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Vinita Surukan knew the mosquitoes were trouble. They attacked her in swarms, biting through her clothes as she worked to collect rubber tree sap near her village in Sabah, the northern state of Malaysia. The 30-year-old woman described the situation as nearly unbearable. But she needed the job.

There were few alternatives in her village surrounded by fragments of forest reserves and larger swaths of farms, oil palm plantations and rubber tree estates. So she endured until a week of high fever and vomiting forced her to stop.
The night of July 23, Surukan was trying to sleep off her fever when the clinic she visited earlier in the day called with results: Her blood was teeming with malaria parasites, about a million in each drop. Her family rushed her to the town hospital where she received intravenous antimalarial drugs before being transferred to a city hospital equipped to treat severe malaria. The drugs cleared most of the parasites, and the lucky woman was smiling by morning.

Malaria has terrorized humans for millennia, its fevers carved into our earliest writing on ancient Sumerian clay tablets from Mesopotamia. In 2016, four species of human malaria parasites, which are spread by mosquito from person to person, infected more than 210 million people worldwide, killing almost 450,000. The deadliest species, Plasmodium falciparum, causes most of the infections.

But Surukan’s malaria was different. Hers was not a human malaria parasite. She had P. knowlesi, which infects several monkey species. The same parasite had recently infected two other people in Surukan’s village — a man who hunts in the forest and a teenager. Surukan suspects that her parasites came from the monkeys that live in the forest bordering the rubber tree estate where she worked. Some villagers quit working there after hearing of Surukan’s illness.

Monkey malaria, discovered in the early 1900s, became a public health concern only in the last 15 years. Before that, scientists thought it was extremely rare for monkey malaria parasites, of which there are at least 30 species, to infect humans.
Yet since 2008, Malaysia has reported more than 15,000 cases of P. knowlesi infection and about 50 deaths. Infections in 2017 alone hit 3,600.
People infected with monkey malaria are found across Southeast Asia near forests with wild monkeys. In 2017, another species of monkey malaria parasite, P. cynomolgi, was found in five Malaysians and 13 Cambodians. And by 2018, at least 19 travelers to the region, mostly Europeans, had brought monkey malaria back to their home countries.

The rise of monkey malaria in Malaysia is closely tied to rapid deforestation, says Kimberly Fornace, an epidemiologist at the London School of Hygiene and Tropical Medicine. After testing blood samples of nearly 2,000 people from areas in Sabah with various levels of deforestation, she found that people staying or working near cut forests were more likely than people living away from forests to have P. knowlesi infections, she and colleagues reported in June in PLOS Neglected Tropical Diseases. Stepping over felled trees, humans move closer to the monkeys and the parasite-carrying mosquitoes that thrive in cleared forests.
It’s out there
There’s no feasible way to treat wild monkeys for an infection that they show no signs of. “That’s the problem with P. knowlesi,” says Singapore-based infectious disease specialist Fe Espino, a director of the Asia Pacific Malaria Elimination Network.

In 2015, the World Health Organization set a goal for 2030: to stop malaria transmission in at least 35 of the 91 malaria-endemic countries. WHO targets the four human malaria parasites: P. falciparum, P. vivax, P. malariae and P. ovale. Monkey malaria is excluded from the campaign because the agency regards it as an animal disease that has not been shown to transmit among humans.

But as countries reduce human malaria, they will eventually have to deal with monkey malaria, Espino says, echoing an opinion widely shared by monkey malaria scientists.

“Something nasty” could emerge from the pool of malaria parasites in monkeys, says malariologist Richard Culleton of Nagasaki University in Japan. Culleton studies the genetics of human and monkey malaria. Malaria parasites can mutate quickly — possibly into new types that can more easily infect humans (SN: 9/6/14, p. 9). To Culleton, the monkey malaria reservoir “is like a black box. Things come flying out of it occasionally and you don’t know what’s coming next.”
Malaysia is very close to reaching the WHO target of human malaria elimination. In 2017, only 85 people there were infected with human malaria. But that success feels hollow as monkey malaria gains a foothold. And while monkey malaria has swelled into a public health threat only in Malaysia, the same could happen in other parts of Southeast Asia and beyond. Even in southeastern Brazil, where human malaria was eliminated 50 years ago, the P. simium malaria parasite that resides in howler monkeys caused outbreaks in humans in 2015 and 2016.

From tool to threat
In the late 1800s, scientists discovered the Plasmodium parasite and its Anopheles mosquito carriers. Humans retaliated by draining marshes to stop mosquito breeding and spraying insecticides over whole communities. Governments and militaries pursued antimalarial drugs as the disease claimed countless soldiers during the two World Wars.

Scientists soon found malaria parasites in birds, rodents, apes and monkeys. To the researchers, the parasites found in monkeys were a tool for testing antimalarial drugs, not a threat. An accident, however, showed otherwise.
In 1960, biologist Don Eyles had been studying the monkey malaria P. cynomolgi at a National Institutes of Health lab in Memphis, Tenn., when he fell ill with malarial fevers. He had been infected with the parasites found in his research monkeys. His team quickly confirmed that the malaria parasites in his monkeys could be carried by mosquitoes to humans. Suddenly, monkey malaria was not just a tool; it was an animal disease that could naturally infect humans.
The news shook WHO, McWilson Warren said in a 2005 interview recorded by the Office of NIH History. Warren, a parasitologist, had been Eyles’ colleague. Five years before Eyles became infected, WHO had launched the Global Malaria Eradication Programme. Banking on insecticides and antimalarial drugs, the agency had aimed to end all malaria transmissions outside of Africa. A monkey malaria that easily infects humans would sink the program because there would be no way to treat all the monkeys.

A team of American scientists, including Eyles and Warren, traveled to Malaysia — then the Federation of Malaya — where the P. cynomolgi parasites that infected Eyles came from. Funded by NIH, the scientists worked with colleagues from the Institute of Medical Research in Kuala Lumpur, established in 1900 by the British to study tropical diseases.

From 1961 to 1965, the researchers discovered five new species of monkey malaria parasites and about two dozen mosquito species that carry the parasites. But the researchers did not find any human infections. Then, in 1965, an American surveyor became infected with P. knowlesi after spending several nights camping on a hill about 160 kilometers inland from Kuala Lumpur.

Warren surveyed the forested area where the infected American had camped. The hill sat beside a meandering river. Monkeys and gibbons, a type of ape, lived on the hill and in adjacent forests. The closest house was about two kilometers away. Warren sampled the blood of four monkeys and more than 1,100 villagers around the hill; he collected mosquitoes too.

He found P. knowlesi parasites in the monkeys, but none among the villagers. Only one mosquito species, A. maculatus, appeared capable of transmitting malaria between monkeys and humans, but Warren deemed its numbers too low to matter. He concluded that monkey malaria stayed in the forests and rarely ever spilled into humans.

