The windy and chaotic remains surrounding recently exploded stars may be launching the fastest particles in the universe.

Highly magnetic neutron stars known as pulsars whip up a fast and strong magnetic wind. When charged particles, specifically electrons, get caught in those turbulent conditions, they can be boosted to extreme energies, astrophysicists report April 28 in the Astrophysical Journal Letters. What’s more, those zippy electrons can then go on to boost some ambient light to equally extreme energies, possibly creating the very high-energy gamma-ray photons that led astronomers to detect these particle launchers in the first place.

“This is the first step in exploring the connection between the pulsars and the ultrahigh-energy emissions,” says astrophysicist Ke Fang of the University of Wisconsin, Madison, who was not involved in this new work.

Last year, researchers with the Large High Altitude Air Shower Observatory, or LHAASO, in China announced the discovery of the highest-energy gamma rays ever detected, up to 1.4 quadrillion electron volts (SN: 2/2/21). That’s roughly 100 times as energetic as the highest energies achievable with the world’s premier particle accelerator, the Large Hadron Collider near Geneva. Identifying what’s causing these and other extremely high-energy gamma rays could point, literally, to the locations of cosmic rays — the zippy protons, heavier atomic nuclei and electrons that bombard Earth from locales beyond our solar system.
Some gamma rays are thought to originate in the same environs as cosmic rays. One way they’re produced is that cosmic rays, shortly after being launched, can slam into relatively low-energy ambient photons, boosting them to high-energy gamma rays. But the electrically charged cosmic rays are buffeted by galactic magnetic fields, which means they don’t travel in a straight line, thus complicating efforts to trace the zippy particles back to their source. Gamma rays, however, are impervious to magnetic fields, so astrophysicists can trace their unwavering paths back to their origins — and figure out where cosmic rays are created.

To that end, the LHAASO team traced the hundreds of gamma-ray photons that it detected to 12 spots on the sky. While the team identified one spot as the Crab Nebula, the remnant of a supernova about 6,500 light-years from Earth, the researchers suggested that the rest could be associated with other sites of stellar explosions or even young massive star clusters (SN: 6/24/19).

In the new study, astrophysicist Emma de Oña Wilhelmi and colleagues zeroed in one of those possible points of origin: pulsar wind nebulas, the clouds of turbulence and charged particles surrounding a pulsar. The researchers weren’t convinced such locales could create such high-energy particles and light, so they set out to show through calculations that pulsar wind nebulas weren’t the sources of extreme gamma rays. “But to our surprise, we saw at the very extreme conditions, you can explain all the sources [that LHAASO saw],” says de Oña Wilhelmi, of the German Electron Synchrotron in Hamburg.

The young pulsars at the heart of these nebulas — no more than 200,000 years old — can provide all that oomph because of their ultrastrong magnetic fields, which create a turbulent magnetic bubble called a magnetosphere.

Any charged particles moving in an intense magnetic field get accelerated, says de Oña Wilhelmi. That’s how the Large Hadron Collider boosts particles to extreme energies (SN: 4/22/22). A pulsar-powered accelerator, though, can boost particles to even higher energies, the team calculates. That’s because the electrons escape the pulsar’s magnetosphere and meet up with the material and magnetic fields from the stellar explosion that created the pulsar. These magnetic fields can further accelerate the electrons to even higher energies, the team finds, and if those electrons slam into ambient photons, they can boost those particles of light to ultrahigh energies, turning them into gamma rays.

“Pulsars are definitely very powerful accelerators,” Fang says, with “several places where particle acceleration can happen.”

And that could lead to a bit of confusion. Gamma-ray telescopes have pretty fuzzy vision. For example, LHASSO can make out details only as small as about half the size of the full moon. So the gamma-ray sources that the telescope detected look like blobs or bubbles, says de Oña Wilhelmi. There could be multiple energetic sources within those blobs, unresolved to current observatories.

“With better angular resolution and better sensitivity, we should be able to identify what [and] where the accelerator is,” she says. A few future observatories — such as the Cherenkov Telescope Array and the Southern Wide-field Gamma-ray Observatory — could help, but they’re several years out.

The U.S. defense and intelligence communities are taking unidentified flying objects, officially known as unidentified aerial phenomena, seriously. And some researchers think the scientific community should too.

On May 17, the U.S. Congress held its first public hearing about these objects in decades (SN: 6/26/71). Two Pentagon officials described efforts to catalog and analyze sightings, many by military personnel such as pilots, of the unexplained phenomena because of their potential threat to national security.

