DENVER — An invasive beetle has unexpected — and potentially troublesome — tastes in trees. Now two new studies are clarifying the insects’ dining habits, researchers reported at the annual Entomological Society of America meeting.
Metallic-green Asian beetles called emerald ash borers (Agrilus planipennis) have devastated wide swaths of forest in North America. For years, researchers believed that only various kinds of ash trees were at risk. But in 2014, researchers noticed infestations in white fringe trees (Chionanthus virginicus), a multi-stemmed tree native to the southeastern United States with flowers like a cluster of streamers. And after looking at trees related to ashes, researchers reported lab evidence in 2017 that the beetle larvae can grow to adulthood in the Manzanilla variety of commercial olive trees (Olea europaea). Whether the beetle poses a serious or slight risk to the overlooked targets is still being researched. Emerald ash borers, accidentally imported probably in wood packing materials during the 1980s or 1990s, have killed hundreds of millions of ash trees in 31 states and two Canadian provinces. Larvae chewing tunnels through trees’ internal nutrient channels can doom a tree. It’s “a major, major pest,” says entomologist Jackie Hoban of the University of Maryland in College Park. “It’s so sad — you see entire patches of trees just dead.” Lab tests of the recently discovered threat to olive trees show that adult borers don’t eat as much of these leaves as they do of ash leaves, forest entomologist Donnie Peterson of Wright State University in Dayton, Ohio, reported November 6 at the meeting. These adults also die prematurely if those leaves are the only food option. But adult borers’ distaste for this variety of olive doesn’t yet mean the trees are safe. Female beetles feeding on ash trees might, in theory, fly to a nearby olive to lay eggs. To compare beetles’ preferences for laying eggs on olive versus ash will take a larger study. But Peterson’s first results are a little worrying. When he put olives and green ashes in a known infested zone, one of the few eggs he found was on an olive tree.
Free-flying beetles do lay eggs on white fringe trees, attacks that long went unreported. But the trees may not be as healthful a feeding site for beetle larvae as ash trees. In indoor tests, fewer larvae survived to their later stages on the fringe trees compared with larvae on white ashes, David Olson of the University of Kentucky in Lexington reported November 5. Olson works on whether biocontrol strategies developed for ash trees might also work on white fringe trees. So far, it doesn’t look encouraging. In outdoor tests, the most successful of four tiny parasitic wasp species released in North America did what they’re supposed to: Tetrastichus planipennisi doomed some beetle larvae in ash trees by using the youngsters as living food for baby wasps. Beetle larvae in nearby fringe trees, however, escaped wasp attacks.
Even if fringe trees don’t turn out to suffer massive damage, they could still present a very real threat if nurseries shipping trees from infested areas accidentally transport beetle larvae, too, Hoban says. Besides spreading the pests, that could make it tougher for ashes to weather existing invasions. The hope for ashes is that wasps will help keep beetles in check, and some exceptional ash trees will prove resistant enough to rebuild some sort of population.
Editor’s note: This story was updated November 23 to change the photo at the top of the story. The original photo was not an emerald ash borer.
There’s so much water on some of TRAPPIST-1’s seven Earth-sized planets that any life lurking there might be difficult to detect.
New estimates of the makeup of these potentially habitable worlds suggests that two of them are more than half water, by mass, researchers report March 19 in Nature Astronomy. Earth, by comparison, is less than 0.1 percent water.
TRAPPIST-1’s planets are so wet that most of the water probably isn’t even liquid, but ice formed under high pressure, says Cayman Unterborn, an exogeologist at Arizona State University in Tempe. That would change the chemistry happening on the planet in a way that could make any signs of life tricky to distinguish from geochemical processes. TRAPPIST-1 is a cool, dim star about 39 light-years from Earth. Since the star system’s discovery in 2017, it’s been a prime focus for scientists seeking life outside of our solar system because some of the seven planets might have the right conditions to host life (SN: 12/23/17, p. 25). They’re rocky rather than gaseous, and at least three are at a distance from the star that could let them host liquid water.
Unterborn and his colleagues used previous estimates of the mass and diameter of TRAPPIST-1’s planets to calculate the worlds’ densities. Then, the team used a computer program to test different compositions of basic planetary building blocks to determine which makeups would yield planets with those densities. Frozen or liquid water is less dense than rock, but more dense than a gas. So a less dense planet might have a higher proportion of water or gases compared with a denser, rockier world. But Unterborn doesn’t think the TRAPPIST-1 planets are massive enough to hold onto much of an atmosphere — it would probably escape into space. So the team concluded the lower densities in this system probably come from the presence of water. The researchers focused on four of the seven planets for which they had the best data. The first and second planets from the dwarf star are probably less than 15 percent water by mass, still far wetter than Earth, the researchers found.
The fifth and sixth planets, both in the habitable zone, are more than half water — a volume so large that the water pressure alone could force much of it into a form of ice, Unterborn says. He estimates that on the fifth planet, TRAPPIST-1f, liquid water extends down about 200 kilometers — about 20 times deeper than the Mariana Trench on Earth. Below that, a nearly 2,300-kilometer layer of ice stretches almost halfway to the center of the planet.
