Three exocomets discovered around the star Beta Pictoris

Comet illustration.

Three extrasolar comets have been discovered around the star Beta Pictoris, 63 light years away, by the University of Innsbruck. Analysis of data from the current NASA mission TESS by Sebastian Zieba and Konstanze Zwintz from the Institute for Astro- and Particle Physics, together with colleagues from Leiden University and the University of Warwick has revealed the extrasolar objects.

Just about a year after the launch of the NASA mission TESS, the first three comets orbiting the nearby star Beta Pictoris outside our solar system were discovered in data from the space telescope. The main goal of TESS is to search for exoplanets -- planets orbiting other stars. The recognition of signals from much smaller exocomets compared to planets requires the analysis of a precise light curve, which can now be obtained using the technical sophistication of the new space telescope.

Sebastian Zieba, Master's student in the team of Konstanze Zwintz at the Institute of Astro- and Particle Physics at the University of Innsbruck, discovered the signal of the exocomets when he investigated the TESS light curve of Beta Pictoris in March this year. "The data showed a significant decrease in the intensity of the light of the observed star. These variations due to darkening by an object in the star's orbit can clearly be related to a comet," Sebastian Zieba and Konstanze Zwintz explain the sensational discovery.

In collaboration with Matthew Kenworthy from Leiden University (Netherlands) and Grant Kennedy from the University of Warwick (UK), they analysed and interpreted the signals of the exocomets. The results will now be published in the international journal Astronomy and Astrophysics. Three similar exocomet systems have recently been found around three other stars during data analysis by NASA's Kepler mission. The researchers suggest that exocomets are more likely to be found around young stars. "The space telescope Kepler concentrated on older stars similar to the Sun in a relatively small area in the sky. TESS, on the other hand, observes stars all over the sky, including young stars. We therefore expect further discoveries of this kind in the future," says Konstanze Zwintz. Zwintz's research focuses on young stars and she is regarded as an internationally renowned expert in the field of asteroseismology.

Dr Grant Kennedy, from the University of Warwick Department of Physics, assisted with the modelling and interpretation of the data. He said: "This discovery is really important for the science of extrasolar comets for several reasons. Beta Pictoris had been thought to host exocomets for three decades from a different technique, and the TESS data provide long overdue and independent evidence for their existence. Our next aim is to find similar signatures around other stars, and this discovery shows that TESS is up to the task."

Famous star

The young and very bright star Beta Pictoris is a "celebrity" among astronomers for many reasons: "Already in the 1980s, investigations of Beta Pictoris provided convincing evidence for planetary systems around stars other than our Sun -- a decade before exoplanets were even discovered for the first time. In addition, there was already indirect evidence for comets at that time based on the characteristic signature of evaporating gas coming off them," adds Konstanze Zwintz. At about 23 million years old, Beta Pictoris is a relatively young star, "a young adult star compared to human age," says the astronomer.

The discovery of exocomets around Beta Pictoris was predicted in 1999 in a paper by the astrophysicists Alain Lecavelier des Etangs, Alfred Vidal-Madjar and Roger Ferlet. "Together with our colleagues from Leiden and Warwick, we are pleased to have finally confirmed this theory," say Zieba and Zwintz. The scientists expect to discover many more comets and asteroids in this area, as it is a young star. "In the future, we want to find answers to the question of how often exocomets occur and whether their number really decreases with the age of a star. Information about this is important because by analysing the comets around a young star we can also draw conclusions about the history of our own solar system. Because we know that our solar system showed considerably more comets in 'young years'," explains Konstanze Zwintz.

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18 Earth-sized exoplanets discovered

Extrasolar planet illustration.

Somewhat more than 4000 planets orbiting stars outside our solar system are known so far. Of these so-called exoplanets, about 96 percent are significantly larger than our Earth, most of them more comparable with the dimensions of the gas giants Neptune or Jupiter. This percentage likely does not reflect the real conditions in space, however, since small planets are much harder to track down than big ones. Moreover, small worlds are fascinating targets in the search for Earth-like, potentially habitable planets outside the solar system.

