Why is there any matter in the universe at all? New study sheds light

Subatomic particles abstract illustration (stock image).

Scientists at the University of Sussex have measured a property of the neutron -- a fundamental particle in the universe -- more precisely than ever before. Their research is part of an investigation into why there is matter left over in the universe, that is, why all the antimatter created in the Big Bang didn't just cancel out the matter.

The team -- which included the Science and Technology Facilities Council's (STFC) Rutherford Appleton Laboratory in the UK, the Paul Scherrer Institute (PSI) in Switzerland, and a number of other institutions -- was looking into whether or not the neutron acts like an "electric compass." Neutrons are believed to be slightly asymmetrical in shape, being slightly positive at one end and slightly negative at the other -- a bit like the electrical equivalent of a bar magnet. This is the so-called "electric dipole moment" (EDM), and is what the team was looking for.

This is an important piece of the puzzle in the mystery of why matter remains in the Universe, because scientific theories about why there is matter left over also predict that neutrons have the "electric compass" property, to a greater or lesser extent. Measuring it then it helps scientists to get closer to the truth about why matter remains.

The team of physicists found that the neutron has a significantly smaller EDM than predicted by various theories about why matter remains in the universe; this makes these theories less likely to be correct, so they have to be altered, or new theories found. In fact it's been said in the literature that over the years, these EDM measurements, considered as a set, have probably disproved more theories than any other experiment in the history of physics. The results are reported today, Friday 28 February 2020, in the journal Physical Review Letters.

Professor Philip Harris, Head of the School of Mathematical and Physical Sciences and leader of the EDM group at the University of Sussex, said:

"After more than two decades of work by researchers at the University of Sussex and elsewhere, a final result has emerged from an experiment designed to address one of the most profound problems in cosmology for the last fifty years: namely, the question of why the Universe contains so much more matter than antimatter, and, indeed, why it now contains any matter at all. Why didn't the antimatter cancel out all the matter? Why is there any matter left?

"The answer relates to a structural asymmetry that should appear in fundamental particles like neutrons. This is what we've been looking for. We've found that the "electric dipole moment" is smaller than previously believed. This helps us to rule out theories about why there is matter left over -- because the theories governing the two things are linked.

"We have set a new international standard for the sensitivity of this experiment. What we're searching for in the neutron -- the asymmetry which shows that it is positive at one end and negative at the other -- is incredibly tiny. Our experiment was able to measure this in such detail that if the asymmetry could be scaled up to the size of a football, then a football scaled up by the same amount would fill the visible Universe."

The experiment is an upgraded version of apparatus originally designed by researchers at the University of Sussex and the Rutherford Appleton Laboratory (RAL), and which has held the world sensitivity record continuously from 1999 until now.

Dr Maurits van der Grinten, from the neutron EDM group at the Rutherford Appleton Laboratory (RAL), said:

"The experiment combines various state of the art technologies that all need to perform simultaneously. We're pleased that the equipment, technology and expertise developed by scientists from RAL has contributed to the work to push the limit on this important parameter"

Dr Clark Griffith, Lecturer in Physics from the School of Mathematical and Physical Sciences at the University of Sussex, said:

"This experiment brings together techniques from atomic and low energy nuclear physics, including laser-based optical magnetometry and quantum-spin manipulation. By using these multi-disciplinary tools to measure the properties of the neutron extremely precisely, we are able to probe questions relevant to high-energy particle physics and the fundamental nature of the symmetries underlying the universe. "

50,000 measurements

Any electric dipole moment that a neutron may have is tiny, and so is extremely difficult to measure. Previous measurements by other researchers have borne this out. In particular, the team had to go to great lengths to keep the local magnetic field very constant during their latest measurement. For example, every truck that drove by on the road next to the institute disturbed the magnetic field on a scale that would have been significant for the experiment, so this effect had to be compensated for during the measurement.