Scott Bray, the deputy director of naval intelligence, shared new details on a database of images and videos that now includes about 400 reports of sightings of unidentified phenomena from 2004 to 2021. While officials were able to attribute some of the sightings to artifacts of certain sensors or other mundane explanations, there were others the officials “can’t explain,” Bray said.

Bray stressed that nothing in the database or studied by a task force set up to investigate the sightings “would suggest it’s anything nonterrestrial in origin.”
Both Bray and Ronald Moultrie, the undersecretary of defense for intelligence and security, identified “insufficient data” as a barrier to understanding what the unidentified phenomena are. “That’s one of the challenges we have,” Moultrie said.

That’s something that other scientists can help with, say astrobiologists Jacob Haqq Misra and Ravi Kopparapu.

Science News spoke with Haqq Misra, of Blue Marble Space Institute of Science in Seattle, and Kopparapu, of NASA’s Goddard Space Flight Center in Greenbelt, Md., to learn more about how and why. Their answers have been edited for brevity and clarity.

What are unidentified aerial phenomena?
Haqq Misra: “What are they” is the billion-dollar question. We don’t know what they are, and that’s what makes them interesting.

Unidentified aerial phenomena, or UAP, is the term that the military has been using. It’s a little different from the term UFO in the sense that a phenomenon could be something that’s not necessarily a physical solid object. So UAP is maybe a more all-encompassing term.

Should we scientifically study them? Why?
Kopparapu: Yes. We conduct scientific studies of unknown phenomena all the time. This should not be any different. The most critical point to remember is that when conducting those studies, we should not let our speculations drive the conclusions. The collected data should do it.

Haqq Misra: As scientists, what we should do is study things that we don’t understand.

With UAP, there seem to be some anomalous observations that are difficult to explain. Maybe they’re a sign of something like new physics, or maybe it’s just instrumental artifacts that we don’t understand or things that birds are doing.

It could be anything, but any of those possibilities, anything from the most extreme to the most mundane, would teach us something.

So there’s the scientific curiosity. And it’s also about safety for pilots too, especially if there’s something in the sky that pilots are seeing that they consider a flight safety risk.

How can we study these phenomena?
Haqq Misra: The problem with studying UAP so far is that all of the data are held by the government. From the hearing, there does seem to be a plan to declassify some data, once it’s been vetted for possible security risks, but I’m not holding my breath for that to happen soon. It was nice to hear, though.

The reality is if you want to understand a particular set of data, you need to know something about the instrument that collected the data. Military instruments are probably classified for good reason, for our safety. I think we’re not going to get the kind of data from the government that we need to scientifically answer the question. Even if you had that data, from the government or commercial pilots or others, it has not been intentionally collected. These have been accidental, sporadic observations.

So what you would need is to set up a network of detectors all around the world. Ideally, you’d have ground-based sensors and you’d have satellite coverage. It’s not enough for someone to just see something. You need to measure a detection with multiple sensors and multiple wavelengths.

Kopparapu: Some of these are transient events. We need, for example, fast-tracking cameras and optical, infrared and radar observations to collect more data to find patterns in the events’ behaviors.

And we need to share such data with scientists so that independent groups can reach a consensus. This is how science progresses. There are some initiatives from academics in this direction, so that is a good sign.

What are some possible next steps for the scientific community for studying them?
Haqq Misra: There are some groups that are trying to build detectors now. Fundraising is the hardest part. [The nonprofit] UAPx is one, and the Galileo Project [at Harvard University] is another.

And this was underscored in the hearing, but stigma has been a big problem. It seems like the military is trying to not only streamline the reporting process but also destigmatize it. That’s important for science too. If that starts to change more in the culture, that would go a long way.

Kopparapu: I think the scientific study of UAP should not be stigmatized. There should be open discussions, comments and constructive criticisms that can help further the study of UAP.

There should be discussions about how and which kinds of instruments are needed to collect data. The focus should be on collecting and sharing the data and then commenting on the topic.

How did you get interested in this topic?
Kopparapu: Over a couple of years, I read several articles either dismissing or advocating for a particular explanation regarding UAP. Then I started digging into it, and I found physicist James McDonald’s “Science in Default” report from 1969. That one particular report about UFOs changed my perspective. It was written similar to how we write our scientific articles. That resonated with me as a scientist, and I started to think that a science investigation is the only way we can understand UAP.

