Asteroids and comets appear to be a much more important supplier of organic molecules on Mars than expected. Until now, astronomers assumed that the organics on Mars mainly came from dust particles from space. Now, computer simulations by an international team of researchers led by Dutch astronomers indicate that one third of the material comes from asteroids and comets. The findings have been accepted for publication in the scientific journal Icarus.

Cartoon of the planet Mars that is showered with organics. According to calculations, 33% of the organic material on Mars comes from asteroids and comets. Only 67% comes from interplanetary dust [Credit: Anastasia Kruchevska]

In 2015, the Mars rover Curiosity discovered remnants of organic molecules on Mars. Scientists wondered how these organic molecules had ended up on Mars. The prevailing theory was that the molecules were tied to interplanetary dust particles. Those particles are everywhere. For example, around our earth we see the dust particles when they enter our atmosphere and cause "shooting stars."

An international team of researchers from SRON Netherlands Institute for Space Research, the University of Groningen, Utrecht University and the University of California Santa Barbara, suspected that the theory of the dust particles could not be the whole story. The scientists assumed that some of the organic molecules might be delivered by asteroids and comets. To investigate this, they built a computer model of our solar system including hundreds of thousands of asteroids and comets. Then they used Peregrine, the supercomputer of the University of Groningen, to run the computer model for a few weeks.

The calculations show that 192 tons of carbon per year end up on Mars. That is comparable to 8 truckloads. Approximately 129 tons (67 percent) of carbon come from interplanetary dust particles. But asteroids also deliver another 50 tons per year (26 percent) and comets provide about 13 tons (7 percent) of the organic material.

The research has consequences for future and current Mars missions. Mars rovers, according to the astronomers, should look closely at the impact craters of asteroids. In those places, a lot of organic material could be found.

Furthermore, the research also has implications for the chance of life on exoplanets. The Groningen Ph.D. student Kateryna Frantseva, who led the research, explains: "Near other stars, there are also exo-asteroids and exocomets that can shower the surfaces of exoplanets with carbon. If, on top of that, there is water, then you have the required ingredients for life."

Now, the researchers focus on the planet Mercury, where water has been found. They want to estimate how much water on Mercury can be delivered by asteroids and comets. After that they want to extend their research to planetary systems around other stars.

Source: Netherlands Research School for Astronomy [March 14, 2018]

Scientists have used lab experiments to retrace the chemical steps leading to the creation of complex hydrocarbons in space, showing pathways to forming 2-D carbon-based nanostructures in a mix of heated gases.

An asteroid belt orbits a star in this artist's rendering. In a new study, experiments at Berkeley Lab explored possible chemical pathways that could form complex hydrocarbons -- like those found in some meteorite samples -- in space  [Credit: NASA/JPL-Caltech]

The latest study, which featured experiments at the Department of Energy's Lawrence Berkeley National Laboratory (Berkeley Lab), could help explain the presence of pyrene, which is a chemical compound known as a polycyclic aromatic hydrocarbon, and similar compounds in some meteorites.

A team of scientists, including researchers from Berkeley Lab and UC Berkeley, participated in the study, published in Nature Astronomy. The study was led by scientists at the University of Hawaii at Manoa and also involved theoretical chemists at Florida International University.

"This is how we believe some of the first carbon-based structures evolved in the universe," said Musahid Ahmed, a scientist in Berkeley Lab's Chemical Sciences Division who joined other team members to perform experiments at Berkeley Lab's Advanced Light Source (ALS).

"Starting off from simple gases, you can generate one-dimensional and two-dimensional structures, and pyrene could lead you to 2-D graphene," Ahmed said. "From there you can get to graphite, and the evolution of more complex chemistry begins."

Pyrene has a molecular structure composed of 16 carbon atoms and 10 hydrogen atoms. Researchers found that the same heated chemical processes that give rise to the formation of pyrene are also relevant to combustion processes in vehicle engines, for example, and the formation of soot particles.

The latest study builds on earlier work that analyzed hydrocarbons with smaller molecular rings that have also been observed in space, including in Saturn's moon Titan -- namely benzene and naphthalene.

Ralf I. Kaiser, one of the study's lead authors and a chemistry professor at the University of Hawaii at Manoa, said, "When these hydrocarbons were first seen in space, people got very excited. There was the question of how they formed." Were they purely formed through reactions in a mix of gases, or did they form on a watery surface, for example?

Reaction pathways that can form a hydrocarbon called pyrene through a chemical method known as hydrogen- abstraction/acetylene-addition, or HACA, is shown at the top. At bottom, some possible steps by which pyrene can form  more complex hydrocarbons via HACA (red) or another mechanism (blue) called hydrogen abstraction -- vinylacetylene addition (HAVA) [Credit: Long Zhao, Ralf I. Kaiser, et al./Nature Astronomy]

Ahmed said there is an interplay between astronomers and chemists in this detective work that seeks to retell the story of how life's chemical precursors formed in the universe.

"We talk to astronomers a lot because we want their help in figuring out what's out there," Ahmed said, "and it informs us to think about how it got there."

Kaiser noted that physical chemists, on the other hand, can help shine a light on reaction mechanisms that can lead to the synthesis of specific molecules in space.

Pyrene belongs to a family known as polycyclic aromatic hydrocarbons, or PAHs, that are estimated to account for about 20 percent of all carbon in our galaxy. PAHs are organic molecules that are composed of a sequence of fused molecular rings. To explore how these rings develop in space, scientists work to synthesize these molecules and other surrounding molecules known to exist in space.

Alexander M. Mebel, a chemistry professor at Florida International University who participated in the study, said, "You build them up one ring at a time, and we've been making these rings bigger and bigger. This is a very reductionist way of looking at the origins of life: one building block at a time."

For this study, researchers explored the chemical reactions stemming from a combination of a complex hydrocarbon known as the 4-phenanthrenyl radical, which has a molecular structure that includes a sequence of three rings and contains a total of 14 carbon atoms and nine hydrogen atoms, with acetylene (two carbon atoms and two hydrogen atoms).

Chemical compounds needed for the study were not commercially available, said Felix Fischer, an assistant professor of chemistry at UC Berkeley who also contributed to the study, so his lab prepared the samples. "These chemicals are very tedious to synthesize in the laboratory," he said.

At the ALS, researchers injected the gas mixture into a microreactor that heated the sample to a high temperature to simulate the proximity of a star. The ALS generates beams of light, from infrared to X-ray wavelengths, to support a range of science experiments by visiting and in-house researchers.

The mixture of gases was jetted out of the microreactor through a tiny nozzle at supersonic speeds, arresting the active chemistry within the heated cell. The research team then focused a beam of vacuum ultraviolet light from the synchrotron on the heated gas mixture that knocked away electrons (an effect known as ionization).

They then analyzed the chemistry taking place using a charged-particle detector that measured the varied arrival times of particles that formed after ionization. These arrival times carried the telltale signatures of the parent molecules. These experimental measurements, coupled with Mebel's theoretical calculations, helped researchers to see the intermediate steps of the chemistry at play and to confirm the production of pyrene in the reactions.

Mebel's work showed how pyrene (a four-ringed molecular structure) could develop from a compound known as phenanthrene (a three-ringed structure). These theoretical calculations can be useful for studying a variety of phenomena, "from combustion flames on Earth to outflows of carbon stars and the interstellar medium," Mebel said.