With those results, NIH ended the monkey malaria project, Warren said, and the Institute of Medical Research in Kuala Lumpur returned to its primary focus: human malaria, dengue and other mosquito-borne diseases. Monkey malaria was struck off the list of public health concerns.

Wake-up call
P. knowlesi landed back in the spotlight in 2004, with a report in the Lancet by malariologist Balbir Singh and his team. The group had found 120 people infected over two years in southern Malaysian Borneo. The patients were mostly indigenous people who lived near forests. Clinicians initially had checked the patients’ blood samples under microscopes — the standard test — and diagnosed the parasites as human malaria. But when Singh, of Universiti Malaysia Sarawak, applied molecular tools that identify parasite species by their DNA, he revealed that all the samples were P. knowlesi. Monkey malaria was breaking out of the diminishing forests.

By 2018, P. knowlesi had infected humans in all Southeast Asian countries except for East Timor. Singapore, declared malaria free in 1982, reported that six soldiers were infected with P. knowlesi from wild monkeys in a forest reserve. The parasite also turned up in almost 380 out of 3,700 visitors to health clinics in North Sumatra, Indonesia, an area that is close to being deemed free of human malaria.
Many scientists now recognize P. knowlesi as the fifth malaria parasite species that can naturally infect humans. It is also the only one to multiply in the blood every 24 hours, and it can kill if treatment is delayed. People pick up P. knowlesi parasites from long-tailed macaques, pig-tailed macaques and Mitred leaf monkeys. These monkeys range across Southeast Asia. So far, malaria parasites have been found in monkeys near or in forests, but rarely in monkeys in towns or cities.

Scientists propose several reasons for the recent rise in monkey malaria infections, but two stand out: improvement in malaria detection and forest loss.

Malaysia, for instance, finds more monkey malaria cases than other Southeast Asian countries because it added molecular diagnostic tools in 2009. Other countries use only microscopy for detection, says Rose Nani Mudin, who heads the vectorborne disease sector at Malaysia’s Ministry of Health. Since 2008, annual monkey malaria cases in Malaysia have climbed tenfold, even as human malaria cases have plummeted. “Maybe there is a genuine increase in [monkey malaria] cases. But with strengthening of surveillance, of course you would detect more cases,” she says.

Data collected by Malaysia’s malaria surveillance system have also revealed strong links between infection risk and deforestation. Fornace, the epidemiologist, examined the underlying drivers of monkey malaria in Surukan’s home state of Sabah. Fornace mapped monkey malaria cases in 405 villages, based on patient records from 2008 to 2012. Satellite data showed changes in forested areas around those villages. The villages most likely to report monkey malaria infections were those that had cut more than 8 percent of their surrounding forests within the last five years, she and colleagues reported in 2016 in Emerging Infectious Diseases.
Fornace’s team went into the field for a follow-up study, published in June in PLOS Neglected Tropical Diseases. The team collected blood samples from almost 2,000 people in two areas in Sabah and checked for current and past malaria infection. People who farmed or worked in plantations near forests had at least a 63 percent higher risk of P. knowlesi infection, and — like in the 2016 study — forests and cleared areas escalated risk of infection.

“It feels almost like P. knowlesi follows deforestation,” Fornace says. Several years after a forest is cut back, nearby communities “get a peak of P. knowlesi.”

Today, the hill where the American surveyor camped in 1965 is a small island in a sea of oil palm estates. From 2000 to 2012, Malaysia cleared a total amount of forest equaling 14.4 percent of its land area, more than any other country, according to a study published in 2013 in Science. A study in 2013 in PLOS ONE used satellite images to show that in 2009, only one-fifth of Malaysian Borneo was intact forest. Almost one-fourth of all forest there had been logged, regrown and logged many times over.

Since 2008, oil palm acreage in Malaysian Borneo has increased from 2.08 million hectares to 3.1 million, according to the Malaysian Palm Oil Board. In Malaysia, the four states hit hardest by deforestation — Sabah, Sarawak, Kelantan and Pahang — report 95 percent of the country’s P. knowlesi cases.
Fornace thinks deforestation and the ecological changes that come with it are the main drivers of monkey malaria’s rise in Malaysia. She has seen long-tailed macaques spend more time in farms and near houses after their home forests were being logged. Macaques thrive near human communities where food is abundant and predators stay out. Parasite-carrying mosquitoes breed in puddles made by farming and logging vehicles.

Where monkeys go, mosquitoes follow. Indra Vythilingam, a parasitologist at University of Malaya in Kuala Lumpur, studied human malaria in indigenous communities in the early 1990s. Back then, she rarely found A. cracens, the mosquito species that carries monkey malaria in Peninsular Malaysia. But in 2007, that species made up over 60 percent of mosquitoes collected at forest edges and in orchards, she reported in 2012 in Malaria Journal. “It’s so much easier to find them” now, she says.

As Fornace points out, “P. knowlesi is a really good example of how a disease can emerge and change” as land use changes. She recommends that when big projects are evaluated for their impact on the economy and the environment, human health should be considered as well.

What to expect
While P. knowlesi cases are climbing in Malaysia, scientists have found no evidence that P. knowlesi transmits directly from human to mosquito to human (though many suspect it happens, albeit inefficiently).
Following a review by experts in 2017, WHO continues to exclude P. knowlesi from its malaria elimination efforts. Rabindra Abeyasinghe, a tropical medicine specialist who coordinates WHO malaria control in the western Pacific region, says the agency will reconsider P. knowlesi as human malaria if there is new evidence to show that the parasite transmits within human communities.

In Malaysia last year, only one person died from human malaria, but P. knowlesi killed 11. “We don’t want that to happen, which is why [P. knowlesi] is our priority even though it is not in the elimination program,” says Rose Nani Mudin from the country’s Ministry of Health.

Unable to do much with the monkeys in the trees, Malaysian health officers focus on the people most likely to be infected with P. knowlesi. Programs raise awareness of monkey malaria and aim to reduce mosquitoes around houses. New mosquito-control methods are needed, however, because conventional methods like insecticide-treated bed nets do not work for monkey malaria mosquitoes that bite outdoors around dusk.

Fighting malaria is like playing chess against an opponent that counters every good move we make, says Culleton in Japan. Malaria parasites can mutate quickly and “go away and hide in places and come out again.” Against malaria, he says, “we can never let our guard down.”

This article appears in the November 10, 2018 Science News with the headline, “The Next Malaria Menace: Deforestation brings monkeys and humans close enough to share an age-old disease.”

Editor’s note: This story was updated on November 6, 2018 to correct the WHO’s position on monkey malaria. The agency excludes monkey malaria parasites from its malaria eradication goals, not because those particular parasites rarely infect humans, but because the parasites have not been shown to transmit among humans.