The 18 newly discovered worlds fall into the category of Earth-sized planets. The smallest of them is only 69 percent of the size of the Earth; the largest is barely more than twice the Earth's radius. And they have another thing in common: all 18 planets could not be detected in the data from the Kepler Space Telescope so far. Common search algorithms were not sensitive enough.

In their search for distant worlds, scientists often use the so-called transit method to look for stars with periodically recurring drops in brightness. If a star happens to have a planet whose orbital plane is aligned with the line of sight from Earth, the planet occults a small fraction of the stellar light as it passes in front of the star once per orbit.

"Standard search algorithms attempt to identify sudden drops in brightness," explains Dr. Rene Heller from MPS, first author of the current publications. "In reality, however, a stellar disk appears slightly darker at the edge than in the center. When a planet moves in front of a star, it therefore initially blocks less starlight than at the mid-time of the transit. The maximum dimming of the star occurs in the center of the transit just before the star becomes gradually brighter again," he explains.

Large planets tend to produce deep and clear brightness variations of their host stars so that the subtle center-to-limb brightness variation on the star hardly plays a role in their discovery. Small planets, however, present scientists with immense challenges. Their effect on the stellar brightness is so small that it is extremely hard to distinguish from the natural brightness fluctuations of the star and from the noise that necessarily comes with any kind of observation. René Heller's team has now been able to show that the sensitivity of the transit method can be significantly improved, if a more realistic light curve is assumed in the search algorithm.

"Our new algorithm helps to draw a more realistic picture of the exoplanet population in space," summarizes Michael Hippke of Sonneberg Observatory. "This method constitutes a significant step forward, especially in the search for Earth-like planets."

The researchers used data from NASA's Kepler space telescope as a test bed for their new algorithm. In the first mission phase from 2009 to 2013, Kepler recorded the light curves of more than 100,000 stars, resulting in the discovery of over 2300 planets. After a technical defect, the telescope had to be used in an alternative observing mode, called the K2 mission, but it nevertheless monitored more than another 100,000 stars by the end of the mission in 2018. As a first test sample for their new algorithm, the researchers decided to re-analyze all 517 stars from K2 that were already known to host at least one transiting planet.

In addition to the previously known planets, the researchers discovered 18 new objects that had previously been overlooked. "In most of the planetary systems that we studied, the new planets are the smallest," co-author Kai Rodenbeck of the University of Göttingen and MPS describes the results. What is more, most of the new planets orbit their star closer than their previously known planetary companions. The surfaces of these new planets therefore likely have temperatures well in excess of 100 degrees Celsius; some even have temperatures of up to 1000 degrees Celsius. Only one of the bodies is an exception: it likely orbits its red dwarf star within the so-called habitable zone. At this favorable distance from its star, this planet may offer conditions under which liquid water could occur on its surface -- one of the basic prerequisites for life as we know it on Earth.

Of course, the researchers cannot rule out that their method, too, is blind to other planets in the systems they investigated. In particular, small planets at large distances to their host stars are known to be problematic. They require more time to complete a full orbit than planets orbiting their stars closer in. As a consequence, the transits of planets in wide orbits occur less often, which makes their signals even harder to detect.

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Ammonium fertilized early life on Earth

Early Earth concept.

A team of international scientists -- including researchers at the University of St. Andrews, Syracuse University and Royal Holloway, University of London -- has demonstrated a new source of food for early life on the planet.

Life on Earth relies on the availability of critical elements such as nitrogen and phosphorus. These nutrient elements are ubiquitous to all life, as they are required for the formation of DNA, the blueprints of life, and proteins, the machinery. They are originally sourced from rocks and the atmosphere, so their availability to life has fluctuated alongside significant changes in the chemistry of Earth's surface environments over geologic time.