Kaiser added, "Future studies could study how to create even larger chains of ringed molecules using the same technique, and to explore how to form graphene from pyrene chemistry."

Other experiments conducted by team members at the University of Hawaii will explore what happens when researchers mix hydrocarbon gases in icy conditions and simulate cosmic radiation to see whether that may spark the creation of life-bearing molecules.

"Is this enough of a trigger?" Ahmed said. "There has to be some self-organization and self-assembly involved" to create life forms. "The big question is whether this is something that, inherently, the laws of physics do allow."

Source: DOE/Lawrence Berkeley National Laboratory [March 05, 2018]

For the first time, researchers have seen life rebounding in the world's driest desert, demonstrating that it could also be lurking in the soils of Mars.

Hyperarid core of the Atacama Desert [Credit: Dirk Schulze-Makuch]

Led by Washington State University planetary scientist Dirk Schulze-Makuch, an international team studied the driest corner of South America's Atacama Desert, where decades pass without any rain.

Scientists have long wondered whether microbes in the soil of this hyperarid environment, the most similar place on Earth to the Martian surface, are permanent residents or merely dying vestiges of life, blown in by the weather.

In a new study published in the Proceedings of the National Academy of Sciences, Schulze-Makuch and his collaborators reveal that even the hyper-arid Atacama Desert can provide a habitable environment for microorganisms.

The researchers found that specialized bacteria are able to live in the soil, going dormant for decades, without water and then reactivating and reproducing when it rains.

"It has always fascinated me to go to the places where people don't think anything could possibly survive and discover that life has somehow found a way to make it work," Schulze-Makuch said. "Jurassic Park references aside, our research tell us that if life can persist in Earth's driest environment there is a good chance it could be hanging in there on Mars in a similar fashion."

The dry limit of life

When Schulze-Makuch and his collaborators went to the Atacama for the first time in 2015 to study how organisms survive in the soil of Earth's driest environment, the craziest of things happened. It rained.

After the extremely rare shower, the researchers detected an explosion of biological activity in the Atacama soil.

These are the surfaces of Mars and the Atacama Desert [Credit: NASA (left) / Alessandro Airo, TU Berlin (right)]

They used sterilized spoons and other delicate instrumentation to scoop soil samples from various depths and then performed genomic analyses to identify the different microbial communities that were reproducing in the samples. The researchers found several indigenous species of microbial life that had adapted to live in the harsh environment.

The researchers returned to the Atacama in 2016 and 2017 to follow up on their initial sampling and found that the same microbial communities in the soil were gradually reverting to a dormant state as the moisture went away.

"In the past researchers have found dying organisms near the surface and remnants of DNA but this is really the first time that anyone has been able to identify a persistent form of life living in the soil of the Atacama Desert," Schulze-Makuch said. "We believe these microbial communities can lay dormant for hundreds or even thousands of years in conditions very similar to what you would find on a planet like Mars and then come back to life when it rains."

Implications for life on Mars

While life in the driest regions of Earth is tough, the Martian surface is an even harsher environment.

It is akin to a drier and much colder version of the Atacama Desert. However it wasn't always this way.

Billions of years ago, Mars had small oceans and lakes where early lifeforms may have thrived. As the planet dried up and grew colder, these organisms could have evolved many of the adaptations lifeforms in the Atacama soil use to survive on Earth, Schulze-Makuch said.

"We know there is water frozen in the Martian soil and recent research strongly suggests nightly snowfalls and other increased moisture events near the surface," he said. "If life ever evolved on Mars, our research suggests it could have found a subsurface niche beneath today's severely hyper-arid surface."

Next Steps

On March 15, Schulze-Makuch is returning to the Atacama for two weeks to investigate how the Atacama's native inhabitants have adapted to survive. He said his research team also would like to look for lifeforms in the Don Juan Pond in Antarctica, a very shallow lake that is so salty it remains liquid even at temperatures as low as -58 degrees Fahrenheit.

"There are only a few places left on Earth to go looking for new lifeforms that survive in the kind of environments you would find on Mars," Schulze-Makuch said. "Our goal is to understand how they are able to do it so we will know what to look for on the Martian surface."

Author: Will Ferguson | Source: Washington State University [February 26, 2018]

Jupiter's icy moon Europa is a major target of astrobiology research in light of the possibility that it offers a habitable environment in the Solar System. Under its ice crust, estimated to be 10 km thick, is an ocean of liquid water of over 100 km deep. A huge source of energy deriving from gravitational interaction with Jupiter keeps this water warm.

Europa has an enormous ocean of warm liquid water under its frozen crust. The bottom of this ocean could be a similar environment to primitive Earth, potentially hosting microorganisms [Credit: NASA]

Theoretical research to evaluate the microbial habitability of Europa using data collected from analogous environments on Earth has been conducted by a group of Brazilian researchers linked to the University of Sao Paulo (USP) that jointly authored an article published in Scientific Reports.

"We studied the possible effects of a biologically usable energy source on Europa based on information obtained from an analogous environment on Earth," said Douglas Galante, a researcher at Brazil's National Synchrotron Light Laboratory (LNLS) and the Astrobiology Research Center (NAP-Astrobio) of the University of Sao Paulo's Institute of Astronomy, Geophysics & Atmospheric Sciences (IAG-USP).

Galante coordinates the study, supported by the Sao Paulo Research Foundation -- FAPESP through a Master's fellowship from chemist Thiago Pereira, co-author of the article who has in Galante his supervisor, and through a Thematic Project which aims at investigating places in Brazil and Africa with possible vestiges of geochemical and isotopical transformations related to the emergence of multicelular life in Neoproterozoic Age.

Similarities with primitive earth

In the Mponeng gold mine near Johannesburg, South Africa, at a depth of 2.8 km, the research project not only found traces of major changes linked to history of life on Earth, but also a terrestrial context analogous to Europa. It was recently discovered that the bacterium Candidatus Desulforudis audaxviator survives inside the mine without sunlight by means of water radiolysis, the dissociation of water molecules by ionizing radiation.

"This very deep subterranean mine has water leaking through cracks that contain radioactive uranium," Galante said. "The uranium breaks down the water molecules to produce free radicals [H+, OH-, and others]. The free radicals attack the surrounding rocks, especially pyrite [iron disulfide, FeS2], producing sulfate. The bacteria use the sulfate to synthesize ATP [adenosine triphosphate], the nucleotide responsible for energy storage in cells. This is the first time an ecosystem has been found to survive directly on the basis of nuclear energy."

According to Galante and colleagues, the environment colonized by bacteria in the Mponeng mine is an excellent analogue of the environment assumed to exist at the bottom of Europa's ocean.

Although the temperature in Europa's surface is next to absolute zero, there is an enormous amount of thermal energy in its core, as an effect of Europa's interaction with Jupiter's powerful gravitational attraction, which causes the satellite's orbit to be extremely elliptical, meaning Europa finds itself either to close or too far from the Gas Giant. That makes the icy moon to suffer geometrical deformation as it moves at the mercy of Jupiter's immense tidal force. The energy released by the alternating states of elongation and relaxation makes Europa's subsurface capable of hosting an ocean of liquid water.

"However, it's not enough for there to be heated liquid water," said Galante. According to the researcher, the basis for all biological activity known to Earth are the chemical gradients, i.e., differences in concentrations of molecules, ions or electrons in distinct regions which produce a flow in a certain direction, allowing the occurrence of cellular respiration, photosynthesis, ATP production and other processes common to living beings.

