Big, rogue planets — ones without parent stars — are rare.

A new census of free-floating Jupiter-mass planets determined that these worlds are a tenth as common as previous estimates suggested. The results appear online July 24 in Nature.

Planets can go rogue in two ways: They can get kicked out of their parent planetary systems or form when a ball of gas and dust collapses (SN: 4/4/15, p. 22).

In the new study, Przemek Mróz of the Astronomical Observatory of the University of Warsaw and colleagues estimated the number of large, rogue planets in our galaxy using a technique called microlensing. When an object with a mass of a planet passes in front of a distant, background star, the gravity of the planet acts as a gravitational magnifying glass. It distorts and focuses the light, giving up the planet’s existence.
Mróz and colleagues looked at 2,617 microlensing events recorded between 2010 and 2015 and determined which were caused by a rogue planet. For every typical star, called main sequence stars, there are 0.25 free-floating Jupiter-mass planets, the analysis suggests.

The new result sharply contrasts an estimate published in 2011, which suggested that rogue Jupiters are almost twice as common as main sequence stars. About 90 percent of stars in the universe are main sequence stars, so if that estimate were accurate, there should be a lot of free-floating Jupiters.

“That result changed our conceptual framework of the universe just a little bit,” says astronomer Michael Liu of the University of Hawaii in Honolulu. It challenged long-held ideas about how planets go rogue because the known methods wouldn’t generate enough planets to account for all the wanderers.

The 2011 result was based on a relatively small sample of microlensing events, only 474. Since then, infrared telescope images haven’t detected as many free-floating planets as expected. “Over the years, serious doubts were cast over the claims of a large population of Jupiter-mass free-floaters,” Mróz says.

David Bennett, coauthor of the 2011 study, agrees that the new census failed to find evidence for a large population of Jupiter-mass rogue planets. He notes, however, that the new data do reveal four times as many Jupiter-mass failed stars called brown dwarfs than predicted in the original census. So some of the rogues that were originally classified as planets may, in fact, be failed stars. Bennett, of NASA’s Goddard Space Flight Center in Greenbelt, Md., and colleagues are working on a new analysis of potential rogues with nearly 3,000 microlensing events and plan to compare their results with those from the new census.
Liu says the latest census is much more in line with theories of how planets form. Most rogues should be Earth-mass or a little heavier. Those lighter planets get tossed out of their planetary systems much easier than behemoths like Jupiter. Still, the smaller planets are harder to detect.

The new microlensing analysis did identify several events in which stars brightened and dimmed in less than half a day. Such short events hint at the existence of Earth-mass free-floaters because smaller planets with less gravity should brighten a distant star more briefly than more massive stars. Determining whether those small planets are really rogue and counting how many there are will take better telescopes, the team notes.

Some dinosaurs liked to cheat on their vegetarian diet.

Based on the shape of their teeth and jaws, large plant-eating dinosaurs are generally thought to have been exclusively herbivorous. But for one group of dinosaurs, roughly 75-million-year-old poop tells another story. Their fossilized droppings, or coprolites, contained tiny fragments of mollusk and other crustacean shells along with an abundance of rotten wood, researchers report September 21 in Scientific Reports. Eating the crustaceans as well as the wood might have given the dinosaurs an extra dose of nutrients during breeding season to help form eggs and nourish the embryos.
“Living herd animals do occasionally turn carnivore to fulfill a particular nutritional need,” says vertebrate paleontologist Paul Barrett of the Natural History Museum in London. “Sheep and cows are known to eat carcasses or bone when they have a deficiency in a mineral such as phosphorus or calcium, or if they’re pregnant or ill.” But the discovery that some plant-eating dinos also ate crustaceans is the first example of this behavior in an extinct herbivore, says Barrett, who was not involved in the new study.

Ten years ago, paleoecologist Karen Chin of the University of Colorado Boulder described finding large pieces of rotted wood in dino dung. The coprolites were within a layer of rock in Montana, known as the Two Medicine Formation, dating to between 80 million and 74 million years ago. That layer also contained numerous fossils of Maiasaura, a type of large, herbivorous duck-billed dinosaur, or hadrosaur (SN: 8/9/14, p. 20).
Chin wondered whether the wood itself was the dino’s real dietary target. “The coprolites in Montana were associated with the nesting grounds of the Maiasaura ,” she says. “I suspected that the dinosaurs were after insects in the wood. But I never found any insects in the coprolites there.”