Also, the number of neutrons observed needed to be large enough to provide a chance to measure the electric dipole moment. The measurements ran over a period of two years. So-called ultracold neutrons, that is, neutrons with a comparatively slow speed, were measured. Every 300 seconds, a bunch of more than 10,000 neutrons was directed to the experiment and examined in detail. The researchers measured a total of 50,000 such bunches.

A new international standard is set

The researchers' latest results supported and enhanced those of their predecessors: a new international standard has been set. The size of the EDM is still too small to measure with the instruments that have been used up until now, so some theories that attempted to explain the excess of matter have become less likely. The mystery therefore remains, for the time being.

The next, more precise, measurement is already being constructed at PSI. The PSI collaboration expects to start their next series of measurements by 2021.

Search for "new physics"

The new result was determined by a group of researchers at 18 institutes and universities in Europe and the USA on the basis of data collected at PSI's ultracold neutron source. The researchers collected measurement data there over a period of two years, evaluated it very carefully in two separate teams, and were then able to obtain a more accurate result than ever before.

The research project is part of the search for "new physics" that would go beyond the so-called Standard Model of Physics, which sets out the properties of all known particles. This is also a major goal of experiments at larger facilities such as the Large Hadron Collider (LHC) at CERN.

The techniques originally developed for the first EDM measurement in the 1950s led to world-changing developments such as atomic clocks and MRI scanners, and to this day it retains its huge and ongoing impact in the field of particle physics.

---

Story Source:

Materials provided by University of Sussex. Original written by Anna Ford. Note: Content may be edited for style and length.

Why is there any matter in the universe at all? New study sheds light

Subatomic particles abstract illustration (stock image).

Scientists at the University of Sussex have measured a property of the neutron -- a fundamental particle in the universe -- more precisely than ever before. Their research is part of an investigation into why there is matter left over in the universe, that is, why all the antimatter created in the Big Bang didn't just cancel out the matter.

The team -- which included the Science and Technology Facilities Council's (STFC) Rutherford Appleton Laboratory in the UK, the Paul Scherrer Institute (PSI) in Switzerland, and a number of other institutions -- was looking into whether or not the neutron acts like an "electric compass." Neutrons are believed to be slightly asymmetrical in shape, being slightly positive at one end and slightly negative at the other -- a bit like the electrical equivalent of a bar magnet. This is the so-called "electric dipole moment" (EDM), and is what the team was looking for.

This is an important piece of the puzzle in the mystery of why matter remains in the Universe, because scientific theories about why there is matter left over also predict that neutrons have the "electric compass" property, to a greater or lesser extent. Measuring it then it helps scientists to get closer to the truth about why matter remains.

The team of physicists found that the neutron has a significantly smaller EDM than predicted by various theories about why matter remains in the universe; this makes these theories less likely to be correct, so they have to be altered, or new theories found. In fact it's been said in the literature that over the years, these EDM measurements, considered as a set, have probably disproved more theories than any other experiment in the history of physics. The results are reported today, Friday 28 February 2020, in the journal Physical Review Letters.

Professor Philip Harris, Head of the School of Mathematical and Physical Sciences and leader of the EDM group at the University of Sussex, said:

"After more than two decades of work by researchers at the University of Sussex and elsewhere, a final result has emerged from an experiment designed to address one of the most profound problems in cosmology for the last fifty years: namely, the question of why the Universe contains so much more matter than antimatter, and, indeed, why it now contains any matter at all. Why didn't the antimatter cancel out all the matter? Why is there any matter left?

"The answer relates to a structural asymmetry that should appear in fundamental particles like neutrons. This is what we've been looking for. We've found that the "electric dipole moment" is smaller than previously believed. This helps us to rule out theories about why there is matter left over -- because the theories governing the two things are linked.

"We have set a new international standard for the sensitivity of this experiment. What we're searching for in the neutron -- the asymmetry which shows that it is positive at one end and negative at the other -- is incredibly tiny. Our experiment was able to measure this in such detail that if the asymmetry could be scaled up to the size of a football, then a football scaled up by the same amount would fill the visible Universe."