"Hydrothermal emanations -- of molecular hydrogen [H2], hydrogen sulfide [H2S], sulfuric acid [H2SO4], methane [CH4] and so on -- are important sources of chemical imbalance and potential factors of 'biological transduction', i.e., transformation of the imbalance into biologically useful energy," Galante said. "These hydrothermal sources are the most plausible scenario for the origin of life on Earth."

Investigating conditions in Europa for ATP production

The group evaluated how chemical imbalance in Europa could be initiated through the emanation of water leading to chain reactions between water and chemical elements found in Europa's crust -- however, a total lack of empirical data prevents scientists from unequivocally presuming any of these events (an "Europa Mission" may take place as late as 2030, stated Nasa, the US space agency). "That's why we looked for a more universal physical effect that was highly likely to occur. That effect was precisely the action of radioactivity," Galante said.

Celestial bodies in the Solar System with rocky cores share the same radioactive materials, ejected in space by the Supernova explosion that originated the Sun and the planets. Uranium, thorium and potassium are the radioactive elements considered by the research, which estimated the concentrations for these materials in Europa, based on the quantities already observed and measured on Earth, in meteorites and in Mars.

"From these amounts, we were able to estimate the energy released, how this energy interacts with the surrounding water, and the efficiency of the water radiolysis resulting from this interaction in generating free radicals," Galante said.

According to the study, along with radionuclides, pyrite is a crucial ingredient whose presence is indispensable for life in Europa. "One of the proposals deriving from our study is that traces of pyrite should be looked for as part of any assessment of the habitability of a celestial body," stated Galante. Chances for finding pyrite in a hypothetical mission to Europa are good, since sulfur (S) and iron (Fe) are elements found in abundance across the Solar System.

"The ocean bed on Europa appears to offer very similar conditions to those that existed on primitive Earth during its first billion years. So studying Europa today is to some extent like looking back at our own planet in the past. In addition to the intrinsic interest of Europa's habitability and the existence of biological activity there, the study is also a gateway to understanding the origin and evolution of life in the Universe."

Author: Jose Tadeu Arantes | Source: Fundacao de Amparo a Pesquisa do Estado de Sao Paulo [February 23, 2018]

New research in to how Earth's atmosphere evolved over time could hold the key to detecting life on exoplanets, according to scientists from the University of St Andrews and Cornell University.

Credit: NASA

The new study, published in The Astrophysical Journal, details how Earth's atmosphere evolved over time and how this corresponds to the appearance of different forms of life.

The team, led by Dr Sarah Rugheimer, astronomer and astrobiologist from the School of Earth and Environmental Sciences at the University, studied different geological epochs from Earth's history, modelling the atmospheres around different stars, bigger and smaller than our Sun. The researchers found that a planet's star type is an important factor in how an exoplanet's atmosphere develops and in how detectable signs of life, aka biosignatures, will be.

The study focussed on Earth’s atmosphere at four distinct points in history: before microbes (3.9 billion years ago), after microbes and the first rise of oxygen (2 billion years ago), during the second rise of oxygen (800 million years ago), and Earth as it is today. At each of these points, oxygen, methane and carbon dioxide were in drastically different abundances.

The new findings in to how life evolves in different atmospheres could lay the foundation for scientists to interpret early biosignatures and signs of life on Earth-size exoplanets.

Lead researcher Dr Rugheimer said: “We expect to find a myriad of exoplanets beyond even our wildest imagination. Even looking back at our own planet, the atmosphere has changed dramatically many times. By looking at the history of Earth and how different host star light would interact with a planet’s atmosphere, we can start to create a grid of models to help us understand future observations. In particular, in this paper we wanted to find out how detectable biosignature gases have been both in Earth's history and if these planets were orbiting a different star.”

Varied cloud cover and surface features such as oceans and continents were also factored in during the study to see how these affected the models, however in order to accurately reflect the findings on distant exoplanets larger telescopes are required.

Dr Rugheimer notes: “The 2019 launch of the James Webb Space Telescope should allow us to study a handful of habitable, Earth-size exoplanets transiting red dwarf stars. The European Extremely Large Telescope, which should be online in the mid-2020s, may also be able to directly image a handful of exoplanets.”

Source: University of St Andrews [February 19, 2018]

In popular culture, asteroids play the role of apocalyptic threat, get blamed for wiping out the dinosaurs -- and offer an extraterrestrial source for mineral mining.

Credit: Pixabay

But for researcher Nicholas Hud, asteroids play an entirely different role: that of time capsules showing what molecules originally existed in our solar system. Having that information gives scientists the starting point they need to reconstruct the complex pathway that got life started on Earth.

Director of the NSF-NASA Center for Chemical Evolution at the Georgia Institute of Technology, Hud says finding molecules in asteroids provides the strongest evidence that such compounds were present on the Earth before life formed. Knowing what molecules were present helps establish the initial conditions that led to the formation of amino acids and related compounds that, in turn, came together to form peptides, small protein-like molecules that may have kicked off life on this planet.

"We can look to the asteroids to help us understand what chemistry is possible in the universe," said Hud. "It's important for us to study materials from asteroids and meteorites, the smaller versions of asteroids that fall to Earth, to test the validity of our models for how molecules in them could have helped give rise to life. We also need to catalog the molecules from asteroids and meteorites because there might be compounds there that we had not even considered important for starting life."

Hud will be a panelist at a press briefing "Asteroids for Research, Discovery, and Commerce" on February 17 at the 2018 annual meeting of the American Association for the Advancement of Science (AAAS) in Austin, Texas.

NASA scientists have been analyzing compounds found in asteroids and meteorites for decades, and their work provides a solid understanding for what might have been present when the Earth itself was formed, Hud says.

"If you model a prebiotic chemical reaction in the laboratory, scientists can argue about whether or not you had the right starting materials," said Hud. "Detection of a molecule in an asteroid or meteorite is about the only evidence everyone will accept for that molecule being prebiotic. It's something we can really lean on."

The Miller-Urey experiment, conducted in 1952 to simulate conditions believed to have existed on the early Earth, produced more than 20 different amino acids, organic compounds that are the building blocks for peptides. The experiment was kicked off by sparks inside a flask containing water, methane, ammonia and hydrogen, all materials believed to have existed in the atmosphere when the Earth was very young.

Nicolas Hud, director of the NSF-NASA Center for Chemical Evolution at the Georgia Institute of Technology [Credit: Fitrah Hamid, Georgia Tech]

Since the Miller-Urey experiment, scientists have demonstrated the feasibility of other chemical pathways to amino acids and compounds necessary for life. In Hud's laboratory, for instance, researchers used cycles of alternating wet and dry conditions to create complex organic molecules over time. Under such conditions, amino acids and hydroxy acids, compounds that differ chemically by just a single atom, could have formed short peptides that led to the formation of larger and more complex molecules -- ultimately exhibiting properties that we now associate with biological molecules.

"We now have a really good way to synthesize peptides with amino acids and hydroxy acids working together that could have been common on the early Earth," he said. "Even today, hydroxy acids are found with amino acids in living organisms -- and in some meteorite samples that have been examined."

Hud believes there are many possible ways that the molecules of life could have formed. Life could have gotten started with molecules that are less sophisticated and less efficient than what we see today. Like life itself, these molecules could have evolved over time.