Haqq Misra: I got interested in this subject because I’m an astrobiologist and other people asked me about UFOs. UFOs are not necessarily an astrobiology topic, because we don’t know what they are. But lots of people think that they’re extraterrestrials. And I felt a little silly, being an astrobiologist and having nothing to say.

So I went to Carl Sagan’s files, and I realized that even though he lived decades before me, there are things in his files that we’re talking about now, that are related to airborne anomalies seen by pilots.

Ultimately, I realized for a scientist who wants to understand what’s going on with this UFO thing, there’s a lot of noise to sift through. There’s a lot of public discourse about other topics like crop circles, alien abductions and paranormal stories that muddy the waters, and the more we can be clear about the specific aerial anomalies that we’re talking about, the more we can actually solve the problem.

Deep in the human brain, a very specific kind of cell dies during Parkinson’s disease.

For the first time, researchers have sorted large numbers of human brain cells in the substantia nigra into 10 distinct types. Just one is especially vulnerable in Parkinson’s disease, the team reports May 5 in Nature Neuroscience. The result could lead to a clearer view of how Parkinson’s takes hold, and perhaps even ways to stop it.

The new research “goes right to the core of the matter,” says neuroscientist Raj Awatramani of Northwestern University Feinberg School of Medicine in Chicago. Pinpointing the brain cells that seem to be especially susceptible to the devastating disease is “the strength of this paper,” says Awatramani, who was not involved in the study.

Parkinson’s disease steals people’s ability to move smoothly, leaving balance problems, tremors and rigidity. In the United States, nearly 1 million people are estimated to have Parkinson’s. Scientists have known for decades that these symptoms come with the death of nerve cells in the substantia nigra. Neurons there churn out dopamine, a chemical signal involved in movement, among other jobs (SN: 9/7/17).

But those dopamine-making neurons are not all equally vulnerable in Parkinson’s, it turns out.

“This seemed like an opportunity to … really clarify which kinds of cells are actually dying in Parkinson’s disease,” says Evan Macosko, a psychiatrist and neuroscientist at Massachusetts General Hospital in Boston and the Broad Institute of MIT and Harvard.
The tricky part was that dopamine-making neurons in the substantia nigra are rare. In samples of postmortem brains, “we couldn’t survey enough of [the cells] to really get an answer,” Macosko says. But Abdulraouf Abdulraouf, a researcher in Macosko’s laboratory, led experiments that sorted these cells, figuring out a way to selectively pull the cells’ nuclei out from the rest of the cells present in the substantia nigra. That enrichment ultimately led to an abundance of nuclei to analyze.

By studying over 15,000 nuclei from the brains of eight formerly healthy people, the researchers further sorted dopamine-making cells in the substantia nigra into 10 distinct groups. Each of these cell groups was defined by a specific brain location and certain combinations of genes that were active.

When the researchers looked at substantia nigra neurons in the brains of people who died with either Parkinson’s disease or the related Lewy body dementia, the team noticed something curious: One of these 10 cell types was drastically diminished.

These missing neurons were identified by their location in the lower part of the substantia nigra and an active AGTR1 gene, lab member Tushar Kamath and colleagues found. That gene was thought to serve simply as a good way to identify these cells, Macosko says; researchers don’t know whether the gene has a role in these dopamine-making cells’ fate in people.

The new finding points to ways to perhaps counter the debilitating diseases. Scientists have been keen to replace the missing dopamine-making neurons in the brains of people with Parkinson’s. The new study shows what those cells would need to look like, Awatramani says. “If a particular subtype is more vulnerable in Parkinson’s disease, maybe that’s the one we should be trying to replace,” he says.

In fact, Macosko says that stem cell scientists have already been in contact, eager to make these specific cells. “We hope this is a guidepost,” Macosko says.

The new study involved only a small number of human brains. Going forward, Macosko and his colleagues hope to study more brains, and more parts of those brains. “We were able to get some pretty interesting insights with a relatively small number of people,” he says. “When we get to larger numbers of people with other kinds of diseases, I think we’re going to learn a lot.”

When Igor de Almeida moved to Japan from Brazil nine years ago, the transition should have been relatively easy. Both Japan and Brazil are collectivist nations, where people tend to value the group’s needs over their own. And research shows that immigrants adapt more easily when the home and new country’s cultures match.