These water estimates might throw a wet blanket on the chances of finding life on any of TRAPPIST-1’s planets, if it exists at all. The thick covering of ice and water might mess up some of the geological processes that, at least on Earth, help regulate the planet’s temperature over long periods of time. If so, that might be an impediment to life getting a foothold. Having so much water might also slow or halt the movement of building blocks of life, such as carbon and phosphorus (the backbone of DNA), into oceans. That could make it harder for us to detect whether certain molecules in the water are hints of the presence of living organisms, or just the by-products of geological processes.
It doesn’t rule out life, Unterborn says, but it does make it harder to find. When it comes to understanding the way a planet’s geologic composition affects chemical processes, “the vast majority of data that’s out there is for one planet, and it’s ours,” he says. The TRAPPIST-1 system is “such an extreme of rocky planet chemistry.”
Updated estimates of the TRAPPIST-1 planets’ masses were published in February (SN Online: 2/5/18), and this study doesn’t use those numbers, says Billy Quarles, a physicist at the University of Oklahoma in Norman who wasn’t part of the study. Based on the newer estimates, TRAPPIST-1’s planets aren’t quite as wet as this study predicts. But the big-picture conclusion — that some of the planets contain far more water than Earth — still holds up, he says.
People call Lucy Jones the “earthquake lady.” For nearly 40 years, Jones, a seismologist, has been a leading voice in California on earthquake science and safety. A few months after retiring from the U.S. Geological Survey in 2016, she founded the Dr. Lucy Jones Center for Science and Society to bring policy makers and scientists together to discuss disaster resilience.
Now Jones is bringing that discussion to the public in her new book, The Big Ones. She offers a fascinating history of how catastrophic natural events — including the Lisbon earthquake of 1755, Iceland’s Laki volcanic eruption in 1783 (SN: 2/17/15, p. 29) and Hurricane Katrina in 2005 — have shaped politics, culture and society. Science News talked with Jones about the book, which she hopes will be a wake-up call, encouraging people to be ready for when, not if, the next disaster strikes. The discussion that follows has been edited for length and clarity. Why is now the time to write about the science behind natural disasters and the stories of people affected? We need stories to believe that these disasters can really happen to us. I’m a scientist. I know that research isn’t based on stories, but the stories help communicate the science. And disasters all have such cool stories, don’t they?
How did you choose which disasters to include? I wrote about disasters that were big enough to imperil the nature of society. Look at the Laki eruption. The country of Iceland completely changed. They lost a quarter of their population. Most of their records, like the church records of baptisms and deaths, disappeared. People can’t trace their families back before that time because the country fell apart. That’s one of the things that I wanted to do: discuss that level of catastrophe.
You write that you were surprised that presenting data, like earthquake probabilities, doesn’t move people to act. Why do you think hard numbers don’t motivate people? The numbers are often about the things we don’t understand, the uncertainty. Scientists and engineers actually like uncertainty; that’s why we spend our lives studying it. When we talk about the probabilities of an earthquake, we’re talking about the part we don’t understand, which is: When will it happen? That gives people a reason to say, I won’t deal with it now. If we have a 50 percent chance of rain today, and the storm veers off and doesn’t happen, then the rain never gets to us. So if it doesn’t happen today, it’s just not going to happen at all. We use exactly the same words to say we’ve got a 50 percent chance of an earthquake in the next 50 years. And that allows people to think, well, maybe if it doesn’t happen in this time, then it’s not going to happen. I want people to realize it’s going to happen; we just don’t know when. When people ask me what’s the probability of an earthquake, I say, it’s 100 percent, just give me enough time. One of the themes in The Big Ones is disaster preparedness. How can people be ready for a disaster? What matters is community. And when you have a disruption that imperils society itself, people will leave unless they’ve got a good reason to stay. The reason you stay is the people you care about. That whole “prepper” movement, I think, is a counterproductive approach because it tends to be, “I’m sure society is falling apart, so I’m getting my guns. I’m getting my stuff. I’m going to protect my family.” And that’s an implicit message that your neighbor is going to be your enemy. It becomes self-fulfilling. That type of prepper is one of the contributions to the world falling apart.
Bootlace worms with spooky-stretchy bodies secrete a family of toxins new to scientists. These compounds might inspire novel ways to attack pests such as cockroaches.
Tests first identified the toxins in mucus coating a bootlace species that holds the record as the world’s longest animal, says pharmacognosist Ulf Göransson of Uppsala University in Sweden. This champion marine worm (Lineus longissimus) can stretch up to 55 meters, longer than an Olympic-sized pool, and coats itself in mucus smelling a bit like iron or sewage. That goo holds small toxic proteins, now dubbed nemertides, that are also found in 16 other bootlace worm species, Göransson and colleagues write March 22 in Scientific Reports. The newly described nemertides attack tiny channels in cell walls that control the amount of sodium flowing in and out of the cell. Much vital cell business, such as communications between nerves, depends on the right flux through these voltage-gated sodium channels, as they’re called. Injections of small amounts of one of these nemertides permanently paralyzed or killed invasive green crabs (Carcinus maenas) and young cockroaches (Blattella germanica).
“This study certainly has a lot of novelty to it, since marine worms are a tremendously neglected area of venom research,” says Bryan Grieg Fry at the University of Queensland in Australia, where he explores the evolution of animal poisons.
Unlike earthworms, the 1,300 or so species of bootlace, or ribbon, worms have no segments. Some scientists give these animals their own phylum, Nemertea. Bootlace worms have a brain but no lungs. Like many other slender marine creatures, bootlace worms breathe directly through the skin. The worms are carnivorous, supping on crustaceans, mollusks and other worms.
