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In the basement of MIT's Building 3, a robot is carefully contemplating its next move. It gently pokes at a tower of blocks, looking for the best block to extract without toppling the tower, in a solitary, slow-moving, yet surprisingly agile game of Jenga.

The robot, developed by MIT engineers, is equipped with a soft-pronged gripper, a force-sensing wrist cuff, and an external camera, all of which it uses to see and feel the tower and its individual blocks.

As the robot carefully pushes against a block, a computer takes in visual and tactile feedback from its camera and cuff, and compares these measurements to moves that the robot previously made. It also considers the outcomes of those moves -- specifically, whether a block, in a certain configuration and pushed with a certain amount of force, was successfully extracted or not. In real-time, the robot then "learns" whether to keep pushing or move to a new block, in order to keep the tower from falling.

Details of the Jenga-playing robot are published in the journal Science Robotics. Alberto Rodriguez, the Walter Henry Gale Career Development Assistant Professor in the Department of Mechanical Engineering at MIT, says the robot demonstrates something that's been tricky to attain in previous systems: the ability to quickly learn the best way to carry out a task, not just from visual cues, as it is commonly studied today, but also from tactile, physical interactions.

"Unlike in more purely cognitive tasks or games such as chess or Go, playing the game of Jenga also requires mastery of physical skills such as probing, pushing, pulling, placing, and aligning pieces. It requires interactive perception and manipulation, where you have to go and touch the tower to learn how and when to move blocks," Rodriguez says. "This is very difficult to simulate, so the robot has to learn in the real world, by interacting with the real Jenga tower. The key challenge is to learn from a relatively small number of experiments by exploiting common sense about objects and physics."

He says the tactile learning system the researchers have developed can be used in applications beyond Jenga, especially in tasks that need careful physical interaction, including separating recyclable objects from landfill trash and assembling consumer products.

"In a cellphone assembly line, in almost every single step, the feeling of a snap-fit, or a threaded screw, is coming from force and touch rather than vision," Rodriguez says. "Learning models for those actions is prime real-estate for this kind of technology."

The paper's lead author is MIT graduate student Nima Fazeli. The team also includes Miquel Oller, Jiajun Wu, Zheng Wu, and Joshua Tenenbaum, professor of brain and cognitive sciences at MIT.
Push and pull
In the game of Jenga -- Swahili for "build" -- 54 rectangular blocks are stacked in 18 layers of three blocks each, with the blocks in each layer oriented perpendicular to the blocks below. The aim of the game is to carefully extract a block and place it at the top of the tower, thus building a new level, without toppling the entire structure.

To program a robot to play Jenga, traditional machine-learning schemes might require capturing everything that could possibly happen between a block, the robot, and the tower -- an expensive computational task requiring data from thousands if not tens of thousands of block-extraction attempts.

Instead, Rodriguez and his colleagues looked for a more data-efficient way for a robot to learn to play Jenga, inspired by human cognition and the way we ourselves might approach the game.

The team customized an industry-standard ABB IRB 120 robotic arm, then set up a Jenga tower within the robot's reach, and began a training period in which the robot first chose a random block and a location on the block against which to push. It then exerted a small amount of force in an attempt to push the block out of the tower.

For each block attempt, a computer recorded the associated visual and force measurements, and labeled whether each attempt was a success.

Rather than carry out tens of thousands of such attempts (which would involve reconstructing the tower almost as many times), the robot trained on just about 300, with attempts of similar measurements and outcomes grouped in clusters representing certain block behaviors. For instance, one cluster of might represent attempts on a block that was hard to move, versus one that was easier to move, or that toppled the tower when moved. For each data cluster, the robot developed a simple model to predict a block's behavior given its current visual and tactile measurements.

Fazeli says this clustering technique dramatically increases the efficiency with which the robot can learn to play the game, and is inspired by the natural way in which humans cluster similar behavior: "The robot builds clusters and then learns models for each of these clusters, instead of learning a model that captures absolutely everything that could happen."
Stacking up
The researchers tested their approach against other state-of-the-art machine learning algorithms, in a computer simulation of the game using the simulator MuJoCo. The lessons learned in the simulator informed the researchers of the way the robot would learn in the real world.

"We provide to these algorithms the same information our system gets, to see how they learn to play Jenga at a similar level," Oller says. "Compared with our approach, these algorithms need to explore orders of magnitude more towers to learn the game."

Curious as to how their machine-learning approach stacks up against actual human players, the team carried out a few informal trials with several volunteers.

"We saw how many blocks a human was able to extract before the tower fell, and the difference was not that much," Oller says.

But there is still a way to go if the researchers want to competitively pit their robot against a human player. In addition to physical interactions, Jenga requires strategy, such as extracting just the right block that will make it difficult for an opponent to pull out the next block without toppling the tower.

For now, the team is less interested in developing a robotic Jenga champion, and more focused on applying the robot's new skills to other application domains.

"There are many tasks that we do with our hands where the feeling of doing it 'the right way' comes in the language of forces and tactile cues," Rodriguez says. "For tasks like these, a similar approach to ours could figure it out."

This research was supported, in part, by the National Science Foundation through the National Robotics Initiative.

Video: https://www.youtube.com/watch?v=o1j_amoldMs

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robotics research; engineering; telecommunications; vehicles; robotics; artificial intelligence; video games; educational technology

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Robot combines vision and touch to learn the game of Jenga: Machine-learning approach could help robots assemble cellphones and other small parts in a manufacturing line

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In the basement of MIT's Building 3, a robot is carefully contemplating its next move. It gently pokes at a tower of blocks, looking for the best block to extract without toppling the tower, in a solitary, slow-moving, yet surprisingly agile game of Jenga.

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https://www.sciencenews.org/blog/wild-things/tiger-sharks-feast-migratory-birds-fall-out-sky?tgt=nr

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https://www.sciencedaily.com/releases/2019/05/190521124519.htm

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https://www.newscientist.com/article/2204076-plastic-straws-will-be-banned-in-the-uk-from-april-2020/

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https://www.bbc.com/news/38183588

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So is this the news we were all waiting for? The suggestion that drinking prosecco is good for us has resurfaced on social media just in time for the Christmas party season. But is it true?

Well, it actually crops up fairly regularly

Quite a few studies have looked at the potential health benefits of a moderate amount of champagne/prosecco/cava - though not recently.

It appears the seasonal tradition for having sparkling alcoholic drinks has sparked renewed interest.

The suggestion is that these drinks can help your heart and circulation by improving the way blood vessels work, because they contain polyphenols, which are plant chemicals from red and white grapes. These increase the availability of nitric oxide which controls blood pressure.

There have also been a number of stories about a polyphenol called reservatrol found in red wine - but in 2014 those claims were said to be "overhyped".

What do the experts say?

NHS Choices - which looks into medical research reports - and the British Heart Foundation have both examined the benefits of polyphenols.

They do not dismiss their potential benefits, but point out that they are also present in the healthier option of a wide range of other foods which are all better for the liver.

A BHF spokeswoman said: "Polyphenols are antioxidant type substances which are in a range of food and drink, including some of our favourite festive treats like wine and chocolate.

"A better bet for eating well for your heart is to go for healthier sources of polyphenols like fruits and vegetables which come with all of the benefits and without the downsides to your blood pressure and waistline that drinking too much alcohol and eating too much chocolate can have."

What does it mean for my Christmas party?

Basically that it is not good for your health to drink lots of prosecco, champagne or cava.

Experts stress people still need to drink responsibly.

University of Reading researchers - one of the teams that has looked into sparkling alcohol and protective benefits - have suggested drinking three glasses a week could be of benefit.

But that does not change the official guidance about alcohol intake which says that men and women should drink no more than 14 units in a week.

The rules also say that it is best not to "save up units" and drink them all in one go and to make sure you have alcohol-free days.

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So is this the news we were all waiting for? The suggestion that drinking prosecco is good for us has resurfaced on social media just in time for the Christmas party season. But is it true? Quite a few studies have looked at the potential health benefits of a moderate amount of champagne/prosecco/cava - though not recently.

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The first mission to the farside of the moon may have found bits of the moon's interior on its surface.