But to de Almeida, a cultural psychologist now at Kyoto University, the countries’ cultural differences were striking. Japanese people prioritize formal relationships, such as with coworkers or members of the same “bukatsu,” or extracurricular club, for instance, while Brazilian people prioritize friends in their informal social network. “Sometimes I try to find [cultural] similarities but it’s really hard,” de Almeida says.

Now, new research helps explain that disconnect. For decades, psychologists have studied how culture shapes the mind, or people’s thoughts and behaviors, by comparing Eastern and Western nations. But two research groups working independently in Latin America are finding that a cultural framework that splits the world in two is overly simplistic, obscuring nuances elsewhere in the world.

Due to differences in methodology and interpretation, the teams’ findings about how people living in the collectivist nations of Latin America think are also contradictory. And that raises a larger question: Will overarching cultural theories based on East-West divisions hold up over time, or are new theories needed?

However this debate unfolds, cultural psychologists argue that the field must expand. “If you make most of the cultures of the world … invisible,” says Vivian Vignoles, a cultural psychologist at the University of Sussex in England, “you will get all sorts of things wrong.”

Such misconceptions can jeopardize political alliances, business relationships, public health initiatives and general theories for how people find happiness and meaning. “Culture shapes what it means to be a person,” says Stanford University behavioral scientist Hazel Rose Markus. “What it means to be a person guides all of our behavior, how we think, how we feel, what motivates us [and] how we respond to other individuals and groups.”
Culture and the mind
Until four decades ago, most psychologists believed that culture had little bearing on the mind. That changed in 1980. Surveys of IBM employees taken across some 70 countries showed that attitudes toward work largely depended on workers’ home country, IBM organizational psychologist Geert Hofstede’s wrote in Culture’s Consequences.

Markus and Shinobu Kitayama, a cultural psychologist at the University of Michigan in Ann Arbor, subsequently fleshed out one Hofstede’s four cultural principles: Individualism versus collectivism. Culture does influence thinking, the duo claimed in a now widely cited paper in the 1991 Psychological Review. By comparing people in mostly the East and West, they surmised that living in individualist countries (i.e. Western ones) led people to think independently while living in collectivist countries (the East) led people to think interdependently.

That paper was pioneering at the time, Vignoles says. Before that, with psychological research based almost exclusively in the West, the Western mind had become the default mind. Now, “instead of being only one kind of person in the world, there [were] two kinds of persons in the world.”
Latin America: A case study
How individualism/collectivism shape the mind now undergirds the field of cross-cultural psychology. But researchers continue to treat the East and West, chiefly Japan and the United States, as prototypes, Vignoles and colleagues say.

To expand beyond that narrow lens, the team surveyed 7,279 participants in 33 nations and 55 cultures. Participants read such statements as “I prefer to turn to other people for help rather than solely rely on myself” and “I consider my happiness separate from the happiness of my friends and family.” They then responded to how well those comments reflected their values on a scale from 1 for “not at all” to 9 for “exactly.”

That analysis allowed the researchers to identify seven dimensions of independence/interdependence, including self-reliance versus dependence on others and emphasis on self-expression versus harmony. Strikingly, Latin Americans were as, or more, independent as Westerners in six out of the seven dimensions, the team reported in 2016 in the Journal of Experimental Psychology: General.

The researchers’ subsequent analysis of four studies comprising 17,255 participants across 53 nations largely reaffirmed that surprising finding. For instance, Latin Americans are more expressive than even Westerners, Vignoles, de Almeida and colleagues report in February in Perspectives in Psychological Science. But that finding violates the common view that people living in collectivist societies suppress their emotions to foster harmony, while people in individualistic countries emote as a form of self-expression.
Latin American nations are collectivist, as defined by Hofstede and others, but the people think and behave independently, the team concludes.

Kitayama’s team has a different take: Latin Americans are interdependent, just in a wholly different way than East Asians. Rather than suppressing emotions, Latin Americans tend to express positive, socially engaging emotions to communicate with others, says cultural psychologist Cristina Salvador of Duke University. That fosters interdependence, unlike the way Westerners express emotions to show their personal feelings. Westerners’ feelings can be negative or positive and often have little to do with their social surroundings — a sign of independence.

Salvador, Kitayama and colleagues had more than 1,000 respondents in Chile, Colombia, Mexico, Japan and the United States reflect on various social scenarios, instead of asking explicit questions like Vignoles’ team. For instance, respondents were asked to imagine winning a prize. They then picked what emotions — such as shame, guilt, anger, friendliness or closeness to others — they would express with family and friends.