They’re marvels of body expansion and contraction. An L. longissimus “of about 10 meters can be held in your hand as a slimy heap,” says study coauthor Malin Strand, a marine biologist and molecular systematist at the Swedish University of Agricultural Sciences in Uppsala. She estimates the worms could live for around 10 years “or maybe much longer.” How L. longissimus or the other species in the study use their toxins isn’t clear, she says. The stringy creatures aren’t easy to keep in captivity, Strand says. She has some worms that have deigned to eat in her lab only once in three to four years.
Göransson proposes that toxic mucus may be useful for defense. He has seen video with Nemertean worms stretched out on the seafloor. “If you’re a crab or a fish, it must be tempting to take a nip,” he says, but there’s little sign of anything bothering them.
He once tried some bare-handed contact with a small lab specimen and didn’t feel much of anything, although he’s been warned about “tingling” or even hands going temporarily numb. One of the nemertide toxins tested in the new paper was 100 times as effective on sodium channels in insect cells as in mammal ones, the researchers found.
For the first time, researchers have played matchmaker between two specific atoms, joining them together to form a molecule.
Typically, chemists make molecules by mixing up many constituent atoms, some of which stick to each other to form the desired compounds. In the new, supercontrolled chemical reaction, researchers trapped a single sodium atom in one optical tweezer — a device that snares small particles in a laser beam — and a cesium atom in another tweezer. Both atoms were cooled to less than one ten-thousandth of a degree above absolute zero.
The researchers moved these tweezers closer together until the laser beams overlapped, allowing the sodium and cesium atoms to collide. A third laser shot a pulse of light at the atoms to provide a boost of energy that helped the atoms bond into a sodium cesium molecule, researchers report online April 12 in Science.
Fashioning individual molecules atom by atom could allow researchers to study atomic collisions in the most controlled environment possible, as well as to observe how molecules behave in isolation. Researchers could also use optical tweezers to construct molecules with specific quantum properties, says study coauthor Kang-Kuen Ni, a chemist at Harvard University. These designer molecules could store qubits of data in future quantum computers, she says (SN: 3/10/12, p. 26).
An ultraprecise new measurement has given some weird particle physics theories a black eye.
By measuring one of nature’s most fundamental constants more precisely than before, scientists have tested proposed tweaks to the standard model, the theory governing fundamental particles. The result, reported April 13 in Science, casts doubt on hypothetical particles called dark photons and other potential oddities.
The quantity in question is the fine-structure constant, a number that governs the strength of electromagnetic interactions (SN: 11/12/16, p. 24), such as those that confine electrons within atoms. Previously, the most precise measurement of the constant was indirect, relying on a measurement of the electron’s magnetic properties and using complex theoretical calculations to infer the constant’s value. Now, physicist Holger Müller of the University of California, Berkeley and colleagues have measured the constant more directly. The team fired lasers at cesium atoms to create a quantum superposition — a bizarre state in which each atom is in two places at once — and watched how the atoms interfered with themselves as they recombined. This interference reveals how fast the atom moved when hit by the laser, which scientists then used to calculate the fine-structure constant.
The answer: The fine-structure constant is approximately 1/137.035999046.
If the new measurement disagreed with the earlier one, that might be an indication of new particles. But the two agree reasonably well, which confirms that the electron is probably not composed of smaller particles and disfavors the possibility of dark photons. These hypothetical particles are similar to run-of-the-mill photons, or particles of light, but unlike normal photons would have mass and interact very weakly with known particles. But while close, the two measurements didn’t match perfectly, a result which leaves some wiggle room for physicists to think up other types of strange new particles.
Scientists forged quantum connections between separate regions within clouds of ultracold atoms, demonstrating entanglement between thousands of particles in two different locations. Previous similar experiments had entangled several thousand atoms, but only within one entire cloud (SN Online: 3/25/15).
Now researchers have split up a cloud of entangled atoms into separate regions, either by considering two areas in a single cloud to be distinct or by actually forming two separate clouds, according to a trio of papers (found here, here and here) published in the April 27 Science. The new technique is a step toward quantum devices that make precise measurements, for example of electric fields.
Entanglement is a bizarre quantum phenomenon where separate objects, whether individual particles or groups of particles, behave as a conjoined entity. Measuring one object immediately reveals information about the other, even when the two are in different locations, such as distinct atomic clouds.
Nicholas Blackwell and his father went to a hardware store about three years ago seeking parts for a mystery device from the past. They carefully selected wood and other materials to assemble a stonecutting pendulum that, if Blackwell is right, resembles contraptions once used to build majestic Bronze Age palaces.
With no ancient drawings or blueprints of the tool for guidance, the two men relied on their combined knowledge of archaeology and construction.
Blackwell, an archaeologist at Indiana University Bloomington, had the necessary Bronze Age background. His father, George, brought construction cred to the project. Blackwell grew up watching George, a plumber who owned his own business, fix and build stuff around the house. By high school, the younger Blackwell worked summers helping his dad install heating systems and plumbing at construction sites. The menial tasks Nicholas took on, such as measuring and cutting pipes, were not his idea of fun. But that earlier work paid off as the two put together their version of a Bronze Age pendulum saw — a stonecutting tool from around 3,300 years ago that has long intrigued researchers. Power drills, ratchets and other tools that George regularly used around the house made the project, built in George’s Virginia backyard, possible.