The Yutu-2 rover, deployed by the Chinese Chang'e-4 spacecraft that landed on the moon in January, detected soil that appears rich in minerals thought to make up the lunar mantle, researchers report in the May 16 Nature. Those origins, if confirmed, could offer insight into the moon's early development.

"Understanding the composition of the lunar mantle is key to determining how the moon formed and evolved," says Mark Wieczorek, a geophysicist at the Côte d'Azur Observatory in Nice, France, not involved in the work. "We do not have any clear, unaltered samples of the lunar mantle" from past moon missions.

In hopes of finding mantle samples, Chang'e-4 touched down in the moon's largest impact basin, the South Pole-Aitken basin ( SN: 2/2/19, p. 5). The collision that formed this enormous divot is thought to have been powerful enough to punch through the moon's crust and expose mantle rocks to the lunar surface ( SN: 11/24/18, p. 14). During its first lunar day on the moon, Yutu-2 recorded the spectra of light reflected off lunar soil at two spots using its Visible and Near-Infrared Spectrometer.

When researchers analyzed these spectra, "what we saw was quite different" than normal lunar surface material, says study coauthor Dawei Liu, a planetary scientist at the Chinese Academy of Sciences National Astronomical Observatories in Beijing.
Yutu-2's spectra revealed soil dominated by olivine and low-calcium pyroxene, which are thought to be ingredients in the lunar mantle. One site appeared to contain about 48 percent olivine and 42 percent low-calcium pyroxene; only 10 percent was a component of the lunar crust called high-calcium pyroxene. The other site showed 55 percent olivine, 38 percent low-calcium pyroxene and a mere 7 percent high-calcium pyroxene.
"There need to be some follow-up observations" to confirm that this material really is from the mantle, says Daniel Moriarty, a lunar geologist at NASA's Goddard Space Flight Center in Greenbelt, Md., not involved in the work. That's because other materials in the lunar crust, such as plagioclase, can create spectral signatures similar to those of olivine.

Yutu-2 could identify mantle material more conclusively by examining the spectra of specific rocks, rather than mineral mixtures in soil, says Jay Melosh, a planetary scientist at Purdue University in West Lafayette, Ind., not involved in the study. "It would really be best if we could have samples back on the Earth" for lab analyses to tease apart different mineral components.

The Yutu-2 rover will continue investigating candidate mantle materials on the moon in preparation for a potential future sample return mission to Earth, the researchers say.

If from the mantle, the material's chemical makeup could help clarify the moon's early history. Billions of years ago, scientists think, the moon was partially or completely molten. As the moon cooled and solidified, materials of different densities separated into the mantle and crust. "We're currently in this stage where we have a lot of different models" for how this crystallization process occurred, Moriarty says. These models predict different abundances of minerals like olivine and pyroxene in the upper mantle. Samples of the lunar interior could help determine which models best describe how the moon evolved.

A more detailed picture of the moon's interior may also shed light on planetary evolution in general, says Briony Horgan, a planetary scientist at Purdue not involved in the research. Unlike Earth, the moon doesn't have tectonic plates that shuffle surface material around or draw ocean water into the mantle when they slip underneath one another ( SN Online: 5/13/19). The moon offers "a unique window" into the inner workings of a planetary body that's quite different from Earth, she says.

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China's lunar rover may have found minerals from the moon's mantle

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The first mission to the farside of the moon may have found bits of the moon's interior on its surface. The Yutu-2 rover, deployed by the Chinese Chang'e-4 spacecraft that landed on the moon in January, detected soil that appears rich in minerals thought to make up the lunar mantle, researchers report in the May 16 Nature.

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When making a complex decision, we often break the problem down into a series of smaller decisions. For example, when deciding how to treat a patient, a doctor may go through a hierarchy of steps -- choosing a diagnostic test, interpreting the results, and then prescribing a medication.

Making hierarchical decisions is straightforward when the sequence of choices leads to the desired outcome. But when the result is unfavorable, it can be tough to decipher what went wrong. For example, if a patient doesn't improve after treatment, there are many possible reasons why: Maybe the diagnostic test is accurate only 75 percent of the time, or perhaps the medication only works for 50 percent of the patients. To decide what do to next, the doctor must take these probabilities into account.

In a new study, MIT neuroscientists explored how the brain reasons about probable causes of failure after a hierarchy of decisions. They discovered that the brain performs two computations using a distributed network of areas in the frontal cortex. First, the brain computes confidence over the outcome of each decision to figure out the most likely cause of a failure, and second, when it is not easy to discern the cause, the brain makes additional attempts to gain more confidence.

"Creating a hierarchy in one's mind and navigating that hierarchy while reasoning about outcomes is one of the exciting frontiers of cognitive neuroscience," says Mehrdad Jazayeri, the Robert A. Swanson Career Development Professor of Life Sciences, a member of MIT's McGovern Institute for Brain Research, and the senior author of the study.

MIT graduate student Morteza Sarafyzad is the lead author of the paper, which appears in Science on May 16.
Hierarchical reasoning
Previous studies of decision-making in animal models have focused on relatively simple tasks. One line of research has focused on how the brain makes rapid decisions by evaluating momentary evidence. For example, a large body of work has characterized the neural substrates and mechanisms that allow animals to categorize unreliable stimuli on a trial-by-trial basis. Other research has focused on how the brain chooses among multiple options by relying on previous outcomes across multiple trials.

"These have been very fruitful lines of work," Jazayeri says. "However, they really are the tip of the iceberg of what humans do when they make decisions. As soon as you put yourself in any real decision-making situation, be it choosing a partner, choosing a car, deciding whether to take this drug or not, these become really complicated decisions. Oftentimes there are many factors that influence the decision, and those factors can operate at different timescales."

The MIT team devised a behavioral task that allowed them to study how the brain processes information at multiple timescales to make decisions. The basic design was that animals would make one of two eye movements depending on whether the time interval between two flashes of light was shorter or longer than 850 milliseconds.

A twist required the animals to solve the task through hierarchical reasoning: The rule that determined which of the two eye movements had to be made switched covertly after 10 to 28 trials. Therefore, to receive reward, the animals had to choose the correct rule, and then make the correct eye movement depending on the rule and interval. However, because the animals were not instructed about the rule switches, they could not straightforwardly determine whether an error was caused because they chose the wrong rule or because they misjudged the interval.

The researchers used this experimental design to probe the computational principles and neural mechanisms that support hierarchical reasoning. Theory and behavioral experiments in humans suggest that reasoning about the potential causes of errors depends in large part on the brain's ability to measure the degree of confidence in each step of the process. "One of the things that is thought to be critical for hierarchical reasoning is to have some level of confidence about how likely it is that different nodes [of a hierarchy] could have led to the negative outcome," Jazayeri says.

The researchers were able to study the effect of confidence by adjusting the difficulty of the task. In some trials, the interval between the two flashes was much shorter or longer than 850 milliseconds. These trials were relatively easy and afforded a high degree of confidence. In other trials, the animals were less confident in their judgments because the interval was closer to the boundary and difficult to discriminate.

As they had hypothesized, the researchers found that the animals' behavior was influenced by their confidence in their performance. When the interval was easy to judge, the animals were much quicker to switch to the other rule when they found out they were wrong. When the interval was harder to judge, the animals were less confident in their performance and applied the same rule a few more times before switching.

"They know that they're not confident, and they know that if they're not confident, it's not necessarily the case that the rule has changed. They know they might have made a mistake [in their interval judgment]," Jazayeri says.
Decision-making circuit
By recording neural activity in the frontal cortex just after each trial was finished, the researchers were able to identify two regions that are key to hierarchical decision-making. They found that both of these regions, known as the anterior cingulate cortex (ACC) and dorsomedial frontal cortex (DMFC), became active after the animals were informed about an incorrect response. When the researchers analyzed the neural activity in relation to the animals' behavior, it became clear that neurons in both areas signaled the animals' belief about a possible rule switch. Notably, the activity related to animals' belief was "louder" when animals made a mistake after an easy trial, and after consecutive mistakes.