In a broad swath of northwestern Alaska, small groups of recent immigrants are hard at work. Like many residents of this remote area, they’re living off the land. But these industrious foreigners are neither prospecting for gold nor trapping animals for their pelts. In fact, their own luxurious fur was once a hot commodity. Say hello to Castor canadensis, the American beaver.

Much like humans, beavers can have an oversized effect on the landscape (SN: 8/4/18, p. 28). People who live near beaver habitat complain of downed trees and flooded land. But in areas populated mostly by critters, the effects can be positive. Beaver dams broaden and deepen small streams, forming new ponds and warming up local waters. Those beaver-built enhancements create or expand habitats hospitable to many other species — one of the main reasons that researchers refer to beavers as ecosystem engineers.
Beavers’ tireless toils — to erect lodges that provide a measure of security against land-based predators and to build a larder of limbs, bark and other vegetation to tide them over until spring thaw — benefit the wildlife community.

A couple of decades ago, the dam-building rodents were hard to find in northwestern Alaska. “There’s a lot of beaver around here now, a lot of lodges and dams,” says Robert Kirk, a long-time resident of Noatak, Alaska — ground zero for much of the recent beaver expansion. His village of less than 600 people is the only human population center in the Noatak River watershed.
Beavers may be infiltrating the region for the first time in recent history as climate change makes conditions more hospitable, says Ken Tape, an ecologist at the University of Alaska Fairbanks. Or maybe the expansion is a rebound after trapping reduced beaver numbers to imperceptible levels in the early 1900s, he says. Nobody knows for sure.
And the full range of changes the rodents are generating in their new Arctic ecosystems hasn’t been studied in detail. But from what Tape and a few other researchers can tell so far, the effects could be profound, and most of them will probably be beneficial for other species.

In the areas newly colonized by beavers, “some really interesting processes are unfolding,” says John Benson, a wildlife ecologist at the University of Nebraska–Lincoln who studies wolves and coyotes, among other beaver predators. “I’d expect some pretty dramatic changes to the areas they take over.”

Beavers’ biggest effects on Arctic ecosystems may come from the added biodiversity within the ponds they create, says James Roth, an ecologist at the University of Manitoba in Winnipeg, Canada. These “oases on the tundra” will not only provide permanent habitat for fish and amphibians, they’ll serve as seasonal stopover spots for migratory waterfowl. Physical changes to the environment could be just as dramatic, thawing permafrost decades faster than climate change alone would.

The Arctic tundra isn’t the first place beavers have made their mark. Changes seen in beaver-rich areas at lower latitudes may offer some clues to the future of the Alaskan tundra, home to moose, caribou and snowshoe hares.

North through Alaska
As Earth’s climate has warmed in recent years, some plants and animals — such as the mountain-dwelling pika, a small mammal related to rabbits — have fled the heat by moving to higher altitudes (SN: 6/30/12, p. 16). Others, from moose and snowshoe hares to bull sharks and bottlenosed dolphins, have moved toward the poles to take advantage of newly hospitable ecosystems (SN: 5/26/18, p. 9).

Arctic environments have changed more than most, Tape says. Polar regions are warming much faster than other parts of the world, he says. Studies estimate that average temperatures in the Arctic have risen about 1.8 degrees Celsius since 1900, about 60 percent faster than the Northern Hemisphere as a whole.

This warming is bringing great change to the Alaskan tundra, Tape says. Winter snow cover doesn’t persist as long as it used to. Streams freeze later in the fall and melt earlier in the spring. Permafrost, the perennially frozen ground, is thawing, allowing shrubs to take hold. New species are moving in, few more noticeable than the beaver. The dams they build and the ponds they create are hard to miss; these newly formed bodies of water even show up on satellite images.
Beavers have infiltrated three watersheds in northwestern Alaska in the last couple of decades. Together these drainages cover more than 18,000 square kilometers — an area larger than Connecticut.

On images of the region collected by Landsat satellites in summer months from 1999 through 2014, Tape and colleagues looked for new areas of wetness that covered at least half a hectare (1.24 acres), or about four times the area covered by an Olympic swimming pool.

The researchers then used newer, high-resolution satellite images to verify the presence of beaver ponds. Available aerial photographs taken before 1999 didn’t pick up any signs of beaver activity in the area, Tape says. Kirk notes that beavers were present in the Lower Noatak River watershed before 1999, but in vastly smaller numbers than they are today.

Based on the images at hand, the researchers found 56 new complexes of beaver ponds in the area over the 16-year study period. On average, beavers expanded their range about 8 kilometers per year, Tape and colleagues reported in the October Global Change Biology.

“This is remarkable, but it shouldn’t come as a surprise,” Tape says. “Beavers are engineers that work every day, all summer long.”

The animals have also made their way into western Alaska’s Seward Peninsula and the northern foothills of the Brooks Range, mountains that stretch east to west across northern Alaska, the researchers found. If the animals’ recent rate of expansion continues, beavers could spread throughout Alaska’s North Slope in the next 20 to 40 years, the researchers say.
The Lower Noatak River watershed, one of the areas that Tape and colleagues studied, is mostly tundra. By definition that means treeless plain. But the area also is about 3.5 percent forest, mainly concentrated along the river and its tributaries. The watersheds just to the north are completely tundra. So how do the beavers there build dams without trees? In those areas, Tape says, the animals construct smaller dams than they might at lower latitudes, using the branches, twigs and foliage of willows and other shrubs.

“I never expected to see beavers on the tundra,” Roth says, intrigued by Tape’s team’s findings.

Happy place
The beavers are not only persisting on the tundra, they’re thriving. The moderately sized streams and flat terrain provide ideal habitat. And once they gain a foothold, these industrious creatures set about making improvements that are probably an overall plus for myriad other species, Tape says.

For instance, frigid conditions in the region cause shallow streams to freeze solid in winter. But when a beaver builds a dam, the water that gathers upstream of the structure becomes deep enough to remain liquid below a sheet of ice that provides insulation from the chilly winter air.

That persistent liquid lets the beavers move about under the ice even in the depths of winter. The water gives them a place to stockpile food, too, Tape notes. That constant supply of liquid water also provides year-round habitat for fish, amphibians and even some insects in their larval stages. None of these species are part of the beaver’s diet, but they could serve as food for other creatures. “All that diversity would add whole new layers to food webs,” Roth says.
Ecological changes could extend well beyond the beaver pond. The water impounded by beaver dams sometimes finds its way past the dam, Tape says. The satellite photos that he and his colleagues analyzed revealed that some stretches of river just downstream of beaver dams now remain unfrozen even in winter. That flowing water probably spills over the dam or around its edges, but some may seep through or under the structure.

That liquid water also helps thaw the underlying permafrost. Previous studies have shown that even a shallow pond less than a meter deep can boost sediment temperature by as much as 10 degrees C above the locale’s average air temperature. That kind of warming causes permafrost to thaw decades earlier than it would without the pond. Although scientists are concerned that permafrost thawing will release stored carbon into the atmosphere, no one yet knows how that thawing will affect the balance of carbon emissions to the atmosphere (SN: 1/21/17, p. 15).