“My father enjoyed working on the pendulum saw, although he and my mother were a bit concerned about what the neighbors would think when they saw this big wooden thing in their backyard,” Blackwell says. Anyone walking by the fenceless yard had a prime view of a 2.5-meter-tall, blade-swinging apparatus reminiscent of Edgar Allan Poe’s literary torture device. No one alive today has seen an actual Bronze Age pendulum saw. No frameworks or blades have been excavated. Yet archaeologists have suspected for nearly 30 years that a contraption capable of swinging a sharp piece of metal back and forth with human guidance must have created curved incisions on large pieces of stonework from Greece’s Mycenaean civilization. These distinctive cuts appeared during a century of palace construction, from nearly 3,300 years ago until the ancient Greek society collapsed along with a handful of other Bronze Age civilizations. Mycenaeans built palaces for kings and administrative centers for a centralized government. These ancient people spoke a precursor language to that of Classical Greek civilization, which emerged around 2,600 years ago.
In Blackwell’s view, only one tool — a pendulum saw — could have harnessed enough speed and power to slice through the especially tough type of rock that Mycenaeans used for pillars, gateways and thresholds in palaces and some large tombs.
Kings at the time valued this especially hard rock, known as conglomerate, for the look of its mineral and rock fragments, which form colorful circular and angled shapes.
In the early 20th century, archaeologists excavating a Mycenaean hill fort called Tiryns first noticed curved cut marks on the sides of pillar bases and other parts of a royal palace. The researchers assumed that ancient workers sliced through conglomerate blocks with curved, handheld saws and a lot of elbow grease. Some investigators still suspect that handheld saws make more sense than a swinging pendulum blade. But scholarly opinions began to change as similar marks were found on stonework at other Mycenaean sites, including the fortified town and citadel of Mycenae. Separate reports in the 1990s by German archaeologists proposed that a pendulum device produced curved Mycenaean masonry marks. One of the researchers estimated that a pendulum saw would have needed to swing from a massive arm, between 3 meters and 8 meters high, to create the observed curved cuts. His calculations rested on an assumption that the curved saw marks represented segments of perfect, geometric circles, which in some cases would have required the wide arc of an especially tall pendulum. Blackwell doubted that Mycenaeans used pendulum saws as tall as 8 meters, the equivalent of about 2½ stories. But there was only one way to find out. His experiments, described in the February Antiquity, indicate that a wooden contraption supporting a blade-tipped swinging arm had to reach only about 2½ meters high to create stone marks like those at Tiryns and Mycenae.
The Indiana researcher’s homemade pendulum saw “is the most persuasive reconstruction of a Mycenaean sawing machine that was used to cut hard stones, especially conglomerate,” says archaeologist Joseph Maran of the University of Heidelberg in Germany. Only one other life-size model of a pendulum saw exists.
Swing time Blackwell’s experimental cutting device swung into action in December 2015 right where it was built, in his parents’ Virginia backyard.
Positioned on opposite sides of the apparatus, Blackwell and his brother-in-law, Brandon Synan, pulled the sawing arm back and forth with a rope. A metal blade bolted to the bottom of the arm sliced into a limestone block. Unlike the type of conglomerate used in the Mediterranean region, limestone was readily available. The two tested four types of saw blades in the initial trials and again in February 2017.
Blackwell reviewed seven previously published designs and the one actual model of a pendulum saw that may have been used by a nearby Bronze Age society; they offered little encouragement. No consensus existed on the best shape for the blade or the most effective framework option. Designers were most notably stumped by how to build a pendulum that adjusted downward as the blade cut deeper into the stone.
Blackwell decided to build a device with two side posts, each studded with five holes drilled along its upper half, supported by a base and diagonal struts. A removable steel bar ran through opposite holes on the posts and could be set at different heights. In between the posts, the bar passed through an oval notch in the upper half of a long piece of wood — the pendulum. The notch is slightly longer than a dollar bill, giving the steel bar some leeway so the pendulum could move up and down freely while sawing.
Finally, the apparatus needed a tough, sharp business end. A Greek archaeologist that Blackwell met while working at the American School of Classical Studies at Athens from 2012 to 2015 put him in touch with a metalsmith from Crete. The craftsman fashioned four bronze blades with different shapes for testing on the pendulum saw: a long, curved blade; a triangular blade with a rounded tip; a short, straight-edged saw and a long, straight-edged saw with rounded corners. During tests with each blade, Blackwell added water and sand to the limestone surface every two minutes for lubrication and to enhance the saw’s grinding power. Blackwell suspected the triangular blade would penetrate the limestone enough to produce the best replicas of Mycenaeans’ arced cuts. He was wrong. Putting that blade through its paces, he found that only the tip creased the stone as the pendulum swung. The triangular blade yielded a shallow, wobbly groove that would have sorely disappointed status-conscious Mycenaean elites.
The short, straight blade did even worse. It repeatedly got stuck in the stone block during trials.
But in a dramatic showing, the long, curved blade left three concave incisions that looked much like saw marks at Tiryns. It took 45 minutes of sawing to reach a depth of 25.5 millimeters, a partial cut by Mycenaean standards. Blackwell and his brother-in-law took short breaks after every 12 minutes of pendulum pulling. “It takes a lot of physical effort to use a pendulum saw,” Blackwell says.
