The order of life

At first glance, a pack of wolves has little to do with a vinaigrette. However, a team led by Ramin Golestanian, Director at the Max Planck Institute for Dynamics and Self-Organization, has developed a model that establishes a link between the movement of predators and prey and the segregation of vinegar and oil. They expanded a theoretical framework that until now was only valid for inanimate matter. In addition to predators and prey, other living systems such as enzymes or self-organizing cells can now be described.

Particles of two types (red and green) interact with each other. While particles of the same type
inevitably experience reciprocal attraction or repulsion, particles of different types can interact
 non-reciprocally. Here the green particles chase the red particles. On a large scale, the highly
compressed bands of the green particles chase the bands of the red particles. This creates
order and movement in the system [Credit: MPIDS/Novak, Saha,
Agudo-Canalejo, Golestania]

Order is not always apparent at first glance. If you ran with a pack of wolves hunting deer, the movements would appear disordered. However, if the hunt is observed from a bird's eye view and over a longer period of time, patterns become apparent in the movement of the animals. In physics, such behaviour is considered orderly. But how does this order emerge? 

The Department of "Living Matter Physics" of Ramin Golestanian is dedicated to this question and investigates the physical rules that govern motion in living or active systems. Golestanian's aim is to reveal universal characteristics of active, living matter. This includes not only larger organisms such as predators and prey but also bacteria, enzymes and motor proteins as well as artificial systems such as micro-robots. "When we describe a group of such active systems over great distances and long periods of time, the specific details of the systems lose importance. Their overall distribution in space ultimately becomes the decisive characteristic", explains Golestanian.

From inanimate to living system

His team in Gottingen has recently made a breakthrough in describing living matter. To achieve this, Suropriya Saha, Jaime Agudo-Canalejo, and Ramin Golestanian started with the well-known description of the behaviour of inanimate matter and expanded it. The main point was to take into account the fundamental difference between living and inanimate matter. In contrast to inanimate, passive matter, living, active matter can move on its own. Physicists use the Cahn-Hilliard equation to describe how inanimate mixtures such as an emulsion of oil and water separate.

The characterization developed in the 1950s is considered the standard model of phase separation. It is based on the principle of reciprocity: Tit for tat. Oil thus repels water in the same way as water repels oil. However, this is not always the case for living matter or active systems. A predator pursues its prey, while the prey tries to escape from the predator. Only recently has it been shown that there is non-reciprocal (i.e. active) behaviour even in the movement of the smallest systems such as enzymes. Enzymes can thus concentrate specifically in individual cell areas - something that is necessary for many biological processes. Following this discovery, the Gottingen researchers investigated how large accumulations of different enzymes behave. Would they mix together or form groups? Would new and unforeseen characteristics arise? With the aim of answering these questions, the research team set to work.

Suddenly waves appear

The first task was to modify the Cahn-Hilliard equation to include non-reciprocal interactions. Because the equation describes non-living systems, the reciprocity of passive interactions is deeply embedded in its structure. Thus, every process described by it ends in thermodynamic equilibrium. In other words, all participants ultimately enter a resting state. Life, however, takes place outside the thermodynamic equilibrium. This is because living systems do not remain at rest but rather use energy in order to achieve something (e.g. their own reproduction). Suropriya Saha and her colleagues take this behaviour into account by expanding the Cahn-Hilliard equation by a parameter that characterizes non-reciprocal activities. In this way, they can now also describe processes that differ from passive processes to any extent.

Saha and her colleagues used computer simulations to study the effects of the introduced modifications. "Surprisingly, even minimal non-reciprocity leads to radical deviations from the behaviour of passive systems", says Saha. For example, the researcher observed the formation of travelling waves in a mixture of two different types of particles. In this phenomenon, bands of one component chase the bands of the other component, thereby resulting in a pattern of moving stripes. In addition, complex lattices can form in particle mixtures in which small clusters of one component chase groups of the other component. With their work, the researchers hope to contribute to scientific progress in both physics and biology. For example, the new model can describe and predict the behaviour of different cells, bacteria, or enzymes. "We have taught an old dog new tricks with this model", says Golestanian. "Our research shows that physics contributes to our understanding of biology and that the challenges posed by studying living matter open up new avenues for fundamental research in physics."

The findings are published in Physical Review X.

Source: Max-Planck-Gesellschaft [October 29, 2020]

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Where were Jupiter and Saturn born?

New work led by Carnegie's Matt Clement reveals the likely original locations of Saturn and Jupiter. These findings refine our understanding of the forces that determined our Solar System's unusual architecture, including the ejection of an additional planet between Saturn and Uranus, ensuring that only small, rocky planets, like Earth, formed inward of Jupiter.

