A new genetic discovery could equip researchers to fight a superbug by stripping it of its power rather than killing it outright.

Scientists have identified a set of genes in Clostridium difficile that turns on its production of toxins. Those toxins can damage intestinal cells, leading to diarrhea, abdominal pain and potentially life-threatening disease. Unlocking the bug’s genetic weapon-making secret could pave the way for new nonantibiotic therapies to disarm the superbug while avoiding collateral damage to other “good” gut bacteria, researchers report August 16 in mBio.
Identifying a specific set of genes that control toxin production is a big step forward, says Matthew Bogyo. Bogyo, a chemical biologist at Stanford University, also studies ways to defuse C. difficile’s toxin-making.

C. difficile bacteria infect a half million people and kill about 29,000 each year in the United States. In some individuals, though, the microbe hangs out in the gut for years without causing trouble. That’s because human intestines normally have plenty of good bacteria to keep disease-causing ones in check. However, a round of antibiotics can throw the system off balance, and if enough good bugs die off, “C. difficile takes over,” says lead author Charles Darkoh, a molecular microbiologist at the University of Texas Health Science Center at Houston. As infection rages, C. difficile can develop resistance to antibiotic drugs, turning it into an intractable superbug.

Darkoh’s team reported last year that C. difficile regulates toxin production with quorum sensing — a system that lets bacteria conserve resources and launch an attack only if their numbers reach a critical threshold. That study identified two sets of quorum-signaling genes, agr1 and agr2, that could potentially activate toxin production.

In the new analysis, Darkoh and colleagues tested the ability of a series of C. difficile strains to make toxins when incubated with human skin cells. Some C. difficile strains had either agr1 or agr2 deleted; others had all their quorum-sensing genes or lacked both gene sets. Agr1 is responsible for packing the superbug’s punch, the researchers found. C. difficile mutants without that set of genes made no detectable toxins, and skin cells growing in close quarters stayed healthy. Feeding those mutant bugs to mice caused no harm, whereas mice that swallowed normal C. difficile lost weight and developed diarrhea within days. In the skin cell cultures, agr2-deficient strains were just as lethal as normal C. difficile, showing that only agr1 is essential for toxin production.

Based on their new findings, Darkoh and colleagues have identified several compounds that inactivate C. difficile toxins or block key steps in the molecular pathway controlling their production. The researchers are testing these agents in mice.

In a mouse study published in Science Translational Medicine last year, Bogyo and colleagues found a different compound that could disarm C. difficile by targeting its toxins. And several companies are trying to fight C. difficile with probiotics — cocktails of good bacteria. Results have been mixed.

How the seafloor quivers under an intense storm called a “weather bomb” could help reveal Earth’s innermost secrets.

Using a network of seismic sensors, researchers in Japan detected a rare type of deep-Earth tremor originating from a rapidly strengthening cyclone over the North Atlantic Ocean. Tracking how these newfound shakes ripple through the globe will help geoscientists map the materials that make up the planet’s depths, the researchers report August 26 in Science.

“We’re potentially getting a suite of new seismic source locations that can be used to investigate the interior of the Earth,” says Peter Bromirski, a geophysical oceanographer at the Scripps Institution of Oceanography in La Jolla, Calif., who wrote a commentary on the new research in the same issue of Science. “Further investigations will refine our understanding of how useful these particular waves will be.”
Tremors traveling through the ground speed up, slow down or change direction depending on the type of material they pass through. Carefully measuring these movements from earthquake waves has allowed scientists to gather clues about the structure and composition of Earth’s deepest layers.

