Study warns of 'oxygen false positives' in search for signs of life on other planets

 In the search for life on other planets, the presence of oxygen in a planet's atmosphere is one potential sign of biological activity that might be detected by future telescopes. A new study, however, describes several scenarios in which a lifeless rocky planet around a sun-like star could evolve to have oxygen in its atmosphere.

The new findings, published April 13 in AGU Advances, highlight the need for next-generation telescopes that are capable of characterizing planetary environments and searching for multiple lines of evidence for life in addition to detecting oxygen.

"This is useful because it shows there are ways to get oxygen in the atmosphere without life, but there are other observations you can make to help distinguish these false positives from the real deal," said first author Joshua Krissansen-Totton, a Sagan Fellow in the Department of Astronomy and Astrophysics at UC Santa Cruz. "For each scenario, we try to say what your telescope would need to be able to do to distinguish this from biological oxygen."

In the coming decades, perhaps by the late 2030s, astronomers hope to have a telescope capable of taking images and spectra of potentially Earth-like planets around sun-like stars. Coauthor Jonathan Fortney, professor of astronomy and astrophysics and director of UCSC's Other Worlds Laboratory, said the idea would be to target planets similar enough to Earth that life might have emerged on them and characterize their atmospheres.

"There has a been a lot of discussion about whether detection of oxygen is 'enough' of a sign of life," he said. "This work really argues for needing to know the context of your detection. What other molecules are found in addition to oxygen, or not found, and what does that tell you about the planet's evolution?"

This means astronomers will want a telescope that is sensitive to a broad range of wavelengths in order to detect different types of molecules in a planet's atmosphere.

The researchers based their findings on a detailed, end-to-end computational model of the evolution of rocky planets, starting from their molten origins and extending through billions of years of cooling and geochemical cycling. By varying the initial inventory of volatile elements in their model planets, the researchers obtained a surprisingly wide range of outcomes.

Oxygen can start to build up in a planet's atmosphere when high-energy ultraviolet light splits water molecules in the upper atmosphere into hydrogen and oxygen. The lightweight hydrogen preferentially escapes into space, leaving the oxygen behind. Other processes can remove oxygen from the atmosphere. Carbon monoxide and hydrogen released by outgassing from molten rock, for example, will react with oxygen, and weathering of rock also mops up oxygen. These are just a few of the processes the researchers incorporated into their model of the geochemical evolution of a rocky planet.

"If you run the model for Earth, with what we think was the initial inventory of volatiles, you reliably get the same outcome every time -- without life you don't get oxygen in the atmosphere," Krissansen-Totton said. "But we also found multiple scenarios where you can get oxygen without life."

For example, a planet that is otherwise like Earth but starts off with more water will end up with very deep oceans, putting immense pressure on the crust. This effectively shuts down geological activity, including all of the processes such as melting or weathering of rocks that would remove oxygen from the atmosphere.

In the opposite case, where the planet starts off with a relatively small amount of water, the magma surface of the initially molten planet can freeze quickly while the water remains in the atmosphere. This "steam atmosphere" puts enough water in the upper atmosphere to allow accumulation of oxygen as the water breaks up and hydrogen escapes.

"The typical sequence is that the magma surface solidifies simultaneously with water condensing out into oceans on the surface," Krissansen-Totton said. "On Earth, once water condensed on the surface, escape rates were low. But if you retain a steam atmosphere after the molten surface has solidified, there's a window of about a million years when oxygen can build up because there are high water concentrations in the upper atmosphere and no molten surface to consume the oxygen produced by hydrogen escape."

A third scenario that can lead to oxygen in the atmosphere involves a planet that is otherwise like Earth but starts off with a higher ratio of carbon dioxide to water. This leads to a runaway greenhouse effect, making it too hot for water to ever condense out of the atmosphere onto the surface of the planet.

"In this Venus-like scenario, all the volatiles start off in the atmosphere and few are left behind in the mantle to be outgassed and mop up oxygen," Krissansen-Totton said.

He noted that previous studies have focused on atmospheric processes, whereas the model used in this study explores the geochemical and thermal evolution of the planet's mantle and crust, as well as the interactions between the crust and atmosphere.

"It's not computationally intensive, but there are a lot of moving parts and interconnected processes," he said.

