The solar system doesn’t have a long, twisted tail after all.
Data from the Cassini and Voyager spacecraft show that the bubble of particles surrounding the solar system is spherical, not comet-shaped. Observing a spherical bubble runs counter to 55 years of speculation on the shape of this solar system feature, says Tom Krimigis of the Johns Hopkins Applied Physics Laboratory in Laurel, Md. He and colleagues report the result online April 24 in Nature Astronomy. “You can’t really argue with the new result,” says Merav Opher of Boston University, who was not involved in the study. “The data so loudly say that there is no tail.”
The bubble, called the heliosphere, is inflated by particles streaming from the sun and envelops all of the material in the solar system. Its shape is important because it provides clues about how the solar system interacts with interstellar space.
In the 1960s, researchers proposed that the heliosphere was either shaped like a comet or was spherical. Magnetic fields surrounding the sun and the planets look sort of like comets, with long tails extending behind them. So, scientists speculated that the heliosphere would have a tail, too. In 2013, data from the Interstellar Boundary Explorer, or IBEX, spacecraft found signs that the tail assumption was right. The probe counted the number of fast-moving atoms that are thought to be kicked inward from the edge of the solar system when they collide with charged particles from the sun. Detecting those atoms offers clues to the shape of the heliosphere, and the images suggested that solar system had a long, twisted tail that looked like a four-leaf clover (SN: 8/24/13, p. 9).
But it wasn’t clear from the data exactly how far away from the spacecraft the atoms were and therefore how far the heliosphere’s tail extended, Krimigis says. By combining more than a decade’s worth of data from the Voyager and Cassini probes, he and colleagues sought a clearer picture. The team specifically tracked how the abundance of the speedy atoms changed in different parts of the heliosphere as the intensity of charged particles streaming from the sun, the solar wind, waxed and waned.
At the front of the heliosphere, where the Voyager probes sit, when the intensity of the solar wind decreased, so did the abundance of speedy atoms. When it increased, the number went up, in lockstep. Looking at speedy atoms at the back of the heliosphere, the team saw the same changes. If there were a long tail, Krimigis says, the changes in the number of atoms wouldn’t be the same in both directions. Because the atoms would have farther to travel in a tail, it would take longer for their abundance to build up there again.
While the observational evidence now favors a spherical shape for the heliosphere, recent simulations suggest something more exotic. The bubble might actually be shaped like a croissant, Opher says. The simulations, which incorporate data from Voyager 1, show that the interaction of the magnetic fields from the sun and interstellar space squish the solar wind into two jets — what might be observed as two short tails. These jets haven’t been detected yet. But if they are, she says, they could give clues to other sets of jets seen in the universe such as those shooting from young stars or possibly even black holes.
Most people who eat octopus prefer it immobile, cut into pieces and nicely grilled or otherwise cooked. For some, though, the wiggly, sucker-covered arms of a live octopus are a treat — even though those arms can stick to the throat and suffocate the diner if they haven’t been chopped into small enough pieces.
Dolphins risk the same fate when eating octopus — and they can’t cook it or cut it up with a chef’s knife. “Octopus is a dangerous meal,” notes Kate Sprogis of Murdoch University in Australia. Even if a dolphin manages to remove an octopus’ head, it still has to deal with those sucker-covered tentacles. “The suckered arms would be difficult to handle considering dolphins don’t have hands to assist them,” Sprogis says.
A group of hungry dolphins off the coast of Western Australia have figured out a solution. They shake and toss their prey until the head falls off, the animal is in pieces and its arms are tender and not wiggling anymore, Sprogis and her colleagues report April 2 in Marine Mammal Science.
The behavior, never before reported, was discovered during observations between March 2007 and August 2013 of bottlenose dolphins living in the waters off Bunbury, Western Australia. During that time, researchers witnessed 33 events in which dolphins handled an octopus with two different methods.
In one technique, a dolphin held an octopus in its mouth and shook it, slamming its prey into the water’s surface until the meal was in pieces. Each dolphin would repeat its preferred motion, or combine the two, usually around a dozen times, over several minutes until the octopus was safe to eat. (See video below.)
“If the dolphins haven’t prepared their meal enough, then this can cause problems,” Sprogis notes. There have been two dead dolphins found in this area with whole octopuses lodged in their throats. The researchers assume that the dolphins suffocated.
