee says.)

But scientists are learning that even a little physical activity can be helpful, Lee says. Most of the studies underpinning the 2018 recommendations relied on self-reported data, Lee and colleagues wrote in a JAMA opinion piece in October. People tend to remember exercises like running or swimming laps, Lee says. But the myriad movements we take in a typical day — movements that scientists now know can improve health — were difficult to document via self-reports.

Today, wearable technology has yanked those missing movements out of obscurity and into the spotlight. Outfitting participants with tracking devices lets scientists collect mountains of in-depth data throughout a person’s day, such as step count, acceleration and heart rate. That’s helping reveal all the things that physical activity (or the lack of it) can do for people’s health.

In the last year, scientists have shown people who did more physical activity were less likely to be hospitalized for common conditions like gallbladder disease, diabetes and urinary tract infections. These data add to recent survey-based studies and clinical trials linking exercise with lower risk of death due to flu and pneumonia, improvements in memory and attention, and better outcomes after a COVID-19 infection.

“Study after study has demonstrated the benefit of physical activity,” says Bryant Webber, a preventative medicine physician at the U.S. Air Force Academy in Colorado Springs, Colo. His team has shown that it’s never too late to start. In a study of more than 100,000 people age 65 and older, both aerobic training and muscle strengthening seemed to lower the risk of dying over the next eight years. Even people older than 85 saw benefits, says Webber, who did the work while at the U.S. Centers for Disease Control and Prevention. “We were impressed.” 

Some people may be getting the benefits of physical activity without realizing it. Stamatakis’ team in Australia studies incidental activity: the typical, routine movements people perform in their daily lives. His team analyzed data from people who don’t exercise in their free time but had worn tracking devices for a week. Just a minute or two of intense activity — like taking the stairs or dashing to catch a train — a few times per day reduced the risk of dying in the following seven or so years by about 40 percent, Stamatakis and colleagues reported in 2022 (SN: 12/8/22). The more activity, the better, he says. And last year, his team linked just three and a half minutes of daily vigorous activity with a roughly 18 percent reduction in cancer risk.

Walk uphill, carry a heavy grocery basket, “get a little bit out of breath,” Stamatakis says. Any burst of exertion that briefly boosts your heart rate a few times per day could have long term health benefits, he says. That’s something many people don’t understand. In interviews with middle-aged people, Stamatakis has heard a common misconception. “The majority of them still think that you need to go to the gym, otherwise there’s no point.”

Don’t get him wrong, Stamatakis isn’t saying people should skip the gym. “I want to make it absolutely clear that exercise is a fantastic option,” he says. But for people who can’t afford a gym membership or aren’t able or willing to exercise in traditional ways, short bursts of vigorous activities several times per day could be good, too.

Scientists still have questions about exercise, but they know even a little bit helps

At Harvard, Lee has worked to dispel another popular misconception: that people need to take 10,000 steps every day to stay healthy.

She started looking into the idea in 2018, when her hospital launched a campaign to get employees to walk more. Because Lee studies physical activity, her administrators asked her to form a team. It was mostly middle-aged and older folks, she says. “For some of these people, if you’re asking them to do 10,000 steps — I mean, no way,” she says. “Even doing 5,000 steps is a stretch.”

In 2019, Lee’s team found that older women who took around 8,500 steps per day were 66 percent less likely to die during the study than those who took roughly 2,500 steps per day. In a 2022 analysis, Lee and her colleagues reported something similar in men and women of different ages. Bottom line: For mortality benefits, people age 60 or older should shoot for 7,000 steps a day, and people younger should shoot for 9,000, she says.

But those targets shouldn’t be discouraging, she says. Lee takes a tiered approach. “If you do nothing, just do a little bit,” she says. “If you already do a little bit, do a little bit more.”

She follows that advice herself. Lee grew up in the tropics in Malaysia, where it was hot, and she didn’t see many people exercising, including herself. “I did diddly-squat,” she laughs. That changed after she came to the United States for her doctorate. “It got to be so embarrassing to do physical activity research without being physically active,” she says. So she started running. “I run slowly, and I don’t run a lot, but I do it,” she says.

Stepping up

As people take more steps per day, the relative risk of dying over the next seven years drops sharply (below the horizontal line represents lower risk). This decrease slows around 7,000 steps for people age 60 or older (blue) and around 9,000 steps for those under 60 (red).

