Jan 21, 2019

Our genes affect where fat is stored in our bodies

A recent study from Uppsala University has found that whether you store your fat around the trunk or in other parts of your body is highly influenced by genetic factors and that this effect is present predominantly in women and to a much lower extent in men. In the study, which is published in Nature Communications, the researchers measured how fat was distributed in nearly 360,000 voluntary participants.

"We know that women and men tend to store fat differently -- women have the ability to more easily store fat on the hips and legs, while men tend to accumulate fat around the abdomen to a higher extent," says lead author Mathias Rask-Andersen, Ph.D. and postdoctoral researcher at the department of Immunology, Genetics and Pathology at Uppsala University. "This has been attributed to the effects of sex hormones such as estrogen. But the molecular mechanisms that control this phenomenon are fairly unknown."

The researchers used data from UK Biobank, which is a cohort study of half a million participants in the UK. The participants gave blood samples for genotyping and the distribution of fat tissue was estimated using impedance measurements, i.e. measurements of electrical resistance when an electrical current is fed through the body. In the current study, millions of genetic variants across the genome were tested for association with distribution of fat to the arms, legs or trunk, and the research team identified nearly a hundred genes that affect distribution of adipose tissue to the different compartments of the human body. The researchers also saw a high degree of heterogeneity between sexes.

"We were struck by the large number of genetic effects that were stronger, or only present, in females. Upon closer examination, several of the associated genes were found to encode proteins that actively shape the extracellular matrix, which makes up the supporting structure around cells," says the group leader docent Åsa Johansson. The findings suggest that remodeling of the extracellular matrix is one of the mechanisms that generates differences in body fat distribution.

Fat stored in the trunk has previously been associated with increased disease risk. Men have a greater amount of abdominal fat than women and this may explain the increased prevalence of cardiovascular disease observed in males. Epidemiological studies have even shown that the ability to store fat around hips and legs gives women some protection against cardiovascular disease. The result of the current study may therefore lead to the development of new interventions to reduce the risk of cardiovascular disease.

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Genetic study provides novel insights into the evolution of skin color

Variation of light skin among Eurasian people evolved independently from different genetic backgrounds.
Skin colour is one of the most visible and variable traits among humans and scientists have always been curious about how this variation evolved. Now, a study of diverse Latin American populations led by UCL geneticists has identified new genetic variations associated with skin colour.

The study, published in the journal Nature Communications, found that the variation of light skin among Eurasian people evolved independently from different genetic backgrounds.

The genetic study analysed pigmentation in over 6,000 Latin Americans, who have a mix of Native American, European and African ancestry.

It is well established that Native Americans are genetically closely related to East Asians, the initial settlement of the Americas occurring some 15-20,000 years ago, through migration from Eastern Siberia into North America. As a consequence, genetic variations in Native Americans are often shared with East Asians.

This study identifies five new associated regions involving skin, eye and hair colour. Genes affecting skin colour in Europeans have been extensively studied, but here researchers identified an important variation in the gene MFSD12 seen uniquely in East Asians and Native Americans.

They show it was under natural selection in East Asians after they split from Europeans around 40,000 years ago, and was then carried over to America by ancient migrations of Native Americans. It is the first time this gene has been linked to skin colour in Native Americans and East Asians.

Dr Kaustubh Adhikari (UCL Genetics Institute), said: "Our work demonstrates that lighter skin colour evolved independently in Europe and East Asia. We also show that this gene was under strong natural selection in East Asia, possibly as adaptation to changes in sunlight levels and ultraviolet radiation."

Human physical diversity has fascinated biologists for centuries and despite the discovery of hundreds of genes related to such variation, there is still a lot to be understood in order to gain a fuller picture. Scientists have been calling for more diversity in genetics research to ensure that everyone benefits from the medical outcomes of research.

Only recently scientists published the first major study on the genes linked to skin tone diversity in Africa. Latin Americans are similarly underrepresented in genetics research, in particular in pigmentation research.

"It is commonly thought that variation in pigmentation, such as skin colour, in Latin Americans primarily arises due to people's varying degree of European or African ancestry. But our new study shows that there is variation inherited from their Native ancestors as well", said Dr Javier Mendoza-Revilla (UCL Genetics Institute).