The researchers also found that while these areas showed similar patterns of activity, it was activity in the ACC in particular that predicted when the animal would switch rules, suggesting that ACC plays a central role in switching decision strategies. Indeed, the researchers found that direct manipulation of neural activity in ACC was sufficient to interfere with the animals' rational behavior.

"There exists a distributed circuit in the frontal cortex involving these two areas, and they seem to be hierarchically organized, just like the task would demand," Jazayeri says.

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neuroscience; brain-computer interfaces; consumer behavior; psychology; intelligence; brain injury; social psychology; disorders and syndromes

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How we make complex decisions: Neuroscientists identify a brain circuit that helps break decisions down into smaller pieces

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When making a complex decision, we often break the problem down into a series of smaller decisions. For example, when deciding how to treat a patient, a doctor may go through a hierarchy of steps -- choosing a diagnostic test, interpreting the results, and then prescribing a medication.

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Researchers at the Icahn School of Medicine at Mount Sinai have demonstrated that stem cells derived from the placenta known as Cdx2 cells can regenerate healthy heart cells after heart attacks in animal models. The findings, published in the May 20 issue of Proceedings of the National Academy of Sciences ( PNAS), may represent a novel treatment for regenerating the heart and other organs.

"Cdx2 cells have historically been thought to only generate the placenta in early embryonic development, but never before were shown to have the ability to regenerate other organs, which is why this is so exciting. These findings may also pave the way to regenerative therapy of other organs besides the heart," said principal investigator Hina Chaudhry, MD, Director of Cardiovascular Regenerative Medicine at the Icahn School of Medicine at Mount Sinai. "They almost seem like a super-charged population of stem cells, in that they can target the site of an injury and travel directly to the injury through the circulatory system and are able to avoid rejection by the host immune system."

This team of Mount Sinai researchers had previously discovered that a mixed population of mouse placental stem cells can help the hearts of pregnant female mice recover after an injury that could otherwise lead to heart failure. In that study, they showed that the placental stem cells migrated to the mother's heart and directly to the site of the heart injury. The stem cells then programmed themselves as beating heart cells to help the repair process.

The new study was aimed at determining what type of stem cells made the heart cells regenerate. The investigators started by looking at Cdx2 cells, the most prevalent stem cell type in the previously identified mixed population, and found them to comprise the highest percentage (40 percent) of those assisting the heart from the placenta.

To test the Cdx2 cells' regenerative properties, the researchers induced heart attacks in three groups of male mice. One group received Cdx2 stem cell treatments derived from end-gestation mouse placentas, one group received placenta cells that did not express Cdx2, and the third group received a saline control. The team used magnetic resonance imaging to analyze all mice immediately after the heart attacks, and three months after induction with cells or saline. They found that every mouse in the group with Cdx2 stem cell treatments had significant improvement and regeneration of healthy tissue in the heart. By three months, the stem cells had migrated directly to the heart injury and formed new blood vessels and new cardiomyocytes (beating heart muscle cells). The mice injected with saline and the non-Cdx2 placenta cells went into heart failure and their hearts had no evidence of regeneration.

Researchers noted two other properties of the Cdx2 cells: they have all the proteins of embryonic stem cells, which are known to generate all organs of the body, but also additional proteins, giving them the ability to travel directly to the injury site, which is something embryonic stem cells cannot do, and they appear to avoid the host immune response. The immune system did not reject these cells when administered from the placenta to another animal.

"These properties are critical to the development of a human stem cell treatment strategy, which we have embarked on, as this could be a promising therapy in humans. We have been able to isolate Cdx2 cells from term human placentas also; therefore, we are now hopeful that we can design a better human stem cell treatment for the heart than we have seen in the past," explained Dr. Chaudhry. "Past strategies tested in humans were not based on stem cell types that were actually shown to form heart cells, and use of embryonic stem cells for this goal is associated with ethics and feasibility concerns. Placentas are routinely discarded around the world and thus almost a limitless source."

"These results were very surprising to us, as no other cell type tested in clinical trials of human heart disease were ever shown to become beating heart cells in petri dishes, but these did and they knew exactly where to go when we injected them into the circulation," said first author Sangeetha Vadakke-Madathil, PhD, postdoctoral fellow in Medicine (Cardiology) at the Icahn School of Medicine at Mount Sinai.

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stem cells; heart disease; immune system; skin cancer; prostate cancer; lymphoma; stroke prevention; medical topics

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Certain placental stem cells can regenerate heart after heart attack

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Researchers at the Icahn School of Medicine at Mount Sinai have demonstrated that stem cells derived from the placenta known as Cdx2 cells can regenerate healthy heart cells after heart attacks in animal models. The findings, published in the May 20 issue of Proceedings of the National Academy of Sciences ( PNAS), may represent a novel treatment for regenerating the heart and other organs.

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In 1965, an emaciated male lion attacked and killed a villager in the Darajani region of Tsavo, Kenya. Locals led American hunter John Perrott to the animal, where he shot and killed it. While admiring his trophy shortly thereafter, Perrott noticed something unusual: a sharp quill jutting out of the lion's left nostril.

Now, more than 50 years later, researchers have revealed that the quill belonged to a porcupine-and may have been behind the lion's taste for people. "Every time [the lion] opened his mouth to eat, the damn quill pushed in further," says Gastone Celesia, a volunteer at the Field Museum of Natural History and professor emeritus of neurology at Loyola University, both in Chicago, Illinois. Celesia and his colleagues speculate that-starving and with a compromised sense of smell-the lion turned from its standard prey to an easier-to-catch quarry: humans.

This may not be an isolated incident. A number of lion attacks on humans may have been prompted by porcupines injuring the big cats, Celesia and colleagues write this month in the Journal of East African Natural History.

"It's a very interesting and important study," says Laurence Frank, project director of the Kenya-based conservation group Living with Lions, who wasn't involved with the work. "I was actually surprised by the high rate of porcupine killing and eating" by the big cats, he says.

As far back as the 1600s, people have encountered lions injured by porcupines. In 1656 alone, Jan van Riebeeck, commander for the Dutch East India Company, observed two dead lions in Cape Town, South Africa, with porcupine injuries: One, shot after it ate a cow, had numerous quills in its skin; the other, found dead on a beach, had a porcupine quill sticking deep in its chest. Lions don't often attack porcupines, but they can when prey is scarce or if they are young and inexperienced hunters.

To get a better sense of how often these encounters occur, and what impact they have on humans and other animals, Celesia-along with team leader Julian Kerbis Peterhans, a researcher at the Field Museum, and Thomas Gnoske, an assistant collections manager at the museum-scanned the scientific literature for evidence of porcupine attacks on lions. They also analyzed anecdotes such as van Riebeeck's, which he recorded in his personal journal. Altogether, the researchers identified approximately 50 lions injured by porcupines, at least five of which went on to attack or kill people or livestock. Young male lions were the most likely to be injured, possibly because they're inexperienced hunters, the team speculates.

Perrott's trophy, which was part of the 50, was CT scanned at the University of Chicago Pritzker School of Medicine on behalf of the researchers. The scans confirmed that, based on the quill's proximity to the lion's frontal sinuses and other key nasal structures, the animal likely had difficulty smelling and had other impairments that would have made it hard to hunt. The researchers also deduced that the lion was approximately 4 years old when it died.

The researchers don't know how many porcupine-injured lions actually go on to kill people or livestock, but they believe it "greatly increases the risk," Kerbis Peterhans says. He and his colleagues suspect that the wounded lions are more likely to go after people and livestock because the cats are too weak or ill to pursue their typical prey, wildebeest and zebra, which are bigger, faster, and harder to locate. Indeed, at the time of its death, the "Darajani maneater" was "emaciated ... with protruding backbone, scapula, ribs, limbs and pelvic carriage," the researchers report.

One major limitation of the study is that it contains no direct observation of lions being impaled by quills, writes Craig Packer in an email. Packer, who directs the University of Minnesota's Lion Research Center in St. Paul, Minnesota, also questions the finding that young male lions-which tend to be solitary-are more likely to be injured by porcupines "I've seen females remove quills from their pride mates, so it may just be that males are more likely to be seen with quills still stuck in their bodies."