Relative mortality risk by age and steps taken per day

The message that people can reap health benefits from even a little bit of physical activity is seeping into the mainstream, says Lyndon Joseph, an exercise physiologist at the National Institute on Aging in Bethesda, Md. “You don’t have to be able to sprint like Usain Bolt,” he says. “You just need to be active.”

Scientists know physical activity works, Joseph says, though they don’t fully understand how. Why does walking, for example, which relies on leg muscles, also help the heart, lungs, kidneys and immune system? “The whole body responds to exercise,” Joseph says. Scientists are trying to figure out the molecules at play, and how those released from one tissue can improve the health of another. “That is the big question.”

How to get people to move — and do it consistently — is another big question. Changing people’s behavior is no easy feat, Stamatakis says. And massive structural barriers often stand in the way. Even if scientists get people on board with upping their step counts, if their neighborhoods don’t have sidewalks, hitting daily step goals becomes a lot more difficult.

More sidewalks, trails and bike paths would make it easier for people to rack up incidental physical activity. “The role of the environment is critical,” Stamatakis says. Lee agrees. Physical activity is not simply a personal choice, she says. Government policies can influence how much or little we’re able to do. Again, she emphasizes, it doesn’t take much to get substantial health benefits (SN: 11/5/19). And people can start at any level.

In fact, Lee says, “the biggest bang for your buck actually comes among people who go from doing nothing to doing just a little bit.”

From the pristine dark of his backyard in rural Alberta, Canada, Alan Dyer has taken stunning photos of a rare sky glow called STEVE. To capture this ribbon of mauve, he and other citizen scientists typically let their cameras collect light for seconds at a time. Long exposures smear out STEVE’s finer details in favor of making its color pop. But when a STEVE stretched over his house one August night in 2022, Dyer tried a different approach.

He zoomed in on the sky glow with his camera and took a video of STEVE’s nitty-gritty details at a rate of 24 snapshots per second. Instead of the largely smooth drift of purple seen in past images, Dyer’s footage exposed STEVE as a frenetically flickering torrent of purplish-white fuzz.

“It didn’t look that beautiful,” Dyer says, but on the off chance it might be scientifically useful, he sent the video to Toshi Nishimura, a space physicist at Boston University. 

“I said, ‘Oh my God, no one has ever seen this before,’” says Nishimura, who was eager to analyze such a high-resolution view of STEVE. But upon inspection, STEVE’s fine details didn’t jibe with scientists’ tentative understanding of the atmospheric chemistry behind the airglow. “This fine-scale structure gave us a huge headache, actually,” Nishimura says.

That confusion is par for the course when it comes to the science of STEVE — short for Strong Thermal Emission Velocity Enhancement. Ever since citizen scientists first showed researchers their images of STEVE a few years ago, they’ve raised more questions than they answered.

“Every time we find something new [about STEVE], the number of physics questions that it opens up is triple what we expected,” says Bea Gallardo-Lacourt, a space physicist at NASA’s Goddard Space Flight Center in Greenbelt, Md.

At a meeting of the American Geophysical Union in San Francisco, on December 14, Nishimura’s team presented the new high-res view of STEVE. Other researchers described similarly perplexing observations that another non-aurora sky glow can morph into STEVE. But there was a glimmer of clarity too: a computer model shared by still other sky detectives may explain what causes the “picket fence” of green stripes that sometimes appears below STEVE.

“STEVE and the picket fence are arguably the biggest mystery in space physics right now,” says space physicist Claire Gasque of the University of California, Berkeley. And because satellite signals can be affected by the conditions in Earth’s atmosphere where STEVE appears, explaining this airglow could have uses beyond understanding a pretty light show.  

STEVE’s mysteries are multiplying

When aurora chasers in Canada first introduced STEVE to the scientific community in 2016, researchers knew it was no aurora (SN: 3/15/18). Auroras form when charged particles from the magnetic bubble, or magnetosphere, around Earth rain down into the atmosphere (SN: 2/7/20). Those particles crash into oxygen and nitrogen near Earth’s poles, painting the sky with brushes of red, green and blue. But STEVE was purple. And it appeared closer to the equator than the northern and southern lights do.

“For us here in southern western Canada,” Dyer says, “the aurora is typically to the north.” STEVE, meanwhile, can come right overhead.

STEVE was later linked to a river of charged particles surging through the atmosphere (SN: 4/30/19). That plasma stream, moving at several kilometers per second, is thought to energize the air around 200 kilometers off the ground to the point of glowing purple — but what molecules give STEVE its signature color remain unclear, especially in light of Dyer’s new footage.