The experiment is an upgraded version of apparatus originally designed by researchers at the University of Sussex and the Rutherford Appleton Laboratory (RAL), and which has held the world sensitivity record continuously from 1999 until now.

Dr Maurits van der Grinten, from the neutron EDM group at the Rutherford Appleton Laboratory (RAL), said:

"The experiment combines various state of the art technologies that all need to perform simultaneously. We're pleased that the equipment, technology and expertise developed by scientists from RAL has contributed to the work to push the limit on this important parameter"

Dr Clark Griffith, Lecturer in Physics from the School of Mathematical and Physical Sciences at the University of Sussex, said:

"This experiment brings together techniques from atomic and low energy nuclear physics, including laser-based optical magnetometry and quantum-spin manipulation. By using these multi-disciplinary tools to measure the properties of the neutron extremely precisely, we are able to probe questions relevant to high-energy particle physics and the fundamental nature of the symmetries underlying the universe. "

50,000 measurements

Any electric dipole moment that a neutron may have is tiny, and so is extremely difficult to measure. Previous measurements by other researchers have borne this out. In particular, the team had to go to great lengths to keep the local magnetic field very constant during their latest measurement. For example, every truck that drove by on the road next to the institute disturbed the magnetic field on a scale that would have been significant for the experiment, so this effect had to be compensated for during the measurement.

Also, the number of neutrons observed needed to be large enough to provide a chance to measure the electric dipole moment. The measurements ran over a period of two years. So-called ultracold neutrons, that is, neutrons with a comparatively slow speed, were measured. Every 300 seconds, a bunch of more than 10,000 neutrons was directed to the experiment and examined in detail. The researchers measured a total of 50,000 such bunches.

A new international standard is set

The researchers' latest results supported and enhanced those of their predecessors: a new international standard has been set. The size of the EDM is still too small to measure with the instruments that have been used up until now, so some theories that attempted to explain the excess of matter have become less likely. The mystery therefore remains, for the time being.

The next, more precise, measurement is already being constructed at PSI. The PSI collaboration expects to start their next series of measurements by 2021.

Search for "new physics"

The new result was determined by a group of researchers at 18 institutes and universities in Europe and the USA on the basis of data collected at PSI's ultracold neutron source. The researchers collected measurement data there over a period of two years, evaluated it very carefully in two separate teams, and were then able to obtain a more accurate result than ever before.

The research project is part of the search for "new physics" that would go beyond the so-called Standard Model of Physics, which sets out the properties of all known particles. This is also a major goal of experiments at larger facilities such as the Large Hadron Collider (LHC) at CERN.

The techniques originally developed for the first EDM measurement in the 1950s led to world-changing developments such as atomic clocks and MRI scanners, and to this day it retains its huge and ongoing impact in the field of particle physics.

---

Story Source:

Materials provided by University of Sussex. Original written by Anna Ford. Note: Content may be edited for style and length.

First childhood flu helps explain why virus hits some people harder than others

Taking temperature of child (stock image).

Why are some people better able to fight off the flu than others? Part of the answer, according to a new study, is related to the first flu strain we encounter in childhood.

Scientists from UCLA and the University of Arizona have found that people's ability to fight off the flu virus is determined not only by the subtypes of flu they have had throughout their lives, but also by the sequence in which they are been infected by the viruses. Their study is published in the open-access journal PLoS Pathogens.

The research offers an explanation for why some people fare much worse than others when infected with the same strain of the flu virus, and the findings could help inform strategies for minimizing the effects of the seasonal flu.

In addition, UCLA scientists, including Professor James Lloyd-Smith, who also was a senior author of the PLoS Pathogens research, recently completed a study that analyzes travel-related screening for the new novel coronavirus 2019-nCoV.

The researchers report that screening travelers is not very effective for the 2019 coronavirus -- that it will catch less than half of infected travelers, on average -- and that most infected travelers are undetectable, meaning that they have no symptoms yet, and are unaware that they have been exposed. So stopping the spread of the virus is not a matter of just enhancing screening methods at airports and other travel hubs.