Some regions — the middle of tectonic plates under the ocean, for instance — don’t see many earthquakes, though. Luckily, weather bombs can generate their own seismicity. Whipping winds can stir up towering ocean swells. When two opposing ocean swells collide, the meet-up can send a pressure pulse down to the ocean floor. The pulse thumps the seafloor, producing seismic waves that penetrate deep into the planet.
Scientists had previously detected only one type —called P waves —of these storm-generated seismic waves. P waves cause a material to compress and stretch like an accordion in the same direction that the wave travels. The other variety, called S waves, has proved more elusive. S waves formed by storms are typically weaker than P waves and cause material to ripple perpendicular to the wave’s path. The effect is similar to when one end of a garden hose is jerked up and down, producing waves that travel along the hose’s length.
Seismologists Kiwamu Nishida of the University of Tokyo and Ryota Takagi of Tohoku University in Sendai, Japan, hunted for the elusive S waves using a network of 202 seismic stations in Japan. Typically, the waves are lost within Earth’s natural seismic background noise. By combining and analyzing the data collected by the extra-sensitive seismometers, however, the researchers were able to tease out the S wave signals.

The waves originated from a North Atlantic cyclone, the researchers found. That storm actually produced two types of S waves. SV waves shift material vertically relative to Earth’s surface and can form from P waves. SH waves shift material horizontally and their origins are more of a mystery. Those SH waves may form from complex interactions between the ocean and seafloor, Nishida says.

Combining measurements of P, SV and SH waves will “ultimately provide better maps of Earth’s mantle and maybe even the core,” says Keith Koper, a seismologist at the University of Utah in Salt Lake City. Koper and colleagues report similar observations of S waves generated in the Pacific Ocean and detected by a Chinese seismic network in the Sept. 1 Earth and Planetary Sciences Letters. “It’s nice to see someone else get similar results —it makes me feel more confident about what we observed,” Koper says.

Two days after my first daughter was born, her pediatrician paid a house call to examine her newest patient. After packing up her gear, she told me something alarming: “For the next few months, a fever is an emergency.” If we measured a rectal temperature at or above 100.4° Fahrenheit, go to the hospital, she said. Call her on the way, but don’t wait.

I, of course, had no idea that a fever constituted an emergency. But our pediatrician explained that a fever in a very young infant can signal a fast-moving and dangerous bacterial infection. These infections are rare (and fortunately becoming even rarer thanks to newly created vaccines). But they’re serious, and newborns are particularly susceptible.

I’ve since heard from friends who have been through this emergency. Their newborns were poked, prodded and monitored by anxious doctors, in the hopes of quickly ruling out a serious bacterial infection. For infants younger than two months, it’s “enormously difficult to tell if an infant is seriously ill and requires antibiotics and/or hospitalization,” says Howard Bauchner, a pediatrician formerly at Boston University School of Medicine and now editor in chief of the Journal of the American Medical Association.

A new research approach, described in two JAMA papers published in August, may ultimately lead to better ways to find the cause of a fever.

These days, for most (but not all) very young infants, their arrival at a hospital will trigger a workup that includes a urine culture and a blood draw. Often doctors will perform a lumbar puncture, more commonly known as a spinal tap, to draw a sample of cerebrospinal fluid from the area around the spinal cord.

Doctors collect these fluids to look for bacteria. Blood, urine and cerebrospinal fluid are smeared onto culture dishes, and doctors wait and see if any bacteria grow. In the meantime, the feverish infant may be started on antibiotics, just in case. But this approach has its limitations. Bacterial cultivation can take several days. The antibiotics may not be necessary. And needless to say, it’s not easy to get those fluids, particularly from a newborn.

Some scientists believe that instead of looking for bacteria or viruses directly, we ought to be looking at how our body responds to them. Unfortunately, the symptoms of a bacterial and viral infection are frustratingly similar. “You get a fever. You feel sick,” says computational immunologist Purvesh Khatri of Stanford University. Sadly, there are no obvious telltale symptoms of one or the other, not even green snot. In very young infants, a fever might be the only sign that something is amiss.
But more subtle clues could betray the cause of the fever. When confronted with an infection, our immune systems ramp up in specific ways. Depending on whether we are fighting a viral or bacterial foe, different genes turn up their activity. “The immune system knows what’s going on,” Khatri says. That means that if we could identify the genes that reliably get ramped up by viruses and those that get ramped up by bacteria, then we could categorize the infection based on our genetic response.