Her hunch wasn’t too far off. Now she’s found evidence of some kind of crustaceans in dino poop. The new evidence comes from an 860-meter-thick layer of rock in Utah known as the Kaiparowits Formation, which dates to between 76.1 million and 74 million years ago. Ten of the 15 coprolites that Chin and her team examined contained tiny fragments of shell that were scattered throughout the dung. They were too small to identify by species, and may have been crabs, insects or some other type of shelled animal, Chin says. Based on the scattering of shell fragments, the animals were certainly eaten along with the wood rather than being later visitors to the dung heap.

Since bones from hadrosaurs are especially abundant in the Kaiparowits Formation, Chin suspects those kinds of dinos deposited the dung. Other large herbivores, such as three-horned ceratopsians and armored ankylosaurs, also roamed the area (SN: 6/24/17, p. 4).

The crustacean diet cheat may have been a seasonal event, related perhaps to breeding to obtain extra nutrients, Chin and colleagues say.

But how often — or why — the dinosaurs ate the shelled critters is hard to prove from the fossil dung alone, Barrett says. Herbivore coprolites are rare in the fossil record because a diet of leaves and other green plant material doesn’t leave a lot of hard material to preserve (unlike bones in carnivore dung). Coprolites with crustaceans, on the other hand, are more likely to get fossilized — and that preferential preservation might make it appear that this behavior was more frequent than it actually was. “These kinds of things give neat snapshots of specific behaviors that those animals are doing at any one time,” he adds. “But it’s difficult to build that into a bigger picture.”

When Hurricane Maria’s 250-kilometer-per-hour winds slammed into Puerto Rico on September 20, they spurred floods, destroyed roads and flattened homes across the island. A week-and-a-half later, parts of the island remain without power, and its people are facing a humanitarian crisis.

The storm also temporarily knocked out one of the best and biggest eyes on the sky: the Arecibo Observatory, some 95 kilometers west of San Juan. The observatory’s 305-meter-wide main dish was until recently the largest radio telescope in the world (a bigger one, the FAST radio telescope, opened in China in 2016).

As news trickled out over the past week, it appeared that the damage may not be as bad as initially reported. The observatory is conserving fuel, but plans to resume limited astronomy observations September 29, deputy director Joan Schmelz tweeted earlier that day. “#AreciboScience is coming back after #MariaPR.”

But the direct whack still raises the issue of when – and even whether – to repair the observatory: Funding for it has repeatedly been on the chopping block despite its historic contributions to astronomy.

Arecibo’s recent work includes searching for gravitational waves by the effect they have on the clocklike regularity of dead stars called pulsars; watching for mysterious blasts of energy called fast radio bursts (SN Online: 12/21/16); and keeping tabs on near-Earth asteroids.

It played a key role in the history of the search for extraterrestrial intelligence: In 1974, astronomers Frank Drake, Jill Tarter and Carl Sagan used it to send messages to any extraterrestrial civilizations that might be listening (SN Online: 2/13/15). It was also the telescope that, in 1992, discovered the first planets outside the solar system.

Arecibo also holds a special place in my personal history: Watching actress Jodie Foster use the giant dish to listen for aliens in the movie Contact when I was 13 cemented my desire to study astronomy. I chose to go to Cornell University for undergrad in part because the university managed Arecibo at the time, and I hoped I might get to go there. (I never did, but my undergrad adviser, Martha Haynes, uses Arecibo to study the distribution of galaxies in the local universe.) And one of the first science stories I ever had published was about Cornell professors testifying to the National Science Foundation, which owns Arecibo, to defend the observatory’s funding.
Ten years after that story ran in the Cornell Daily Sun, Arecibo’s funding situation is still in doubt. It’s not clear how the recent damage will affect its future.

Telescope operator Ángel Vázquez sent the first damage reports via short-wave radio on September 21. A line feed antenna, used to receive and transmit radio waves to study the Earth’s ionosphere, broke off and fell onto the observatory’s main dish, damaging some of its panels. A second, 12-meter dish was thought to have been destroyed entirely.

