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Patience is a virtue in the hunt for dark matter. Experiment after experiment has come up empty in the search — and the newest crop is no exception.

Astronomical observations hint at the presence of an unknown kind of matter sprinkled throughout the cosmos. Several experiments are focused on the search for one likely dark matter candidate: weakly interacting massive particles, or WIMPs. But those particles are yet to be spotted.

New results, posted online at arXiv.org in recent months, continue the trend. The PandaX-II experiment, based in China, found no hint of the particles, scientists reported August 23. The XENON1T experiment in Italy also came up WIMPless according to a May 18 paper. Scientists with the DEAP-3600 experiment in Sudbury, Canada, reported their first results on July 25. Signs of dark matter? Nada. And the SuperCDMS experiment in the Soudan mine in Minnesota likewise found no WIMP hints, scientists reported August 29.

Another experiment, PICO-60, also located in Sudbury, reported its contribution to the smorgasbord of negative results June 23 in Physical Review Letters.

Scientists haven’t given up hope. Researchers are building ever-larger detectors, retooling their experiments and expanding the search beyond WIMPs, in hopes of glimpsing a dark matter particle.

It’s not every day that a spacecraft gets vaporized by the very planet it sought to explore.

After 13 years studying Saturn and its moons, NASA’s Cassini spacecraft will plunge into the ringed gas giant’s atmosphere. The mission will come to a close at about 7:55 a.m. EDT (4:55 a.m. PDT) Friday, when Saturn’s atmosphere pushes Cassini’s antenna away from Earth, terminating the signal. Shortly thereafter, the spacecraft will disintegrate.

If you want to keep tabs on the action, you’ve got a few options. Science News astronomy writer Lisa Grossman is at the Jet Propulsion Laboratory in Pasadena, Calif. — home of mission control for the Cassini probe. She’ll be popping on to the Science News Facebook page throughout the day Thursday with live updates, and she (@astrolisa) and Science News (@ScienceNews) will have details for you on Twitter as well.

Cassini’s death won’t be captured on film. But thanks to the internet, you can watch NASA scientists react to the probe’s impending doom live. In the early hours of Friday morning (7-8:30 a.m. EDT/4-5:30 a.m. PDT), NASA plans to stream a live video feed from the control room, which you can watch here:
And, you can also watch on NASA JPL’s YouTube channel and NASA’s Facebook page.

For more on Cassini’s exploits, check out all of our past coverage of the mission.

For some poison dart frogs, gaining resistance to one of their own toxins came with a price.

The genetic change that gives one group of frogs immunity to a particularly lethal toxin also disrupts a key chemical messenger in the brain. But the frogs have managed to sidestep the potentially damaging side effect through other genetic tweaks, researchers report in the Sept. 22 Science.

While other studies have identified genetic changes that give frogs resistance to particular toxins, this study “lets you look under the hood” to see the full effects of those changes and how the frogs are compensating, says Butch Brodie, an evolutionary biologist at the University of Virginia in Charlottesville who wasn’t involved in the research.
Many poison dart frogs carry cocktails of toxic alkaloid molecules in their skin as a defense against predators (SN Online: 3/24/14). These toxins, picked up through the frogs’ diets, vary by species. Here, researchers studied frogs that carry epibatidine, a substance so poisonous that just a few millionths of a gram can kill a mouse.

Previous studies have shown that poisonous frogs have become resistant to the toxins the amphibians carry by messing with the proteins that these toxins bind to in the body. Switching out certain protein building blocks, or amino acids, changes the shape of the protein, which can prevent toxins from latching on. But making that change could have unintended side effects, too, says study coauthor Rebecca Tarvin, an evolutionary biologist at the University of Texas at Austin.