Field studies at lower latitudes hint that beavers will probably bring about other ecological changes, too, Tape says, which might shift over time. For example, moose and snowshoe hares eat the same willow shrubs that beavers consume and build their dams with. And ptarmigan, a crow-sized bird in the grouse family, rely on those shrubs for cover, especially during winter. So immediately after beavers move into an area and start clearing that brush, populations of those species may decline.

But the long-term benefits will probably outweigh the short-term impacts on those species, says Matthew Mumma, an ecologist at the University of Northern British Columbia in Prince George, Canada. Permafrost that thaws along the fringe of a beaver pond will probably boost numbers of the shrubs that these species depend on, Tape and colleagues suggest. So in the long run, the overall numbers of moose, hares and ptarmigan may rise.
Likewise, Mumma notes, beavers could provide big benefits for salmon and other migratory fish. Beaver dams were once thought to impede the travel of such fish upstream or to reduce the number of places where fish could spawn. But studies in the western United States, among other places, have suggested that the presence of beavers actually helps boost populations of salmon. For instance, the aquatic grasses in beaver ponds offer hiding places for young fish. Also, the languid ponds provide a resting spot for adult fish migrating upstream to spawning sites.

Better-fed wolves
Boosting herbivore populations on the tundra would be a boon for local predators, of course. Larger numbers of snowshoe hares, for example, could feed the populations of the arctic foxes that prey upon them, Mumma says. And more moose could mean better-fed wolves.

Beavers themselves make a meal for bears, wolverines and wolves. In areas where wolves and beavers coexist, the rodents make up as much as 30 percent of the wolf diet, Roth says. The presence of a more reliable and more diversified food supply could lead wolves to settle down in smaller territories rather than migrating widely.

Benson and his team have already seen the impact of beaver populations on wolves, coyotes and wolf-coyote hybrids in Ontario’s Algonquin Provincial Park from August 2002 until April 2011.

In that time, 37 of the 105 pups that had been tagged with radio transmitters died, Benson says. The second-highest cause of death was starvation. Every one of those starvation-related deaths took place in the western portion of the park, which has relatively rugged terrain and few beavers. In the eastern portion of the park, where beavers are plentiful, none of the pups starved, Benson and his team reported in 2013 in Biological Conservation.
In a separate study, Mumma and colleagues analyzed aerial surveys of beaver populations within seven broad regions in northeastern British Columbia in 2011 and 2012. Proximity to human activity, such as roadbuilding or oil and gas exploration, didn’t seem to affect beavers’ decisions to build at a particular locale. Nor did the presence of wolves in the area, the researchers reported in February in the Canadian Journal of Zoology.

Although having wolves nearby seemed to affect the number of beavers present (quite possibly via consumption), the predators didn’t seem to scare the rodents away entirely, Mumma notes.

More beavers, fewer sick moose
Whether the presence of beavers on the Alaskan tundra ends up boosting the numbers of moose and other ungulates, the dam builders could have a big, though indirect, impact on the hoofed browsers’ health.

Roth and parasitologist Olwyn Friesen, now at the University of Otago in Dunedin, New Zealand, recently studied how a wolf’s diet affects the parasites it carries — which can then be passed on to other creatures in the environment. The researchers analyzed 32 wolf carcasses collected by provincial conservation officers in southeastern Manitoba in 2011 and 2012. Those remains came from hunters, trappers and roadkill.

In particular, the team tallied the parasites in the wolves’ lungs, liver, heart and intestines. The group also measured the ratio of carbon-12 and carbon-13 isotopes in the wolf tissues, which provided insight into what sorts of prey each individual wolf had eaten near the time those tissues formed.

Typical prey for wolves in this area are, from most consumed to least: white-tailed deer, snowshoe hare, moose, beaver and caribou, Roth says. Each of these creatures has a distinct ratio of the two carbon isotopes in its tissues. That ratio gets passed along to the predators that eat them.

The wolves with diets heavier in beaver had, on average, fewer intestinal parasites called cestodes. (Tapeworms are the best-known members of that group.)

The implications are clear, Roth and Friesen reported in 2016 in the Journal of Animal Ecology. Beaver-eating wolves are much less likely to excrete parasites into the environment where they could be picked up by ungulates, such as moose and caribou. Wolves don’t seem to be detrimentally affected by such parasites. But ungulates that become infected — especially older animals — may have reduced lung capacity, making escape from predators more difficult.
A new resource
Although beavers may speed changes in the Arctic, those effects may still take a long time to manifest.

Despite the proliferation of beavers in the Lower Noatak River watershed in the last couple of decades, “things around here grow so slowly, they’re not really having a long-term impact yet,” says local resident Kirk. Shrubs haven’t yet noticeably spread into any areas of permafrost that have been thawed by waters impounded by recent dam-building.

Nor have the beavers made much of a mark on the local economy, he says. “There’s a lot of people harvesting them now, since there’s so many of them around,” he adds. However, the pelts from those rodents are so far used by the trappers themselves, not sold to others.

The beavers haven’t become a big draw on the local food scene, either. Even connoisseurs say the meat has a gamey, greasy taste. As Kirk puts it, “we haven’t adjusted our taste buds to them yet.”

The United States is poised to take a powerful economic hit from climate change over the next century. Heat waves, wildfires, extreme weather events and rising sea levels could cost the country hundreds of billions of dollars in lost labor, reduced crop yields, health problems and crumbling infrastructure.

A report authored by hundreds of U.S. climate scientists from 13 federal agencies presents a stark picture of the country’s fate due to climate change. The Fourth National Climate Assessment, released November 23, predicts the U.S. economy will shrink by as much as 10 percent by the end of the century if global warming continues apace.
A separate report released November 27 by the United Nations Environment Programme reveals that in 2017, global emissions of carbon dioxide — a major driver of warming — rose for the first time in three years. That suggests that the nations that promised to curb emissions as part of the historic 2015 Paris agreement are falling short (SN: 1/9/16, p. 6).

It’s unclear what effect, if any, the reports will have on the U.S. government’s strategy on dealing with climate change and its consequences. President Donald Trump has previously announced he would withdraw the United States from the Paris agreement (SN Online: 6/1/17). And on November 26, Trump told reporters that he had read “some of” his scientists’ report. “It’s fine,” he said. But when it comes to the dire predictions of economic losses, he added, “I don’t believe it.”

The National Climate Assessments are mandated by Congress and produced every four years, focusing on the risks of climate change specifically to the United States. What’s different about the new report compared with previous editions is its precision about the risks to different parts of the U.S. economy, putting a price tag on the potential losses in agriculture, trade and energy generation.