Professor Desmond Tobin (Charles Institute of Dermatology, University College Dublin) explained: "The pigment melanin determines our hair, skin and eye colour. This gene MFSD12 influences how melanin is produced and stored in the skin, thus affecting our skin colour. A darker skin produces more melanin, which can help prevent UV light from damaging our DNA and so offers protection against skin cancer."

"Interestingly, this gene also turned up in the skin colour study in Africans, but the variants were entirely different than those we observe in our study, highlighting the huge genetic diversity in humans and the need to diversify our study populations", emphasized Professor Andres Ruiz-Linares (UCL Genetics Institute), who led the CANDELA project spanning participants from five countries: Brazil, Colombia, Chile, Mexico and Peru.

In addition to skin tone variation, the scientists also noted a wide variation in eye colour among Latin Americans. "Just like skin colour, early research on eye colour was Europe-centric, and mostly focused on the distinction between blue vs. brown eyes. But we show that eye colour is a broad continuum, and by studying the subtler variation within brown to black, we found two new genes linked to it", said Dr Anood Sohail (University of Cambridge).

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Ancient carpet shark discovered with 'spaceship-shaped' teeth

One of the tiny fossilized teeth recovered from Galagadon, so named for the shape of its teeth, which resemble the spaceships in the video game Galaga.
The world of the dinosaurs just got a bit more bizarre with a newly discovered species of freshwater shark whose tiny teeth resemble the alien ships from the popular 1980s video game Galaga.

Unlike its gargantuan cousin the megalodon, Galagadon nordquistae was a small shark (approximately 12 to 18 inches long), related to modern-day carpet sharks such as the "whiskered" wobbegong. Galagadon once swam in the Cretaceous rivers of what is now South Dakota, and its remains were uncovered beside "Sue," the world's most famous T. rex fossil.

"The more we discover about the Cretaceous period just before the non-bird dinosaurs went extinct, the more fantastic that world becomes," says Terry Gates, lecturer at North Carolina State University and research affiliate with the North Carolina Museum of Natural Sciences. Gates is lead author of a paper describing the new species along with colleagues Eric Gorscak and Peter J. Makovicky of the Field Museum of Natural History.

"It may seem odd today, but about 67 million years ago, what is now South Dakota was covered in forests, swamps and winding rivers," Gates says. "Galagadon was not swooping in to prey on T. rex, Triceratops, or any other dinosaurs that happened into its streams. This shark had teeth that were good for catching small fish or crushing snails and crawdads."

The tiny teeth -- each one measuring less than a millimeter across -- were discovered in the sediment left behind when paleontologists at the Field Museum uncovered the bones of "Sue," currently the most complete T. rex specimen ever described. Gates sifted through the almost two tons of dirt with the help of volunteer Karen Nordquist, whom the species name, nordquistae, honors. Together, the pair recovered over two dozen teeth belonging to the new shark species.

"It amazes me that we can find microscopic shark teeth sitting right beside the bones of the largest predators of all time," Gates says. "These teeth are the size of a sand grain. Without a microscope you'd just throw them away."

Despite its diminutive size, Gates sees the discovery of Galagadon as an important addition to the fossil record. "Every species in an ecosystem plays a supporting role, keeping the whole network together," he says. "There is no way for us to understand what changed in the ecosystem during the mass extinction at the end of the Cretaceous without knowing all the wonderful species that existed before."

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Mystery orbits in outermost reaches of solar system not caused by 'Planet Nine'

This is an artist's impression of a Kuiper Belt object, located on the outer rim of our solar system.
The strange orbits of some objects in the farthest reaches of our solar system, hypothesised by some astronomers to be shaped by an unknown ninth planet, can instead be explained by the combined gravitational force of small objects orbiting the Sun beyond Neptune, say researchers.

The alternative explanation to the so-called 'Planet Nine' hypothesis, put forward by researchers at the University of Cambridge and the American University of Beirut, proposes a disc made up of small icy bodies with a combined mass as much as ten times that of Earth. When combined with a simplified model of the solar system, the gravitational forces of the hypothesised disc can account for the unusual orbital architecture exhibited by some objects at the outer reaches of the solar system.