For example, the toxin epibatidine binds to proteins that are usually targeted by acetylcholine, a chemical messenger that’s necessary for normal brain function. So Tarvin and her colleagues looked at how this acetylcholine receptor protein differed between poison frog species that are resistant to epibatidine and some of their close relatives that aren’t.
Identifying differences between the frogs in the receptor protein’s amino acids allowed researchers to systematically test the effects of each change. To do so, the scientists put the genetic instructions for the same protein in humans, who aren’t resistant to epibatidine, into frog eggs. The researchers then replaced select amino acids in the human code with different poison frog substitutions to find an amino acid “switch” that would make the resulting receptor protein resistant to epibatidine.

But epibatidine resistance wasn’t a straightforward deal, it turned out. “We noticed that replacing one of those amino acids in the human [protein] made it resistant to epibatidine, but also affected its interaction with acetylcholine,” says study coauthor Cecilia Borghese, a neuropharmacologist also at the University of Texas at Austin. “Both are binding in the exact same region of the protein. It’s a very delicate situation.” That is, the amino acid change that made the receptor protein resistant to epibatidine also made it harder for acetylcholine to attach, potentially impeding the chemical messenger’s ability to do its job.

But the frogs themselves don’t seem impaired. That’s because other amino acid replacements elsewhere in the receptor protein appear to have compensated, Borghese and Tarvin found, creating a protein that won’t let the toxin latch on, but that still responds normally to acetylcholine.

The resistance-giving amino acid change appears to have evolved three separate times in poison frogs, Tarvin says. Three different lineages of the frogs have resistance to the poison, and all of them got that immunity by flipping the same switch. But the amino acid changes that bring back a normal acetylcholine response aren’t the same across those three groups.

“It’s a cool convergence that these other switches weren’t identical, but they all seem to recover that function,” Brodie says.

Six years after the Fukushima nuclear reactor disaster in Japan, radioactive material is leaching into the Pacific Ocean from an unexpected place. Some of the highest levels of radioactive cesium-137, a major by-product of nuclear power generation, are now found in the somewhat salty groundwater beneath sand beaches tens of kilometers away, a new study shows.

Scientists tested for radioactivity at eight different beaches within 100 kilometers of the plant, which experienced three reactor meltdowns when an earthquake and tsunami on March 11, 2011, knocked out its power. Oceans, rivers and fresh groundwater sources are typically monitored for radioactivity following a nuclear accident, but several years following the disaster, those weren’t the most contaminated water sources. Instead, brackish groundwater underneath the beaches has accumulated the second highest levels of the radioactive element (surpassed only by the groundwater directly beneath the reactor), researchers report October 2 in the Proceedings of the National Academy of Sciences.

In the wake of the 2011 accident, seawater tainted with high levels of cesium-137 probably traveled along the coast and lapped against these beaches, proposes study coauthor Virginie Sanial, who did the work while at Woods Hole Oceanographic Institution in Massachusetts. Some cesium stuck to the sand and, over time, percolated down to the brackish groundwater beneath. Now, the radioactive material is steadily making its way back into the ocean. The groundwater is releasing the cesium into the coastal ocean at a rate that’s on par with the leakage of cesium into the ocean from the reactor site itself, Sanial’s team estimates.

Since this water isn’t a source of drinking water and is underground, the contamination isn’t an immediate public health threat, says Sanial, now a geochemist at the University of Southern Mississippi in Hattiesburg. But with about half of the world’s nuclear power plants located on coastlines, such areas are potentially important contamination reservoirs and release sites to monitor after future accidents.

Vaping e-cigarettes with high amounts of nicotine appears to impact how often and how heavily teens smoke and vape in the future, a new study finds.

In 2016, an estimated 11 percent of U.S. high school students used e-cigarettes. Past research has found that that teen vaping can lead to smoking (SN: 9/19/15, p. 14). The new study, published online October 23 in JAMA Pediatrics, is the first look at whether vaping higher amounts of nicotine is associated with more frequent and more intense vaping and cigarette use in the future.
Researchers at the University of Southern California surveyed 181 10th-graders from 10 high schools in the Los Angeles area who had reported vaping in the previous 30 days, then followed up six months later, when the students were 11th-graders. The teens answered questions about how much and how often they had smoked and vaped in the past 30 days and about the amount of nicotine in their vaping liquid. The researchers categorized the amount of nicotine as none, low (up to 5 milligrams per milliliter), medium (6 to 17 mg/mL) or high (18 mg/mL or more).

