Flicker from the dark: Reading between the lines to model our galaxy's central black hole

Looks can be deceiving. The light from an incandescent bulb seems steady, but it flickers 120 times per second. Because the brain only perceives an average of the information it receives, this flickering is blurred and the perception of constant illumination is a mere illusion.

While light cannot escape a black hole, the bright glow of rapidly orbiting gas (recall the images of M87's black hole and Sgr A*) has its own unique flicker. In a recent paper, published in Astrophysical Journal Letters, Lena Murchikova, William D. Loughlin Member at the Institute for Advanced Study; Chris White of Princeton University; and Sean Ressler of University of California Santa Barbara were able to use this subtle flickering to construct the most accurate model to date of our own galaxy's central black hole -- Sagittarius A* (Sgr A*) -- providing insight into properties such as its structure and motion.

For the first time, researchers have shown in a single model the full story of how gas travels in the center of the Milky Way -- from being blown off by stars to falling into the black hole. By reading between the proverbial lines (or flickering light), the team concluded that the most likely picture of black hole feeding in the galactic center involves directly infalling gas from large distances, rather than a slow siphoning off of orbiting material over a long period of time.

"Black holes are the gatekeepers of their own secrets," stated Murchikova. "In order to better understand these mysterious objects, we are dependent on direct observation and high-resolution modeling."

Although the existence of black holes was predicted about 100 years ago by Karl Schwarzschild, based on Albert Einstein's new theory of gravity, researchers are only now starting to probe them through observations.

In October 2021, Murchikova published a paper in Astrophysical Journal Letters, introducing a method to study black hole flickering on the timescale of a few seconds, instead of few minutes. This advance enabled a more accurate quantification of Sgr A*'s properties based on its flickering.

White has been working on the details of what happens to the gas near black holes (where the strong effects of general relativity are important) and how this affects the light coming to us. An Astrophysical Journal publication earlier this year summarizes some of his findings.

Ressler has spent years attempting to construct the most realistic simulations to date of the gas around Sgr A*. He has done this by incorporating observations of nearby stars directly into the simulations and meticulously tracking the material that they shed as it falls into the black hole. His recent work culminated in an Astrophysical Journal paper in 2020.

Murchikova, White, and Ressler then teamed up to compare the observed flickering pattern of Sgr A* with those predicted by their respective numerical models.

"The result turned out to be very interesting," explained Murchikova. "For a long time, we thought that we could largely disregard where the gas around the black hole came from. Typical models imagine an artificial ring of gas, roughly donut shaped, at some large distance from the black hole. We found that such models produce patterns of flickering inconsistent with observations."

Ressler's stellar wind model takes a more realistic approach, in which the gas consumed by black holes is originally shed by stars near the galactic center. When this gas falls into the black hole, it reproduces the correct pattern of flickering. "The model was not built with the intent to explain this particular phenomenon. Success was by no means a guarantee," commented Ressler. "So, it was very encouraging to see the model succeed so dramatically after years of work."

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Reducing air pollution can support healthy brain development

A new study finds that having a portable air cleaner in the home can reduce the negative impacts of air pollution on brain development in children.

Simon Fraser University researchers collaborated with U.S. and Mongolian scientists to study the benefits of using air filters to reduce exposure to air pollution during pregnancy, and assessed the impact on children's intelligence.

The researchers note that their randomized controlled trial is the first study of its kind to document the impacts of air pollution reduction on cognition in children.

Beginning in 2014, the team recruited 540 pregnant women in Ulaanbaatar, Mongolia to participate in the Ulaanbaatar Gestation and Air Pollution Research (UGAAR) study. Ulaanbaatar has some of the worst air quality in the world, well exceeding guidelines set by the World Health Organization (WHO).

The women were less than 18 weeks into their pregnancies and non-smokers who had not previously used air filtering devices in their homes. They were randomly assigned to either the control or intervention group. The intervention group was provided with one or two HEPA filter air cleaners and encouraged to run the air cleaners continuously for the duration of their pregnancies. The air cleaners were removed from the home once the child was born.

The researchers later measured the children's full-scale intelligence quotient (FSIQ) at four years of age using the Weschler Preschool and Primary Scale of Intelligence.

They found that the children born to mothers who had used the air cleaners had an average FSIQ that was 2.8-points higher than the group that did not use an air cleaner during pregnancy.

"These results, combined with evidence from previous studies, strongly implicate air pollution as a threat to brain development," says Ryan Allen, professor of environmental health in SFU's Faculty of Health Sciences. "But the good news is that reducing exposure had clear benefits."

Children in the intervention group also had significantly greater average verbal comprehension index scores, which is consistent with results from previous observational studies. The research suggests that a child's verbal skills may be particularly sensitive to air pollution exposure.

More than 90 per cent of the world's population breathes air with particulate matter concentrations above the WHO guidelines. The researchers suggest the population-level impact of air pollution on brain development could be substantive even if the individual-level effects are modest.

Their study results indicate that reducing exposure to air pollution during pregnancy could improve children's cognitive development around the world.

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Hair-raising research: Scientists find surprising link between immune system, hair growth

Salk scientists have uncovered an unexpected molecular target of a common treatment for alopecia, a condition in which a person's immune system attacks their own hair follicles, causing hair loss. The findings, published in Nature Immunology on June 23, 2022, describe how immune cells called regulatory T cells interact with skin cells using a hormone as a messenger to generate new hair follicles and hair growth.

"For the longest time, regulatory T cells have been studied for how they decrease excessive immune reactions in autoimmune diseases," says corresponding author Ye Zheng, associate professor in Salk's NOMIS Center for Immunobiology and Microbial Pathogenesis. "Now we've identified the upstream hormonal signal and downstream growth factor that actually promote hair growth and regeneration completely separate from suppressing immune response."

The scientists didn't begin by studying hair loss. They were interested in researching the roles of regulatory T cells and glucocorticoid hormones in autoimmune diseases. (Glucocorticoid hormones are cholesterol-derived steroid hormones produced by the adrenal gland and other tissues.) They first investigated how these immune components functioned in multiple sclerosis, Crohn's disease and asthma.

They found that glucocorticoids and regulatory T cells did not function together to play a significant role in any of these conditions. So, they thought they'd have more luck looking at environments where regulatory T cells expressed particularly high levels of glucocorticoid receptors (which respond to glucocorticoid hormones), such as in skin tissue. The scientists induced hair loss in normal mice and mice lacking glucocorticoid receptors in their regulatory T cells.

"After two weeks, we saw a noticeable difference between the mice -- the normal mice grew back their hair, but the mice without glucocorticoid receptors barely could," says first author Zhi Liu, a postdoctoral fellow in the Zheng lab. "It was very striking, and it showed us the right direction for moving forward."

The findings suggested that some sort of communication must be occurring between regulatory T cells and hair follicle stem cells to allow for hair regeneration.

Using a variety of techniques for monitoring multicellular communication, the scientists then investigated how the regulatory T cells and glucocorticoid receptors behaved in skin tissue samples. They found that glucocorticoids instruct the regulatory T cells to activate hair follicle stem cells, which leads to hair growth. This crosstalk between the T cells and the stem cells depends on a mechanism whereby glucocorticoid receptors induce production of the protein TGF-beta3, all within the regulatory T cells. TGF-beta3 then activates the hair follicle stem cells to differentiate into new hair follicles, promoting hair growth. Additional analysis confirmed that this pathway was completely independent of regulatory T cells' ability to maintain immune balance.

However, regulatory T cells don't normally produce TGF-beta3, as they did here. When the scientists scanned databases, they found that this phenomenon occurs in injured muscle and heart tissue, similar to how hair removal simulated a skin tissue injury in this study.

"In acute cases of alopecia, immune cells attack the skin tissue, causing hair loss. The usual remedy is to use glucocorticoids to inhibit the immune reaction in the skin, so they don't keep attacking the hair follicles," says Zheng. "Applying glucocorticoids has the double benefit of triggering the regulatory T cells in the skin to produce TGF-beta3, stimulating the activation of the hair follicle stem cells."