To put a dollar value on bad air quality or worsening heat waves, for instance, scientists try to assess the measurable impacts of those issues — for example, the number of days of work or school missed, or the number of doctors’ visits triggered (SN Online: 10/14/18).
The more-than-1,600-page report includes detailed examinations of the effects of climate change on the country’s different regions. People living in the northeastern United States, for example, will be among the hardest hit by deaths due to poor air quality and temperature extremes by the end of the century. Labor losses in the southeastern United States are the highest of all regions, as are projected damages to roads and bridges, the report found.

Meanwhile, the Midwest will see the highest increase in premature deaths from increased amounts of ozone. And the Southwest, which includes California in these analyses, will suffer from extreme heat, drought and an increase in future cases of the mosquito-borne West Nile virus.

The report estimates that cumulatively the country will spend $23 billion responding to wildfires by the end of the century, even if greenhouse gas emissions are modestly reduced. The Southwest will bear the brunt of that impact, spending $13 billion dollars.

The report also details the many ways in which climate change is already hurting the country economically. For example, three storms that made landfall during the 2017 Atlantic hurricane season — Harvey, Irma and Maria — together cost the United States at least $265 billion, according to the National Oceanic and Atmospheric Administration.

By continuing on its current trajectory of greenhouse gas emissions, the “business-as-usual” scenario, the United States will see the greatest losses, the assessments concludes. However, the report also considers climate impacts in an alternate future, in which the world has taken modest actions to curb greenhouse emissions, including using more carbon-neutral fuels and the growth of technological innovations to remove carbon dioxide from the atmosphere (SN Online: 10/20/18).

When most people were thinking about summer vacation, we were contemplating the biggest science stories of 2018.

Yep, it takes more than six months of effort to put together Science News’ annual issue on the Top 10 science stories of the year. 2018 was no different, though we were hit with some exciting twists that had us revisiting our decisions just a week or so before closing the issue.

The early discussions tend to be more about themes — climate emerged as a big one, even before the recent reports linking increased severity of hurricanes, floods and wildfires to climate change. Reporters lobby to get the stories that intrigued them the most or the discoveries that mark critical turning points onto the short list.
By August, our editors have identified contenders for the top of the list and are assigning stories so writers can get to work. We try to keep the choices under wraps; it’s part of the fun. All of the stories are assigned by October 1. By then, we’re also planning illustrations, graphics and bonus items, like our much-loved list of favorite science books of the year. By Thanksgiving, we’ve nailed down the “map” for the magazine, including story order and page designs.

And then news happens. This year was particularly rich in breaking news that had us reshuffling the deck. That included the discovery of an impact crater hidden under Greenland’s ice, which some scientists argue contributed to the die-off of the mammoths. That story broke on November 14 (SN: 12/8/18, p. 6).

Then there was the U.S. report on domestic climate change impacts, which was released the Friday after Thanksgiving. A few days later came an even bigger surprise: A Chinese scientist claimed that he had created the world’s first gene-edited babies. The announcement unleashed a torrent of criticism from scientists around the world.
So what would you pick as the No. 1 science story of the year? After much discussion, our editorial team decided to stick with our original choice of climate change, considering the extraordinary amount of new data released this year and the import of those findings. The Chinese babies elbowed their way into the No. 2 slot. Even though the scientist’s claim may prove false, the technology has clearly advanced to the point where scientists and governments must act to set ethical standards for human gene editing.

Note to our readers: The magazine will be taking a break over the holidays. The next issue you receive will be dated January 19. But we’ll still be hard at work reporting on developments in science, medicine and technology; visit us at www.sciencenews.org for the latest. In 2019, we’ll publish four double issues, in May, July, October and December. These special issues include more features and in-depth coverage of topics like last summer’s “Water woes,” which included reporting from Mumbai, India. We love having the opportunity to dig deep on pressing issues and hope you enjoy the results. Thank you for being part of the Science News community. We wish you joyous holidays and an evidence-based new year.

Earth’s heart may have a secret chamber. The planet’s inner core isn’t just a solid ball of nickel and iron, researchers say, but contains two layers of its own: a distinct central region nestled within an outer shell.

Scientists say they have confirmed the existence of this innermost inner core using a type of previously undescribed seismic wave that not only travels through Earth’s core but also bounces back and forth through the interior, collecting invaluable data about the core’s structure along the way.
Focusing on earthquakes of magnitude 6 or larger that struck in the last decade, the researchers combined data on these quakes that were collected at seismic stations around the world. Combining these signals made it possible to detect even very faint reflections of the seismic waves. Of the 200 or so quakes analyzed, 16 events spawned seismic waves that detectably bounced through the inner core multiple times.

The origin, structure and fate of Earth’s core is of intense interest because the core generates the planet’s magnetic field, which shields the Earth from charged particles ejected by the sun and helps keep the planet’s denizens safe from too much radiation.

“Understanding how the magnetic field evolves is extremely important for the life on Earth’s surface,” says Hrvoje Tkalčić, a seismologist at the Australian National University in Canberra.

The entire core, about 6,600 kilometers across, consists of two main parts: a liquid outer core and a solid inner core (SN: 1/23/23). As iron-rich fluid circulates in the outer core, some of the material cools and crystallizes, sinking to form a solid center. That interplay generates Earth’s magnetic field.

When this swirling dance first began isn’t certain, but some studies suggest it was as recent as 565 million years ago, just a fraction of Earth’s 4.6-billion-year-long life span (SN: 1/28/19). That dance has faltered from time to time, its stuttering steps preserved in tiny magnetic grains in rocks. These data suggest the planet’s magnetic poles have flip-flopped many times over the years, temporarily weakening the magnetic field (SN: 2/18/21). As more and more crystals cool, the dance will eventually slow and stop, shutting off the planet’s magnetic field millions or billions of years from now.

Different types and structures of minerals, as well as different amounts of liquid in the subsurface, can change the speed of seismic waves traveling through Earth, offering clues to the makeup of the interior. In 2002, researchers noted that seismic waves traveling through the innermost part of Earth move slightly slower in one direction relative to the planet’s poles than in other directions. That suggests there’s some oddity there — a difference in crystal structure, perhaps. That hidden heart, the team suggested, might be a kind of fossil: a long-preserved remnant of the core’s early formation.

Since that observation, Tkalčić and others have pored over seismic data, finding independent lines of evidence that help support the idea of an innermost inner core. The reverberating seismic waves, described February 21 in Nature Communications, also show a slowdown, and are the strongest evidence yet that this hidden heart exists.
Using that seismic data, Tkalčić and seismologist Thanh-Son Phạm, also of the Australian National University, estimate that this inner heart is roughly 600 kilometers across, or about half the diameter of the full inner core. And the pair was able to assess the direction of the slowest waves at about 50 degrees relative to the Earth’s rotation axis, providing more insight into the region.