"What we find is that these compounds can form molecules that look a lot like modern peptides, except in the backbone that is holding the units together," said Hud. "The overall structure can be very similar and would be easier to make, though it doesn't have the ability to fold into as complex structures as modern proteins. There is a tradeoff between the simplicity of forming these molecules and how close these molecules are to those found in contemporary life."

Geologists believe the Earth was very different billions of years ago. Instead of continents, there were islands protruding from the oceans. Even the sun was different, producing less light but more cosmic rays -- which could have helped power the protein-forming chemical reactions.

"The islands could have been potential incubators for life, with molecules raining down from the atmosphere," Hud said. "We think the key process that would have allowed these molecules to go to the next stage is a wet-dry cycling like what we are doing in the lab. That would have been perfect for an island out in the ocean."

Rather than a single spark of life, the molecules could have evolved slowly over time in gradual progression that may have taken place at different rates in different locations, perhaps simultaneously. Different components of cells, for example, may have developed separately where conditions favored them before they ultimately came together.

"There is something very special about peptides, nucleic acids, polysaccharides and lipids and their ability to work together to do something they couldn't have done separately," he said. "And there could have been any number of chemical processes on the early Earth that never led to life."

Knowing what conditions were like on the early Earth therefore gives scientists a stronger foundation for hypothesizing what could have taken place, and could offer hints to other pathways that may not have been considered yet.

"There are probably a lot more clues in the asteroids about what molecules were really there," said Hud. "We may not even know what we should be looking for in these asteroids, but by looking at what molecules we find, we can ask different and more questions about how they could have helped get life started."

Source: Georgia Institute of Technology [February 17, 2018]

On January 9, 1992, astronomers announced a momentous discovery: two planets orbiting a pulsar 2,300 light years from our sun. The two planets, later named Poltergeist and Draugr, were the first confirmed “exoplanets”—worlds outside our solar system, circling a distant star. Scientists now know of 3,728 (confirmed) exoplanets in 2,794 systems, each one begging the question: “Is anyone else out there?”

The search for extraterrestrial life has focused mostly on exoplanets like Kepler-186f, shown here, which circle M-class stars in a “habitable zone” where water may exist. But “not all habitable zones are created equal,” says Mendillo, who notes that  some exoplanets are dangerously close to their stars, exposing them to hazardous radiation that might prevent life as we know it. “Earth’s habitable zone has a little more hospitality” [Credit: NASA Ames/SETI Institute/JPL-Caltech]

“What more important question could we ask? Are we alone?” asks Boston University professor of astronomy Michael Mendillo. “I don’t know of any more fascinating question in science.”

For decades, astronomers have been searching these distant exoplanets for signs of life, mostly looking for that most essential molecule, water. But Mendillo and his colleagues have a different idea. In a paper published in Nature Astronomy, Mendillo, BU associate professor of astronomy Paul Withers, and PhD candidate Paul Dalba (GRS’18) suggest looking instead at an exoplanet’s ionosphere, the thin uppermost layer of atmosphere, which is whizzing with charged particles. Find one like Earth’s, they say, packed with single oxygen ions, and you have found life. Or, at least, life as we know it.

“Throughout the history of human civilization, we have never gotten to the point—until basically the last 15 years—where we could see planets around other stars. And now we’re at the point where we’re coming up with ideas to discover life outside Earth,” says John Clarke, professor of astronomy at Boston University, and director of the Center for Space Physics. “This is a great intellectual adventure that we’re on.”

Their work began when Mendillo and Withers received a grant from the National Science Foundation (NSF) to compare all planetary ionospheres in the solar system. (All the planets have them except Mercury, which is so close to the sun that its atmosphere is stripped off entirely.) Simultaneously, the team was also working with NASA’s MAVEN mission, trying to understand how the molecules that made up Mars’ ionosphere had escaped that planet. Since the early years of the Space Age, scientists have known that planetary ionospheres differ greatly, and the BU team started to focus on why that was the case, and why Earth’s was so different. While other planets stuff their ionospheres full of complicated charged molecules arising from carbon dioxide or hydrogen, Earth keeps it simple, with mostly oxygen filling the space. And it’s a specific type of oxygen—single atoms with a positive charge.

“I started thinking, how come our ionosphere is different than the other six?” recalls Mendillo.

The team ticked off numerous possibilities for Earth’s high concentration of O+ before settling on a culprit: green plants and algae.

“It’s because we have this atomic oxygen that traces its origin back to photosynthesis,” says Mendillo. “We have atomic oxygen ions, O+, in the ionosphere as a direct consequence of having life on the planet. So why don’t we see if we can come up with a criterion where the ionosphere could be a biomarker, not just of possible life but of actual life.”

A 10-minute, infrared exposure of Earth taken from the moon during the Apollo 16 mission. The bright yellow is “dayglow” from atomic oxygen (O). On the dark side, “nightglow” bands, arising from atomic oxygen ions (O+) in the ionosphere, can be seen near the equator [Credit: NASA]

Most planets in our solar system have some oxygen in their lower atmospheres, but Earth has much more, about 21 percent. This is because so many organisms have been busy turning light, water, and carbon dioxide into sugar and oxygen—the process called photosynthesis—for the past 3.8 billion years.

“Destroy all the plants on Earth and our atmosphere’s oxygen will vanish away in mere thousands of years,” says Withers, who notes that all this oxygen exhaled by plants doesn’t just stick around the Earth’s surface. “To most people, O2, the oxygen we breathe, is not a very exciting molecule. To chemists, however, O2 is a wild, exhilarating, and perilous beast. It just will not sit still; it chemically reacts with almost any other molecule it can find and it does so very quickly.”

On Earth today, excess oxygen molecules, in the form of O2, float upward. When the O2 gets about 150 kilometers above the Earth’s surface, ultraviolet light splits it in two. The single oxygen atoms float higher, into the ionosphere, where more ultraviolet light and x-rays from the sun rip electrons from their outer shells, leaving charged oxygen zipping through the air. The abundance of O2 near the Earth’s surface—so different than the other planets—leads to an abundance of O+ high in the sky.

This finding, says Mendillo, suggests that scientists seeking extraterrestrial life could perhaps narrow their search area. Paul Dalba, who was working on exoplanet atmospheres with BU assistant professor of astronomy Philip Muirhead, joined the team to weigh in. “Dalba’s knowledge of star-exoplanet systems really helped,” Mendillo says. Currently, most scientists on this quest focus on M-class stars—the most abundant in the galaxy—and the planets circling them in the “habitable zone,” where water might exist.

This makes sense, because life as we know it needs water. But scientists don’t know exactly how much water a planet needs to support life. “If we only had the Mediterranean, would that have been enough? Do we need the Pacific, but not the Atlantic?” asks Mendillo. “If you look at the ionosphere, you don’t need to know the number. You just need to know that if the maximum electron density is associated with oxygen ions, then you’ve nailed it—you’ve got a planet where there’s photosynthesis and life.”

Of course, this assumes that “life” is at least somewhat analogous to life on Earth, which requires not only water and oxygen, but also a certain temperature range, probably a magnetic field, and other factors. “That’s a good starting point,” says Clarke. “But in the back of our mind, we are all aware that there may be kinds of life we’re not thinking about that may surprise us.”

There’s one other catch, at least for now: scientists don’t have the tools to detect an ionosphere on any exoplanet—yet. “If you look at the space telescopes that might come next, a lot is going to be possible,” says Clarke. “I think in ten years we will have the technology to do this experiment.”