This study revealed that regulatory T cells and glucocorticoid hormones are not just immunosuppressants but also have a regenerative function. Next, the scientists will look at other injury models and isolate regulatory T cells from injured tissues to monitor increased levels of TGF-beta3 and other growth factors.

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What did Megalodon eat? Anything it wanted -- including other predators.

New Princeton research shows that prehistoric megatooth sharks -- the biggest sharks that ever lived -- were apex predators at the highest level ever measured.

Megatooth sharks get their name from their massive teeth, which can each be bigger than a human hand. The group includes Megalodon, the largest shark that ever lived, as well as several related species.

While sharks of one kind or another have existed since long before the dinosaurs -- for more than 400 million years -- these megatooth sharks evolved after the dinosaurs went extinct and ruled the seas until just 3 million years ago.

"We're used to thinking of the largest species -- blue whales, whale sharks, even elephants and diplodocuses -- as filter feeders or herbivores, not predators," said Emma Kast, a 2019 Ph.D. graduate in geosciences who is the first author on a new study in the current issue of Science Advances. "But Megalodon and the other megatooth sharks were genuinely enormous carnivores that ate other predators, and Meg went extinct only a few million years ago."

Her adviser Danny Sigman, Princeton's Dusenbury Professor of Geological and Geophysical Sciences, added, "If Megalodon existed in the modern ocean, it would thoroughly change humans' interaction with the marine environment."

A team of Princeton researchers has now discovered clear evidence that Megalodon and some of its ancestors were at the very highest rung of the prehistoric food chain -- what scientists call the highest "trophic level." Indeed, their trophic signature is so high that they must have eaten other predators and predators-of-predators in a complicated food web, say the researchers.

"Ocean food webs do tend to be longer than the grass-deer-wolf food chain of land animals, because you start with such small organisms," said Kast, now at the University of Cambridge, who wrote the first iteration of this research as a chapter in her dissertation. "To reach the trophic levels we're measuring in these megatooth sharks, we don't just need to add one trophic level -- one apex predator on top of the marine food chain -- we need to add several onto the top the modern marine food web."

Megalodon has been conservatively estimated at 15 meters long -- 50 feet -- while modern great white sharks typically top out around five meters (15 feet).

To reach their conclusions about the prehistoric marine food web, Kast, Sigman and their colleagues used a novel technique to measure the nitrogen isotopes in the sharks' teeth. Ecologists have long known that the more nitrogen-15 an organism has, the higher its trophic level, but scientists have never before been able to measure the tiny amounts of nitrogen preserved in the enamel layer of these extinct predators' teeth.

"We have a series of shark teeth from different time periods, and we were able to trace their trophic level versus their size," said Zixuan (Crystal) Rao, a graduate student in Sigman's research group and a co-author on the current paper.

One way to tuck in an extra trophic level or two is cannibalism, and several lines of evidence point to that in both megatooth sharks and other prehistoric marine predators.

The nitrogen time machine

Without a time machine, there's no easy way to recreate the food webs of extinct creatures; very few bones have survived with teeth marks that say, "I was chewed on by a massive shark."

Fortunately, Sigman and his team have spent decades developing other methods, based on the knowledge that the nitrogen isotope levels in a creature's cells reveal whether it is at the top, middle or bottom of a food chain.

"The whole direction of my research team is to look for chemically fresh, but physically protected, organic matter -- including nitrogen -- in organisms from the distant geologic past," said Sigman.

A few plants, algae and other species at the bottom of the food web have mastered the knack of turning nitrogen from the air or water into nitrogen in their tissues. Organisms that eat them then incorporate that nitrogen into their own bodies, and critically, they preferentially excrete (sometimes via urine) more of nitrogen's lighter isotope, N-14, than its heavier cousin, N-15.

In other words, N-15 builds up, relative to N-14, as you climb up the food chain.

Other researchers have used this approach on creatures from the recent past -- the most recent 10-15 thousand years -- but there hasn't been enough nitrogen left in older animals to measure, until now.

Why? Soft tissue like muscles and skin are hardly ever preserved. To complicate matters, sharks don't have bones -- their skeletons are made of cartilage.

But sharks do have one golden ticket into the fossil record: teeth. Teeth are more easily preserved than bones because they are encased in enamel, a rock-hard material that is virtually immune to most decomposing bacteria.

"Teeth are designed to be chemically and physically resistant so they can survive in the very chemically reactive environment of the mouth and break apart food that can have hard parts," Sigman explained. And in addition, sharks aren't limited to the 30 or so pearly whites that humans have. They are constantly growing and losing teeth -- modern sand sharks lose a tooth every day of their decades-long lives, on average -- which means that every shark produces thousands of teeth over its lifetime.

"When you look in the geologic record, one of the most abundant fossil types are shark teeth," said Sigman. "And within the teeth, there is a tiny amount of organic matter that was used to build the enamel of the teeth -- and is now trapped within that enamel."

Since shark teeth are so abundant and are preserved so well, the nitrogen signatures in enamel provide a way to measure status in the food web, whether the tooth fell from a shark's mouth millions of years ago or yesterday.

Even the largest tooth has only a thin casing of enamel, of which the nitrogen component is only a tiny trace. But Sigman's team has been developing more and more refined techniques for extracting and measuring these nitrogen isotope ratios, and with a little help from dentist drills, cleaning chemicals and microbes that ultimately convert the nitrogen from within the enamel into nitrous oxide, they're now able to precisely measure the N15-N14 ratio in these ancient teeth.

"We're a little bit like a brewery," he said. "We grow microbes and feed our samples to them. They produce nitrous oxide for us, and then we analyze the nitrous oxide they produced."

The analysis requires a custom-built, automated nitrous oxide preparation system that extracts, purifies, concentrates and delivers the gas to a specialized stable isotope ratio mass spectrometer.

"This has been a multiple-decades-long quest that I've been on, to develop a core method to measure these trace amounts of nitrogen," Sigman said. From microfossils in sediments, they moved on to other types of fossils, like corals, fish ear bones and shark teeth. "Next, we and our collaborators are applying this to mammalian teeth and dinosaur teeth."

A deep dive into the literature during lockdown

Early in the pandemic, while her friends were making sourdough starters and bingeing Netflix, Kast pored through the ecologic literature to look for nitrogen isotope measurements of modern marine animals.

"One of the cool things that Emma did was really dig into the literature -- all the data that's been published over decades -- and relate that to the fossil record," said Michael (Mick) Griffiths, a paleoclimatologist and geochemist at William Patterson University and a co-author on the paper.

As Kast quarantined at home, she painstakingly built up a record with more than 20,000 marine mammal individuals and more than 5,000 sharks. She wants to take things much further. "Our tool has the potential to decode ancient food webs; what we need now is samples," said Kast. "I'd love to find a museum or other archive with a snapshot of an ecosystem -- a collection of different kinds of fossils from one time and place, from forams near the very base of the food web, to otoliths -- inner ear bones -- from different kinds of fish, to teeth from marine mammals, plus shark teeth. We could do the same nitrogen isotope analysis and put together the whole story of an ancient ecosystem."

In addition to the literature search, their database includes their own samples of shark teeth. Co-author Kenshu Shimada of DePaul University connected with aquariums and museums, while co-authors Martin Becker of William Patterson University and Harry Maisch of Florida Gulf Coast University gathered megatooth specimens on the sea floor.

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Scientists map sulfur residue on Jupiter's icy moon Europa

A Southwest Research Institute-led team used the Hubble Space Telescope to observe Jupiter's moon, Europa, at ultraviolet wavelengths, filling in a "gap" in the various wavelengths used to observe this icy water world. The team's near-global UV maps show concentrations of sulfur dioxide on Europa's trailing side.

SwRI will further these studies using the Europa Ultraviolet Spectrograph (Europa-UVS), which will observe Jupiter's fourth largest moon from aboard NASA's Europa Clipper, scheduled to launch in 2024. Scientists are almost certain that hidden beneath Europa's icy surface is a saltwater ocean containing nearly twice as much water as is in all of Earth's oceans. This moon may be the most promising place in our solar system suitable for some form of life beyond Earth.