The research, published in Nature Geoscience, reveals how the supply of these elements directly impacted the growth of Earth's oxygen-rich atmosphere and were key to the evolution of early life on Earth.

The most dramatic change in Earth history followed the evolution of oxygenic photosynthesis, which fundamentally transformed the planet by providing a source of carbon to the biosphere and a source of oxygen to the atmosphere, the latter culminating in the Great Oxidation Event (GOE) some 2.3 billion years ago.

Despite the critical importance of nutrients to life, the availability of nitrogen and phosphorus in pre-GOE oceans is not well understood, particularly how the supply of these elements drove and/or responded to planetary oxygenation.

Using samples of exceptionally well-preserved rocks that have been associated with early evidence for oxygenic photosynthesis 2.7 billion year ago, the team of researchers examined Earth's early nitrogen cycle to decipher feedbacks associated with the initial stages of planetary oxygenation.

"There is precious little rock available from this time interval that is suitable for the type of analyses we performed. Most rocks that are this old have been deformed and heated during 2.7 billion years of plate tectonic activity, rendering the original signals of life lost," says Christopher Junium, associate professor of Earth sciences in the College of Arts and Sciences.

The rock samples showed the first direct evidence of the build-up of a large pool of ammonium in the pre-GOE oceans. This ammonium would have provided an ample source of nitrogen to fuel the early biosphere and associated oxygen production.

Research team leader Aubrey Zerkle, reader in the School of Earth and Environmental Sciences at the University of St Andrews, says: "Today we think of ammonium as the unpleasant odor in our cleaning supplies, but it would've served as an all-you-can-eat buffet for the first oxygen-generating organisms, a significant improvement on the dumpster scraps they relied on earlier in Earth's history."

As well as helping scientists better understand the role of the nitrogen cycle in global oxygenation, the new findings also provide context for other nutrient feedbacks during early planetary evolution.

"It is becoming ever more clear that the game of nutrient limitation has tipped back and forth through Earth's history as life has evolved and as conditions have changed," Junium says.

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New lens manufacturing technique

Researchers from Washington State University and Ohio State University have developed a low-cost, easy way to make custom lenses that could help manufacturers avoid the expensive molds required for optical manufacturing.

Led by Lei Li, assistant professor in the School of Mechanical and Materials Engineering, and graduate student, Mojtaba Falahati, the researchers developed a liquid mold from droplets that they can manipulate with magnets to create lenses in a variety of shapes and sizes. Their work is featured on the cover of the journal, Applied Physics Letters.

High-quality lenses are increasingly used in everything from cameras, to self-driving cars, and virtually all robotics, but the traditional molding and casting processes used in their manufacturing require sophisticated and expensive metal molds. So, manufacturers are mostly limited to mass producing one kind of lens.

"The molds are precisely finished and are difficult to make," said Li. "It isn't worthwhile to make a mold for low-volume production."

The researchers ran into the problem firsthand as they searched for lenses for their work to develop a portable laboratory reader on a phone.

They first tried to make their own lenses using 3D printing but found it difficult to control the lens shape. They then came up with the idea of using magnets and the surface tension of liquids to literally create free-flowing molds.

They placed tiny, magnetic iron particles into liquid droplets and built a device to surround the droplets with magnets. They then poured the plastic material used in lenses over the droplet. As they applied a magnetic field, the droplet took on a conical lens shape -- creating a mold for the plastic lens material. Once they cured the plastic, it hardened and had the same optical properties and imaging quality as a commercially purchased lens. The liquid droplet remains separate and can be re-used.

The magnets can be moved to change the magnetic field, the shape of the mold, and the resulting lens. The researchers also used bigger or smaller droplets to create lenses of varying sizes.

"We brought the concept of interfacial tension to the field of optics by introducing an innovative controllable liquid mold," said Li. "This novel process allowed us to regulate the shape of a magnetic drop and to create lenses without having to fabricate expensive molds."