Mendillo hopes his team’s work makes a case for further research, development, and exploration in this area. “Just the idea of using the ionosphere as a signature is a captivating idea,” he says. “We don’t have the observational capability yet, but I’m optimistic. We offer this up as a challenge.”

Author: Barbara Moran | Source: Boston University [February 16, 2018]

Fossils that preserve entire organisms (including both hard and soft body parts) are critical to our understanding of evolution and ancient life on Earth. However, these exceptional deposits are extremely rare. The fossil record is heavily biased towards the preservation of harder parts of organisms, such as shells, teeth and bones, as soft parts such as internal organs, eyes, or even completely soft organisms, like worms, tend to decay before they can be fossilised. Little is known about the environmental conditions which stop this process soon enough for the organism to be fossilised.

The fossil Waptia from the Burgess Shale, Canada. New Oxford University research suggests that the mineralogy of the surrounding earth is key to conserving soft parts of organisms, and finding more exceptional fossils like the Waptia [Credit: Yale University]

New Oxford University research suggests that the mineralogy of the surrounding earth is key to conserving soft parts of organisms, and finding more exceptional fossils. Part-funded by NASA, the work could potentially support the Mars Rover Curiosity in its sample analysis, and speed up the search for traces of life on other planets.

Perhaps the most iconic of all exceptional fossil deposits is the Burgess Shale of Canada, popularised by Stephen J. Gould's Wonderful Life. Dating to around 500 million years ago, the deposit preserves exceptional fossils from the Cambrian Explosion, an event which saw the rapid diversification of early animal life from simpler single-celled ancestors. Burgess Shale-type fossil localities are now known across the globe and without them roughly 80% of Cambrian organisms (those that have no hard skeleton or shell) would be unknown, distorting our picture of early animal evolution.

Published in Geology, the study, conducted by researchers from Oxford's Department of Earth Sciences, Yale University, and Pomona College, builds on their previous research which revealed that certain clay minerals are toxic to bacteria that decay marine animals. This time around, the team set out to find geological evidence that rocks composed of the same clay minerals are the hosts of Burgess Shale-type fossils.

The team examined more than 200 Cambrian rock samples using powder X-ray diffraction analysis to determine their mineralogical composition, comparing rocks with Burgess Shale-type fossils with those with only fossilised shells and bones. Nicholas Tosca, Associate Professor of Sedimentary Geology at Oxford, said: 'The number of samples required for this study was made possible because the diffractometer at Oxford collects mineralogical data 250 times faster than a conventional instrument.'

The findings reveals that soft tissue fossils are generally found in rocks rich in the mineral berthierine, one of the main clay minerals identified by the previous study as being toxic to decay bacteria. Ross Anderson, lead author and fellow at All Souls College, Oxford, explains: 'Berthierine is an interesting mineral because it forms in tropical settings when the sediments contain elevated concentrations of iron. This means that Burgess Shale-type fossils are likely confined to rocks which were formed at tropical latitudes and which come from locations or time periods that have enhanced iron. This observation is exciting because it means for the first time we can more accurately interpret the geographic and temporal distribution of these iconic fossils, crucial if we want to understand their biology and ecology.'

The study provides a mineralogical signature which can be used to find the more elusive sites that are home to these extraordinary fossils. 'The mineralogical associations we identified mean that for a given Cambrian sedimentary mudrock we can predict with around 80% accuracy whether it is likely to contain Burgess Shale-type fossils,' explains Anderson.

Of the project's wider applications, potentially supporting the search for life beyond our own planet, Anderson adds: 'For the vast majority of Earth's history, life has not possessed hard shells or skeletons. This means that if we want to look for fossil evidence of life on other planets like Mars, the chances are we probably need to find fossils of entirely soft organisms, and Burgess Shale-type fossilisation provides a way. NASA's Curiosity rover has the ability to record mineralogy on the Martian surface, so it could potentially look for the types of rocks which might be most conducive to preserving these fossils.'

To expand their understanding of the exceptional preservation of soft organisms, the team are currently delving further back into Earth history, to investigate the preservation of microbes before macroscopic organisms with skeletons or shells evolved.

Source: University of Oxford [February 15, 2018]

The planet Mars has long drawn interest from scientists and non-scientists as a possible place to search for evidence of life beyond Earth because the surface contains numerous familiar features such as dried river channels and dried lake beds that hint at a warmer, wetter, more earthlike climate in the past. However, Dr Joseph Michalski of the Department of Earth Sciences & Laboratory for Space Research at The University of Hong Kong (HKU) and his colleagues have published papers recently that cast increased doubt on the idea of surface life evolving on Mars. These paradigm changing publications have recently been published in Nature Geoscience and Nature Astronomy.

Diverse mineralogy exhumed from the Martian subsurface: A false color image from the HiRISE instrument aboard NASA's Mars Reconnaissance Orbiter shows amazing diversity of rocks exhumed from the Martian subsurface  a meteor impact in the Nili Fossae area. The image is 1 km across. This site and others like it contain rocks that were altered by fluids in the Martian crust billions of years ago, at the time when life first emerged on Earth. These rocks represent exploration targets that could teach us about the origin of life [Credit: NASA/JPL/University of Arizona]

For the last 2.5 billion years, surface life on Earth has thrived largely due to the evolution of photosynthesis. Surface life is abundant and very successful because of the availability of sunlight, surface water, generally moderate climate conditions, and the protection of our magnetic field. But the planet Mars would have never experienced such habitable conditions at the surface. Michalski and colleagues published results in Nature Astronomy showing that the climate of Mars has probably been extremely cold and dry most of the time. They argue that the familiar aqueous features on Mars included widespread, weathered soil horizons, could have formed in geologically short climate "excursions." In other words, Mars was cold and dry throughout its history and only had abundant liquid water at its surface during short episodes of climate change.

However, all hope for life on Mars is not lost. In another paper led by Michalski and published recently, the scientists point out that the prospects for surface life on Mars might be dim, but the possibilities for subsurface life are promising. Life on Earth likely began in hydrothermal systems (environments where hot water reacts with rocks), and there is abundant evidence for many locations where hydrothermal environments exists on Mars at the time when life might have originated in similar environments on Earth. They argue that, in order to understand how life formed on Earth, we should ignore the surface environments on Mars and focus exploration on hydrothermal deposits.

Dr. Michalski and his team in the Department of Earth Sciences and Laboratory for Space Research at HKU explore Mars using remote sensing and infrared spectroscopy. Using infrared data collected at Mars by spacecraft, they can interpret which minerals are there and describe the geology of ancient hydrothermal systems. This type of work is based on laboratory measurements, which provide the required mineralogical background in which to interpret spectroscopic data from Mars. The HKU' Faculty of Sciences new Infrared Spectroscopy Laboratory is a facility where scientists from around the world can come to measure geological samples in order to compare the measured spectra to data from returned from spacecraft. Michalski and his team use infrared measurements of hydrothermal minerals as a basis to interpret the detection of important minerals on Mars.

"This is an extraordinarily exciting time in Mars exploration" said Michalski. "We are getting very close to being able to detect evidence of ancient life on Mars or, perhaps more importantly, the chemical building blocks on which life forms."