While the new theory is not the first to propose that the gravitational forces of a massive disc made of small objects could avoid the need for a ninth planet, it is the first such theory which is able to explain the significant features of the observed orbits while accounting for the mass and gravity of the other eight planets in our solar system. The results are reported in the Astronomical Journal.

Beyond the orbit of Neptune lies the Kuiper Belt, which is made up of small bodies left over from the formation of the solar system. Neptune and the other giant planets gravitationally influence the objects in the Kuiper Belt and beyond, collectively known as trans-Neptunian Objects (TNOs), which encircle the Sun on nearly-circular paths from almost all directions.

However, astronomers have discovered some mysterious outliers. Since 2003, around 30 TNOs on highly elliptical orbits have been spotted: they stand out from the rest of the TNOs by sharing, on average, the same spatial orientation. This type of clustering cannot be explained by our existing eight-planet solar system architecture and has led to some astronomers hypothesising that the unusual orbits could be influenced by the existence of an as-yet-unknown ninth planet.

The 'Planet Nine' hypothesis suggests that to account for the unusual orbits of these TNOs, there would have to be another planet, believed to be about ten times more massive than Earth, lurking in the distant reaches of the solar system and 'shepherding' the TNOs in the same direction through the combined effect of its gravity and that of the rest of the solar system.

"The Planet Nine hypothesis is a fascinating one, but if the hypothesised ninth planet exists, it has so far avoided detection," said co-author Antranik Sefilian, a PhD student in Cambridge's Department of Applied Mathematics and Theoretical Physics. "We wanted to see whether there could be another, less dramatic and perhaps more natural, cause for the unusual orbits we see in some TNOs. We thought, rather than allowing for a ninth planet, and then worry about its formation and unusual orbit, why not simply account for the gravity of small objects constituting a disc beyond the orbit of Neptune and see what it does for us?"

Professor Jihad Touma, from the American University of Beirut, and his former student Sefilian modelled the full spatial dynamics of TNOs with the combined action of the giant outer planets and a massive, extended disc beyond Neptune. The duo's calculations, which grew out of a seminar at the American University of Beirut, revealed that such a model can explain the perplexing spatially clustered orbits of some TNOs. In the process, they were able to identify ranges in the disc's mass, its 'roundness' (or eccentricity), and forced gradual shifts in its orientations (or precession rate), which faithfully reproduced the outlier TNO orbits.

"If you remove planet nine from the model and instead allow for lots of small objects scattered across a wide area, collective attractions between those objects could just as easily account for the eccentric orbits we see in some TNOs," said Sefilian, who is a Gates Cambridge Scholar and a member of Darwin College.

Earlier attempts to estimate the total mass of objects beyond Neptune have only added up to around one-tenth the mass of Earth. However, in order for the TNOs to have the observed orbits and for there to be no Planet Nine, the model put forward by Sefilian and Touma requires the combined mass of the Kuiper Belt to be between a few to ten times the mass of Earth.

"When observing other systems, we often study the disc surrounding the host star to infer the properties of any planets in orbit around it," said Sefilian. "The problem is when you're observing the disc from inside the system, it's almost impossible to see the whole thing at once. While we don't have direct observational evidence for the disc, neither do we have it for Planet Nine, which is why we're investigating other possibilities. Nevertheless, it is interesting to note that observations of Kuiper belt analogues around other stars, as well as planet formation models, reveal massive remnant populations of debris.

Read more at Science Daily

Jan 20, 2019

Green turtle: The success of the reintroduction program in Cayman Islands

Overexploitation of the green turtle in the Cayman Islands caused the disappearance of nesting populations.
The reintroduction program for the green turtle in the Cayman Islands is crucial in order to recover this species, which are threatened by the effects of human overexploitation, according to a study published in the journal Molecular Ecology and led by the experts Marta Pascual and Carlos Carreras, from the Evolutionary Genetics laboratory of the Faculty of Biology and the Biodiversity Research Institute (IRBio) of the University of Barcelona.