The elongated, straight blade with rounded corners proved easiest to use. It made one Mycenaean-like cut after only 24 minutes of sawing. Either the straight or the curved blade could have fit the bill for Mycenaean stoneworkers.
Close inspection of successful experimental cuts showed that Blackwell’s pendulum saw created curved incisions that were not segments of perfect circles. So an actual Mycenaean pendulum saw need not have been as tall as those earlier calculations had called for. Blackwell suspects that Mycenaean masons tied or glued blades to one side of a pendulum’s arm. After sawing deep enough so that the pendulum’s wooden end hit rock, a worker chiseled and hammered off stone on one side of the incision so that the blade could be lowered for deeper sawing. Repeating those steps several times eventually left a flat face at the incision.
A half-finished pillar base from Mycenae preserves evidence of this procedure, Blackwell says. The stone displays a long, curved cut on a flat, vertical surface near one of its sides. The cut abruptly stops partway down. At that level, stone abutting the incision shows signs of having been pounded off.
Ghost saw Even after Blackwell’s hands-on experiments, the Mycenaean pendulum saw remains an archaeological apparition. Some researchers believe it existed. Others don’t.
“Pendulum saws could have been a solution to Mycenaeans’ specific problem of having to work with conglomerate,” says archaeologist James Wright of Bryn Mawr College in Pennsylvania. Mycenaean conglomerate is considerably harder and more resistant to cutting than other types of rock that were available to the Mycenaeans and neighboring societies. Blackwell’s successful experimental incisions in limestone “conform with cut marks on Mycenaean stones,” Wright adds. The next step is to see how Blackwell’s pendulum saw performs on the tougher challenge of slicing through conglomerate. While Blackwell’s experimental device produces Mycenaean-style curved cuts, that doesn’t mean Mycenaeans invented and used pendulum saws, contends archaeologist Jürgen Seeher of the German Archaeological Institute’s branch in Istanbul. Seeher built and tested the only other reconstruction of a pendulum saw.
In a 2007 paper published in German, Seeher concluded that there was a better option than his pendulum saw: a long, curved saw attached to a wooden bar and pulled back and forth by two people, like a loggers’ saw. A loggers’ saw could have produced curved marks on palace stones of ancient Hittite society, which existed at the same time as the Mycenaeans in what is now Turkey.
Unlike their Greek neighbors, Hittites did not construct pillars and gateways out of conglomerate. But a handheld, two-man saw would have enabled something a pendulum saw could not: precise cutting of conglomerate blocks from different angles, Seeher says.
“A handheld saw moved by two men is much more under control than a free-hanging pendulum,” he says.
Seeher has archaeological evidence on his side. Double-handled loggers’ saws have been excavated at sites from the Late Bronze Age Minoan society on Crete. Hittites and Mycenaeans, contemporaries of the Minoans, could easily have modified that design to cut stone instead of wood, Seeher proposes. They would have had to substitute rock-grinding straight edges for wood-cutting serrated edges.
Blackwell disagrees. He is convinced that Mycenaean craft workers trained for years to operate pendulum saws, just as skilled artisans like his dad go through a long apprenticeship to learn their trade. Mycenaeans may have worked in teams that took turns using pendulum saws to cut conglomerate into palace structures, he speculates. Those workers probably used highly abrasive emery sand from the Greek island of Naxos to amplify the grinding power of their swinging saws, Wright adds.
Blackwell worked with his own family team to create a rough approximation of what a Mycenaean pendulum saw may have looked like and how it was handled. His father’s construction expertise was crucial to the project. But those teenage summers doing scut work at building sites probably didn’t hurt, either.
After wild rubber prices collapsed in the early 20th century, rubber merchants in the Amazon turned to the wildlife trade to keep their businesses afloat. They targeted many species, including two river otters: the giant otter and the neotropical otter. Only one of these species, though, the giant otter, was driven to near extinction. And new research on the patterns of the hunting trade has revealed how the giant otter’s biology, including its monogamous tendencies and boisterous social lifestyle, may have undermined its survival.
At least 23 million Amazonian animals, including the otters, were hunted for their hides from 1904 to 1969. They were killed mostly for their fur, which was desirable in U.S. and European markets. A 1967 law outlawed commercial hunting, but demand for otter fur didn’t really decline until 1975, when Brazil adhered to the Convention on the International Trade in Endangered Species, known as CITES. By that time, however, the neotropical otter had declined in numbers and the giant otter had been driven to near extinction, disappearing entirely from parts of its historical range. Since then, the neotropical otter has recovered its numbers, and the giant otter population, while still endangered, appears to be increasing in Peru, Colombia and Brazil.
That includes the upper Rio Negro of northwest Brazil, home to the indigenous Baniwa people. The Baniwa were curious whether their fishing habits would somehow affect the return of the giant otters, a question that eventually came to the attention of ecologist Natalia Pimenta, of the National Institute for Amazonian Research in Manaus, Brazil, and her colleagues. But before the scientists could answer the Baniwa’s question, they needed to know more about the otters’ past.