"Europa's relatively young surface is primarily composed of water ice, although other materials have been detected across its surface," said Dr. Tracy Becker, lead author of a paper describing these UV observations. "Determining whether these other materials are native to Europa is important for understanding Europa's formation and subsequent evolution."

Assessing the surface material can provide insights into the composition of the subsurface ocean. SwRI's dataset is the first to produce a near-global map of sulfur dioxide that correlates with large-scale darker regions in both the visible and the ultraviolet wavelengths.

"The results were not surprising, but we did get much better coverage and resolution than previous observations," said SwRI's Dr. Philippa Molyneux, a co-author of the paper. "Most of the sulfur dioxide is seen on the 'trailing' hemisphere of Europa. It's likely concentrated there because Jupiter's co-rotating magnetic field traps sulfur particles spewing from Io's volcanoes and slams them against the backside of Europa."

Io is another of Jupiter's largest moons but, in contrast, is considered the most volcanic body in the solar system. Jupiter's magnetic field can cause chemical reactions between the water ice and the sulfur, creating sulfur dioxide on Europa's surface.

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Can we save more lives if we let resistant bacteria live?

Antibiotic resistance is a ticking bomb under public health. WHO predicts that in 2050 more people will die from infections than from cancer -- and we are talking about infections that we today consider harmless; infections that occur in a cut or wound -- or perhaps cystitis.

The reason is that bacteria are masters at adapting. When their existence is threatened, they mutate into a new and improved version of themselves that can no longer be threatened by eg antibiotics. Consequently, many disease-causing bacteria today are resistant to antibiotics.

"That's bacteria for you. They always find a way! Of course, resistance will occur; that's how evolution works," says professor and head of research, Birgitte Kallipolitis, who studies disease-causing bacteria at the Department of Biochemistry and Molecular Biology at University of Southern Denmark.

The talents of fatty acids

And that's exactly why, like other researchers around the world, she thinks it's time to find new ways to fight or neutralize the perpetually mutating bacteria.

For some years now, she and her research group have studied a particular type of fatty acid, which has proven itself interesting in this context. The researchers use listeria as a bacterial model to test the effect of these fatty acids. Elsewhere in the world, colleagues are using salmonella and cholera bacteria for similar tests.

The particular fatty acids are interesting not only because they can kill the listeria bacteria in Kallipolitis' laboratory, but they can also turn off their ability to infect and spread infection.

The researchers' experiments have shown that the fatty acids have an antimicrobial effect, ie that they can kill listeria bacteria. At first, this sounds good, but then there is the mutation thing; trying to kill the bacteria only makes it mutate into a new and resistant version of itself.

Enter the special talent of the fatty acids: They can make the resistant bacteria harmless, so that no infection occurs at all.

"Thus, the resistant bacterium is no longer a bacterium that we must try to kill -- instead, we prevent it from spreading and making us sick," Birgitte Kallipolitis explains.

No more spreading

The concept of making a disease-carrying bacterium unable to spread or make us sick is called turning off its virulence.

When you turn off the virulence of a bacterium, you prevent it from producing proteins like adhesins and invasins, which the bacterium needs to attach to a cell so that it can enter the cell.

"If a listeria bacterium cannot enter a cell, it cannot spread, and then no infection will occur," Birgitte Kallipolitis explains.

Extra help for the elderly and weak

The Listeria bacteria in Kallipolitis' experiments are only harmless as long as their virulence is switched off. When they are no longer exposed to the fatty acids that turn off their virulence, they regain the ability to spread

"But this may be the extra help that allows a patient to cope with an infection. Antivirulent medication or supplements could be good for the prevention of infections, especially in the elderly and weak," says Birgitte Kallipolitis.

The fatty acids that she and her colleagues work with, are so-called medium and long free fatty acids.

In nuts, plants and seeds

"We have especially focused on the free fatty acids, palmitoleic acid and lauric acid, which are found in nuts, seeds, plants and milk, etc. In our experiments, they show an antivirulent effect," she says.

Kallipolitis points out that you cannot eat your way to an antivirulent effect by, for example, eating nuts and seeds containing palmitoleic acid and lauric acid.

"The fatty acids must be in the free form, and that does not generally occur in food. You can buy free fatty acids as supplements but be aware that most fatty acids in supplements are locked and not in the free form.

"We do not yet know if you can achieve the effect by consuming free fatty acids. Maybe the fatty acids are metabolized before they reach the battle ground in the intestinal system, where the fight against many resistant bacteria takes place. Maybe we need pharmacists or chemists to find a way to transport the fatty acids to the scene of the battle," she explains.

Hence, a special dietary supplement or tablet is not just around the corner, she emphasizes. Before we get there, a number of tests are needed.

"The next step will be to test the antivirulence effect in a laboratory system reminiscent of the human intestinal system; here we will add listeria bacteria and see if the fatty acids will make them avirulent. If this works, it goes on to mouse experiments, and eventually it can hopefully be used prophylactically in humans," says Birgitte Kallipolitis.

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The younger we feel, the better we rehabilitate, research shows

As scientists gradually discover evidence that people who feel younger than their chronological age are typically healthier and more psychologically resilient, the saying "you're only as old as you feel" rings increasingly true.

Could the expression also hold true for older people recuperating from physical disabilities? Apparently so. Researchers from Bar-Ilan University in Israel have found that feeling young can increase the chances of successful rehabilitation from medical conditions, even in old age. Their study was recently published in the journal Gerontology.

The study tracked 194 adult patients aged 73-84 undergoing rehabilitation from osteoporotic fractures or stroke in several rehabilitation facilities across Israel. Fractures (mostly due to falls) and stroke are frequent health events that result in the loss of one's functional independence, considered the greatest fear of older adults.

Patients were interviewed several times throughout their rehabilitation. They were asked about their subjective age (how young they felt), feelings and experiences. Their functional independence was assessed by nursing personnel who rated their functioning level at admission and at discharge using the Functional Independence Measurement (FIM) test.

Patients who felt younger (had a younger subjective age) at hospital admission showed better functional independence at discharge approximately one month later. The beneficial effect of feeling younger was found both for patients who rehabilitated from osteoporotic fractures (mainly due to falls) and for those who rehabilitated from a stroke. The researchers also found that those who felt younger rehabilitated better because they were more optimistic about their chances of regaining their functional abilities.

"The effect of subjective age at admission on functional independence at discharge was confirmed," says Prof. Amit Shrira, from the Gerontology Program at the Department of Interdisciplinary Social Sciences, who led the study together with Prof. Ehud Bodner, also from the Interdisciplinary Social Sciences department. "However, the reverse effect -- that of functional independence at admission on subjective age at discharge -- was not confirmed. This supports the conclusion that a younger age identity is an important psychological construct that contributes to a more successful rehabilitation," added Shrira, who conducted the research with Dr. Daphna Magda Kalir from the Gender Studies Program, among others.

Surprisingly, subjective age was the strongest predictor of rehabilitation outcomes, stronger even than patients' chronological age and multiple chronic health conditions occurring simultaneously (physical multimorbidity) at admission. Chronological age and physical multimorbidity are generally considered by health care practitioners in determining prognosis, whereas subjective age is unknown to most practitioners. "Those who feel younger can maintain their health and functioning for longer periods, and as the current study shows, can recuperate better from disability. Therefore, by perceiving themselves to age successfully people may preserve a healthy and vigorous lifestyle," says Shrira.

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Robotic lightning bugs take flight

Fireflies that light up dusky backyards on warm summer evenings use their luminescence for communication -- to attract a mate, ward off predators, or lure prey.

These glimmering bugs also sparked the inspiration of scientists at MIT. Taking a cue from nature, they built electroluminescent soft artificial muscles for flying, insect-scale robots. The tiny artificial muscles that control the robots' wings emit colored light during flight.

This electroluminescence could enable the robots to communicate with each other. If sent on a search-and-rescue mission into a collapsed building, for instance, a robot that finds survivors could use lights to signal others and call for help.