From Science Daily

Counter-intuitive climate change solution

Gas burning.

A relatively simple process could help turn the tide of climate change while also turning a healthy profit. That's one of the hopeful visions outlined in a new Stanford-led paper that highlights a seemingly counterintuitive solution: converting one greenhouse gas into another.

The study, published in Nature Sustainability on May 20, describes a potential process for converting the extremely potent greenhouse gas methane into carbon dioxide, which is a much less potent driver of global warming. The idea of intentionally releasing carbon dioxide into the atmosphere may seem surprising, but the authors argue that swapping methane for carbon dioxide is a significant net benefit for the climate.

"If perfected, this technology could return the atmosphere to pre-industrial concentrations of methane and other gases," said lead author Rob Jackson, the Michelle and Kevin Douglas Provostial Professor in Earth System Science in Stanford's School of Earth, Energy & Environmental Sciences.

The basic idea is that some sources of methane emissions -- from rice cultivation or cattle, for example -- may be very difficult or expensive to eliminate. "An alternative is to offset these emissions via methane removal, so there is no net effect on warming the atmosphere," said study coauthor Chris Field, the Perry L. McCarty Director of the Stanford Woods Institute for the Environment.

A problem and a possible solution

In 2018, methane -- about 60 percent of which is generated by humans -- reached atmospheric concentrations two and a half times greater than pre-industrial levels. Although the amount of carbon dioxide in the atmosphere is much greater, methane is 84 times more potent in terms of warming the climate system over the first 20 years after its release.

Most scenarios for stabilizing average global temperatures at 2 degrees Celsius above pre-industrial levels depend on strategies for both reducing the overall amount of carbon dioxide entering the atmosphere and removing what's already in the atmosphere through approaches such as tree planting or underground sequestration. However, removing other greenhouse gases, particularly methane, could provide a complementary approach, according to the study's authors, who point to the gas's outsized influence on the climate.

Most scenarios for removing carbon dioxide typically assume hundreds of billions of tons removed over decades and do not restore the atmosphere to pre-industrial levels. In contrast, methane concentrations could be restored to pre-industrial levels by removing about 3.2 billion tons of the gas from the atmosphere and converting it into an amount of carbon dioxide equivalent to a few months of global industrial emissions, according to the researchers. If successful, the approach would eliminate approximately one-sixth of all causes of global warming to date.

Methane is challenging to capture from air because its concentration is so low. However, the authors point out that zeolite, a crystalline material that consists primarily of aluminum, silicon and oxygen, could act essentially as a sponge to soak up methane. "The porous molecular structure, relatively large surface area and ability to host copper and iron in zeolites make them promising catalysts for capturing methane and other gases," said Ed Solomon, the Monroe E. Spaght Professor of Chemistry in the School of Humanities and Sciences.

The whole process might take the form of a giant contraption with electric fans forcing air through tumbling chambers or reactors full of powdered or pelletized zeolites and other catalysts. The trapped methane could then be heated to form and release carbon dioxide, the authors suggest.

A profitable future

The process of converting methane to carbon dioxide could be profitable with a price on carbon emissions or an appropriate policy. If market prices for carbon offsets rise to $500 or more per ton this century, as predicted by most relevant assessment models, each ton of methane removed from the atmosphere could be worth more than $12,000.

A zeolite array about the size of a football field could generate millions of dollars a year in income while removing harmful methane from the air. In principle, the researchers argue that the approach of converting a more harmful greenhouse gas to one that's less potent could also apply to other greenhouse gases.

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Formation of the moon brought water to Earth

Earth seen from the moon.

The Earth is unique in our solar system: It is the only terrestrial planet with a large amount of water and a relatively large moon, which stabilizes the Earth's axis. Both were essential for Earth to develop life.