During the years that the otters were hunted commercially, Pimenta says, it was common for companies to register their fur sales. These historical documents — many of which are in the Amazonas Museum at the Federal University of Amazona, in Manaus, thanks to Pimenta’s coauthor André Antunes of the National Institute for Amazonian Research — let the research team reconstruct how many otter hides were sold and how prices changed over time. The other key source of data was the Baniwa people themselves. Baniwa hunted river otters in the Rio Içana, part of the upper Rio Negro, and sold the skins to white traders. Pimenta and her colleagues interviewed 11 Baniwa men who were old enough to have participated in otter hunts. “I was very well received in the communities where I went,” Pimenta says. “Although few hunters are alive, I encountered many indigenous [people] who had witnessed their relatives on otter [hunts] and who were able to reproduce in detail how the activity was carried out in the region.” One Baniwa recalled, “I must have been less than 10, but I remember the Içana full of white traders’ boats, in search of skins of jaguar, margay, river otter and giant otter. The trade lasted nearly 10 years, until the animals disappeared from around here. No one saw giant otters again.” This would have been somewhere around 1960.
The historical records confirm that giant otter hides had become rarer in trade by then, with neotropical otters taking their place. But why did the giant otters nearly disappear before their neotropical cousins? For one, they were the larger otter species, which made a single pelt more valuable than the smaller neotropical otter’s. However, the two otters have vastly different lifestyles that make the giant species far more vulnerable to human hunting.
Giant otters live in social groups of up to 20 especially noisy animals. That makes them easy to find and efficient to hunt. In those groups, there’s usually just one monogamous pair of breeding animals. Kill one of that pair — and the large male would be a good target — and you could break up the whole group, the team notes March 30 in PLOS ONE.
Neotropical otters, in contrast, are smaller, solitary, quiet creatures that usually come out in the daytime but, when faced with pressures from humans, can turn nocturnal. That makes them harder to hunt, as well as less profitable. The female otters can mate with multiple males in a territory, so even if hunters take out a few big male otters, females still have options. As a result, the neotropical otters were not only never subjected to the same intensity of hunting as their larger cousins, but there were also better equipped to handle their losses.
The researchers’ detective work paints a historical picture of the hunting practices and the economy of the time. But the work also has practical implications for modern otter populations. “From the species’ response to hunting pressure, we can suggest management and conservation strategies directed to each species,” Pimenta says.
With a mortar and pestle, Christy Till blends together the makings of a distant planet. In her geology lab at Arizona State University in Tempe, Till carefully measures out powdered minerals, tips them into a metal capsule and bakes them in a high-pressure furnace that can reach close to 35,000 times Earth’s atmospheric pressure and 2,000° Celsius.
In this interplanetary test kitchen, Till and colleagues are figuring out what might go into a planet outside of our solar system.
“We’re mixing together high-purity powders of silica and iron and magnesium in the right proportions to make the composition we want to study,” Till says. She’s starting with the makings of what might resemble a rocky planet that’s much different from Earth. “We literally make a recipe.” Scientists have a few good ideas for how to concoct our own solar system. One method: Mix up a cloud of hydrogen and helium, season generously with oxygen and carbon, and sprinkle lightly with magnesium, iron and silicon. Condense and spin until the cloud forms a star surrounded by a disk. Let rest about 10 million years, until a few large lumps appear. After about 600 million years, shake gently.
But that’s only one recipe in the solar systems cookbook. Many of the planets orbiting other stars are wildly different from anything seen close to home. As the number of known exoplanets has climbed — 3,717 confirmed as of April 12 — scientists are creating new recipes.
Seven of those exoplanets are in the TRAPPIST-1 system, one of the most exciting families of planets astronomers have discovered to date. At least three TRAPPIST-1 planets might host liquid water on their surface, making them top spots to look for signs of life (SN: 12/23/17, p. 25).
Yet those planets shouldn’t exist. Astronomers calculated that the small star’s preplanet disk shouldn’t have contained enough rocky material to make even one Earth-sized orb, says astrophysicist Elisa Quintana of NASA’s Goddard Space Flight Center in Greenbelt, Md. Yet the disk whipped up seven. TRAPPIST-1 is just one of the latest in a long line of rule breakers. Other systems host odd characters not seen in our solar system: super-Earths, mini-Neptunes, hot Jupiters and more. Many exoplanets must have had chaotic beginnings to exist where we find them.
These oddballs raise exciting questions about how solar systems form. Scientists want to know how much of a planet’s ultimate fate depends on its parent star, which ingredients are essential for planet building and which are just frosting on the planetary cake. NASA’s Transiting Exoplanet Survey Satellite, or TESS, which launched April 18, should bring in some answers. TESS is expected to find thousands more exoplanets in the next two years. That crowd will help illuminate which planetary processes are the most common — and will help scientists zero in on the best planets to check for signs of life. Beyond the bare necessities All solar system recipes share some basic elements. The star and its planets form from the same cloud of gas and dust. The densest region of the cloud collapses to form the star, and the remaining material spreads itself into a rotating disk, parts of which will eventually coalesce into planets. That similarity between the star and its progeny tells Till and other scientists what to toss into the planetary stand mixer.
“If you know the composition of the star, you can know the composition of the planets,” says astronomer Johanna Teske of the Carnegie Observatories in Pasadena, Calif. A star’s composition is revealed in the wavelengths of light the star emits and absorbs.