If porcupines really are causing lions to attack people more frequently, Kerbis Peterhans says it's critical that injured animals be treated as soon as possible. That won't just save the big cats, he says, it could help save people as well.

doi:10.1126/science.aay1145

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Lions wounded by porcupines may be more likely to attack people

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In 1965, an emaciated male lion attacked and killed a villager in the Darajani region of Tsavo, Kenya. Locals led American hunter John Perrott to the animal, where he shot and killed it. While admiring his trophy shortly thereafter, Perrott noticed something unusual: a sharp quill jutting out of the lion's left nostril.

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https://www.sciencedaily.com/releases/2019/01/190131101016.htm

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This image illustrates Jupiter's magnetic fields at a single moment in time.

Credit: NASA/JPL-Caltech/Harvard/Moore et al.

Jupiter's magnetic field has changed since the 1970s, and physicists have proved it.

That's not exactly a surprise. Earth's magnetic field, the only planetary field for which we have good ongoing measurements, changes all the time. But the new information is important, because these small changes reveal hidden details of a planet's internal "dynamo," the system that produces its magnetic field.

In a paper published May 20 in the journal Nature Astronomy, a team of researchers looked at magnetic field data from four past missions to Jupiter (Pioneer 10, which reached Jupiter in 1973; Pioneer 11, which reached Jupiter in 1974; Voyager 1, which reached Jupiter in 1979; and Ulysses, which reached Jupiter in 1992). [ 10 Places in the Solar System We'd Most Like to Visit]

They compared that data to a map of the planet's magnetic field produced by the spacecraft Juno, which conducted the most recent and most thorough probe of the giant planet. In 2016, Juno orbited very close to Jupiter, passing from pole to pole, gathering detailed gravitational and magnetic field data. That allowed researchers to develop a thorough model of the planet's magnetic field and some detailed theories as to how it's produced.

The researchers behind this paper showed that data from those four older probes, though more limited (each of them just swung by the planet once), didn't quite fit with the 2016 model of Jupiter's magnetic field.

"Finding something as minute as these changes in something so immense as Jupiter's magnetic field was a challenge," Kimee Moore, a Juno scientist at Harvard and lead author on the paper, said in a statement. "Having a baseline of close-up observations over four decades long provided us with just enough data to confirm that Jupiter's magnetic field does indeed change over time."

One challenge: The researchers were only interested in changes to Jupiter's internal magnetic field, but the planet also has magnetism coming from its upper atmosphere. Charged particles from volcanic eruptions on Io, Jupiter's most volatile moon, end up in the Jovian magnetosphere and ionosphere (a region of charged particles in the outer reaches of Jupiter's atmosphere) and can also change the magnetic field. But the researchers developed methods to subtract those effects from their data set, leaving them with data based almost entirely on the internal dynamo of the planet.

So the question was, what caused the changes to happen? What's going on in Jupiter's dynamo?

The researchers looked at several different causes of magnetic field changes. Their data most closely matched the predictions of a model in which winds in the planet's interior change the magnetic field.

Jupiter's southern hemisphere, as photographed by NASA's Juno spacecraft.

Credit: Gerald Eichstädt/Seán Doran/NASA/JPL-Caltech/SwRI/MSSS

"These winds extend from the planet's surface to over 1,860 miles (3,000 kilometers) deep, where the planet's interior begins changing from gas to highly conductive liquid metal," the statement said.

In truth, researchers can't see that deep into Jupiter, so the depth measurements are really best estimates, with several uncertainties, the researchers wrote in the paper. Still, scientists have robust theories to explain how the winds behave.

"They are believed to shear the magnetic fields, stretching them and carrying them around the planet," the statement said.

Most of those wind-driven changes seem to be concentrated in Jupiter's Great Blue Spot, a region of intense magnetic energy near Jupiter's equator. (This is not the same thing as the Great Red Spot.) The northern and southern parts of the blue spot are shifting east on Jupiter, and the central third is shifting west, causing changes to the planet's magnetic field.

"It is incredible that one narrow magnetic hot spot, the Great Blue Spot, could be responsible for almost all of Jupiter's secular variation, but the numbers bear it out," Moore said in the statement. "With this new understanding of magnetic fields, during future science passes we will begin to create a planetwide map of Jupiter's [magnetic] variation. It may also have applications for scientists studying Earth's magnetic field, which still contains many mysteries to be solved."

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Hidden Winds on Jupiter May Be Messing with Its Enormous Magnetic Field

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Jupiter's magnetic field has changed since the 1970s, and physicists have proved it. That's not exactly a surprise. Earth's magnetic field, the only planetary field for which we have good ongoing measurements, changes all the time. But the new information is important, because these small changes reveal hidden details of a planet's internal "dynamo," the system that produces its magnetic field.

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Lead author Jennifer Lavers looks out at the plastic debris covering a Cocos (Keeling) Island beach.

Credit: Silke Stuckenbrock

The amount of plastic pollution previously thought to exist around the world may be a dramatic underestimate - because the vast majority of plastic pollution may actually be below the surface.

That's the takeaway from a survey of plastic pollution on the beaches of Australia's Cocos Islands, made up of two coral atolls.

An estimated 414 million pieces of debris are now littering the remote islands, and the vast majority of that waste is buried below the surface, according to a new study. But even that is likely an underestimate, a group of researchers reported May 16 in the journal Scientific Reports.

What's more, because most of this plastic is buried below the surface, and most global surveys don't look below the surface, the amount of plastic pollution worldwide may be way more than we previously thought, they reported. [ In Images: The Great Pacific Garbage Patch]

The scientists surveyed seven of the 27 islands, which made up 88 percent of the total landmass of the islands, and estimated that they were littered with 262 tons (238 metric tons) of plastic. A quarter of those pieces of debris were single-use or disposable items such as straws, bags and toothbrushes (about 373,000 of them), The researchers also identified some 977,000 shoes.

Roughly 93% of the debris found, most of it tiny micro-debris, was actually buried below the surface. But because they only dug 3.94 inches (10 centimeters) into the sand, and couldn't access some beaches that are known to have a lot of debris, these numbers are likely conservative, lead author Jennifer Lavers, a research scientist at the University of Tasmania, said in a statement.

"Plastic pollution is now ubiquitous in our oceans, and remote islands are an ideal place to get an objective view of the volume of plastic debris now circling the globe," Lavers said. Back in 2017, the same group of researchers revealed that the Henderson Island, a remote, uninhabited island in the South Pacific, was also the world's most polluted one.

Plastic production has increased dramatically over the last decade - in the last 13 years alone, we've manufactured nearly half of all the plastic produced in the last six decades A recent global estimate finds that 5.25 trillion items of plastic are now in the ocean, which is more than the number of stars in the Milky Way, according to the paper.

The amount of debris buried up to about 4 inches (10 cm) below the surface of the beach is 26 times higher than the amount visible on its surface, the researchers wrote. "This suggests global debris surveys, the majority of which are focused solely on surface debris, have drastically underestimated the scale of debris accumulation."

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Scientists Went to One of the World's Most Remote Island Atolls. They Found 414 Million Pieces of Plastic

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The amount of plastic pollution previously thought to exist around the world may be a dramatic underestimate - because the vast majority of plastic pollution may actually be below the surface. That's the takeaway from a survey of plastic pollution on the beaches of Australia's Cocos Islands, made up of two coral atolls.

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https://www.sciencedaily.com/releases/2019/05/190516114601.htm

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By combining 25 years of European Space Agency satellite altimeter measurements and a model of the regional climate, the UK Centre for Polar Observation and Modelling (CPOM) have tracked changes in snow and ice cover across the continent.

A team of researchers, led by Professor Andy Shepherd from the University of Leeds, found that Antarctica's ice sheet has thinned by up to 122 metres in places, with the most rapid changes occurring in West Antarctica where ocean melting has triggered glacier imbalance.

This means that the affected glaciers are unstable as they are losing more mass through melting and iceberg calving than they are gaining through snowfall.

The team found that the pattern of glacier thinning has not been static. Since 1992, the thinning has spread across 24% of West Antarctica and over the majority of its largest ice streams -- the Pine Island and Thwaites Glaciers -- which are now losing ice five times faster than they were at the start of the survey.