Planetologists at the University of Münster (Germany) have now been able to show, for the first time, that water came to Earth with the formation of the Moon some 4.4 billion years ago. The Moon was formed when Earth was hit by a body about the size of Mars, also called Theia. Until now, scientists had assumed that Theia originated in the inner solar system near the Earth. However, researchers from Münster can now show that Theia comes from the outer solar system, and it delivered large quantities of water to Earth. The results are published in the current issue of Nature Astronomy.

From the outer into the inner solar system

The Earth formed in the 'dry' inner solar system, and so it is somewhat surprising that there is water on Earth. To understand why this the case, we have to go back in time when the solar system was formed about 4.5 billion years ago. From earlier studies, we know that the solar system became structured such that the 'dry' materials were separated from the 'wet' materials: the so-called 'carbonaceous' meteorites, which are relatively rich in water, come from the outer solar system, whereas the drier 'non-carbonaceous' meteorites come from the inner solar system. While previous studies have shown that carbonaceous materials were likely responsible for delivering the water to Earth, it was unknown when and how this carbonaceous material -- and thus the water -- came to Earth.

"We have used molybdenum isotopes to answer this question. The molybdenum isotopes allow us to clearly distinguish carbonaceous and non-carbonaceous material, and as such represent a 'genetic fingerprint' of material from the outer and inner solar system," explains Dr. Gerrit Budde of the Institute of Planetology in Münster and lead author of the study.

The measurements made by the researchers from Münster show that the molybdenum isotopic composition of the Earth lies between those of the carbonaceous and non-carbonaceous meteorites, demonstrating that some of Earth's molybdenum originated in the outer solar system. In this context, the chemical properties of molybdenum play a key role because, as it is an iron-loving element, most of the Earth's molybdenum is located in the core.

"The molybdenum which is accessible today in the Earth's mantle, therefore, originates from the late stages of Earth's formation, while the molybdenum from earlier phases is entirely in the core," explains Dr. Christoph Burkhardt, second author of the study. The scientists' results therefore show, for the first time, that carbonaceous material from the outer solar system arrived on Earth late.

But the scientists are going one step further. They show that most of the molybdenum in Earth's mantle was supplied by the protoplanet Theia, whose collision with Earth 4.4 billion years ago led to the formation of the Moon. However, since a large part of the molybdenum in Earth's mantle originates from the outer solar system, this means that Theia itself also originated from the outer solar system. According to the scientists, the collision provided sufficient carbonaceous material to account for the entire amount of water on Earth.

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Bonobo mothers help their sons to have more offspring

Bonobos.

In many social animal species individuals share child-rearing duties, but new research from the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, finds that bonobo mothers go the extra step and actually take action to ensure their sons will become fathers. This way bonobo mothers increase their sons' chance of fatherhood three-fold.

"This is the first time that we can show the impact of the mother's presence on a very important male fitness trait, which is their fertility," says Martin Surbeck, a primatologist at the Max Planck Institute for Evolutionary Anthropology. "We were surprised to see that the mothers have such a strong, direct influence on the number of grandchildren they get."

Surbeck and his colleagues observed wild populations of bonobos in the Democratic Republic of Congo, as well as wild populations of chimpanzees in Ivory Coast, Tanzania, and Uganda. They found that while both bonobo and chimpanzee mothers would advocate for their sons in male-on-male conflicts, bonobo moms went the extra mile to aid their sons' copulation efforts. This involved protecting their sons' mating attempts from other males and intervening in other male's mating attempts.

The bonobo mothers were also able to use their rank in the bonobo's matriarchal society to give their sons access to popular spots within social groups in the community and help them achieve higher male status -- and therefore, better mating opportunities. The authors note that these interactions were rare in chimpanzee societies and did not have an effect on male fertility; in chimpanzees males hold dominant positions over females, making the actions of chimp mothers less influential than those of bonobo mothers.

Interestingly, bonobo moms did not extend similar help to their daughters, nor were there any observations of daughters receiving assistance in rearing their offspring. "In bonobo social systems, the daughters disperse from the native community and the sons stay," Surbeck says. "And for the few daughters that stay in the community, which we don't have many examples of, we don't see them receiving much help from their mothers."