But the smaller dish survived with only minor damage. “Initial reports said it had just been blown away, but it turned out that was not correct,” says Nicholas White of the Universities Space Research Association, which co-operates the observatory with SRI International, a nonprofit headquartered in Menlo Park, Calif., and Metropolitan University in San Juan, Puerto Rico. “That looks like it’s fine, although obviously we have to get up there and check it out.”

On September 23, observatory director Francisco Córdova posted a picture to the observatory’s Facebook page of two staff members standing in front of the big telescope dish with an outstretched Puerto Rican flag. “Still standing after #HurricaneMaria!” the post declares. “We suffered some damages, but nothing that can’t be repaired or replaced!”
The line feed antenna is a big loss, but it should be replaceable eventually, White says. And the damage to the main dish is fixable. Among the tasks was to get inside the Gregorian dome — the golf ball‒like structure suspended over the giant dish — and make sure the reflectors within it were aligned correctly. (Those reflectors were knocked askew by Hurricane George in 1998, says Cornell radio astronomer Donald Campbell.)

Meantime, Arecibo staff, who managed to safely shelter in place during the storm, “have been showing up for work, funnily enough,” White says. “People just want to get back to normal.”

But normal is also a state of uncertainty. The NSF, which foots $8.3 million of the observatory’s nearly $12 million a year operating costs, has been trying to offload their responsibility for it for several years. (NASA covers the balance.) And NSF’s agreement with the three groups that jointly maintain and operate the observatory runs out in March 2018. In 2016, the NSF called for proposals for other organizations to take over after that.

The NSF can’t estimate yet how expensive the repairs will be or how long they will take to complete, so it’s reserving comment on how the damage will affect decisions about the observatory’s future. “We need to make a complete assessment,” says NSF program director Joseph Pesce.

Personally, I hope the observatory remains open, both for science and for inspiration. I’m still waiting for a reply to that 1974 Arecibo message.

Spacetime ripples from black holes are becoming routine.

For a fifth time, scientists have reported the detection of two colliding black holes via their gravitational waves, tiny vibrations that warp the fabric of spacetime. Unlike previous gravitational wave detections, which were heralded with news conferences often featuring panels of scientists squinting at journalists under bright lights, this was a low-key announcement. The event, caught on June 8, 2017, by the Advanced Laser Interferometer Gravitational-Wave Observatory, LIGO, was unceremoniously unveiled in a paper published online November 15 at arXiv.org.

With masses 7 and 12 times that of the sun, the pair of black holes was the lightest LIGO has spotted so far. The lack of fanfare over the detection signals a shift. Scientists are now aiming to collect data from many black hole crashes. That data can be analyzed to answer questions about the population as a whole, such as how two black holes get paired up in the first place.

Some birds of paradise really know how to work their angles. Tilted, microscopic filaments in some of the showy birds’ black feathers make that plumage look much darker than traditional black feathers, researchers report online January 9 in Nature Communications.

Dakota McCoy, an evolutionary biologist at Harvard University, and colleagues measured how much light each type of black feather absorbs. Superblack feathers absorb up to 99.95 percent of light that shines directly on them, while traditional black feathers absorb up to 96.8 percent, the researchers found.
Using scanning electron microscopy and nano-CT scanning, the team observed that ultrablack feathers have ragged, spike-studded barbules that curve upward at a roughly 30-degree angle to the tip, creating an array of deep, curved cavities. Traditional black feathers are smoother and lack such detailed microstructures. These spikes and pits scatter light multiple times, allowing for more light absorption and darker plumage, the scientists say. Even when the researchers dusted the feathers with gold, the darkest ones still retained their blackness, while traditional black plumes looked gilded in SEM images.

Superblack patches probably evolved to “exaggerate the perceived brilliance of adjacent color patches” during mating displays, the researchers write.

Like sailors and spelunkers, physicists know the power of a sturdy knot.

Some physicists have tied their hopes for a new generation of data storage to minuscule knotlike structures called skyrmions, which can form in magnetic materials. Incredibly tiny and tough to undo, magnetic skyrmions could help feed humankind’s hunger for ever-smaller electronics.