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Study showing how the brain retrieves facts and may help people with memory problems

 A shared set of systems in the brain may play an important role in controlling the retrieval of facts and personal memories utilised in everyday life, new research shows.

Scientists from the University of York say their findings may have relevance to memory disorders, including dementia, where problems remembering relevant information can impact on the daily life of patients.

Researchers say the findings may also have important implications for the development of a new generation of artificial intelligence systems, which use long-term memory in solving computational problems.

The brain's long-term memory stores are categorised into two: factual memory and memory of personal experiences.

Together, these two long-term memory stores help us understand and respond to the world around us.

Decades of clinical and experimental research has shown that these two memory stores are represented across two separate brain regions.

But the new study suggests that a shared set of brain regions play an important role in controlling the successful retrieval of weak memories.

Using functional magnetic resonance imaging technology, researchers studied how these regions were shown to increase their activity when participants were asked to retrieve fact memories and personal memories.

Lead researcher Dr Deniz Vatansever, formerly of the University of York and now working for the Institute of Science and Technology for Brain-inspired Intelligence, Fudan University said: "The new research suggests that despite their functional differences, successfully retrieving weak information from these two memory systems might be dependent upon a shared brain mechanism.

"Our memories allow us to make sense and flexibly interact with the world around us. Although in most cases, our strongly encoded memories might be sufficient for the task at hand, remembering to pack a beach towel for an upcoming seaside holiday, this strong memory may be irrelevant in other instances, such as when packing for a business trip. As such, we need to tightly control the retrieval of relevant memories to solve different tasks under different circumstances. Our results indicate that this control process might be shared across both factual and personal memory types."

Senior author Prof. Elizabeth Jefferies from the Department of Psychology, University of York, said: "In order to generate appropriate thoughts and behaviours, we have to draw on our memory stores in a highly flexible way. This new study highlights control processes within the brain that allow us to focus on unusual aspects of the meanings of words and to retrieve weakly encoded personal experiences. This control over memory allows us to be creative and to adapt as our goals or circumstances change."

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People may trust computers more than humans

 Despite increasing concern over the intrusion of algorithms in daily life, people may be more willing to trust a computer program than their fellow humans, especially if a task becomes too challenging, according to new research from data scientists at the University of Georgia.

From choosing the next song on your playlist to choosing the right size pants, people are relying more on the advice of algorithms to help make everyday decisions and streamline their lives.

"Algorithms are able to do a huge number of tasks, and the number of tasks that they are able to do is expanding practically every day," said Eric Bogert, a Ph.D. student in the Terry College of Business Department of Management Information Systems. "It seems like there's a bias towards leaning more heavily on algorithms as a task gets harder and that effect is stronger than the bias towards relying on advice from other people."

Bogert worked with management information systems professor Rick Watson and assistant professor Aaron Schecter on the paper, "Humans rely more on algorithms than social influence as a task becomes more difficult," which was published April 13 in Nature's Scientific Reports journal.

Their study, which involved 1,500 individuals evaluating photographs, is part of a larger body of work analyzing how and when people work with algorithms to process information and make decisions.

For this study, the team asked volunteers to count the number of people in a photograph of a crowd and supplied suggestions that were generated by a group of other people and suggestions generated by an algorithm.

As the number of people in the photograph expanded, counting became more difficult and people were more likely to follow the suggestion generated by an algorithm rather than count themselves¬ or follow the "wisdom of the crowd," Schecter said.

Schecter explained that the choice of counting as the trial task was an important one because the number of people in the photo makes the task objectively harder as it increases. It also is the type of task that laypeople expect computers to be good at.

"This is a task that people perceive that a computer will be good at, even though it might be more subject to bias than counting objects," Schecter said. "One of the common problems with AI is when it is used for awarding credit or approving someone for loans. While that is a subjective decision, there are a lot of numbers in there -- like income and credit score -- so people feel like this is a good job for an algorithm. But we know that dependence leads to discriminatory practices in many cases because of social factors that aren't considered."

Facial recognition and hiring algorithms have come under scrutiny in recent years as well because their use has revealed cultural biases in the way they were built, which can cause inaccuracies when matching faces to identities or screening for qualified job candidates, Schecter said.

Those biases may not be present in a simple task like counting, but their presence in other trusted algorithms is a reason why it's important to understand how people rely on algorithms when making decisions, he added.