The new study, with its first author being Anna Barbanti (UB-IRBio), represents the first genetic study of the reintroduction project of this endangered species, and the wild population of green turtles in the Cayman Islands, a British Overseas Territory.

According to the conclusions, the current wild population of green turtle in the Cayman Islands has been recovered as a result of the reintroduction process; it presents a high genetic diversity and shows no difficulties regarding breeding. However, the authors of the study recommend conducting a genetic monitoring of the species in this Atlantic Ocean region since it shows a differential genetic heritage compared to other populations of the Caribbean. Other participants in this study were Clara Martín and Víctor Ordóñez (UB-IRBio), and other experts from the University of Exeter, the Cayman Turtle Farm (CTF) and the Department of Environment of the Cayman Islands Government (United Kingdom).

At the limits of survival due human overexploitation

The green turtle (Chelonia mydas) is a migratory species globally distributed in tropical and subtropical latitudes -nesting beaches in the Mediterranean basin- which has been quite exploited by human activity. This species is the biggest one within the family of Cheloniidae -adults can weigh over 200 kg- and one of the species of marine turtles with a more natal phylopatric behaviour (it comes back to their birth place to lay its eggs). Factors such as marine pollution, loss of natural habitat, fishing pressure and bycatches endanger the survival of these turtles, classified as an endangered species according to the International Union for Conservation of Nature (IUCN).

During the eighties, overexploitation of the green turtle in the Cayman Islands caused the disappearance of nesting populations. To recover this endangered population, a program of reintroduction of the species was launched, with individuals of the Cayman Turtle Farm (CTF). Forty years later, data show that the nesting population of the Cayman Islands has been restored but researchers did not know if this was the result of the reintroduction process or the natural recovery of the population for the improvement of threatening factors.

In the new study, experts analyse several genetic markers to see the degree of parentage of the natural population of the green turtle in the Cayman Islands with the breeding individuals in the farm, and therefore evaluate the effect of the reintroduction process on wild population.

"In wildlife, genetic diversity is a key factor that eases the adaptation of populations in the natural environment and their tolerance to environmental changes. In this context, it is crucial to conduct a genetic monitoring of the reintroduction processes to evaluate their success and the potential consequences for the target species of the reintroduction," says Carlos Carreras, member of the Department of Genetics, Microbiology and Statistics of the UB and IRBio. "A threatened population -he continues- reduces their survival options due excessive inbreeding but a poorly planned reintroduction can have negative consequences because of the mix of genetically different beings, since they could create hybrids that are not feasible to the environmental conditions of the population."

The population of the wild green turtle has a tight genetic relationship with the ones in CTF, the new study reveals. According to Marta Pascal, member of the mentioned Department and IRBio, "90 % of the wild individuals were related to the captive stock. This means the reintroduction process was very important in the recovery of threatened populations."

The reintroduction process started in the farm with individuals of distant populations, and this explains why the genetic diversity of first generation turtles is higher than their parents'. This genetic diversity of the initial population has been changing as a consequence of the captivity process -as expected- but also because of the effects of the CTF population management. For instance, they use beings from the same cohort as reproductive adults to replace the losses hurricane Michelle caused in 2001, a strategy that has increased the degree of parentage among reproductive individuals in the farm. Therefore, scientific studies like the one in Molecular Ecology, are essential tools to take the right decisions in the management of threatened species.

Lights and shades in the reintroduction of endangered species

Current labelling studies show that there is a population between one hundred and one hundred and fifty reproductive female adults in the Cayman Islands. In this situation of biodiversity protection, the reintroduction programs for endangered species can become an effective tool of preservation but can also be inefficient, and can even have negative consequences for the threatened populations and natural ecosystems. "Therefore, it is essential to design these programs of reintroduction of threatened species with scientific rigor and to conduct a long term scientific monitoring to assess its success and the potential consequences for the species," warn the experts.

Read more at Science Daily

Using bacteria to create a water filter that kills bacteria

More than one in 10 people in the world lack basic drinking water access, and by 2025, half of the world's population will be living in water-stressed areas, which is why access to clean water is one of the National Academy of Engineering's Grand Challenges. Engineers at Washington University in St. Louis have designed a novel membrane technology that purifies water while preventing biofouling, or buildup of bacteria and other harmful microorganisms that reduce the flow of water.