The ability to emit light also brings these microscale robots, which weigh barely more than a paper clip, one step closer to flying on their own outside the lab. These robots are so lightweight that they can't carry sensors, so researchers must track them using bulky infrared cameras that don't work well outdoors. Now, they've shown that they can track the robots precisely using the light they emit and just three smartphone cameras.

"If you think of large-scale robots, they can communicate using a lot of different tools -- Bluetooth, wireless, all those sorts of things. But for a tiny, power-constrained robot, we are forced to think about new modes of communication. This is a major step toward flying these robots in outdoor environments where we don't have a well-tuned, state-of-the-art motion tracking system," says Kevin Chen, who is the D. Reid Weedon, Jr. Assistant Professor in the Department of Electrical Engineering and Computer Science (EECS), the head of the Soft and Micro Robotics Laboratory in the Research Laboratory of Electronics (RLE), and the senior author of the paper.

He and his collaborators accomplished this by embedding miniscule electroluminescent particles into the artificial muscles. The process adds just 2.5 percent more weight without impacting the flight performance of the robot.

Joining Chen on the paper are EECS graduate students Suhan Kim, the lead author, and Yi-Hsuan Hsiao; Yu Fan Chen SM '14, PhD '17; and Jie Mao, an associate professor at Ningxia University. The research was published this month in IEEE Robotics and Automation Letters.

A light-up actuator

These researchers previously demonstrated a new fabrication technique to build soft actuators, or artificial muscles, that flap the wings of the robot. These durable actuators are made by alternating ultrathin layers of elastomer and carbon nanotube electrode in a stack and then rolling it into a squishy cylinder. When a voltage is applied to that cylinder, the electrodes squeeze the elastomer, and the mechanical strain flaps the wing.

To fabricate a glowing actuator, the team incorporated electroluminescent zinc sulphate particles into the elastomer but had to overcome several challenges along the way.

First, the researchers had to create an electrode that would not block light. They built it using highly transparent carbon nanotubes, which are only a few nanometers thick and enable light to pass through.

However, the zinc particles only light up in the presence of a very strong and high-frequency electric field. This electric field excites the electrons in the zinc particles, which then emit subatomic particles of light known as photons. The researchers use high voltage to create a strong electric field in the soft actuator, and then drive the robot at a high frequency, which enables the particles to light up brightly.

"Traditionally, electroluminescent materials are very energetically costly, but in a sense, we get that electroluminescence for free because we just use the electric field at the frequency we need for flying. We don't need new actuation, new wires, or anything. It only takes about 3 percent more energy to shine out light," Kevin Chen says.

As they prototyped the actuator, they found that adding zinc particles reduced its quality, causing it to break down more easily. To get around this, Kim mixed zinc particles into the top elastomer layer only. He made that layer a few micrometers thicker to accommodate for any reduction in output power.

While this made the actuator 2.5 percent heavier, it emitted light without impacting flight performance.

"We put a lot of care into maintaining the quality of the elastomer layers between the electrodes. Adding these particles was almost like adding dust to our elastomer layer. It took many different approaches and a lot of testing, but we came up with a way to ensure the quality of the actuator," Kim says.

Adjusting the chemical combination of the zinc particles changes the light color. The researchers made green, orange, and blue particles for the actuators they built; each actuator shines one solid color.

They also tweaked the fabrication process so the actuators could emit multicolored and patterned light. The researchers placed a tiny mask over the top layer, added zinc particles, then cured the actuator. They repeated this process three times with different masks and colored particles to create a light pattern that spelled M-I-T.

Following the fireflies

Once they had finetuned the fabrication process, they tested the mechanical properties of the actuators and used a luminescence meter to measure the intensity of the light.

From there, they ran flight tests using a specially designed motion-tracking system. Each electroluminescent actuator served as an active marker that could be tracked using iPhone cameras. The cameras detect each light color, and a computer program they developed tracks the position and attitude of the robots to within 2 millimeters of state-of-the-art infrared motion capture systems.

"We are very proud of how good the tracking result is, compared to the state-of-the-art. We were using cheap hardware, compared to the tens of thousands of dollars these large motion-tracking systems cost, and the tracking results were very close," Kevin Chen says.

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How elliptical craters could shed light on age of Saturn's moons

A new SwRI study describes how unique populations of craters on two of Saturn's moons could help indicate the satellites' age and the conditions of their formation. Using data from NASA's Cassini mission, SwRI postdoctoral researcher Dr. Sierra Ferguson surveyed elliptical craters on Saturn's moons Tethys and Dione for this study, which was co-authored by SwRI Principal Scientist Dr. Alyssa Rhoden, Lead Scientist Dr. Michelle Kirchoff and Lead Analyst Dr. Julien Salmon.

"Our work aims to answer the broader question of how old these moons are. To get at this question, my colleagues and I mapped elliptical craters on the surfaces of these moons to determine their size, direction and location on the moon," Ferguson said.

Circular craters are very common and can be formed from a wide range of impact conditions. However, elliptical craters are rarer and form from slow and shallow impacts, which make them especially useful in determining an object's age because shape and orientation also indicate their impactor's trajectory.

"By measuring the direction these craters point, we can get an idea of what the impactors that made these craters looked like in a dynamical sense and from which direction they might have hit the surface," she said.

At first, Ferguson was not expecting to find a pattern among the directions of the elliptical craters, but she eventually noticed a trend along the equator of Dione, one of Saturn's small moons. There, elliptical craters were overwhelmingly oriented in an east/west pattern, while the directions were more random close to the moon's poles.

"We initially interpreted this pattern to be representative of two distinct impactor populations creating these craters," she said. "One group was responsible for creating the elliptical craters at the equator, while another, less concentrated population may be more representative of the regular background population of impactors around Saturn."

Ferguson also mapped elliptical craters on Tethys, Saturn's fifth largest moon, and found that a similar size-frequency distribution of craters is unusual for objects orbiting the Sun, but curiously matches estimates for the impactor population that appears to be present on Neptune's moon, Triton. Because that population is thought to be planetocentric, or drawn in by the ice giant's massive gravity, Ferguson's results point to the importance of considering planetocentric impactors when examining the age of objects in the Saturnian system.

"It was really astonishing to see these patterns," she said.

Ferguson believes the equatorial craters could have formed from independent disks of debris orbiting each moon or potentially a single disk that affected both moons.

"Using Triton as a guide, Tethys could reasonably be billions of years old. This age estimate is dependent on how much material was available for impacting the surface and when it was available" Ferguson said. "To be certain, of course, we will need more data, but this research tells us a lot. It can give us an idea of what the formation conditions of these moons were like. Was this a system that was completely chaotic with materials hitting these satellites every which way, or was there a neat and orderly system?"

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A blueprint for life forms on Mars?

Microbes taken from surface sediment near Lost Hammer Spring, Canada, about 900 km south of the North Pole, could provide a blueprint for the kind of life forms that may once have existed, or may still exist, on Mars.

The extremely salty, very cold, and almost oxygen-free environment under the permafrost of Lost Hammer Spring in Canada's High Arctic is the one that most closely resembles certain areas on Mars. So, if you want to learn more about the kinds of life forms that could once have existed -- or may still exist -- on Mars, this is a good place to look. After much searching under extremely difficult conditions, McGill University researchers have found microbes that have never been identified before. Moreover, by using state-of-the-art genomic techniques, they have gained insight into their metabolisms. In a recent paper in ISME, the scientists demonstrate, for the first time, that microbial communities found living in Canada's High Arctic, in conditions analogous to those on Mars, can survive by eating and breathing simple inorganic compounds of a kind that have been detected on Mars (such as methane, sulfide, sulfate, carbon monoxide, and carbon dioxide). This discovery is so compelling that samples of the Lost Hammer surface sediments were selected by the European Space Agency to test the life detection capabilities of the instruments they plan to use on the next ExoMars Mission.