New work led by Carnegie's Matt Clement reveals the likely original locations of Saturn and Jupiter 
[Credit: NASA/JPL-Caltech/Space Science Institute]

In its youth, our Sun was surrounded by a rotating disk of gas and dust from which the planets were born. The orbits of early formed planets were thought to be initially close-packed and circular, but gravitational interactions between the larger objects perturbed the arrangement and caused the baby giant planets to rapidly reshuffle, creating the configuration we see today.

"We now know that there are thousands of planetary systems in our Milky Way galaxy alone," Clement said. "But it turns out that the arrangement of planets in our own Solar System is highly unusual, so we are using models to reverse engineer and replicate its formative processes. This is a bit like trying to figure out what happened in a car crash after the fact--how fast were the cars going, in what directions, and so on."

Clement and his co-authors--Carnegie's John Chambers, Sean Raymond of the University of Bordeaux, Nathan Kaib of University of Oklahoma, Rogerio Deienno of the Southwest Research Institute, and Andre Izidoro of Rice University--conducted 6,000 simulations of our Solar System's evolution, revealing an unexpected detail about Jupiter and Saturn's original relationship.

Jupiter in its infancy was thought to orbit the Sun three times for every two orbits that Saturn 
completed. But this arrangement is not able to satisfactorily explain the configuration 
of the giant planets that we see today. Matt Clement and his co-authors showed that 
a ratio of two Jupiter orbits to one Saturnian orbit more consistently produced 
results that look like our familiar planetary architecture [Credit: NASA]

Jupiter in its infancy was thought to orbit the Sun three times for every two orbits that Saturn completed. But this arrangement is not able to satisfactorily explain the configuration of the giant planets that we see today. The team's models showed that a ratio of two Jupiter orbits to one Saturnian orbit more consistently produced results that look like our familiar planetary architecture.

"This indicates that while our Solar System is a bit of an oddball, it wasn't always the case," explained Clement, who is presenting the team's work at the American Astronomical Society's Division for Planetary Sciences virtual meeting today. "What's more, now that we've established the effectiveness of this model, we can use it to help us look at the formation of the terrestrial planets, including our own, and to perhaps inform our ability to look for similar systems elsewhere that could have the potential to host life."

The model also showed that the positions of Uranus and Neptune were shaped by the mass of the Kuiper belt--an icy region on the Solar System's edges composed of dwarf planets and planetoids of which Pluto is the largest member--and by an ice giant planet that was kicked out in the Solar System's infancy.

The study is published in the journal Icarus.

Source: Carnegie Institution for Science [October 29, 2020]

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Earth-sized rogue planet discovered in the Milky Way

Our Galaxy may be teeming with rogue planets, gravitationally unbound to any star. An international team of scientists, led by Polish astronomers, has announced the discovery of the smallest Earth-sized free-floating planet found to date.

Artist's impression of a gravitational microlensing event by a free-floating planet
[Credit: Jan Skowron/Astronomical Observatory, University of Warsaw]

Over four thousand extrasolar planets have been discovered to date. Although many of the known exoplanets do not resemble those in our solar system, they have one thing in common - they all orbit a star. However, theories of planet formation and evolution predict the existence of free-floating (rogue) planets, gravitationally unattached to any star. Indeed, a few years ago Polish astronomers from the OGLE team from the Astronomical Observatory of the University of Warsaw provided the first evidence for the existence of such planets in the Milky Way. Writing in Astrophysical Journal Letters, OGLE astronomers announced the discovery of the smallest rogue planet found to date.

Exoplanets can be only rarely directly observed. Usually, astronomers find planets using observations of the light from the planet's host star. For example, if a planet crosses in front of its parent star's disk, then the observed brightness of the star periodically drops by a small amount causing so called transits. Astronomers can also measure the motion of the star caused by the planet.

Free-floating planets emit virtually no radiation and - by definition - they do not orbit any host star, so they cannot be discovered using traditional methods of astrophysical detection. Nevertheless, rogue planets can be spotted using an astronomical phenomenon called gravitational microlensing. Microlensing results from Einstein's theory of general relativity - a massive object (the lens) may bend the light of a bright background object (the source). The lens' gravity acts as a huge magnifying glass which bends and magnifies the light of distant stars.

'If a massive object (a star or a planet) passes between an Earth-based observer and a distant source star, its gravity may deflect and focus light from the source. The observer will measure a short brightening of the source star' - explains dr Przemek Mroz, a postdoctoral scholar at the California Institute of Technology and a lead author of the study. 'Chances of observing microlensing are extremely slim because three objects - source, lens, and observer - must be nearly perfectly aligned. If we observed only one source star, we would have to wait almost a million year to see the source being microlensed' - he adds.