And they used bacteria to build such filtering membranes.

Srikanth Singamaneni, professor of mechanical engineering & materials science, and Young-Shin Jun, professor of energy, environmental & chemical engineering, and their teams blended their expertise to develop an ultrafiltration membrane using graphene oxide and bacterial nanocellulose that they found to be highly efficient, long-lasting and environmentally friendly. If their technique were to be scaled up to a large size, it could benefit many developing countries where clean water is scarce.

The results of their work were published as the cover story in the Jan. 2 issue of Environmental Science & Technology.

Biofouling accounts for nearly half of all membrane fouling and is highly challenging to eradicate completely. Singamaneni and Jun have been tackling this challenge together for nearly five years. They previously developed other membranes using gold nanostars, but wanted to design one that used less expensive materials.

Their new membrane begins with feeding Gluconacetobacter hansenii bacteria a sugary substance so that they form cellulose nanofibers when in water. The team then incorporated graphene oxide (GO) flakes into the bacterial nanocellulose while it was growing, essentially trapping GO in the membrane to make it stable and durable.

After GO is incorporated, the membrane is treated with base solution to kill Gluconacetobacter. During this process, the oxygen groups of GO are eliminated, making it reduced GO. When the team shone sunlight onto the membrane, the reduced GO flakes immediately generated heat, which is dissipated into the surrounding water and bacteria nanocellulose.

Ironically, the membrane created from bacteria also can kill bacteria.

"If you want to purify water with microorganisms in it, the reduced graphene oxide in the membrane can absorb the sunlight, heat the membrane and kill the bacteria," Singamaneni said.

Singamaneni and Jun and their team exposed the membrane to E. coli bacteria, then shone light on the membrane's surface. After being irradiated with light for just 3 minutes, the E. coli bacteria died. The team determined that the membrane quickly heated to above the 70 degrees Celsius required to deteriorate the cell walls of E. coli bacteria.

While the bacteria are killed, the researchers had a pristine membrane with a high quality of nanocellulose fibers that was able to filter water twice as fast as commercially available ultrafiltration membranes under a high operating pressure.

When they did the same experiment on a membrane made from bacterial nanocellulose without the reduced GO, the E. coli bacteria stayed alive.

"This is like 3-D printing with microorganisms," Jun said. "We can add whatever we like to the bacteria nanocellulose during its growth. We looked at it under different pH conditions similar to what we encounter in the environment, and these membranes are much more stable compared to membranes prepared by vacuum filtration or spin-coating of graphene oxide."

Read more at Science Daily

Jan 19, 2019

How musicians communicate non-verbally during performance

A team of researchers from McMaster University has discovered a new technique to examine how musicians intuitively coordinate with one another during a performance, silently predicting how each will express the music.

The findings, published today in the journal Scientific Reports, provide new insights into how musicians synchronize their movements so they are playing exactly in time, as one single unit.

"Successfully performing music with a group is a highly complex endeavor," explains Laurel Trainor, the senior author on the study and director of the LIVELab at McMaster University where the work was conducted.

"How do musicians coordinate with each other to perform expressive music that has changes in tempo and dynamics? Accomplishing this relies on predicting what your fellow musicians will do next so that you can plan the motor movements so as to express the same emotions in a coordinated way. If you wait to hear what your fellow musicians will do, it is too late," she says.

For this study, researchers turned to the Gryphon Trio, an acclaimed chamber music ensemble. Each performer was fitted with motion capture markers to track their movements while the musicians played happy or sad musical excerpts, once with musical expression, once without.

Using mathematical techniques, investigators measured how much the movements of each musician were predicting the movements of the others.

Whether they were portraying joy or sadness, the musicians predicted each others' movements to a greater extent when they played expressively, compared to when they played with no emotion.

"Our work shows we can measure communication of emotion between musicians by analyzing their movements in detail, and that achieving a common emotion expression as a group requires a lot of communication," says Andrew Chang, the lead author on the study.

Researchers suggest this novel technique can be applied to other situations, such as communication between non-verbal patients and their family and caregivers. They are also testing the technique in a study on romantic attraction.