The study, published today in Geophysical Research Letters, used over 800 million measurements of the Antarctic ice sheet height recorded by the ERS-1, ERS-2, Envisat, and CryoSat-2 satellite altimeter missions between 1992 and 2017 and simulations of snowfall over the same period produced by the RACMO regional climate model.

Together, these measurements allow changes in the ice sheet height to be separated into those due to weather patterns, such as less snowfall, and those due to longer term changes in climate, such as increasing ocean temperatures that eat away ice.

Lead author and CPOM Director Professor Andy Shepherd explained: "In parts of Antarctica the ice sheet has thinned by extraordinary amounts, and so we set out to show how much was due to changes in climate and how much was due to weather."

To do this, the team compared the measured surface height change to the simulated changes in snowfall, and where the discrepancy was greater they attributed its origin to glacier imbalance.

They found that fluctuations in snowfall tend to drive small changes in height over large areas for a few years at a time, but the most pronounced changes in ice thickness are signals of glacier imbalance that have persisted for decades.

Professor Shepherd added: "Knowing how much snow has fallen has really helped us to detect the underlying change in glacier ice within the satellite record. We can see clearly now that a wave of thinning has spread rapidly across some of Antarctica's most vulnerable glaciers, and their losses are driving up sea levels around the planet.

"Altogether, ice losses from East and West Antarctica have contributed 4.6 mm to global sea level rise since 1992."

Dr Marcus Engdahl of the European Space Agency, a co-author of the study, added: "This is an important demonstration of how satellite missions can help us to understand how our planet is changing. The polar regions are hostile environments and are extremely difficult to access from the ground. Because of this, the view from space is an essential tool for tracking the effects of climate change."

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global warming; snow and avalanches; climate; ice ages; weather; oceanography; environmental awareness; severe weather

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Nearly a quarter of West Antarctic ice is now unstable

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By combining 25 years of European Space Agency satellite altimeter measurements and a model of the regional climate, the UK Centre for Polar Observation and Modelling (CPOM) have tracked changes in snow and ice cover across the continent.

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Norwich terriers don't have flat snouts, but can suffer the same wheezing as bulldogs

Dogs with flat faces aren't alone in their struggle to breathe. It turns out that Norwich terriers can develop the same wheezing - caused not by the shape of their snouts, but possibly by a wayward gene.

DNA from 401 Norwich terriers revealed that those suffering a respiratory tract disorder shared the same variant of gene ADAMTS3 that's associated with swelling around airways. Nearly a third of the dogs had two copies of that mutated gene. And those same dogs scored worse on airway-function tests than dogs with just one copy or the normal versions of the gene, researchers report online May 16 in PLOS Genetics.

The gene variant, which does not hinder the gene's main function in the development of lymphatic vessels, also turned up in the DNA of French and English bulldogs. That finding indicates that those pooches' smooshed snouts might not be the only factor behind their labored breaths.

"This is the first evidence to show that it's not just all about skull shape," says study coauthor Jeffrey Schoenebeck, an animal geneticist at the University of Edinburgh's Roslin Institute.

The research might someday help dog breeders build healthier pups. Schoenebeck suggests that a genetic test could be developed to identify Norwich terriers with the genetic variant. Breeders could then use the test to keep those dogs from reproducing and passing the mutation along.

T.H. Saey. Genes might explain why dogs can't sniff out some people under stress. Science News. Vol. 195, March 30, 2019, p. 9.

T.H. Saey. These genes may be why dogs are so friendly. Science News. Vol. 192, August 19, 2017, p. 8.

H. Thompson. Dog DNA study maps breeds across the world. Science News Online, April 26, 2017.

T.H. Saey. Darwin's Dogs wants your dog's DNA. Science News. Vol. 190, September 3, 2016, p. 26.

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A mutated gene, not just smooshed snouts, may cause some dogs' breathing trouble

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Norwich terriers don't have flat snouts, but can suffer the same wheezing as bulldogs Dogs with flat faces aren't alone in their struggle to breathe. It turns out that Norwich terriers can develop the same wheezing - caused not by the shape of their snouts, but possibly by a wayward gene.

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Presented by Maggie Aderin-Pocock Astronomer & broadcaster

Academic consultant Professor Gilles Chabrier University of Exeter

Presented by Maggie Aderin-Pocock Astronomer & broadcaster

Academic consultant Professor Gilles Chabrier University of Exeter

Exoplanets - planets outside our Solar System - were first proposed in the 16th Century. Galileo realised our Sun was a star like any other and Copernicus showed how our Solar System's planets orbit around it. So it seemed fair to assume that planets existed elsewhere in the galaxy, orbiting stars of their own. But it would take hundreds of years to develop telescopes powerful enough to find out whether they did.

The first exoplanet was detected in 1995 and thousands more have been discovered since. At first, we could only see gas giants, similar to Jupiter. Now instruments are sensitive enough to detect planets tantalisingly similar to Earth. We don't know whether different planets could be home to alien life, very different to us. But for us, we'd need a planet similar to Earth to have any chance of living there.

But we may never find a suitable second home. Find out why.

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Where's the nearest planet where we could all live?

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Presented by Maggie Aderin-Pocock Astronomer & broadcaster Academic consultant Professor Gilles Chabrier University of Exeter Presented by Maggie Aderin-Pocock Astronomer & broadcaster Academic consultant Professor Gilles Chabrier University of Exeter Exoplanets - planets outside our Solar System - were first proposed in the 16th Century.

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Oral vaccines could give wild bats a better chance at surviving white nose syndrome, the fungal disease that has ravaged bat colonies in North America. In lab tests conducted on captured little brown bats, vaccination led to fewer infected bats developing lesions and more of the bats surviving, researchers report May 1 in Scientific Reports.

White nose syndrome, caused by the fungus Pseudogymnoascus destructans, has killed around 7 million bats in the United States since 2006. In some regions, the disease cut some bat colonies by 75 percent. The white fuzz grows across bats' skin when the animals hibernate, eventually making them wake up, fly around and waste energy needed to survive winter ( SN Online: 1/29/16).

"It's just devastating to some bat populations," says veterinarian Elizabeth Falendysz at the U.S. Geological Survey National Wildlife Health Center in Madison, Wis.

Falendysz and colleagues made two vaccines against the fungus by implanting raccoon poxviruses with DNA instructions for making one of two fungal proteins, in order to trick the bats' immune system into recognizing and fighting the fungus. (Vaccines that helped in rabies eradication efforts and in fighting plague in prairie dogs rely on the same mechanism.)

Wild little brown bats ( Myotis lucifugus) were vaccinated before being exposed to the fungus. Of 10 bats given a combination of both vaccines, only one developed lesions within the experiment's 100-day hibernation period. Because little brown bats don't do well in captivity, the team struggled with dwindling sample sizes, so it was hard to compare these numbers to other individual treatments. But 14 of the other 23 bats, or 61 percent, that didn't get this vaccine combo developed lesions.

In a second trial aimed at confirming the results, researchers vaccinated bats both orally and by injection. After 126 days, about 88 percent of bats that received oral versions of both vaccines survived the effects of the fungus, compared with 30 percent of unvaccinated bats (and 80 percent of bats vaccinated by injection). Bats that survived the experiments lost an average of about 34 percent of their body weight, while bats that died had lost about 55 percent. Researchers suspect that slowing the fungus growth or reducing the intensity of infections may have helped vaccinated bats sleep more peacefully and maintain more of their weight and energy.

The team has since combined DNA for both proteins into a single vaccine and hopes to add more proteins for an even stronger jolt to the immune system. "Mortality rates are extremely high for some species that get white nose syndrome, so even modest gains in immunity and survival could make a big difference," says Winifred Frick, a biologist at the University of California, Santa Cruz.

Researchers have also looked at using antifungal compounds from plants and bacteria to control the fungus, but haven't deployed them in the field over concerns about possibly harming cave ecosystems.