The gravity of a free-floating planet may deflect and focus light from a distant star when passing 

closely in front of it. Due to the distorted image the star temporarily seems much brighter 

[Credit: Jan Skowron/Astronomical Observatory, University of Warsaw]

This is why modern surveys hunting for gravitational microlensing events are monitoring hundreds of millions of stars in the Milky Way center, where the chances of microlensing are highest. The OGLE survey - led by Warsaw University astronomers - carries out one of such experiments. OGLE is one of the largest and longest sky surveys, it started operations over 28 years ago. Currently, OGLE astronomers are using a 1.3-meter Warsaw Telescope located at Las Campanas Observatory, Chile. Each clear night, they point their telescope to the central regions of the Galaxy and observe hundreds of millions of stars, searching for those which change their brightness.

Gravitational microlensing does not depend on the lens' brightness, so it enables the study of faint or dark objects such as planets. Duration of microlensing events depends on the mass of the lensing object - the less massive the lens, the shorter the microlensing event. Most of the observed events, which typically last several days, are caused by stars. Microlensing events attributed to free-floating planets have timescales of barely a few hours. By measuring the duration of a microlensing event (and shape of its light curve) we can estimate the mass of the lensing object.

The scientists announced the discovery of the shortest-timescale microlensing event ever found, called OGLE-2016-BLG-1928, which has the timescale of just 42 minutes. 'When we first spotted this event, it was clear that it must have been caused by an extremely tiny object' - says dr Radoslaw Poleski from the Astronomical Observatory of the University of Warsaw, a co-author of the study. Indeed, models of the event indicate that the lens must have been less massive than Earth, it was probably a Mars-mass object. Moreover, the lens is likely a rogue planet. 'If the lens were orbiting a star, we would detect its presence in the light curve of the event' - adds dr Poleski. 'We can rule out the planet having a star within about 8 astronomical units (the astronomical unit is the distance between the Earth and the Sun)'.

OGLE astronomers provided the first evidence for a large population of rogue planets in the Milky Way a few years ago. However, the newly-detected planet is the smallest rogue world ever found. 'Our discovery demonstrates that low-mass free-floating planets can be detected and characterized using ground-based telescopes' - says Prof. Andrzej Udalski, the PI of the OGLE project.

The gravity of a free-floating planet may deflect and focus light from a distant star when passing 

closely in front of it. Due to the distorted image the star temporarily seems much brighter 

[Credit: Jan Skowron/Astronomical Observatory, University of Warsaw]

Astronomers suspect that free-floating planets actually formed in protoplanetary disks around stars (as "ordinary" planets) and they have been ejected from their parent planetary systems after gravitational interactions with other bodies, for example, with other planets in the system. Theories of planet formation predict that the ejected planets should be typically smaller than Earth. Thus studying free-floating planets enables us to understand the turbulent past of young planetary systems, such as our solar system.

The search for free-floating planets is one of the science drivers of the Nancy Grace Roman Space Telescope, which is currently being constructed by NASA. The observatory is scheduled to start operations in the mid-2020s.

Because of the brevity of the event, additional observations collected by the Korea Microlensing Telescope Network (KMTNet) were needed to characterize the event. KMTNet operates a network of three telescopes - in Chile, Australia, and South Africa.

Source: University of Warsaw [October 29, 2020]

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Grave of Viking woman found in central Norway

Norwegian University of Science and Technology (NTNU) field manager Eystein Østmo and a team of archaeologists have made a unique discovery which has puzzled archaeologists across the country.

Maria Vestvik and Elise Kjørsvik from the NTNU Science Museum at the Viking grave
[Credit: Eystein Østmoe/NTNU University Museum]

Soil that was visibly black and greasy initially gave away the gravesite. This also gave away the site’s longevity. It pointed to the fact that a person had been buried underground her a long time ago. The grave has, in fact, been dated to around 1,000 years ago.

Some of the grave beads found [Credit: Åge Hojem/ 
NTNU University Museum]

Archaeological finds of Viking graves aren’t necessarily unusual. This particular site, however, gave researchers a surprise. Graves are usually found in groups, but this was the only burial site for miles around. But that’s not all. Remains of a square encasement showed that this no ordinary grave. It was a burial chamber.

Ingvild Mjelde and Elise Kjørsvik clean the beads [Credit: Eystein Østmoe/
NTNU University Museum]

Such chambers were usually reserved for city folk and elite members of Viking society. But Hestnes in Trøndelag was a countryside location since the Viking Age, far from larger settlements.