Moving forward, Surbeck and his team would like to better understand the benefits these behaviors confer on bonobo mothers. Currently, they think that it allows for an indirect continuation of their genes. "These females have found a way to increase their reproductive success without having more offspring themselves," he says, noting that the prolongation of the post-reproductive human female lifespan, as well as the early-age at which human women can no longer bare children, may have evolved from this indirect method of continuing their genetic line.

Surbeck acknowledges that gathering data on post-reproductive lifespans of females in chimp and bonobo communities will require a long-term, collaborative study, similar to this one. "Without the help and participation from all of the field sites where data was collected, these important interactions could have been overlooked," he says. "Now as the director of a bonobo field site, I'm looking forward to further exploring this topic."

Read more at Science Daily

Evolution in the gut

They are a part of us: we all carry about ten times as many bacteria and archaea as our own cells. The bacterial ecosystem in our digestive tract, the so-called microbiome, is not only of great importance for our metabolism, but also for the immune system and even our behaviour. The same is true to animals, but the composition of the microbiome differs greatly between animal species. For the first time, a large-scale study was carried out to explain the development of the microbiome using faecal samples from free-living animals. 128 different species from very classes fish, amphibians, reptiles, birds and mammals were examined. The research groups involved were able to show how evolution and dietary habits interact and determine the composition of bacteria in the digestive tract. Many microorganisms in the intestine seem to have developed in sync with their host animals over millions of years. These results should also help in the characterisation of faecal pollution in water by allowing attribution to certain animal species in a much more precise way in the future.

Samples from all branches of the family tree

"So far there have been studies on the microbiome of humans, or special data for individual species such as rats. However, we wanted to select many animal species that were as representative as possible of the entire evolutionary tree of vertebrates -- from birds to mammals to fish," says Prof. Andreas Farnleitner, Co-Leader of the Interuniversity Research Centre "Water and Health" at the TU Wien (ICC Water & Health) and Professor of Microbiological Diagnostics in extension of the ICC Water & Health group at Karl Landsteiner Private University in Krems.

It was important to get samples from wild animals, as zoo animals can have a completely different microbiome than their wild counterparts. The Institute for Wildlife Science and Ecology of the University of Veterinary Medicine Vienna was the lead partner for the sample collection. The DNA of the microorganisms studied was then sequenced -- partly at the TU Wien and partly at the Max Planck Institute for Developmental Biology in Tübingen.

"A total of more than 400 samples from 180 different species were analysed, resulting in 20 million gene sequences," said Dr. Georg Reischer (TU Vienna). The cooperation partners of the MPI in Tübingen contributed their know-how in bioinformatic data analysis and evolutionary biology to the study. This revealed striking relationships that can be explained by evolutionary history: The microbiome has developed over many millions of years in co-evolution with the host animals. Closely related species that are close to the evolutionary family tree also have similarities in the microbiome. "Nutrition also plays a role, but it is never the only decisive factor," explains Georg Reischer. "If a mammal eats the same food as a bird, it still does not have the same bacteria in its intestines."

The contamination bio-detector
The data collected in this study not only allows the interpretation of the co-evolution of host animals and the microorganisms in their digestive tract, it also facilitates the development of methods to assist in the provision of clean water. In recent years, a technology has been developed at the TU Wien that uses DNA tests to provide information on the source of fecal pollution in water. Thus it became possible to find out whether the contamination was caused by human wastewater or grazing animals. "Now we have a very extensive data set at our disposal that will make such tests possible in a much more comprehensive and accurate way," says Andreas Farnleitner.

From Science Daily

True identity of imposter 'pigs' on 17th century map overturns early colonial history of Barbados

Peccary.

Which came first, the pigs or the pioneers? In Barbados, that has been a historical mystery ever since the first English colonists arrived on the island in 1627 to encounter what they thought was a herd of wild European pigs.