Developing a blueprint for life on Mars

Lost Hammer Spring, in Nunavut in Canada's High Arctic, is one of the coldest and saltiest terrestrial springs discovered to date. The water which travels up through 600 metres of permafrost to the surface is extremely salty (~24% salinity), perennially at sub-zero temperatures (~ -- 5 °C) and contains almost no oxygen (<1ppm dissolved oxygen). The very high salt concentrations keep the Lost Hammer spring from freezing, thus maintaining a liquid water habitat even at sub-zero temperatures. These conditions are analogous to those found in certain areas on Mars, where widespread salt deposits and possible cold salt springs have been observed. And while earlier studies have found evidence of microbes in this kind of Mars-like environment -- this is one of a very few studies to find microbes alive and active

To gain insight into the kind of life forms that could exist on Mars, a McGill University research team, led by Lyle Whyte of the Department of Natural Resource Sciences, has used state-of-the-art genomic tools and single cell microbiology methods to identify and characterize a novel, and more importantly, an active microbial community in this unique spring. Finding the microbes and then sequencing their DNA and mRNA was no easy task.

It takes an unusual life form to survive in difficult conditions

"It took a couple of years of working with the sediment before we were able to successfully detect active microbial communities," explains Elisse Magnuson, a PhD student in Whyte's lab, and the first author on the paper. "The saltiness of the environment interferes with both the extraction and the sequencing of the microbes, so when we were able to find evidence of active microbial communities, it was a very satisfying experience."

The team isolated and sequenced DNA from the spring community, allowing them to reconstruct genomes from approximately 110 microorganisms, most of which have never been seen before. These genomes have allowed the team to determine how such creatures survive and thrive in this unique extreme environment, acted as blueprints for potential life forms in similar environments. Through mRNA sequencing, the team were able to identify active genes in the genomes and essentially identify some very unusual microbes actively metabolizing in the extreme spring environment.

No need for organic material to support life

"The microbes we found and described at Lost Hammer Spring are surprising, because, unlike other microorganisms, they don't depend on organic material or oxygen to live," adds Whyte. "Instead, they survive by eating and breathing simple inorganic compounds such as methane, sulfides, sulfate, carbon monoxide and carbon dioxide, all of which are found on Mars. They can also fix carbon dioxide and nitrogen gasses from the atmosphere, all of which makes them highly adapted to both surviving and thriving in very extreme environments on Earth and beyond."

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Evolutionary biology: The greening ashore

A team led by evolutionary biologist Prof. Dr. Sven Gould of Heinrich Heine University Düsseldorf (HHU) has been studying the current state of research on the plant colonisation of land that occurred some 500 million years ago. The findings from this illustrated overview study published by Dr. Mona Schreiber as lead author have now appeared in the latest issue of the journal Trends in Plant Science.

It took several hundred million years after the formation of Earth some 4½ billion years ago for the initially fiery globe to cool down, allowing the first oceans and land masses to form. The land was barren rock for the next three billion years.

The blue planet with green continents that we know today did not exist as such in that era. For conditions on the continents were largely hostile to life, with a much higher volcanic activity releasing toxic gases into the atmosphere, a weaker magnetic field than exists today exposing the land more to cosmic rays, and a thinner ozone layer to filter out UV light.

This started changing approximately 500 million years ago when plants began colonizing land. The invasion catalysed a metamorphosis of the hostile environment, accelerating the transformation of the atmosphere, to lay the foundations for the development of life on land as we know it today. All this could only occur once plants, which had only lived in the oceans and inland freshwater, had conquered the continents.

Now Prof. Dr. Sven Gould of the Institute of Molecular Evolution at HHU, Prof. Dr. Stefan Rensing and Dr. Mona Schreiber, a bioinformatics specialist and artist from the University of Marburg, are providing an overview of the current state of research on the plant colonization of land in the journal Trends in Plant Science. Their paper was written in connection with priority programme 2237 "MAdLand" (Molecular Adaptation to Land), funded by the German Research Foundation. The purpose of the MAdLand programme is to explore the beginnings of the evolutionary adaptation of plant organisms to life on land.

The continents only began turning green after a streptophyte alga moved from an aquatic habitat into shore zones before completely transitioning onto land over 500 million years ago, in a process involving numerous molecular and morphological adaptations. Throughout Earth's ongoing changes, plants demonstrated tremendous adaptational capability and altered the climate in crucial fashion, chiefly by fixing carbon dioxide (CO2) on a massive scale.

Terrestrial flora spread in a dominant tour de force, with flowering plants proliferating in explosive fashion; today they comprise over 90% of all known terrestrial plant species. In the history of our planet, land plants have caused several climatic changes, demonstrating tremendous adaptive capability again and again.

Researchers are studying the genomes of species of evolutionary significance with regards to terrestrilization, including mosses, lycopods, ferns and certain algae, in an effort to advance our knowledge of evolutionary processes and molecular adaptation. Their work aims at identifying the mechanisms that served to mitigate hostile life conditions on land, which changed in the course of this evolution. These may indeed prove relevant with regard to climate change, including for crop modification in response to shifting environmental conditions.

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Agriculture emissions pose risks to health and climate

Agricultural pollution comes from the prairie, but its economic impact on humans is a problem for cities.

A study led by environmental scientists at Rice University's George R. Brown School of Engineering puts numbers to the toll of reactive nitrogen species produced in America's croplands.

The study led by Daniel Cohan, an associate professor of civil and environmental engineering, and graduate student Lina Luo quantifies emissions of nitrogen oxides, ammonia and nitrous oxide from fertilized soils over three years (2011, 2012 and 2017) and compares their impacts by region on air quality, health and climate.

While seasonal and regional impacts differ across types of emission, the study found total annual damages from ammonia were much larger overall -- at $72 billion -- than those from nitrogen oxides ($12 billion) and nitrous oxide ($13 billion).

Air pollution damages are measured by increased mortality and morbidity and the value of statistical life, while monetized damages from climate change include the threats to crops, property, ecosystem services and human health.

On that basis, the researchers found the health impact of air pollution from ammonia and nitrogen oxides, which react to form particulate matter and ozone, substantially outweighed climate impact from nitrous oxide in all regions and years.

The highest social costs arose from agriculture-heavy regions of California, Florida and the Midwest, where ammonia and nitrogen oxides form air pollution upwind of population centers. For both pollutants, emissions peak in the spring after fertilizers are applied.

The study in the American Chemical Society journal Environmental Science & Technology concludes air pollution, health and climate should all be considered in future assessments of how farming practices affect reactive nitrogen emissions.

"We always talk about how carbon dioxide and methane contribute to greenhouse gases, but nitrous oxide is about 300 times more potent than carbon dioxide for its global warming potential," Luo said.

She noted farming strategies that reduce greenhouse gases can increase air pollutants and vice versa. "We need to see if they can reduce all three nitrogen species -- or make some tradeoffs -- and still not decrease crop yield," Luo said.

Nitrogen is essential for crop growth, Cohan added, but the study shows the importance of controlling agricultural emissions has been largely neglected by air quality management and climate policy, even as the Environmental Protection Agency considers tightening air quality standards and the Biden administration seeks to slash greenhouse gas emissions.

He said federal agencies have focused on controlling transportation and industrial emissions, leaving agriculture as the largest source of damaging nitrogen pollutants in the United States, a problem exacerbated by climate change and increased crop production.

"Our group had been studying nitrogen oxide emissions for a number of years and began to realize that we can't just focus on that," Cohan said. "We needed to consider the range of emissions that come from soils, and we became curious about the relative impacts of different air pollutants and greenhouse gases the emanate from agricultural soils.

"A big part of our motivation was realizing that choices in farming practices might cause some emissions to go up and other emissions to go down," he said. For instance, switching from surface broadcast to deep injection of fertilizers would lower ammonia but raise nitrogen oxide emissions. That would benefit nearby cities sensitive to particulate matter levels, but harm regions where ozone is of more concern.

Cohan said when all the emissions are quantified on a monetary basis, ammonia and nitrogen oxides that form air-polluting particulate matter and ozone and contribute to global warming have the greatest impact.

"Those of us who study these pollutants for a living know how potent ammonia is, but the message hasn't gotten through to most regulators and policymakers," Cohan said. "In fact, ammonia is one of the most potent sources of particulate matter because of how it binds with other pollutants to have a multiplying effect.

"That's an important message: We need to take more steps to control ammonia," he said.