This study was part of Schecter's larger research program into human-machine collaboration, which is funded by a $300,000 grant from the U.S. Army Research Office.

"The eventual goal is to look at groups of humans and machines making decisions and find how we can get them to trust each other and how that changes their behavior," Schecter said. "Because there's very little research in that setting, we're starting with the fundamentals."

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Simple genetic modification aims to stop mosquitoes spreading malaria

Altering a mosquito's gut genes to make them spread antimalarial genes to the next generation of their species shows promise as an approach to curb malaria, suggests a preliminary study published today in eLife.

The study is the latest in a series of steps toward using CRISPR-Cas9 gene-editing technology to make changes in mosquito genes that could reduce their ability to spread malaria. If further studies support this approach, it could provide a new way to reduce illnesses and deaths caused by malaria.

Growing mosquito resistance to pesticides, as well as malaria parasite resistance to antimalarial drugs, has created an urgent need for new ways to fight the disease. Gene drives are being tested as a new approach. They work by creating genetically modified mosquitoes that, when released into the environment, would spread genes that either reduce mosquito populations or make the insects less likely to spread the malaria parasite. But scientists must prove that this approach is safe and effective before releasing genetically modified mosquitoes into the wild.

"Gene drives are promising tools for malaria control," says first author Astrid Hoermann, Research Associate at Imperial College London, UK. "But we wanted a clear pathway for safely testing such tools in countries where the disease most commonly occurs."

In the study, Hoermann and colleagues genetically modified the malaria-transmitting mosquito Anopheles gambiae. They used the CRISPR-Cas9 technology to insert a gene that encodes an antimalarial protein amidst genes that are turned on after the mosquito eats a blood meal. The team did this in a manner that allowed the whole section of DNA to also function as a gene drive that could be passed on to most of the mosquitoes' offspring. They initially inserted the gene along with a fluorescent marker to help them track it in three different spots in the DNA, and then later removed the marker, leaving only a minor genetic modification behind.

Next, the team bred the mosquitoes to see if they were able to successfully reproduce and remain healthy. They also tested how well the malaria parasite developed in the mosquitoes' guts. Their experiments provide preliminary evidence that this approach to genetic modifications could create successful gene drives.

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Life on Venus? First we need to know more about molecules in the atmosphere

The search for life on other planets has received a major boost after scientists revealed the spectral signatures of almost 1000 atmospheric molecules that may be involved in the production or consumption of phosphine, a study led by UNSW Sydney revealed.

Scientists have long conjectured that phosphine -- a chemical compound made of one phosphorus atom surrounded by three hydrogen atoms (PH3) -- may indicate evidence of life if found in the atmospheres of small rocky planets like our own, where it is produced by the biological activity of bacteria.

So when an international team of scientists last year claimed to have detected phosphine in the atmosphere of Venus, it raised the tantalising prospect of the first evidence of life on another planet -- albeit the primitive, single-celled variety.

But not everyone was convinced, with some scientists questioning whether the phosphine in Venus's atmosphere was really produced by biological activity, or whether phosphine was detected at all.

Now an international team, led by UNSW Sydney scientists, has made a key contribution to this and any future searches for life on other planets by demonstrating how an initial detection of a potential biosignature must be followed by searches for related molecules.

In a paper published today in the journal Frontiers in Astronomy and Space Sciences, they described how the team used computer algorithms to produce a database of approximate infrared spectral barcodes for 958 molecular species containing phosphorus.

LOOK AND LEARN

As UNSW School of Chemistry's Dr Laura McKemmish explains, when scientists look for evidence of life on other planets, they don't need to go into space, they can simply point a telescope at the planet in question.

"To identify life on a planet, we need spectral data," she says.

"With the right spectral data, light from a planet can tell you what molecules are in the planet's atmosphere."

Phosphorus is an essential element for life, yet up until now, she says, astronomers could only look for one polyatomic phosphorus-containing molecule, phosphine.

"Phosphine is a very promising biosignature because it is only produced in tiny concentrations by natural processes. However, if we can't trace how it is produced or consumed, we can't answer the question of whether it is unusual chemistry or little green men who are producing phosphine on a planet," says Dr McKemmish.

To provide insight, Dr McKemmish brought together a large interdisciplinary team to understand how phosphorus behaves chemically, biologically and geologically and ask how this can be investigated remotely through atmospheric molecules alone.