"This puts the onus on government officials and public health officials to follow up with travelers after they arrive, to isolate them and trace their contacts if they get sick later," said Lloyd-Smith, a UCLA professor of ecology and evolutionary biology. Many governments have started to impose quarantines, or even travel bans, as they realize that screening is not sufficient to stop the spread of the coronavirus.

One major concern, Lloyd-Smith said, is that other countries, especially developing nations, lack the infrastructure and resources for those measures, and are therefore vulnerable to importing the disease.

"Much of the public health world is very concerned about the virus being introduced into Africa or India, where large populations exist do not have access to advanced medical care," he said.

The researchers, including scientists from the University of Chicago and the London School of Tropical Hygiene and Medicine, have developed a free online app where people can calculate the effectiveness of travel screening based on a range of parameters.

Solving a decades-old question

The PLoS Pathogens study may help solve a problem that had for decades vexed scientists and health care professionals: why the same strain of the flu virus affects people with various degrees of severity.

A team that included some of the same UCLA and Arizona scientists reported in 2016 that exposure to influenza viruses during childhood gives people partial protection for the rest of their lives against distantly related influenza viruses. Biologists call the idea that past exposure to the flu virus determines a person's future response to infections "immunological imprinting."

The 2016 research helped overturn a commonly held belief that previous exposure to a flu virus conferred little or no immunological protection against strains that can jump from animals into humans, such as those causing the strains known as swine flu or bird flu. Those strains, which have caused hundreds of spillover cases of severe illness and death in humans, are of global concern because they could gain mutations that allow them to readily jump not only from animal populations to humans, but also to spread rapidly from person to person.

In the new study, the researchers investigated whether immunological imprinting could explain people's response to flu strains already circulating in the human population and to what extent it could account for observed discrepancies in how severely the seasonal flu affects people in different age groups.

To track how different strains of the flu virus affect people at different ages, the team analyzed health records that the Arizona Department of Health Services obtains from hospitals and private physicians.

Two subtypes of influenza virus, H3N2 and H1N1, have been responsible for seasonal outbreaks of the flu over the past several decades. H3N2 causes the majority of severe cases in high-risk elderly people and the majority of deaths from the flu. H1N1 is more likely to affect young and middle-aged adults, and causes fewer deaths.

The health record data revealed a pattern: People first exposed to the less severe strain, H1N1, during childhood were less likely to end up hospitalized if they encountered H1N1 again later in life than people who were first exposed to H3N2. And people first exposed to H3N2 received extra protection against H3N2 later in life.

The researchers also analyzed the evolutionary relationships between the flu strains. H1N1 and H3N2, they learned, belong to two separate branches on the influenza "family tree," said James Lloyd-Smith, a UCLA professor of ecology and evolutionary biology and one of the study's senior authors. While infection with one does result in the immune system being better prepared to fight a future infection from the other, protection against future infections is much stronger when one is exposed to strains from the same group one has battled before, he said.

The records also revealed another pattern: People whose first childhood exposure was to H2N2, a close cousin of H1N1, did not have a protective advantage when they later encountered H1N1. That phenomenon was much more difficult to explain, because the two subtypes are in the same group, and the researchers' earlier work showed that exposure to one can, in some cases, grant considerable protection against the other.

"Our immune system often struggles to recognize and defend against closely related strains of seasonal flu, even though these are essentially the genetic sisters and brothers of strains that circulated just a few years ago," said lead author Katelyn Gostic, who was a UCLA doctoral student in Lloyd-Smith's laboratory when the study was conducted and is now a postdoctoral fellow at the University of Chicago. "This is perplexing because our research on bird flu shows that deep in our immune memory, we have some ability to recognize and defend against the distantly related, genetic third cousins of the strains we saw as children.

"We hope that by studying differences in immunity against bird flus -- where our immune system shows a natural ability to deploy broadly effective protection -- and against seasonal flus -- where our immune system seems to have bigger blind spots -- we can uncover clues useful to universal influenza vaccine development."