"This cutting edge and ground-breaking HKU based research is both exciting and thought provoking. It speaks to the very heart of trying to understand how life may have evolved not just on Earth but on other terrestrial bodies both in our own solar system and indeed around other stars that have planets that lie in the so-called "habitable zone" (where liquid water can exist on the surface). The discovery of bacteria two miles down in a Goldmine in South Africa a decade ago chimes perfectly with the thesis Dr. Michalski is proposing here," said Professor Quentin Parker, Director of Laboratory for Space Research and Associate Dean (Global) of Faculty of Science, The University of Hong Kong.

Source: The University of Hong Kong [February 06, 2018]

Planets around the faint red star TRAPPIST-1, just 40 light-years from Earth, were first detected by the TRAPPIST-South telescope at ESO's La Silla Observatory in 2016. In the following year further observations from ground-based telescopes, including ESO's Very Large Telescope and NASA's Spitzer Space Telescope, revealed that there were no fewer than seven planets in the system, each roughly the same size as the Earth. They are named TRAPPIST-1b,c,d,e,f,g and h, with increasing distance from the central star [1].

This artist's impression shows several of the planets orbiting the ultra-cool red dwarf star TRAPPIST-1. New observations, when combined with very sophisticated analysis, have now yielded good estimates of the densities of all seven of the Earth-sized planets and suggest  that they are rich in volatile materials, probably water [Credit: ESO/M. Kornmesser]

Further observations have now been made, both from telescopes on the ground, including the nearly-complete SPECULOOS facility at ESO's Paranal Observatory, and from NASA's Spitzer Space Telescope and the Kepler Space Telescope. A team of scientists led by Simon Grimm at the University of Bern in Switzerland have now applied very complex computer modelling methods to all the available data and have determined the planets' densities with much better precision than was possible before [2].

Simon Grimm explains how the masses are found: "The TRAPPIST-1 planets are so close together that they interfere with each other gravitationally, so the times when they pass in front of the star shift slightly. These shifts depend on the planets' masses, their distances and other orbital parameters. With a computer model, we simulate the planets' orbits until the calculated transits agree with the observed values, and hence derive the planetary masses."

Team member Eric Agol comments on the significance: "A goal of exoplanet studies for some time has been to probe the composition of planets that are Earth-like in size and temperature. The discovery of TRAPPIST-1 and the capabilities of ESO's facilities in Chile and the NASA Spitzer Space Telescope in orbit have made this possible -- giving us our first glimpse of what Earth-sized exoplanets are made of!"

This diagram compares the sizes, masses and estimated temperatures of the TRAPPIST-1 planets with Solar System planets. The colours indicate temperatures and the black line matches the densities  and composition of the terrestrial planets in the Solar System. Planets above the line are less dense and planets below are more dense [Credit: ESO/S. Grimm et al.]

The measurements of the densities, when combined with models of the planets' compositions, strongly suggest that the seven TRAPPIST-1 planets are not barren rocky worlds. They seem to contain significant amounts of volatile material, probably water [3], amounting to up to 5% the planet's mass in some cases -- a huge amount; by comparison the Earth has only about 0.02% water by mass!

"Densities, while important clues to the planets' compositions, do not say anything about habitability. However, our study is an important step forward as we continue to explore whether these planets could support life," said Brice-Olivier Demory, co-author at the University of Bern.

TRAPPIST-1b and c, the innermost planets, are likely to have rocky cores and be surrounded by atmospheres much thicker than Earth's. TRAPPIST-1d, meanwhile, is the lightest of the planets at about 30 percent the mass of Earth. Scientists are uncertain whether it has a large atmosphere, an ocean or an ice layer.

This diagram compares the masses and incident flux from the star for the TRAPPIST-1 and many other exoplanets as well as several planets in the Solar System [Credit: ESO/S. Grimm et al.]

Scientists were surprised that TRAPPIST-1e is the only planet in the system slightly denser than Earth, suggesting that it may have a denser iron core and that it does not necessarily have a thick atmosphere, ocean or ice layer. It is mysterious that TRAPPIST-1e appears to be so much rockier in its composition than the rest of the planets. In terms of size, density and the amount of radiation it receives from its star, this is the planet that is most similar to Earth.

TRAPPIST-1f, g and h are far enough from the host star that water could be frozen into ice across their surfaces. If they have thin atmospheres, they would be unlikely to contain the heavy molecules that we find on Earth, such as carbon dioxide.

"It is interesting that the densest planets are not the ones that are the closest to the star, and that the colder planets cannot harbour thick atmospheres," notes Caroline Dorn, study co-author based at the University of Zurich, Switzerland.


The TRAPPIST-1 system will continue to be a focus for intense scrutiny in the future with many facilities on the ground and in space, including ESO's Extremely Large Telescope and the NASA/ESA/CSA James Webb Space Telescope.

Astronomers are also working hard to search for further planets around faint red stars like TRAPPIST-1. As team member Michaël Gillon explains [4]: "This result highlights the huge interest of exploring nearby ultracool dwarf stars -- like TRAPPIST-1 -- for transiting terrestrial planets. This is exactly the goal of SPECULOOS, our new exoplanet search that is about to start operations at ESO's Paranal Observatory in Chile."

The study is published in Astronomy & Astrophysics.

Notes

[1] The planets were discovered using the ground-based TRAPPIST-South at ESO's La Silla Observatory in Chile; TRAPPIST-North in Morocco; the orbiting NASA Spitzer Space Telescope; ESO's HAWK-I instrument on the Very Large Telescope at the Paranal Observatory in Chile; the 3.8-metre UKIRT in Hawaii; the 2-metre Liverpool and 4-metre William Herschel telescopes on La Palma in the Canary Islands; and the 1-metre SAAOtelescope in South Africa.

[2] Measuring the densities of exoplanets is not easy. You need to find out both the size of the planet and its mass. The TRAPPIST-1 planets were found using the transit method -- by searching for small dips in the brightness of the star as a planet passes across its disc and blocks some light. This gives a good estimate of the planet's size. However, measuring a planet's mass is harder -- if no other effects are present planets with different masses have the same orbits and there is no direct way to tell them apart. But there is a way in a multi-planet system -- more massive planets disturb the orbits of the other planets more than lighter ones. This in turn affects the timing of transits. The team led by Simon Grimm have used these complicated and very subtle effects to estimate the most likely masses for all seven planets, based on a large body of timing data and very sophisticated data analysis and modelling.

[3] The models used also consider alternative volatiles, such as carbon dioxide. However, they favour water, as vapour, liquid or ice, as the most likely largest component of the planets' surface material as water is the most abundant source of volatiles for solar abundance protoplanetary discs.

[4] The SPECULOOS survey telescopes facility is nearly complete at ESO's Paranal Observatory.

Source: ESO [February 05, 2018]

An international team of astronomers has used the NASA/ESA Hubble Space Telescope to look for atmospheres around four Earth-sized planets orbiting within or near TRAPPIST-1's habitable zone. The new results further support the terrestrial and potentially habitable nature of three of the studied planets. The results are published in Nature Astronomy.

This is an artist’s impression of the TRAPPIST-1 system, showcasing all seven planets  in various phases [Credit: NASA]

Seven Earth-sized planets orbit the ultracool dwarf star TRAPPIST-1, 40 light-years away from the Earth [1]. This makes TRAPPIST-1 the planetary system with the largest number of Earth-sized planets discovered so far. These planets are also relatively temperate, making them a tantalizing place to search for signs of life beyond our Solar System. Now, an international team of astronomers has presented a study in which they used the NASA/ESA Hubble Space Telescope to screen four planets in the system -- TRAPPIST-1d, e, f and g -- for traces of atmospheres [2].