On traditional hard drives, the magnetic regions that store data are about 10 times as large as the smallest skyrmions. Ranging from a nanometer to hundreds of nanometers in diameter, skyrmions “are probably the smallest magnetic systems … that can be imagined or that can be realized in nature,” says physicist Vincent Cros of Unité Mixte de Physique CNRS/Thales in Palaiseau, France.
What’s more, skyrmions can easily move through a material, pushed along by an electric current. The magnetic knots’ nimble nature suggests that skyrmions storing data in a computer could be shuttled to a sensor that would read off the information as the skyrmions pass by. In contrast, traditional hard drives read and write data by moving a mechanical arm to the appropriate region on a spinning platter (SN: 10/19/13, p. 28). Those moving parts tend to be fragile, and the task slows down data recall. Scientists hope that skyrmions could one day make for more durable, faster, tinier gadgets.

One thing, however, has held skyrmions back: Until recently, they could be created and controlled only in the frigid cold. When solid-state physicist Christian Pfleiderer and colleagues first reported the detection of magnetic skyrmions, in Science in 2009, the knots were impractical to work with, requiring very low temperatures of about 30 kelvins (–243° Celsius). Those are “conditions where you’d say, ‘This is of no use for anybody,’ ” says Pfleiderer of the Technical University of Munich.

Skyrmions have finally come out of the cold, though they are finicky and difficult to control. Now, scientists are on the cusp of working out the kinks to create thawed-out skyrmions with all the desired characteristics. At the same time, researchers are chasing after new kinds of skyrmions, which may be an even better fit for data storage. The skyrmion field, Pfleiderer says, has “started to develop its own life.”
In a magnetic material, such as iron, each atom acts like a tiny bar magnet with its own north and south poles. This magnetization arises from spin, a quantum property of the atom’s electrons. In a ferromagnet, a standard magnet like the one holding up the grocery list on your refrigerator, the atoms’ magnetic poles point in the same direction (SN Online: 5/14/12).

Skyrmions, which dwell within such magnetic habitats, are composed of groups of atoms with their magnetic poles oriented in whorls. Those spirals of magnetization disrupt the otherwise orderly alignment of atoms in the magnet, like a cowlick in freshly combed hair. Within a skyrmion, the direction of the atoms’ poles twists until the magnetization in the center points in the opposite direction of the magnetization outside. That twisting is difficult to undo, like a strong knot (SN Online: 10/31/08). So skyrmions won’t spontaneously disappear — a plus for long-term data storage.

Using knots of various kinds to store information has a long history. Ancient Incas used khipu, a system of knotted cord, to keep records or send messages (SN Online: 5/8/17). In a more modern example, Pfleiderer says, “if you don’t want to forget something then you put a knot in your handkerchief.” Skyrmions could continue that tradition.
On the right track
Skyrmions are a type of “quasiparticle,” a disturbance within a material that behaves like a single particle, despite being a collective of many individual particles. Although skyrmions are made up of atoms, which remain stationary within the material, skyrmions can move around like a true particle, by sliding from one group of atoms to another. “The magnetism just twists around, and thus the skyrmion travels,” says condensed matter physicist Kirsten von Bergmann of the University of Hamburg.

In fact, skyrmions were first proposed in the context of particles. British physicist Tony Skyrme, who lends his name to the knots, suggested about 60 years ago that particles such as neutrons and protons could be thought of as a kind of knot. In the late 1980s, physicists realized the math that supported Skyrme’s idea could also represent knots in the magnetization of solid materials.

Such skyrmions could be used in futuristic data storage schemes, researchers later proposed. A chain of skyrmions could encode bits within a computer, with the presence of a skyrmion representing 1 and the absence representing 0.

In particular, skyrmions might be ideal for what are known as “racetrack” memories, Cros and colleagues proposed in Nature Nanotechnology in 2013. In racetrack devices, information-holding skyrmions would speed along a magnetic nanoribbon, like cars on the Indianapolis Motor Speedway.

Solid-state physicist Stuart Parkin proposed a first version of the racetrack concept years earlier. In a 2008 paper in Science, Parkin and colleagues demonstrated the beginnings of a racetrack memory based not on skyrmions, but on magnetic features called domain walls, which separate regions with different directions of magnetization in a material. Those domain walls could be pushed along the track using electric currents to a sensor that would read out the data encoded within. To maximize the available space, the racetrack could loop straight up and back down (like a wild Mario Kart ride), allowing for 3-D memory that could pack in more data than a flat chip.
“When I first proposed [racetrack memories] many years ago, I think people were very skeptical,” says Parkin, now at the Max Planck Institute of Microstructure Physics in Halle, Germany. Today, the idea — with and without skyrmions — has caught on. Racetrack memories are being tested in laboratories, though the technology is not yet available in computers.