Around the world, influenza remains a major killer. The past two flu seasons have been more severe than expected, said Michael Worobey, a co-author of the study and head of the University of Arizona's department of ecology and evolutionary biology. In the 2017-18 season, 80,000 people died in the U.S., more than in the swine flu pandemic of 2009, he said.

People who had their first bout of flu as children in 1955 -- when the H1N1 was circulating but the H3N2 virus was not -- were much more likely to be hospitalized with an H3N2 infection than an H1N1 infection last year, when both strains were circulating, Worobey said.

"The second subtype you're exposed to is not able to create an immune response that is as protective and durable as the first," he said.

The researchers hope that their findings could help predict which age groups might be severely affected during future flu seasons based on the subtype circulating. That information could also help health officials prepare their response, including decisions about who should receive certain vaccines that are only available in limited quantities.

The research was funded by the National Institutes of Health, the National Science Foundation, DARPA and the David and Lucile Packard Foundation. In 2018, the NIH's National Institute of Allergy and Infectious Diseases announced a strategic plan to develop a universal flu vaccine.

The study's co-authors are Rebecca Bridge of the Arizona Department of Health Services and Cecile Viboud of the Fogarty International Center at the NIH.

---

Story Source:

Materials provided by University of California - Los Angeles. Original written by Stuart Wolpert and Daniel Stolte. Note: Content may be edited for style and length.

First childhood flu helps explain why virus hits some people harder than others

Taking temperature of child (stock image).

Why are some people better able to fight off the flu than others? Part of the answer, according to a new study, is related to the first flu strain we encounter in childhood.

Scientists from UCLA and the University of Arizona have found that people's ability to fight off the flu virus is determined not only by the subtypes of flu they have had throughout their lives, but also by the sequence in which they are been infected by the viruses. Their study is published in the open-access journal PLoS Pathogens.

The research offers an explanation for why some people fare much worse than others when infected with the same strain of the flu virus, and the findings could help inform strategies for minimizing the effects of the seasonal flu.

In addition, UCLA scientists, including Professor James Lloyd-Smith, who also was a senior author of the PLoS Pathogens research, recently completed a study that analyzes travel-related screening for the new novel coronavirus 2019-nCoV.

The researchers report that screening travelers is not very effective for the 2019 coronavirus -- that it will catch less than half of infected travelers, on average -- and that most infected travelers are undetectable, meaning that they have no symptoms yet, and are unaware that they have been exposed. So stopping the spread of the virus is not a matter of just enhancing screening methods at airports and other travel hubs.

"This puts the onus on government officials and public health officials to follow up with travelers after they arrive, to isolate them and trace their contacts if they get sick later," said Lloyd-Smith, a UCLA professor of ecology and evolutionary biology. Many governments have started to impose quarantines, or even travel bans, as they realize that screening is not sufficient to stop the spread of the coronavirus.

One major concern, Lloyd-Smith said, is that other countries, especially developing nations, lack the infrastructure and resources for those measures, and are therefore vulnerable to importing the disease.

"Much of the public health world is very concerned about the virus being introduced into Africa or India, where large populations exist do not have access to advanced medical care," he said.

The researchers, including scientists from the University of Chicago and the London School of Tropical Hygiene and Medicine, have developed a free online app where people can calculate the effectiveness of travel screening based on a range of parameters.

Solving a decades-old question

The PLoS Pathogens study may help solve a problem that had for decades vexed scientists and health care professionals: why the same strain of the flu virus affects people with various degrees of severity.

A team that included some of the same UCLA and Arizona scientists reported in 2016 that exposure to influenza viruses during childhood gives people partial protection for the rest of their lives against distantly related influenza viruses. Biologists call the idea that past exposure to the flu virus determines a person's future response to infections "immunological imprinting."

The 2016 research helped overturn a commonly held belief that previous exposure to a flu virus conferred little or no immunological protection against strains that can jump from animals into humans, such as those causing the strains known as swine flu or bird flu. Those strains, which have caused hundreds of spillover cases of severe illness and death in humans, are of global concern because they could gain mutations that allow them to readily jump not only from animal populations to humans, but also to spread rapidly from person to person.