That’s the approach used by two groups of researchers, whose study results both appear in the August 23/30 JAMA. One group found that in children younger than 2, two specific genes could help make the call on infection type. Using blood samples, the scientists found that one of the genes ramped up its activity in response to a viral infection, and the other responded to a bacterial infection.

The other study looked at immune responses in even younger children. In infants younger than 60 days, the activity of 66 genes measured in blood samples did a pretty good job of distinguishing between bacterial and viral infections. “These are really exciting preliminary results,” says Khatri, who has used a similar method for adults. “We need to do more work.”

Bauchner points out that in order to be useful, “the test would have to be very, very accurate in very young infants.” There’s very little room for error. “Only time will tell how good these tests will be,” he says. In an editorial that accompanied the two studies, he evoked the promise of these methods. If other experiments replicate and refine the results of these studies, he could envision a day in which the parents of a feverish newborn could do a test at home, call their doctor and together decide if the child needs more care.

That kind of test isn’t here yet, but scientists are working on it. The technology couldn’t come soon enough for doctors and parents desperate to figure out a fever.

A second kind of crow, native to Hawaii, joins the famous New Caledonian crows as proven natural tool-users.

Tested in big aviaries, Hawaiian crows (Corvus hawaiiensis) frequently picked up a little stick and deftly worked it around to nudge out hard-to-reach tidbits of meat that researchers had pushed into holes in a log, scientists report September 14 in Nature.

“A goosebump moment,” says study coauthor Christian Rutz of his first sight of Hawaiian crows tackling the test. Their nimble handling is “not some little fluke where a bird picks up a stick and pokes it in a hole,” he says. Anecdotes of such flukes abound, especially for crows. What’s rare are demonstrations that most able-bodied adults in a species show a capacity for tool use in chores important for life in the wild. Because Hawaiian crows are extinct in the wild, Rutz and his colleagues had the bittersweet ability to test literally all adult members of the species. Youngsters too developed tool skills on their own.

Rutz, of the University of St. Andrews in Scotland, has worked with New Caledonian crows, which routinely shape and wield food-snagging tools. These birds, like the Hawaiian crows, are native to remote tropical islands. So is the Galapagos woodpecker finch, one of the handful of other bird species proven expert in tool use. Remote islands may favor the evolution of such capacities, Rutz muses. There are no true woodpeckers to compete with birds for treats in crevices there. And few predators lurk to pounce on a bird distracted with its head practically in a hole.
GOOD STICKWORK A Hawaiian crow manipulates a twig in its beak to wiggle out a meaty tidbit hidden in a log. Crows dissatisfied with sticks that researchers set out for snagging food sometimes flew into the shrubbery and selected their own tools for the task.

Use it or lose it, triathletes.

Muscles don’t have long-term memory for exercises like running, biking and swimming, a new study suggests. The old adage that once you’ve been in shape, it’s easier to get fit again could be a myth, at least for endurance athletes, researchers in Sweden report September 22 in PLOS Genetics.

“We really challenged the statement that your muscles can remember previous training,” says Maléne Lindholm of the Karolinska Institute in Stockholm. But even if muscles forget endurance exercise, the researchers say, other parts of the body may remember, and that could make retraining easier for people who’ve been in shape before.
Endurance training is amazingly good for the body. Weak muscle contractions, sustained over a long period of time — as in during a bike ride — change proteins, mainly ones involved in metabolism. This translates into more energy-efficient muscle that can help stave off illnesses like diabetes, cardiovascular disease and some cancers. The question is, how long do those improvements last?