"What was great about this study is that it brought together scientists from disparate fields -- chemistry, biology, geology -- to address these fundamental questions around the search for life elsewhere that one field alone could not answer," says astrobiologist and co-author on the study, Associate Professor Brendan Burns.

Dr McKemmish continues: "At the start, we looked for which phosphorus-bearing molecules -- what we called P-molecules -- are most important in atmospheres but it turns out very little is known. So we decided to look at a large number of P-molecules that could be found in the gas-phase which would otherwise go undetected by telescopes sensitive to infrared light."

Barcode data for new molecular species are normally produced for one molecule at a time, Dr McKemmish says, a process that often takes years. But the team involved in this research used what she calls "high-throughput computational quantum chemistry" to predict the spectra of 958 molecules within only a couple of weeks.

"Though this new dataset doesn't yet have the accuracy to enable new detections, it can help prevent misassignments by highlighting the potential for multiple molecular species having similar spectral barcodes -- for example, at low resolution with some telescopes, water and alcohol could be indistinguishable.

"The data can also be used to rank how easy a molecule is to detect. For example, counter-intuitively, alien astronomers looking at Earth would find it much easier to detect 0.04% CO2 in our atmosphere than the 20% O2. This is because CO2 absorbs light much more strongly than O2 -- this is actually what causes the greenhouse effect on Earth."

LIFE ON EXOPLANETS

Regardless of the outcomes from the debate about the existence of phosphine in Venus's atmosphere and the potential signs of life on the planet, this recent addition to the knowledge of what can be detected using telescopes will be important in the detection of potential signs of life on exoplanets -- planets in other solar systems.

"The only way we're going to be able to look at exoplanets and see whether there's life there is to use spectral data collected by telescopes -- that is our one and only tool," says Dr McKemmish.

"Our paper provides a novel scientific approach to following up the detection of potential biosignatures and has relevance to the study of astrochemistry within and outside the Solar System," says Dr McKemmish. "Further studies will rapidly improve the accuracy of the data and expand the range of molecules considered, paving the way for its use in future detections and identifications of molecules."

Fellow co-author and CSIRO astronomer Dr Chenoa Tremblay says the team's contribution will be beneficial as more powerful telescopes come online in the near future.

"This information has come at a critical time in astronomy," she says.

"A new infrared telescope called the James Web Space Telescope is due to launch later this year and it will be far more sensitive and cover more wavelengths than its predecessors like the Herschel Space Observatory. We will need this information at a very rapid rate to identify new molecules in the data."

She says although the team's work was focused on the vibrational motions of molecules detected with telescopes sensitive to infrared light, they are currently working to extend the technique to the radio wavelengths as well.

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Search for sterile neutrinos: It's all about a bend in the curve

 There are many questions surrounding the elementary particle neutrino, in particular regarding its mass. Physicists are also interested in whether besides the "classic" neutrinos there are variants such as the so-called sterile neutrinos. The KATRIN experiment has now succeeded in strongly narrowing the search for these elusive particles. The publication appeared recently in the journal Physical Review Letters.

Strictly speaking, the neutrino is not a singleparticle but rather comprises several species: the electron neutrino, the muon neutrino, and the tau neutrino. These particles are constantly transforming into each other in a process referred to as neutrino oscillation. It is assumed that neutrinos have mass; this is to be determined in the KATRIN experiment, which started in 2019 at the Karlsruhe Institute for Technology (KIT). According to the results to date, the neutrino has a mass less than 1 electron volt.

KATRIN could also be used to track down related species that have so far only been hypothetical: The sterile neutrinos. The heavier branch (mass in kiloelectronvolt range) is considered a candidate for dark matter and will be sought after a new detector is installed in KATRIN. Besides this, there could also a lighter sterile neutrino type.

New exclusion criteria for the light sterile neutrino

Quite a few experiments are looking for light sterile neutrinos (mass in the electronvolt range). It could also reveal itself in the KATRIN experiment. The mass and the mixing ratio of active (normal) and sterile neutrinos play an essential real in the search for the light sterile neutrino.

Susanne Mertens and her team at the Max Planck Institute for Physics (MPP) succeeded in defining new exclusion limits with the help of KATRIN. "With our evaluations, we were able to significantly reduce the search area for this neutrino," says Mertens.