In the new study, the researchers investigated whether immunological imprinting could explain people's response to flu strains already circulating in the human population and to what extent it could account for observed discrepancies in how severely the seasonal flu affects people in different age groups.

To track how different strains of the flu virus affect people at different ages, the team analyzed health records that the Arizona Department of Health Services obtains from hospitals and private physicians.

Two subtypes of influenza virus, H3N2 and H1N1, have been responsible for seasonal outbreaks of the flu over the past several decades. H3N2 causes the majority of severe cases in high-risk elderly people and the majority of deaths from the flu. H1N1 is more likely to affect young and middle-aged adults, and causes fewer deaths.

The health record data revealed a pattern: People first exposed to the less severe strain, H1N1, during childhood were less likely to end up hospitalized if they encountered H1N1 again later in life than people who were first exposed to H3N2. And people first exposed to H3N2 received extra protection against H3N2 later in life.

The researchers also analyzed the evolutionary relationships between the flu strains. H1N1 and H3N2, they learned, belong to two separate branches on the influenza "family tree," said James Lloyd-Smith, a UCLA professor of ecology and evolutionary biology and one of the study's senior authors. While infection with one does result in the immune system being better prepared to fight a future infection from the other, protection against future infections is much stronger when one is exposed to strains from the same group one has battled before, he said.

The records also revealed another pattern: People whose first childhood exposure was to H2N2, a close cousin of H1N1, did not have a protective advantage when they later encountered H1N1. That phenomenon was much more difficult to explain, because the two subtypes are in the same group, and the researchers' earlier work showed that exposure to one can, in some cases, grant considerable protection against the other.

"Our immune system often struggles to recognize and defend against closely related strains of seasonal flu, even though these are essentially the genetic sisters and brothers of strains that circulated just a few years ago," said lead author Katelyn Gostic, who was a UCLA doctoral student in Lloyd-Smith's laboratory when the study was conducted and is now a postdoctoral fellow at the University of Chicago. "This is perplexing because our research on bird flu shows that deep in our immune memory, we have some ability to recognize and defend against the distantly related, genetic third cousins of the strains we saw as children.

"We hope that by studying differences in immunity against bird flus -- where our immune system shows a natural ability to deploy broadly effective protection -- and against seasonal flus -- where our immune system seems to have bigger blind spots -- we can uncover clues useful to universal influenza vaccine development."

Around the world, influenza remains a major killer. The past two flu seasons have been more severe than expected, said Michael Worobey, a co-author of the study and head of the University of Arizona's department of ecology and evolutionary biology. In the 2017-18 season, 80,000 people died in the U.S., more than in the swine flu pandemic of 2009, he said.

People who had their first bout of flu as children in 1955 -- when the H1N1 was circulating but the H3N2 virus was not -- were much more likely to be hospitalized with an H3N2 infection than an H1N1 infection last year, when both strains were circulating, Worobey said.

"The second subtype you're exposed to is not able to create an immune response that is as protective and durable as the first," he said.

The researchers hope that their findings could help predict which age groups might be severely affected during future flu seasons based on the subtype circulating. That information could also help health officials prepare their response, including decisions about who should receive certain vaccines that are only available in limited quantities.

The research was funded by the National Institutes of Health, the National Science Foundation, DARPA and the David and Lucile Packard Foundation. In 2018, the NIH's National Institute of Allergy and Infectious Diseases announced a strategic plan to develop a universal flu vaccine.

The study's co-authors are Rebecca Bridge of the Arizona Department of Health Services and Cecile Viboud of the Fogarty International Center at the NIH.

---

Story Source:

Materials provided by University of California - Los Angeles. Original written by Stuart Wolpert and Daniel Stolte. Note: Content may be edited for style and length.

How the solar system got its 'Great Divide,' and why it matters for life on Earth

Illustration of inner solar system (stock image).

Scientists, including those from the University of Colorado Boulder, have finally scaled the solar system's equivalent of the Rocky Mountain range.