"The early results indicate that communication measured in body sway can predict which couples will want to see each other again," says Chang.

From Science Daily

Waves in Saturn's rings give precise measurement of planet's rotation rate

This image of Saturn's rings was taken by NASA's Cassini spacecraft on Sept. 13, 2017. It is among the last images Cassini sent back to Earth.
Saturn's distinctive rings were observed in unprecedented detail by NASA's Cassini spacecraft, and scientists have now used those observations to probe the interior of the giant planet and obtain the first precise determination of its rotation rate. The length of a day on Saturn, according to their calculations, is 10 hours 33 minutes and 38 seconds.

The researchers studied wave patterns created within Saturn's rings by the planet's internal vibrations. In effect, the rings act as an extremely sensitive seismograph by responding to vibrations within the planet itself.

Similar to Earth's vibrations from an earthquake, Saturn responds to perturbations by vibrating at frequencies determined by its internal structure. Heat-driven convection in the interior is the most likely source of the vibrations. These internal oscillations cause the density at any particular place within the planet to fluctuate, which makes the gravitational field outside the planet oscillate at the same frequencies.

"Particles in the rings feel this oscillation in the gravitational field. At places where this oscillation resonates with ring orbits, energy builds up and gets carried away as a wave," explained Christopher Mankovich, a graduate student in astronomy and astrophysics at UC Santa Cruz.

Mankovich is lead author of a paper, published January 17 in the Astrophysical Journal, comparing the wave patterns in the rings with models of Saturn's interior structure.

Most of the waves observed in Saturn's rings are due to the gravitational effects of the moons orbiting outside the rings, said coauthor Jonathan Fortney, professor of astronomy and astrophysics at UC Santa Cruz. "But some of the features in the rings are due to the oscillations of the planet itself, and we can use those to understand the planet's internal oscillations and internal structure," he said.

Mankovich developed a set of models of the internal structure of Saturn, used them to predict the frequency spectrum of Saturn's internal vibrations, and compared those predictions with the waves observed by Cassini in Saturn's C ring. One of the main results of his analysis is the new calculation of Saturn's rotation rate, which has been surprisingly difficult to measure.

As a gas giant planet, Saturn has no solid surface with landmarks that could be tracked as it rotates. Saturn is also unusual in having its magnetic axis nearly perfectly aligned with its rotational axis. Jupiter's magnetic axis, like Earth's, is not aligned with its rotational axis, which means the magnetic pole swings around as the planet rotates, enabling astronomers to measure a periodic signal in radio waves and calculate the rotation rate.

The rotation rate of 10:33:38 determined by Mankovich's analysis is several minutes faster than previous estimates based on radiometry from the Voyager and Cassini spacecraft.

"We now have the length of Saturn's day, when we thought we wouldn't be able to find it," said Cassini Project Scientist Linda Spilker. "They used the rings to peer into Saturn's interior, and out popped this long-sought, fundamental quality of the planet. And it's a really solid result. The rings held the answer."

The idea that Saturn's rings could be used to study the seismology of the planet was first suggested in 1982, long before the necessary observations were possible. Coauthor Mark Marley, now at NASA's Ames Research Center in Silicon Valley, subsequently fleshed out the idea for his Ph.D. thesis in 1990, showed how the calculations could be done, and predicted where features in Saturn's rings would be. He also noted that the Cassini mission, then in the planning stages, would be able to make the observations needed to test the idea.

Read more at Science Daily

Jan 18, 2019

Big Bang query: Mapping how a mysterious liquid became all matter

The leading theory about how the universe began is the Big Bang, which says that 14 billion years ago the universe existed as a singularity, a one-dimensional point, with a vast array of fundamental particles contained within it. Extremely high heat and energy caused it to inflate and then expand into the cosmos as we know it -- and, the expansion continues to this day.

The initial result of the Big Bang was an intensely hot and energetic liquid that existed for mere microseconds that was around 10 billion degrees Fahrenheit (5.5 billion Celsius). This liquid contained nothing less than the building blocks of all matter. As the universe cooled, the particles decayed or combined giving rise to...well, everything.