With the new analysis of the KATRIN data, developed by the group of Susanne Mertens and Thierry Lasserre at MPP, the existence of sterile neutrinos with a mass between about 3 and 30 electronvolts and a mixing ratio greater than 10% can now be ruled out. This result complements previously achieved exclusion limits.

Search by measuring the neutrino mass

But how can KATRIN find sterile neutrinos? Using the same method, the experiment also determines the mass of the active neutrino. The mass of the neutrino can be measured via radioactive decay. KATRIN uses tritium (heavy water) for this purpose. When a proton is converted into a neutron, one neutrino and one electron are produced. The decay energy of 18.6 kiloelectronvolts is divided between them.

"We know that the neutrino is extremely light and receives only a tiny fraction of the decay energy," says Mertens. "The maximum energy of the electron is reduced by the mass of the neutrino." The mass of the neutrino therefore results from the difference between the decay energy and the maximum energy of the electron.

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Major risk of injury for recreational runners

 Almost half of all recreational runners incur injuries, mostly relating to knees, calves or Achilles tendons, and the level of risk is equally high whatever your age, gender or running experience. These are the findings of a thesis within sport science.

Doctoral student Jonatan Jungmalm recruited a little over 200 recreational runners from the list of entrants for the Göteborgsvarvet Half Marathon and monitored them over a period of one year. To take part in the study, they had to have been running for at least a year, have run an average of at least 15 km per week over the past year and have been injury free for at least six months. The participants were men and women in the age range 18-55.

Calculation shows injury for half of runners

Over the year of the study, the recreational runners filled in a training diary, entering information about how far they ran each day and whether they felt any pain. Those who suffered sudden injury or felt pain for a prolonged period were examined by a sports doctor.

"A third of the participants were injured over the course of the study. But if you also take account of the participants who dropped out of the study, it is reasonable to assume that almost half of all recreational runners injure themselves in a year," states Jonatan Jungmalm.

Jonatan used a particular statistical method to calculate the proportion of injured runners, taking into account the rate of dropout that is common in studies based on voluntary participation.

Injuries to knee, calf and Achilles tendon

Of those hit by injury, half had problems with their knees, calves or Achilles tendons.

"Few of the injuries were long-lasting. But all the injuries prevented the runners from exercising as usual," says Jonatan.

No difference was found in terms of gender, age, running experience or weight between those who injured themselves and those who did not.

"However, those who had previously been injured were more likely to be affected again."

Multiple physical tests

All the participants were put through a series of physical tests before the study, ranging from strength tests and mobility tests to tests of running style.

"Those who had relatively weak outer thighs faced a higher risk of injury. Those with late pronation in their running gait were also at higher risk. However, having a weak torso or limited muscle flexibility was of no great significance."

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Prehistoric Pacific Coast diets had salmon limits

 Humans cannot live on protein alone -- even for the ancient indigenous people of the Pacific Northwest whose diet was once thought to be almost all salmon.

In a new paper led by Washington State University anthropologist Shannon Tushingham, researchers document the many dietary solutions ancient Pacific Coast people in North America likely employed to avoid "salmon starvation," a toxic and potentially fatal condition brought on by eating too much lean protein.

"Salmon was a critical resource for thousands of years throughout the Pacific Rim, but there were a lot of foods that were important," said Tushingham the lead author of the paper published online on April 8 in the American Journal of Physical Anthropology. "Native people were not just eating salmon. There's a bigger picture."

Some archeologists have contended for years that prehistoric Northwest people had an "extreme salmon specialization," a theory primarily based on the amount of salmon bone found at archeological sites.

Tushingham and her co-authors argue that such a protein-intensive diet would be unsustainable. They point to nutritional studies and a global database of hunter-gatherer diets that indicate people have dietary limit on lean protein of around 35%. While it can vary by individual, exceeding that ceiling can be physically debilitating within a few days and fatal within weeks. Early explorers in the U.S. West subsisting on lean wild game discovered this problem the hard way and called it "rabbit starvation" or "caribou sickness."

This toxic situation can apply to any lean meat, including salmon, Tushingham said. To avoid "salmon starvation," early Pacific Coast people had to find ways to get other nutrients, especially for children and nursing mothers who have even lower dietary thresholds for lean protein.