With each step up in nicotine concentration, teens were about twice as likely to report frequent smoking versus no smoking at the six-month follow-up. Teens who vaped a high-nicotine liquid smoked seven times as many cigarettes per day as those who vaped without nicotine.

Also with each nicotine level increase, teens were about 1½ times as likely to report frequent vaping than no vaping at all. Vaping high-nicotine liquid led to almost 2½ times as many episodes of vaping per day compared with no-nicotine vaping, and kids took more puffs each time they vaped.

“This study is important because it begins to chip away at the ‘black box’ that links e-cigarette use with later use of regular cigarettes,” says sociologist Richard Miech of the University of Michigan in Ann Arbor. “Ideally, studies like this will encourage government agencies to develop policies that will make it very difficult for youth to obtain e-liquids with nicotine.”
In 2016, then-U.S. Surgeon General Vivek Murthy released a report on e-cigarettes, concluding that using nicotine-containing products in any form is not safe for youth. Studies find an association between nicotine use in teens and problems with learning, attention and impulse control, as well as addiction (SN: 7/11/15, p. 18).

A soft heart keeps Enceladus warm from the inside. Friction within its porous core could help Saturn’s icy moon maintain a liquid ocean for billions of years and explain why it sprays plumes from its south pole, astronomers report November 6 in Nature Astronomy.

Observations in 2015 showed that Enceladus’ icy surface is a shell that’s completely detached from its rocky core, meaning the ocean spans the entire globe (SN: 10/17/15, p. 8). Those measurements also showed that the ice is not thick enough to keep the ocean liquid.
Other icy moons, like Jupiter’s Europa, keep subsurface oceans warm through the energy generated by gravitational flexing of the ice itself. But if that were Enceladus’ only heat source, its ocean would have frozen within 30 million years, a fraction of the age of the solar system, which formed roughly 4.6 billion years ago.

Planetary scientist Gaël Choblet of the University of Nantes in France and his colleagues tested whether friction in the sand and gravel thought to make up Enceladus’ core could heat things up.

The team made computer simulations of water circulating through the spongy core using data from the Cassini spacecraft and geoengineering experiments with sand and gravel on Earth. They found that, depending on the core’s makeup, the ocean should get enough heat to stay liquid for tens of millions to billions of years.

The simulations also showed that certain hot spots in the core, including at the poles, correspond to regions where the ice shell is thinner.
“That was quite cool,” Choblet says. “It explains the internal structure and the way things are organized and the dynamics interior to Enceladus.”

And that could explain why the moon spews plumes of water from its south pole: More heat from the core at that spot could melt the ice and let water out. It doesn’t explain why the north pole is plume-free, though.

Recent reports of African and North American animal fossils bearing stone-tool marks from being butchered a remarkably long time ago may be a crock. Make that a croc.

Crocodile bites damage animal bones in virtually the same ways that stone tools do, say paleoanthropologist Yonatan Sahle of the University of Tübingen in Germany and his colleagues. Animal bones allegedly cut up for meat around 3.4 million years ago in East Africa (SN: 9/11/10, p. 8) and around 130,000 years ago in what’s now California (SN: 5/27/17, p. 7) come from lakeside and coastal areas. Those are places where crocodiles could have wreaked damage now mistaken for butchery, the scientists report online the week of November 6 in the Proceedings of the National Academy of Sciences.
Larger samples of animal fossils, including complete bones from various parts of the body, are needed to begin to tease apart the types of damage caused by stone tools, crocodile bites and trampling of bones by living animals, Sahle’s team concludes. “More experimental work on bone damage caused by big, hungry crocs is also critical,” says coauthor Tim White, a paleoanthropologist at the University of California, Berkeley.