Three of the planets are within the system's habitable zone, the region at a distance from the star where liquid water -- the key to life as we know it -- could exist on the surface. The fourth planet orbits in a borderline region at the inner edge of the habitable zone. The data obtained rule out a cloud-free hydrogen-rich atmosphere for three of the planets -- but for the fourth planet, TRAPPIST-1g, such an atmosphere could not be excluded [3].

Artist's illustrations of planets in TRAPPIST-1 system and Solar System rocky planets [Credit: NASA]

Lead author Julien de Wit, from the Massachusetts Institute of Technology, USA, describes the positive implications of these measurements: "The presence of puffy, hydrogen-dominated atmospheres would have indicated that these planets are more likely gaseous worlds like Neptune. The lack of hydrogen in their atmospheres further supports theories about the planets being terrestrial in nature. This discovery is an important step towards determining if the planets might harbour liquid water on their surfaces, which could enable them to support living organisms."

The habitable zone in the TRAPPIST-1 system [Credit: NASA/JPL-Caltech]

The observations were made while the planets were in transit in front of TRAPPIST-1. In this configuration a small section of the star's light passes through the atmosphere of the exoplanet and interacts with the atoms and molecules in it. This leaves a weak fingerprint of the atmosphere in the spectrum of the star.

Spectra of planets in TRAPPIST-1 system: The purple curves show the predicted signatures of gases such as water and methane that absorb certain wavelengths of light. These gases would be found in a puffy hydrogen-dominated atmosphere similar to those of gaseous planets such as Neptune. The Hubble results, indicated by the green crosses, reveal no evidence of an extended atmosphere in three of the exoplanets (TRAPPIST-1d, f, and e). Additional observations are needed to rule  out a hydrogen-dominated atmosphere for the fourth planet (TRAPPIST-1g) [Credit: NASA, ESA and Z. Levy (STScI)]

While the results rule out one type of atmosphere, many alternative atmospheric scenarios are still consistent with the data gathered by de Wit and his team. The exoplanets may possess a range of atmospheres, just like the terrestrial planets in our Solar System [4].

Starlight yields clues to exoplanets’ atmospheres: The graphic at the top shows a model spectrum containing the signatures of gases that the astronomers would expect to see if the exoplanets’ atmospheres were puffy and dominated by primordial hydrogen from the distant worlds’ formation. The Hubble observations, however, revealed that the planets do not have hydrogen-dominated atmospheres. The flatter spectrum shown in the lower illustration indicates that Hubble did not spot  any traces of water or methane, which are abundant in hydrogen-rich atmospheres. The researchers concluded that  the atmospheres are composed of heavier elements residing at much lower altitudes than could be measured by the Hubble observations [Credit: NASA, ESA and Z. Levy (STScI)]

"Our results demonstrate Hubble's ability to study the atmospheres of Earth-sized planets. But the telescope is really working at the limit of what it can do," adds co-author Hannah Wakeford from the Space Telescope Science Institute, illustrating both the power and limitation of Hubble.

These latest findings complement the analysis of ultraviolet observations made with Hubble in 2017 (heic1713 ) and help us understand more about whether life might be possible in the TRAPPIST-1 system.


By ruling out the presence of a large abundance of hydrogen in the planets' atmospheres, Hubble is helping to pave the way for the NASA/ESA/CSA James Webb Space Telescope .

"Spectroscopic observations of the TRAPPIST-1 planets with the next generation of telescopes -- including the James Webb Space Telescope -- will allow us to probe deeper into their atmospheres," concludes Michael Gillon, from the University of Líege, Belgium. "This will allow us to search for heavier gases such as carbon, methane, water, and oxygen, which could offer biosignatures for life."

Notes

[1] The planets were discovered using the ground-based TRAPPIST-South at ESO's La Silla Observatory in Chile; TRAPPIST-North in Morocco; the orbiting NASA Spitzer Space Telescope; ESO's HAWK-I instrument on the Very Large Telescope at the Paranal Observatory in Chile; the 3.8-metre UKIRT (http://www.ukirt.hawaii.edu/) in Hawaii; the 2-metre Liverpool and 4-metre William Herschel telescopes on La Palma in the Canary Islands; and the 1-metre SAAO telescope in South Africa.

[2] The observations were performed in the infrared with the Wide Field Camera 3 (WFC3) between December 2016 and January 2017.

[3] An atmosphere largely dominated by hydrogen, if cloud-free, should yield prominent spectroscopic signatures in the near infrared. However, the spectra for TRAPPIST-1d, -e, and -f do not show significant features.

[4] This includes atmospheres dominated by water vapor, nitrogen, carbon dioxide or tenuous atmospheres composed of a variety of chemical species.

Source: ESA/Hubble Information Centre [February 05, 2018]

NASA researchers have confirmed the existence in Titan's atmosphere of vinyl cyanide, which is an organic compound that could potentially provide the cellular membranes for microbial life to form in Titan's vast methane oceans. If true, it could prove to us that life can flourish without the ubiquitous H2O.

This image shows Titan in ultraviolet and infrared wavelengths. Red and green colors indicate where atmospheric methane is absorbing light, while the blue color shows the upper atmospheric haze [Credit: NASA/JPL/Space Science Institute]

Earth-based cell membranes are made of phospholipids: molecular chains with phosphorus-oxygen heads and carbon-chain tails that bind to each other to form a flexible membrane in water. Methane-based life, should it exist, would need an alternative to Earth's phospholipid-based existence and would open up a much wider range of planets and moons to the possibility of extraterrestrial life. one possible alternative is vinyl cyanide.

The Cassini spacecraft first inferred the presence of vinyl cyanide on the Saturnian moon through the use of its mass spectrometer, but it took the highly sensitive gaze of the Atacama Large Millimeter/submillimeter Array (ALMA), in the desert of Chile, to confirm vinyl cyanide is, indeed, there.

Maureen Palmer, a researcher at NASA's Goddard Space Flight Center in Greenbelt, Maryland, and lead author of a paper describing the research in Science Advances, collected archival data from ALMA and saw vinyl cyanide high in Titan's atmosphere, at altitudes greater than 200 kilometers, with its highest concentrations in areas above Titan's southern pole.

In the low temperatures on Titan, which reach –179 degrees Celsius (-290 degrees Fahrenheit), organic molecules in the atmosphere form droplets that rain down to fill methane lakes in a weather cycle similar to that of Earth's water cycle. There, they could potentially create simple, microscopic life forms. Palmer's group performed modeling studies that showed there is enough vinyl cyanide in Ligeia Mare, Titan's northern lake, to form about 10 million cells per cubic centimeter, roughly 10 times more than the bacteria in Earth's coastal oceans.

Titan’s northernmost giant lake, Ligeia Mare, contains enough vinyl cyanide to form the cell membranes of ten million cells per cubic centimeter [Credit: NASA/JPL–Caltech/ASI/Cornell]

Vinyl cyanide has yet to be proven to produce life, but an earlier study by Cornell University researchers that was also published in Science Advances made it an intriguing prospect. The Cornell researchers, led by Professor of Chemical and Biological Engineering Paulette Clancy, set out to discover whether molecules that exist on Titan could form cell membranes called azotosomes, which is the name given to cell membranes that might form in Titan's liquid methane conditions.