"There were ingenious nutritional and cultural solutions to the circumstances in the Northwest," said Tushingham. "Yes, salmon was important, but it wasn't that simple. It wasn't just a matter of going fishing and getting everything they needed. They also had to think about balancing their diet and making sure everybody could make it through the winter."

The researchers point to evidence in California that people offset stored salmon protein with acorns; in Oregon and Washington, they ate root crops like camas as well as more fat-heavy fish such as eulachon. Further north, where plants are more limited, communities often ate marine mammals with high fat content such as seals and walrus. In far north interior, where there are few plants and the salmon runs can go thousands of miles inland, this was particularly challenging. Lean dried salmon was an important food source, and people circumvented salmon starvation through trading for oil with coastal peoples or obtaining fat through processing bone marrow from caribou and elk.

The authors focus on the limits of salmon, which used to be considered a "prime mover" of Pacific Northwest populations, but their analysis also has implications for the study of historical human nutrition. If their argument is correct, it is unlikely that any human society was fully driven by pursuit of protein alone as their diets had to be more complex.

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Curiosity rover explores stratigraphy of Gale crater

Gale Crater's central sedimentary mound (Aeolis Mons or, informally, Mount Sharp) is a 5.5-km-tall remnant of the infilling and erosion of this ancient impact crater. Given its thickness and age, Mount Sharp preserves one of the best records of early Martian climatic, hydrological, and sedimentary history.

In this paper, published today in Geology, William Rapin and colleagues present the first description of key facies in the sulfate-bearing unit, recently observed in the distance by the rover, and propose a model for changes in depositional environments.

The basal part of this sedimentary sequence is ahead of the Curiosity rover traverse and was recently analyzed with unprecedented resolution by the rover cameras. The telescopic imager of the ChemCam instrument was used here in particular, and its images show sedimentary structures that reveal evolution of environments on Mars during the Hesperian age (3.7-2.9 billion years ago).

Analysis of the structures shows that on top of the ancient lake deposits currently explored by the rover (Murray formation), vast aeolian deposits were formed by a dune field during a prolonged dry climatic episode. Yet, higher up, the stratigraphy reveals the resumption of wetter climatic conditions.

The climate of Mars appears therefore to have fluctuated several times at high order between dry conditions and wet conditions in the Hesperian age, a period during which Mars' environment is thought to have changed globally due to the gradual loss of its atmosphere to space.

From Science Daily

Thinking with your stomach? The brain may have evolved to regulate digestion

Many life forms use light as an important biological signal, including animals with visual and non-visual systems. But now, researchers from Japan have found that neuronal cells may have initially evolved to regulate digestion according to light information.

In a study published this month in BMC Biology, researchers from the University of Tsukuba have revealed that sea urchins use light to regulate the opening and closing of the pylorus, which is an important component of the digestive tract.

Light-dependent systems often rely on the activity of proteins in the Opsin family, and these are found across the animal kingdom, including in organisms with visual and non-visual systems. Understanding the function of Opsins in animals from different taxonomic groups may provide important clues regarding how visual/non-visual systems evolved in different creatures to use light as an external signal. The function of Opsins in the Ambulacraria groups of animals, which include sea urchins, has not been characterized, something the researchers aimed to address.

"The functions of eyes and visual systems have been well-characterized," says senior author of the study Professor Shunsuke Yaguchi. "However, the way in which light dependent systems were acquired and diversified throughout evolution is unclear especially in deuterostomes because of the lack of data regarding the signaling pathway in the Ambulacraria group."

To address this, the researchers tested whether light exposure caused changes in digestive tract activity in sea urchins. They then conducted micro-surgical and genetic knockdown experiments to test whether Opsin cells in the sea urchin digestive system mediated the effect of light.

"The results provided new information about the role of Opsins in sea urchins," explains Professor Yaguchi. "Specifically, we found that stimulation of sea urchin larvae via light caused changes in digestive system function, even in the absence of food stimuli."

Furthermore, the researchers identified brain serotonergic neurons near the Opsin-expressing cells that were essential for mediating the light-stimulated release of nitric oxide, which acts as a neurotransmitter.

"Our results have important implications for understanding the process of evolution, specifically, that of light-dependent systems controlled via neurotransmitters," says Professor Yaguchi.

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