Dyer’s video captured details of STEVE down to about 90 meters across — fairly small for an airglow that can span thousands of kilometers. The footage showed a clumpy, speckled stream of purple rushing westward at about 9 kilometers per second, sporting variations in brightness as small as a few kilometers across, some of which popped in and out of view within seconds, Nishimura and colleagues reported in the December JGR Space Physics. 

“The leading theory of the STEVE emission is that there’s nitric oxide that is excited by the fast plasma stream,” Nishimura says. That nitric oxide is thought to give off the purple light. But excited nitric oxide can glow for an hour, Nishimura notes. That’s about how long STEVE lasts overall; the granular bursts of brightness that last mere seconds add a wrinkle to that idea.

Firing a sensor-strapped rocket through STEVE could identify the molecules responsible, Nishimura says. “But the challenge is that we need to know when and where STEVE is going to happen, and that’s extremely difficult.”

STEVE can appear just after the peaks of substorms, which are disturbances in the magnetosphere that can stir up spectacular auroras. “STEVE generally appears after the main aurora show has kind of faded,” Dyer says. But not every substorm comes with a STEVE encore, and research presented by Gallardo-Lacourt and her colleagues at AGU suggests not all STEVEs need a substorm to appear.

One thing that might help researchers refine their STEVE predictions, Nishimura says, is better understanding the light show’s relationship to another non-auroral airglow called a stable auroral red (SAR) arc — which citizen science photos now suggest can morph into STEVE.

How STEVE and SAR arcs interact

In March 2015, citizen scientist Ian Griffin set out to photograph a particularly dazzling auroral display near Dunedin, New Zealand. But just north of the southern lights, he spotted something strange — a wide, red sky glow that morphed into the mauve strand of STEVE. Griffin’s footage offered researchers their first glimpse of a STEVE blooming out of a SAR arc. Space physicist Carlos Martinis of Boston University and colleagues reported it in June 2022 in Geophysical Research Letters.

Scientists have studied SAR arcs for decades. Like STEVE, these airglows stretch east-to-west across the sky closer to the equator than the northern and southern lights. But unlike STEVE’s roughly hour-long set, SAR arcs can stain the sky for hours to days at a time — visible with cameras, though usually too dim to see with the naked eye.

SAR arcs form when disturbances in Earth’s magnetosphere cause charged particles thousands of kilometers out in space to collide, creating heat that seeps down into the ionosphere — the layer of the atmosphere home to STEVE. That heat energizes electrons to excite oxygen atoms to shed red light that’s normally about one-tenth as bright as auroras. But the SAR arc that Griffin saw was radiant enough to rival red southern lights.

“It was just stunning,” says Megan Gillies, who studies auroras at the University of Calgary in Canada. Griffin’s footage inspired her to search for other cases of STEVE emerging from SAR arcs. Her team found one spotted by the Transition Region Explorer, or TREx, Spectrograph at Lucky Lake, Saskatchewan in April 2022. The group reported it in Geophysical Research Letters in March. STEVE’s bright purple streak emerged from a SAR arc’s red glow, hung around for about half an hour, then gave way to more red.

“It’s like watching a fire smoldering, and then you throw more wood on it and then it blazes up … Whoosh, there it goes! And then it kind of dies back down,” says Gillies, whose group described the SAR arc–STEVE connection at the AGU meeting. “There’s something that happens that triggers a STEVE,” she says, but because not all SAR arcs mutate into STEVEs, it’s not clear what causes this transition.

It might have something to do with the plasma torrent that powers STEVE. SAR arcs have similarly been linked to westward plasma flows in the atmosphere — though not as fast as the plasma flows that power STEVEs, Martinis notes. As the SAR arc seen in 2015 evolved into STEVE, satellite data did show a wide stream of plasma in the atmosphere narrow and quicken into the kind of intense filament typical of STEVE. But what triggered this switch remains an open question, Martinis says. Further complicating matters: citizen scientists have also spotted STEVEs and SAR arcs existing alongside but seemingly independent of each other.

With researchers left scratching their heads over these observations, “this is where modeling comes in,” Gillies says. Theorists can use computers to test whether the physics they think is happening produces light patterns resembling STEVE, she explains. Computer models are already helping piece together another STEVE-related puzzle: the source of the picket fence.