If there's a silver lining, Cohan said, it's that pollution from other sources has dropped enough to make agriculture's impact prevalent.

"What's crucial is to take steps that have more of the nitrogen go to the crops, and less of it be released to the air and water," he said. That could involve adding biochar or other amendments to soil, a topic of ongoing study at Rice.

"Before we can do that, we needed to establish a baseline of emissions coming from the soil," Cohan said. "This paper lays that out."

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Gaia space telescope rocks the science of asteroids

The European Gaia space mission has produced an unprecedented amount of new, improved, and detailed data for almost two billion objects in the Milky Way galaxy and the surrounding cosmos. The Gaia Data Release 3 on Monday revolutionizes our knowledge of the Solar System and the Milky Way and its satellite galaxies.

The Gaia space mission of the European Space Agency ESA is constructing an ultraprecise three-dimensional map of our Milky Way galaxy, observing almost two billion stars or roughly one percent of all the stars in our galaxy. Gaia was launched in December 2013 and has collected science data from July 2014. On Monday, June 13, ESA released Gaia data in Data Release 3 (DR3). Finnish researchers were strongly involved in the release.

Gaia data allows, for example, for the derivation of asteroid and exoplanet orbits and physical properties. The data helps unveil the origin and future evolution of the Solar System and the Milky Way and helps understand stellar and planetary-system evolution and our place in the cosmos.

Gaia revolves about its axis slowly in about six hours and is composed of two optical space telescopes. Three science instruments allow for accurate determination of stellar positions and velocities as well as the spectral properties. Gaia resides at about 1,5 million kilometers from the Earth in the anti-Sun direction, where it orbits the Sun together with the Earth in the proximity of the so-called Sun-Earth Lagrange L2-point.

Gaia DR3 on June 13, 2022 was significant across astronomy. Some 50 scientific articles are being published with DR3, of which nine articles have been devoted to underscoring the exceptionally significant potential of DR3 for future research.

The new DR3 data comprises, for example, the chemical compositions, temperatures, colors, masses, brightnesses, ages, and radial velocities of stars. DR3 includes the largest ever binary star catalog for the Milky Way, more than 150 000 Solar System objects, largely asteroids but also planetary satellites, as well as millions of galaxies and quasars beyond the Milky Way.

"There are so many revolutionary advances that it is difficult to pinpoint a single most significant advance. Based on Gaia DR3, Finnish researchers will change the conception of asteroids in our Solar System, exoplanets and stars in our Milky Way galaxy, as well as galaxies themselves, including the Milky Way and its surrounding satellite galaxies. Returning to our home planet, Gaia will produce an ultraprecise reference frame for navigation and positioning," says Academy Professor Karri Muinonen from the University of Helsinki.

Gaia and asteroids

The ten-fold increase in the number of asteroids reported in Gaia DR3 as compared to DR2 means that there is a significant increase in the number of close encounters between Gaia-detected asteroids. These close encounters can be utilized for asteroid mass estimation and we expect a significant increase in the number of asteroid masses to be derived by using Gaia DR3 astrometry, in particular, when combined with astrometry obtained by other telescopes.

In the conventional computation of an asteroid's orbit, the asteroid is assumed to be a point-like object and its size, shape, rotation and surface light scattering properties are not taken into account. The Gaia DR3 astrometry is, however, so accurate that the angular offset between the asteroid's center of mass and the center of the area illuminated by the Sun and visible to Gaia must be accounted for. Based on Gaia DR3, the offset has been certified for asteroid (21) Lutetia (Figure 2). The ESA Rosetta space mission imaged Lutetia during the flyby on July 10, 2010. With the help of the Rosetta Lutetia imagery and ground-based astronomical observations, a rotation period, rotational pole orientation, and detailed shape model were derived. When the physical modeling is incorporated into orbit computation, the systematic errors are removed and, contrary to conventional computation, all observations can be incorporated into the orbit solution. Consequently, the Gaia astrometry provides information about the physical properties of asteroids. These properties need to be taken into account using physical models or empirical error models for the astrometry.

The Gaia DR3 includes, for the first time, spectral observations. The spectrum measures the color of the target, meaning the brightness at different wavelengths. One especially interesting feature is that the new release contains about 60 000 spectra of asteroids in our Solar System (Figure 3). The asteroid spectrum contains information on their composition and, thus, about their origin and the evolution of the whole Solar System. Before the Gaia DR3, there has been only few thousand asteroid spectra available, so Gaia will multiply the amount of data by more than an order of magnitude.

Gaia and exoplanets

Gaia is expected to produce detections of up to 20 000 giant exoplanets by measuring their gravitational effect on the movement of their host stars. This will enable finding virtually all Jupiter-like exoplanets in the Solar neighbourhood over the coming years and determining how common are Solar System -like architectures. The first such astrometric Gaia detection was a giant exoplanet around epsilon Indi A, that corresponds to the nearest Jupiter-like exoplanet only 12 light years away. The first such detections are possible because acceleration observed in radial velocity surveys can be combined with movement data from Gaia to determine the orbits and planetary masses.

Gaia and galaxies

The microarcsecond resolution of Gaia DR3 provides precise measurements of the motions of stars, not only within our own Milky Way galaxy, but also for the many satellite galaxies that surround it. From the motion of stars within the Milky Way itself, we can accurately measure its mass, and together with the proper motion of satellites, we can now accurately determine their orbits. This lets us look both into the past and into the future of the Milky Way galaxy system. For example, we can find out which of the galaxies that surround the Milky Way are true satellites, and which are just passing by. We can also investigate if the evolution of the Milky Way conforms to cosmological models, and in particular, whether the satellite orbits fit the standard dark matter model.

Gaia and reference frames

The International Celestial Reference Frame, ICRF3, is based on the position of a few thousand quasars determined by Very Long Baseline Interferometry (VLBI) at radio wavelengths. ICRF3 is used to obtain the coordinates of celestial objects and to determine the orbits of satellites. Quasars of ICRF3 are also fixed points on the sky that can be used to determine the precise orientation of the Earth in space at any time. Without this information, for example, satellite positioning would not work.

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Unique Viking shipyard discovered at Birka

Archaeologists from Stockholm University's Archaeological Research Laboratory have located a unique Viking Age shipyard site at Birka on Björkö in Lake Mälaren. The discovery challenges previous theories about how the maritime activities of the Viking Age were organised.

"A site like this has never been found before, it is the first of its kind, but the finds convincingly show that it was a shipyard," says Sven Isaksson, Professor of Archaeological Science at Stockholm University, who led the investigations together with Sven Kalmring, associate professor at Stockholm University and expert on ports and urbanisation in the Viking Age at the Zentrum für Baltische und Skandinavische Archäologie in Schleswig.

The site found consisted of a stone-lined depression in the Viking Age shore zone with a wooden boat slip at the bottom. The finds at the site consist of large quantities of both unused and used boat rivets, whetstones made from slate and woodworking tools. "The finds of artefacts from the area shows with great clarity that this is where people have served their ships," says Sven Isaksson.

Previous investigations have observed several of the remains before, but it is through the latest finds that it has become possible to take a comprehensive view. "Through systematic survey, mapping and drone investigations, we can now show that Birka, in addition to the urban environment, also has a very rich maritime cultural landscape with remains of everything from jetties to boat launches and shipyards," says Sven Isaksson.

Ships and shipping are characteristic of the Viking Age in the Nordic countries, both for warfare and for trade. One expression of Viking Age long-distance trade is the city-like trading posts that sprang up in the Nordic countries at the time. In Sweden, the best-preserved example is the UNESCO World Heritage site of Birka on Björkö in Lake Mälaren. "It's not just about the first urban environments, but shows an intensive exchange of trade goods and ideas between people," says Sven Kalmring.

The town ramparts around Birka functioned not only as a defence, but also as a legal, economic and social boundary. Previous investigations of harbour facilities in Birka have mostly been carried out inside the town rampart, in the area known as the Black Earth harbour area, and below the so-called Garrison. The newly discovered shipyard at *Kugghamn is located, along with a number of other maritime remains, outside Birka's town rampart, along the northern shore of Björkö. "By investigating various maritime elements in connection with a possible house site in Kugghamn, we are now trying to get an overall view of a very exciting and previously archaeologically completely unexplored environment," says Sven Kalmring.