Previous work in mice has shown that muscles “remember” strength training (SN: 9/11/10, p. 15). But rather than making muscles more efficient, strength-training moves like squats and push-ups make muscles bigger and stronger. The muscles bulk up as they develop more nuclei. More nuclei lead to more production of proteins that build muscle fibers. Cells keep their extra nuclei even after regular exercise stops, to make protein easily once strength training restarts, says physiologist Kristian Gundersen at the University of Oslo in Norway. Since endurance training has a different effect on muscles, scientists weren’t sure if the cells would remember it or not.
To answer that question, Lindholm’s team ran volunteers through a 15-month endurance training experiment. In the first three months, 23 volunteers trained four times a week, kicking one leg 60 times per minute for 45 minutes. Volunteers rested their other leg. Lindholm’s team took muscle biopsies before and after the three-month period to see how gene activity changed with training. Specifically, the scientists looked for changes in the number of mRNAs (the blueprints for proteins) that each gene was making. Genes associated with energy production showed the greatest degree of change in activity with training.
At a follow-up, after participants had stopped training for nine months, scientists again biopsied muscle from the thighs of 12 volunteers, but didn’t find any major differences in patterns of gene activity between the previously trained legs and the untrained legs. “The training effects were presumed to have been lost,” says Lindholm. After another three-month bout of training, this time in both legs, the researchers saw no differences between the previously trained and untrained legs.
While this study didn’t find muscle memory for endurance — most existing evidence is anecdotal — it still might be easier for former athletes to get triathalon-ready, researchers say. The new result has “no bearing on the possible memory in other organ systems,” Gundersen says. The heart and cardiovascular system could remember and more easily regain previous fitness levels, for example, he says.

Even within muscle tissue, immune cells or stem cells could also have some memory not found in this study, says molecular exercise physiologist Monica Hubal of George Washington University in Washington, D.C. Lindholm adds that well-trained connections between nerves and muscles could also help lapsed athletes get in shape faster than people who have never exercised before. “They know how to exercise, how it’s supposed to feel,” Lindholm says. “Your brain knows exactly how to activate your muscles, you don’t forget how to do that.”

To human observers, bumblebees sipping nectar from flowers appear cheerful. It turns out that the insects may actually enjoy their work. A new study suggests that bees experience a “happy” buzz after receiving a sugary snack, although it’s probably not the same joy that humans experience chomping on a candy bar.

Scientists can’t ask bees or other animals how they feel. Instead, researchers must look for signs of positive or negative emotions in an animal’s decision making or behavior, says Clint Perry, a neuroethologist at Queen Mary University of London. In one such study, for example, scientists shook bees vigorously in a machine for 60 seconds — hard enough to annoy, but not hard enough to cause injury — and found that stressed bees made more pessimistic decisions while foraging for food.
The new study, published in the Sept. 30 Science, is the first to look for signs of positive bias in bee decision making, Perry says. His team trained 24 bees to navigate a small arena connected to a plastic tunnel. When the tunnel was marked with a blue “flower” (a placard), the bees learned that a tasty vial of sugar water awaited them at its end. When a green “flower” was present, there was no reward. Once the bees learned the difference, the scientists threw the bees a curveball: Rather than being blue or green, the “flower” had a confusing blue-green hue.

Faced with the ambiguous color, the bees appeared to dither, meandering around for roughly 100 seconds before deciding whether to enter the tunnel. Some didn’t enter at all. But when the scientists gave half the bees a treat — a drop of concentrated sugar water — that group spent just 50 seconds circling the entrance before deciding to check it out. Overall, the two groups flew roughly the same distances at the same speeds, suggesting that the group that had gotten a treat first had not simply experienced a boost in energy from the sugar, but were in a more positive, optimistic state, Perry says.

In a separate experiment, Perry and colleagues simulated a spider attack on the bees by engineering a tiny arm that darted out and immobilized them with a sponge. Sugar-free bees took about 50 seconds longer than treated bees to resume foraging after the harrowing encounter.

The researchers then applied a solution to the bees’ thoraxes that blocked the action of dopamine, one of several chemicals that transmit rewarding signals in the insect brain. With dopamine blocked, the effects of the sugar treat disappeared, further suggesting that a change in mood, and not just increased energy, was responsible for the bees’ behavior.

The results provide the first evidence for positive, emotion-like states in bees, says Ralph Adolphs, a neuroscientist at Caltech. Yet he suspects that the metabolic effects of sugar did influence the bees’ behavior.
Geraldine Wright, a neuroethologist at Newcastle University in England, shares that concern. “The data reported in the paper doesn’t quite convince me that eating sucrose didn’t change how they behaved, even though they say it didn’t affect flight time or speed of flight,” she says. “I would be very cautious in interpreting the responses of bees in this assay as a positive emotional state.”