To make such a system work with skyrmions, scientists need to make the knots easier to wrangle at room temperature. For skyrmion-based racetrack memories to compete with current technologies, skyrmions must be small and move quickly and easily through a material. And they should be easy to create and destroy, using something simple like an electric current. Those are lofty demands: A step forward on one requirement sometimes leads to a step backward on the others. But scientists are drawing closer to reining in the magnetic marvels.

Heating up
Those first magnetic skyrmions found by Pfleiderer and colleagues appeared spontaneously in crystals with asymmetric structures that induce a twist between neighboring atoms. Only certain materials have that skyrmion-friendly asymmetric structure, limiting the possibilities for studying the quasiparticles or coaxing them to form under warmer conditions.

Soon, physicists developed a way to artificially create an asymmetric structure by depositing material in thin layers. Interactions between atoms in different layers can induce a twist in the atoms’ orientations. “Now, we can suddenly use ordinary magnetic materials, combine them in a clever way with other materials, and make them work at room temperature,” says materials scientist Axel Hoffmann of Argonne National Laboratory in Illinois.

Scientists produced such thin film skyrmions for the first time in a one-atom-thick layer of iron on top of iridium, but temperatures were still very low. Reported in Nature Physics in 2011, those thin film skyrmions required a chilly 11 kelvins (–262° C). That’s because the thin film of iron loses its magnetic properties above a certain temperature, says von Bergmann, who coauthored the study, along with nanoscientist Roland Wiesendanger of the University of Hamburg and colleagues. But thicker films can stay magnetic at higher temperatures. And so, “one important step was to increase the amount of magnetic material,” von Bergmann says.

To go thicker, scientists began stacking sheets of various magnetic and nonmagnetic materials, like a club sandwich with repeating layers of meat, cheese and bread. Stacking multiple layers of iridium, platinum and cobalt, Cros and colleagues created the first room-temperature skyrmions smaller than 100 nanometers, the researchers reported in May 2016 in Nature Nanotechnology.

By adjusting the types of materials, the number of layers and their thicknesses, scientists can fashion designer skyrmions with desirable properties. When condensed matter physicist Christos Panagopoulos of Nanyang Technological University in Singapore and colleagues fiddled with the composition of layers of iridium, iron, cobalt and platinum, a variety of skyrmions swirled into existence. The resulting knots came in different sizes, and some were more stable than others, the researchers reported in Nature Materials in September 2017.

Although scientists now know how to make room-temperature skyrmions, the heat-tolerant swirls, tens to hundreds of nanometers in diameter, tend to be too big to be very useful. “If we want to compete with current state-of-the-art technology, we have to go for skyrmionic objects [that] are much smaller in size than 100 nanometers,” Wiesendanger says. The aim is to bring warmed-up skyrmions down to a few nanometers.
As some try to shrink room-temp skyrmions down, others are bringing them up to speed, to make for fast reading and writing of data. In a study reported in Nature Materials in 2016, skyrmions at room temperature reached top speeds of 100 meters per second (about 220 miles per hour). Fittingly, that’s right around the fastest speed NASCAR drivers achieve. The result showed that a skyrmion racetrack might actually work, says study coauthor Mathias Kläui, a condensed matter physicist at Johannes Gutenberg University Mainz in Germany. “Fundamentally, it’s feasible at room temperature.” But to compete against domain walls, which can reach speeds of over 700 m/s, skyrmions still need to hit the gas.

Despite progress, there are a few more challenges to work out. One possible issue: A skyrmion’s swirling pattern makes it behave like a rotating object. “When you have a rotating object moving, it may not want to move in a straight line,” Hoffmann says. “If you’re a bad golf player, you know this.” Skyrmions don’t move in the same direction as an electric current, but at an angle to it. On the racetrack, skyrmions might hit a wall instead of staying in their lanes. Now, researchers are seeking new kinds of skyrmions that stay on track.

A new twist
Just as there’s more than one way to tie a knot, there are several different types of skyrmions, formed with various shapes of magnetic twists. The two best known types are Bloch and Néel. Bloch skyrmions are found in the thick, asymmetric crystals in which skyrmions were first detected, and Néel skyrmions tend to show up in thin films.