Respondents from Latin America and the United States both expressed strong emotions, Salvador reported in February at the Society for Personality and Social Psychology conference in San Francisco. But people in the United States expressed egocentric emotions, such as pride, while people in Latin America expressed emotions that emphasize connection with others.

Because Latin America’s high ethnic and linguistic diversity made communication with words difficult, people learned how to communicate in other ways, Kitayama says. “Emotion became a very important means of social communication.”

Decentering the West
More research is needed to reconcile those findings. But how should that research proceed? Though a shift to a broader framework has begun, research in cultural psychology still hinges on the East-West binary, researchers from both teams say.

Psychologists who peer review studies for acceptance into scientific journals still “want a mainstream, white, U.S. comparison sample,” Salvador says. “[Often] you need an Asian sample, as well.”

The primacy of the East and West means that psychological differences between those two regions dominate research and discussions. But both teams are expanding the scope of their research despite those challenges.

Kitayama’s team, for instance, maps out how interdependence, which it argues precedes the emergence of independence, might have morphed as it spread around the globe, in a theory paper also presented at the San Francisco conference (SN: 11/7/19). Besides diversity giving way to “expressive interdependence” in Latin America, the team describes “self-effacing interdependence in East Asia” stemming from the communal nature of rice farming, “self-assertive interdependence” in Arab regions arising from the nomadic life and “argumentative interdependence” in South Asia arising from its central role in trade (SN: 7/14/14).
This research started with a “West and the rest” mentality, Kitayama says. His work with Markus created an “East-West and the rest” mentality. Now finally, psychologists are grappling with “the rest,” he says. “The time is really ready to expand this [research] to cover the rest of the world.”

De Almeida imagines decentering the West yet further. What if researchers had started off by comparing Japan and Brazil instead of Japan and the United States, he wonders. Instead of the current laser focus on individualism/collectivism, some other defining facet of culture would have likely risen to prominence. “I would say emotional expression, that’s the most important thing,” de Almeida says.

He sees a straightforward solution. “We could increase the number of studies not involving the United States,” he says. “Then we could develop new paradigms.”

Turns out we may be unfairly stereotyping dogs.

Modern breeds are shaped around aesthetics: Chihuahuas’ batlike ears, poodles’ curly fur, dachshunds’ hot dog shape. But breeds are frequently associated with certain behaviors, too. For instance, the American Kennel Club describes border collies as “affectionate, smart, energetic” and beagles as “friendly, curious, merry.”

Now, genetic information from more than 2,000 dogs, paired with self-reported surveys from dog owners, indicates that a dog’s breed is a poor predictor of its behavior. On average, breed explains only 9 percent of the behavioral differences between individual dogs, researchers report April 28 in Science.
“Everybody was assuming that breed was predictive of behavior in dogs,” geneticist Elinor Karlsson of the University of Massachusetts Chan Medical School in Worcester said in an April 26 news briefing. But “that had never really been asked particularly well.”

Geneticists had asked the question before in different ways. One study in 2019 looked at whether genetics might explain collective variation between breeds and found that genes could explain some of the differences between, say, poodles and chihuahuas (SN: 10/1/19). But Karlsson and her colleagues wanted to learn how much breed can predict variation in individual dogs’ behavior.

To study variation at the individual level, the team needed genetic and behavior data from a lot of dogs. So they developed Darwin’s Ark, an open-source database where more than 18,000 pet owners responded to surveys about their dog’s traits and behavior. The survey asked over 100 questions about observable behaviors, which the researchers grouped into eight “behavioral factors,” including human sociability (how comfortable a dog is around humans) and biddability (how responsive it is to commands).

The researchers also collected genetic data from 2,155 purebred and mixed-breed dogs, including 1,715 dogs from Darwin’s Ark whose owners sent in dog saliva swabs. The inclusion of mixed-breed dogs, or mutts, shed light on how ancestry affects behavior while removing the purebred stereotypes that could affect the way the dog is treated — and thus behaves.

Studying mutts also makes it easier to decouple traits from one another, says Kathleen Morrill, a geneticist in Karlsson’s lab. “And that means on an individual basis, you’re going to have a better shot at mapping a gene that is actually tied to the question you’re asking.”