Dolphins have garnered a reputation for tackling difficult-to-eat foods in creative ways. Some have been spotted using cone-shaped sponges to flush out little fish from the sandy ocean floor. Others use a six-step process to prepare a cuttlefish meal. The Bunbury dolphins eat both octopus and cuttlefish, and those meals appear to be more common in the winter and spring, when waters are cooler, Sprogis notes. That may be when the octopus and cuttlefish breed and lose some of their camouflage abilities — making them easy prey for dolphins brave or knowledgeable enough to take advantage of the potential meal.
A stone tool found in Syria more than 80 years ago has sharpened scientists’ understanding of Stone Age networking.
Small enough to fit in the palm of an adult’s hand, this chipped piece of obsidian dates to between 41,000 and 32,000 years ago, say archaeologists Ellery Frahm and Thomas Hauck. It was fashioned out of volcanic rock from outcrops in central Turkey, a minimum of 700 kilometers from where the artifact was found, the researchers report in the June Journal of Archaeological Science: Reports. Until now, the earliest transport of obsidian into the Middle East was thought to have occurred between 14,500 and 11,500 years ago, when Natufian foragers began to live in year-round settlements (SN: 9/25/10, p. 14). Someone probably shaped the obsidian chunk into a usable tool near its Turkish source, say Frahm, of Yale University, and Hauck, of the University of Cologne in Germany. The tool, which could have been used for various cutting and scraping tasks, was then passed from one mobile group to another, perhaps several times, before reaching Syria’s Yabroud II rock-shelter. Along the way, the implement underwent reshaping and resharpening.
The most direct path between the Turkish and Syrian sites stretches about 700 kilometers. But hunter-gatherers meander, following prey animals and searching for other food. So, Stone Age bearers of the obsidian tool probably traveled considerably farther to reach one of several rock-shelters clustered near what’s now the Syrian town of Yabroud, the investigators say. “They didn’t type ‘Yabroud’ into a GPS unit and make their way to the rock-shelter as fast as possible,” Frahm says. Excavations at the Yabroud sites between 1930 and 1933 yielded the obsidian tool and hundreds of artifacts made from a type of rock called chert found a mere five to 10 kilometers away. Some researchers suspect the obsidian tool was mistakenly included among much older finds shortly after being excavated. But a copy of the lead excavator’s book describing his fieldwork, housed at Yale, confirms that the implement was found in sediment dating to around the time ancient humans and Neandertals inhabited the Middle East, Frahm says. Since excavators did not collect material for radiocarbon dating, Frahm and Hauck estimated the Syrian rock-shelter’s age by comparing its sediment layers and artifacts with those at several nearby, better-dated sites. Neandertals survived in the Middle East and elsewhere until at least 40,000 years ago (SN: 9/20/14, p. 11), so they might have been the final recipients of the obsidian tool. But Frahm considers Homo sapiens a better candidate. Humans occupied the Middle East and nearby regions throughout the period when the tool may have been used. No hominid fossils have been recovered at the Syrian site.
Using a portable X-ray device, Frahm and Hauck determined the chemical composition of the obsidian tool and 230 obsidian samples from known sites throughout southwestern Asia. That let the researchers match the Syrian find to its Turkish source.
Outside the Middle East, previous evidence suggested that long-distance obsidian transport occurred in Stone Age Eurasia. Researchers reported in 1966 that two obsidian pieces with sharpened edges found at northern Iraq’s Shanidar Cave originated roughly 450 kilometers to the north. That analysis used an earlier technique for measuring a stone’s chemical composition. Shanidar’s obsidian finds date to about the same time as that of the Yabroud II obsidian tool, perhaps to as early as 48,000 years ago, Frahm says.
Recent investigations of obsidian artifacts at late Stone Age sites in Eurasia not far from Shanidar Cave, in what’s now Armenia and Georgia, indicate that hunter-gatherers there also exploited vast territories, says archaeologist Daniel Adler of the University of Connecticut in Storrs. Frahm has contributed to some of that research. As for the Yabroud II obsidian tool, “a 700-kilometer transport distance is fully within the realm of possibility for a single person over an extended period of time,” Adler says.
Eurasia may have a far older tradition of extensive hunter-gatherer networking than the Middle East does. Evidence of long-distance obsidian transport in Armenia dates to as early as around 500,000 years ago, notes archaeologist Andrew Kandel of the University of Tübingen in Germany. That means Neandertals or other now-extinct hominid species first transported obsidian across hundreds of kilometers, he says.