Falendysz says the team hopes to develop a vaccine spray, which bats could lick from their fur as they groom themselves and spread as they nuzzle other bats - a strategy that's worked with a rabies vaccine in lab tests on big brown bats. Reaching a large enough number of some wild bat species will require creativity, Frick says, but "there are regions and species where this will be achievable."

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Vaccines may help bats fight white nose syndrome

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Oral vaccines could give wild bats a better chance at surviving white nose syndrome, the fungal disease that has ravaged bat colonies in North America. In lab tests conducted on captured little brown bats, vaccination led to fewer infected bats developing lesions and more of the bats surviving, researchers report May 1 in Scientific Reports.

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https://www.livescience.com/65493-ptsd-suicidal-thoughts-biomarker.html

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https://www.sciencenews.org/article/deep-sea-fish-eye-chemistry-might-let-them-see-colors-near-dark

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Some fishes in the deep, dark sea may see their world in more than just shades of gray.

A survey of 101 fish species reveals that four from the deep sea had a surprising number of genes for light-sensitive eye proteins called rod opsins, researchers report in the May 10 Science. Depending on how the animals use those light catchers, the discovery might challenge the widespread idea that deep-sea fishes don't see color, says coauthor Zuzana Musilová, an evolutionary biologist at Charles University in Prague.

To see, many fishes, humans and most other vertebrates rely on two types of light-detecting cells in the eye known as rods and cones. Cone cells use two or more kinds of opsins and need decent amounts of light to work. Rods generally use only one opsin called RH1, which works in dim light. That variety in opsins in cones, but not in rods, lets vertebrates see a range of colors in well-lit conditions but be color-blind in the near dark.

In the new study, Musilová and Fabio Cortesi of the University of Queensland in Brisbane, Australia sailed on research ships equipped to reach into the ocean depths for fish. The deep-sea specimens came from the "twilight" zone 200 to 1,000 meters below the surface, where sunlight becomes only a subtle lessening of darkness. The most colorful things to look at would be bioluminescent spots on animals' bodies.

The four deep-sea fishes with the special eyes came from three different lineages that had independently evolved genes for more than one kind of RH1 rod opsin, Musilová, Cortesi and their colleagues report. A glacier lantern fish ( Benthosema glaciale) had genes for five different forms of RH1, and a tube-eye ( Stylephorus chordatus) had six. Two kinds of spinyfin had even more, 18 genes for the longwing spinyfin ( Diretmoides pauciradiatus) and a stunning 38 for the silver spinyfin ( Diretmus argenteus).

Finding even two rod opsins would have been notable, but the silver spinyfin's tally is "astounding," says evolutionary biologist Megan Porter at the University of Hawaii at Manoa, who was not involved in the new research. But she and others warn against jumping to conclusions about how fishes use all this variety, because there are no tests with fish behavior.

Considering where these fishes live, such tests may not even be possible, Musilová says. When brought to the surface, "most of them simply die due to the pressures changes," she says. " Even getting them to the surface alive doesn't guarantee they would behave the same way they do in the depths."

The fish that the researchers caught let them check which opsin genes were actually turned on in the animals' retinas. That work confirmed that the silver spinyfin actually uses at least 14 of its 38 RH1 genes to make proteins.

The researchers also put the silver spinyfin's various RHI genes into bacteria, which manufactured fish opsins. Tests of those opsins' function showed they have the potential to capture both very faint daylight and a wide range of blue and green light from living bioluminescent creatures, the scientists found.

Overall, the authors are rightly "cautious" in not claiming that deep-sea fish can see color, says Almut Kelber of Lund University in Sweden, who has studied low-light color vision in frogs.

The new fish results, for example, don't say whether different RH1 opsins cluster in individual rod cells or are scattered, with different rod cells carrying different opsins. To differentiate colors, the rod opsins would need to be in different cells. But if the proteins clump in each rod, then the fish probably just have enhanced sensitivity to light and could pick out fainter objects in shades of black and white.

Even with the uncertainties, finding all these unexpected opsins "is still exciting," Kelber says.

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Surprising eye chemistry may let deep-sea fishes see color in near darkness

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Some fishes in the deep, dark sea may see their world in more than just shades of gray. A survey of 101 fish species reveals that four from the deep sea had a surprising number of genes for light-sensitive eye proteins called rod opsins, researchers report in the May 10 Science.

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We are here by the skin of our teeth. Evolution could well have turned out differently, and the fact that it did not may well be down to freak, chance events. Life on Earth has faced a string of accidents, weird situations and outright catastrophes, from sudden ice ages to collisions with asteroids - and it is how life responded to these contingencies that ultimately led to us.

If that is so, we can only understand the story of life by taking the broadest possible view. Organisms are shaped by their environments, and those environments are shaped in turn by huge geological forces like volcanoes and ice sheets, and by the shifting climate.

But we should cast the net even wider. What if these great forces were influenced by even greater forces from the wider Universe? Might cosmic events in our Solar System and even our galaxy have also played roles? Do we literally have to thank our stars that we are here?

The most well-known example of an evolutionary shift caused by astronomical events is the hypothesis that the dinosaurs were driven to extinction by a gigantic meteorite impact 66 million years ago. This was proposed in 1980 by physicist Luis Alvarez, his geologist son Walter, and their coworkers.

The researchers discovered that sedimentary rocks, laid down all over the world at the time of the extinction, contain large amounts of a rare element called iridium. The team suggested that the iridium might have come from the dusty debris of a meteorite that smashed into the Earth. Iridium is more abundant in asteroids, the most likely source of such a meteorite, than it is on Earth.

Such a dramatic event would leave some mark on evolutionary history

Quite how such an impact might have killed off the dinosaurs remains a matter of debate, but there are many possibilities.

The energy released could have triggered global wildfires. The researchers estimated that, to deliver the required amount of iridium, the meteorite would have to be about 6 miles (10km) across. The impact of such a monster would have released millions of times more energy than a hydrogen bomb. What's more, the dust and debris thrown up into the air by the blast could have blocked sunlight and sent temperatures plunging for several years after.

In 1991 the impact hypothesis got a boost when scientists found an impact crater more than 100 miles wide at Chicxulub on Mexico's Yucatan peninsula. Its geological age coincided precisely with the extinction.

How much the impact drove the dinosaurs' demise is not clear; there is evidence that they were already on the wane. Still, there is good reason to expect that such a dramatic event would leave some mark on evolutionary history. The discovery helped to prompt concerns about potentially devastating meteorite impacts today.

Besides, a meteorite impact is not the only explanation for the extinctions 66 million years ago.

Tokuhiro Nimura is a researcher at the Japan Spaceguard Association, which was formed to monitor near-Earth objects that might strike the planet. In March 2016, Nimura and his coworkers suggested that the extinctions, global cooling and iridium layer might have been caused by the Solar System passing through a molecular cloud: one of the great clouds of gas and dust in space from which stars form. As dust accumulated in the atmosphere, it would have formed a haze that reflected sunlight and cooled the planet.

The event 66 million years ago is just one of several known "mass extinctions"

The basic idea goes back to a 1975 suggestion by British astronomer William McCrea. He thought that if Earth passed through an interstellar "dust lane" it could cause an ice age. At the time, astronomers Mitchell Begelman and Martin Rees pointed out that such dust might instead affect the way particles streaming from the Sun impinge on the Earth's atmosphere and expose the planet to high doses of radiation, causing extinctions as well as climate changes.

Nimura has now resurrected McCrea's idea, arguing that the Chicxulub impact does not seem to have been catastrophic enough to account for the extinctions at the end of the Cretaceous.

However, for now this is mostly speculation. "The idea strikes me as highly interesting and plausible, but as yet undeveloped and without clear supporting evidence," says astronomer Martin Beech of Campion College at the University of Regina in Saskatchewan, Canada.

The event 66 million years ago is just one of several known "mass extinctions", in which many species worldwide seem to have died out suddenly.

At least some mass extinctions are caused by influences outside the living world

The biggest was at the end of the Permian period 252 million years ago, when no less than 96% of all life on Earth seems to have died out. All life today is descended from the surviving 4%, so it is easy to see that evolutionary history would have been very different if this extinction had not happened. When species die off, those that survive get opportunities to expand and diversify that they would not otherwise have had.