In order to secure source material that can add nuance to our knowledge of Birka's maritime cultural landscape, the archaeological investigations are continuing. Among other things, the remains of a boat landing site located outside the town rampart are being investigated, similar to the shipyard site and unlike the previously investigated harbour remains in the Black Earth. Another question the archaeologists are trying to answer is who was allowed to dock were. "Could anyone land anywhere, or did it matter if it was inside or outside the town rampart? There is much to ponder here. But for us, the investigation doesn't end with the fieldwork, we continue in the lab. By using analytical laboratory techniques, we get more information out of the fragmentary source material than is otherwise possible," says Sven Isaksson.

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A rare discovery of long-term memory in wild frog-eating bats

Frog-eating bats trained by researchers to associate a phone ringtone with a tasty treat were able to remember what they learned for up to four years in the wild, new research has found.

The study acquainted 49 bats with a series of ringtones that attracted their attention, and trained them to associate flying toward just one of the tones with a reward: a baitfish snack.

Between one and four years later, eight of those bats were recaptured and exposed again to the food-related ringtone. All of them flew toward the sound, and six flew all the way to the speaker and grabbed the food reward, meaning they expected to find food. Control bats without previous training on the sounds were comparatively unmoved by the exposure to the unfamiliar tones.

"I was surprised -- I went into this thinking that at least a year would be a reasonable time for them to remember, given all the other things they need to know and given that long-term memory does have real costs. Four years strikes me as a long time to hold on to a sound that you might never hear again," said lead author May Dixon, a postdoctoral scholar in evolution, ecology and organismal biology at The Ohio State University.

Dixon led this study at the Smithsonian Tropical Research Institute in Panama while she was a graduate student at the University of Texas at Austin.

"The environment that previous generations experienced can be extremely different from the environment an animal is born into -- and it may also change throughout an animal's life," she said. "Trying to figure out how animals use learning and memory is one way to figure out how they're going to make it in a life full of change in the modern world."

The study is published today (June 20, 2022) in Current Biology.

In the first phase, individual frog-eating bats captured for a series of cognition tests were exposed to a highly attractive sound in the lab: the mating call of the male túngara frog, one of this species of bats' preferred prey. Flying to that sound was rewarded with a piece of baitfish placed on mesh above the speaker.

Over time, the sound was mingled with and gradually replaced by a ringtone, but the reward was the same. Researchers then introduced three other ringtones, none of which was connected to a food reward. Bats were trained to discern the differences and eventually no longer flew toward the unrewarded sounds. Each bat secured at least 40 snacks by flying to the trained ringtone over 11 to 27 days. All bats were microchipped and returned to the wild.

Beginning a year later and for three additional years, Dixon captured bats and identified eight from the initial trial by their microchips. In a follow-up test of their response to the original rewarded ringtone, all eight trained bats quickly flew to the sound and were able to tell the difference between that ringtone and a new, steady tone, though many of the bats did fly to an unrewarded sound from the initial training.

When 17 untrained bats were exposed to these sounds, they mostly twitched their ears in response to the sounds, but didn't fly toward them.

"The study taught us a lot because there are relatively few studies of long-term memory in wild animals and we don't have systematic understanding of long-term memories in nature yet," Dixon said. "If we can collect additional data on different species of bats, we could pick this apart and see what life histories select for long memories."

The paper lists 39 previous studies that have documented memory in species ranging from fish, birds and bats to goats and primates. Some of the longest of those experiments -- documenting memory in sea lions for 10 years, tortoises for nine years and dolphins for 20 years -- were all conducted on animals that lived in captivity the entire time.

"Being able to study memory in the wild is important," said study co-author Gerald Carter, assistant professor of evolution, ecology and organismal biology at Ohio State. "You can't necessarily extrapolate from the wealth of data we have on animals in the lab to what they're facing in the wild, where there are many more things they have to remember. The environment is different and the brain is different in the wild versus captivity."

Despite the human tendency to assume a long memory gives our species the intelligence advantage, nature shows us that memory flexibility -- also called adaptive forgetting -- may be important for survival.

"It's not always true that being the smartest or having the longest memory is actually advantageous. Research has shown that fruitflies selected for improved memories can't compete as well against other fruitflies," Dixon said. "Just because it's useful for humans to be so smart and have such good memories doesn't necessarily mean it's going to be the best thing for other animals.

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New model helps identify mutations that drive cancer

Cancer cells can have thousands of mutations in their DNA. However, only a handful of those actually drive the progression of cancer; the rest are just along for the ride.

Distinguishing these harmful driver mutations from the neutral passengers could help researchers identify better drug targets. To boost those efforts, an MIT-led team has built a new computer model that can rapidly scan the entire genome of cancer cells and identify mutations that occur more frequently than expected, suggesting that they are driving tumor growth. This type of prediction has been challenging because some genomic regions have an extremely high frequency of passenger mutations, drowning out the signal of actual drivers

"We created a probabilistic, deep-learning method that allowed us to get a really accurate model of the number of passenger mutations that should exist anywhere in the genome," says Maxwell Sherman, an MIT graduate student. "Then we can look all across the genome for regions where you have an unexpected accumulation of mutations, which suggests that those are driver mutations."

In their new study, the researchers found additional mutations across the genome that appear to contribute to tumor growth in 5 to 10 percent of cancer patients. The findings could help doctors to identify drugs that would have greater chance of successfully treating those patients, the researchers say. Currently, at least 30 percent of cancer patients have no detectable driver mutation that can be used to guide treatment.

Sherman, MIT graduate student Adam Yaari, and former MIT research assistant Oliver Priebe are the lead authors of the study, which appears today in Nature Biotechnology. Bonnie Berger, the Simons Professor of Mathematics at MIT and head of the Computation and Biology group at the Computer Science and Artificial Intelligence Laboratory (CSAIL), is a senior author of the study, along with Po-Ru Loh, an assistant professor at Harvard Medical School and associate member of the Broad Institute of MIT and Harvard. Felix Dietlein, an associate professor at Harvard Medical School and Boston Children's Hospital, is also an author of the paper.

A new tool

Since the human genome was sequenced two decades ago, researchers have been scouring the genome to try to find mutations that contribute to cancer by causing cells to grow uncontrollably or evade the immune system. This has successfully yielded targets such as epidermal growth factor receptor (EGFR), which is commonly mutated in lung tumors, and BRAF, a common driver of melanoma. Both of these mutations can now be targeted by specific drugs.

While those targets have proven useful, protein-coding genes make up only about 2 percent of the genome. The other 98 percent also contains mutations that can occur in cancer cells, but it has been much more difficult to figure out if any of those mutations contribute to cancer development.

"There has really been a lack of computational tools that allow us to search for these driver mutations outside of protein-coding regions," Berger says. "That's what we were trying to do here: design a computational method to let us look at not only the 2 percent of the genome that codes for proteins, but 100 percent of it."

To do that, the researchers trained a type of computational model known as a deep neural network to search cancer genomes for mutations that occur more frequently than expected. As a first step, they trained the model on genomic data from 37 different types of cancer, which allowed the model to determine the background mutation rates for each of those types.

"The really nice thing about our model is that you train it once for a given cancer type, and it learns the mutation rate everywhere across the genome simultaneously for that particular type of cancer," Sherman says. "Then you can query the mutations that you see in a patient cohort against the number of mutations you should expect to see."

The data used to train the models came from the Roadmap Epigenomics Project and an international collection of data called the Pan-Cancer Analysis of Whole Genomes (PCAWG). The model's analysis of this data gave the researchers a map of the expected passenger mutation rate across the genome, such that the expected rate in any set of regions (down to the single base pair) can be compared to the observed mutation count anywhere across the genome.

Changing the landscape

Using this model, the MIT team was able to add to the known landscape of mutations that can drive cancer. Currently, when cancer patients' tumors are screened for cancer-causing mutations, a known driver will turn up about two-thirds of the time. The new results of the MIT study offer possible driver mutations for an additional 5 to 10 percent of the pool of patients.