The woman's buckle [Credit: Eystein Østmoe/
NTNU University Museum]

Grave items indicate that the woman was buried about a thousand years ago. Bone and teeth remains have been discovered in the grave. Once they’re analyzed further, they might give key clues as to who the Viking woman was.

Finds from the grave. Spinning wheel and buckle [Credit: Thora Nyborg/
 NTNU Science Museum]

Green and purple-coloured beads are also among found artifacts. So far, researchers have counted over 300. Various brooches and combs were retrieved, too.

The excavation area at Hestnes [Credit: Kristoffer Rantala/
NTNU Science Museum]

Given the elaborate nature of the grave and items within, scientists believe the woman was among the more powerful members of the local community.

As of now, the mystery lady’s identity remains to be unravelled.

Source: Norway Today [October 28, 2020]

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Bison engravings in Spanish caves reveal a common art culture across ancient Europe

Recently discovered rock art from caves in Northern Spain represents an artistic cultural style common across ancient Europe, but previously unknown from the Iberian Peninsula, according to a study published in the open-access journal PLOS ONE by Diego Garate of the Instituto Internacional de Investigaciones Prehistoricas de Cantabria, Spain, and colleagues.

Photograph and tracing of horse B.II.1, engraved on the right-hand wall in Aitzbitarte
Cave III (O. Rivero and D. Garate) [Credit: Garate et al., 2020]

The history of ancient human art includes various cultural complexes characterized by different artistic styles and conventions. In 2015, new instances of rock art were discovered in three caves in Aitzbitarte Hill in northern Spain, representing an artistic style previously unknown from the Iberian Peninsula. In this study, Garate and colleagues compare this artistic style to others from across Europe.

The artwork in the Aitzbitarte caves consists mostly of engravings of bison, complete with the animals' characteristic horns and humps. The authors note the particular style in which the animals' horns and legs are drawn, typically without proper perspective. Pairs of limbs are consistently depicted as a "double Y" with both legs visible, and the horns are similarly draw side-by-side with a series of lines in between.

This is consistent with the artistic style of the Gravettian cultural complex, characterized by specific customs in art, tools, and burial practices between about 34,000 and 24,000 years ago. This culture is known from across Europe but has not been seen before on the Iberian Peninsula. The authors combine this new discovery with data from around Europe to show that the Gravettian culture was more widespread and varied than previously appreciated.

The authors add: "The study analyses the particularities of Palaeolithic animal engravings found in the Aitzbitarte Caves (Basque Country, Spain) in 2016. These prehistoric images, mainly depicting bison, were drawn in a way that has never before been seen in northern Spain; in a kind of fashion in the way of drawing the engravings that is more characteristic of southern France and some parts of the Mediterranean. The study has shown the close regional relationships in Western Europe cave art since very early times, at least, 25,000 years ago."

Source: Public Library of Science [October 28, 2020]

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Cracking the secrets of dinosaur eggshells

Since the famous discovery of dinosaur eggs in the Gobi Desert in the early 1920s, the fossilized remains have captured the imaginations of paleontologists and the public, alike. Although dinosaur eggs have now been found on every continent, it's not always clear to scientists which species laid them. Now, researchers reporting in ACS Omega have narrowed down the list for an unknown eggshell from Mexico by comparing its microstructure and composition with four known samples.

Researchers studied eggshell microstructures to help estimate whether an unknown sample
was laid by an ornithopod (herbivorous; top) or a theropod (carnivorous; bottom)
[Credit: Nerith R. Elejalde-Cadena et al. 2020]

Because many dinosaur eggs are similar in size and shape, it can be difficult to determine what type of dinosaur laid them. Clues can come from fossilized embryos (which are rare), hatchlings in the same nest or nearby adult remains. Scientists also have identified microscopic features of eggshells that differ among groups of dinosaurs. In addition, researchers have studied the elemental composition of fossil eggshells to learn more about the paleoenvironment and conditions that led to the eggs' fossilization. 

Abel Moreno and colleagues wanted to compare the microstructure and composition of five dinosaur eggshells from nests in the El Gallo Formation of Baja California, Mexico. Based on the eggs' shapes and sizes and the fossil record of the area, the researchers had concluded that three of the eggs were laid by ornithopods (bipedal herbivores) of the hadrosaur family (duck-billed dinosaurs) and one by a theropod (bipedal carnivores) of the troodontidae family (small, bird-like dinosaurs). The remaining sample was too damaged to classify by the naked eye.