In a field where researchers reap big rewards for publishing media-grabbing results in high-profile journals, such evidence could rein in temptations to over-interpret results, says archaeologist David Braun of George Washington University in Washington, D.C., who did not participate in the new study or the two earlier ones. “There’s a push to publish extraordinary findings, but evolutionary researchers always have to weigh what’s interesting versus what’s correct.”

Authors of the ancient butchery papers agree that bone marks made by crocodiles deserve closer study and careful comparison with proposed stone-tool marks. But the researchers stand their ground on their original conclusions.

Microscopic investigations in the 1980s led some researchers to conclude that carnivores such as hyenas leave U-shaped marks on bones. In contrast, they argued, stone tools leave V-shaped incisions with internal ridges. And hammering stones create signature pits and striations.
Sahle’s group expanded on research previously conducted by paleoanthropologist Jackson Njau of Indiana University Bloomington. In his 2006 doctoral dissertation, Njau reported that bone damage produced by feeding crocodiles looks much like stone-tool incisions and pits, with a few distinctive twists such as deep scratches. Njau retrieved and studied cow and goat bones from carcasses that had been eaten by crocodiles housed at two animal farms in Tanzania.

In the new study, the scientists used Njau’s findings to reassess marks on fossils previously excavated in Ethiopia and dating to around 4.2 million, 3.4 million and 2.5 million years ago. Damage to these fossils has generally been attributed to butchery with stone tools.

Incisions and pits on arm bones from an ancient hominid, Australopithecus anamensis, and similar marks on a horse’s leg bone likely resulted from crocodile bites and not stone-tool use, as initially suspected, the investigators say. If stone tools had indeed damaged the A. anamensis remains, that would raise the possibility of cannibalism — a difficult behavior to confirm with fossils. Tellingly, Sahle’s team argues, these bones come from what were once waterside areas. Some were found in the same sediment layer as crocodile remains. Marks on these bones include deep scratches consistent with crocodile bites.

The horse fossil comes from a spot along an ancient lakeshore where no stone tools have been found, a further clue in favor of damage from croc bites.

Jagged pits, incisions and other marks scar a leg fragment and lower jaw from an ancient hoofed animal. But microscopic analyses could not definitively attribute the damage to stone tools or crocodile bites.

In light of these findings, the ancient California and 3.4-million-year-old East Africa bones should also be reexamined with the possibility of croc damage in mind, White says. For now, the earliest confirmed stone-tool marks occur on animal bones from two East African sites dating to around 2.5 million years ago (SN: 4/17/04, p. 254), he adds.

The range of crocodile marks described in the new study doesn’t look “especially like” damage to the 130,000-year-old mastodon bones on California’s coast, says paleontologist Daniel Fisher of the University of Michigan in Ann Arbor, a coauthor of the ancient California bones paper. No fossil evidence indicates crocodiles lived there at that time, he adds. Several lines of evidence, including pounding marks and damage near joints, point to stone-tool use at the West Coast site, says archaeologist Richard Fullagar of the University of Wollongong in Australia, also a coauthor of the mastodon paper.

Further studies of the 3.4-million-year-old African bones previously reported as probable examples of animal butchery will statistically compare the probability of various causes for particular marks, including crocodile bites, says Shannon McPherron, the lead author of the earlier study and an archaeologist at the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany. In that way, researchers can assess whether any one cause stands out as the strongest candidate.

Two days before plunging into Saturn, the Cassini spacecraft took one last look around the planet it had orbited for more than 13 years.

The view of Saturn above, released November 21, is actually made from 42 images that have been stitched together. Six moons — Enceladus, Epimetheus, Janus, Mimas, Pandora and Prometheus — are faintly visible as dots surrounding the gas giant (see the annotated image below). Cassini was about 1.1 million kilometers away from Saturn when it took the images on September 13. The whole observation took a little over two hours.