The picket fence may be built right in Earth’s backyard

At first, researchers thought STEVE’s sometimes sidekick of green stripes was a plain old aurora. After all, the picket fence’s bright green glow is a similar hue as some normal northern lights. But the specific wavelengths of light emanating from the picket fence hint that it might not be an aurora, after all (SN: 11/12/20).

Showers of charged particles from way out in the magnetosphere light up normal auroras. “When they collide with the atmosphere, they’re going to create a pretty wide spectrum of colors,” Gasque says. That includes green from oxygen and red and blue from nitrogen. “That blue is kind of the smoking gun that we didn’t see with the picket fence,” Gasque says. Its absence hints that the picket fence’s green spires don’t arise from the same process as auroras.

An alternative explanation for the picket fence might be electric fields embedded within Earth’s atmosphere that run parallel to the planet’s magnetic field, Gasque says. Those fields could energize local electrons to excite oxygen into glowing green and coax nitrogen to give off a bit of red but not blue. Gasque and colleagues ran a computer model of Earth’s atmosphere with electrons energized by electric fields. The team compared the light produced inside their simulated atmosphere with light from a picket fence seen by the TREx Spectrograph at Lucky Lake in April 2018.

The model did indeed reproduce the ratio of red to green light seen in the real-life picket fence without a tinge of blue — bolstering the idea that atmospheric electric fields could construct the picket fence, the researchers reported November 16 in Geophysical Research Letters and at the AGU meeting. But scientists need to confirm that such electric fields actually exist at the altitudes where picket fences appear. 

“The plan now is to try and fly a rocket through one of these structures,” says Gallardo-Lacourt. Gasque and her colleagues have just proposed such a mission to NASA. The rocket wouldn’t fly through the picket fence — which, like STEVE, is too hard to predict. Instead, it would target phenomena with similar coloring that are far more common: enhanced auroras.

“With enhanced aurorae, you have kind of these sharp, bright layers within the aurora,” Gasque says. The sharpness of those variations in auroral light and their picket fence–like color scheme hints that they might be powered by electric fields as well. If a future rocket mission detects electric fields threaded through enhanced auroras, that would help confirm that similar fields build the picket fence.

NASA’s Geospace Dynamics Constellation mission will also launch a fleet of spacecraft as early as 2027 to probe Earth’s magnetosphere and ionosphere — which might yield more data that help explain aspects of STEVE, Gallardo-Lacourt notes. In the meantime, STEVE’s dedicated paparazzi of citizen scientists will continue snapping photos of the phenomenon from the ground.

“We’re out specifically looking for STEVE and knowing that there’s scientific interest in it,” Dyer says. “Prior to the era of STEVE … you might have thought, well, there’s nothing amateurs can contribute now to aurora research, it’s all done with rockets and satellites and the like. But nope! There’s a lot we can contribute” — even if those contributions are often new puzzles for scientists to solve.

From birds repurposing antiavian architecture to jellyfish that can learn, here are dispatches from the animal kingdom that we went wild for in 2023.

Intelligent jellies

No brain? No problem. The fingernail-sized Caribbean box jellyfish (Tripedalia cystophora) uses its clusters of eyes and nerve cells to learn to avoid bumping into things, experiments in an aquatic obstacle course suggest (SN: 9/22/23). In the box jelly’s natural habitat, where the creature must swerve to dodge mangrove roots in murky water, it pays to be a good pupil.

Prehistoric pout

Tyrannosaurus rex’s menacing grin may have been less toothy than previously thought. Artistic renderings commonly depict the ravenous reptile as lipless, constantly baring its pearly whites. But T. rex may actually have had a pout that kept rows of pointy teeth covered, similar to Komodo dragons, an analysis of the skulls and teeth of dinosaurs and modern reptile suggests (SN: 4/22/23, p. 6).

Revenge of the birds

City life can be hostile for birds. Municipalities across the world have put up spikes to prevent birds from roosting — and pooping — on streetlights, buildings and other structures. But some Eurasian magpies (Pica pica) and carrion crows (Corvus corone) in parts of Europe found a way to stick it to humans. The birds rip up antibird spikes and build nests with them (SN: 9/9/23, p. 4). Magpies may even use the spikes as humans do, to ward off avian pests.

Swashbuckling spiders

Pirates on the high seas would be proud of their landlubbing arachnid counterparts. A species of cannibalistic pirate spider in Costa Rica tricks prey into walking the plank, right into its clutches (SN: 10/7/23 & 10/21/23, p. 11). Gelanor siquirres casts a silk thread to intercept that of an unsuspecting orb weaver trying to build a web. When the eight-legged victim scuttles across its own silk thread to secure the other end, the orb weaver finds impending doom rather than harmless vegetation.