One type of noncoding mutation the researchers focused on is called "cryptic splice mutations." Most genes consist of sequences of exons, which encode protein-building instructions, and introns, which are spacer elements that usually get trimmed out of messenger RNA before it is translated into protein. Cryptic splice mutations are found in introns, where they can confuse the cellular machinery that splices them out. This results in introns being included when they shouldn't be.

Using their model, the researchers found that many cryptic splice mutations appear to disrupt tumor suppressor genes. When these mutations are present, the tumor suppressors are spliced incorrectly and stop working, and the cell loses one of its defenses against cancer. The number of cryptic splice sites that the researchers found in this study accounts for about 5 percent of the driver mutations found in tumor suppressor genes.

Targeting these mutations could offer a new way to potentially treat those patients, the researchers say. One possible approach that is still in development uses short strands of RNA called antisense oligonucleotides (ASOs) to patch over a mutated piece of DNA with the correct sequence.

"If you could make the mutation disappear in a way, then you solve the problem. Those tumor suppressor genes could keep operating and perhaps combat the cancer," Yaari says. "The ASO technology is actively being developed, and this could be a very good application for it."

Another region where the researchers found a high concentration of noncoding driver mutations is in the untranslated regions of some tumor suppressor genes. The tumor suppressor gene TP53, which is defective in many types of cancer, was already known to accumulate many deletions in these sequences, known as 5' untranslated regions. The MIT team found the same pattern in a tumor suppressor called ELF3.

The researchers also used their model to investigate whether common mutations that were already known might also be driving different types of cancers. As one example, the researchers found that BRAF, previously linked to melanoma, also contributes to cancer progression in smaller percentages of other types of cancers, including pancreatic, liver, and gastroesophageal.

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Mysterious 'blue blobs' reveal a new kind of star system

University of Arizona astronomers have identified five examples of a new class of stellar system. They're not quite galaxies and only exist in isolation.

The new stellar systems contain only young, blue stars, which are distributed in an irregular pattern and seem to exist in surprising isolation from any potential parent galaxy.

The stellar systems -- which astronomers say appear through a telescope as "blue blobs" and are about the size of tiny dwarf galaxies -- are located within the relatively nearby Virgo galaxy cluster. The five systems are separated from any potential parent galaxies by over 300,000 light years in some cases, making it challenging to identify their origins.

The astronomers found the new systems after another research group, led by the Netherlands Institute for Radio Astronomy's Elizabeth Adams, compiled a catalog of nearby gas clouds, providing a list of potential sites of new galaxies. Once that catalog was published, several research groups, including one led by UArizona associate astronomy professor David Sand, started looking for stars that could be associated with those gas clouds.

The gas clouds were thought to be associated with our own galaxy, and most of them probably are, but when the first collection of stars, called SECCO1, was discovered, astronomers realized that it was not near the Milky Way at all, but rather in the Virgo cluster, which is much farther away but still very nearby in the scale of the universe.

SECCO1 was one of the very unusual "blue blobs," said Michael Jones, a postdoctoral fellow in the UArizona Steward Observatory and lead author of a study that describes the new stellar systems. Jones presented the findings, which Sand co-authored, during the 240th American Astronomical Society meeting in Pasadena, California, Wednesday.

"It's a lesson in the unexpected," Jones said. "When you're looking for things, you're not necessarily going to find the thing you're looking for, but you might find something else very interesting."

The team obtained their observations from the Hubble Space Telescope, the Very Large Array telescope in New Mexico and the Very Large Telescope in Chile. Study co-author Michele Bellazzini, with the Istituto Nazionale di Astrofisica in Italy, led the analysis of the data from Very Large Telescope and has submitted a companion paper focusing on that data.

Together, the team learned that most of the stars in each system are very blue and very young and that they contain very little atomic hydrogen gas. This is significant because star formation begins with atomic hydrogen gas, which eventually evolves into dense clouds of molecular hydrogen gas before forming into stars.

"We observed that most of the systems lack atomic gas, but that doesn't mean there isn't molecular gas," Jones said. "In fact, there must be some molecular gas because they are still forming stars. The existence of mostly young stars and little gas signals that these systems must have lost their gas recently."

The combination of blue stars and lack of gas was unexpected, as was a lack of older stars in the systems. Most galaxies have older stars, which astronomers refer to as being "red and dead."

"Stars that are born red are lower mass and therefore live longer than blue stars, which burn fast and die young, so old red stars are usually the last ones left living," Jones said. "And they're dead because they don't have any more gas with which to form new stars. These blue stars are like an oasis in the desert, basically."

The fact that the new stellar systems are abundant in metals hints at how they might have formed.

"To astronomers, metals are any element heavier than helium," Jones said. "This tells us that these stellar systems formed from gas that was stripped from a big galaxy, because how metals are built up is by many repeated episodes of star formation, and you only really get that in a big galaxy."

There are two main ways gas can be stripped from a galaxy. The first is tidal stripping, which occurs when two big galaxies pass by each other and gravitationally tear away gas and stars.

The other is what's known as ram pressure stripping.

"This is like if you belly flop into a swimming pool," Jones said. "When a galaxy belly flops into a cluster that is full of hot gas, then its gas gets forced out behind it. That's the mechanism that we think we're seeing here to create these objects."

The team prefers the ram pressure stripping explanation because in order for the blue blobs to have become as isolated as they are, they must have been moving very quickly, and the speed of tidal stripping is low compared to ram pressure stripping.

Astronomers expect that one day these systems will eventually split off into individual clusters of stars and spread out across the larger galaxy cluster.

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Who wants to be a billionaire? Most don't -- which is good news for the planet

A founding economic principle that everyone is motivated by 'unlimited wants', stuck on a consumerist treadmill and striving to accumulate as much wealth as they can, is untrue, say the authors of a new study.

The long-held economic belief that people have unlimited wants has permeated economic thinking and government policies and has shaped much of modern society, including advertising and consumerism.

But belief in this principle has also had dire consequences for the health of the planet. Striving to continually increase individual wealth, and pursuing unending economic growth, has come at a heavy cost. As wealth has increased, so too has resource use and pollution.

Up until now, researchers have struggled to find appropriate ways to decouple economic growth from damaging economic principles. Now though, a new study led by psychologists at the universities of Bath, Bath Spa and Exeter challenges the idea that unlimited wants are human nature, which could have important implications for the planet.

Across nearly 8000 people from 33 countries spanning six continents, they surveyed how much money people wanted to achieve their 'absolutely ideal life'. In 86% of countries most people thought they could achieve this with US $10 million or less, and in some countries as little as $1 million.

Whilst these figures may still sound a lot, when considered that they represent a person's ideal wealth across their whole life they are relatively moderate. Expressed differently, the wealth of the world's single richest person, at over $200 billion, is enough for more than two hundred thousand people to achieve their 'absolutely ideal lives'.

The researchers collected responses about ideal wealth from individuals in countries across all inhabited continents, including countries rarely used in cross-cultural psychology such as Saudi Arabia, Uganda, Tunisia, Nicaragua, and Vietnam. People with unlimited wants were identified in every country, but they were always in the minority.

They found that those with unlimited wants tended to be younger and city-dwellers, who placed more value on success, power, and independence. Unlimited wants were also more common in countries with greater acceptance of inequality and in countries that are more collectivistic: focused more on group than individual responsibilities and outcomes.

For example, Indonesia, which is considered more collectivistic and accepting of inequality, had the most people with unlimited wants whilst the more individualistic and equality-concerned UK had fewer. However, there were anomalies like China, where few people had unlimited wants despite high cultural collectivism and acceptance of inequality.

Lead researcher, Dr Paul Bain from the Department of Psychology at the University of Bath (UK) explained: "The ideology of unlimited wants, when portrayed as human nature, can create social pressure for people to buy more than they actually want.

"Discovering that most people's ideal lives are actually quite moderate could make it socially easier for people to behave in ways that are more aligned with what makes them genuinely happy and to support stronger policies to help safeguard the planet."

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