Palaeontologists have long debated what causes these mass extinctions.

It is possible that, just like smaller-scale population crashes, they could be an inherent part of the way ecosystems work. Because all life is interdependent, a small shift in one population might occasionally create a domino effect that sends shockwaves through the entire system.

But it is more likely that at least some mass extinctions are caused by influences outside the living world.

One such mass extinction occurred at the end of the Triassic period. About half of all species on Earth disappeared. The event might have been triggered by increases in volcanic activity, perhaps producing changes in climate, but it might also have been caused by a meteorite impact.

Mass extinctions have happened at regular intervals, about 26 million years apart

Such catastrophic collisions might not be the result of sheer chance, of stray asteroids or comets blundering into Earth. Instead, cosmic circumstances could systematically cause such objects to come close to our world.

The most well-known of these ideas is that our Sun has a dim companion star, which is so far away that it has never been observed directly. This star, dubbed "Nemesis" or the "Death Star", might periodically pull lumps of icy rock from the fringes of the Solar System and send them careening through our neighbourhood.

This idea was proposed in 1984 by two teams of astronomers: Daniel Whitmire and Albert Jackson, and Marc Davis, Richard Muller and Piet Hut. They were all prompted by the apparent discovery earlier that year that mass extinctions have happened at regular intervals, about 26 million years apart, over the past 500 million years.

The idea is that the gravitational pull of Nemesis, circling the Sun in an orbit about 1.5 light years away, would disturb the Oort cloud: a host of icy objects that lie beyond the orbit of Pluto at distances of about 0.8 to 3 light years, and which are only loosely bound by the Sun's gravity. The Oort cloud is the source of "long-period" comets, which return to the inner Solar System every few hundred years or more.

It is completely possibly that we have failed to spot another planet in the Solar System

Nemesis would be a tiny star: perhaps a red dwarf, or even a brown dwarf not much bigger than a giant planet like Jupiter. So it is not altogether surprising that it has never been spotted. It would be hard to see at such a distance, even with the most powerful telescopes.

But that is not the only problem with the Nemesis theory.

In a study published in 2010, astrophysicist Adrian Melott of the University of Kansas and palaeontologist Richard Bambach of the Smithsonian Institution in Washington DC re-examined the fossil record using the latest data. They confirmed that mass extinctions recur every 27 million years. However, they say this pattern is actually too regular to fit with the Nemesis idea. Such a distant dwarf star would inevitably be disturbed by other nearby stars, producing a more irregular influx of comets.

Instead, maybe the waves of mass extinction are caused, not by a companion star, but by another planet.

In 1985, Whitmire and his colleague John Matese suggested that there might be a relatively small rocky planet, around five times the mass of the Earth, orbiting in the Solar System far beyond Neptune. This planet might pull comets, not from the Oort cloud, but from the much nearer Kuiper belt. This is another disk of icy rocks on the edge of the solar system, of which Pluto and its moon Charon are now recognized as members. Whitmire and Matese called their hypothetical object "Planet X".

It is completely possibly that we have failed to spot another planet in the Solar System, even one bigger than the Earth. Before the New Horizons spacecraft reached Pluto and Charon in 2015, the best view we had of those objects was a vague blur, and we are only now starting to be able to make out some of the other large bodies in the Kuiper belt. If Planet X is dark and unreflective, it could well have eluded all our astronomical surveys.

The diversity of marine species goes up and down every 62 million years

What's more, in January 2016 astronomers proposed that there could be a ninth planet in the Solar System; orbiting beyond Neptune, with a mass about 10 times that of Earth. The suggestion was prompted by observations of visible Kuiper-belt objects, which seemed to be disturbed by an unseen influence.

If this planet exists, it probably would not do what Planet X is said to do. But the story illustrates that we do not know what is out there.

Whitmire, who is now at the University of Arkansas, has taken the Planet X hypothesis even further. In a 2015 study he showed that the idea fits with the regular 27-million-year extinction periodicity seen by Melott and Bambach. What's more, Whitmire says a second such object - Planet Y? - could explain yet another oscillation in the fossil record.

This pattern was reported in 2005 by Richard Muller and Robert Rohde. They found that the diversity of marine species goes up and down every 62 million years: a change that could be caused by changes either in extinction rates or the rate at which new species form.

Waves of comet impacts caused by "hidden" planets are a plausible explanation for these patterns, says Melott. But he says the patterns could also be caused by other, more distant cosmic events.

In 2007, Melott and his colleague Mikhail Medvedev argued that the 62-million-year pulse might be caused by a regular feature in the Solar System's journey through our Milky Way galaxy.

Cosmic-ray collisions could change the chemistry of the atmosphere

Our galaxy is shaped a bit like a plate. As it rotates, the Sun rises and falls in the galactic plane, rather like a merry-go-round horse. These shifts in position could change the amount of cosmic rays that stream through the Solar System and hit Earth.

Cosmic rays are high-energy subatomic particles, such as protons and electrons, shooting through space. They are thought to be produced in high-energy astronomical processes. Some seem to originate in supernovae: stars that explode when their fuel is exhausted. Others may come from black holes at the centres of other galaxies.

There are various ways that they could affect Earth's environment and thereby influence evolution.

Cosmic rays could themselves be harmful. When they collide with molecules in the air, they produce showers of particles that could induce mutations in DNA. That is typically bad for life. However, a low level of mutation could actually boost the variety upon which natural selection operates, making life more diverse

Cosmic-ray collisions could also change the chemistry of the atmosphere. They might produce electrically-charged particles that affect cloud formation and thus climate, or they could destroy the ozone layer that protects the Earth from the Sun's harmful ultraviolet rays.

Deadly rays from space do seem to be a good candidate cause for some evolutionary shifts

Because many cosmic rays are thought to be created in supernovae within our galaxy, the Solar System's bobbing up and down in the galaxy could alter the cosmic-ray flux, with knock-on effects for Earth's life.

However, it is strange that these effects only show up in marine fossils. If anything, you might expect sea-dwelling organisms to be better protected from hazardous particle showers than land-based ones.

Even Melott now thinks that this idea cannot account for the 62-million-year cycle in the fossil record after all. In 2011 he suggested that it might instead be an innate, geological "pulse of the Earth", perhaps related to changes in tectonic activity.

There is a similar pattern of changes in the makeup of marine sedimentary rocks, Melott and his coworkers say. This is what would be expected from changes in the rates of mountain-building and erosion, caused by shifts in the movements of tectonic plates.

All the same, deadly rays from space do seem to be a good candidate cause for some evolutionary shifts seen in the fossil record.

We are constantly exposed to low levels of cosmic rays. But a single supernova could unleash a lethal blast of such particles if it happened near enough to our Solar System.

A supernova would need to be within about 30 light years for it to have devastating consequences on Earth

Stars explode as supernovae all the time; when they do, they can temporarily outshine their entire host galaxies. Many are seen every year in other galaxies, but the most recent one known to have happened in our own galaxy became visible about 140 years ago. Another in our galaxy that appeared in 1572 was so bright, it was visible to the naked eye and was seen by the astronomer Tycho Brahe.

" Tycho's supernova" was safely distant: 7,500 light years away. If such an explosion happened much closer to us, we would be in serious trouble. The Earth would be raked not just with high-energy particles but with X-rays and gamma-rays, which could be fatal.

Has that ever happened?

It is estimated that a supernova would need to be within about 30 light years for it to have devastating consequences on Earth. There are not many stars that close.

However, in a 2002 study astronomers estimated that there may have been as many as 20 supernovae within about 420 light years of Earth over the past 11 million years, just from one group of stars, some of which are as close as 130 light years. Such events might well leave imprints in the fossil record.

The rays could create an indirect hazard by damaging the ozone layer

They certainly seem to have left traces in sedimentary rocks. Supernovae scatter the outer layers of the exploding star into space, including some atoms that are rare on Earth.

One of these tell-tale products of a supernova is a kind of iron called iron-60, which is not naturally formed on Earth. In 1999, physicists found high levels of iron-60 in geological structures from the deep ocean called ferromanganese crusts formed over the past 5 million years or so. Iron-60 has also been found in lunar "soil", and it seems to have come from two supernovae about 320 light years away, one about seven and the other two million years ago.