People may think they act independently. But we catch social behaviors faster than colds. Whether or not we vote, try a new food or wear clear plastic pants will have something to do with whether other people are doing it. Unfortunately, it’s often hard to prove exactly how contagious a particular behavior is, or which behaviors will actually spread.
A new study shows that among runners using a fitness social network, logging miles is infectious — if the runner you’re comparing yourself to is slightly worse than you. The work shows a clever new way to determine if a behavior is socially contagious. But the results also confirm something about runners: We might be a little too competitive.
Glance at any group of kids with fidget spinners or teens wearing the same brand of shoes, and it’s easy to buy into the idea of social contagions. But it’s actually not so simple to distinguish between that kind of peer influence and other outside factors. says Johan Ugander, an applied mathematician at Stanford University. It’s easy for marketers to say they want something to go viral. But it’s a lot harder to be confident that the thing that’s spreading is really a social contagion and not a common factor like location or a group of people with common interests.
For one thing, birds of a feather really do flock together. People become friends because they have things in common. You might share an important article to Facebook, and find a friend has shared the same article 20 minutes later. But is that because you influenced your friend? Or because you have the same interests and read the same kind of articles, and you just happened to see it 20 minutes before they did?
Similarly, people tend to have friends who are near them geographically. So if two neighbors gain weight, Ugander notes, it could be “because the McDonald’s opened down the street, not because I gained weight then you gained weight.”
To get around this problem of homophily, Sinan Aral, a computational social scientist at MIT, decided to look at a single behavior — running. “Running is one of the most pervasive forms of this type of exercise,” he says. “I thought it would be most generalizable.”
Runners also like to log their miles and share them with their peers. Aral was able to get data from one of several social media platforms designed for jogging buffs. Aral can’t disclose the exact app or program he used in the study (and received some funding from), but there are a few social apps out there that fit the bill, including MapMyRun, RunKeeper and Strava. Aral ended up with a vast, anonymized dataset of more than 1.1 million runners who logged more than 359 million kilometers (223 million miles) over five years. To figure out if running is contagious, there would have to be a way to make some people run and other people stay home. “The ideal study to show [a causal effect] would be to go around with a cattle prod, prodding some people to exercise more,” but leaving others alone, Aral says. “But that’s not an experiment you can run.” (Obviously.)
So Aral and colleagues used the weather as their cattle prod. Good weather beckons a runner outdoors. Rain, snow, sleet or hail will keep a runner off the street. The researchers combed through data, noting what the weather was like on a given day and how far a runner went. They then compared that runner’s logs to their friends in other cities — places far enough away that the weather would be different. With the weather serving as the prod for some to put on their running shoes or keep others at home, the scientists got a good idea of who socially infected who with the running bug.
They found that for every additional kilometer run by someone’s distant friends, the runner would add another 0.3 km (0.18 mi). Timewise, a friend spending an additional 10 minutes running will inspire an extra three minutes in someone else, Aral and his group reported April 18 in Nature Communications.
But social contagion didn’t affect everyone the same way. The runners most influenced were those who compared themselves to runners slightly worse than they were. “In the loose analogy of a race, I’m more motivated by the guy behind me than I am motivated by the person ahead of me,” Aral says.
The study also showed some gender effects. Men were most influenced by other men, but were also ready to outrace the women. In contrast, women did not tend to be influenced by men. “There have been experimental studies showing men are more competitive with one another, while women are more self-directed and motivated by internal factors,” Aral says. But that doesn’t mean that women aren’t competitive. Women were just influenced by other women.
“It’s usually very difficult to identify causal effects from correlational data, in the absence of a randomized controlled trial,” says Edoardo Airoldi, a statistician at Harvard University. The data in this study may not translate to other behaviors — even to other forms of exercise. But that isn’t the point. The beauty, Airoldi says, is in the methods. “People should know you can use the weather as an instrument to uncover patterns of human behavior that are otherwise hard to elicit,” he says.
Ugander is also a fan of the new study, but he notes that this doesn’t mean all social behaviors, or even all sports, will prove similarly contagious, especially with regard to the gender differences. “It’s not clear that that will generalize to yoga or some other sport with other gender norms,” he says.