The exact source of the wave slowdown isn’t clear, Tkalčić says. The phenomenon might be related to the structure of the iron crystals, which may be packed together differently farther into the center. Or it could be from a different crystal alignment caused by some long-ago global event that changed how inner core crystals solidified out of the outer core.

The inner core holds many other mysteries too. Lighter elements present in small amounts in the core — hydrogen, carbon, oxygen — may flow around the solid iron in a liquidlike “superionic” state, further complicating the seismic picture (SN: 2/9/22).

By identifying and reporting seismic waves that bounced back and forth through the planet’s interior multiple times, the researchers have made an invaluable contribution that will help researchers study the core in new ways, says seismologist Paul Richards of Columbia University’s Lamont-Doherty Earth Observatory in Palisades, N.Y.

Still, the team’s interpretation of the inner core’s structure from those waves “is probably more iffy,” says Richards, who wasn’t involved in the work.

One reason for this uncertainty is that as the waves bounce back and forth, they can become weaker and more difficult to see in the data, he says. “Many further observations will help decide” what these new data can reveal about the heart of the planet.

Future therapy patients may spend a lot more time exploring virtual environments than sitting on sofas.

In a clinical trial of a new virtual reality treatment for fear of heights, participants reported being much less afraid after using the program for just two weeks. Unlike other VR therapies, which required that a real-life therapist guide patients through treatment, the new system uses an animated avatar to coach patients through ascending a virtual high-rise. This kind of fully automated counseling system, described online July 11 in the Lancet Psychiatry, may make psychological treatments for phobias and other disorders far more accessible.
This is “a huge step forward” for therapeutic VR, says Jennifer Hames, a clinical psychologist at the University of Notre Dame in Indiana, who wasn’t involved in the work. By bringing expert therapy out of the counselor’s office and into primary care clinics — or even people’s homes — the new system could help those who aren’t comfortable or don’t have the means to speak with a therapist face-to-face, she says.
Users immerse themselves in this virtual reality program using a VR headset, handheld controllers and headphones. An animated counselor guides the user through a virtual 10-story office complex, where upper floors overlook a ground-level atrium. On every floor, the user performs tasks designed to test their fear responses and help them learn that they’re safer than they might think. The tasks start out relatively easy — like standing close to a drop-off where a safety barrier gradually lowers — and progress to more difficult challenges — like riding a moving platform out into the open space over the atrium.
By working through these activities, “the person builds up memories that being around heights is safe, and this counteracts the old fear beliefs,” says Daniel Freeman, a clinical psychologist at the University of Oxford.

To test their program’s effectiveness, Freeman and colleagues recruited 100 adult volunteers who were moderately to severely afraid of heights. The researchers randomly assigned 49 people to undergo VR treatment, which involved using the program for about six 30-minute sessions over two weeks, while the other 51 participants received no treatment.

Participants filled out a questionnaire that rated their fear of heights from 16 to 80 (with 80 being most severe), before treatment, immediately afterward, and two weeks later. People who underwent VR treatment dropped about 25 points on average on the questionnaire’s scale, while patients who received no treatment remained stable. Participants who used the VR program found they “could go to places that they wouldn’t have imagined possible,” Freeman says, like steep mountains, rope bridges or simply escalators in shopping malls.

“When I’ve always got anxious about an edge, I could feel the adrenaline in my legs, that fight/flight thing; that’s not happening as much now,” one participant said. “I’m still getting a bit of a reaction to it, both in VR and outside as well, but it’s much more brief, and I can then feel my thighs soften up as I’m not bracing up against that edge.”

While the clinical trial results provide strong evidence that the new VR program mitigates fear better than no treatment at all, researchers still need to investigate how VR therapy stacks up against sessions with a therapist, Hames says. And since Freeman’s team only tracked treatment effects up to a couple of weeks after their experiment, it remains to be seen how long the effects of this therapy last — although previous research on therapist-led VR treatment have shown lasting impacts for at least a year.

While fully automated VR therapy may be good news for people who fear heights, it’s not clear how well this type of system could address more complex mental health issues, says Mark Hayward, a clinical psychologist at the University of Sussex in England whose commentary on the study appears in the same issue of the Lancet Psychiatry. Virtual environments may be well suited for helping people who fear everyday situations, like those who suffer from common phobias, social anxiety or paranoia, Hayward says. But when it comes to helping people with more severe symptoms, like psychosis, VR probably won’t stand in for trained therapists any time soon.

“We can’t get carried away and say we can automate all [mental health] treatment,” says Albert Rizzo, a clinical virtual reality developer at the University of Southern California in Playa Vista not involved in the work. But the new standalone system for curbing fear of heights is “an excellent first effort.”

Today’s young women are more likely to experience depression and anxiety during pregnancy than their mothers were, a generation-spanning survey finds.

From 1990 to 1992, about 17 percent of young pregnant women in southwest England who participated in the study had signs of depressed mood. But the generation that followed, including these women’s daughters and sons’ partners, fared worse. Twenty-five percent of these young women, pregnant in 2012 to 2016, showed signs of depression, researchers report July 13 in JAMA Network Open.
“We are talking about a lot of women,” says study coauthor Rebecca Pearson, a psychiatric epidemiologist at Bristol University in England.

Earlier studies also had suggested that depression during and after pregnancy is relatively common (SN: 3/17/18, p. 16). But those studies are dated, Pearson says. “We know very little about the levels of depression and anxiety in new mums today,” she says.

To measure symptoms of depression and anxiety, researchers used the Edinburgh Postnatal Depression Scale — 10 questions, each with a score of 0 to 3, written to reveal risk of depression during and after pregnancy. A combined score of 13 and above signals high levels of symptoms.

From 1990 to 1992, 2,390 women between the ages of 19 and 24 took the survey while pregnant. Of these women, 408 — or 17 percent — scored 13 or higher, indicating worrisome levels of depression or anxiety.
When researchers surveyed the second-generation women, including both daughters of the original participants and sons’ partners ages 19 to 24, the numbers were higher. Of 180 women pregnant in 2012 to 2016, 45 of them — or 25 percent — scored 13 or more. It’s not clear whether the findings would be similar for pregnant women who are older than 24 or younger than 19.
That generational increase in young women scoring high for symptoms of depression comes in large part from higher scores on questions that indicate anxiety and stress, Pearson says. Today’s pregnant women reported frequent feelings of “unnecessary panic or fear” and “things getting too much,” for instance.

Those findings fit with observations by psychiatrist Anna Glezer of the University of California, San Francisco. “A very significant portion of my patients present with their primary problem as anxiety, as opposed to a low mood,” says Glezer, who has a practice in Burlingame, Calif.

The study’s cutoff score for indicating high depression risk was 13, but Pearson points out that a lower score can signal mild depression. Women who score an 8 or 9 “still aren’t feeling great,” she says. It’s likely that even more pregnant women might have less severe, but still unpleasant symptoms, she says.