When a planet is born can affect its final makeup, too. A gas giant like Jupiter first needs a rocky core about 10 times Earth’s mass before it can begin gobbling up gas. That much growth probably happens well before the disk’s gas disappears, around 10 million years after the star forms. Small, rocky planets like Earth probably form later.
Finally, location matters. Close to the hot star, most elements are gas, which is no help for building planets from scratch. Where the disk cools toward its outer edge, more elements freeze to solid crystals or condense onto dust grains. The boundary where water freezes is called the snow line. Scientists thought that water-rich planets must either form beyond their star’s snow line, where water is abundant, or must have water delivered to them later (SN: 5/16/15, p. 8). Giant planets are also thought to form beyond the snow line, where there’s more material available.
But the material in the disk might not stay where it began, Teske says. “There’s a lot of transport of material, both toward and away from the star,” she says. “Where that material ends up is going to impact whether it goes into planets and what types of planets form.” The amount of mixing and turbulence in the disk could contribute to which page of the cookbook astronomers turn to: Is this system making a rocky terrestrial planet, a relatively small but gaseous Neptune or a massive Jupiter? Some like it hot Like that roiling disk material, a full-grown planet can also travel far from where it formed.
Consider “Hoptunes” (or hot Neptunes), a new class of planets first named in December in Proceedings of the National Academy of Sciences. Hoptunes are between two and six times Earth’s size (as measured by the planet’s radius) and sidled up close to their stars, orbiting in less than 10 days. That close in, there shouldn’t have been enough rocky material in the disk to form such big planets. The star’s heat should mean no solids, just gases.
Hoptunes share certain characteristics — and unanswered questions — with hot Jupiters, the first type of exoplanet discovered, in the mid-1990s.
“Because we’ve known about hot Jupiters for so long, some people kind of think they’re old hat,” says astronomer Rebekah Dawson of Penn State, who coauthored a review about hot Jupiters posted in January at arXiv.org. “But we still by no means have a consensus about how they got so close to their star.”
Since the first known hot Jupiter, 51 Pegasi b, was confirmed in 1995, two explanations for that proximity have emerged. A Jupiter that formed past the star’s snow line could migrate in smoothly through the disk by trading orbital positions with the disk material itself in a sort of gravitational do-si-do. Or interactions with other planets or a nearby star could knock the planet onto an extremely elliptical or even backward orbit (SN Online: 11/1/13). Over time, the star’s gravity would steal energy from the orbit, shrinking it into a tight, close circle. Dawson thinks both processes probably happen.
Hot Jupiters are more common around stars that contain a lot of elements heavier than hydrogen and helium, which astronomers call metals, astronomer Erik Petigura of Caltech and colleagues reported in February in the Astronomical Journal. High-metal stars probably form more planets because their disks have more solids to work with. Once a Jupiter-sized planet forms, a game of gravitational billiards could send it onto an eccentric orbit — and send smaller worlds out into space. That fits the data, too; hot Jupiters tend to lack companion worlds.
Hoptunes follow the same pattern: They prefer metal-rich stars and have few sibling planets. But Hoptunes probably arrived at their hot orbits later in the star’s life. Getting close to a young star, a Hoptune would risk having its atmosphere stripped away. “They’re sort of in the danger zone,” Dawson says. Since Hoptunes do, in fact, have atmospheres, they were probably knocked onto an elliptical, and eventually close-in, orbit later.
One striking exception to the hot loner rule is WASP-47b, a hot Jupiter with two nearby siblings between the sizes of Earth and Neptune. That planet is one reason Dawson thinks there’s more than one way to cook up a hot Jupiter.
Rock or gas Hot Jupiters are so large that astronomers assume these exoplanets have thick atmospheres. But it’s harder to tell if a smaller planet is gassy like Neptune or rocky like Earth.
To make a first guess at a planet’s composition, astronomers need to know the planet’s size and mass. Together, those numbers yield the planet’s density, which gives a sense of how much of the planet is solid like rock or diffuse like an atmosphere. The most popular planet detection strategies each measure one of those factors. The transit method, used by the Kepler space telescope, watches a star wink as the planet passes in front. Comparing the star’s light before and during the transit reveals the planet’s size. The radial velocity method, used with telescopes on the ground, watches the star wobble in response to a planet’s gravity, which reveals the planet’s mass.
Most of the stars observed by Kepler are too far away and too dim for direct, accurate measures of planet masses. But astronomers have inferred a size cutoff for rocky planets. Last June, researchers analyzing the full Kepler dataset noticed a surprising lack of planets between 1.5 and two times Earth’s size and suggested those 1.5 times Earth’s radius or smaller are probably rocky; two to 3.5 times Earth’s radius are probably gassy (SN Online: 6/19/17).
Dozens more planets have had their masses inferred indirectly, mostly those in multiplanet systems where astronomers can observe how planets tug on one another. From what astronomers can tell, super-Earths — planets between one and about 10 times Earth’s mass — come in a wide range of compositions.
The Kepler mission is about to end, as the spacecraft’s fuel is running out. TESS will pick up where Kepler leaves off. The new planet-hunting space telescope will revolutionize the study of super-Earth densities. It will scan 85 percent of the sky for bright, nearby stars to pick out the best planets for follow-up study. As part of its primary mission, TESS will find at least 50 planets smaller than Neptune that can have their masses measured precisely, too. “Having masses … will help us understand the compositions,” says Quintana, a TESS team member. “We can see: Is there a true transition line where planets go rocky to gaseous? Or is it totally random? Or does it depend on the star?”