Then the team combined the genetic and survey data for the individual dogs to identify genes associated with particular traits. The new study revealed that the most heritable behavioral factor for dogs is human sociability, and that motor patterns — such as howling and retrieving — are generally more heritable than other behaviors.

That makes sense, Kathryn Lord, an evolutionary canine biologist in Karlsson’s lab, said during the briefing. Before modern breeding started within the last couple hundred years or so, dogs were selected for the functional roles they could provide, such as hunting or herding (SN: 4/26/17). Today, these selections still show up in breed groups. For instance, herding dogs on average tend to be more biddable and interested in toys. It also follows that, within breed groups, individual breeds are more likely to display certain motor patterns: Retrievers, unsurprisingly, are more likely to retrieve.

Still, even though breed was associated with certain behaviors, it was not a reliable predictor of individual behavior. While retrievers are less likely to howl, some owners reported that their retrievers howled often; greyhounds rarely bury toys, except some do.

The research solidifies what people have observed: Dog breeds differ on average in behavior, but there’s a lot of variation within breeds, says Adam Boyko, a canine geneticist at Cornell University who was not involved in the study.

Surprisingly, size had even less of an effect — as in, virtually none — on an individual’s behavior, despite the yappiness commonly associated with small dogs. Boyko points out that small dogs may often behave worse than large dogs, but rather than that being built into their genetics, “I think it’s that we typically tolerate poor behavior more in small dogs than we do in big dogs.”

As a dog trainer, Curtis Kelley of Pet Parent Allies in Philadelphia says that he meets a dog where it’s at. “Dogs are as individual as people are,” he says. Breed gives a loose guideline for what kind of behaviors to expect, “but it’s certainly not a hard-and-fast rule.”

If a person is looking to buy a dog, he says, they shouldn’t put too much stock in the dog’s breed. Even within a litter, dogs can show very different personalities. “A puppy will show you who they are at eight weeks old,” Kelley says. “It’s just our job to believe them.”

More of the ingredients for life have been found in meteorites.

Space rocks that fell to Earth within the last century contain the five bases that store information in DNA and RNA, scientists report April 26 in Nature Communications.

These “nucleobases” — adenine, guanine, cytosine, thymine and uracil — combine with sugars and phosphates to make up the genetic code of all life on Earth. Whether these basic ingredients for life first came from space or instead formed in a warm soup of earthly chemistry is still not known (SN: 9/24/20). But the discovery adds to evidence that suggests life’s precursors originally came from space, the researchers say.
Scientists have detected bits of adenine, guanine and other organic compounds in meteorites since the 1960s (SN: 8/10/11, SN: 12/4/20). Researchers have also seen hints of uracil, but cytosine and thymine remained elusive, until now.

“We’ve completed the set of all the bases found in DNA and RNA and life on Earth, and they’re present in meteorites,” says astrochemist Daniel Glavin of NASA’s Goddard Space Flight Center in Greenbelt, Md.

A few years ago, geochemist Yasuhiro Oba of Hokkaido University in Sapporo, Japan, and colleagues came up with a technique to gently extract and separate different chemical compounds in liquified meteorite dust and then analyze them.

“Our detection method has orders of magnitude higher sensitivity than that applied in previous studies,” Oba says. Three years ago, the researchers used this same technique to discover ribose, a sugar needed for life, in three meteorites (SN: 11/22/19).

In the new study, Oba and colleagues combined forces with astrochemists at NASA to analyze one of those three meteorite samples and three additional ones, looking for another type of crucial ingredient for life: nucleobases.

The researchers think their milder extraction technique, which uses cold water instead of the usual acid, keeps the compounds intact. “We’re finding this extraction approach is very amenable for these fragile nucleobases,” Glavin says. “It’s more like a cold brew, rather than making hot tea.”

With this technique, Glavin, Oba and their colleagues measured the abundances of the bases and other compounds related to life in four samples from meteorites that fell decades ago in Australia, Kentucky and British Columbia. In all four, the team detected and measured adenine, guanine, cytosine, uracil, thymine, several compounds related to those bases and a few amino acids.

Using the same technique, the team also measured chemical abundances within soil collected from the Australia site and then compared the measured meteorite values with that of the soil. For some detected compounds, the meteorite values were greater than the surrounding soil, which suggests that the compounds came to Earth in these rocks.