The researchers also found that depression moves through families. Daughters of women who were depressed during pregnancy were about three times as likely to be depressed during their own pregnancy than women whose mothers weren’t depressed. That elevated risk “was news to me,” says obstetrician and gynecologist John Keats, who chaired a group of the American College of Obstetricians and Gynecologists that studied maternal mental health. Asking about whether a patient’s mother experienced depression or anxiety while pregnant might help identify women at risk, he says.

Negative effects of stress can be transmitted during pregnancy in ways that scientists are just beginning to understand, and stopping this cycle is important (SN Online: 7/9/18). “You’re not only talking about the effects on a patient and her family, but potential effects on her growing fetus and newborn,” says Keats, of the David Geffen School of Medicine at UCLA.

Although researchers don’t yet know what’s behind the increase, they have some guesses. More mothers work today than in the 1990s, and tougher financial straits push women to work inflexible jobs. More stress, less sleep and more time sitting may contribute to the difference.

Time on social media may also increase feelings of isolation and anxiety, Glezer says. Social media can help new moms get information, but that often comes with “a whole lot of comparisons, judgments and expectations.”

Just a few powerful storms in Antarctica can have an outsized effect on how much snow parts of the southernmost continent get. Those ephemeral storms, preserved in ice cores, might give a skewed view of how quickly the continent’s ice sheet has grown or shrunk over time.

Relatively rare extreme precipitation events are responsible for more than 40 percent of the total annual snowfall across most of the continent — and in some places, as much as 60 percent, researchers report March 22 in Geophysical Research Letters.
Climatologist John Turner of the British Antarctic Survey in Cambridge and his colleagues used regional climate simulations to estimate daily precipitation across the continent from 1979 to 2016. Then, the team zoomed in on 10 locations — representing different climates from the dry interior desert to the often snowy coasts and the open ocean — to determine regional differences in snowfall.

While snowfall amounts vary greatly by location, extreme events packed the biggest wallop along Antarctica’s coasts, especially on the floating ice shelves, the researchers found. For instance, the Amery ice shelf in East Antarctica gets roughly half of its annual precipitation — which typically totals about half a meter of snow — in just 10 days, on average. In 1994, the ice shelf got 44 percent of its entire annual precipitation on a single day in September.

Ice cores aren’t just a window into the past; they are also used to predict the continent’s future in a warming world. So characterizing these coastal regions is crucial for understanding Antarctica’s ice sheet — and its potential future contribution to sea level rise.
Editor’s note: This story was updated April 5, 2019, to correct that the results were reported March 22 (not March 25).

Editor’s note: On April 10, the Event Horizon Telescope collaboration released a picture of the supermassive black hole at the center of galaxy M87. Read the full story here.

We’re about to see the first close-up of a black hole.

The Event Horizon Telescope, a network of eight radio observatories spanning the globe, has set its sights on a pair of behemoths: Sagittarius A*, the supermassive black hole at the Milky Way’s center, and an even more massive black hole 53.5 million light-years away in galaxy M87 (SN Online: 4/5/17).
In April 2017, the observatories teamed up to observe the black holes’ event horizons, the boundary beyond which gravity is so extreme that even light can’t escape (SN: 5/31/14, p. 16). After almost two years of rendering the data, scientists are gearing up to release the first images in April.

Here’s what scientists hope those images can tell us.

What does a black hole really look like?
Black holes live up to their names: The great gravitational beasts emit no light in any part of the electromagnetic spectrum, so they themselves don’t look like much.

But astronomers know the objects are there because of a black hole’s entourage. As a black hole’s gravity pulls in gas and dust, matter settles into an orbiting disk, with atoms jostling one another at extreme speeds. All that activity heats the matter white-hot, so it emits X-rays and other high-energy radiation. The most voraciously feeding black holes in the universe have disks that outshine all the stars in their galaxies (SN Online: 3/16/18).
The EHT’s image of the Milky Way’s Sagittarius A, also called SgrA, is expected to capture the black hole’s shadow on its accompanying disk of bright material. Computer simulations and the laws of gravitational physics give astronomers a pretty good idea of what to expect. Because of the intense gravity near a black hole, the disk’s light will be warped around the event horizon in a ring, so even the material behind the black hole will be visible.
And the image will probably look asymmetrical: Gravity will bend light from the inner part of the disk toward Earth more strongly than the outer part, making one side appear brighter in a lopsided ring.

Does general relativity hold up close to a black hole?
The exact shape of the ring may help break one of the most frustrating stalemates in theoretical physics.

The twin pillars of physics are Einstein’s theory of general relativity, which governs massive and gravitationally rich things like black holes, and quantum mechanics, which governs the weird world of subatomic particles. Each works precisely in its own domain. But they can’t work together.

“General relativity as it is and quantum mechanics as it is are incompatible with each other,” says physicist Lia Medeiros of the University of Arizona in Tucson. “Rock, hard place. Something has to give.” If general relativity buckles at a black hole’s boundary, it may point the way forward for theorists.

Since black holes are the most extreme gravitational environments in the universe, they’re the best environment to crash test theories of gravity. It’s like throwing theories at a wall and seeing whether — or how — they break. If general relativity does hold up, scientists expect that the black hole will have a particular shadow and thus ring shape; if Einstein’s theory of gravity breaks down, a different shadow.

Medeiros and her colleagues ran computer simulations of 12,000 different black hole shadows that could differ from Einstein’s predictions. “If it’s anything different, [alternative theories of gravity] just got a Christmas present,” says Medeiros, who presented the simulation results in January in Seattle at the American Astronomical Society meeting. Even slight deviations from general relativity could create different enough shadows for EHT to probe, allowing astronomers to quantify how different what they see is from what they expect.
Do stellar corpses called pulsars surround the Milky Way’s black hole?
Another way to test general relativity around black holes is to watch how stars careen around them. As light flees the extreme gravity in a black hole’s vicinity, its waves get stretched out, making the light appear redder. This process, called gravitational redshift, is predicted by general relativity and was observed near SgrA* last year (SN: 8/18/18, p. 12). So far, so good for Einstein.

An even better way to do the same test would be with a pulsar, a rapidly spinning stellar corpse that sweeps the sky with a beam of radiation in a regular cadence that makes it appear to pulse (SN: 3/17/18, p. 4). Gravitational redshift would mess up the pulsars’ metronomic pacing, potentially giving a far more precise test of general relativity.

“The dream for most people who are trying to do SgrA* science, in general, is to try to find a pulsar or pulsars orbiting” the black hole, says astronomer Scott Ransom of the National Radio Astronomy Observatory in Charlottesville, Va. “There are a lot of quite interesting and quite deep tests of [general relativity] that pulsars can provide, that EHT [alone] won’t.”

Despite careful searches, no pulsars have been found near enough to SgrA* yet, partly because gas and dust in the galactic center scatters their beams and makes them difficult to spot. But EHT is taking the best look yet at that center in radio wavelengths, so Ransom and colleagues hope it might be able to spot some.