The latter explosions seems to have left traces in the fossil record.

In a study published in August 2016, astrophysicist Shawn Bishop of the Technical University of Munich and his colleagues reported finding iron-60 in fossil iron oxide crystals. The crystals were originally made by bacteria that use the magnetic oxide to align themselves with Earth's magnetic field. The iron-60 began to appear in such fossils in marine sediments that formed 2.6-2.8 million years ago.

Life could have been disturbed by these supernovae.

X-rays and gamma rays coming from so distant a source are not a direct problem in themselves. "They don't penetrate our atmosphere, and so can't directly cause sterilisation or mass extinctions," says Bishop.

But he says the rays could create an indirect hazard by damaging the ozone layer. "With a reduced ozone layer, as we know from the days of the Antarctic ozone layer hole, ultraviolet light from the Sun will penetrate to the Earth's surface and can then become a problem for organisms."

This will be extremely difficult to prove after millions of years

According to calculations by astronomer Narciso Benítez and his colleagues, supernovae at these distances could potentially deplete atmospheric ozone.

What's more, in a study published in July 2016 Melott and his colleagues estimated that cosmic rays from the supernovae could have boosted the numbers of high-energy neutrons and muons reaching ground level, tripling the overall radiation dose to ground-dwelling organisms. That could have induced cancer-causing mutations, as well as triggering changes in climate, the researchers say.

There does seem to have been a small mass extinction about 2.6 million years ago, at the boundary of the Pliocene and Pleistocene eras. But we cannot say for sure if a supernova played a role.

Indeed, there is no direct evidence of supernovae ever having a causal impact on the evolutionary history of life, says Bishop. "This will be extremely difficult to prove after millions of years." For example, there is no way to collect and examine fossil DNA for mutations after such long periods of time, let alone to make a comparison before and after the event.

However, there is another kind of cosmic outburst that is even more powerful.

The heavens are occasionally riven by blasts called gamma-ray bursts: extremely intense explosions that release gamma rays, lasting between a fraction of a second and a few hours. Gamma-ray bursts are among the most energetic events known in the Universe. They may be produced when particularly massive stars explode.

Earth has been around long enough to have been struck many times over

Fortunately, gamma-ray bursts have so far been seen only in very distant galaxies. But if one went off nearby, a supernova would be like a firecracker in comparison. Worse, "we probably couldn't see one coming, at least sooner than a few hours before," says Melott.

Fortunately, Melott says they are only likely to happen close enough to matter, meaning within 10,000 light years or so, about every 170 million years.

That is rare, but Earth has been around long enough to have been struck many times over. Indeed, in 2004 Melott suggested that a mass extinction around the end of the Ordovician period, 440 million years ago, might have been related to a gamma-ray burst.

The idea is that, again, X-rays and gamma rays from this event could have severely damaged the ozone layer, as well as triggering global cooling by inducing the formation of thick, smoggy nitrogen oxides in the atmosphere.

Melott argues that the pattern of extinctions in the late Ordovician fits this picture. For example, shallow-water marine organisms, which would have been more exposed to ultraviolet radiation than deep-water ones, seem to have been hit harder. Also the climate became markedly cooler.

They might head off the explosion by making the star lose mass

Could this happen again? Earth has about two billion years of life left to it, after which the Sun will expand and render it uninhabitable. In a 2011 analysis, Beech estimated that in that time there are likely to be about 20 supernovae and one gamma-ray burst near enough to do harm. Those are hardly alarming numbers.

Besides, Melott says we should be able to see nearby supernovae well in advance, since we can measure the ages of nearby stars. The nearest one that might detonate soon - meaning any time within the next few million years - is Betelgeuse in the constellation of Orion. It is too far away to do any damage.

Beech says it might even be possible to engineer stars to avoid a catastrophic supernova. "If a civilisation knew that a supernova was going to occur in their neighbourhood, then one survival option would be to try some super-astroengineering project," he says.

For example, they might head off the explosion by making the star lose mass or by mixing in some material that could delay its collapse. "How such engineering might be physically performed I don't know," says Beech. "But the physics of the situation and what one would need to do to prolong a star's life is reasonably well-understood".

Beech suggests that stars about to turn supernova might be good places to look for advanced aliens. If such a star started behaving oddly, it might be a sign of deliberate tampering.

The cosmic threats to life on Earth can get even more exotic.

In her 2015 book Dark Matter and the Dinosaurs, physicist Lisa Randall of Harvard University suggested that a mysterious cosmic substance called dark matter might have been the dinosaurs' ultimate killer.

The exotic dark matter could form a disk in the galactic plane

Dark matter does not interact with light, so we cannot see it directly. It only affects ordinary matter via gravity: it has mass, so it exerts a gravitational tug like any other matter.

We do not know what dark matter is. No one has ever detected a single particle of it. But most physicists and astronomers are sure it exists. If it were not there, galaxies could not rotate as fast as they do without falling apart.

Dark matter is estimated to outweigh ordinary matter in the Universe by about 5 to 1. It is thought to surround each galaxy in a roughly spherical halo.

Randall has suggested that some dark matter differs from the rest.

This "exotic dark matter" might feel another force as well as gravity, akin to the electromagnetic force that makes ordinary matter interact with light. The exotic dark matter could then form a disk in the galactic plane, and the passage of the Solar System through the disk could have perturbed the path of an Oort-cloud comet, causing the giant impact 66 million years ago.

Biologist Michael Rampino of New York University has extended this idea. In a study published in 2015, he proposed that some dark matter particles might be captured and destroyed in Earth's core. This could release enough energy to boost volcanic activity, creating the "pulse of the Earth" that Melott had previously linked to extinctions.

No planet-sterilising meteorite impact is anticipated in the foreseeable future

Well, maybe. But some scientists feel that the idea is way too speculative, and would not have got much attention if it had not been put forward by someone as famous as Randall, who achieved something close to scientific superstardom for her work on cosmology.

"You have to invent new physics in order to get the mechanism to work," says Melott.

"The argument seems rather contrived to me," agrees Beech.

But he adds that, while it is far from clear that our galaxy really has a disk of dark matter, "we know so little about the distribution and make-up of dark matter within the galactic disk and halo that the premise is certainly viable within our present uncertainty."

At this point that might be a rather too-familiar refrain: "interesting idea but it's all speculation". Should we believe any of these notions?

All the individual stories we have discussed are unproven, and many are speculative. But take a step back and there seems no doubt that, one way or another, life on Earth is connected to - and contingent on - cosmic forces. The difficulty is figuring out which cosmic phenomena played a role in a given incident.

These influences play out over such vast timescales that we need not fear any impending existential threat to the biosphere. No planet-sterilising meteorite impact is anticipated in the foreseeable future, though of course it is wise to keep looking.

However, that is not to say that human civilisation is completely safe from space threats.

Melott says our biggest concern should be solar flares: abrupt outbursts from the Sun that shower the planet with high-energy particles and radiation. The electromagnetic pulse they produce could cripple telecommunications.

Astronomical events might for once prove a boon to life on Earth rather than a burden

One such event in 1859 played havoc with the early telegraph network, giving some operators shocks and causing sparks and fires. Today, with our far greater dependence on telecommunications networks, the consequences could be devastating. We narrowly escaped this fate in 2012, when a solar superstorm narrowly missed us - but there was a big one in 1989 that disrupted the Canadian power grid.

If an event like this were indeed to bring civilisation to its knees, it might leave an imprint in the evolutionary record - because, ironically, it could actually stop the latest mass extinction, which is happening right now and is entirely of our own doing.

In that case, astronomical events might for once prove a boon to life on Earth rather than a burden. They would have put us firmly in our place and shown just how puny we are in the face of the cosmos.
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Asteroids are not the only threat to life from space

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We are here by the skin of our teeth. Evolution could well have turned out differently, and the fact that it did not may well be down to freak, chance events. Life on Earth has faced a string of accidents, weird situations and outright catastrophes, from sudden ice ages to collisions with asteroids - and it is how life responded to these contingencies that ultimately led to us.