But for other detected compounds, including cytosine and uracil, the soil abundances are as much as 20 times as high as in the meteorites. That could point to earthly contamination, says cosmochemist Michael Callahan of Boise State University in Idaho.

“I think [the researchers] positively identified these compounds,” Callahan says. But “they didn’t present enough compelling data to convince me that they’re truly extraterrestrial.” Callahan previously worked at NASA and collaborated with Glavin and others to measure organic materials in meteorites.

But Glavin and his colleagues point to a few specific detected chemicals to support the hypothesis of an interplanetary origin. In the new analysis, the researchers measured more than a dozen other life-related compounds, including isomers of the nucleobases, Glavin says. Isomers have the same chemical formulas as their associated bases, but their ingredients are organized differently. The team found some of those isomers in the meteorites but not in the soil. “If there had been contamination from the soil, we should have seen those isomers in the soil as well. And we didn’t,” he says.

Going directly to the source of such meteorites — pristine asteroids — could clear up the matter. Oba and colleagues are already using their extraction technique on pieces from the surface of the asteroid Ryugu, which Japan’s Hayabusa2 mission brought to Earth in late 2020 (SN: 12/7/20). NASA’s OSIRIS-REx mission is expected to return in September 2023 with similar samples from the asteroid Bennu (SN: 1/15/19).

“We’re really excited about what stories those materials have to tell,” Glavin says.

Leonardo da Vinci was wrong about trees.

The multitalented, Renaissance genius wrote down his “rule of trees” over 500 years ago. It described the way he thought that trees branch. Though it was a brilliant insight that helped him to draw realistic landscapes, Leonardo’s rule breaks down for many types of trees. Now, a new branching rule — dubbed “Leonardo-like” — works for virtually any leafy tree, researchers report in a paper accepted April 13 in Physical Review E.

“The older Leonardo rule describes the thickness of the branches, while the length of the branch was not taken into account,” says physicist Sergey Grigoriev of the Petersburg Nuclear Physics Institute in Gatchina, Russia. “Therefore, the description using the older rule is not complete.”
Leonardo’s rule says that the thickness of a limb before it branches into smaller ones is the same as the combined thickness of the limbs sprouting from it (SN: 6/1/11). But according to Grigoriev and his colleagues, it’s the surface area that stays the same.

Using surface area as a guide, the new rule incorporates limb widths and lengths, and predicts that long branches end up being thinner than short ones. Unlike Leonardo’s guess, the updated rule works for slender birches as well as it does for sturdy oaks, the team reports.

The connection between the surface area of branches and overall tree structure shows that it’s the living, outer layers that guide tree structure, the researchers say. “The life of a tree flows according to the laws of conservation of area in two-dimensional space,” the authors write in their study, “as if the tree were a two-dimensional object.” In other words, it’s as if just two dimensions — the width of each limb and the distance between branchings on a limb — determine any tree’s structure. As a result, when trees are rendered in two dimensions in a painting or on a screen, the new rule describes them particularly well.
The new Leonardo-like rule is an improvement, says Katherine McCulloh, a botanist at the University of Wisconsin–Madison who was not involved with this study. But she has her doubts about the Russian group’s rationale for it. In most trees, she says, the living portion extends much deeper than the thin surface layer.

“It’s really species-dependent, and even age-dependent,” McCulloh says. “A giant, old oak tree might have a centimeter of living wood … [but] there are certainly tropical tree species that have very deep sapwood and may have living wood for most of their cross sections.”

Still, the fact that the Leonardo-like rule appears to hold for many trees intrigues McCulloh. “To me, it drives home the question of why are [trees] conserving this geometry for their external tissue, and how is that related to the microscopic level differences that we observe in wood,” she says. “It’s a really interesting question.”

To test their rule, Grigoriev and colleagues took photographs of trees from a variety of species and analyzed the branches to confirm that the real-world patterns matched the predictions. The photos offer “a direct measurement of the characteristics of a tree without touching it, which can be important when dealing with a living object,” Grigoriev says.

Though the team hasn’t studied evergreens yet, the rule holds for all of the deciduous trees that the researchers have looked at. “We have applied our methodology to maple, linden, apple,” Grigoriev says, in addition to oak, birch and chestnut. “They show the same general structure and obey the Leonardo-like rule.”

While it’s possible to confirm the rule by measuring branches by hand, it would require climbing into trees and checking all the limbs — a risky exercise for trees and scientists alike. “Note,” the researchers write, “that not a single tree was harmed during these experiments.”