We don’t really know what exactly drives social contagion. One theory — the complex contagion theory — posits that costly behaviors (like going for an exhausting run) require a lot of signals from a lot of people. In other words, the more people in your network are running, the more likely you are to run.
Another theory developed by Ugander’s group posits that it’s not quantity that matters, but variety, a theory called structural diversity. Your family all going running is one thing. A family member, a friend and coworker is another. “If you’re getting it from two people from different parts of your life, say sibling and coworkers, it carries more weight,” Ugander says. “But two coworkers probably got it from each other.”
A third theory suggests that embeddedness — the number of mutual connections — matters most. After all, seeing all your friends virtuously running and knowing that they are also seeing each other live the wholesome life is a lot of peer pressure.
The data from Aral’s group suggests that for running, embeddedness and structural diversity may prove the most catching. “This doesn’t mean the complex theory is wrong,” Aral notes. “We just didn’t see it for running.”
Aral himself is a runner, and admits he’s not immune to the social contagion he found. “When I have friends who are close to me in fitness in terms of their level of activity, I may be influenced,” he says. “I also feel like I’d be more influenced by someone who was slightly less of a runner than I am. If they were running more, I would think, ‘Wow, even so-and-so is out there, I need to get out there.’” This social behavior might be catching, but the vulnerable population already has a raging competition infection.
A weird new particle imitator flouts the established rules of particle physics. The discovery could help scientists simulate how particles behaved just after the Big Bang or lead to the development of new devices with unusual electromagnetic properties.
The curious new phenomenon involves a particle-like entity called a quasiparticle, formed from a jostling mosh pit of electrons that collectively act like a single particle in a solid. Found in a compound of lanthanum, aluminum and germanium, the new quasiparticle is a bit of a renegade, physicist M. Zahid Hasan of Princeton University and colleagues report June 2 in Science Advances. Known as a type-II Weyl fermion, the quasiparticle breaks a rule called Lorentz symmetry, which states that the laws of physics are the same no matter the observer’s perspective, whether moving or stationary. Lorentz symmetry is the foundation of Einstein’s special theory of relativity, which details the physics of observers zipping along near the speed of light. For a real particle, violating Lorentz symmetry would be an unallowable faux pas, but for quasiparticles, the rules are looser, so type-II Weyl fermions can behave in a way a normal particle wouldn’t.
Fermions are a class of elementary particle that includes quarks, which make up protons and neutrons, and electrons. There are three different types of fermions: Dirac, Majorana and Weyl. Dirac fermions are the garden-variety type and include electrons and quarks. Majorana fermions are their own antiparticles. Neutrinos, notoriously lightweight and elusive particles, could be either Majorana or Dirac fermions; scientists aren’t yet sure which.
Weyl fermions are a massless variety of fermion. No examples have been found in particle physics. But the quasiparticle version of Weyl fermions burst onto the scene in 2015, when scientists first discovered them in a compound made of tantalum and arsenic (SN: 8/22/15, p. 11). Soon, scientists realized that their Lorentz-violating relatives, type-II Weyl fermions, might likewise pop up in solids.
In the new study, Hasan and colleagues measured the relationship between the energy and momentum of the quasiparticles, showing that they were consistent with type-II Weyl fermions. Although previous experiments have shown hints of the unusual quasiparticles, those measurements were skin-deep, assessing particles only on the surface of the material, Hasan says. With surface measurements alone, it’s hard to confirm the type-II Weyl fermions are there, says physicist Alexey Soluyanov of ETH Zurich. But Hasan and colleagues peered inside the material. “Experimentally, this work really is a nice example,” Soluyanov says.
In solids, Weyl fermions lead to unusual behavior. Put a normal material in a magnetic field, and resistance to the flow of electricity grows, but in a solid with Weyl fermions, a magnetic field makes current flow more easily. Type-II Weyl fermions are even stranger, due to their Lorentz-violating properties. In a material with these quasiparticles, a magnetic field in one direction can increase conductivity, while in another direction it can decrease conductivity. “This type of thing can have interesting applications,” says Hasan. “In a single material, just by changing the direction of the field, now we can get different behaviors,” flipping between insulating and conducting, for example. The new material could also provide insight for particle physicists. “Of course, people have wondered what happens when you break Lorentz invariance,” says physicist Adolfo Grushin of Institut Néel in Grenoble, France. Type-II Weyl fermions could help scientists better understand theories that violate the rule. “It’s a good test-bed,” says Grushin.