Quark-gluon plasma (QGP) is the name for this mysterious substance so called because it was made up of quarks -- the fundamental particles -- and gluons, which physicist Rosi J. Reed describes as "what quarks use to talk to each other."

Scientists like Reed, an assistant professor in Lehigh University's Department of Physics whose research includes experimental high-energy physics, cannot go back in time to study how the Universe began. So they re-create the circumstances, by colliding heavy ions, such as Gold, at nearly the speed of light, generating an environment that is 100,000 times hotter than the interior of the sun. The collision mimics how quark-gluon plasma became matter after the Big Bang, but in reverse: the heat melts the ions' protons and neutrons, releasing the quarks and gluons hidden inside them.

There are currently only two operational accelerators in the world capable of colliding heavy ions -- and only one in the U.S.: Brookhaven National Lab's Relativistic Heavy Ion Collider (RHIC). It is about a three-hour drive from Lehigh, in Long Island, New York.

Reed is part of the STAR Collaboration , an international group of scientists and engineers running experiments on the Solenoidal Tracker at RHIC (STAR). The STAR detector is massive and is actually made up of many detectors. It is as large as a house and weighs 1,200 tons. STAR's specialty is tracking the thousands of particles produced by each ion collision at RHIC in search of the signatures of quark-gluon plasma.

"When running experiments there are two 'knobs' we can change: the species -- such as gold on gold or proton on proton -- and the collision energy," says Reed. "We can accelerate the ions differently to achieve different energy-to-mass ratio."

Using the various STAR detectors, the team collides ions at different collision energies. The goal is to map quark-gluon plasma's phase diagram, or the different points of transition as the material changes under varying pressure and temperature conditions. Mapping quark-gluon plasma's phase diagram is also mapping the nuclear strong force, otherwise known as Quantum Chromodynamics (QCD), which is the force that holds positively charged protons together.

"There are a bunch of protons and neutrons in the center of an ion," explains Reed. "These are positively charged and should repel, but there's a 'strong force' that keeps them together --  strong enough to overcome their tendency to come apart."

Understanding quark-gluon plasma's phase diagram, and the location and existence of the phase transition between the plasma and normal matter is of fundamental importance, says Reed.

"It's a unique opportunity to learn how one of the four fundamental forces of nature operates at temperature and energy densities similar to those that existed only microseconds after the Big Bang," says Reed.

Upgrading the RHIC detectors to better map the "strong force"

The STAR team uses a Beam Energy Scan (BES) to do the phase transition mapping. During the first part of the project, known as BES-I, the team collected observable evidence with "intriguing results." Reed presented these results at the 5th Joint Meeting of the APS Division of Nuclear Physics and the Physical Society of Japan in Hawaii in October 2018 in a talk titled: "Testing the quark-gluon plasma limits with energy and species scans at RHIC."

However, limited statistics, acceptance, and poor event plane resolution did not allow firm conclusions for a discovery. The second phase of the project, known as BES-II, is going forward and includes an improvement that Reed is working on with STAR team members: an upgrade of the Event Plan Detector. Collaborators include scientists at Brookhaven as well as at Ohio State University.

The STAR team plans to continue to run experiments and collect data in 2019 and 2020, using the new Event Plan Detector. According to Reed, the new detector is designed to precisely locate where the collision happens and will help characterize the collision, specifically how "head on" it is.

"It will also help improve the measurement capabilities of all the other detectors," says Reed.

The STAR collaboration expects to run their next experiments at RHIC in March 2019.

Read more at Science Daily

Scientists find increase in asteroid impacts on ancient Earth by studying the Moon

Image depicts the change in impact rate modeled in this paper. Some of the craters used in the study on both the moon and Earth are highlighted in the background.
An international team of scientists is challenging our understanding of a part of Earth's history by looking at the Moon, the most complete and accessible chronicle of the asteroid collisions that carved our solar system.

In a study published today in Science, the team shows the number of asteroid impacts on the Moon and Earth increased by two to three times starting around 290 million years ago.