Star power All kinds of planets’ fates do, in fact, depend on the stars, Petigura’s recent work suggests. In a February report in the Astronomical Journal, he and colleagues measured the metal contents of 1,305 planet-hosting stars in Kepler’s field of view.
The researchers learned that large planets and close-in planets — with orbital periods of 10 days or less — are more common around metal-rich stars. But the team was surprised to find that small planets and planets that orbit far from their stars show up around stars of all sorts of compositions. “They form efficiently everywhere,” Petigura says.
That could mean that metal-rich stars had disks that extended closer to the stars. With enough material close to the star, hot super-Earths could have formed where they currently spin. The existence of hot super-Earths might even suggest that hot Jupiters can form close to the star after all. A super-Earth or mini-Neptune could represent the core of what was once a hot Jupiter that didn’t quite gather enough gas before the disk dissipated, or whose atmosphere was blown off by the star (SN Online: 10/31/17).
Weird water Some scientists are looking to stars to reveal what’s inside a planet. The help is welcome because density is a crude measure for understanding what a planet is made of. Planets with the same mass and radius can have very different compositions and natures — look at hellish Venus and livable Earth.
Take the case of TRAPPIST-1, which has seven Earth-sized worlds and is 39 light-years away. Astronomers are anxious to check at least three of the planets for signs of life (SN: 12/23/17, p. 25). But those planets might be so waterlogged that any signs of life would be hard to detect, says exogeologist Cayman Unterborn of Arizona State. So much water would change a planet’s chemistry in a way that makes it hard to tell life from nonlife. Based on the planets’ radii (measured by their transits) and their masses (measured by their gravitational influence on one another), Unterborn and colleagues used density to calculate a bizarre set of interiors for the worlds, which the team reported March 19 in Nature Astronomy.
The TRAPPIST-1 planets have low densities for their size, Unterborn says, suggesting that their masses are mostly light material like water ice. TRAPPIST-1b, the innermost planet, seems to be 15 percent water by mass (Earth is less than 0.1 percent water). The fifth planet out, TRAPPIST-1f, may be at least half water by mass. If the planet formed with all that water already in it, it would have had 1,000 Earth oceans’ worth of water. That amount of water would compress into exotic phases of ice not found at normal pressures on Earth. “That is so much water that the chemistry of how that planet crystallized is not something we have ever imagined,” Unterborn says. But there’s a glitch. Unterborn’s analysis was based on the most accurate published masses for the TRAPPIST-1 worlds at the time. But on February 5, the same day his paper was accepted in Nature Astronomy, a group led by astronomer Simon Grimm of the University of Bern in Switzerland posted more precise mass measurements at arXiv.org. Those masses make the soggiest planets look merely damp.
Clearly, Unterborn says, density is not destiny. Studying a planet based on its mass and radius has its limits.
Looking deeper As a next step, Unterborn and colleagues have published a series of papers suggesting how stellar compositions can tell the likelihood that a group of planets have plate tectonics, or how much oxygen the planet atmospheres may have. Better geologic models may ultimately help reveal if a single planet is habitable.
But Unterborn is wary of translating composition from a star to any individual planet — existing geochemical models aren’t good enough. The recent case of K2-229b makes that clear. Astronomer Alexandre Santerne of the Laboratory of Astrophysics of Marseille in France and colleagues recently tried to see if a star’s composition could describe the interior of its newly discovered exoplanet, K2-229b. The team reported online March 26 in Nature Astronomy that the planet has a size similar to Earth’s but a makeup more like Mercury’s: 70 percent metallic core, 30 percent silicate mantle by mass. (The researchers nicknamed the planet Freddy, for Queen front man Freddie Mercury, Santerne wrote on Twitter.) That composition is not what they’d expect from the star alone. Geologic models need to catch up quickly. After TESS finds the best worlds for follow-up observations, the James Webb Space Telescope, due to launch in 2020, will search some of those planets’ atmospheres for signs of life (SN: 4/30/16, p. 32). For that strategy to work, Unterborn says, scientists need a better read on the exoplanet cookbook.
Christy Till’s pressure-packed test kitchen may help. Till is primarily a volcanologist who studies how magma erupting onto Earth’s surface can reveal conditions in Earth’s interior. “The goal is to start doing that for exoplanets,” she says.
Till and colleagues are redoing some foundational experiments conducted for Earth 50 years ago but not yet done for exoplanets. The experiments predict which elements can go into planets’ mantles and cores, and which will form solid crusts. (Early results that Till and grad student Mitchell Phillips presented in December in New Orleans at the American Geophysical Union meeting suggest that multiplying the sun’s magnesium-to-silicon ratio by 1.33 still bakes a rocky planet, but with a different flavored crust than Earth’s.)
Till uses three piston cylinders to squash and singe synthetic exoplanets for 24 hours to see what minerals form and melt at different pressures and temperatures. The results may help answer questions like what kind of lava would erupt on a planet’s surface, what would the crust be made of and what gases might end up in the planet’s atmosphere.
It’s early days, but Till’s recipe testing may mean scientists won’t have to wait decades for telescopes to get a close enough look at an exoplanet to judge how much like home it really is. With new cookbook chapters, Unterborn says, “we can figure out which stars are the best places to build an Earth.”