“The type of skyrmions you get is related to the crystal structure of the materials,” says physical chemist Claudia Felser of the Max Planck Institute for Chemical Physics of Solids in Dresden, Germany. Felser studies Heusler compounds, materials that have unusual properties particularly useful for manipulating magnetism. Felser, Parkin and colleagues detected a new kind of skyrmion, an antiskyrmion, in a thin layer of such a material. They reported the find in August 2017 in Nature.

Antiskyrmions might avoid some of the pitfalls that their relatives face, Parkin says. “Potentially, they can move in straight lines with currents, rather than moving to the side.” Such straight-shooting skyrmions may be better suited for racetrack schemes. And the observed antiskyrmions are stable at a wide range of temperatures, including room temperature. Antiskyrmions also might be able to shrink down smaller than other kinds of skyrmions.

Physicists are now on the hunt for skyrmions within a different realm: antiferromagnetic materials. Unlike in ferromagnetic materials — in which atoms all align their poles — in antiferromagnets, atoms’ poles point in alternating directions. If one atom points up, its neighbor points down. Like antiskyrmions, antiferromagnetic skyrmions wouldn’t zip off at an angle to an electric current, so they should be easier to control. Antiferromagnetic skyrmions might also move faster, Kläui says.

Materials scientists still need to find an antiferromagnetic material with the necessary properties to form skyrmions, Kläui says. “I would expect that this would be realized in the next couple of years.”

Finding the knots’ niche
Once skyrmions behave as desired, creating a racetrack memory with them is an obvious next step. “It is a technology that combines the best of multiple worlds,” Kläui says — stability, easily accessible data and low energy requirements. But Kläui and others acknowledge the hurdles ahead for skyrmion racetrack memories. It will be difficult, these researchers say, to beat traditional magnetic hard drives — not to mention the flash memories available in newer computers — on storage density, speed and cost simultaneously.

“The racetrack idea, I’m skeptical about,” Hoffmann says. Instead, skyrmions might be useful in devices meant for performing calculations. Because only a small electric current is required to move skyrmions around, such devices might be used to create energy-efficient computer processors.

Another idea is to use skyrmions for biologically inspired computers, which attempt to mimic the human brain (SN: 9/6/14, p. 10). Brains consume about as much power as a lightbulb, yet can perform calculations that computers still can’t match, thanks to large interconnected networks of nerve cells. Skyrmions could help scientists achieve this kind of computation in the lab, without sapping much power.
A single skyrmion could behave like a nerve cell , or neuron, electrical engineer Sai Li of Beihang University in Beijing and colleagues suggest. In the human body, a neuron can add up signals from its neighbors, gradually building up a voltage across its membrane. When that voltage reaches a certain threshold, ions begin shifting across the membrane in waves, generating an electric pulse. Skyrmions could imitate this behavior: An electric current would push a skyrmion along a track, with the distance traveled acting as an analog for the neuron’s increasing voltage. A skyrmion reaching a detector at the end would be equivalent to a firing neuron, the researchers proposed in July 2017 in Nanotechnology .
By combining a large number of neuron-imitating skyrmions, the thinking goes, scientists could create a computer that operates something like a brain.

Additional ideas for how to use the magnetic whirls keep cropping up. “It’s still a growing field,” von Bergmann says. “There are several new ideas ahead.”

Whether or not skyrmions end up in future gadgets, the swirls are part of a burgeoning electronics ecosystem. Ever since electricity was discovered, researchers have focused on the motion of electric charges. But physicists are now fashioning a new parallel system called spintronics — of which skyrmions are a part — based on the motion of electron spin, that property that makes atoms magnetic (SN Online: 9/26/17). By studying skyrmions, researchers are expanding their understanding of how spins move through materials.

Like a kindergartner fumbling with shoelaces, studying how to tie spins up in knots is a learning process.

Dying, it turns out, is not like flipping a switch. Genes keep working for a while after a person dies, and scientists have used that activity in the lab to pinpoint time of death to within about nine minutes.

During the first 24 hours after death, genetic changes kick in across various human tissues, creating patterns of activity that can be used to roughly predict when someone died, researchers report February 13 in Nature Communications.
“This is really cool, just from a biological discovery standpoint,” says microbial ecologist Jennifer DeBruyn of the University of Tennessee in Knoxville who was not part of the study. “What do our cells do after we die, and what actually is death?”