"Our research provides evidence for a dramatic change in the rate of asteroid impacts on both Earth and the Moon that occurred around the end of the Paleozoic era," said lead author Sara Mazrouei, who recently earned her PhD in the Department of Earth Sciences in the Faculty of Arts & Science at the University of Toronto (U of T). "The implication is that since that time we have been in a period of relatively high rate of asteroid impacts that is 2.6 times higher than it was prior to 290 million years ago."

It had been previously assumed that most of Earth's older craters produced by asteroid impacts have been erased by erosion and other geologic processes. But the new research shows otherwise.

"The relative rarity of large craters on Earth older than 290 million years and younger than 650 million years is not because we lost the craters, but because the impact rate during that time was lower than it is now," said Rebecca Ghent, an associate professor in U of T's Department of Earth Sciences and one of the paper's co-authors. "We expect this to be of interest to anyone interested in the impact history of both Earth and the Moon, and the role that it might have played in the history of life on Earth."

Scientists have for decades tried to understand the rate that asteroids hit Earth by using radiometric dating of the rocks around them to determine their ages. But because it was believed erosion caused some craters to disappear, it was difficult to find an accurate impact rate and determine whether it had changed over time.

A way to sidestep this problem is to examine the Moon, which is hit by asteroids in the same proportions over time as Earth. But there was no way to determine the ages of lunar craters until NASA's Lunar Reconnaissance Orbiter (LRO) started circling the Moon a decade ago and studying its surface.

"The LRO's instruments have allowed scientists to peer back in time at the forces that shaped the Moon," said Noah Petro, an LRO project scientist based at NASA Goddard Space Flight Center.

Using LRO data, the team was able to assemble a list of ages of all lunar craters younger than about a billion years. They did this by using data from LRO's Diviner instrument, a radiometer that measures the heat radiating from the Moon's surface, to monitor the rate of degradation of young craters.

During the lunar night, rocks radiate much more heat than fine-grained soil called regolith. This allows scientists to distinguish rocks from fine particles in thermal images. Ghent had previously used this information to calculate the rate at which large rocks around the Moon's young craters -- ejected onto the surface during asteroid impact -- break down into soil as a result of a constant rain of tiny meteorites over tens of millions of years. By applying this idea, the team was able to calculate ages for previously un-dated lunar craters.

When compared to a similar timeline of Earth's craters, they found the two bodies had recorded the same history of asteroid bombardment.

"It became clear that the reason why Earth has fewer older craters on its most stable regions is because the impact rate was lower up until about 290 million years ago," said William Bottke, an asteroid expert at the Southwest Research Institute in Boulder, Colorado and another of the paper's coauthors. "The answer to Earth's impact rate was staring everyone right in the face."

The reason for the jump in the impact rate is unknown, though the researchers speculate it might be related to large collisions taking place more than 300 million years ago in the main asteroid belt between the orbits of Mars and Jupiter. Such events can create debris that can reach the inner solar system.

Ghent and her colleagues found strong supporting evidence for their findings through a collaboration with Thomas Gernon, an Earth scientist based at the University of Southampton in England who works on a terrestrial feature called kimberlite pipes. These underground pipes are long-extinct volcanoes that stretch, in a carrot shape, a couple of kilometers below the surface, and are found on some of the least eroded regions of Earth in the same places preserved impact craters are found.

"The Canadian shield hosts some of the best-preserved and best-studied of this terrain -- and also some of the best-studied large impact craters," said Mazrouei.

Gernon showed that kimberlite pipes formed since about 650 million years ago had not experienced much erosion, indicating that the large impact craters younger than this on stable terrains must also be intact.

"This is how we know those craters represent a near-complete record," Ghent said.

While the researchers weren't the first to propose that the rate of asteroid strikes to Earth has fluctuated over the past billion years, they are the first to show it statistically and to quantify the rate.

"The findings may also have implications for the history of life on Earth, which is punctuated by extinction events and rapid evolution of new species," said Ghent. "Though the forces driving these events are complicated and may include other geologic causes, such as large volcanic eruptions, combined with biological factors, asteroid impacts have surely played a role in this ongoing saga.

"The question is whether the predicted change in asteroid impacts can be directly linked to events that occurred long ago on Earth."

Read more at Science Daily