Using scanning electron microscopy, the team examined the external and internal surfaces and a cross-section of each eggshell. In contrast to the smooth outer surface of the theropod shell, the shells from the ornithopods and the unknown sample had nodes at different distances across the shell. Images of shell cross-sections from the ornithopods revealed that mammillary cones -- calcite crystals on the inner surface of the shell -- formed thin, elongated columns arranged in parallel, with irregular pores. 

In contrast, the eggshell from the theropod showed thicker, shorter cones arranged in a bilayer, with wider pores. The unknown sample more closely resembled the ornithopod eggshells, leading the researchers to hypothesize that it was probably also from the hadrosaur family. In addition, the researchers conducted an elemental composition analysis, which they say is the first such analysis on dinosaur eggshells collected in Mexico. They say the findings might help reveal how the fossilization process varied among species and locales.

Source: American Chemical Society [October 28, 2020]

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Giant lizards learnt to fly over millions of years

Pterodactyls and other related winged reptiles that lived alongside the dinosaurs steadily improved their ability to fly to become the deadly masters of the sky over the course of millions of years.

Rhamphohynchus - one of 75 pterosaur species studied by the researchers
[Credit: Mark Witton]

A new study published in the journal Nature has shown that pterosaurs - a group of creatures that became Earth's first flying vertebrates - evolved to improve their flight performance over their 150 million-year existence, before they went extinct at the same time as the dinosaurs 66 million years ago.

Scientists from the Universities of Reading, Lincoln and Bristol carried out the most detailed study yet into how animals evolve to become better suited to their environments over time. They combined fossil records with a new model of flight based on today's living birds to measure their flight efficiency and fill in the gaps in our knowledge of their evolutionary story.

This allowed the scientists to track the gradual evolution of pterosaurs and demonstrate that they became twice as good at flying over the course of their history. It also showed that their evolution was caused by consistent small improvements over a long period, rather than sudden evolutionary bursts as had been previously suggested.

Professor Chris Venditti, an evolutionary biologist at the University of Reading and lead author of the study, funded by the Leverhulme Trust, said: "Pterosaurs were a diverse group of winged lizards, with some the size of sparrows and others with the wingspan of a light aircraft. Fans of the movie Jurassic World will have seen a dramatisation of just how huge and lethal these creatures would have been. Their diet consisted mostly of other animals, from insects to smaller dinosaurs.

"Despite their eventual prowess in the air being well-known, the question of whether pterosaurs got better at flying and whether this gave them an advantage over their ancestors has puzzled scientists for decades. There are many examples of how natural selection works on relatively short time scales, but until now it has been very difficult to demonstrate whether plants or animals adapt to become more efficient over a long period.

"Our new method has allowed us to study long-term evolution in a completely new way, and answer this question at last by comparing the creatures at different stages of their evolutionary sequence over many millions of years."

Cimoliopterus - one of 75 pterosaur species studies by the researchers
[Credit: Mark Witton]

Pterosaurs evolved from land-based animals and first emerged as flyers in the Early Triassic period, around 245 million years ago. The first fossils are from 25 million years later.

The scientists monitored changes to pterosaur flight efficiency by using fossils to measure their wingspan and body size at different stages. Their new model based on living birds was applied to the data for 75 pterosaur species, which showed that pterosaurs gradually got better at flying over millions of years.

The models showed that pterosaurs adapted their body shape and size to use 50% less energy when flying over their 150 million-year history. They showed that the creatures increased in mass by 10 times, some to eventually weigh more than 300kg.

The new method also revealed that one group of pterosaurs - azhdarchoids - was an exception to the rule. Scientists have disagreed over how well these animals flew, but the new study showed that they did not get any better throughout their existence.

The enlarged size of azhdarchoids appeared to provide their survival advantage instead, with one animal - Quetzlcoatlus - growing to the height of a giraffe.

Dr Joanna Baker, evolutionary biologist and co-author at the University of Reading said: "This is unique evidence that although these animals were competent fliers, they probably spent much of their time on the ground. Highly efficient flight probably didn't offer them much of an advantage, and our finding that they had smaller wings for their body size is in line with fossil evidence for their reduced reliance on flight."

Professor Stuart Humphries, biophysicist and author from the University of Lincoln said: "One of the few things that haven't changed over the last 300 million years are the laws of physics, so it has been great to use those laws to understand the evolution of flight in these amazing animals."

Professor Mike Benton at the University of Bristol said, "Until recently, paleontologists could describe the anatomy of creatures based on their fossils and work out their functions. It's really exciting now to be able to calculate the operational efficiency of extinct animals, and then to compare them through their evolution to see how efficiency has changed. We don't just have to look at the fossils with amazement, but can really get to grips with what they tell us."

Source: University of Reading [October 28, 2020]

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