Phosphorus and oxygen, found in Earth cell membranes, don't exist in Titan's frigid methane oceans, so any cell-like membranes would have to be based on nitrogen, hydrogen and carbon, all of which are abundant on Titan. Molecular modeling studies of a variety of molecules containing these elements showed that vinyl cyanide was the molecule most likely to form a stable and flexible membrane that acts like Earth-based membranes under Titan's conditions.

Still, vinyl cyanide-based life, like any other, would face challenging circumstances on Titan. However, Palmer says that "if membranes can be made in a lab with a simulation of Titan's ocean conditions, it would make us more optimistic about them really forming on Titan."

She notes further that because of its extensive atmospheric chemistry, and its bodies of surface liquid, Titan is "an interesting chemical laboratory to study the boundaries of possible biochemistry for creating life."

Clancy says that Palmer's lab findings were "an exciting validation of our prediction, since they also find that the concentration of vinyl cyanide is considerable enough to make self-assembly into azotosome-like vesicles a viable process."

She adds, "It also shows the power of molecular simulation to shine a flashlight onto the most promising candidates for prebiotic life in conditions that are difficult to emulate in the lab."

Author: Lisa Kaspin-Powell | Source: Astrobiology Magazine [February 01, 2018]

As NASA's James Webb Space Telescope and other new giant telescopes come online they will need novel strategies to look for evidence of life on other planets. A University of Washington study has found a simple approach to look for life that might be more promising than just looking for oxygen.

Future telescopes like the James Webb Space Telescope (right) will observe the atmospheres of distant planets to seek evidence of life. Earth (top left) has several gases in its atmosphere that reveal the presence of life, primarily oxygen and ozone. The new study finds that for the early Earth (bottom left), the combination of abundant methane and carbon dioxide would provide an alternative sign of life [Credit: NASA/WikiCommons/Joshua Krissansen-Totton]

The paper, published in Science Advances, offers a new recipe for providing evidence that a distant planet harbors life.

"This idea of looking for atmospheric oxygen as a biosignature has been around for a long time. And it's a good strategy -- it's very hard to make much oxygen without life," said corresponding author Joshua Krissansen-Totton, a UW doctoral student in Earth and space sciences. "But we don't want to put all our eggs in one basket. Even if life is common in the cosmos, we have no idea if it will be life that makes oxygen. The biochemistry of oxygen production is very complex and could be quite rare."

The new study looks at the history of life on Earth, the one inhabited planet we know of, to find times where the planet's atmosphere contained a mixture of gases that are out of equilibrium and could exist only in the presence of living organisms -- anything from pond scum to giant redwoods. In fact, life's ability to make large amounts of oxygen has only occurred in the past one-eighth of Earth's history.

By taking a longer view, the researchers identified a new combination of gases that would provide evidence of life: methane plus carbon dioxide, minus carbon monoxide.

"We need to look for fairly abundant methane and carbon dioxide on a world that has liquid water at its surface, and find an absence of carbon monoxide," said co-author David Catling, a UW professor of Earth and space sciences. "Our study shows that this combination would be a compelling sign of life. What's exciting is that our suggestion is doable, and may lead to the historic discovery of an extraterrestrial biosphere in the not-too-distant future."

The paper looks at all the ways that a planet could produce methane -- from asteroid impacts, outgassing from the planet's interior, reactions of rocks and water -- and finds that it would be hard to produce a lot of methane on a rocky, Earth-like planet without any living organisms.

If methane and carbon dioxide are detected together, especially without carbon monoxide, that's a chemical imbalance that signals life. The carbon atoms in the two molecules represent opposite levels of oxidation. Carbon dioxide holds as many oxygen molecules as it can, while the carbon in methane lacks oxygen and instead has oxygen's chemical adversary, hydrogen.

"So you've got these extreme levels of oxidation. And it's hard to do that through non-biological processes without also producing carbon monoxide, which is intermediate," Krissansen-Totton said. "For example, planets with volcanoes that belch out carbon dioxide and methane will also tend to belch out carbon monoxide."

What's more, carbon monoxide tends not to build up in the atmosphere of a planet that harbors life.

"Carbon monoxide is a gas that would be readily eaten by microbes," Krissansen-Totton said. "So if carbon monoxide were abundant, that would be a clue that perhaps you're looking at a planet that doesn't have biology."

The authors agree that oxygen is a good way to look for signs of life, but think that this new combination is at least as likely to pop up through the new telescopes' sights.

"Life that makes methane uses a simple metabolism, is ubiquitous, and has been around through much of Earth's history," Krissansen-Totton said. "It's an easy thing to do so it's potentially more common than oxygen-producing life. This is definitely something we should be looking for as new telescopes come online."

Author: Hannah Hickey | Source: University of Washington [January 24, 2018]

Two exoplanets in the TRAPPIST-1 system have been identified as most likely to be habitable, a paper by PSI Senior Scientist Amy Barr says.

Artist's concept of the TRAPPIST-1 star, an ultra-cool dwarf, which has seven Earth-size planets orbiting it  [Credit: NASA/JPL-Caltech/R. Hurt (IPAC)]

The TRAPPIST-1 system has been of great interest to observers and planetary scientists because it seems to contain seven planets that are all roughly Earth-sized, Barr and co-authors Vera Dobos and Laszlo L. Kiss said in "Interior Structures and Tidal Heating in the TRAPPIST-1 Planets" that appears in Astronomy & Astrophysics.

"Because the TRAPPIST-1 star is very old and dim, the surfaces of the planets have relatively cool temperatures by planetary standards, ranging from 400 degrees Kelvin (260 degrees Fahrenheit), which is cooler than Venus, to 167 degrees Kelvin (-159 degrees Fahrenheit), which is colder than Earth's poles," Barr said. "The planets also orbit very close to the star, with orbital periods of a few days. Because their orbits are eccentric –not quite circular – these planets could experience tidal heating just like the moons of Jupiter and Saturn."

A size comparison of the planets of the TRAPPIST-1 system, lined up in order of increasing distance from their host star. The planetary surfaces are portrayed with an artist’s impression of their potential surface features, including water, ice, and atmospheres. Amy Barr's paper “Interior Structures and Tidal Heating in the TRAPPIST-1 Planets” shows that planets d and e are the most likely to be habitable due to their moderate surface temperatures, modest amounts of tidal heating, and because their heat fluxes are low enough to avoid entering a runaway greenhouse state. Planet d is likely covered by a global water ocean [Credit: NASA/R. Hurt/T. Pyle]

"Assuming the planets are composed of water ice, rock, and iron, we determine how much of each might be present, and how thick the different layers would be. Because the masses and radii of the planets are not very well-constrained, we show the full range of possible interior structures and interior compositions." Barr said. The team's results show that improved estimates of the masses of each planet can help determine whether each of the planets has a significant amount of water.

The planets studied are referred to by letter, planets b through h, in order of their distance from the star. Analyses performed by co-author Vera Dobos show that planets d and e are the most likely to be habitable due to their moderate surface temperatures, modest amounts of tidal heating, and because their heat fluxes are low enough to avoid entering a runaway greenhouse state. A global water ocean likely covers planet d.

The team calculated the balance between tidal heating and heat transport by convection in the mantles of each planet. Results show that planets b and c likely have partially molten rock mantles. The paper also shows that planet c likely has a solid rock surface, and could have eruptions of silicate magmas on its surface driven by tidal heating, similar to Jupiter's moon Io.

Source: Planetary Science Institute [January 23, 2018]