For example, Hasan says, “we can test theoretical ideas in the early universe,” simulating how particles may have behaved just after the Big Bang, when Lorentz symmetry may not have been obeyed.
PORTLAND, ORE. — A great flower shape for a moth trying to get a drink in the dark turns out to be awful from the plant’s point of view.
Offering hawk moths (Manduca sexta) a range of 3-D printed flowers with different curvatures shows that a moderately curved trumpet shape lets moths sip most efficiently, Foen Peng reported June 24 at the Evolution 2017 meeting. That’s a win for a nocturnal flying insect searching for nectar. Yet drinking ease wasn’t best for the plant. During swift sips, the moths did less inadvertent bumping against the artificial flowers’ simulated sex organs than moths struggling to sip from an inconvenient shape. Less contact with real flower parts would mean less delivery and pickup of pollen.
Peng, of the University of Washington in Seattle, offered the moths three other shapes besides the gently curved trumpet. The best for the plant was a flat-topped “flower” with a right angle drop to a nectar well in the center. Previous work suggested that lack of curves made it very difficult for hawk moths hovering above a flower and extending their tonguelike proboscises to tap and probe the way to nectar in dim light.
Pollination at first glance may look like an easy mutualism evolving with the best interests of both plant and pollinator. But these experiments reveal a hidden, underlying conflict, Peng said.
Out-of-whack microbes in the vagina can raise HIV risk — and now there’s evidence that the makeup of the penis microbiome matters, too. The greater the number of anaerobic bacteria tucked under the foreskin, the more likely an uncircumcised man is to become infected with the virus, researchers report July 25 in mBio.
“This mirrors what’s been seen in women, but it’s the first study of its kind in men,” says Deborah Anderson, a microbiologist and gynecologist at Boston University School of Medicine. The data come from heterosexual Ugandan men followed for two years as part of a larger study on circumcision. Researchers swabbed the men’s penises to collect bacteria samples at the beginning of the two-year study. Then they compared the penile bacterial composition of the 46 uncircumcised men who became infected with HIV over the course of the study with that of 136 uncircumcised men who didn’t.
The total amount of penile bacteria didn’t differ, but men with higher levels of anaerobic bacteria were more likely to have contracted HIV, researchers found. Having 10 times more Prevotella, Dialister, Finegoldia and Peptoniphilus bacteria raised the risk of contracting HIV by 54 to 63 percent after controlling for other factors that might affect risk, such as condom use habits and number of sexual partners.
The results might help explain why circumcision cuts the risk of HIV, says Thomas Hope, a cell biologist at Northwestern University Feinberg School of Medicine in Chicago: Removing the flap of foreskin takes away a moist hideout for bacteria that thrive in oxygen-starved environments. But, Hope cautions, the study only draws an association between the microbiome and HIV — not necessarily a cause and effect.
It’s not clear how certain bacteria might raise HIV risk, but the new study revealed one possible clue: Men with more anaerobic penis bacteria also had higher levels of inflammatory cytokine proteins, which call immune cells to the scene.
“Specific bacteria might cause inflammatory response that would cause the immune cells to congregate in the penis, where they’re more likely to be exposed to the virus,” says study coauthor Cindy Liu, a pathologist at George Washington University in Washington, D.C. HIV targets particular immune cells, so recruiting an immune response to the penis might have an unintended consequence — a free ferry ride for the virus into the bloodstream. Liu and colleagues hope to test that explanation more thoroughly by looking at tissue samples from circumcised foreskins, and seeing whether there’s a relationship between the penis microbiome and the kinds of immune cells found in the foreskin.
Some of these same bacteria are also linked to increased HIV risk in women, and the microbes can be swapped between partners during sex. While practicing safe sex is still the best HIV-prevention strategy, topical creams that adjust the bacterial balance on the penis might someday help lower the risk of infection, Liu says.
After some initial waffling, President Trump signed a budget bill March 23 that lays out spending details for the rest of fiscal year 2018, which goes through September. The $1.3-trillion spending deal boosts funding for nearly all science agencies, avoiding cuts the White House had proposed.
These increases stem largely from February’s budget deal, which raised caps on discretionary spending. The National Institutes of Health, which got a $3 billion bump over the 2017 level, comes out especially well, as does the Department of Energy’s Office of Science. It receives an $868 million boost, a 16 percent increase. Climate science research and programs across several agencies also avoided big cuts that the administration had proposed. The one outlier: the Environmental Protection Agency. At about $8.1 billion, its budget remains flat at the 2017 level.