Butterflies look so delicate as they flitter from flower to flower. And yet, they are capable of migrating incredibly long distances. The monarch, for example, migrates between Canada and Mexico, covering distances of up to 4,800 kilometers, riding a combination of columns of rising air, called thermals, and air currents to travel around 80 to 160 kilometers per day.

No single monarch makes this entire journey, though. The round trip is done by a succession of as many as five generations of butterflies. But now scientists have found that there’s a species of butterfly that may rival the monarch’s migratory record — the painted lady (Vanessa cardui).

Painted ladies are found throughout much of the world, except for South America and Australia. They’ve been seen as far north as Svalbard, Norway, and nearly as far south as Antarctica. The butterflies are known to migrate, particularly between Europe and Africa, but their route has been largely unknown. Scientists had tracked the butterflies to northern Africa (the region known as the Maghreb), but there have been hints that they may fly across the Sahara. Two new studies back up this claim.

Gerard Talavera and Roger Vila of Harvard University visited four sub-Saharan nations — Benin, Chad, Ethiopia and Senegal — in 2014. They found butterflies moving south through Chad. There were dense aggregations of breeding butterflies in Benin and Ethiopia. And as the dry season approached in Senegal, the pair found butterflies old and worn, as if they had just finished a long, tortuous journey. Plus, the timing of these appearances coincided with the butterflies’ fall and winter disappearance from Europe.

“Taken together, the results of our fieldwork provide evidence suggesting that most European populations may undertake long-range migratory flights to tropical Africa, thus crossing the combined hazards of the Mediterranean Sea and the completely hostile Sahara,” the pair write September 21 in the Biological Journal of the Linnean Society.

If butterflies truly are making that flight, they could be traveling more than 4,000 kilometers in a single generation — a potential record for a migratory insect, the researchers note. And while this seems nearly impossible, it may not be. A previous study found that with favorable winds, painted butterflies could travel as fast as 45 kilometers per hour. At that speed, it would take them as little as four days to make it from Central Europe to Central Africa. Since an adult painted butterfly lives for around four weeks, such a journey is feasible, Talavera and Vila argue.

But this evidence is only circumstantial; it doesn’t prove that butterflies are truly making that journey. So while Tavalera and Vila were in sub-Saharan Africa, they collected hundreds of adult painted ladies and larvae. Some of these were used in a second study, published October 4 in Biology Letters and led by Constantí Stefanescu of the Natural History Museum of Granollers in Spain. In this study, the team analyzed the isotopes of hydrogen found in the adult butterflies’ wings.
The hydrogen in the water that falls as precipitation can come in different isotopes, or forms, that vary in the number of neutrons. The ratio of these isotopes varies geographically. And the ratio present wherever the butterflies lived as larvae correlates with that later found in the adults’ wings. So researchers can tell where the adults were born.

Stefanescu and his team analyzed butterflies collected in seven European and seven African countries and developed a rough map of where the adults were moving. Those in sub-Saharan Africa had indeed started in Europe. But those in the Maghreb came from both sub-Saharan Africa and Europe.

What explains all this movement? The butterflies are following a combination of prevailing winds and favorable conditions for breeding. As rains come and go, the butterflies breed and move on. And while crossing the Sahara may seem like quite a way to go just for some rainy days and lush vegetation, painted lady butterflies are hardly the only creatures willing to go that far, Stefanescu and his colleagues note. There are plenty of other insects that make such a journey — as well as billions of birds.

Pain is contagious, at least for mice. After encountering bedding where mice in pain had slept, other mice became more sensitive to pain themselves. The experiment, described online October 19 in Science Advances, shows that pain can move from one animal to another — no injury or illness required.