Desperate flies, desperate measures

Snow flies (Chinoea spp.) have a macabre method to survive the frigid mountains and forests they call home. Dozens of flies that researchers subjected to below-zero temperatures self-amputated their limbs, but only when the limbs began to freeze (SN: 7/15/23, p. 14). The flies probably shed the appendages to keep ice crystals from reaching the rest of the body.

Self-aware fish

When it comes to brainpower, this fish is no small fry. Not only can the bluestreak cleaner wrasse (Labroides dimidiatus) recognize itself in a mirror, the fish can also identify a picture of itself out of a lineup (SN: 3/11/23, p. 13). The finding suggests the wrasse forms a mental image of itself — similar to what humans do — and that self-awareness may be more common in the animal kingdom than once thought.

Tight-gilled sharks

Regulating body temperature in chilly water is a challenge even for scalloped hammerhead sharks (Sphyrna lewini). To stay warm while hunting in the deep ocean, the sharks use a method normally seen in diving mammals: They hold their breath (SN: 6/17/23, p. 10). Keeping gills closed holds in body heat, preventing the predators from becoming fish ice pops.

Big-mouthed snake

This African egg-eating snake redefines what it means to open wide. The Gans’ egg-eater (Dasypeltis gansi) can open its mouth wider than any other snake relative to its size, lab experiments suggest (SN: 10/7/23 & 10/21/23, p. 36). An egg-eater with a 1-centimeter-wide head could fit a cylinder 5 centimeters across in its mouth. The reptile edges out the previous record holder: the Burmese python (Python molurus bivittatus).

Disaster dogs

The irradiated zone around Ukraine’s Chernobyl Nuclear Power Plant might be off-limits for humans, but other animals didn’t get the memo. Packs of feral dogs that for years have roamed the area abandoned since 1986 are genetically distinct from canines of similar breeds that live outside the zone (SN: 4/8/23, p. 15). The differences probably aren’t due to radiation, researchers say. Whether Chernobyl’s radioactivity has had any effect on the dogs remains to be seen, but knowing their genetic makeup will help scientists spot potential radiation damage.

Landscaping ants

Many ants are expert navigators who use local landmarks to find their way around. But what’s an ant to do when the world around them is almost completely flat and featureless? Desert ants (Cataglyphis fortis) in Tunisia’s salt pans take matters into their own mandibles. Workers build tall mounds over their colonies’ nests so wayward foragers can find their way home (SN: 7/1/23, p. 16).

Science occasionally gives us clearer views of the distant past. This year, researchers opened windows into the life and times of ancient Romans, impressionist painters and other towering historical figures.

Huygens’ hazy telescopes

Christiaan Huygens, the 17th-century Dutch astronomer best known for his studies of Saturn’s moons and rings, may have needed glasses. That would explain why the telescopes he designed weren’t as sharp as those of his peers, a researcher argues (SN: 4/22/23, p. 5). A closer look at Huygens’ telescope lenses suggests the scientist was nearsighted. The lenses probably overmagnified his view of the cosmos, making distant objects appear clear to him but fuzzy to others.

Vintage essence

What did the ancient Romans smell like? Chemical analyses of a 2,000-year-old perfume bottle from an elite woman’s grave suggest a familiar earthy scent: patchouli (SN: 7/1/23, p. 14). Patchouli oil permeates modern fragrances, but its use in ancient Rome had been unknown. Perfume extracts that are this old typically dissipate and become lost to history. But the quartz flask was found intact with a bitumen seal that adsorbed some of the perfume molecules, preserving them for millennia.

Forgery fighter

Infrared and X-ray scans of more than 600 paper bills made by Benjamin Franklin’s prolific printing press revealed colorful threads and shiny mineral residues (SN: 8/26/23, p. 5). The additives, used to stymie counterfeiters and boost the bills’ durability, helped set the standard for paper currency in colonial America, researchers say.

Decoding Beethoven’s coda

Ludwig van Beethoven’s DNA supports what many historians have suspected: The composer likely died of liver failure (SN: 4/22/23, p. 16). Until now, the theory largely rested on reports that Beethoven had been drinking a lot of alcohol shortly before his death in 1827. While reconstructing Beethoven’s genome from samples of his hair, researchers discovered he also had a genetic risk for liver disease. The composer also suffered from a hepatitis B infection, the team determined, further compounding his susceptibility to liver damage.