On September 11, Cassini set itself on a collision course with Saturn, and on September 15, the probe ended its mission by burning up in Saturn’s atmosphere, taking data all the way down.

MINNEAPOLIS — Pesticides that kill insects can also have short-term effects on seed-eating birds. Ingesting even small amounts of imidacloprid, a common neonicotinoid pesticide, can disorient migratory white-crowned sparrows, researchers report.

Neonicotinoid pesticides were designed to be safer than traditional pesticides: toxic to insects, but comparatively harmless to other animals. But the new findings add to evidence suggesting that the widely used pesticides, which are chemically similar to nicotine, might be sending ecological ripples beyond the intended targets.
In lab studies, researchers captured wild white-crowned sparrows, Zonotrichia leucophrys, that were migrating north and fed them small doses of imidacloprid for three days — the amount that birds would get from eating a few pesticide-coated wheat seeds. The birds that ate the pesticides lost weight, study coauthor Margaret Eng reported November 15 at the annual meeting of the Society of Environmental Toxicology and Chemistry North America.

And when placed in a large, inverted funnel used to study birds’ migratory orientations, the neonic-fed birds tried to fly in directions other than north. Birds that consumed sunflower oil instead showed no ill effects.

For the birds that ate pesticides, the damage was temporary — after two weeks, the birds regained normal function and body weight, Eng, a toxicologist at the University of Saskatchewan in Saskatoon, Canada, and her colleagues also reported November 9 in Scientific Reports.

The fact that the effects reverse after a period of time is “good news,” says Thomas Bean, a toxicologist at the University of Maryland in College Park who wasn’t part of the study. The short-term malaise might incentivize birds to avoid that food in the future. Bean has found that Japanese quail, Coturnix japonica, also show similar temporary behavioral effects in response to neonicotinoids.
Preliminary results from field studies also appear to confirm the published lab findings. Eng’s team outfitted white-crowned sparrows in the wild with tiny tracking tags. The scientists gave the birds small amounts of pesticides, held the birds for six hours, and then released them.

When released, the birds still had traces of the chemicals in their blood plasma, the researchers reported at the November meeting. On average, there wasn’t a difference between groups in how long the birds hung around before resuming migration, but all of the birds that waited an abnormally long time had eaten neonics. Those animals’ flight paths also appeared to be slightly skewed from the route favored by the control birds.

Those analyses are preliminary, cautions Eng, and a closer look at the data could change the story.

A skull and other fossils from northeastern Australia belong to a new species in the extinct family of marsupial lions.

This newly named species, Wakaleo schouteni, was a predator about the size of a border collie, says vertebrate paleontologist Anna Gillespie of the University of New South Wales in Sydney. At least 18 million years ago (and perhaps as early as 23 million years ago), it roamed what were then hot, humid forests. Its sturdy forelimbs suggest it could chase possums, lizards and other small prey up into trees. Gillespie expects W. shouteni — the 10th species named in its family — carried its young in a pouch as kangaroos, koalas and other marsupials do.
Actual lions evolved on a different fork in the mammal genealogical tree, but Australia’s marsupial lions got their feline nickname from the size and slicing teeth of the first species named, in 1859. Thylacoleo carnifex was about as big as a lion. And its formidable teeth could cut flesh. But unlike other pointy-toothed predators, marsupial lions evolved a horizontal cutting edge. A bottom tooth stretched back along the jawline on each side, its slicer edge as long as four regular teeth. An upper tooth extended too, giving this marsupial lion a bite like a “bolt cutter,” Gillespie says.

The newly identified species lived some 17 million years before its big bolt-cutter relative. Though the new species’ tooth number matched those of typical early marsupials, W. schouteni already had a somewhat elongated tooth just in front of the molars, Gillespie and colleagues report December 7 in the Journal of Systematic Paleontology. W. schouteni is “pushing the history of marsupial lions deeper into time,” she says.