The results “add to a growing body of research showing that animals communicate distress and are affected by the distress of others,” says neuroscientist Inbal Ben-Ami Bartal of the University of California, Berkeley.
Neuroscientist Andrey Ryabinin and colleagues didn’t set out to study pain transfer. But the researchers noticed something curious during their experiments on mice who were undergoing alcohol withdrawal. Mice in the throes of withdrawal have a higher sensitivity to pokes on the foot. And surprisingly, so did these mice’s perfectly healthy roommates that were in nearby cages. “We realized that there was some transfer of information about pain” from injured mouse to bystander, says Ryabinin, of Oregon Health & Science University in Portland.

When mice suffered from alcohol withdrawal, morphine withdrawal or an inflaming injection, they become more sensitive to a poke in the paw with a thin fiber — a touchy reaction that signals a decreased pain tolerance. Mice that had been housed in the same room with the mice in pain also grew more sensitive to the poke, Ryabinin and colleagues found. These bystander mice showed other signs of heightened pain sensitivity, such as quickly pulling their tails out of hot water and licking a paw after an irritating shot.

The results are compelling evidence for the social transmission of pain, says neuroscientist Christian Keysers of the Netherlands Institute for Neuroscience in Amsterdam.

Pain’s contagion seemed to spread through the nose, further experiments revealed. After spending time with bedding used by mice in pain, healthy mice’s pain sensitivity went up. Some olfactory signals may have been transferred from the pained mouse onto the bedding before a mouse not experiencing pain showed up and began sniffing around. Ryabinin and colleagues are looking for compounds that might carry this pain signal mouse-to-mouse.

Implications for people are unknown. Humans’ olfactory skills fall short of other animals’, so it’s unclear whether odors can actually transmit information about pain, Ryabinin says.
While the data suggest that scent signals can carry the pain message, Keysers points out that other senses, such as hearing or vision, may be important too. Mice could see their compatriot in distress or hear pained squeaks. Still, the new paper fits with other work that shows “rodents exchange information about their states in many exciting and complex ways,” Keysers says.

A better understanding of the various ways animals can become more sensitive to pain may help explain more generally why pain comes and goes. The results suggest that sometimes, “there is no need for a specific injury for an animal to feel pain,” Ryabinin says. Instead, social factors or cues can influence pain perception. That idea may help explain the experience of some people who suffer from chronic pain, a condition that can begin mysteriously or persist long after an injury heals.

It may sound like science fiction, but it’s not: Scientists have created the first time crystal, using a chain of ions. Just as a standard crystal repeats in a regular spatial pattern, a time crystal repeats in time, returning to a similar configuration at regular intervals.

“This is a remarkable experiment,” says physicist Chetan Nayak of Microsoft Station Q at the University of California, Santa Barbara. “There is a ‘wow factor.’”

Scientists at the University of Maryland and the University of California, Berkeley created a chain of 10 ytterbium ions. These ions behave like particles with spin, a sort of quantum mechanical version of angular momentum, which can point either up or down. Using a laser, the physicists flipped the spins in a chain of ions halfway around, from up to down, and allowed the ions to interact so that the spin of each ion would influence the others. The researchers repeated this sequence at regular intervals, flipping the ions halfway each time and letting them interact. When scientists measured the ions’ spins, on average the ions went full circle, returning to their original states, in twice the time interval at which they were flipped halfway.
This behavior is sensible — if each flip turns something halfway around, it takes two flips to return to its original position. But scientists found that the ions’ spins would return to their original orientation at that same rate even if they were not flipped perfectly halfway. This result indicates that the system of ions prefers to respond at a certain regular period — the hallmark of a time crystal — just as atoms in a crystal prefer a perfectly spaced lattice. Such time crystals are “one of the first examples of a new phase of matter,” says physicist Norman Yao of UC Berkeley, a coauthor of the new result, posted online September 27 at arXiv.org.