What has become clear is that death isn’t the immediate end for genes. Some mouse and zebrafish genes remain active for up to four days after the animals die, scientists reported in 2017 in Open Biology.
In the new work, researchers examined changes in DNA’s chemical cousin, RNA. “There’s been a dogma that RNA is a weak, unstable molecule,” says Tom Gilbert, a geneticist at the Natural History Museum of Denmark in Copenhagen who has studied postmortem genetics. “So people always assumed that DNA might survive after death, but RNA would be gone.”
But recent research has found that RNA can be surprisingly stable, and some genes in our DNA even continue to be transcribed, or written, into RNA after we die, Gilbert says. “It’s not like you need a brain for gene expression,” he says. Molecular processes can continue until the necessary enzymes and chemical components run out.

“It’s no different than if you’re cooking a pasta and it’s boiling — if you turn the cooker off, it’s still going to bubble away, just at a slower and slower rate,” he says.

No one knows exactly how long a human’s molecular pot might keep bubbling, but geneticist and study leader Roderic Guigó of the Centre for Genomic Regulation in Barcelona says his team’s work may help toward figuring that out. “I think it’s an interesting question,” he says. “When does everything stop?”

Tissues from the dead are frequently used in genetic research, and Guigó and his colleagues had initially set out to learn how genetic activity, or gene expression, compares in dead and living tissues.

The researchers analyzed gene activity and degradation in 36 different kinds of human tissue, such as the brain, skin and lungs. Tissue samples were collected from more than 500 donors who had been dead for up to 29 hours. Postmortem gene activity varied in each tissue, the scientists found, and they used a computer to search for patterns in this activity. Just four tissues, taken together, could give a reliable time of death: subcutaneous fat, lung, thyroid and skin exposed to the sun.

Based on those results, the team developed an algorithm that a medical examiner might one day use to determine time of death. Using tissues in the lab, the algorithm could estimate the time of death to within about nine minutes, performing best during the first few hours after death, DeBruyn says.

For medical examiners, real-world conditions might not allow for such accuracy.

Traditionally, medical examiners use body temperature and physical signs such as rigor mortis to determine time of death. But scientists including DeBruyn are also starting to look at timing death using changes in the microbial community during decomposition (SN Online: 7/22/15).

These approaches — tracking microbial communities and gene activity — are “definitely complementary,” DeBruyn says. In the first 24 hours after death, bacteria, unlike genes, haven’t changed much, so a person’s genetic activity may be more useful for zeroing in on how long ago he or she died during that time frame. At longer time scales, microbes may work better.

“The biggest challenge is nailing down variability,” DeBruyn says. Everything from the temperature where a body is found to the deceased’s age could potentially affect how many and which genes are active after death. So scientists will have to do more experiments to account for these factors before the new method can be widely used.

Knocking back an enzyme swept mouse brains clean of protein globs that are a sign of Alzheimer’s disease. Reducing the enzyme is known to keep these nerve-damaging plaques from forming. But the disappearance of existing plaques was unexpected, researchers report online February 14 in the Journal of Experimental Medicine.

The brains of mice engineered to develop Alzheimer’s disease were riddled with these plaques, clumps of amyloid-beta protein fragments, by the time the animals were 10 months old. But the brains of 10-month-old Alzheimer’s mice that had a severely reduced amount of an enzyme called BACE1 were essentially clear of new and old plaques.
Studies rarely demonstrate the removal of existing plaques, says neuroscientist John Cirrito of Washington University in St. Louis who was not involved in the study. “It suggests there is something special about BACE1,” he says, but exactly what that might be remains unclear.

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One theory to how Alzheimer’s develops is called the amyloid cascade hypothesis. Accumulation of globs of A-beta protein bits, the idea goes, drives the nerve cell loss and dementia seen in the disease, which an estimated 5.5 million Americans had in 2017. If the theory is right, then targeting the BACE1 enzyme, which cuts up another protein to make A-beta, may help patients.
BACE1 was discovered about 20 years ago. Initial studies turned off the gene that makes BACE1 in mice for their entire lives, and those animals produced almost no A-beta. In humans, however, any drug that combats Alzheimer’s by going after the enzyme would be given to adults. So Riqiang Yan, one of the discoverers of BACE1 and a neuroscientist at the Cleveland Clinic, and colleagues set out to learn what happens when mice who start life with normal amounts of BACE1 lose much of the enzyme later on.