In a study published today in Nature Astronomy, researchers from the United States and Japan unveil the possible origins of our cosmic neighborhood's "Great Divide." This well-known schism may have separated the solar system just after the sun first formed.

The phenomenon is a bit like how the Rocky Mountains divide North America into east and west. On the one side are "terrestrial" planet, such as Earth and Mars. They are made up of fundamentally different types of materials than the more distant "jovians," such as Jupiter and Saturn.

"The question is: How do you create this compositional dichotomy?" said lead author Ramon Brasser, a researcher at the Earth-Life Science Institute (ELSI) at the Tokyo Institute of Technology in Japan. "How do you ensure that material from the inner and outer solar system didn't mix from very early on in its history?"

Brasser and coauthor Stephen Mojzsis, a professor in CU Boulder's Department of Geological Sciences, think they have the answer, and it may just shed new light on how life originated on Earth.

A sun disk holds vital clues

The duo suggests that the early solar system was partitioned into at least two regions by a ring-like structure that formed a disk around the young sun. This disk might have held major implications for the evolution of planets and asteroids, and even the history of life on Earth.

"The most likely explanation for that compositional difference is that it emerged from an intrinsic structure of this disk of gas and dust," Mojzsis said.

Mojzsis noted that the Great Divide, a term that he and Brasser coined, does not look like much today. It is a relatively empty stretch of space that sits near Jupiter, just beyond what astronomers call the asteroid belt.

But you can still detect its presence throughout the solar system. Move sunward from that line, and most planets and asteroids tend to carry relatively low abundances of organic molecules. Go the other direction toward Jupiter and beyond, however, and a different picture emerges: Almost everything in this distant part of the solar system is made up of materials that are rich in carbon.

This dichotomy "was really a surprise when it was first found," Mojzsis said.

Many scientists assumed that Jupiter was the agent responsible for that surprise. The thinking went that the planet is so massive that it may have acted as a gravitational barrier, preventing pebbles and dust from the outer solar system from spiraling toward the sun.

But Mojzsis and Brasser were not convinced. The scientists used a series of computer simulations to explore Jupiter's role in the evolving solar system. They found that while Jupiter is big, it was probably never big enough early in its formation to entirely block the flow of rocky material from moving sunward.

"We banged our head against the wall," Brasser said. "If Jupiter wasn't the agent responsible for creating and maintaining that compositional dichotomy, what else could be?"

A solution in plain sight

For years, scientists operating an observatory in Chile called the Atacama Large Millimeter/submillimeter Array (ALMA) had noticed something unusual around distant stars: Young stellar systems were often surrounded by disks of gas and dust that, in infrared light, looked a bit like a tiger's eye.

If a similar ring existed in our own solar system billions of years ago, Brasser and Mojzsis reasoned, it could theoretically be responsible for the Great Divide.

That's because such a ring would create alternating bands of high- and low-pressure gas and dust. Those bands, in turn, might pull the solar system's earliest building blocks into several distinct sinks -- one that would have given rise to Jupiter and Saturn, and another Earth and Mars.

In the mountains, "the Great Divide causes water to drain one way or another," Mojzsis said. "It's similar to how this pressure bump would have divided material" in the solar system.

But, he added, there's a caveat: That barrier in space likely was not perfect. Some outer solar system material may still have climbed across the divide. And those fugitives could have been important for the evolution of our own world.

"Those materials that might go to the Earth would be those volatile, carbon-rich materials," Mojzsis said. "And that gives you water. It gives you organics."

The rest is Earth history.

---

Story Source:

Materials provided by University of Colorado at Boulder. Original written by Daniel Strain. Note: Content may be edited for style and length.

Why are giant pandas born so tiny?

Panda babies

Born pink, blind, and helpless, giant pandas typically weigh about 100 grams at birth -- the equivalent of a stick of butter. Their mothers are 900 times more massive than that.

This unusual size difference has left researchers puzzled for years. With a few exceptions among animals such as echidnas and kangaroos, no other mammal newborns are so tiny relative to their mothers. No one knows why, but a Duke University study of bones across 10 species of bears and other animals finds that some of the current theories don't hold up.