Shrouded in smoke

The Industrial Revolution may have shaped impressionist art — literally. An analysis of more than 100 paintings by artists such as Claude Monet and Joseph Mallord William Turner found that changes in contrast, color and visibility track over time with rising air pollution in London and Paris (SN: 3/25/23, p. 4). Particles in smog absorb and scatter light, reducing contrast and making colors whiter. As air pollution worsened throughout the 19th century, impressionist paintings grew paler and hazier just as artists’ views of their subjects did.

WASHINGTON — Tiny, sinking flakes of detritus in the ocean fall more slowly thanks to the goop that surrounds each flake, new observations reveal.

The invisible mucus makes “comet tails” that surround each flake, physicist Rahul Chajwa of Stanford University reported November 19 at the American Physical Society’s Division of Fluid Dynamics meeting. Those mucus tails slow the speed at which the flakes fall. That could affect the rate at which carbon gets sequestered deep in the oceans, making the physics of this sticky goo important for understanding Earth’s climate.

Although scientists knew the goo was a component of the “marine snow” that falls in the ocean, they hadn’t previously measured its impact on sinking speed.

Marine snow is made of dead and living phytoplankton, decaying organic matter, feces, bacteria and other aquatic sundries, all wrapped up in mucus that’s produced by the organisms. Like the gunk known for clogging airways during respiratory virus season, the mucus is what’s called a viscoelastic fluid (SN: 3/17/16). That’s something that flows like a liquid but exhibits elastic behavior as well, springing back after being stretched.

This underwater blizzard is not easy to study. When observed in the ocean, the particles sink swiftly out of view. In the laboratory, the particles can be viewed for longer periods, but the trek ashore degrades the delicate marine snow and kills the living organisms within it.

So Chajwa and colleagues built a physics lab at sea. Aboard a research vessel in the Gulf of Maine, the team collected marine snow particles in traps 80 meters below the water’s surface. Then they loaded their catch into a device onboard, designed to observe the particles falling.

Nicknamed “the gravity machine,” it’s a fluid-filled wheel that rotates in order to keep an individual flake in view of a camera. It’s a bit like a hamster wheel for falling debris. As the flake sinks, the wheel turns so as to move the snow in the opposite direction, allowing the snowfall to be observed indefinitely. The gravity machine was itself mounted on a gimbal designed to stave off sloshing from the rocking of the ship.

“It’s a very nice compromise between the real marine snow that you get in the ocean versus what you can do practically in the lab,” says biophysicist Anupam Sengupta of the University of Luxembourg, who was not involved with the research.

To observe how the fluid flowed around the particles, the researchers added tiny beads within the fluid in the gravity machine. That revealed the rate of fluid flow around the particles. The speed of fluid flow was slowed in a comet tail–shaped region around the particle, revealing the invisible mucus that sinks along with the particle.

The particles sank at speeds up to 200 meters per day. The mucus played a big role in sinking speed. “The more the mucus, the slower the particles sink,” Chajwa says. On average, the mucus causes the marine snow particles to linger twice as long in the upper 100 meters of the ocean as they otherwise would, Chajwa and colleagues determined.

If it falls deep enough, marine snow can sequester carbon away from the atmosphere. That’s because living phytoplankton, like plants, take in carbon dioxide and release oxygen. When phytoplankton form marine snow, they take that carbon along with them as they sink. If a flake reaches the ocean floor, it can settle into a scum at the bottom that caches that carbon over long time periods. The faster the particles sink, the more likely they are to make it to the abyss before being eaten by critters (SN: 6/23/22).

Knowing how fast the particles sink is important for calculating the ocean’s impact on Earth’s climate, and how that might change as the climate warms, the researchers say. The oceans are major players in the planet’s carbon cycle (SN: 12/2/21), and scientists estimate that oceans have taken up roughly 30 percent of the carbon dioxide released by humans since industrialization. Chajwa and colleagues hope that their results can be used to refine climate models, which currently do not take the mucus into account.

So this mucus is nothing to sneeze at. “We’re talking about microscopic physics,” says Stanford physicist Manu Prakash, a coauthor of the work, which is also reported in a paper submitted October 3 at arXiv.org. “But multiply that by the volume of the ocean … that’s what gives you the scale of the problem.”