Here are a few details that stood out to us.
NIH NIH gets an extra $414 million for Alzheimer’s disease research, along with $400 million for the BRAIN Initiative, a research project announced by President Obama in 2013 that aims to improve our understanding of the human brain. DOE Office of Science Trump had proposed eliminating the Advanced Research Projects Agency-Energy, which funds research into long-shot but potentially high-reward projects. But the bill allocates an additional $47 million to the agency, a resounding rejection of the administration’s request.
NASA The Wide-Field Infrared Survey Telescope, or WFIRST, is a proposed mission to study, in part, planets orbiting stars outside the solar system. It was recommended by the most recent decadal survey for astrophysics and remains one of NASA’s top astrophysics priorities after the James Webb Space Telescope. Trump has proposed canceling WFIRST, but the spending package includes $150 million for the telescope. Four earth science programs that Trump had targeted for elimination were also funded.
CDC The agreement includes wording clarifying that the Centers for Disease Control and Prevention isn’t barred from studying gun violence under a 1996 amendment. The CDC has shied away from such research since that time. On Twitter, some celebrated the news, but others hailed it as a partial victory. Megan Ranney, an emergency physician and researcher at Brown University in Providence, R.I., who studies firearm injuries, tweeted the “announcement changes nothing. The issue has been, and continues to be, lack of appropriations for research.”
EPA The agency’s overall budget remains flat as do projects with EPA’s Office of Science & Technology. Although not research related, the agency’s regulatory programs are cut by $23.5 million. The bill includes wording that prohibits the regulation of lead content in ammunition and fishing tackle and exempting livestock producers from EPA greenhouse gas regulations.
USGS The bill includes $23 million for ShakeAlert, an earthquake early warning system on the West Coast that could be rolled out as early as October, another project that had been facing elimination. All eight of the U.S. Geological Survey’s climate science centers are funded in the agreement. The administration had proposed cutting their numbers in half, to four.
It’s tough to be a frog once a killer skin fungus moves in. But, in Panama, the amphibians might be fighting back, researchers propose.
More than a decade ago, an amphibian-killing chytrid fungus nicknamed Bd swept through the country. Now some frog species that had nearly vanished from three regions are growing easier to spot again. But tests of the pathogen find no signs that it is weakening, says disease ecologist Jamie Voyles at the University of Nevada, Reno. With the fungus as dangerous as ever, frogs becoming resistant to the pathogen might be enabling the recovery, Voyles and her colleagues report in the March 30 Science. Despite any glimmer of hope, it’s too early to celebrate frog recovery, protests ecologist Karen Lips at the University of Maryland in College Park. She doesn’t doubt that researchers have found frogs in the devastated regions, but wants more rigorous monitoring before talking population trends.
The three areas in the study have special resonance. They’re where Lips and other scientists set up a disaster watch as they realized that Bd, short for Batrachochytrium dendrobatidis, was sweeping through Central America, killing many amphibians in its path. As the deadly wave approached, the researchers collected data and living animals in the hope they would help in before-and-after studies. The fungus attacked Lips’ site, El Copé, in 2004 and the other two sites in 2006 and 2007.
Voyles was working at El Copé as a graduate student when Bd arrived. She remembers the abundance of sick and dying animals, and the task of collecting the dead. “That was shocking, really — there’s just no other word for it.”
Using archived, frozen samples of the fungus from those sites, Voyles and colleagues present the first comparison of Bd as it was in 2004 versus in 2012 to 2013, when amphibian communities showed signs of recovering. At first, Voyles suspected that the pathogen was growing less dangerous. Bd attacks a wide range of hosts but evolutionarily speaking, pathogens don’t persist if they drive too many of their hosts extinct. A waning fungal menace could have explained how nine frog species that had almost disappeared in the area were now easier to spot. But the pathogen appears as lethal as ever, she and her colleagues report. Compared with the older versions, the more recent fungus samples grew and reproduced at about the same speeds, and inhibited immune cells at about the same rates. All fungi killed the test frogs of two species.