Duke biology professor Kathleen Smith and her former student Peishu Li published their findings this month in the Journal of Anatomy.

Baby panda skeletons are hard to come by, but the researchers were able to study the preserved remains of baby pandas born at the Smithsonian's National Zoo in Washington, D.C.

The National Zoo's first panda couple, Ling-Ling and Hsing-Hsing, had five full-term cubs in the 1980s, but none of them survived long after birth.

The researchers took micro-CT scans of two of those cubs, along with newborn grizzlies, sloth bears, polar bears, dogs, a fox, and other closely related animals from the Smithsonian National Museum of Natural History and the North Carolina State College of Veterinary Medicine.

They used the scans to create 3-D digital models of each baby's bony interior at birth.

As a baby animal grows and develops inside the womb, its bones and teeth do, too. The researchers examined the degree of ossification, or how much the skeleton has formed by the time of birth. They looked at whether the teeth had started to calcify or erupt, and the degree of fusion between the bony plates that make up the skull.

The panda may be an extreme example, but all bears have disproportionately small babies, Li said. A newborn polar bear's birthweight as a fraction of mom's is less than 1:400, or less than one-half of one percent of her body mass. For the vast majority of baby mammals, including humans, the average is closer to 1:26.

One decades-old idea links low birthweights in bears to the fact that, for some species, pregnancy overlaps with winter hibernation. Pregnant females don't eat or drink during this time, relying mostly on their fat reserves to survive, but also breaking down muscle to supply protein to the fetus.

The thinking is that, energetically, females can only afford to nourish their babies this way for so long before this tissue breakdown threatens their health. By cutting pregnancy short and giving birth to small, immature babies, bears would shift more of their growth to outside the womb, where babies can live off their mother's fat-rich milk instead of depleting her muscles.

Proponents of the theory concede that not all bears -- including pandas -- hibernate during the winter. But the idea is that small birthweight is 'locked in' to the bear family tree, preventing non-hibernating relatives from evolving bigger babies too.

"It's certainly an appealing hypothesis," Smith said.

But the Duke team's research shows this scenario is unlikely. The researchers didn't find any significant differences in bone growth between hibernating bears and their counterparts that stay active year-round and don't fast during pregnancy.

In fact, despite being small, the researchers found that most bear skeletons are just as mature at birth as their close animal cousins.

The panda bear is the one exception to this rule, results show. Even in a full-term baby panda, the bones look a lot like those of a beagle puppy delivered several weeks premature.

"That would be like a 28-week human fetus" at the beginning of the third trimester, Smith said.

Other factors might have pushed panda babies toward smaller sizes over time -- some researchers blame their bamboo-only diet -- but data are scarce, Li said. The researchers say the panda bear's embryonic appearance likely has to do with a quirk of panda pregnancy.

All bears experience what's called "delayed implantation." After the egg is fertilized, the future fetus enters a state of suspended animation, floating in the womb for several months before implanting in the uterine wall to resume its development and get ready for birth.

But while other bears gestate for two months after implantation, giant pandas are done in a month.

"They're basically undercooked," said Li, now a Ph.D. student at the University of Chicago.

The researchers say they only looked at skeletons in this study, and it could be that other organs like the brain tell a different story. But the new study suggests that baby pandas follow the same trajectory as other mammal relatives -- their bones mature in the same sequence and at similar rates -- but on a truncated timetable.

"Development is just cut short," Smith said.

Scientists are still searching for a complete explanation of why the panda's peculiar size differential evolved over geological time, and how.

"We really need more information about their ecology and reproduction in the wild," Smith said, and we may not have much time given their risk of extinction. But this study brings them one step closer to an answer.

This research was supported by a Shared Material Instrumentation Facility Undergraduate User Program grant, the Duke Department of Biology, and the Undergraduate Research Office at Duke.

Story Source:

Materials provided by Duke University. Original written by Robin A. Smith. Note: Content may be edited for style and length.

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