The researchers studied mice engineered to develop plaques in their brains when the animals are about 10 weeks old. Some of these mice were also engineered so that levels of the BACE1 enzyme, which is mostly found in the brain, gradually tapered off over time. When these mice were 4 months old, the animals had lost about 80 percent of the enzyme.
Alzheimer’s mice with normal BACE1 levels experienced a steady increase in plaques, clearly seen in samples of their brains. In Alzheimer’s mice without BACE1, however, the clumps followed a different trajectory. The number of plaques initially grew, but by the time the mice were around 6 months old, those plaques had mostly disappeared. And by 10 months, “we hardly see any,” Yan says.

Cirrito was surprised that getting rid of BACE1 later in life didn’t just stop plaques from forming, but removed them, too. “It is possible that perhaps a therapeutic agent targeting BACE1 in humans might have a similar effect,” he says.

Drugs that target BACE1 are already in development. But the enzyme has other jobs in the brain, such as potentially affecting the ability of nerve cells to communicate properly. It may be necessary for a drug to inhibit some, but not all, of the enzyme, enough to prevent plaque formation but also preserve normal signaling between nerve cells, Yan says.

What a spectacular Easter basket tardigrade eggs would make — at least for those celebrating in miniature.

A new species of the pudgy, eight-legged, water creatures lays pale, spherical microscopic eggs studded with domes crowned in long, trailing streamers.

Eggs of many land-based tardigrades have bumps, spines, filaments and such, presumably to help attach to a surface, says species codiscoverer Kazuharu Arakawa. The combination of a relatively plain surface on the egg itself (no pores, for instance) plus a filament crown helps distinguish this water bear as a new species, now named Macrobiotus shonaicus, he and colleagues report February 28 in PLOS ONE.
With about 20 new species added each year to the existing 1,200 or so known worldwide, tardigrades have become tiny icons of extreme survival (SN Online: 7/14/17).

“I was actually not looking for a new species,” Arakawa says. He happened on it when searching through moss he plucked from the concrete parking lot at his apartment. He routinely samples such stray spots to search for tardigrades, one of his main interests as a genome biologist at Keio University’s Institute for Advanced Biosciences in Tsuruoka City, Japan.
These particular moss-loving creatures managed to grow and reproduce in the lab —“very rare for a tardigrade,” he says. He didn’t realize it was an unknown species until he started deciphering the DNA that makes up some of its genes. The sequences he found didn’t match any in a worldwide database.

His two coauthors, at Jagiellonian University in Krakow, Poland, worked out that he had found a new member of a storied cluster of relatives of the tardigrade M. hufelandi. That species, described in 1834, kept turning up across continents around the world — or so biologists thought for more than a century. Realization eventually dawned that the single species that could live in such varied places was actually a complex of close cousins.

And now M. shonaicus adds yet another cousin to a group of about 30. Who knows where the next one will turn up. “I think there are lots more to be identified,” Arakawa says.

Adult mice and other rodents sprout new nerve cells in memory-related parts of their brains. People, not so much. That’s the surprising conclusion of a series of experiments on human brains of various ages first described at a meeting in November (SN: 12/9/17, p. 10). A more complete description of the finding, published online March 7 in Nature, gives heft to the controversial result, as well as ammo to researchers looking for reasons to be skeptical of the findings.

In contrast to earlier prominent studies, Shawn Sorrells of the University of California, San Francisco and his colleagues failed to find newborn nerve cells in the memory-related hippocampi of adult brains. The team looked for these cells in nonliving brain samples in two ways: molecular markers that tag dividing cells and young nerve cells, and telltale shapes of newborn cells. Using these metrics, the researchers saw signs of newborn nerve cells in fetal brains and brains from the first year of life, but they became rarer in older children. And the brains of adults had none.

There is no surefire way to spot new nerve cells, particularly in live brains; each way comes with caveats. “These findings are certain to stir up controversy,” neuroscientist Jason Snyder of the University of British Columbia writes in an accompanying commentary in the same issue of Nature.