“That’s an important result,” says evolutionary ecologist James Collins of Arizona State University in Tempe. Biologists who study the interplay of pathogen and host often ask how the two change in relation to one another over time. But having real data on the relationship is much rarer. Also important, he says, is recognizing that “many species at the Panama sites are still missing, so wholesale recovery isn’t occurring.” To explain the encouraging cases, the researchers propose that in some species, frog skin secretions may be getting better at repelling the fungus. For wild animals of six amphibian species, secretions from pre-disease days were worse at inhibiting fungal growth in a lab test than secretions from the same species at sites that the fungus had hit. In another test, secretions from wild variable harlequin frogs (Atelopus varius) were about eight times as effective at inhibiting the fungus as were those from zoo animals descended from frogs collected before Bd reached their site.
Of the many amphibian populations that Bd savaged around the world (SN: 3/5/16, p. 14), a few have bounced back in numbers. Sierra Nevada yellow-legged frogs now abound again in the California mountains, ecologist Vance Vredenburg of San Francisco State University points out. Yet these animals are descendants of a worryingly tiny percentage of the original, diverse population. Despite rebounds, attacks by deadly fungi are still “a really big deal,” he says.
NASA is stepping up its search for planets outside our solar system. Its next exoplanet hunting telescope, the Transiting Exoplanet Survey Satellite (TESS), is due to launch from Cape Canaveral on the evening of April 16.
Following the Kepler space telescope’s discovery of more than 5,000 possible exoplanets since 2009, TESS will continue the galactic census — flagging more planetary candidates for further study.
Astronomers expect TESS to find about 20,000 planets in its first two years in operation, focusing on nearby, bright stars that will be easy for other telescopes to investigate later. About 500 of those expected exoplanets would be less than twice the size of Earth — and therefore may be good places to look for life. The TESS mission is “a whole new opening for exoplanet studies,” MIT astronomer Sara Seager, TESS’ deputy science director, said during a news conference describing the upcoming launch. TESS will be the first NASA science mission launched on the SpaceX Falcon 9 rocket. Once in orbit, the spacecraft will trace an unusual, elliptical path between Earth and the moon that will enable it to observe at least 85 percent of the sky — 350 times as much sky as Kepler saw. Most of the planets found by Kepler orbit stars 1,000 light-years away or farther. TESS will focus on 200,000 stars that are a few hundred light-years away at most, and shine between 30 to 100 times brighter on average than Kepler’s.
The brighter the star, the easier it is to determine its planet’s characteristics, such as its mass and whether it has an atmosphere, Seager says. “Photons are our currency — the more, the better,” she says.
That follow-up will help TESS avoid some of Kepler’s pitfalls. Because Kepler’s stars were so far and so dim, some of its planet candidates were confirmed as actual planets only by statistics rather than by other telescopes. And not all those confirmations may stick. A recent paper posted at arXiv.org showed that Kepler 452b, an Earth-sized planet that orbits a sunlike star at the same distance Earth orbits the sun, may be a mirage (SN: 8/22/15, p. 16). Many of TESS’ planets won’t face the same uncertainty. But the way TESS will search for exoplanets is the same as Kepler: The satellite will watch stars for signs of dimming, which can indicate that a planet is transiting, or crossing in front of, the star. Measuring how much starlight is blocked can tell astronomers the size of the planet.
Once TESS finds a planet, astronomers will need more information to understand its qualities, such as whether it’s rocky or gassy (SN Online: 6/19/17). For that, other telescopes will follow up. Ground-based telescopes will measure the gravitational tug of a planet on its host star to learn the planet’s density, which is a clue to its composition. Astronomers plan to measure masses for at least 50 TESS planets that are smaller than Neptune in the hopes that many of them will have rocky, and therefore potentially habitable, surfaces. NASA’s James Webb Space Telescope, now scheduled to launch in 2020, will then check some of those planets for signs of life (SN: 4/30/16, p. 32).
“This is one of the major questions that TESS is intended to answer: Where will we be pointing Webb?” said the mission’s principal investigator, MIT astronomer George Ricker, at the press conference. Webb will peer at the starlight filtering through planetary atmospheres to try to detect molecules that could be produced by something living on the surface.
It will take a few months for TESS to swing into its regular orbit before it begins collecting data. At that point, it will be able to use the moon’s gravity to stabilize itself for decades in orbit without using extra fuel. The mission is set to last two years, but could continue taking data almost indefinitely.
“TESS is not going to be limited by any expendable or other aspects,” Ricker said. “It will be basically limited by how long NASA has the patience to fund the mission.”