Time crystals take an important unifying concept in physics — the idea of symmetry breaking — and extend it to time. Physical laws typically treat all points in space equally — no one location is different from any other. In a liquid, for example, atoms are equally likely to be found at any point in space. This is a continuous symmetry, as the conditions are the same at any point along the spatial continuum. If the liquid solidifies into a crystal, that symmetry is broken: Atoms are found only at certain regularly spaced positions, with voids in between. Likewise, if you rotate a crystal, on a microscopic level it would look different from different angles, but liquid will look the same however it’s rotated. In physics, such broken symmetries underlie topics ranging from magnets to superconductors to the Higgs mechanism, which imbues elementary particles with mass and gives rise to the Higgs boson.

In 2012, theoretical physicist Frank Wilczek of MIT proposed that symmetry breaking in time might produce time crystals (SN: 3/24/12, p. 8). But follow-up work indicated that time crystals couldn’t emerge in a system in a state of equilibrium, which is settled into a stable configuration. Instead, physicists realized, driven systems, which are periodically perturbed by an external force — like the laser flipping the ions — could create such crystals. “The original examples were either flawed or too simple,” says Wilczek. “This is much more interesting.”

Unlike the continuous symmetry that is broken in the transition from a liquid to a solid crystal, in the driven systems that the scientists used to create time crystals, the symmetry is discrete, appearing at time intervals corresponding to the time between perturbations. If the system repeats itself at a longer time interval than the one it’s driven at — as the scientists’ time crystal does — that symmetry is broken.

Time crystals are too new for scientists to have a handle on their potential practical applications. “It’s like a baby, you don’t know what it’s going to grow up to be,” Wilczek says. But, he says, “I don’t think we’ve heard the last of this by a long shot.”
There probably are related systems yet to be uncovered, says Nayak. “We’re just kind of scratching the surface of the kinds of amazing phenomena — such as time crystals — that we can have in nonequilibrium quantum systems. So I think it’s the first window into a whole new arena for us to explore.”

X-rays appear to be trickling away from Pluto, even though the dwarf planet has no obvious way of making the high-energy photons, a new study reports.

Given what researchers have learned about Pluto since the New Horizons spacecraft flew by in 2015 (SN: 8/8/15, p. 6), the discovery is surprising. For many planets and comets, X-rays are generated when the solar wind, a stream of charged particles from the sun, runs into neutral gas atoms or magnetic fields from these bodies. But the environment around Pluto isn’t conducive to producing X-rays: the dwarf planet has no measurable magnetic field, its atmosphere is very thin, and it’s losing that atmosphere at rates much lower than expected.
“We naively thought Pluto might be losing its atmosphere at the same rate as [some] comets,” says Carey Lisse, a planetary astronomer at the Applied Physics Laboratory in Laurel, Md. “We knew comets make X-rays, so we hoped that Pluto did, too.” Instead, interactions between the solar wind and a tenuous tail of methane gas hundreds of times longer than Pluto’s diameter might be the culprit, Lisse and colleagues suggest online October 25 on arXiv.org.

Lisse’s team used the Chandra X-ray telescope, once in 2014 and three more times in 2015, to look for Pluto X-rays. Chandra detected just seven photons streaming from Pluto in a total of about two days’ worth of observing time. Though the signal isn’t strong, that’s about six or seven more photons than expected based on New Horizons’ measurements of Pluto’s atmosphere and the solar wind.

“It’s a very puzzling finding,” says Konrad Dennerl, an astrophysicist at the Max Planck Institute for Extraterrestrial Physics in Garching, Germany. “I’m not fully convinced,” he adds. “It’s a very low signal.”

Lisse and collaborators note that the signal appears to follow Pluto across the sky. They detected X-ray photons on four separate occasions. The energy of the photons doesn’t appear to match that of the spurious X-ray noise that peppers the telescope, so the signal appears genuine. Still, Lisse and Dennerl are teaming up to get some Pluto time with another X-ray observatory, the European Space Agency’s XMM-Newton satellite.

“We understand that there’s a bit of skepticism,” Lisse says. “We’re going to do some follow-up with a totally different instrument to verify this.”

X-rays from Pluto aren’t just a quirky detail about this specific dwarf planet. If other bodies in the Kuiper belt, the ring of icy debris just past Neptune’s orbit, have atmospheres, then X-ray observations could help detect them.