“It’s a fishing expedition, and the chances of catching a whopper are really small,” Ransom says. “But if we do, it’s totally worth it.”
How do some black holes make jets?
Some black holes are ravenous gluttons, pulling in massive amounts of gas and dust, while others are picky eaters. No one knows why. SgrA* seems to be one of the fussy ones, with a surprisingly dim accretion disk despite its 4 million solar mass heft. EHT’s other target, the black hole in galaxy M87, is a voracious eater, weighing in at between about 3.5 billion and 7.22 billion solar masses. And it doesn’t just amass a bright accretion disk. It also launches a bright, fast jet of charged subatomic particles that stretches for about 5,000 light-years.

“It’s a little bit counterintuitive to think a black hole spills out something,” says astrophysicist Thomas Krichbaum of the Max Planck Institute for Radio Astronomy in Bonn, Germany. “Usually people think it only swallows something.”

Many other black holes produce jets that are longer and wider than entire galaxies and can extend billions of light-years from the black hole. “The natural question arises: What is so powerful to launch these jets to such large distances?” Krichbaum says. “Now with the EHT, we can for the first time trace what is happening.”

EHT’s measurements of M87’s black hole will help estimate the strength of its magnetic field, which astronomers think is related to the jet-launching mechanism. And measurements of the jet’s properties when it’s close to the black hole will help determine where the jet originates — in the innermost part of the accretion disk, farther out in the disk or from the black hole itself. Those observations might also reveal whether the jet is launched by something about the black hole itself or by the fast-flowing material in the accretion disk.

Since jets can carry material out of the galactic center and into the regions between galaxies, they can influence how galaxies grow and evolve, and even where stars and planets form (SN: 7/21/18, p. 16).

“It is important to understanding the evolution of galaxies, from the early formation of black holes to the formation of stars and later to the formation of life,” Krichbaum says. “This is a big, big story. We are just contributing with our studies of black hole jets a little bit to the bigger puzzle.”

Editor’s note: This story was updated April 1, 2019, to correct the mass of M87’s black hole; the entire galaxy’s mass is 2.4 trillion solar masses, but the black hole itself weighs in at several billion solar masses. In addition, the black hole simulation is an example of one that uphold’s Einstein’s theory of general relativity, not one that deviates from it.

We live in a sea of neutrinos. Every second, trillions of them pass through our bodies. They come from the sun, nuclear reactors, collisions of cosmic rays hitting Earth’s atmosphere, even the Big Bang. Among fundamental particles, only photons are more numerous. Yet because neutrinos barely interact with matter, they are notoriously difficult to detect.

The existence of the neutrino was first proposed in the 1930s and then verified in the 1950s (SN: 2/13/54). Decades later, much about the neutrino — named in part because it has no electric charge — remains a mystery, including how many varieties of neutrinos exist, how much mass they have, where that mass comes from and whether they have any magnetic properties.
These mysteries are at the heart of Ghost Particle by physicist Alan Chodos and science journalist James Riordon. The book is an informative, easy-to-follow introduction to the perplexing particle. Chodos and Riordon guide readers through how the neutrino was discovered, what we know — and don’t know — about it, and the ongoing and future experiments that (fingers crossed) will provide the answers.

It’s not just neutrino physicists who await those answers. Neutrinos, Riordon says, “are incredibly important both for understanding the universe and our existence in it.” Unmasking the neutrino could be key to unlocking the nature of dark matter, for instance. Or it could clear up the universe’s matter conundrum: The Big Bang should have produced equal amounts of matter and antimatter, the oppositely charged counterparts of electrons, protons and so on. When matter and antimatter come into contact, they annihilate each other. So in theory, the universe today should be empty — yet it’s not (SN: 9/22/22). It’s filled with matter and, for some reason, very little antimatter.

Science News spoke with Riordon, a frequent contributor to the magazine, about these puzzles and how neutrinos could act as a tool to observe the cosmos or even see into our own planet. The following conversation has been edited for length and clarity.

SN: In the first chapter, you list eight unanswered questions about neutrinos. Which is the most pressing to answer?

Riordon: Whether they’re their own antiparticles is probably one of the grandest. The proposal that neutrinos are their own antiparticles is an elegant solution to all sorts of problems, including the existence of this residue of matter we live in. Another one is figuring out how neutrinos fit in the standard model [of particle physics]. It’s one of the most successful theories there is, but it can’t explain the fact that neutrinos have mass.
SN: Why is now a good time to write a book about neutrinos?

Riordon: All of these questions about neutrinos are sort of coming to a head right now — the hints that neutrinos may be their own antiparticles, the issues of neutrinos not quite fitting the standard model, whether there are sterile neutrinos [a hypothetical neutrino that is a candidate for dark matter]. In the next few years, a decade or so, there will be a lot of experiments that will [help answer these questions,] and the resolution either way will be exciting.

SN: Neutrinos could also be used to help scientists observe a range of phenomena. What are some of the most interesting questions neutrinos could help with?

Riordon: There are some observations that simply have to be done with neutrinos, that there are no other technological alternatives for. There’s a problem with using light-based telescopes to look back in history. We have this really amazing James Webb Space Telescope that can see really far back in history. But at some point, when you go far enough back, the universe is basically opaque to light; you can’t see into it. Once we narrow down how to detect and how to measure the cosmic neutrino background [neutrinos that formed less than a second after the Big Bang], it will be a way to look back at the very beginning. Other than with gravitational waves, you can’t see back that far with anything else. So it’ll give us sort of a telescope back to the beginning of the universe.

The other thing is, when a supernova happens, all kinds of really cool stuff happens inside, and you can see it with neutrinos because neutrinos come out immediately in a burst. We call it the “cosmic neutrino bomb,” but you can track the supernova as it’s going along. With light, it takes a while for it to get out [of the stellar explosion]. We’re due for a [nearby] supernova. We haven’t had one since 1987. It was the last visible supernova in the sky and was a boon for research. Now that we have neutrino detectors around the world, this next one is going to be even better [for research], even more exciting.

And if we develop better instrumentation, we could use neutrinos to understand what’s going on in the center of the Earth. There’s no other way that you could probe the center of the Earth. We use seismic waves, but the resolution is really low. So we could resolve a lot of questions about what the planet is made of with neutrinos.

SN: Do you have a favorite “character” in the story of neutrinos?

Riordon: I’m certainly very fond of my grandfather Clyde Cowan [he and Frederick Reines were the first physicists to detect neutrinos]. But Reines is a riveting character. He was poetic. He was a singer. He really was this creative force. I mentioned [in the book] that they put this “SNEWS” sign on their detector for “supernova early warning system,” which sort of echoed the ballistic missile early warning systems at the time [during the Cold War]. That’s so ripe.