A recent discovery by an SFU archaeologist is shedding new light on the matter. Christina Giovas uncovered the jaw bone of a peccary, a South American mammal that resembles a wild pig, while researching a larger project on prehistoric animal introductions in the Caribbean.

"I didn't give it much notice at the time, but simply collected it along with other bones," says Giovas, the lead author of a study just published in PLOS ONE. "It was completely unexpected and I honestly thought I must have made a mistake with the species identification."

Giovas and collaborators George Kamenov and John Krigbaum of the University of Florida radiocarbon-dated the bone and conducted strontium isotope analysis to determine the age and whether the peccary was born on Barbados or had been imported from elsewhere.

The results showed the peccary was local and dated to 1645-1670, when the English wrote their account of finding wild European pigs on the Caribbean island. The researchers were not only able to show there had been a previously undetected historic peccary introduction but that the region's earliest celebrated maps depicted peccaries that had been mistaken for pigs by the English.

Giovas says the findings upend Barbados' accepted colonial history and reflect how quickly Europeans began to alter New World environments by altering species distributions.

"Checking historical and archaeological records, we determined the most likely source of peccary introduction was from Spanish or Portuguese ships passing the island in the 16th century -- and most likely left as a source of meat for future visiting sailors," she says.

From Science Daily

Gas insulation could be protecting an ocean inside Pluto

Pluto.

A gassy insulating layer beneath the icy surfaces of distant celestial objects could mean there are more oceans in the universe than previously thought.

Computer simulations provide compelling evidence that an insulating layer of gas hydrates could keep a subsurface ocean from freezing beneath Pluto's icy exterior, according to a study published in the journal Nature Geoscience.

In July 2015, NASA's New Horizons spacecraft flew through Pluto's system, providing the first-ever close-up images of this distant dwarf planet and its moons. The images showed Pluto's unexpected topography, including a white-colored ellipsoidal basin named Sputnik Planitia, located near the equator and roughly the size of Texas.

Because of its location and topography, scientists believe a subsurface ocean exists beneath the ice shell which is thinned at Sputnik Planitia. However, these observations are contradictory to the age of the dwarf planet because the ocean should have frozen a long time ago and the inner surface of the ice shell facing the ocean should have also been flattened.

Researchers at Japan's Hokkaido University, the Tokyo Institute of Technology, Tokushima University, Osaka University, Kobe University, and at the University of California, Santa Cruz, considered what could keep the subsurface ocean warm while keeping the ice shell's inner surface frozen and uneven on Pluto. The team hypothesized that an "insulating layer" of gas hydrates exists beneath the icy surface of Sputnik Planitia. Gas hydrates are crystalline ice-like solids formed of gas trapped within molecular water cages. They are highly viscous, have low thermal conductivity, and could therefore provide insulating properties.

The researchers conducted computer simulations covering a timescale of 4.6 billion years, when the solar system began to form. The simulations showed the thermal and structural evolution of Pluto's interior and the time required for a subsurface ocean to freeze and for the icy shell covering it to become uniformly thick. They simulated two scenarios: one where an insulating layer of gas hydrates existed between the ocean and the icy shell, and one where it did not.

The simulations showed that, without a gas hydrate insulating layer, the subsurface sea would have frozen completely hundreds of millions of years ago; but with one, it hardly freezes at all. Also, it takes about one million years for a uniformly thick ice crust to completely form over the ocean, but with a gas hydrate insulating layer, it takes more than one billion years.

The simulation's results support the possibility of a long-lived liquid ocean existing beneath the icy crust of Sputnik Planitia.

The team believes that the most likely gas within the hypothesized insulating layer is methane originating from Pluto's rocky core. This theory, in which methane is trapped as a gas hydrate, is consistent with the unusual composition of Pluto's atmosphere -- methane-poor and nitrogen-rich.

Read more at Science Daily